第44回統計地震学セミナー / The 44th Statistical Seismology Seminar

※This seminar has been rescheduled as follows.

Date&Time

2014年8月5日（火）
/ 5 August, 2014 (Tuesday)　16:00～

Place

統計数理研究所 セミナー室4　D312B
/ Room D312B @ The Institute of Statistical Mathematics

Speaker1

Prof. ZHOU ShiYong
(Department of Geophysics , Peking University , China)

Time

16:00～

Title

"Seismicity simulation in Western Sichuan of China based on the fault interactions and its implication on the estimation of the regional earthquake risk"

Abstract

Seismicity over 10000 years in Western Sichuan of China has been simulated based on the mechanical synthetic seismicity model we developed. According to the analysis of the simulated synthetic seismic catalogue , the occurrence of strong earthquakes with Ms ≥710 in the whole region of Western Sichuan is rather random , very close to the Poisson process with seismic rate 010454Pyear , which means it is reasonable to estimate the regional earthquake risk with Poisson model in Western Sichuan. However, the occurrence of strong earthquakes with Ms ≥710 on the individual faults of Western Sichuan is far from Poisson process and could be predicted with a time2dependent prediction model.

The fault interaction matrices and earthquake transfer possibility matrices among the faults in Western Sichuan have been calculated based on the analysis of the simulated synthetic catalogues. We have also calculated the static change in Coulomb failure stress (CFS) on one fault induced by a strong earthquake on another fault in Western Sichuan to discuss the physical implications of the earthquake transfer possibility matrices inferred from the synthetic catalogue.

Keywords

Simulation of earthquake generation , Poisson model , Coulomb stress , Seismic hazard

Speaker2

Dr. Dun Wang (ERI)

Time

17:00～

Title

"Rupture speeds for recent large earthquakes"

Abstract

Studying the rupture speeds of earthquakes is of broad interesting for earthquake research because it has a large effect on the strong near- field shaking that causes damage during earthquakes. Also rupture speed is a key observation for understanding the controlling stresses and friction during an earthquake, yet the speed and its variations are usually difficult to determine. Using only far-field seismic waveforms, which is the only data available for many large earthquakes, there are problems for estimating the rupture speed with standard waveform inversions, due to trade-off between the rupture speed and the slip location.

Here we applied a back projection method to estimate the rupture speeds of Mw ≥ 7.5 strike-slip earthquakes since 2001 which could be analyzed using Hi-net in Japan. We found that all events had very fast average rupture speeds of 3.0-6.0 km/s, which are near or greater than the local shear wave velocity (supershear). These values are faster than for thrust and normal faulting earthquakes that generally rupture with speeds of 1.0-3.0 km/s. Considering the depth-dependent shear-wave velocity, the average propagation speeds for all of the strike-slip events are closer to or greater than the shear wave velocity. For large strike-slip events, transition from subshear to supershear usually occurs within distances of 15 to 30 km from the initiation, which is probably the reason for the scarcity of observed supershear earthquakes for smaller magnitudes.

Earthquakes with supershear ruptures can cause more damage than events with subshear ruptures because of the concentration of energy in the forward direction of the rupture. Numerical modeling shows strong focusing and other effects of energy at the rupture front which can intensify the ground motions. A recent example is the April 13, 2010 Qinghai, China earthquake (Mw 6.9), where a moderate-size event caused extensive damage in the Yushu region at the southeastern end of the fault. Careful evaluation of long and straight strike-slip faults should be emphasized for predicting strong ground motions due to supershear rupture.