This document discusses seismic vulnerability assessment and seismic hazard assessment parameters. It defines vulnerability as physical, social, economic and environmental factors that increase susceptibility to hazards. A seismic vulnerability assessment evaluates structural susceptibility to seismic damage based on performance objectives. Key parameters for ground shaking analysis include peak ground acceleration, peak ground velocity, and spectral acceleration. The document also discusses factors that affect earthquake ground shaking and different types of seismically induced ground failure like surface fault rupture, liquefaction, landslides and seismic compression. Methods to evaluate past earthquake activity and locate active fault zones through paleoseismological study are also mentioned.

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Seismic vulnerability and seismic
hazard assessment parameters
3/8/2016
SUBMITTED BY- PUJA PLABONA
GOGOI
MSc geology ,DEPT. OF
GEOLOGY,gauhati university

2. INTRODUCTION
In the last few decades, a dramatic increase in the losses caused by natural
catastrophes has been observed worldwide. Reasons for the increased losses are
manifold, though these certainly include the increase in world population, the
development of new “super-cities” (with a population greater than 2 million),
many of which are located in zones of high seismic hazard, and the high
vulnerability of modern societies and technologies (e.g., Smolka et al., 2004).
The 1994 Northridge (California, US) earthquake produced the highest ever
insured earthquake loss at approximately US$14 billion, and the US$150
billion cost of the 1995 Kobe (Japan) earthquake was the highest ever absolute
earthquake loss. Although the dollar value of economic losses in other parts of
the world may be far lower than in Japan and the US,the impact on the national
economy may be much greater due to losses being a larger proportion of the
gross national product (GNP) in that year. Coburn and Spence (2002) report the
economic losses due to earthquakes from 1972 to 1990; the three largest losses
as proportions of the GNP are in the Central American countries of Nicaragua
(1972, 40% GNP), Guatemala (1976, 18% GNP) and El Salvador (1986, 31%
GNP). When the economic burden falls entirely on the government (such as
occurred after the 1999 Kocaeli earthquake in Turkey), the impact on the
national economy can be crippling; one possible solution is to privatise the risk
by offering insurance to homeowners and then to export large parts of the risk to
the world’s reinsurance markets (e.g., Bommer et al., 2002). In order to design
such insurance and reinsurance schemes, a reliable earthquake loss model for
the region under consideration needs to be compiled such that the future losses
due to earthquakes can be determined with relative accuracy.
India also faces threats from a large number of natural hazards
such as earthquakes, floods, droughts, landslides, cyclones and tsunamis.
During the period 1990 to 2010, India experienced 9 damaging earthquakes that
have resulted in over 30,000 deaths and caused enormous damage to property,
assets and infrastructure. In many cases buildings and structures have proven
inadequate to resist earthquake forces and the failure of these can be held
responsible for most of the resulting human fatalities.
To mitigate earthquake losses,it is necessary to evaluate the earthquake hazards
across the country.In order to predict the impact of an earthquake on the

3. environment,it is essential to know the seismic vulnerability of the built
environmemt.So there is a necessity of seismic vulnerability and seismic hazard
assessments.
SEISMIC VULNERABILITY ASSESMENT
VULNERABILITY means the conditions determined by physical, educational,
social, economic, and environmental factors or processes that increase the
susceptibility of a community to the impact of hazards. For factors that increase
the ability of people to cope with hazards..A seismic vulnerability assessment
is a comprehensive engineering study to evaluate susceptibility of structural
systems to potential damage from seismic shaking based on the performance
objectives established by the Client and using methods,which generally follow
guidelines.
A vulnerability assessment needs to be made for a particular characterisation of
the ground motion, which will represent the seismic demand of the earthquake
on the building. The selected parameter should be able to correlate the ground
motion with the damage to the buildings. Traditionally, macroseismic
intensity and peak ground acceleration (PGA) have been used, whilst more
recent proposals have linked the seismic vulnerability of the buildings to
response spectra obtained from the ground motions.
POST-EARTHQUAKE EVALUATION
First we have to evaluate the earth quake. It is
important to conduct post-earthquake evaluations as soon following the
earthquake as is practical. Aftershock activity in the months immediately
following an earthquake is likely to produce additional strong ground motion at
the site of a damaged building. If there is adequate reason to assume that
damage has occurred, then such damage should be expeditiously uncovered and
repaired. However, since adequate resources for post-earthquake evaluation
may be limited, a staggered schedule is presented, with those buildings
having a greater likelihood of damage recommended for evaluation first.
Large magnitude earthquakes are often followed by large magnitude
aftershocks. Therefore, it is particularly urgent that post-earthquake evaluations
be performed expeditiously following such events. If visual inspection reveals

