Coulomb stresses imparted by the 25 March 2007 M_w=6.6 Noto-Hanto, Japan, earthquake explain its 'butterfly' distribution of aftershocks and suggest a heightened seismic hazard

摘要

The well-recorded aftershocks and well-determined Source model of the Noto Hanto earthquake provide an excellent opportunity to examine earthquake triggering associated with a blind thrust event. The aftershock zone rapidly expanded into a 'butterfly pattern predicted by Static Coulomb stress transfer associated With thrust faulting. We found that abundant aftershocks occured where the static Coulomb stress increased by more than 0.5 bars. while few shocks Occurred in the Stress Shadow calculated to extend northwest and Southeast of the Now Hanto rupture. To explore the three-dimensional distribution of the observed aftershocks and the calculated stress imparted by the mainshock, WC further resolved Coulomb stress changes oil file nodal planes of all aftershocks for which focal mechanisms are available. About 75% of the possible faults associated with the moderate-sized aftershocks, Were Calculated to have been brought closer to failure by the mainshock. with the correlation best low apparent fault friction. Out-interpretation is that most of the aftershocks struck oil the steeply dipping source fault and on a conjugate northwest-dipping reverse fault contiguous with the source fault. Since we found that the Coulomb hypothesis works well for the Noto Hanto sequence, we subsequently computed stress changes on the nearby active faults. Although the calculated Stress changes were found to be negligible on the major faults south of the Noto Peninsula, several Short active falults near the epicentral area were calculated to have been brought several bars closer to failure. Thus, the probability of strong shaking in and around the epicentral area may still be high due to the transfer of stress to the adjacent faults by a short blind thrust fault.