Deformation of an island arc: rates of moment release and crustal shortening in intraplate Japan determined from seismicity and Quaternary fault data.

Abstract

The historical record of large (M= or >6.9) earthquakes and geologically determined rates of slip on Quaternary faults in intraplate Japan (Honshu and Shikoku) are used to estimate the average rate of seismic moment release (M) for the last 400yr and during the late Quaternary, respectively. Values of M estimated from the two data sets are similar in regions where seismic activity is concentrated on land. We interpret this observation to suggest that M in intraplate Japan has been constant during the late Quaternary and is relatively free from secular variation when averaged over hundreds of years. M in Shikoku may be attributed almost solely to right-lateral slip of the median tectonic line (MTL). The E strike of the MTL is consistent with a compressive stress field that trends NW. The predominant deformation in central and W Honshu takes place as slip on a conjugate system of strike slip faults that strike NE and SE and show right-lateral and left-lateral motion, respectively. Crustal shortening, resulting from slip on faults, in central and W Honshu is 5 and 0.5mm/yr, respectively, in an E direction. Central and W Honshu are in closest proximity to the Nankai trough, and hence, the stress field in these regions cannot simply be attributed to the accommodation of the relative (NW) convergence of the Philippine Sea plate. The N impingement of the Izu Peninsula into Honshu may influence stresses in central and W Japan, but a conclusive explanation of the stress field in central and W Honshu remains an enigma.from Authors