1. WoodsHighlights of employee work in research, technology, techniques, and
the application of science to natural resource management
Page 1Produced by the Forest Resources Division - Forest Informatics and Planning
In the
Issue 1-Vol. 2 ♦ May 2015
AboutThis Article
This article is second in a series to fos-
ter awareness of the great work being
done by DNR's State Lands employ-
ees. In these articles, we will explore
innovative ideas, scientific research,
new techniques, and accomplishments
to inform and inspire.
General questions about this article
can be sent to Cathy Chauvin at 360-
902-1385 or Cathy.Chauvin@dnr.
wa.gov. For technical questions on
geophysical techniques, please con-
tact Recep (Ray) Cakir at 360-902-1460
or Recep.Cakir@dnr.wa.gov. Ques-
tions specific to geology and forest
roads can be directed to John Jenkins
at 360-827-0204 or John.Jenkins2@
dnr.wa.gov. Many thanks to Ray Cakir,
John Jenkins, Venice Goetz, Casey
Hanell, andTimothyWalsh for their
assistance on this article.
Peering Into the Earth
Using geophysical techniques to find rock for forest roads
by Cathy Chauvin, Editor and Publisher, Forest Resources Division
Fresh off the stump and replete with water, fresh-
cut timber is heavy stuff. A fully loaded logging truck can tip the scales
at 68,000 pounds, which is the weight equivalent of approximately 17
average-size cars.
To support this kind of weight, forest roads must be built strong with
good, hard rock. How hard? Generally, the best rock has few fractures
and requires blasting for extraction.
DNR obtains the rock it needs from existing rock pits located across
state trust lands, but new sources often are needed. The farther rock
must be hauled from the pit, the more it costs to build the road. Haul
rock far enough, and a promising timber sale becomes infeasible.
Finding good rock can be a challenge, especially in steep, heavily forested
terrain. Current methods include field reconnaissance and use of geolog-
ic maps to locate deposits and predict which direction they run beneath
the surface. Promising areas may be explored with test pits and drilling.
Unfortunately, rock deposits are seldom uniform, thick in some places
and thin in others, soft and fractured here but harder there. It can be

2. In the Woods
Washington State Department of Natural ResourcesPage 2
Text Box 1. ProjectTeam Membersdifficult to know exactly where to dig or what type of
equipment to use. All of this begs the question: surely,
there must be a better way?
As it turns out, there is.
Looking for Answers
In early 2013, managers in DNR’s South Puget Sound
and Pacific Cascade region offices approached DNR’s
Geology and Earth Resources Division for a new way to
approach this problem. The challenge intrigued Recep
(Ray) Cakir, a hazards geophysicist in the division’s Geo-
logic Hazards group. Ray organized a team of specialists
(Text Box 1) to answer the following question: was there
a cost-effective, practical geophysical technique that
could be used to locate rock for forest roads, character-
ize rock quality, determine the thickness of the overbur-
den soils, and identify any concerns with groundwater,
all without breaking the ground surface? To answer this
question, the team tested a combination of geologic re-
connaissance and the following geophysical techniques:
active and passive seismic, electromagnetic induction,
electrical resistivity, and ground penetrating radar (GPR).
These techniques will be explained in this article.
Test Sites and Equipment
The testing was conducted at three sites on state trust
lands: the BB Pit timber sale on Tiger Mountain, Perry
Creek rock pit in Capitol State Forest, and the Eastern
Panhandle timber sale in the Elochoman block near
Cathlamet, WA. The Perry Creek rock pit was the prima-
ry test site at which all techniques were tested; selected
techniques were tested at the other sites. Since DNR had
only seismic equipment in-house, some equipment was
rented and some was provided by the geotechnical sup-
pliers on the team (Text Box 2).
At each of these sites, the primary rock types were
basalt, basalt breccia, and andesite. Basalt is a dark, fine-
grained rock that forms when molten rock cools on the
DNR
Geology and Earth Resources Division
Recep Cakir, Joseph Schilter,Terran Gufler,
TimothyWalsh, and Patricia Newman (intern)
Forest Resources Division
John Jenkins,Venice Goetz, and Casey Hanell,
Earth Sciences Program; Laura Cummings,
Pacific Cascade Region; and Ana Shafer, South
Puget Sound Region
Geometrics, Inc.
