Focal mechanisms and the stress field in the aftershock area of the 2018 Hokkaido Eastern Iburi earthquake (MJMA = 6.7)

Abstract The tectonic stress field was investigated in and around the aftershock area of Hokkaido Eastern Iburi earthquake ( M JMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations for approximately 2 months located 1785 aftershocks precisely. Among these aftershocks, 894 focal mechanism solutions were determined using first-motion polarity P wave from observation permanent networks University, Japan Meteorological Agency (JMA), High Sensitivity Seismograph Network (Hi-net). found that (1) reverse faulting strike-slip are dominant area, (2) average trend P- T-axes is 78° ± 33° 352° 51°, respectively, (3) plunge 25° 16° 44° 20°, respectively: P-axis close to be horizontal T-axis more vertical than P-axes. applied a inversion method estimate area. As result, we fault type An axis maximum principal ? 1 ) has 72° 7° dipping eastward 19° 4° an intermediate 131° 73° southward 10° 9°, indicating both - -axes horizontal. minimum 3 westward 67° 6° vertical. results strongly suggest reverse-fault-type predominant as over which western boundary Hidaka Collision Zone. ratio R ? )/( 0.61 0.13 whole Although not statistically significant, decreases systematically depth getting deep, modeled by quadratic polynomial depth.