4. substantial damage, consideration should be given to vacating the building until
either an adequate period of time has passed so as to make the likelihood of
very large aftershocks relatively low (e.g. 4 weeks for magnitude 7 and lower,
and 8 weeks for magnitudes above this), complete inspections and repairs are
made, or a detailed evaluation indicates that the structure retains adequate
structural stiffness and strength to resist additional strong ground shaking.
Ground shaking analysis
Shaking of the ground caused by the passage of seismic waves,specially
surface waves near the epicentre of the earthquake. Ground shaking depends on
some factors
- condition of the local geology influence events:solid bedrock is far less
subject to intense shaking than loose sediments.
- duration and intensity of the earthquake are generally subject to the size
of the earthquake.
-distance:the distance from the epicentre drops off so the intensity of the
shaking decreases.This depends on the type of material underlying the area.
FACTORS AFFECTING EARTHQUAKE GROUND SHAKING

5. Parameters for ground shaking analysis –
-Peak ground acceleration(PGA)
-Peak ground velocity(PGV)
-Spectral acceleration
-Duration
-Time history
Ground displacement & failure
During earthquakes, buildings and other improvements can be damaged
directly by strong shaking or from earthquake-induced permanent displacements
of the ground. Seismically-induced ground failure is defined as any
earthquake-generated process that leads to deformations within a soil medium,
which in turn results in permanent horizontal or vertical displacements of the
ground surface. The following modes of seismically-induced ground failure
have been documented in past earthquakes:

• Surface fault rupture Earthquakes result from sudden slip across a fault
surface. Earthquakes on faults are generated in rock deep within the
earth’s crust, with typical focal depths (i.e., the depth at which slip
originates) in California being on the order of 5 to 20 km. The slip of a
fault during an earthquake results in large-scale relative displacements of
the earth on opposite sides of the fault. These relative displacements can
be as large as 10 m. When fault slip extends to the ground surface, the
resulting ground displacements are termed “surface fault rupture.”
Examples of California earthquakes with surface fault rupture include
1906 San Francisco, 1971 San Fernando, 1992 Landers, and 1999 Hector
Mine.
• Liquefaction Liquefaction is defined as the transformation of a granular soil
from a solid state to a liquefied state as a consequenceof increased pore
pressure and reduced effective stress (Committee on Soil Dynamics of the
Geotechnical Engineering Division, 1978). Herein, the initiating
disturbance is assumed to be cyclic shear deformations resulting from an
earthquake. The loss of shear strength associated with liquefaction can
create ground deformations and/or instability. For example, post-
liquefaction dissipation of pore pressures leads to volumetric strains,
which may cause ground settlement and lateral deformations in sloping
ground. Moreover, loss of soil shear strength can lead to instability if

6. static shear stresses are present in the ground. If the soil shear strength
drops below the static shear stress, flow failure occurs in which the
ground will deform until it repositions itself into a configuration with
lower shear stresses matching the soil strength. If the post-liquefaction
strength exceeds the static shear stress, the ground may “lurch” during
strong pulses of motion when the shear strength is temporarily exceeded,
a condition termed cyclic mobility. Cyclic mobility can cause significant
deformations of foundations, retaining walls, and slopes. Cyclic mobility
of slopes or level ground behind a free face is often referred to as lateral
spreading.
Figure - Schematic illustrations of liquefaction induced instabilities. Source: Seed et
al.

