Stress due to the interseismic back slip and its relation with the focal mechanisms of earthquakes occurring in the Kuril and northeastern Japan arcs

Abstract

Assuming a uniform and inhomogeneous distribution of back slip, based on a realistic configuration of the plate boundary that was newly determined from the distribution of earthquakes, we have investigated if the stress due to the interseismic back slip can explain the focal mechanisms of earthquakes occurring in the Kuril and northeastern Japan arcs. The inhomogeneous back-slip model was taken from the distribution of slip deficit estimated from GPS data collected in recent years. We examined the change in the Coulomb Failure Function (ΔCFF) for several target faults to evaluate the fitness of the models to the observed focal mechanisms. The results of ΔCFF are clearly different in the two back-slip models near the down-dip end of the locked zone. Despite this difference, the models can generally explain the earthquake focal mechanisms in the overriding plate as well as those on the megathrust plate boundary. However, they cannot explain the focal mechanisms of intermediate-depth earthquakes in the double-planed deep seismic zone. Neither can they fully explain the focal mechanisms with the pressure axis parallel to the trench that are observed at the junction of the Kuril and northeastern Japan arcs. Other tectonic processes, such as the transcurrent movement of the forearc sliver along the Kuril arc, may be involved in producing the stress anomaly.

Alteration of stress field brought about by the occurrence of the 2011 off the Pacific coast of Tohoku Earthquake (M w 9.0)

“…Figure 1 shows the fault model of this earthquake used for calculating the stress change. This model is based on the configuration of the upper plate interface of the subducted Pacific plate determined by Takeuchi et al (2008) and the coseismic slip distribution estimated by the Geospatial Information Authority of Japan (GSI) (GSI, 2011a). The top of the fault is situated at a depth of 6.5 km along the axis of the Japan Trench.…”

Coulomb stress change for the normal-fault aftershocks triggered near the Japan Trench by the 2011 M w 9.0 Tohoku-Oki earthquake

“…In modeling the fault geometry of the 2011 Tohoku-Oki earthquake, we refer to the depths of the upper plate interface of the subducted Pacific plate determined by Takeuchi et al (2008). These depths were determined using both the earthquake distribution and offshore crustal structures revealed by seismic experiments.…”