Koichi Hayashi
Northwest Geophysics, Inc.
Matt Benson
Text Box 2. Sites and MethodsTested
Perry Creek rock pit
All techniques tested
Geometrics, Inc. provided an "OHMmapper"
for electric resistivity and also participated
in testing.
Northwest Geophysics, Inc. provided a "Ge-
onics EM31-MK2" for electromagnetic
induction.
BB Pit and Eastern Panhandle timber sales
All techniques were tested except electric re-
sistivity and electromagnetic induction; rental
equipment was used for GPR.
ground. Andesite is similar to basalt, but has less iron
and magnesium and more silica. Basalt breccia forms
when the outer layer of a mass of molten rock cracks as
it cools because the inner layer is still flowing.

3. In the Woods
May 2015 Page 3
Geophysical
Techniques
Explained
Active and Passive Seis-
mic Techniques. When some-
thing shakes the earth, such as an
earthquake, an explosion, or a heavy
weight falling to the ground, waves
of seismic energy travel out from
the point of disturbance. By mea-
suring the velocity (speed) of these
waves, inferences can be made about
the composition of the ground.
Generally speaking, the higher the
velocity, the harder the rock. The
types of waves discussed in this sec-
tion are shown in Figure 1.
Seismic techniques can be active
or passive. The active technique
involves hitting the ground with a
hammer, dropping a heavy weight,
or setting off explosives to gener-
ate seismic waves. By contrast, the
passive technique involves measuring
the small seismic waves or micro-
tremors caused by day-to-day life: waves on the beach,
water running in a stream, wind blowing across a field,
traffic rolling past. With both techniques, one or more
ground sensors (“geophones”) are placed directly on the
ground. The geophone(s) feed data through a cable to a
seismograph that records the arrival of the seismic waves,
and the data collected are analyzed using computers.
The team tested two types of active seismic techniques:
P wave refraction and multichannel analysis of surface
waves (MASW). P wave refraction examines P waves,
or primary waves. P waves are the fastest of the seismic
waves (Figure 1) and are sometimes called compression
waves because they push and pull the earth as they pass.
When a P wave hits an area of density contrast, for ex-
ample the boundary between a layer of rock and a layer
of soil, some of its energy travels a distance along that
boundary and then bends or refracts back to the surface,
where its arrival is sensed by the geophones (Figure 2 on
the following page). The remainder of that energy con-
tinues to travel down until it hits another area of density
contrast and refracts upward. The velocity of each layer
is calculated using the time it takes the wave to arrive and
the distance the wave traveled to reach the geophone.
An example of a cross-section built with data from this
technique is shown in Figure 3.
Figure 1.Types of Seismic Waves
Body waves move through the interior of the earth; surface
waves move primarily near the surface.
Direction of wave
Direction of wave
Direction of wave
Particle motion - counter-clockwise
Particle motion - push and pull
Majority of
distortion
at surface
Ground surface
Ground surface
Rayleigh wave (surface wave)
P wave (body wave); also called primary or compression wave
Particle motion - up and down Ground surface
S wave (body wave); also called shear wave or secondary wave
Drawings adapted from http://folk.uio.no/valeriem/spice/Frame/surfacew/index.html
and http://www.colorado.edu/physics/phys2900/homepages/Marianne.Hogan/waves.html

4. In the Woods
Washington State Department of Natural ResourcesPage 4
Once collected, P wave val-
ues must be translated into
information a manager can
use to make decisions. For
example, if the P wave ve-
locity is 2.4 meters per sec-
ond, how hard is the rock?
Does it require blasting? To
answer these questions, the
team created a classifica-
tion system that correlates
P wave velocity values to
hardness characteristics of
western Washington rock.
