The rupture directivity study of moderate earthquakes using empirical Green s function approach:A case study of Panzhihua earthquake
Rupture directivity is an important factor in determining the actual rupture planes of moderate earthquakes and related seismic hazard assessments.In this study,we take the 2008 MS6.1 Panzhihua earthquake as a study case to demonstrate the effectiveness and practicality of the Empirical Green's Function(EGF)approach to estimating the rupture directivities of moderate earthquakes in China.Using the records of a smaller event of similar location and mechanism to the mainshock,we obtain the apparent source time functions at stations of various azimuths and use them to determine the propagation direction,length and speed of the mainshock rupture.Our results show that the rupture propagation direction of the mainshock is 184°(S4°W),consistent with the strike of the NS-trending Yuanmou fault.The relatively high rupture speed of 3.35 km·s-1 close to the shear-wave speed may be the primary reason for the moderate Panzhihua earthquake to have caused disproportionately heavy damages.We also combine the centroid depth,focal mechanism,and rupture directivity of the mainshock as well as regional background stress to further analyze the seismogenic environment of the Panzhihua earthquake to understand its implications to future seismic hazards.
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