Rupture Process of the Kobe, Japan, Earthquake of Jan. 17, 1995, Determined from Teleseismic Body Waves

Abstract

The source process of the 1995 Kobe earthquake is determined using teleseismic body waves. The source parameters obtained for the total source are: focal mechanism [strike, dip, rake] equal to [233°, 86°, 167°], nearly pure strike-slip with an EW compression axis; the seismic moment, M_o= 2.5×10¹⁹ Nm (M_w= 6.9); and source duration T=11s. The rupture process consists mainly of three subevents with source durations of 5-6 s: two are nearly pure strike-slip with slightly different fault strikes, and the other is dip-slip. Combining the source location with the aftershock distribution, we infer that the first subevent is a bilateral rupture and the later subevents are unilateral propagating NE and reaching the Kobe area. The total fault length is 40 km, the averaged dislocation is 2.1 m, and the averaged stress drop is 8 MPa. These source parameters indicate that the Kobe earthquake was a typical shallow inland earthquake which occurred on a previously mapped Quaternary fault zone. The directivity toward Kobe determined from teleseismic data was probably one of the main factors responsible for the heavy damage. The combined use of regional networks and teleseismic networks as demonstrated in this study will continue to be important for rapidly assessing the overall social impact of an earthquake in the very early stage of sequence.