The starting point for this work was the basalt portion
of the D8R/D8T Caterpillar Chart (Figure 4). Devel-
oped in a study sponsored by Caterpillar, Inc., the Cater-
pillar Charts define a range of P wave velocity values for
rock that is rippable (can be excavated manually, usually
Geophones
Seismograph
Shot
Uniform layer 1
Uniform layer 2
Refracted wave
Refracted wave
Signal
(arrives
first)
Time in
miliseconds
Distance in meters
Signal
Signal
Signal
(arrives
last)
Uniform layer 3
Velocity of layer 1 (V1) > Velocity of layer 2 (V2) > Velocity of layer 3 (V3)
Drawing adapted from http://asstgroup.com/techniques.html
Figure 2. P wave RefractionTechnique
Figure 3. P wave RefractionTechnique Cross-section
Categories correspond with classification system in Figure 5. Hardest rock is shown in
blue.
with a ripping head mounted on a tractor, dozer, or
other heavy equipment [Figure 5]), non-rippable (re-
quires blasting), and marginal (hard, but not hard enough
to require blasting) using different types and sizes of
equipment. The “D8R/D8T” chart (Figure 4) is geared
toward a D8R/D8T Caterpillar dozer, which is one of
the larger Caterpillar dozers. Using this type of dozer,

5. In the Woods
May 2015 Page 5
Figure 5. Ripping Head Mounted on an Excavator
Type Mineability Characteristics P wave velocities Comments
I
II
III
Hard:
Non-rippable
Intermediate*: Rippable,
depending on size of
excavator and fracture
characteristics
Soft: Diggable
with a shovel
Very hard to hard (pings with hammer);
fresh to slightly weathered; massive or very
wide fracture spacing: tight or slightly open
and clean or very thin filling
2.4-3.6
0.8-1.8; 0.8-2.4
0-0.8
Medium hard to hard; moderately weath-
ered; close to moderately close fracture
spacing; moderately thin to moderately
thick filling; coarse breccia
Extremely soft to soft; intensely weathered
or decomposed rock; very close to close
fracture spacing and moderately thick to
thick filling. Note: category includes soil
overburden (colluvium and topsoil)
Rock mineable with
blasting; typically clean
with few fines** generated
(gray area at lower veloci-
ties may be rippable)
Gray area exists between
low end of rippable and
diggable; low end of
rippable may be too soft
and have too many fines
Waste material, unusable
rock or soil overburden
Caterpillar chart: Caterpillar Inc., 2010, Caterpillar performance handbook (40th ed): Caterpillar, Inc., Peoria, Ill., 1, 442 p.
*Corresponds to marginal and rippable on Caterpillar Chart
**Rock dust
Seismic velocity
Meters per second x1000
Feet per second x1000
Basalt
Granite
Trap rock
TOPSOIL
CLAY
GLACIAL TILL
IGNEOUS ROCKS
Rippable Marginal Non-rippable
1 2 3 4 5 6 7 8 9 10
0 1 2 3 4
11 12 13 14
Hardness increases with velocity
Soft/diggable with a shovel
Figure 4. Excerpt from the D8R/D8T Caterpillar Chart (top) and theTeam’s Classification System (bottom).
for example, basalt with P wave velocities between 0.8
and approximately 2.4 is rippable; basalt with P wave
velocities above 2.4 is not.
The team’s classification system (Figure 4) assigns ranges
of P wave values from the D8R/D8T Caterpillar Chart
to one of three categories: hard, which is the same as
“non-rippable” on the Caterpillar chart; “intermediate,”
which combines the Caterpillar chart’s “rippable” and
“marginal” categories; and “soft,” for rock that is soft
enough to dig with a shovel and therefore useless for
road construction. Each category includes a description
of the physical characteristics of the rock.
This classification system likely is the first to correlate
P wave velocity values from a Caterpillar Chart to local
rock hardness characteristics. It may be expanded in fu-
ture studies, as will be explained at the end of this article.

6. In the Woods
Washington State Department of Natural ResourcesPage 6
The MASW technique (Figure 6) involves examining
Rayleigh waves, which are a type of seismic surface wave.
