Student Name Bud BennemanGeology 105 Spring 2020Paper Outline.docx

Student Name: Bud Benneman
Geology 105 Spring 2020
Paper Outline
The Newport–Inglewood fault zone (NIFZ) of southern
California.
I. The Newport–Inglewood fault zone (NIFZ) was first
identified as a significant threat to southern California residents
in 1933 when it generated the Magnitude 6.3 Long Beach
Earthquake, killing 115 people.
A. The Newport Inglewood fault is located in southern Los
Angeles County in the city of Inglewood and transverses south
to Newport Beach in Orange County where it becomes an off
shore fault.
B. The NIFZ then connects to the Rose Canyon Fault none,
becomes a landward fault in San Diego County.
C. This is a stress reliever Strike-Slip Fault Zone associated
with the San Andréas Fault Zone.
D. Ground water basins in Los Angeles County may be used as
predictors of fault movement due to sudden changes in ground
water level.
E. In southern California, tectonic deformation between
the Pacific and North American plates is accommodated
primarily by a zone of strike-slip faults,
II. This fault is important to the exploration of Oil.
A. The NIFZ has been studied extensively in the Los Angeles
basin by petroleum geologists.

B. The NIFZ overlies a major tectonic boundary separating
eastern continental basement rocks of granitic and associated
metamorphic rocks of Santa Catalina Island schist.
C. The NIFZ follows along a former Mesozoic subduction zone.
D. This fault is associated with several oil basins including
Newport Beach, Huntington Beach, Seal Beach, Long Beach,
and Signal Hill.
III. Earthquake Potential for Los Angeles, Orange and San
Diego Counties.
A. The epicenter for the 1933 Long Beach Quake was located
in Newport Beach just south of the Santa Ana River discharge
into the Pacific Ocean.
B. Orange County in 1933 consisted of small farm-towns, cattle
ranching and agricultural fields.
C. The closest city of significant development was Lang Beach,
which was devastated by the 1933 6,3 quake.
D. Today cities of Newport Beach, Huntington Beach, Costa
Mesa, are large population centers, which have replaced
agriculture as the primary economic sector.
E. The rate of ground water basin contraction is important in
determining possible earthquake releases in the Los Angeles
Basin.
F. Many Orange and Los Angeles county buildings are located
along high risk development zones during earthquakes.
IV. Earthquake Monitoring and Prediction
a. The location of the 2000 cluster is southwest of an area of
active faulting from 1982 to 1990 along this zone and reported
strike-slip offshore fault between Newport Beach and the San
Joaquin Hills was traced from seismic activity.

b. Analyzed microseismicity from a cluster of epicenters
between 2 and 2.5 km along the fault zone suggest potential
earthquakes of higher magnitude are possible.
c. A possible 7.5 magnitude earthquake could result from
rupture of the entire fault. The 6.5-km depth of the Newport
Beach seismicity cluster does not provide information on the
geometry or interaction between the strike-fault zone and
Oceanside thrust faults.
d. Los Angeles groundwater basin contraction could cause faults
such as the Whittier
E. Oil companies and water basin studies using seismic
studies and human
induced micro-seismic studies have identified several fault
structures such as
blind thrust faults in the Los Angeles basin. Blind thrust
along with strike slip
fault structures suggest potential earthquakes of higher
magnitude are
possible for the Los Angeles and Orange County basins.
IV. Conclusion
a. The Newport Inglewood Fault is a major stress reliever for
the San Andreas Fault Zone.
b. This fault zone is tied in between the North American Plate
and Pacific Plates Strike Slip Zones and follows a Mesozoic
Subduction zone.
c. The location of the NIFZ has potential for a large magnitude
earthquake due to it being sandwiched between the eastern San
Andreas and Pacific Margin plate Boundary.

Effects of episodic fluid flow on hydrocarbon migration in
the Newport-Inglewood Fault Zone, Southern California
B. JUNG1, G. GARVEN 2 AND J. R. BOLES3
1Department of Earth Sciences, Uppsala University, Uppsala,
Sweden; 2Department of Earth and Ocean Sciences, Tufts
University, Medford, MA, USA; 3Department of Earth Science,
University of California, Santa Barbara, CA, USA
ABSTRACT
Fault permeability may vary through time due to tectonic
deformations, transients in pore pressure and effective
stress, and mineralization associated with water-rock reactions.
Time-varying permeability will affect subsurface
fluid migration rates and patterns of petroleum accumulation in
densely faulted sedimentary basins such as those
associated with the borderland basins of Southern California.
This study explores the petroleum fluid dynamics of
this migration. As a multiphase flow and petroleum migration
case study on the role of faults, computational
models for both episodic and continuous hydrocarbon migration
are constructed to investigate large-scale fluid

flow and petroleum accumulation along a northern section of
the Newport-Inglewood fault zone in the Los
Angeles basin, Southern California. The numerical code solves
the governing equations for oil, water, and heat
transport in heterogeneous and anisotropic geologic cross
sections but neglects flow in the third dimension for
practical applications. Our numerical results suggest that fault
permeability and fluid pressure fluctuations are cru-
cial factors for distributing hydrocarbon accumulations
associated with fault zones, and they also play important
roles in controlling the geologic timing for reservoir filling.
Episodic flow appears to enhance hydrocarbon accu-
mulation more strongly by enabling stepwise build-up in oil
saturation in adjacent sedimentary formations due to
temporally high pore pressure and high permeability caused by
periodic fault rupture. Under assumptions that
fault permeability fluctuate within the range of 1–1000
millidarcys (10�15–10�12 m2) and fault pressures fluctuate
within 10–80% of overpressure ratio, the estimated oil volume
in the Inglewood oil field (approximately 450 mil-
lion barrels oil equivalent) can be accumulated in about 24 000
years, assuming a seismically induced fluid flow
event occurs every 2000 years. This episodic petroleum
migration model could be more geologically important
than a continuous-flow model, when considering the observed

patterns of hydrocarbons and seismically active
tectonic setting of the Los Angeles basin.
Key words: episodic fluid flow, fluid flow in faults, multiphase
flow in siliciclastic sedimentary basins, petroleum
migration
Received 21 May 2013; accepted 16 October 2013
Corresponding author: Byeongju Jung, Department of Earth
Sciences, Uppsala University, Gl227 Geocentrum,
Villav€agen 16B, 753 36 Uppsala, Sweden.
Email: [email protected] Tel: +46 018 471 2264. Fax: +1 617
627 3584.
Geofluids (2014) 14, 234–250
INTRODUCTION
Large-scale faults in sedimentary basins have become
increasingly studied due to their important role in convey-
ing and compartmentalizing hydrocarbons (Aydin 2000;
Boles et al. 2004; Karlsen & Skeie 2006; Kroeger et al.
2009; Zhang et al. 2009; Gong et al. 2011). The hydro-
mechanical properties of faults in active continental mar-
gins are strongly affected by tectonic deformation, so

considering the fluid dynamics of faults will likely improve
our understanding of petroleum migration (Reynolds &
Lister 1987; Blanpied et al. 1992; Sibson 1994; Appold &
Garven 2000; Yamaguchi et al. 2011). For example, there
is abundant geological evidence, at both macroscopic and
microscopic scales, that faults focus fluid flow over long
periods of time but later are sealed by mechanical compac-
tion and chemical reactions causing mineral precipitation
(Eichhubl & Boles 2000; Caine et al. 2010; Faulkner et al.
2010). The hydrologic activity of fault zones may also
depend highly on earthquakes, which in turn may induce
periodic fluctuations in pore fluid pressure and fault per-
meability (Evans 1992; Sibson 1994). Furthermore, large-
© 2013 John Wiley & Sons Ltd
Geofluids (2014) 14, 234–250 doi: 10.1111/gfl.12070
scale fault zones may affect regional hydrocarbon migration
by regulating the spatial distribution of overpressure in the

subsurface (Sperrevik et al. 2002; Fisher et al. 2003; Sork-
habi & Tsuji 2005). Laboratory experiments on fractured
rock show that active shear faults are more permeable than
the adjacent country rock by two to three orders in magni-
tude. These faults then become less permeable when deac-
tivated (Aydin 2000).
The mechanism of recurring fluid pressure build-up, hy-
drofracturing, fluid surge, and fault sealing can also be a
potential means for hydrocarbon migration (Bradley 1975;
Walder & Nur 1984; Mandl & Harkness 1987). For exam-
ple, field observations of brecciated rocks and hydrother-
mal veins from the Stillwater fault zone in Nevada indicate
that petroleum migration was not completed as one single
flow event, but rather accumulation too place over many
episodes of oil flow during the deformation history (Caine
et al. 2010). Geochemical evidence from hydrocarbon con-
densates found in the South China basin also support the
notion that petroleum migration occurs simultaneously

