Source characteristics of a moderate earthquake (M 4.9)using empirical Green ’s function technique

The rupture process of a moderate earthquake (M 4.9)on 28th January 1999 was analyzed using velocity records at local distances less than 80 km.The characterization of the rupture process was obtained from studying aftershocks distribution,azimuthal variations of Relative Source Time Functions (RSTFs),and a set of spatio-temporal slip models.RSTFs were retrieved by deconvolution of small aftershock records from those of the mainshock.In addition,velocity P -wave records of the respective event were inverted to recover slip distribution on the fault plane using the records of aftershocks as Empirical Green Functions (EGFs).The waveform inversion was adopted using three EGFs.In the inversion,the rupture propagation velocity was fixed and assumed to be eight-tenths of the local shear wave velocity.The total seismic moment was estimated to range from 0.011 E +18 Nm (Mw =4.6) to 0.017 E +18 Nm (Mw =4.8).The hypocentral distribution of the aftershocks,azimuthal variations of RSTFs, and the set of slip distribution models were exhibited bilateral rupture propagation along the strike and dip of the fault plane.The presence of two to three high slip patches on the fault plane suggested that a complex rupture pattern is detectable for a moderate size earthquake.However,the so-called nucleation phase was invisible in the present analysis.