Outline: Lecture 4Risk Assessment

I. The concepts of risk and hazardII. Shaking hazard of AfghanistanIII. Seismic zone mapsIV. Construction practice

What you should learn from this lecture: (1) The concept of risk.(2) How the earthquake hazard in Afghanistan is calculated.(3) How better construction practice reduces risk

Risk versus Hazard

Earthquake scientists and engineers make an important conceptual distinction between hazard and risk.

• Hazard is the property of an earthquake that causes loss of life or damage

• Risk is the probability of loss of life, injury, or damage

Relation between Risk and Hazard

• Hazard is the frequency of a level of shaking (liquefaction, landslide, fault rupture)

• Vulnerability measures the likelihood that something like a building will be damaged

• Exposure is the number of people, buildings, structures that are exposed to the hazard. This is called an inventory.

Risk = Hazard x Vulnerability x ExposureRisk = Hazard x Vulnerability x Exposure

Unreinforced Masonry, Facility Class 75

Modified Mercalli Intensity

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VulnerabilityVulnerability

V VI VII XIXVIII XI XII

Roles of Engineer and Geologist

• Geologists and seismologists define the earthquake hazard• Engineers (builders, masons, etc.) reduce the risk by

decreasing the vulnerability of structures to ground motion

Risk = Hazard x Vulnerability x ExposureRisk = Hazard x Vulnerability x Exposure

The Geologist

Reducing earthquake risk in Afghanistan begins with understanding the earthquake potential and the ground shaking that is to be expected in future earthquakes.

http://www.seismo.ethz.ch/gshap/

Global Seismic Hazard Assessment Program (GSHAP)

The Global Seismic Hazard Assessment Program (GSHAP) was launched in 1992 by the International Lithosphere Program (ILP) with the support of the International Council of Scientific Unions (ICSU), and endorsed as a demonstration program in the framework of the United Nations International Decade for Natural Disaster Reduction (UN/IDNDR).

In order to mitigate the risk associated to the recurrence of earthquakes, the GSHAP promotes a regionally coordinated, homogeneous approach to seismic hazard evaluation; the ultimate benefits are improved national and regional assessments of seismic hazards, to be used by national decision makers and engineers for land use planning and improved building design and construction.

The GSHAP was implemented in the 1992-1998 period and is coming to conclusion. All regional activities are now completed, and the publication of all regional results and of the GSHAP map of global seismic hazard is under way.

Regional reports, GSHAP yearly reports, summaries and maps of seismicity, source zones and seismic hazard are on the GSHAP homepage on http://www.seismo.ethz.ch/GSHAP/. The report summarizes the development, the regional activities and the achievements of the GSHAP.

Global Seismic Hazard Assessment Program

http://www.seismo.ethz.ch/gshap/eastasia/

Seismic Hazard in East Asia

Afghanistan

Kabul

Peak ground acceleration (m/s2) with return time of about 500 years

Seismic Zone Map of Afghanistan

a b ccEarthquake sourcesGround motion

d2

d1

d3

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r3

San Andreas fault

high seismicityzone

peak ground acceleration (pga)

Hazard curve

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To calculate the hazard curve (annual rate of exceeding ground motions) we:To calculate the hazard curve (annual rate of exceeding ground motions) we:

1. Determine magnitude, M, of earthquake and distance to a point, d2, 1. Determine magnitude, M, of earthquake and distance to a point, d2,

2. Calculate ground motion distribution for that M and d2.2. Calculate ground motion distribution for that M and d2.

3. Calculate the product:3. Calculate the product:

annual rate of earthquake *probability that earthquake will exceed certain ground motion levelannual rate of earthquake *probability that earthquake will exceed certain ground motion level

4. Sum these rates for all earthquakes in the model at each ground motion to get a hazard curve. 4. Sum these rates for all earthquakes in the model at each ground motion to get a hazard curve. This curve shows the annual rate or probability of exceedance of each ground motion.This curve shows the annual rate or probability of exceedance of each ground motion.

PROBABILISTIC SEISMIC HAZARD METHODOLOGYPROBABILISTIC SEISMIC HAZARD METHODOLOGY

M7.6 every 250yrs- 0.004 event/yrM7.6 every 250yrs- 0.004 event/yr

d2

Kabul

Peak ground acceleration (m/s2) with return time of about 500 years

Seismic Zone Map of Afghanistan

The Greatest ChallengeThe Greatest ChallengeIdentifying the Earthquake Identifying the Earthquake

SourcesSources

DATA FOR DEVELOPING SEISMIC SOURCESDATA FOR DEVELOPING SEISMIC SOURCESEARTHQUAKESEARTHQUAKES QUATERNARY FAULTSQUATERNARY FAULTSGEODETIC DATAGEODETIC DATA

Paleoseismology: By trenching faults that intersect the surface and offset Quaternary deposits, geologists can see the evidence for prehistoric earthquakes. If the offset deposits can be dated, usually by radiocarbon, then the frequency of faulting and large earthquakes can be estimated.

Actions that AGS can take to Actions that AGS can take to improve the Afghanistan seismic improve the Afghanistan seismic

zone mapzone map Knowledge of earthquake potentialKnowledge of earthquake potential

Identify active faultsIdentify active faults Characterize recurrence intervals for Characterize recurrence intervals for

large earthquakeslarge earthquakes Attenuation curvesAttenuation curves

Record strong ground motion from Record strong ground motion from earthquakes in Afghanistanearthquakes in Afghanistan

Reducing earthquake Reducing earthquake riskrisk

Partnering with Partnering with BuildersBuilders

It is important for geologists to work with It is important for geologists to work with engineers and builders of structures to engineers and builders of structures to make them aware of the earthquake make them aware of the earthquake hazard so that they can apply this hazard so that they can apply this knowledge to make buildings safer.knowledge to make buildings safer.

World Distribution of World Distribution of Buildings Made with Local Earth MaterialsBuildings Made with Local Earth Materials

(Sensi, 2003)

Earthquake Damage to Earth Earthquake Damage to Earth HousesHouses

CornerCracking loose

WallFailing

TotalCollapse

Stages of Damage

Earthquake Damage to Earth Earthquake Damage to Earth HousesHouses

Inadequate Inadequate maintenance (water maintenance (water reduces strength)reduces strength)

Seismic deficienciesSeismic deficiencies

Seismic DeficienciesSeismic Deficienciesof Adobe Masonryof Adobe Masonry

Damages common in rural homes

Test of Clay MortarTest of Clay Mortar

Summary of Lecture 4Risk Assessment

I. Risk depends on hazardII. The earthquake hazard is not

uniform in AfghanistanIII. To reduce risk requires

improving construction practice

Next lecture will discuss strategies to reduce earthquake risk.