with episodes of hydrothermal fluid flow (Guo et al.
2011).
We further hypothesize that the hydrodynamic effects of
multiphase flow are more effective for long-distance trans-
port, during periods of strong overpressuring associated
with episodes of seismically controlled fluid flow. Episodic
flow associated with large faults may also be more effective
than long-term continuous or steady flow of hydrocarbons,
as might be envisioned for a slowly subsiding sedimentary
basin. To test this hypothesis, we conduct 2D finite ele-
ment simulations for multiphase flow in geologically com-
plex cross sections through a basin. We introduce two
migration scenarios of continuous flow and of episodic
flow, which likely account for the current distribution of
hydrocarbon pools such as the Inglewood oil field. The
continuous models assume constant fault permeability and
fluid pressure throughout the simulation time, while those
conditions are time varying in the episodic models. We first

compared the fluid pressure, subsurface temperature, and
petroleum saturations from these models and then per-
formed sensitivity studies on the fault permeability and the
frequency of episodic flow pulses to understand how these
permeability transients might affect overall hydrocarbon
migration and accumulation patterns in a faulted sedimen-
tary basin.
GEOLOGIC SETTING
The Los Angeles (LA) basin is one of the most prolific
hydrocarbon-producing areas on Earth, and it hosts histor-
ically giant oil fields. From the geological survey, it was
recognized that the upper Miocene formations contain
organic-rich sediments and play an important role as the
primary hydrocarbon source rock. Most of the hydrocar-
bons were thermally matured in the central part of the
basin (the central syncline area) and have migrated to the
edges, which are laterally confined by regional-scale fault
zones (Biddle 1991; Jeffrey et al. 1991). The Newport-

Inglewood fault zone is one of the major regional fault sys-
tems that structurally border the southwestern side of the
LA basin, and numerous hydrocarbon reservoirs are closely
associated with the fault structure (Fig. 1A). In the Ingle-
(A) (B)
Fig. 1. Faults and oil fields in the Los Angeles basin (after
Wright 1991): (A) LA basin, (B) Inglewood oil field.
© 2013 John Wiley & Sons Ltd, Geofluids, 14, 234–250
Effects of episodic fluid flow 235
wood oil field located on the northern part of the fault
zone, the main production area exists at the intersection
between the Newport-Inglewood and Sentous faults and is
elongated along the trends of both faults (Fig. 1B). Geo-
chemical indicators and biomarkers also suggest the hydro-
carbons discovered in this area have mostly migrated
approximately 10–15 km from the deep basin center with
minor mixing of indigenous petroleum (Kaplan et al.

2000). Tectonic deformation and subsequent seismic activ-
ity make this region attractive for studying the relationship
between hydrocarbon migration and active fault structures
in young sedimentary basins.
The Newport-Inglewood fault zone consists of a series
of en echelon strike slip faults that were reactivated during
the late Pliocene transpressional deformation (Pasadena
Orogeny) and transformed into more complicated anticline
structures containing normal and reverse faults (Fig. 2).
Hydrocarbon reservoirs exist in multiple sedimentary for-
mations but are more concentrated in Pliocene strata con-
taining a high proportion of sandstone. Many productive
petroleum reservoirs align with the trend of the Newport-
Inglewood fault zone, which extends and merges with the
Central Basin d�ecollement at about 10 km depth (Shaw &
Suppe 1996).
The permeability of these sandstones ranges from 10’s
to 1000’s millidarcys (10�14–10�12 m2) for sandy Plio-
cene formations (Hesson & Olilang 1990). The thickness

of sediments in the central syncline is approximately
10 km and becomes gradually thinner toward the north-
ern and southwestern edges of the basin (Blake 1991;
Fig. 3). Figure 4A shows an outcrop of channel-fill sand-
stones (Sespe Formation) in the adjacent Santa Barbara
area. The faults in these rocks are filled with carbonate
mineral precipitates and lithified hydrocarbons, which is
strong evidence that the fault zone provided active chan-
nels for hydrocarbon fluids, but later these were sealed
by subsequent reactions involving diagenetic-hydrother-
mal mineralization as fluids cooled or the pressure rap-
idly dropped (Fig. 4B). Five separate hydrogeologic units
were considered here: middle and pper Miocene, lower
and upper Pliocene, and Pleistocene formations (Fig. 3).
The middle Miocene unit (Topanga Formation) consists
of medium to coarse sandstones with intercalated shale
layers. The upper Miocene sediments (Puente Formation)
are mostly siltstone and silty sandstone with interbedded

pelagic mudstone and shale layers (nodular shales in
some areas) that contain high organic carbon contents
(10–16%). This formation is often considered to be the
primary source rock for petroleum generation (Jeffrey
et al. 1991). The lower Pliocene unit (Repetto forma-
tion) serves as a major reservoir for hydrocarbon accu-
mulation. The Repetto consists of fine to coarse
sandstones with interbedded siltstone and shale layers
that have relatively high permeability of 10–100 md
(10�14–10�13 m2) (Higgins & Chapman 1984). The
geology of the upper Pliocene unit (Pico formation) is
very similar to the Repetto formation, consisting of inter-
bedded sandstone and siltstone, but with slightly lower
permeability. The Pleistocene unit (San Pedro formation)
consists of relatively uniform and highly permeable sand
layers interbedded with minor gravel, silt, and shale lay-
ers (Olson 1978).
We propose that north–south transpressional tectonic

stresses pressurized the basin continuously from the late
Pliocene to the present. A coupled mechanism of tec-
tonic loading, pore fluid pressure build-up, fault instabil-
ity, and fluid flow may have induced episodic fluid flow
events (Sibson 1994). Elevated effective stress and pore
pressure by tectonic loading compact the sedimentary
rocks during the interseismic periods, making the fault
zone mechanically unstable. When ruptured, high perme-
ability and low pore pressure temporarily create focused
fluid flow in the fault zone. The fault stays open for a
relatively short period of time due to hydromechanical
compaction as the pore pressure decreases, and then
sealed further by hydrothermal mineral precipitation
(Fig. 5). The continuous tectonic stress and rebuilding of
pore pressure cause this cycle to repeat after the fault
zone becomes sealed. Field observations of petroleum
and carbonate mineral deposits in other siliciclastic faults
suggest an episodic nature of injected fluids (Eichhubl &

Boles 2000; Garden et al. 2001), and these episodic flow
patterns may affect the geohydrologic controls on hydro-
carbon accumulation. We modeled this dynamic aspect of
fault zone to understand its effects on petroleum migra-
tion and entrapment.
Fig. 2. Cross section of the Newport-Inglewood fault zone along
the tran-
sect X–X′ (courtesy of Plains Exploration and Production
Company, 2008).
236 B. JUNG et al.
MULTIPHASE FLOW MODEL
To model petroleum migration in the basin, we need to
predict fluid saturation and pressure for both the wetting
phase (formation water) and nonwetting phase (oil). The
governing equations for multiphase fluid flow can be
derived from the fluid mass conservation equations, as
written by Bear (1972):
(A) (B)

Fig. 4. Outcrop pictures of organic-rich sedimentary rocks in
California: (A) channel-fill sandstones in nonmarine Sespe
Formation (Oligocene) from Old San
Marcos road, Santa Barbara County, CA, (B) tar-filled fault
breccia in Monterey Formation at Arroyo Burro beach, Santa
Barbara County, CA.
Fig. 3. Lithostratigraphy of the Los Angeles
basin, modified from Blake (1991).
/
@ðqwSwÞ
@t
¼ �O � ðqwvwÞ þ qwmw ð1Þ
/
@ðqnSnÞ
@t
¼ / @ðqnð1 � SwÞÞ
@t
¼ �O � ðqnvnÞ þ qnmn ð2Þ
where / is the effective porosity of a formation, and S is
the saturation of the phase: the subscripts n and w denote

the nonwetting (liquid petroleum) and wetting (water)
phases, respectively. Additionally, q is mass density of the
fluid, m is a source/sink term, and v is the Darcy velocity
(specific discharge) of each fluid phase, expressed as fol-
lows:
vw ¼ �kwkðOqw � qwgÞ ð3Þ
vn ¼ �knkðOqn � qngÞ ¼ �knðOqw þ Oqc � qgÞ ð4Þ
where k is the intrinsic permeability tensor, p is fluid pres-
sure, g is a gravitational vector (g = (0, 0, �g)), and pc is
capillary pressure (pc = pn – pw). The parameter, k, is the
mobility coefficient and defined by the ratio of relative per-
meability (kr) and dynamic viscosity (l) as:
kw ¼ krw=lw; kn ¼ krn=ln ð5Þ
After a few steps of algebraic manipulation, the pressure
and saturation equations can be decoupled. If slightly com-
pressible fluids are assumed, the final form of average pres-
sure and saturation equations can be written as follows
(Geiger et al. 2004):
/ct
@ �P