Rayleigh waves cause the ground to ripple and heave like
the ocean, and this motion causes particles at the surface
to move in counter-clockwise circles as the wave moves
past (Figure 1).
Because Rayleigh waves are influenced by the shear
strength or stiffness of the rock, their velocities can be
used to derive S wave (shear wave) velocities. Those
derived S wave velocities are then used to create a cross-
section of the subsurface. S waves are a type of body
wave that moves through the ground like a waving flag
(Figure 1) and are also called secondary waves, because
they are the second waves to arrive at a seismograph or
geophone (P waves arrive first).
The team also tested two passive seismic techniques,
one performed with an array of geophones and another
performed with a single, three-component seismograph
(three sensors built in one) called a Tromino seismo-
graph. Passive techniques usually measure surface waves.
Electromagnetic Induction and Electri-
cal Resistivity Techniques. Both of these
techniques use the electrical properties of the ground to
make inferences about its composition. One technique
measures conductivity and the other measures resistivity.
The electromagnetic induction technique measures
the ability of the ground to conduct electricity. In this
technique, a transmitter coil sends an alternating current
Geophones
Seismograph
Shot
Direction of wave
Drawing adapted from http://asstgroup.com/techniques.html
Signal
(arrives
first)
Time in
miliseconds
Distance in meters
Signal
Signal
Signal
Signal
(arrives
last)
Figure 6. Multichannel Analysis of Surface Waves (MASW)Technique

7. In the Woods
May 2015 Page 7
(AC) into the ground (Figure 7).
That current generates an electro-
magnetic field (electromagnetic
fields are generated when electricity
moves from one place to another,
for example along the cord of a
lamp when the lamp is turned on).
This field, called the primary electro-
magnetic field, causes the receiver
coil to react by generating a secondary
electromagnetic field. By measuring
the size of the secondary field—in
other words, determining how much
the receiver coil responds to the
primary field—it is possible to infer
the conductivity of the ground.
The transmitter and receiver coils
often are mounted at opposite ends
of a long pole, which is carried
across the ground. The drawback to
this technique is depth: the shorter
the pole, the shallower the depth.
For example, if the distance between
the centers of the coils is three me-
ters, then the depth of the survey is
approximately 3 meters.
The electrical resistivity technique
measures the ground's resistance to
transmitting an electrical current. In
this technique, transmitter dipoles
(a pair of equally and oppositely
charged poles) induce an electrical
current directly into the ground, and
receiver dipoles are placed nearby.
The difference in electrical potential between the trans-
mitter and receiver dipoles is then measured and used to
calculate resistivity.
At the Perry Creek site, the team used an instrument
called an OHMMapper, which consists of transmit-
Console
Transmitter
coil
Receiver
coil
Primary field
Secondary field
Drawing adapted from http://asstgroup.com/techniques.html
Figure 7. Electromagnetic InductionTechnique
Dipole cable
Transmitter diodes Receiver diodes
Dipole cable Weight
Non-conductive
tow-link cable
Fiber-optic
isolator cable
Current
Console
Drawing adapted from http://terraplus.ca/products/resistivity/ohmmapper.aspx
Figure 8. Electric ResistivityTechnique
ter and receiver dipoles mounted on a cable or rope
that is dragged along the ground (Figure 8). Similar to
electromagnetic induction, the depth of penetration is
determined by how far apart the transmitter and receiver
diodes are placed.

8. In the Woods
Washington State Department of Natural ResourcesPage 8
GPR Technique. The GPR technique makes use of
radio waves, which are a type of electromagnetic wave.
Electromagnetic waves can be arranged in a spectrum
depending on their frequency (Figure 9). Frequency is
the number of waves that pass a fixed point in a given
amount of time, and is often measured in hertz, kilo-
hertz, megahertz (MHz), or gigahertz.
