Normal‐faulting earthquakes beneath the outer slope of the Japan Trench after the 2011 Tohoku earthquake: Implications for the stress regime in the incoming Pacific plate

Abstract

After the 2011 Mw 9.1 Tohoku earthquake, numerous intraplate earthquakes occurred beneath the outer slope of the Japan Trench. Based on ocean bottom seismograph observations, these earthquakes occurred in the oceanic crust and uppermost mantle of the Pacific plate at depths shallower than about 40 km and had normal‐faulting focal mechanisms at all depths. Before the 2011 earthquake, normal‐faulting earthquakes beneath the outer trench slope occurred only at depths shallower than 20 km, whereas those at depths of around 40 km had reverse‐faulting mechanisms. These observations suggest that the stress regime in the Pacific plate was changed by the 2011 earthquake. The tensional stresses that now extend to depths of about 40 km may play an important role not only in the occurrence of large normal‐faulting earthquakes but also in hydration of the uppermost mantle of the incoming Pacific plate prior to the subduction.

Incoming plate faulting in the Northern and Western Pacific and implications for subduction zone water budgets

“…This result is in stark contrast with a recent model of the Earth's water budget that uses slab water flux models, volcanic outputs, and estimates of global sealevel during the Phanerozoic to constrain the maximum amount of water that is brought into the subduction zone (Parai and Mukhopadhyay, 2012). Parai and Mukhopadhyay (2012) suggest that even the conservative estimates of Van Keken et al (2011) overestimate the amount of water input into subduction zones globally. Our results presented in this paper have an even larger discrepancy with the estimates of Parai and Mukhopadhyay (2012).…”

“…Parai and Mukhopadhyay (2012) suggest that even the conservative estimates of Van Keken et al (2011) overestimate the amount of water input into subduction zones globally. Our results presented in this paper have an even larger discrepancy with the estimates of Parai and Mukhopadhyay (2012).…”

Precise aftershock distribution of the 2011 off the Pacific coast of Tohoku Earthquake revealed by an ocean-bottom seismometer network

“…However, aftershocks of the 2011 Tohoku earthquake within the subducting oceanic plate had mostly normal fault type, or strike-slip type, mechanisms. Obana et al (2012) found that earthquakes beneath the seaward slope of the Japan Trench after the mainshock occurred under a tensional stress field in all depths and concluded that the stress regime in the deep part of the subducting oceanic plate in the seaward slope had changed from compression to tension after the mainshock. Our results indicate that the tension stress field extends to the oceanic plate below the landward slope of the Japan Trench.…”

Intra- and intertrench variations in flexural bending of the Manila, Mariana and global trenches: implications on plate weakening in controlling trench dynamics

“…When the bending-induced stress exceeds the yield strength of the lithosphere, pervasive faulting could occur trenchward of the outerrise region (e.g. Jones et al 1978;Masson 1991;Ranero et al 2003Ranero et al , 2005Obana et al 2012;Gou et al 2013;Naliboff et al 2013;Boston et al 2014;Craig et al 2014;Zhou et al 2015). Faulting could in turn cause a significant reduction in the effective elastic thickness of the subducting plate Bodine & Watts 1979;Watts 2001;Ranero et al 2005;Contreras-Reyes & Osses 2010;Zhang et al 2014;Hunter & Watts 2016).…”