Along-strike variations in the Nankai shallow decollement properties and their implications for tsunami earthquake generation

作者：Park Jin Oh^*; Naruse Hajime; Bangs Nathan L

来源：Geophysical Research Letters, 2014, 41(20): 7057-7064.

DOI：10.1002/2014GL061096

• Nankai subduction zone
• seismic reflection data
• shallow decollement
• fault property
• tsunami earthquake

Rupture of slow tsunami earthquakes at subduction zones propagates along a shallow plate-boundary fault (i.e., decollement) nearly all the way to the trench. Seismic reflection profiles reveal that the shallow decollements 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) decollement regions. The fluid-rich decollement regions with reverse-polarity reflections may play a role as conditionally stable patches because of elevated fluid pressures. In contrast, the fluid-poor decollement 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.

• 出版日期2014-10-28