Source process for complex fault system of the 2007 Chuetsu-oki, Niigata, Japan, earthquake

Abstract

Abstract The 2007 Chuetsu-oki earthquake occurred in the offshore area of Niigata Prefecture, central Japan, on 16 July 2007. The aftershock distribution shows two fault planes, dipping to the northwest and southeast, respectively, which form a cross-sectional “V” pattern. We analyze the kinematic source process for the two fault planes consistent with the aftershock distribution using teleseismic body waveform data. Our results indicate that the mainshock initiated rupture on both faults northeast of their intersection and that the rupture propagated unilaterally southwestward along the southeast-dipping fault. The maximum slip is 1.6 m on the southeastdipping fault, and the seismic moments of northwest- and southeast-dipping faults are 8.0 × 1017 N m (M w 5.9) and 7.5 × 1018 N m (M w 6.5), respectively. The forward modeling of geodetic displacement from the obtained fault model is consistent with the GPS and InSAR measurements. Successive conjugate reverse faults around the source region are identified from the reflection seismic sections. We presume that stress changes and complicated structures in property and geometry around the source region are the dominant causal factors for generating the complexity of coseismic fault system.