2013, 35(3):425-431.
Abstract:
On July 22,2013,the Minxian magnitude 6.6 earthquake occurred beneath the northeast margin of the Tibetan plateau,Gansu,China.The earthquake and its aftershocks caused considerable damages,including more than 95 casualties,2414injuries,and approximately 17.5billion yuan in property damage.More information on the source properties of such events can help to characterize fault the structures,which can contribute to an improved understanding of the hazards associated with future great earthquakes.As of August 28,13:35,aftershocks have been recorded by the Gansu seismology network,including a magnitude 5.6event following the mainshock.We analyzed the broadband waveforms for the mainshock with sufficient signal-tonoise levels to invert for seismic moment tensors.All stations involved in this study are broadband stations situated near the July 22mainshock;data showing such problems as misorientation
of horizontal components,mislabeling,and polarity reversal in one or more components(Niu et al.,2010)were removed.During the data processing,we removed the mean value and instrument response,detrended the waveforms,integrated the three-component velocity waveforms to displacement,and rotated the horizontal components to the radial and tangential directions.Before performing moment tensor inversion,waveforms were filtered with a Butterworth filter with frequencies between 0.016Hz and 0.05Hz.On the basis of the Crust 2.0global crustal model,and considering the heterogeneity of the crust and the distances to the recording stations,various velocity models for each station were employed to account for variabilities in the crustal structure.To insure the quality of the results of the inversion process,we retained only the station with variance reduction(VR)is≥80,and got 6stations for the inversion.After depth iteration,the best solutions obtained at a depth of 8km were 87,13,and 93for double couple(DC),the compensated linear vector dipole(CLVD)component,and VR,respectively,which indicates highquality results.The two panel＇s strike,dip,and rake of the solution were 195°,54°,and 149°and 305°,65°,and 40°respectively.The moment tensor solutions showed considerable reverse features and contained part of the strike-slip component.Geologic survey indicated no surface rupture.Regarding tectonic framework and the aftershock distribution features,our inversion results were essentially consistent with the strike of the Lintan-Tanchang fault,and the aftershock distribution occurred near the fault.This phenomenon indicates that the Lintan-Tanchang fault was the main tectonic trigger for the Minxian magnitude 6.6earthquake and that the seismogenic fault of the earthquake was a subfault of the Lintan-Tanchang fault.