@t
¼ O � kfktO�P � 0:5ðkw � knÞOpc�
ðkwqw þ knqnÞggþmt
ð6Þ
/
@Sn
@t
¼ O � ½fnvt � �kkfOqc þ ðpw � pnÞgg� � mt ¼ 0 ð7Þ
where ct is bulk compressibility of a medium, and mt is a
source/sink term. vt is the sum of water and petroleum
velocites (vt = vw + vn). The average pressure �P is an arith-
metic mean of the water and petroleum pressure, and f is a
fractional flow coefficient that is also defined for simplicity:
fw ¼
kw
kt
; fn ¼
kn
kt
; and �k ¼ kwkn
kt
ð8Þ
The first, second, and third terms in the right-hand side

of the pressure equation (Eq. 6) represent advection, capil-
larity, and buoyancy flow terms, respectively.
Conventional multiphase flow equations were decoupled
in terms of average pressure and petroleum saturation.
These equations were solved using the implicit-pressure
explicit-saturation (so called ‘IMPES’) technique (Helmig
1997; Huber & Helmig 2000; Class et al. 2002; Reichen-
berger et al. 2006), a technique that produces solutions
faster than those requiring time-consuming nonlinear itera-
tions.
Solution
s to the pressure and saturation equations
were computed using a hybrid numerical method called
FEFVM suggested by Geiger et al. (2004, 2006). This
method applies a finite element method (FEM) for com-

puting average pressure and then a finite volume method
(FVM) for computing fluid saturation. A fully upwind for-
mulation and total velocity diminishing (TVD) method
(Harten 1997) were also used for solutions to avoid both
numerical dispersion and spurious oscillation at the satura-
tion front.
Capillary pressure and relative permeability models devel-
oped by van Genuchten (1980) were used for describing
two-phase fluid–solid interaction in the porous media.
The van Genuchten model has been widely used in a
multiphase flow modeling and well known for providing
stable numerical solutions when applying continuous capil-
lary pressure functions for a whole saturation interval.

Stress or temperature dependent parameters were not
included in the numerical formulation.
Petroleum density and viscosity were computed using
empirical equations suggested by Glasø (1980) and Eng-
land et al. (1987). Liquid petroleum density generally
decreases with increasing pressure because the solubility of
gaseous component increases. The dynamic viscosity of oil
Fig. 5. Coupled hydromechanic and hydrother-
mal processes for episodic fluid flow (as known
as fault-valve mechanism), adopted from Sibson
(1994). The parameter and variables: pf is fluid
pressure; s is shear stress along the fault; C is

the cohesive strength of the fault; ls is the sta-
tic coefficient of rock friction, and rn is the nor-
mal stress on the fault.
238 B. JUNG et al.
varies between 5 9 10�4 and 5 9 10�2 Pa�s, and generally
decreases exponentially with increasing temperature (Eng-
land et al. 1987). Fluid properties of the formation water
were obtained from a set of state equations proposed by
Phillips et al. (1981, 1983) and Watson et al. (1980),
which consider the effects of temperature, pressure, and
salinity/NaCl concentration on water density.

MODEL CONFIGURATION
The models, in this research, are based on the cross section
in Fig. 2, which illustrates the present geology of the New-
port-Inglewood fault zone and associated oil fields (e.g.,
Inglewood oil field) along the transect X–X′ in Fig. 1B.
This profile, which consists of anticline folds with heavily
faulted rocks, was chosen because it represents the typical
geologic settings of oil reservoirs along the NIFZ. The
numerical grid was discretized into 7655 triangular ele-
ments using a Delaunay triangulation method for detailed
rendering of geological structures (de Berg et al. 2008;
Fig. 6). The Newport-Inglewood fault zone and surround-
ing areas were divided into smaller elements to increase the

resolution of the numerical solution.
Because this model is only two-dimensional, a character-
istic fault length or effective flow field length was intro-
duced for petroleum volume calculation. The total length
of Inglewood Oil Field is about 5 km, so we assume that
20% of the total fault length (Approximately 1 km) in pro-
file is available for petroleum migration. The width of fault
zone in the numerical grid is approximately 50 m. Model
parameters used in the simulations are listed in Table 1.
Permeability and porosity of each hydrogeologic unit were
obtained from several publications (Yerkes 1972; Olson
1978; Higgins & Chapman 1984; Hesson & Olilang

1990; Nishikawa et al. 2009) and chosen within the ranges
considered to be representative for these local formations.
Fault permeability was not available from any local field
measurements, so it was systematically varied or dynami-
cally changed as part of model parameter sensitivity analy-
sis. Anisotropic permeability ratio values of up to 100:1
(kx/kz), typical for a regional-scale flow, were chosen for
most formations except the Pleistocene sediments, which
are known to be the most permeable and yet not fully con-
solidated. A thermal dispersivity a approximately 100 m
was assumed for all formations, reflecting the longitudinal
solute dispersivity value for a regional groundwater flow
system (de Marsily 1986; Gelhar et al. 1992). Matrix ther-

mal conductivity values of 3.0 W m�1°C were assigned to
most sandstone-dominant units and values of 2.5–
2.8 W m�1°C were assigned to the units having high con-
tent of siltstone and interbedded shale (Blackwell & Steele
1989). A specific heat capacity value of 750 J kg�1°C, typi-
cal of sandstone and shale, was assigned for all hydrogeo-
logic units and faults (Sabins 1997). Formation of water
salinity in the LA basin usually ranges from 20 000 to
34 000 ppm TDS (Hesson & Olilang 1990; California
Department of Conservation 1992) for most oil fields. The
groundwater salinity was set to 25 000 ppm TDS for the
entire model profile.
Capillary pressure in porous sandstone is generally
<0.1 bar (approximately 0.01 MPa) but may increase to
tens of bars in source rocks with clay grain size (Ingebrit-

sen et al. 2006). Capillarity model parameters were chosen
within the range of typical rock types obtained from other
publications (Levorsen 1967; Wendebourg 1994; Bloom-
field et al. 2001). Typically, the capillary pressure of more
permeable formations exhibit lower values, but sharp
increases occur near the irreducible water saturation point
(Swr). The sum of water and petroleum relative permeabil-
ity is usually less than one when both phases are mobile.
Initially, hydrostatic conditions and conductive thermal
profile were assumed throughout the basin. The levels of
overpressure were chosen considering that the pore pres-
sure in the Southern California faults may approach

lithostatic pressure due to mechanical compaction (Gra-
tier et al. 2002, 2003). The values of overpressure ratio,
fault permeability, and the period of episodic flow pulses
are presented in Table 2. The over pressure ratio (k*) in
a sedimentary basin can be defined as follows (Wang
et al. 2006)
Fig. 6. Model numerical grid, boundary conditions and
hydrostratigraphy
of the Newport-Inglewood fault zone based on the cross section
along the
transect X–X’ (Fig. 1b). The upper margin is the prescribed
pressure head
of 200 m and the isothermal boundary condition of 4°C. The left
and right
margins of the grid were assigned to be hydrostatic for pressure
and ther-

mally insulated (no flow) for heat. The bottom margin were
assigned as no
flow and a constant temperature of 160°C. Overpressure is
applied to the
right end of the fault boundary (marked as a white arrow) as a
prescribed
pressure condition, and the petroleum saturation at this
boundary is con-
stant (Sn = 0.6).
k� ¼ P � PF
PL � PF
� 100 ð9Þ

where P is pore fluid pressure in the formation, PF is
hydrostatic pressure, and PL is lithostatic pressure. Porosity
of the fault also changes dynamically in the range of 0.1–
0.3, accompanying with the permeability variation.
In middle Miocene to early Pleistocene, the basin is still
under a shallow marine environment (Wright 1991), so
the prescribed pressure head of 200 m and the isothermal
boundary condition of 4°C were assigned to the top
boundary of the grid. The temperature value was chosen
within the ranges of estimated Miocene shallow seawater
temperature (0–6°C) (Zachos et al. 2001). Boundary con-
ditions along the bottom margin of the grid were
assigned as no fluid flow (impermeable) and a constant