7. .
Figure - Schematic illustration of damage to a building from lateral spreading
• Seismically-induced landsliding Inertial forces generated by strong shaking of
earth slopes can cause transient shear stresses(Transient shear stresses are time
varying stresses that are present during shaking, but are not present upon the
conclusion of shaking. ) to develop along potential slip surfaces. When added to
long-term static shear stresses, these transient stresses may cause the strength of
the slope materials to be temporarily exceeded. This process leads to permanent
shear deformations(Permanent shear deformations are ground deformations that
remain upon the conclusion of earthquake shaking.) within the slope materials
and is referred to as seismically-induced landsliding. Shear deformations at the
base of the slide mass may be localized along a basal slip surface, or may be
relatively distributed across broadly stressed zones. Note that liquefaction-
induced lateral spreading is one example of landsliding, although the analysis of
lateral spread displacements are generally evaluated through a different set of
procedures than are used for conventional landsliding.
• Seismic compression Unsaturated soil subject to large transient shear
stresses can experience volumetric strains, which results in ground
surface settlements and potential lateral movements (near slopes). This
process is termed seismic compression and has been observed to be
especially prevalent in artificial fill soils.
When considering whether the above modes of ground failure may have
affected a site, it is important to recognize the requisite conditions for their

8. occurrence. With surface fault rupture, the requisite condition is simply
proximity of the site to the ruptured fault. Ground displacements are naturally
greatest at sites located directly over the ruptured fault, but significant
secondary deformations can also occur away from the main break. Soil
liquefaction requires the presence of ground water, soil materials considered
susceptible to liquefaction (generally sands, gravels, and low plasticity silts at
low densities), and dynamic loading of sufficient amplitude and duration to
trigger liquefaction in those materials. The requisite conditions for landsliding
are the presence of sloping ground and the presence of combined static and
dynamic shear stresses that exceed material strengths. Seismic compression
requires relatively strong shaking and unsaturated soil.
If all sites were pristine and stable in the absence of earthquakes, identification
of seismically-induced ground failure during a post-earthquake site
reconnaissance would be straightforward. However, a number of non-seismic
geotechnical processes can also result in ground displacement that likewise may
damage structures and surface improvements. These are include:
• Consolidation settlement: Volume change due to dissipation of excess
pore pressure( Excess pore pressure is defined as pore pressures
beyond the hydrostatic pore pressure). resulting in expulsion of water
from the soil matrix and increased effective stress. The rate of
settlement is dependent upon soil properties and the length of the
drainage path. The excess pore pressures responsible for consolidation
may result from changes in overburden pressure (i.e., fill placement,
addition of structural loads) or changes in ground water levels.
• Immediate settlement: Settlement caused by small-strain shear and/or
volumetric deformations in soil that are not associated with
consolidation or hydro-compression. These deformations are
sometimes referred to as elastic settlements. A common example of
this phenomenon is young fills that compress under their own weight
and surface loading prior to the introduction of water. If the level of
saturation in the fill is low, the volume reduction is not associated with
pore pressure dissipation, but rather, depends principally on the bulk
and shear modulus of the soil.
• Hydro-compression settlement: Volume reduction of unsaturated soils
upon wetting, which is associated with collapse of the soil fabric. Soils
subject to collapse can include wind-deposited sands and silts, alluvial

9. fan and mudflow sediments, and some man-made fills. Volume
reductions are rapid upon introduction of water; however, settlements
will occur over time until all the collapse potential is achieved through
wetting. The rate of settlement depends on the rate of water infiltration
into the soil.
• Expansive soil movement: Shrink/swell of plastic clays when the water
content is reduced (drying) or increased (wetting). Cycles of shrinking
and swelling typically occur in near-surface soil layers subjected to
transient water content fluctuations. The water content variation can
be seasonal (e.g., summer to winter) or can follow a long-term trend
(e.g., from changes in landscaping and vegetation or installation of
pavements that change surface drainage patterns) or may be more
transient such as from irrigation or utility line leaks. A good indication
that expansive soils are present at a site is desiccation cracks in the
soil surface.
• Landsliding: The movement of a mass of rock, debris, or earth down a
slope. The term “landslide” encompasses a wide range of ground
movements, such as shallow rock falls, deep-seated slope failures, and
flow slides such as earth or debris flows. Other than from earthquakes,
landslides can be triggered by changes in slope geometry (i.e.,
excavation near slope toe), loading of the top of slope, and increased
water pressure within the slope.
Figure-Rockfall from the M 7.8 Peru Earthquake on May 17, 1970. Courtesy of