With the GPR technique, high-frequency (for example,
12.4 to 1,500 MHz) radio waves are pulsed into the
ground by a radar antenna on the GPR unit. When
radio waves encounter an interface between areas
with different dielectric (insulating) properties, such
as soil horizons (layers of soil that differ from layers
above and below), soil/rock interfaces, or man-made
objects, a portion of the wave is reflected up and
detected by the GPR unit (Figure 10). From hun-
dreds of these measurements it is possible to map
the properties of the subsurface.
The depth of the survey is affected by wave frequen-
cy. Pulses of lower-frequency radio waves penetrate
more deeply but provide less detail than pulses of
higher-frequency waves.
Commonly, the GPR unit is pushed or pulled along
the ground. Distance is measured by a wheel on the
back of the unit, or by an additional GPS unit with a
built-in antenna for positioning. Other types of GPR units
can be mounted on a car or even a helicopter for aerial
surveys. The team used a ground-based unit for this study.
Results
Of all the techniques tested, GPR provided the most
detailed information for the depths at which most rock
would be extracted, approximately the first 10 meters
beneath the surface. In addition, GPR was the easiest
technique to perform, although the instrument requires
contact with the ground and may be difficult to deploy
in some forested areas. The GPR technique had the
added benefit of being fully described in the American
Society of Testing Materials (ASTM) standards, which
makes its results more legally defensible.
Active seismic techniques (P wave refraction and
MASW) provide good detail at the right depths; how-
ever, results were less detailed than GPR (Figure 10).
Of the two active seismic techniques, P wave refraction
was better, because P wave velocities can easily be tied to
rippability of various rock types and overburden material
such as topsoil. The P wave refraction technique also is
fully described in the ASTM standards.
Passive seismic techniques provided information for
depths of 100-200 meters, but did not provide enough
detail for the first 10 meters.
Transmitted wave
Interface between layers
Reflected wave
Drawing adapted from http://www.cflhd.gov/resources/agm/
engApplications/SubsurfaceChartacter/
634DetectUnexplodedOrdnance.cfm
Wheel measures distance
Figure 10. GPRTechnique
RadiowavesMicrowavesInfra-red
VisiblelightUltra-violetX-rays
Gammarays
Low frequency High frequency
Drawing adapted from http://www.darvill.clara.net/emag/
Figure 9. Electromagnetic spectrum

9. In the Woods
May 2015 Page 9
Electromagnetic induction and electrical resistivity
provided detailed conductivity and resistivity informa-
tion (respectively) for the shallow soil layers, but did not
penetrate deeply enough to provide adequate informa-
tion for locating rock sources. However, both of these
techniques provided more detailed groundwater infor-
mation than either GPR or P wave refraction.
For the most complete and accurate information, it is
best to combine techniques. The team recommended
that DNR use both GPR and P wave refraction tech-
niques to image the subsurface, determine the thickness
of overburden soil, and locate good rock. At sites where
groundwater conditions are a concern, these methods
could be combined with electromagnetic induction or
electrical resistivity techniques.
Figure 10. Comparison of P wave and GPRTechnique Cross Sections
The GPR technique provides the most detail.
Validation
Up to this point, results were promising but theoretical.
To validate the results, the team compared the GPR and
active seismic data with results obtained through drilling
at the Perry Creek site. The drilling results demonstrated
the accuracy of these techniques.
For further validation, the team will conduct drilling at
the other two sites (BB Pit timber sale on Tiger Moun-
tain and Eastern Panhandle timber sale in the Elocho-
man block). The team also will measure the groundwater
depth at Perry Creek.

10. In the Woods
Washington State Department of Natural ResourcesPage 10
Next Steps
The next step is to begin using these techniques (P wave
refraction and GPR) in the field to locate rock for for-
est roads. DNR recently purchased a GPR unit, which
will be useful not only for rock source surveys, but for
other applications such as locating underground pipes
or culverts, surveying for cultural resources, or develop-
ing more detailed geologic maps. Managers interested in
using P wave refraction and GPR to locate rock sources
are encouraged to contact Casey Hannell (360-902-1657
or Casey.Hannell@dnr.wa.gov).
As these techniques are implemented, the team will
continue to refine its classification system to make it
more specific to western Washington geology. One goal
is to expand the classification system to include more
geophysical parameters, including S wave velocities and
electric properties. This information will be highly useful
in defining boundaries between rocks of different quali-
ties.