temperature of 160°C, based on geothermal gradients
reported in this area of 35–40°C km�1 (Higgins & Chap-
man 1984; Jeffrey et al. 1991). The left and right mar-
gins of the grid were assigned to be hydrostatic for
pressure and thermally insulated for heat. Petroleum was
injected through the fault boundary at the right boundary
(white arrow in Fig. 6), and this condition is physically
possible only when we assume that most of petroleum
was generated in the deep basin center and migrated
through the fault zone.
CONTINUOUS FLOW MODEL
First, we considered a continuous hydrocarbon migration
scenario through the Newport-Inglewood fault zone,
assuming a slightly overpressured sedimentary basin envi-

ronment with constant fault zone permeability. The level
of overpressure at the fault boundary (marked as a white
arrow in Fig. 6) was held constant during the simulation,
and the fault zone was considered as a channel for releas-
ing overpressure of the basin center as well as a conduit for
petroleum migration. For Model 1, the vertical fault per-
meability kz was set to 10 md (10
�14 m2), which is within
the range of kx for the Pliocene unit and higher than that
of Upper Miocene unit. The permeability value was
inferred from the fact that a fault zone may be more per-
meable than its host rock, especially when the fault was
ruptured by shear stresses and brecciated to include sur-

rounding rocks (Aydin 2000). The change of fault perme-
ability during deformation depends on fault rock clay
content and burial history. Laboratory experimental data
show permeability increasing over 2–4 orders of magnitude
(Fisher & Knipe 2001).
Fluid pressure gradients in a compacting sedimentary
basin usually vary between hydrostatic (approximately
10.1 MPa km�1) and lithostatic pressure (approximately
23.3 MPa km�1), and the values used in the simulations
Table 1 Hydrogeologic model parameters.
Parameter Topanga Puente Repetto Pico San Pedro NIFZ
kx, Horizontal permeability (md) 3.2 0.13 18 50 50 1–1000*
kx/kz, Anisotropy 100 100 100 100 100 0.1
/, Porosity 0.16 0.17 0.23 0.33 0.30 0.20

ct, Bulk compressibility (Pa
�1) 1 9 10�10 3 9 10�9 1 9 10�10 1 9 10�10 1 9 10�10 3 9
10�9
e, Thermal dispersivity (m) 100 100 100 100 100 100
k, Bulk thermal conductivity (W m�1°C) 3.0 2.5 2.7 2.8 2.8 3.0
c, Specific heat of matrix (J kg�1 °C) 750 750 750 750 750 750
a, van Genuchten coefficient (m�1) 3.0 9 10�4 4.0 9 10�4 2.5
9 10�3 2.0 9 10�3 2.0 9 10�3 1.0 9 10�2
n, van Genuchten coefficient 5.0 4.0 6.0 4.5 4.3 8.0
Swr, Irreducible wetting phase saturation (%) 10 18 12 12 12 12
Snr, Irreducible nonwetting phase saturation (%) 6 10 7 7 7 3
*Fault zone permeabilities are varied depending on model
settings described in Table 2. Permeability and porosity values
were selected within the ranges
from a technical report written by the California Department of
Conservation (1991) and unpublished data from Plains
Exploration and Production Company.
1 md = 10�15 m2. Capillarity model parameters are obtained
from publications (see the text).
Table 2 Petroleum migration scenarios for the Newport-

Inglewood fault zone.
Model Scenario Overpressure ratio (%) Fault permeability
(md)* Period of fluid pulse (years) Petroleum saturation
1 Continuous 10 10 0.6
5 Episodic 10–80 1–1000 3000 0.6
6 Episodic 10–80 1–1000 2000 0.6
7 Episodic 10–80 1–1000 1000 0.6
8 Episodic 10–80 1–1000 500 0.6
*1 md = 10�15 m2.
240 B. JUNG et al.
were selected based on the current LA basin fluid pressure

gradient of 9.9–12.6 MPa km�1 (Berry 1973; McCulloh
1979). These values can be converted to �1.5 to 19.0% in
overpressure ratio. These relatively low-pressure gradients,
despite the high subsidence and sedimentation rates, seem
to originate from the high content of coarse-grained sedi-
ments that can dissipate pressure very effectively in the LA
basin (Hayba & Bethke 1995).
We assumed the whole domain was initially hydrostatic,
and then, the lower right end of the fault on the boundary
of the mesh (marked by the white arrow in Fig. 6) was set
to 10% overpressure. Petroleum saturation at the inlet of
the fault zone was maintained as a constant value of 0.6,
which is taken from the average value of Miocene strata in
the Inglewood oil field (California Department of Conser-

vation 1992).
Figure 7 illustrates the pore pressure change in terms of
hydraulic head (h) of the continuous flow model, assuming
a constant fault permeability of 10 md (10�14 m2) and
overpressure ratio of 10% during the whole simulation time
(Model 1). The overpressured areas are sustained in the
lower part of the fault zone and the Miocene formations,
but the Pliocene and Pleistocene formations remain largely
hydrostatic (colored in white). The high pore fluid pressure
change is shown in the lower part of the fault. High fluid
pressure in the fault zone is confined in the Upper Mio-
cene formation due to its low permeability. The pressure
pattern reaches the equilibrium state approximately after

40 000 years. Subsurface temperature under the continu-
ous flow model displays dominantly conductive transport
patterns with nearly horizontal isotherms, except for a
slight elevation along the lower part of the fault zone
(Fig. 8A). Elevated temperatures are the result of upward
fluid flow into the fault zone, and contrast in thermal con-
ductivity. The petroleum velocity distribution of the
domain (Fig. 8B) shows that high velocity (approximately
0.2 m year�1) area appears at the lower part of the fault
zone, and it gradually decreases moving up along the fault.
The petroleum velocity at the upper part of the fault is
<0.03 m year�1.
Petroleum migrates mainly through the fault zone, and

the upper Miocene formation provides an effective seal for
the migration (Fig. 9A). Highly saturated areas (warmer
color) are found in the boundaries between the fault zone
and the upper Miocene formation because petroleum dis-
charge away from the fault is retarded by the permeability
contrast. Petroleum continues to rise due to buoyancy and
saturates the tributary fault structures such as the Sentous
fault before smearing into the Pliocene formation near the
fault zone, and eventually vents on the sea floor (Fig. 9C,
D).
EFFECT OF FAULT PERMEABILITY
Effects of fault zone permeability on petroleum distribu-
tion were investigated by comparing four continuous

flow models (Models 1–4). The parameters assumed are
tabulated in Table 2. For each model scenario, the per-
meability and pore pressure in the fault zone are assumed
to be constant. We also compared total accumulation
time required to reach the current estimate of total oil
reserve in the Inglewood oil field: approximately 450
million barrels of oil equivalent (MMBOE = 106 barrels)
(California Department of Conservation 1992). The total
petroleum volume in a unit of barrel of oil equivalent
(BOE), computed to provide a base of comparison, was
obtained by multiplying petroleum saturation, porosity,
and characteristic length (1 km) for considering the vol-
ume as a three-dimensional domain. The total petroleum

volume within the domain can be calculated using petro-
leum saturation, porosity, finite elemental area, and char-
acteristic length:
PV ¼
XN
i¼1
Sn/Ai
!
� Lc ð10Þ
where PV is the total petroleum volume at a specified time
step, N the number of finite elements, Sn the petroleum
saturation, / is porosity, Ai is the area of the i-th finite ele-
ment, and Lc the characteristic length.
The temporal variation of total petroleum volume of

four continuous models are depicted for showing the rela-
tionship of fault permeability and flow simulation time
required for the total volume of 450 million barrels
Fig. 7. Hydraulic head change (Dh = h – h0, h0 is hydrostatic
pressure) of
the Newport-Inglewood fault zone applied with the continuous
petroleum
migration model having constant fault zone permeability of 10
md
(10�14 m2) (Model 1) at 100 000 years after starting
simulation. Overpres-
sure appears along the fault zone. The domain was initially
hydrostatic and
then the 10% overpressure was applied at the lower end of the
fault
boundary. Numbers are in meter.

