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

M Takeuchi,T Sato,T Shinbo

doi:10.1186/bf03353117

Abstract

AbstractAssuming 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.

Highlights

The Hokkaido and Tohoku areas of the Japanese islands are located along the convergent margin between the Pacific plate and North American plate (Fig. 1)
Intermediate and deep-focus earthquakes occurring within the subducted Pacific plate have two distinct types of mechanisms, depending on their locations in the doubled-planed deep seismic zone: those on the upper seismic plane show the mechanism of down-dip compression (DC) while those on the lower seismic plane show the mechanism of downdip extension (DE)
We suggest that it is important to investigate the stress field due to the back slip using a realistic configuration of plate boundary and to clarify if the back-slip model can explain the focal mechanisms of

Summary

Introduction

The Hokkaido and Tohoku areas of the Japanese islands are located along the convergent margin between the Pacific plate and North American plate (Fig. 1). Model (Engdahl and Scholtz, 1977), sagging model (Sleep, 1979), and thermal expansion model (Goto et al, 1985), have been proposed to interpret the pair of focal mechanisms in the double-planed seismic zone Apart from these general trends, the state of stress at the junction of the Kuril and northeastern Japan arcs has been inferred to be anomalous (Shimazaki et al, 1978). The same back-slip model had before been used to estimate the plate coupling coefficient from triangulation data collected during the last century (Shen-Tu and Holt, 1996) Those investigations revealed the usefulness of the back-slip model for representing surface deformation during the interseismic period, few researchers have asked if the same model is applicable to explaining the focal mechanisms of earthquakes at depths. We suggest that it is important to investigate the stress field due to the back slip using a realistic configuration of plate boundary and to clarify if the back-slip model can explain the focal mechanisms of

Back Slip on a Realistic Configuration of Upper Plate Interface

Discussion and Conclusions