Over time, geophysical surveys and the new classifica-
tion system should not only provide greater certainty for
developing new rock sources, but significantly reduce the
amount of drilling needed. Geophysical surveys are far
less expensive than drilling, which could increase revenue
to our trust beneficiaries.
This effort also demonstrated that working across divi-
sion lines can be an effective way to solve one of DNR’s
daily challenges. And that, indeed, is a better way to find
rock for forest roads.
About the Geology and Earth
Resources Division
The Geology and Earth Resources Division consists of
geologists and support staff who serve the state’s gov-
ernment and citizens by providing critical information
and education about the geology of Washington State.
Division geologists actively engage in geologic resource
identification, regulation, and mapping. The Division is
responsible for monitoring, assessing, and researching
the causes of earthquakes, landslides, and volcanoes,
and publishing information on geologic hazards to help
government and private sectors reduce the human and
financial effects of natural disasters.
About the Forest Resources
Division's Earth Sciences
Program
The Forest Resource Division's Earth Sciences Program
provides technical and scientific support for state trust
lands management activities in the fields of geology,
geomorphology, and hydrology. Program staff work
with foresters and engineers to assess the potential ef-
fects of management activities on potentially unstable
slopes, soil erosion, and hydrology, and to develop mea-
sures to mitigate adverse impacts. Their work includes
conducting landslide risk assessments for individual
timber sales, performing hydrologic change analyses,
developing landscape-scale landslide hazard zonation
maps, locating suitable rock sources for constructing and
maintaining forest roads, and carrying out earth scienc-
es-related research and monitoring.

11. In the Woods
May 2015 Page 11
For More Information
Basic Information About Seismic Waves
http://folk.uio.no/valeriem/spice/Frame/surfacew/
index.html
http://en.wikipedia.org/wiki/Seismic_wave
http://www.colorado.edu/physics/phys2900/homep-
ages/Marianne.Hogan/waves.html
More Information on Geophysical
Techniques
http://www.cflhd.gov/resources/agm/engApplications/
SubsurfaceChartacter/611DeterminDepthStructureFrac
tureBedrock.cfm
http://asstgroup.com/techniques.html
http://www.terradat.co.uk/survey-methods/ground-
conductivity-em/
http://terraplus.ca/products/resistivity/ohmmapper.
aspx
http://www.negeophysical.com/
http://www.epa.gov/esd/cmb/GeophysicsWebsite/
pages/reference/methods/Surface_Geophysical_Meth-
ods/Electromagnetic_Methods/Ground-Penetrating_
Radar.htm
http://www.epa.gov/esd/cmb/GeophysicsWebsite/
pages/reference/methods/Surface_Geophysical_Meth-
ods/Seismic_Methods/Surface_Wave_Methods.htm
http://www.cflhd.gov/resources/agm/engApplications/
SubsurfaceChartacter/623DeterminingRippabilityRock.
cfm
http://www.geonics.com
Other References
Caterpillar Inc., 2010, Caterpillar performance handbook
(40th ed.): Caterpillar, Inc., Peoria, Ill., 1, 442 p.
Cakir, R. and Walsh, T.J. (2011) Shallow seismic site char-
acterization at 23 strong-motion station sites in and near
Washington State. U.S. Geological Survey Award No.
G10AP00027. (http://earthquake.usgs.gov/research/
external/reports/G10AP00027.pdf)
Powers, M.H. and Burton, B.L., 2012, Measurement of
near-surface seismic compression wave velocities using
refraction tomography at a proposed construction site
on the Presidio of Monterey, California; U.S. Geologic
Survey Open-File Report 2012-1991, 17 p. (http://www.
cflhd.gov/resources/agm/engApplications/SubsurfaceC
hartacter/623DeterminingRippabilityRock.cfm)
Vendor Websites
http://www.geometrics.com
http://www.tromino.edu
http://www.northwestgeophysics.com/
http://www.gfinstruments.cz