(Fig. 10). Not surprisingly, the results indicate that higher
fault permeability results in faster accumulation. For exam-
ple, the reservoir takes about 62 000 years to fill when the
fault permeability is 10 md (10�14 m2), but this time per-
iod reduces to about 34 000 years when the permeability
increases to 50 md. It is also worth noting that the filling
time increases with decreasing fault permeability almost in
linear proportion. The spatial patterns of petroleum satura-
tion are also affected significantly by fault permeability.
Figure 11 shows petroleum saturations for Models 1–4

when the total volume is equal to 450 million barrels. In
the high fault permeability model (Model 4, Fig. 11D),
petroleum migrates more vigorously laterally to invade
adjacent formations through fingering and channeling
(A) (B)
Fig. 8. (A) Subsurface temperature (°C) and (B)
petroleum velocity of the fault zone (Model 1)
at 100 000 years after starting simulation. The
top margin of the grid was set as the isothermal
boundary condition of 4°C, and the bottom
margin were assigned as a constant tempera-
ture of 160°C, based on geothermal gradients
reported in this area of 35–40°C km�1. The left

and right sides were assumed to be thermally
insulated for heat.
(A) (B)
(C) (D)
Fig. 9. Evolution of petroleum saturation for
Model 1 at (A) 40 000 years, (B) 60 000 years,
(C) 80 000 years, and (D) 100 000 years of
simulation time showing the advancement of
hydrocarbons through the fault zone. Petroleum
invades into the upper Miocene units because
of the relatively high fluid pressure in the lower
part of the fault. The outline of this magnified
area is marked with dashed lines in Fig. 6.

242 B. JUNG et al.
effects and accumulates significantly enhanced pools in the
Pliocene sediments compared with that of low permeabil-
ity cases. In the low permeability model (Fig. 11A, Model
2), however, accumulation tends to be more abundant in
the upper Miocene sediments and less in the Pliocene
unit.
Fig. 10. Effect of fault permeability on flow
duration needed to accumulate the current
known volume of petroleum in the Inglewood

oil field (1 MMBOE = 106 barrels). Flow dura-
tion assumes that 20% of the total fault length
in transverse is available for petroleum migra-
tion and therefore characteristic or effective
flow length of about 1 km.
(A) (B)
(C) (D)
Fig. 11. Comparison of continuous flow models
showing the effects of fault permeability on
petroleum migration and distribution, indicated
by saturation. Numbers in parenthesis indicate
times needed for accumulating total oil reverse
in Inglewood field (see Fig. 10).

EPISODIC FLOW MODEL
Models 5 through 8 were designed to investigate the
effects of episodic fluid flow on petroleum migration,
based on a fault-valve mechanism (Wright 1991), so a
repeating pattern of changing fault permeability and pore
fluid pressure was assigned (Fig. 12). A sharp increase in
permeability from k = 1 to 1000 md (10�15 to 10�12 m2)
denotes fault rupturing caused by tectonic stresses or due
to hydrofracturing by fluid pressure accumulation (Fisher
& Knipe 2001). Elevated fault permeability and accompa-

nied focused fluid flow are, however, considered to be
short-lived (<100 years) events (Sibson 1994), so the fault
will be closed hydromechanically as the pore pressure
decreases and will be assumed to sealed by mineral precipi-
tation (Dieterich & Kilgore 1996; Scholz 2002; Johnson
& Jia 2005). Recent field measurements of time-varying
permeability in faults after large earthquakes also suggest
that transient fluid pulses play a major role for water circu-
lation in deep fault zones (Xue et al. 2013).
To simulate these sealing effects, the fault zone perme-
ability was decreased from 1000 to 10 md during the first
100 years after rupturing, and then, it continued to be
reduced to 1 md until the next pulse occurs 2000 years

later. We assumed that the hydromechanical compaction
causing the first stage of permeability drop is abrupt and
much faster than the second stage of drop dominated by
hydrothermal precipitation.
We also assume that the fault ruptured at overpressure
ratio of 80%, and pore fluid pressure dropped to 10% over-
pressure level for the episodic flow model. The fluid pressure
gradually builds back up to 80% during the sealing period.
Qualitative behavior of these fluctuating pore pressure pat-
terns was first suggested by Sibson (see review by Roberts &
Nunn 1995), and the pressure value at the fault rupture was
chosen from work by Gratier et al. (2003) and Appold et al.

(2007). Petrologic evidence of multiple pulses of petroleum
flow in fault zones is reported in publications that deal with
Neogene basins in southern California (Boles & Ramseyer
1987; Eichhubl & Boles 2000; Perez & Boles 2007), but
there are a lack of articles providing a quantitative estimation
of possible flow duration. In this study, the period of epi-
sodic flow pulse was chosen within the range of 500–
2000 years based on Myers’s research on the Puente Hill
blind fault in the LA basin (Myers et al. 2003), where he
estimated the recurrence period of earthquakes in this fault
zone to be approximately 1700–3200 years, assuming a
Richter magnitude of M = 6.0–7.5. We assume that earth-
quakes in that range could impose significant hydromechan-

ical impacts on the adjacent aquifers.
Fig. 12. Fault permeability and pore fluid pres-
sure settings for the episodic flow model (Model
6). Fault permeability changes applied to the
whole fault zone, and pore pressure changes
applied to the end of the fault on the boundary
elements (marked by the white arrow in Fig. 6)
244 B. JUNG et al.
When the fault zone is sealed, pore fluid pressure builds
up in the lower part of the fault so it cannot reach the upper
formations due to the low fault permeability (Fig. 13A).

After the fault is open, previously accumulated high pressure
is released, and a temporary focus of fluid flow is created in
the fault zone (Fig. 13B). The released overpressure per-
vades the Miocene formations and the center of the anticline
structure. This strong and episodic pressure anomaly may
act as a strong transient driving force for both groundwater
and petroleum. Furthermore, a subsurface heat anomaly is
also detected along the fault zone due to the increased flow
rate and heat advection (Fig. 14). Temperature elevation in
the fault zone can facilitate the petroleum migration by
decreasing viscosity of the fluid. However, the heat anomaly
disappears when the fault is sealed, and isotherms become

horizontal and conductive.
The pattern of petroleum migration in the early stages is
similar to that of continuous migration, which mostly fol-
lows the fault surface (Fig. 15A), but some distinctive and
different patterns appear in later stages. In the episodic
model, petroleum migration seems to be more dispersed
than in the continuous model and accumulates in broader
areas in the middle of the shallow Pliocene sediments.
Petroleum migrates from the fault structures themselves
and extends into the adjacent sedimentary formations.
Effective spreading of petroleum to the adjacent rocks is
due to the high permeability, Darcy flow rates, and fluid
pressure concentrated in this area during the episodic flow

events. Especially, the high fluid pressure facilitates petro-
leum to overcome entry pressure of reservoir rocks sur-
rounding the fault zone.
EFFECT OF EPISODIC FLOW FREQUENCY
To further investigate the effect of frequency of episodic
fluid flow on petroleum accumulation, the temporal varia-
tion of total petroleum volumes for Models 5 to 8 can be
compared graphically (Fig. 16). The total volume of petro-
(A) (B)
Fig. 13. Hydraulic head change (Δh = h – h0)
for the episodic flow model (Model 6): (A) just
before the fault opening due to fault rupture,
and (B) 50 years after the fault opening. h0 is

the hydrostatic pressure. Numbers are in meter.
(A) (B)
Fig. 14. Subsurface temperature for the epi-
sodic flow model (Model 6): (A) before the fault
opening, and (B) 50 years after the fault open.
leum increases with flow frequency. If we set the known
450 million barrels as the comparison base, the flow model
with a shorter period of episodic flow pulses reaches the
base faster than the model with a longer period. For exam-

ple, it takes approximately 5700 years if the period of epi-
sodic pulse is 500 years (Model 8) but takes more than
24 100 years if the period is 3000 years (Model 5). Petro-
leum distributions of Models 5 to 8 at the comparison
base were compared in Fig. 17. The overall patterns of
petroleum distributions from four models look similar.
(A) (B)
(C) (D)
Fig. 15. Evolution of petroleum saturation for
the episodic flow model (Model 6) at four time
steps.
Fig. 16. Comparison of total petroleum volume
changes of episodic flow models, showing the

effect of fault permeability on recharging (fill-
ing) times needed to accumulate the observed
volume of total oil reserve in the Inglewood oil
field. Filling times (durations) assume that only
20% of the fault zone is available for petroleum
migration along the length of the oil field.
246 B. JUNG et al.
They all caused significant accumulations in the Pliocene
unit and channeled flow in the middle Miocene unit, but
the shorter period scenario (Model 8, Fig. 17D) enables

more pervasive accumulations in the center of the Pliocene
unit, in the Sentous fault, and in the upper part of the
Newport-Inglewood fault zone. It also caused relatively
smaller intrusion into the Middle Miocene unit, which
probably means that the episodic migration having a
shorter period is more active in transferring petroleum
upward because the fault zone is open more frequently
and assumed to be sealed for less time.
The episodic flow model having the fault k range of 1–
1000 md (10�15 to 10�12 m2) and a pulse interval of
3000 years (Model 5) can be compared with a continuous
model (Model 4) having k values of 50 md to demonstrate
differences between continuous and episodic flow models.

