Weak Interplate Coupling by Seamounts and Repeating M ~ 7 Earthquakes

Abstract

Subducting seamounts are thought to increase the normal stress between subducting and overriding plates. However, recent seismic surveys and laboratory experiments suggest that interplate coupling is weak. A seismic survey in the Japan Trench shows that a large seamount is being subducted near a region of repeating earthquakes of magnitude M approximately 7. Both observed seismicity and the pattern of rupture propagation during the 1982 M 7.0 event imply that interplate coupling was weak over the seamount. A large rupture area with small slip occurred in front of the seamount. Its northern bound could be determined by a trace of multiple subducted seamounts. Whereas a subducted seamount itself may not define the rupture area, its width may be influenced by that of the seamount.

Rupture process of the largest aftershock of the M 9 Tohoku-oki earthquake obtained from a back-projection approach using the MeSO-net data

“…This idea agrees with strong plate coupling in that region estimated from GPS data (Nishimura et al, 2007). On the other hand, Mochizuki et al (2008) maintains weak interplate coupling around the seamount from the results of seismic surveys and laboratory experiments. In any case, whether the coupling strength at the region near the Japan Trench is strong or weak, we think much attention should be paid to the seismic activity and/or afterslip there.…”

“…From seismic surveys, Mochizuki et al (2008) deduced the existence of a seamount in the region near the Japan Trench. The seamount could be a barrier of the rupture during the 2011 Ibaraki-oki event.…”

P-wave velocity structure in the southernmost source region of the 2011 Tohoku earthquakes, off the Boso Peninsula, deduced by an ocean bottom seismographic survey

“…Since the 1980s, many seismic experiments using controlled sources and Ocean Bottom Seismometers (OBSs) have been conducted to study the seismic structure beneath the landward slope of the JT (e.g. Suyehiro et al, 1985;Takahashi et al, 2004;Mochizuki et al, 2008). The precise structure of the forearc region in the NEJ arc, including the subducting oceanic crust, has been obtained from these studies.…”

Lithospheric dynamics of Earth�s subduction zones and Martian tectonic provinces

“…The presence of the complex fault system could influence the occurrence of megathrust earthquakes. Previous studies suggest that subducted seamount could either trigger [Scholtz and Small, 1997;Cloos, 1992;Yang et al, 2013] or arrest megaearthquakes [Mochizuki et al, 2008;Kodaira et al, 2000;Yang et al, 2012]. However, those studies ignore the fault system caused by seamount subduction, and simply presume a normal stress increase at the location of seamount.…”

“…It has been proposed that a subducted seamount might act as either barrier [Scholtz and Small, 1997;Cloos, 1992;Yang et al, 2013] or asperity [Mochizuki et al, 2008;Kodaira et al, 2000;Yang et al, 2012] for megathrust earthquakes. This study reveals significant increase and decrease of normal stress on the seamount-overriding plate interface that could have a profound influence on the dynamics of magathrust earthquakes.…”