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Along‐strike variations in the Nankai shallow décollement properties and their implications for tsunami earthquake generation
Author(s) -
Park JinOh,
Naruse Hajime,
Bangs Nathan L.
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl061096
Subject(s) - geology , subduction , seismology , décollement , slip (aerodynamics) , fault (geology) , episodic tremor and slip , trench , tectonics , chemistry , physics , organic chemistry , layer (electronics) , thermodynamics
Rupture of slow tsunami earthquakes at subduction zones propagates along a shallow plate‐boundary fault (i.e., décollement) nearly all the way to the trench. Seismic reflection profiles reveal that the shallow décollements have variable reflection characteristics in the Nankai subduction zone, allowing us to divide the subduction zone into impedance‐decreasing (inferred to be fluid‐rich) and impedance‐increasing (fluid‐poor) décollement regions. The fluid‐rich décollement regions with reverse‐polarity reflections may play a role as conditionally stable patches because of elevated fluid pressures. In contrast, the fluid‐poor décollement regions with normal‐polarity reflections could be unstable seismogenic patches with no unusual fluid pressures. We propose that when megathrust earthquakes nucleate at shallow depth, the small unstable fluid‐poor patches are prone to slip. They may also accelerate (velocity‐weakening) adjacent large, conditionally stable patches, generating large shallow slip and large tsunamis. As a result, along‐strike contrast of fault properties can involve large tsunami earthquakes along the Nankai shallow megathrust fault.