Volcanic Subsidence Triggered by Megathrust Earthquakes

Studies using spaceborne interferometric synthetic aperture radar (InSAR) analysis showed that two megathrust earthquakes – the 2011 M w 9.0 Tohoku-oki earthquake in Japan and the 2010 M w 8.8Maule earthquake in Chile – triggered unprecedented subsidence in multiple volcanoes. There are strong similarities in the characteristics of the surface deformation in Japan and Chile: (1) Maximum subsidence is about 15 cm. (2) Areas of subsidence are elliptically elongated in a north-south direction perpendicular to the principal axis of the extensional stress change. (3) Most of this subsidence is coseismic. These similarities imply that volcanic subsidence triggered by the megathrust earthquakes is a ubiquitous phenomenon. Nonetheless, the mechanism of subsidence is yet to be investigated. Two main hypotheses have been proposed thus far: 1) The localized deformation of hot and weak plutonic bodies. 2) Water release from large hydrothermal reservoirs beneath the volcanoes.