Observed change in plate coupling close to the rupture initiation area before the occurrence of the 2011 Tohoku earthquake: Implications from an earthquake cycle model

Abstract

Changes in plate coupling off the coast of Fukushima have been detected by GPS since 2000.These changes occurred close to the rupture initiation area of the M w 9.0 2011 Tohoku earthquake and possibly initiated the earthquake. We investigated these changes with quasi-dynamic earthquake cycle simulations using a hierarchical asperity model. We modeled the entire rupture region as rate weakening but conditionally stable, while areas with huge slips and M w 7 asperities were modeled as strong and ordinary rate-weakening unstable friction, respectively. The following observed characteristics were reproduced: long recurrence time, large rupture region (including a localized huge coseismic slip area and source area of recurring M w 7 earthquakes), and a M w 7 foreshock triggering the Tohoku earthquake. Off Fukushima, repeated aseismic slips propagating northward appeared in the last half of the cycle and possibly caused the decrease in plate coupling. However, it is not necessarily related to the immediate occurrence of the giant earthquake.

A Forecasting Procedure for Plate Boundary Earthquakes Based on Sequential Data Assimilation

“…Laws for fault strength evolution have been proposed (e.g., Dieterich, 1979;Ruina, 1983;Kato and Tullis, 2001 (Kodaira et al, 2006;Kato, 2008). The model of an earthquake generation cycle for an M9 earthquake, with preceding earthquakes of M7~M8 within the source area, is qualitatively consistent with the characteristics of the 2011 Tōhoku-Oki earthquake (Hori and Miyazaki, 2011;Ohtani et al, 2014). In addition to earthquake generation, slow sliding behavior on the plate interface has also been reproduced qualitatively using this mathematical model.…”

“…Tōhoku-Oki earthquake was about to occur, although it is also possible that such phenomena occur without being followed by a larger earthquake (Ohtani et al, 2014). …”

Post-Tsunami Hazard

“…In the previous simulation researches, the result of recurrence cycle simulation indicated the difference patterns and intervals of mega-thrust earthquake recurrences in each cycle (e.g. Kodaira et al 2006 ;Ohtani et al 2014 ). These results were consistent with the recent historical earthquakes in 1854, 1944/1946 and 1707 around the Nankai trough.…”

A possible scenario for earlier occurrence of the next Nankai earthquake due to triggering by an earthquake at Hyuga-nada, off southwest Japan

“…In Japan, for interpreting previous seismic cycles and examining possible future scenarios, quasi-dynamic seismic cycle simulations have been widely conducted based on the rate-and state-dependent friction law and quasi-static slip response functions. For the Japan Trench in the northeastern part of Japan Islands, quasidynamic earthquake cycle modeling with rate-and statedependent friction and stress accumulation due to the subducting Pacific plate have been implemented, with the aim of examining possible seismic cycles including multi-scale asperities with the patch size of 10 0 -10 2 km (e.g., Shibazaki et al 2011;Kato and Yoshida 2011;Ohtani et al 2014;Ariyoshi et al 2014). Additionally, along the Nankai Trough, similar quasi-dynamic seismic cycle simulations of M w 8-class earthquakes due to the subduction of the Philippine Sea plate have been conducted (e.g., Hori et al 2004;Hori 2006).…”