Stress change before and after the 2011 M9 Tohoku-oki earthquake

Thorsten W. Becker , Akinori Hashima, Andrew M. Freed, Hiroshi Sato

Megathrust systems hold important clues for our understanding of
long- and short-term plate boundary dynamics, and the 2011 M9
Tohoku-oki earthquake provides a data-rich case in point. Here, we
show that the F-net moment tensor catalog indicates systematic
changes in crustal stress in the years leading up to the M9, due to
the co-seismic effect, and for the last few years due to viscous
relaxation. We explore the match between imaged stress change and
the perturbations that are expected from 3-D, mechanical models of
the visco-elastic relaxation and afterslip effects of the M9. While
these models were constructed based on geodetic and structural
seismology constraints alone, they match many characteristics of the
seismicity-inferred stress change. This provides additional
confidence in the modeling approach, and new clues for our
understanding of plate boundary dynamics for the Japan trench. The
success of deterministic approaches for exploring crustal stress
change also implies that joint inversions using stress from focal
mechanisms and geodetic constraints may be feasible. Such future
efforts should provide key insights into time-dependent seismic
hazard including earthquake triggering scenarios.