Journal
GEOPHYSICAL RESEARCH LETTERS
Volume 41, Issue 23, Pages 8288-8293Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2014GL062002
Keywords
seismic tomography; structural heterogeneity; megathrust earthquakes; Nankai subduction zone; seafloor topography
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Funding
- Japan Society for the Promotion of Science [Kiban-S 11050123]
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To clarify the causal mechanisms of megathrust earthquakes, we studied the detailed three-dimensional P and S wave velocities (V), attenuation (Q), and Poisson's ratio (sigma) structures of the Nankai subduction zone in southwest Japan, using a large number of high-quality arrival time and t* data measured precisely from seismograms of local earthquakes. The suboceanic earthquakes used are relocated precisely using sP depth phase and ocean bottom seismometer data. Our results show the existence of two prominent high-V, high-Q, and low-sigma patches separated by low-V, low-Q, and high-sigma anomalies in the Nankai megathrust zone. Megathrust earthquakes during 1900 to 2013 nucleated in or around the high-V, high-Q, and low-sigma patches, which may represent strongly coupled areas (i.e., asperities) in the megathrust zone. Our results indicate that structural heterogeneities in the megathrust zone, such as the subducting seafloor topography and compositional variations, control the nucleation of the Nankai megathrust earthquakes.
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