Temporal stress variations along a seismogenic megasplay fault in the subduction zone: A n example from the N obeoka T hrust, southwestern J apan

Abstract

The N obeoka T hrust, an ancient megasplay fault in the S himanto B elt, southwestern J apan, contains fault rocks from the seismogenic zone, providing an accessible analog of active megasplay faults in deep subduction settings. In this study, the paleostress along the N obeoka T hrust was analyzed using multiple inversion techniques, including k ‐means clustering of fault datasets acquired from drillcores that intersected the thrust. The six resultant stress orientation clusters can be divided into two general groups: stress solutions with north–south‐trending σ 1 axes, and those with east–west‐trending σ 1 axes. These groups are characterized by the temporal changes for the orientations of the σ 1 and σ 3 principal stress axes that involve alternation between horizontal and vertical. The findings are probably due to a change in stress state before and after earthquakes that occurred on the fault; similar changes have been observed in active tectonic settings, such as the 2011 T ohoku‐ O ki earthquake ( J apan).

Bibliographic Information