Viscoelastic lower crust and mantle relaxation following the 14–16 April 2016 Kumamoto, Japan, earthquake sequence

Geophysical Research Letters
By: , and 

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Abstract

The 2016 Kumamoto, Japan, earthquake sequence, culminating in the Mw=7.0 16 April 2016 main shock, occurred within an active tectonic belt of central Kyushu. GPS data from GEONET reveal transient crustal motions from several millimeters per year up to ∼3 cm/yr during the first 8.5 months following the sequence. The spatial pattern of horizontal postseismic motions is shaped by both shallow afterslip and viscoelastic relaxation of the lower crust and upper mantle. We construct a suite of 2-D regional viscoelastic structures in order to derive an optimal joint afterslip and viscoelastic relaxation model using forward modeling of the viscoelastic relaxation. We find that afterslip dominates the postseismic relaxation in the near field (within 30 km of the main shock epicenter), while viscoelastic relaxation dominates at greater distance. The viscoelastic modeling strongly favors a very weak lower crust below a ∼65 km wide zone coinciding with the Beppu-Shimabara graben and the locus of central Kyushu volcanism. Inferred uppermost mantle viscosity is relatively low beneath southern Kyushu, consistent with independent inferences of a hydrated mantle wedge within the Nankai trough fore -arc.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Viscoelastic lower crust and mantle relaxation following the 14–16 April 2016 Kumamoto, Japan, earthquake sequence
Series title Geophysical Research Letters
DOI 10.1002/2017GL074783
Volume 44
Issue 17
Year Published 2017
Language English
Publisher AGU
Contributing office(s) Earthquake Science Center
Description 9 p.
First page 8795
Last page 8803
Country Japan
City Kumamoto