Spatiotemporal variations in the stress field in the northeasternmost part of the NE Japan arc: constraints from microearthquakes

We determined focal mechanism solutions of microearthquakes and examined the stress field in the low-seismicity region from southern Hokkaido to eastern Aomori, NE Japan. The stress fields determined in this study comprise (1) a reverse faulting stress regime in southern Hokkaido with the axis of maximum compressional stress (σ) being sub-horizontal and trending WNW–ESE, and (2) a stress regime in eastern Aomori to Tsugaru Strait that shows temporal variations and differential stress of less than tens of MPa. The spatiotemporal variation in stress from eastern Aomori to Tsugaru Strait might reflect the effects of the upper-plate bending and the 2011 M 9.0 Tohoku-Oki earthquake. It also indicates that the compressional stress caused by the descending Pacific plate is relatively weak, which is similar to other areas in eastern parts of the NE Japan arc.[Figure not available: see fulltext.]