10. University of California, Berkeley, National Information Service for Earthquake
Engineering
Figur- Rockfalls from the M 6.6 1971 San Fernando Earthquake. Courtesy of
University of California, Berkeley, National Information Service for Earthquake
Engineering.
• Slope creep: Slow downslope movement of plastic rock and soil
materials. The rate of creep is dependent on factors such as material
type, slope inclination, and water content fluctuations within the slope.
Slope creep occurs within shallow soil/rock materials, and hence
damage from slope creep is generally confined to areas along a slope
face or near the top of slope.
• Retaining walls failure: Tilt, deterioration, and failure of retaining
walls. Excessive movements of retaining walls can result in soil
deformations and ground cracking behind the walls. Retaining wall
failures most often occur because the walls experience lateral earth
pressures beyond their capacity (e.g., from slope creep or poor
drainage).

11. Earthquake hazard assessment
-To locate the active fault zone in terms of 100 of years
an earthquake is caused by sudden slip on a fault,much like what happens
when you snap your fingers.Before the snap,you push your fingers
together and sideways.Because you are pushing them together,friction
keeps them from moving to the side.when you push sideways hard
enough to overcome this friction,your fingers move suddenly,releasing
energy in the form of soundwaves that set the air vibrating and travel
from your hand to your ear,where you hear the snap.
The same process goes on in an earthquake.Stresses in the earth’s outer layer
push the sides of the fault together.The friction across the surface of the
fault holds the rocks together so they do not slip immediately when
pushed sideways.Eventually enough stress builds up and the rocks slip
suddenly,releasing energy in waves that travel through the rock to cause
the shaking that we feel during earth quake.
Earthquakes occur on faults.A fault is a thin zone of crushed rock separating
blocks of the earth’s crust.When an earthquake occurs on one of these
faults,the rock on the one side of the fault slips with respect to the other.
to locate
-past fault movement has brought together rocks that used to be farther apart,
-earthquakes on the fault have left surface evidence,such as surface raptures
orr fault scarps(cliffs made by earthquakes);
-earthquake recorded by seismographic networks are mapped and indicate
the location of a fault.
Paleoseismological study help us to determine the history.
Paleoseismology looks at geologic sediments and rocks,for signs of ancient
earthquakes.It is used to supplement seismic monitoring,for the
calculation of seismic hazard.Paleoseismology is usually restricted to
geologic regimes that have undergone continuous sediment creation for

12. the last few thousand years,such as swamps,lakes,river beds and
shorelines.
In this typical example,a trench is dug in an active sedimentation
regime.Evidence of thrust faulting can be seen in the walls of trench.
San andreas fault
The San Andreas Fault is a continental transform fault that extends roughly
1300km(810 miles)through California.It forms the tectonic boundary
between the pacific plate and the North American Plate and motion is
right-lateral strike- slip(horizontal).Due to this fault in 1906 San
Francisco earthquake struck the coast of Nothern California at 5.12 a.m
on april18 with an estimated magnitude of 7.8MMS.About 3000 people
died and over 80% of the city of San Francisco was destroyed.The
maximum observed surface displacement was about 20 feet(6m).
aaaaae
Photo-Aerial photo of the San Andreas Fault

13. Figure-Evolution of San Andreas fault

14. Geological mapping
Detailed geologic mapping of the faults zone helps us to estimate about the
earthquake prone areas.Geological map give us knowledge about the active
fault zone,landside activity of an area over a long time.
Conclusion
Seismic hazard assessment is an effort to quantify seismic hazard and its
associated uncertainty by earth scientists. As for any natural or man-made
events, such as hurricanes and terrorist attacks, an earthquake has a unique
position in time and space. In other words, how to quantify the temporal and
spatial characteristics of seismic hazard is the core of a seismic hazard
assessment. Various methods have been evolved in the different parts of world
to address different issues of seismic risk assessment. Currently the main
challenge seems to be the verification and calibration of results obtained from
various probabilistic models using available data. Post earthquake data
collection could be only tool to verify various probability density functions.
Finally, it can be said that there is still a long way to go before
we can reach the appropriate level of confidence in vulnerability assessment.