HR: 0830h
AN: S41C-0088    [PDF]
TI: Seismic Hazard Assessment for Large Aftershocks
AU: * Gallovic, F
EM: gallovic@karel.troja.mff.cuni.cz
AF: Frantisek Gallovic, Department of Geophysics, Faculty of Mathematics and Physics, Charles University, Prague, V Holesovisovickach 2, Praha 8, 180 00 Czech Republic
AU: Brokesova, J
EM: johana@seis.karlov.mff.cuni.cz
AF: Johana Brokesova, Department of Geophysics, Faculty of Mathematics and Physics, Charles University, Prague, Ke Karlovu 3, Praha 2, 121 16 Czech Republic
AU: Irikura, K
EM: irikura@egmdpri01.dpri.kyoto-u.ac.jp
AF: Kojiro Irikura, Irikura Lab., Disas. Prev. Res. Inst, Kyoto University, Gokasho, Uji 611, Kyoto, 611-0011 Japan
AB: Coulomb static stress changes provide a promising way to short term probabilistic prediction of spatial occurrence of aftershocks. Main aim of this work is proposing method for seismic hazard assessment due to large aftershocks. Strong-ground motion estimation for the aftershocks has a number of uncertainties, namely aftershock magnitude and location since the Coulomb static stress changes give us only probabilistic information about the next aftershock hypocenters. First we discuss how to treat with such uncertainties. In cases when independent information about fault structure in the area under study is available, we can estimate maximum magnitude of the likely aftershock and its location. Then, we can use any strong motion prediction technique to estimate ground-shaking characteristics (e.g., PGA, PGV, etc.) in the near source region for a number of various scenarios (with varying position of the nucleation point and asperity) and compute mean strong-motion map of each of the characteristics and their standard deviation. After the local conditions (site effects) are taken into account, the possible impact on urban areas can be estimated. We propose a new method based on probabilistic seismic hazard assessment. This method is suitable for cases when 1) not only a single fault is designated to produce likely aftershocks and/or 2) their possible magnitude is unclear and/or 3) the seismogenic zone is known to be capable to produce aftershocks on blind faults. For each given magnitude and fault the strong-motion map is estimated. Presented approach represents a general tool to combine all the strong-motion maps obtained for all magnitudes and faults into a single probabilistic map. The method differs from the commonly used probabilistic seismic hazard methods in the point that the weights for particular epicentral zones are based on the Coulomb stress changes. The output of the method is either the maximum values of ground motion characteristics that have a specified probability of not being exceeded during fixed time period (e.g., one year) or the probability of non-exceedence of given ground motion level for each of the stations. The reliability of the method is shown on the example of Izmit aftershock No. 25 ($M_w=5.8$).
UR: http://karel.troja.mff.cuni.cz/students/gallovic/
DE: 7212 Earthquake ground motions and engineering
DE: 7223 Seismic hazard assessment and prediction
SC: Seismology [S]
MN: 2003 Fall Meeting