These two cases were selected because their simulation
times required for fill the reservoir were most similar
although the pattern of the driving force is different. The
episodic model (Model 5) takes 24 100 years to accumu-
late the petroleum at the level of comparison point
(approximately 450 million barrels). This value is faster
than the elapsed time of the continuous model, which is
34 000 years, having fault permeability of 50 md. When
we consider the relatively short sum of open fault duration
(<1400 years) in Model 5, it could be said that the epi-
sodic flow can drive migration of petroleum more effi-
ciently compared to the continuous models with constant
fault permeability higher than 50 md.

For the given amount of total petroleum volume, epi-
sodic fault pressure-driven migration generates broader and
more highly saturated petroleum accumulations in the Pli-
ocene sediments and also showed more dispersed patterns
in the Middle Miocene unit. On the other hand, the con-
tinuous migration made relatively low-saturated accumula-
tions simply following the fault structures. Petroleum in
the continuous model also tends to stay in the lower part
of the fault zone and rise slowly by the forces of buoyancy.
CONCLUSIONS
To understand the dynamics of petroleum migration in
active margin basins, both continuous and episodic fluid
migration models were constructed for the Newport-Ingle-

wood fault zone in the Los Angeles basin. The effects of
time-varying fault permeability on hydrocarbon accumula-
tion rate and pattern are also quantitatively investigated
using multiphase numerical modeling.
In continuous flow models, the petroleum migration
rate in the fault zone ranges 0.03–0.2 m year�1, and the
(A) (B)
(C) (D)
Fig. 17. Comparison of episodic flow models
showing the effects of flow frequency on petro-
leum migration and distribution. Numbers in
parenthesis indicate times needed for accumu-

lating total oil reverse in Inglewood field (see
Fig. 16).
duration of time needed to form the Inglewood oil field
(approximately 450 million barrels) is approximately
34 000–62 000 years depending on the fault permeability
assigned varying 50–5 md. High fault permeability also
allows more petroleum accumulation and channeling in the
Pliocene formation because larger overpressures can propa-
gate further and reach at the upper part of the fault.
In episodic models, the total oil volume in the reservoir

can be accumulated in about 24 000 years under assump-
tions that fault permeability fluctuates between 1–1000 md
and seismically induced flow pulse occurs every 2000 years.
Episodic migration forms larger areas of oil accumulation
with highly petroleum saturation accumulations in a
broader region surrounding the fault zone. Considering
the observed pattern of hydrocarbon accumulation in this
region, the episodic model could be more geologically
meaningful than continuous migration model.
The frequency of episodic flow affects petroleum migra-
tion and distribution patterns in the fault zone. Faster and
broader accumulations appear in the Pliocene sediments if

the pulse period becomes shorter. The frequent episodic
fluid pulse also forms accumulations with higher petroleum
saturation and flow channels in adjacent formations.
ACKNOWLEDGEMENTS
This research was supported by a grant from the U.S.
Department of Energy – Basic Energy Sciences (Grant
number: DE-FG02-96ER14620), The GDL Foundation
also provided a Ph.D. scholarship to the first author, for
which he is extremely grateful.
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250 B. JUNG et al.

Volume 14, Number 2, May 2014
ISSN 1468-8115
Geofluids
This journal is available online at Wiley Online Library.
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Geofluids is abstracted/indexed in Chemical Abstracts
CONTENTS
127 Review of ‘Too Hot To Touch: The Problem of High-Level
Nuclear Waste’ by
William M. Alley and Rosemarie Alley
E.M. Kwicklis
128 Diffusion and kinetic control of weathering layer
development
D. Reeves and D.H. Rothman
143 Carbon dioxide controlled earthquake distribution pattern in

the NW Bohemian
swarm earthquake region, western Eger Rift, Czech Republic –
gas migration in the
crystalline basement
F.H. Weinlich
160 Fractal analysis of veins in Permian carbonate rocks in the
Lingtanchang anticline,
western China
B. Deng, S. Liu, L. Jansa, S. Yong and Z. Zhang
174 Fluid effect on hydraulic fracture propagation behavior: a
comparison between water
and supercritical CO2-like fluid
X. Zhou and T.J. Burbey
189 Cementation and the hydromechanical behavior of
siliciclastic aquifers and reservoirs
D.F. Boutt, K.E. Plourde, J. Cook and L.B. Goodwin
200 Impacts of Pleistocene glacial loading on abnormal pore-
water pressure in the
eastern Michigan Basin
O. Khader and K. Novakowski

221 Numerical simulation of mylonitization and structural
controls on fluid flow and
mineralization of the Hetai gold deposit, west Guangdong,
China
J. Zhu, Z. Li, G. Lin, Q. Zeng, Y. Zhou, J. Yi, G. Gong and G.
Chen
234 Effects of episodic fluid flow on hydrocarbon migration in
the Newport-Inglewood
Fault Zone, Southern California
B. Jung, G. Garven and J.R. Boles
gfl_14_2_Issue toc_OC 4/11/2014 12:51 PM Page 1
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747
Bulletin of the Seismological Society of America, Vol. 94, No.
2, pp. 747–752, April 2004
Activity of the Offshore Newport–Inglewood Rose Canyon Fault
Zone,
Coastal Southern California, from Relocated Microseismicity
by Lisa B. Grant and Peter M. Shearer
Abstract An offshore zone of faulting approximately 10 km
from the southern
California coast connects the seismically active strike-slip
Newport–Inglewood fault
zone in the Los Angeles metropolitan region with the active
Rose Canyon fault zone
in the San Diego area. Relatively little seismicity has been
recorded along the off-
shore Newport–Inglewood Rose Canyon fault zone, although it
has long been sus-
pected of being seismogenic. Active low-angle thrust faults and
Quaternary folds

have been imaged by seismic reflection profiling along the
offshore fault zone, raising
the question of whether a through-going, active strike-slip fault
zone exists. We
applied a waveform cross-correlation algorithm to identify
clusters of microseis-
micity consisting of similar events. Analysis of two clusters
along the offshore fault
zone shows that they are associated with nearly vertical, north-
northwest-striking
faults, consistent with an offshore extension of the Newport–
Inglewood and Rose
Canyon strike-slip fault zones. P-wave polarities from a 1981
event cluster are con-
sistent with a right-lateral strike-slip focal mechanism solution.
Introduction
The Newport–Inglewood fault zone (NIFZ) was first
identified as a significant threat to southern California resi-
dents in 1933 when it generated the M 6.3 Long Beach earth-
quake, killing 115 people and providing motivation for pas-
sage of the first seismic safety legislation in the United States
(Barrows, 1974; Hauksson and Gross, 1991; Yeats, 2001).
The Rose Canyon fault (RCF) zone in the San Diego area

has ruptured several times during the Holocene (Lindvall
and Rockwell, 1995) and poses significant seismic hazard to
San Diego area residents (Anderson et al., 1989). An off-
shore zone of faulting approximately 10 km from the south-
ern California coast connects the strike-slip NIFZ in the Los
Angeles metropolitan region with the strike-slip RCF zone
in the San Diego area. The activity and seismic potential of
the intervening offshore fault zone, herein referred to as the
offshore Newport–Inglewood Rose Canyon (ONI-RC) fault
zone, has been the subject of debate for decades (e.g., Hill,
1971; Barrows, 1974; Fischer and Mills, 1991; Rivero et al.,
2000; Grant and Rockwell, 2002). Recent attention has fo-
cused on blind thrusts that may intersect the ONI-RC fault
zone and accommodate some of the regional deformation
(Grant et al., 1999; Rivero et al., 2000). Interaction with the
thrust system could limit the magnitude of earthquakes on
strike-slip faults in the ONI-RC fault zone, if they are active.
Sparse offshore microseismicity has been difficult to locate
accurately (Astiz and Shearer, 2000) but has been interpreted
to be associated with an active ONI-RC fault zone (Fischer
and Mills, 1991). We identified, relocated, and analyzed two
clusters of microearthquakes within the northern and central
ONI-RC fault zone to examine the fault structure, minimum
depth of seismic activity, and source fault mechanism. The

results suggest that the ONI-RC fault zone is a steeply dip-
ping, active strike-slip fault to seismogenic depths.
Tectonic and Geologic Setting
In southern California, tectonic deformation between
the Pacific and North American plates is accommodated pri-
marily by a zone of strike-slip faults (Walls et al., 1998)
with maximum deformation along the San Andreas system,
decreasing westward into the offshore inner Continental
Borderland region (Fig. 1). The inner Continental Border-
land has complex structure including low-angle detachment
faults, thrust faults, and high-angle strike-slip faults resulting
from late Cenozoic rifting prior to the current transpressional
tectonic regime (Crouch and Suppe, 1993; Bohannon and
Geist, 1998). The geometry and slip rate of faults in the inner
Continental Borderland are poorly constrained relative to
onshore faults (Astiz and Shearer, 2000), yet they may pose
significant seismic risk because they are close to populated
areas, and several offshore faults appear to displace seafloor
sediments (Legg, 1991). Grant and Rockwell (2002) pro-
posed that an active �300-km-long Coastal Fault zone
(Fig. 2) extends between the Los Angeles basin (USA) and
coastal Baja California (Mexico), including the NIFZ and
RCF zone in southern California, the Agua Blanca fault in

