Usually, only a couple of centuries of earthquake data is available, much shorter than the complete seismic cycle for most plate motions.

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Hollie Harrington
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1 Earthquake Hazard Analysis estimate the hazard presented by earthquakes in a given region Hazard analysis is related to long term prediction and provides a basis to expressed hazard in probabilistic terms. Hazard maps represent historic or instrumentally recorded seismicity in their simplest form represented as intensity distributions or contours of energy release. --- WHAT IS ASSUMED FROM THESE MAP IN ESTIMATING HAZARD? Usually, only a couple of centuries of earthquake data is available, much shorter than the complete seismic cycle for most plate motions. Even regions with exceptionally long histories (e.g. China, Italy, Japan) have insufficient records because they contain faults with recurrence times of thousands to tens of thousands of years. How can a quiet zone on a hazard map be erroneously interpreted?

2 We are able to calculate the probability of shaking over an arbitrary time interval using long-time hazard analysis. Using additional information, such as the date of the last earthquake on each fault segment, we can make a time dependant assessment of earthquake hazards taking into account the periodicity of ruptures. Hazard map showing maximum acceleration with a 2% probability of occurring within the next 50 years, or at least once in the next (=50/.02)

3 Structural damage following an earthquake Unreinforced masonry buildings (URM) Suffer major failures Program to retrofit URM Reinforced concrete building Found to behave poorly Wood structures Inadequate bracing Steel frame buildings Suffer brittle fracture of welded connections Many building exhibited some amount of failure- but typically do not collapse

4 Earthquake Forecasting Where is an earthquake going to happen? When? Probability - What is the probability of an earthquake occurring over a certain period within a certain region? similar to weather forecasting Seismic Gap Hypothesis - Fault segments with a long time since last large earthquake have a greater chance of a large quake in the future. Clustering - Concentrations of earthquakes in time/space. The occurrence of one earthquake increases the probability of another event in that same location in the future. Stress Interactions - A single earthquake changes the stress field in a region and accordingly may help load another nearby fault segment. - can be related to clustering

5 Hazard map developed for the Bay Area along the San Andreas and surrounding faults showing the probability of a magnitude of a certain size occurring before a specified time and distinct regions of a fault. from USGS

6 What data is used to make earthquake hazard maps? historic earthquakes Quaternary faults crustal deformation

sudden changes in stresses surrounding faultsstrong correlation between modeled stress change and

7 Correlation between stress drop at a fault and change in the rate of seismicity. Map comparing earthquake locations before and after San Andreas 1906 event earthquakes produce sudden changes in stresses surrounding faultsstrong correlation between modeled stress change and seismicity suggest that change in stress increases seismicity Before and after 1994 Northridge earthquake from Stein, 1999

8 Seismic Hazards Investigations in Puget Sound Clear past geologic evidence of a major quake, but where are the faults that caused these major quakes. Goal of seismic survey is to identify features that can create or magnify seismic waves. Perform a land based seismic survey augmented by boat based active source experiment. Identifying features that can exacerbate the effects of seismic energy helps delineate regions that are subject to greater seismic risk.

9 Magnitude-frequency relations have been used to attempt to mitigate the effects of incomplete sampling of the seismic cycle.---measure the number of small earthquakes present in a region and extrapolate to determine the recurrence time of potentially damaging earthquakes. However the large earthquake that ruptures a given fault segment is typically one to two orders of magnitude larger than that predicted based on extrapolating small earthquakes. Paleoseismic data, utilizing geologic data on a fault, helps to remedy the incomplete historic record. Look in geologic record for: faulted layers of sediment injection of liquefied sand tsunami deposits landslides rapidly uplifted or lowered regions

10 Factors contributing to strong shaking and amplification Large variations (factor of 2 or more) in amplitudes of shaking over short distances due to site responses Unconsolidated sediments or shallow water Sedimentary basins Surface topography Directivity of rupture Ways to improve hazard analysis Extend methods used for instantaneous hazard analysis for use with smaller secondary faults in California. Improve understanding of non-linear interaction between faults. improvements in models of strong ground motion Understanding both site and building response can facilitate converting from ground motion to damage

11 Steps to take to be prepared for an earthquake: Developed by Southern California Earthquake Center

12 Create my disaster plan. Will everyone in your household do the right thing during the violent shaking of a major earthquake? Before the next earthquake, get together with your family or housemates to plan now what you will do before, during and after.once the earthquake is over, we will have to live with the risk of fire, the potential lack of utilities and basic services, and the certainty of aftershocks. By planning now, you will be ready. This plan will also be useful for other emergencies. Practice "drop, cover, and hold on." (See Step 5) Teach children and adults to use an emergency whistle and/or to knock 3 times if trapped. Rescuers searching collapsed buildings will be listening for sounds. Know the location of utility shutoffs and keep needed tools nearby. Know how to turn off the gas, water, and electricity to your home. The preparedness section of your phone book has detailed information on this topic. Know how to operate the emergency latch on your garage door opener in case of a power outage to your garage door. Get training from your local fire department in how to properly use a fire extinguisher. Install smoke alarms and test them monthly. Change the battery once a year, or when the alarm emits a "chirping" sound which is a low-battery signal. Locate your nearest fire and police stations and emergency medical facility. Take a Red Cross first aid and cardiopulmonary resuscitation (CPR) training course. Learn who in your neighborhood is trained in first aid. Check with your fire department to see if there is a Community Emergency Response Team (CERT) in your area. If not, ask them how to start one. Ask school staff about the earthquake plan developed by your children s school or day care. Ask your babysitters, house sitters, and neighbors about their disaster plans, and share your plan and essential information with them. Have occasional earthquake drills to practice your plan.

Earthquakes. Earthquake Magnitudes 10/1/2013. Environmental Geology Chapter 8 Earthquakes and Related Phenomena

Earthquakes. Earthquake Magnitudes 10/1/2013. Environmental Geology Chapter 8 Earthquakes and Related Phenomena Environmental Geology Chapter 8 Earthquakes and Related Phenomena Fall 2013 Northridge 1994 Kobe 1995 Mexico City 1985 China 2008 Earthquakes Earthquake Magnitudes Earthquake Magnitudes Richter Magnitude