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Seismic Hazard Mathilde B. Sørensen and Jens Havskov Dept. of Earth Science, University of Bergen

Seismic Hazard Mathilde B. Sørensen and Jens Havskov Dept. of Earth Science, University of Bergen. Seismic Hazard Assessment An Introduction. What is seismic hazard?. and seismic risk?. Basic definitions. Seismic hazard

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Seismic Hazard Mathilde B. Sørensen and Jens Havskov Dept. of Earth Science, University of Bergen

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  1. Seismic HazardMathilde B. Sørensen and Jens HavskovDept. of Earth Science, University of Bergen

  2. Seismic Hazard AssessmentAn Introduction

  3. What is seismic hazard? and seismic risk?

  4. Basic definitions Seismic hazard Describes the probability of experiencing a given level of earthquake shaking at a given location within a given time frame Seismic risk Describes the probability of economical or human losses due to earthquake shaking Risk = Hazard · Vulnerability · Value

  5. Earthquakes don’t kill, buildings do!

  6. China, 12. mai 2008

  7. What controls the damage? • Amplitude of the seismic waves • Magnitude • Distance • Local geology • Frequency content of ground shaking • Building quality • Indirect damages (secondary effects) • Fire • Landslide/rock fall • Tsunami • Liquefaction

  8. Effects of local geology

  9. Frequency content

  10. Building quality May 2008 Sichuan, China earthquake

  11. Building quality

  12. Indirect damages - liquefaction

  13. Indirect damages - tsunami

  14. Indirect damages - tsunami Meulaboh, NW Sumatra

  15. Indirect damages - landslides Before After quake After 1st flood After 2nd flood

  16. Indirect damage: Fire Japan

  17. Prevention • Earthquakes cannot be avoided, but disasters can be prevented • Hazard and risk mapping • Building codes and retrofitting • City planning • Early warning

  18. Hazard mapping Based on statistical analysis of the seismicity in an area

  19. Hazard mapping Based on scenarios expected for the future

  20. Hazard mapping Based on scenarios expected for the future

  21. Building codes Regulate the loads a building must withstand Based on hazard maps Depend on the usage of the building

  22. City planning Buildings sinking due to bad foundation at a delta complex (Izmir, Tyrkey)

  23. Early warning systems

  24. Mexico early warning Warning time for coastal events is 60-100 s

  25. Early warning systems

  26. Applications of hazard and risk • Can assist in defining building design specifications or determining if a site is appropriate for a partiular application • Can be accounted for in city planing or used as basis for risk mitigation • Is used by the insurance industry to define insurance level and costs • Allows society to make risk based decisions based on quantitative cost/benefit analyses for multiple hazards • Deagregation of the results can help identifying critical scenarios which can be associated with a specific hazard level

  27. Hazard curves giving annual probability vs. ground motion level Hazard maps showing maximum expected ground motion for a given time frame and probability level Presentation of seismic hazard Petersen et al., 2007 Petersen et al., 2007

  28. Main steps in seismic hazard assessment Data required: • Tectonics, geology, earthquakecatalog • Earthquakecatalog • Groundmotionpredictionequation Reiter, 1990

  29. Step 1: source zones • Defines zones within which the seismicity is assumed to be homogeneous • Can be defined as point, line, area or volume sources • Accurracy in zonation depends mainly on amount of available information • Input information: • Seismicity • Tectonic information • Geological information

  30. 2. Recurrence and Mmax Foreachsourcezone, theearthquakeactivity must bedescribed • Recurrence in termsofthe Gutenberg-Richter relation • Maximum magnitudetobeproducedbythesourcezone • Minimum magnitudetobeconsidered (smallereventsare not expectedtocausedamage) Linear Truncated Grünthal, 2003

  31. 3. Ground motion • For every source, an appropriate GMPE must be chosen • Ideally, relation derived from local data • In most cases, relation from similar tectonic regime Petersen et al. (2004)

  32. For all sources, theeffectof all earthquakesof all sizesand at all locations, with different occurrenceprobabilitiesareintegrated Output: Probabilityofexceeding different GM levels at a sitewithin a given time: 4. Calculation of hazard Mean rate of occurrence of earthquakes with m0≤m≤mmax in source i (from Gutenberg-Richter) From GMPE Expected number of exceedances of z within a given time PDFs of m and r

  33. 4. Calculation of hazard Petersen et al. (2007)

  34. HHaiti earthquake catalog 1900-february 2010 Frankel et al., 2010Frankel

  35. Frankel et al., 2010

  36. Frankel et al., 2010

  37. Shear wave velocity Frankel et al., 2010

  38. Frankel et al., 2010

  39. Conclusion • Calculation of seismic hazard requires: • Good knowledge of past seismicity • Study of local attenuation • Seismic hazard calculation and seismic zonation maps are essential for planning purposes and construction of new buildings • Many areas have no zonation maps despite a high seismic hazard

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