Along‐strike variations in the Nankai shallow décollement properties and their implications for tsunami earthquake generation. Issue 20 (20th October 2014)

• Record Type: Journal Article
• Authors: Park, Jin‐Oh; Naruse, Hajime; Bangs, Nathan L.
• Is Part Of: Geophysical research letters. Volume 41:Issue 20(2014:Oct.)
• Page Start: 7057
• Page End: 7064
• Publication Date: 2014-10-20
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2014GL061096
• Languages: English
• ISSNs: 0094-8276

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>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.</p> </abstract>