748 Short Notes
Figure 1. Regional fault map (modified from Grant and
Rockwell [2002]; after
Walls et al. [1998]) summarizing regional tectonic deformation
according to slip rate
on major faults, including the San Andreas fault (SAF), San
Jacinto fault zone (SJFZ),
Elsinore fault zone (EFZ), Whittier fault (WF), Palos Verdes
fault (PVF), NIFZ near Los
Angeles (LA), RCF zone (RCFZ) near San Diego (SD), Agua
Blanca fault zone (ABFZ),
San Miguel fault zone (SMFZ), Imperial fault (IF), Cerro Prieto
fault (CPF), and Laguna
Salada fault (LSF). Offshore faults of the inner Continental
Borderland include the
Coronado Bank fault zone (CBF), San Diego Trough fault
(SDTF), San Clemente fault
zone (SCFZ), Santa Cruz Island fault (SCIF), and Santa Rosa
Island fault (SRIF). The
San Gabriel fault (SGF), San Cayetano fault (SCF), Oak Ridge
fault (ORF), and Santa

Ynez fault (SYF) are located in the Transverse Ranges.
Baja California, and contiguous offshore fault zones. The
structural style and slip rates of the NIFZ and RCF zone sug-
gest that the intervening ONI-RC fault zone is an active,
strike-slip fault zone with complex structure and a slip rate
of 0.5–2.0 mm/yr.
The NIFZ has been studied extensively in the Los An-
geles basin by petroleum geologists. Hill (1971) proposed
that the NIFZ overlies a major tectonic boundary separating
eastern continental basement facies of granitic and associ-
ated metamorphic rocks from oceanic Catalina schist facies
of the inner Continental Borderland province to the west.
The current strike-slip faulting regime apparently reactivated
a structural weakness along the Mesozoic subduction zone
(Hill, 1971) and initiated right-lateral motion in the mid-to-
late Pliocene (Wright, 1991; Freeman et al., 1992). The NIFZ
is a structurally complex series of discontinuous strike-slip
faults with associated folds and shorter normal and reverse
faults (Yeats, 1973), described by Wilcox et al. (1973) and
Harding (1973) in a set of classic papers on wrench tecton-
ics. Dextral displacement of late Miocene and younger sed-
iments reveals a long-term slip rate of 0.5 mm/yr (Freeman

et al., 1992). Multiple surface ruptures since the early Ho-
locene indicate that the minimum slip rate is at least 0.3–0.6
mm/yr and may be substantially higher (Grant et al., 1997).
A Holocene slip rate of �1 mm/yr has been assumed for
seismic hazard assessment (SCECWG, 1995). Seismically
active strands of the NIFZ have been mapped along the west-
ern margin of the Los Angeles basin between the cities of
Beverly Hills and Newport Beach (Bryant, 1988; Grant et
al., 1997) where the fault steps over and continues offshore
parallel to the coast (Morton and Miller, 1981).
The subsurface structure and tectonic history of the RCF
zone have not been studied as thoroughly as the NIFZ be-
cause it lacks petroleum reserves. The Holocene sense of
movement and slip rate of the RCF have been investigated
for seismic hazard studies. Lindvall and Rockwell (1995)
Short Notes 749
Figure 2. Map shows approximate location of major strands in
the Coastal fault
zone and dates of most recent rupture. The Coastal fault zone
includes the northern

NIFZ near Beverly Hills (BH) (dashed), southern NIFZ (bold)
near Newport Beach (NB),
the ONI-RC fault zone (gray) offshore of the San Joaquin Hills
(SJH) and city of Ocean-
side (O), the RCF zone (bold line) between La Jolla (LJ) and
San Diego, the Coronado
Bank fault zone (CBF), and the Agua Blanca fault zone (ABFZ,
bold). Modified from
Grant and Rockwell (2002); after Grant et al. (1997), Lindvall
and Rockwell (1995),
and Rockwell and Murbach (1999).
and Rockwell and Murbach (1999) reported that it is pri-
marily a strike-slip fault zone with a slip rate of 1–2 mm/yr,
although individual strands display varying amounts of dip-
slip motion in combination with strike slip.
Location and Structural Models of the ONI-RC
Fault Zone
The location of the ONI-RC fault zone has been mapped
by seismic reflection profiling in shallow water along the
inner continental margin between Newport Beach and La
Jolla, north of San Diego. Fischer and Mills (1991) sum-
marized the results of eight investigations between 1972 and

1988, including unpublished mapping for the nuclear gen-
erating station at San Onofre. Interpretations of Fischer and
Mills (1991) and prior studies disagree about the location
and number of traces, but all reveal a fairly continuous zone
of faulting within a few kilometers of the coastline. Fischer
and Mills (1991) presented several interpretive cross sec-
tions with a steeply dipping fault and flower structure sug-
gestive of strike-slip motion. They described an inner and
outer “thrust fault-fold complex” consisting of multiple
thrust faults and thrust-generated folds associated with a
positive flower structure, and they described an offshore ex-
tension of the San Joaquin Hills as being dextrally offset by
the ONI-RC fault zone. Grant and others (1999, 2000, 2002)
reported late Quaternary and Holocene uplift of the San Joa-
quin Hills inboard of the ONI-RC fault zone and suggested
that seismic activity of the San Joaquin Hills blind thrust and
ONI-RC fault zone are linked.
Recent offshore investigations have focused on the
structure and potential activity of a low-angle fault, the
Oceanside thrust, and its relationship to the ONI-RC fault
zone (Bohannon and Geist, 1998; Rivero et al., 2000). Riv-
ero et al. (2000) proposed that the San Joaquin Hills blind
thrust is a backthrust soling into the larger Oceanside thrust.

In this model, Quaternary uplift of the San Joaquin Hills and
coastline south to San Diego is associated with movement
of the Oceanside thrust. They presented four potential con-
figurations for thrust interaction with strike-slip faults in the
ONI-RC fault zone, each leading to a different maximum
magnitude estimate, based on the activity and depth of the
strike-slip system. Our analysis of microseismicity helps
constrain the most viable model for interaction between the
Oceanside thrust and ONI-RC fault zone.
Seismicity and Event Location Method
No significant historic earthquakes have occurred on the
ONI-RC fault zone. Scattered seismicity has been recorded
along the ONI-RC fault zone (Fig. 3), although events are
difficult to locate accurately due to poor station coverage
(Fischer and Mills, 1991; Astiz and Shearer, 2000). With the
exception of the energetic 1986 ML 5.3 Oceanside earth-
quake sequence, rates of microseismicity have been low
since digital waveform data became available in 1981 (Astiz
and Shearer, 2000). Fischer and Mills (1991) reported that
the rate of seismicity along the ONI-RC fault zone is ap-
proximately 10 times lower than along the onshore NIFZ.
Rivero et al. (2000) interpreted the 1986 Oceanside earth-
quake sequence as generated by the Thirtymile Bank thrust

fault, a reactivated low-angle detachment fault.
Figure 3 shows microseismicity of the inner Continental
Borderland between 1981 and February 2003. The earth-
quake locations were computed from the archived P and S
picks using the source-specific station term method of
Richards-Dinger and Shearer (2000). This method improves
the relative location of events within compact clusters by
solving for custom station terms for subsets of the events,
thus removing the biasing effects of unmodeled three-
750 Short Notes
-118.0 -117.5
33.2
33.4
33.6
33.8

