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Tidal sensitivity of shallow very low frequency earthquakes in the Ryukyu Trench
Author(s) -
Nakamura Mamoru,
Kakazu Keito
Publication year - 2017
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2016jb013348
Subject(s) - trench , geology , seismology , slip (aerodynamics) , shear (geology) , pore water pressure , subduction , shear stress , thrust fault , fault (geology) , geotechnical engineering , petrology , tectonics , materials science , physics , layer (electronics) , composite material , thermodynamics
We show that the activity between 2002 and 2014 of shallow very low frequency earthquakes (VLFEs), which occur in shallow subduction zones of the Ryukyu Trench, responds to ocean and Earth tides. Tidal sensitivity is highest in the central portion of the Ryukyu Trench and lowest in the southwest. The lag of peak VLFE activation behind the peaks of shear stress or normal stress is laterally heterogeneous along the Ryukyu Trench. The lateral variation of the lag between the peaks of sensitivity and stresses can be explained by the dependence of VLFE activation on thrust‐encouraging shear stress on the plate. The effective normal stress, which is calculated through rock experiments and from the sensitivity of VLFE for shear stress, is 0.25 MPa in the central Ryukyu Trench, which implies that high pore pressure on the plate interface would induce the VLFEs. The lateral variation of the sensitivity can be explained by differences in pore pressure within the plate interface. Although tidal sensitivity is lowest in the southwestern Ryukyu Trench, it increased temporarily during the middle of the decay of VLFE swarm activity. This is interpreted as reflecting a temporary increase in pore pressure on the fault, frictional heterogeneity, or fault weakening during the slip of slow slip events.