Oceanside
Newport Beach
A
B
Elsinore
San Clemente
Newport-Inglewood
P
alos Verdes
0 10 km
Figure 3. Earthquakes (black dots) near the
coastal cities (circles) of Newport Beach, San Cle-
mente, and Oceanside, California, recorded from
1981 to February 2003. Black boxes indicate clusters
of similar events near the ONI-RC fault zone. A 1981
cluster near Oceanside (box A) is shown in Figure 4,

and a 2000 cluster near Newport Beach (box B) is
shown in Figure 5. The approximate locations of the
Elsinore, Newport–Inglewood, and Palos Verdes
faults are also shown.
-117.52 -117.51
33.26
33.27
A
A'
0.0 0.4 0.8
12.0
12.5
13.0
13.5

Distance (km)
D
e
p
th
(
km
)
A A'
0.5 km0
Figure 4. The 1981 Oceanside cluster (from box
A on Fig. 3) is plotted at higher resolution in
map view and cross section, after relocation using
differential times computed using waveform cross-
correlation.
dimensional velocity and the varying station coverage
among the events. In general, this results in sharper and
better-defined seismicity alignments. The method does not,

however, necessarily yield improvements in the absolute lo-
cations of the clusters. We obtained waveforms for these
events and performed waveform cross-correlation between
each event and 100 neighboring events (Shearer, 1997; Astiz
et al., 2000). We then identified clusters of similar events
and relocated the microearthquakes within similar event
clusters using the method of Shearer (1998, 2002). On Fig-
ure 3, each cluster is so compact that these appear mostly as
single dots. Two of these clusters, in boxes labeled A and B
in Figure 3, are associated with the ONI-RC fault zone and
are the focus of this article.
Results
The Oceanside Cluster
The most interesting cluster is from a 1981 swarm of
19 M �3.0 earthquakes approximately 10 km northwest of
Oceanside. This cluster should not be confused with the
more energetic 1986 ML 5.3 Oceanside earthquake sequence
located much further offshore. As shown in Figure 4, the
events align along a north-northwest trend about 0.5 km
long. In cross section, the events define a nearly vertical
plane between 12.5 and 13.0 km depth. The strike, dip, and

location of a plane fit by these events are consistent with
active strike-slip faulting on the ONI-RC fault zone.
Fischer and Mills (1991) reported that the 1981 cluster
represents “a direct correlation of seismicity” (p. 30) with
the ONI-RC fault zone because they located the earthquakes
within 0.5 km of where they mapped the Oceanside segment
of the fault zone. Our relocation results support this inter-
pretation by showing that the events within the cluster form
a linear trend that is approximately parallel to the fault zone.
Fischer and Mills (1991) also calculated a strike-slip single
event first motion focal mechanism solution for an earth-
quake in the 1981 cluster. We are doubtful that unique focal
mechanisms can be computed for the 1981 events, given the
sparse distribution of seismic stations. However, we did ex-
amine composite waveform polarities from the 1981 cluster
using the method of Shearer et al. (2003) and found that the
polarities are consistent with a right-lateral strike-slip focal
mechanism solution, aligned with the trend of the ONI-RC
Short Notes 751
-117.870 -117.860

33.545
33.550
33.555
B
B'
0.0 0.5 1.0 1.5
6
7
Distance (km)
D
e
p
th

(
km
)
B B'
0.5 km0
Figure 5. The 2000 Newport Beach cluster (from
box B on Fig. 3) is plotted at higher resolution in
map view and cross section, after relocation using
differential times computed using waveform cross-
correlation.
fault zone. We cannot, however, entirely eliminate other
possible focal mechanisms.
The Newport Beach Cluster
A cluster of seven similar microearthquakes occurred
offshore of Newport Beach in 2000 at a depth of approxi-
mately 6.5–7.0 km. The cluster is near the offshore NIFZ as
mapped by Morton and Miller (1981) and compiled by
Fischer and Mills (1991). In map view and cross section

(Fig. 5), five of the seven events are aligned in a pattern
consistent with a shallow (7 km), north-northwest-striking,
vertical or steeply dipping active fault. Observed polarities
for this cluster are too sparse to provide any meaningful
constraint on the focal mechanisms.
The location of the 2000 cluster is southwest of an area
of active faulting reported by Fischer and Mills (1991) from
mapping offshore of Newport Beach and the San Joaquin
Hills. Fischer and Mills (1991) analyzed microseismicity
from 1982 to 1990 along this zone and reported strike-slip
and reverse-fault first motion solutions from a cluster of epi-
centers between 2 and 2.5 km on either side of the mapped
fault zone.
Discussion
The mean locations of each cluster are determined using
a standard 1D velocity model for all of southern California
and are probably not very accurate, particularly in depth. We
estimate uncertainties on the absolute cluster locations as
roughly �2 km in horizontal position and �5 km in depth.
However, the relative location accuracy among events
within each cluster is much better constrained, so the trends
defined by the seismicity alignments should be reliable. The

estimated relative location accuracy is generally less than
50 m for the events in the Oceanside cluster and less than
150 m for the aligned events in the Newport Beach cluster.
The two outlying events in the Newport Beach cluster have
standard errors of about 500 m; thus it is entirely possible
that their true locations lie within the linear trend of the other
events.
The location, alignment, and apparent dip of the Ocean-
side and Newport Beach clusters of microearthquakes are
consistent with the presence of active, steeply dipping faults
in the ONI-RC fault zone. Waveform polarities are also con-
sistent with strike-slip motion, although other mechanisms
cannot be ruled out.
For hazard estimation of offshore faults, it is not as im-
portant to precisely locate active traces as it is for onshore
faults in populated areas. A more important consideration is
the potential for a through-going rupture and an estimate of
the maximum magnitude earthquake. Our relocated micro-
seismicity is too sparse to reveal whether or not there is a
through-going strike-slip fault zone. The structure of the
ONI-RC fault zone may be similar to that of the onshore
NIFZ, which contains multiple strike-slip traces. Others have
mapped a fairly continuous structurally complex zone of

faulting �110 km long, subparallel to and within 10 km of
the coast (Fischer and Mills, 1991). The maximum magni-
tude of an ONI-RC fault rupture can be estimated from the
length of the fault zone. Assuming a 110-km surface rupture
length of a strike-slip fault zone yields an estimated M 7.4
earthquake (Wells and Coppersmith, 1994).
If strike-slip faults do not terminate the Oceanside
thrust, Rivero et al. (2000) estimate an Mw 7.5 maximum
magnitude earthquake could result from rupture of the entire
thrust fault. The �6.5-km depth of the Newport Beach seis-
micity cluster does not provide information on the geometry
or interaction between the strike-slip ONI-RC fault zone and
the Oceanside thrust. However, the location and �13 km
depth of the Oceanside cluster suggests that the Oceanside
thrust is terminated by active strike-slip faults. According to
Rivero et al. (2000), this geometry would lead to an Mw 7.3
maximum magnitude earthquake on the Oceanside thrust.
The maximum magnitude estimate is at the upper range of
magnitude estimated for an earthquake that uplifted the San
Joaquin Hills circa A.D. 1635–1769 (Grant et al., 2002).

752 Short Notes
Acknowledgments
This research was supported by the Southern California
Earthquake
Center. SCEC is funded by NSF Cooperative Agreement EAR-
0106924
and USGS Cooperative Agreement 02HQAG0008. The SCEC
Contribution
Number for this article is 746.
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Department of Environmental Health, Science, and Policy
University of California
Irvine, California 92697-7070
[email protected]
(L.B.G.)
Institute of Geophysics and Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, California 92093-0225
[email protected]
(P.M.S.)
Manuscript received 23 July 2003.
Paper Outline Due Thursday April 23
Posted on GWC Blackboard 3-5-20
Announced in class and illustrated on Thursday March 5, 2020

Required:
1. Two (2) reviewed articles with a person or persons as the
author. The U.S.G.S or the
EPA is not a person. The last pages of your article must
have a reference page. No
reference page or named person or multiple authors are
not acceptable.
2. Two but not more than five pages of text double or 1.5
spaced with normal margins like those in the sample outline.
3. Sources that are good various reviewed journals Science,
Nature, Scientific
American. These publications will have sources at the end
with references
within the text of the paper.
4. Sources to stay away from Science Direct, Geology.com,
National Geographic,
Newspapers, Magazines. If the article you chose has
advertisements then stay away

from these sources, or any with advertising ads.
What to hand in.
1. Your outline as a hard copy.
2. Complete printed out copies of your sources all clipped
together.
3. Must be clipped together with the outline. No folded corners
on the papers
as an attempt to keep them together. Use a clip.
Failure to provide a copy of your sources along with the outline
will result in a failing grade for this outline. No late
assignments will be accepted. No electronic files accepted.

Student Name Bud BennemanGeology 105 Spring 2020Paper Outline.docx

Student Name Bud BennemanGeology 105 Spring 2020Paper Outline.docx

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