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Session: Large Intraslab Earthquakes

Type: Oral

Date: 4/26/2019

Time: 09:30 AM

Room: Cascade II

Source Variations in Intraslab Earthquakes From Data and Modelling

The mechanism of intraslab earthquakes are still incompletely understood. In particular, the relative importance of dehydration embrittlement, thermal shear runaway, hybrid dehydration-induced stress transfer, or some combination, and how these influences might vary in different subduction zones is unclear. To understand the contribution from these mechanisms, we investigate earthquake source parameters from data in the two subduction zones in Japan: the older and colder Pacific Plate east of Hokkaido, and the younger and warmer Philippine Plate south of Kyushu.

We estimate stress drops, radiated energies, and radiated efficiencies of earthquakes greater than M3.6 over a 12-year period using the method of empirical Green’s functions (eGfs). Because intraslab earthquakes produce few aftershocks and because the signal-to-noise-ratio is low for small events, special attention must be given to eGf selection. We also consider the variation in high frequency fall-off rate between different events, noting that the standard omega-2 models used in such studies may be inappropriate for intraslab events. We find, in addition to the generally agreed-upon results of a higher stress drop and lower radiated efficiency for intraslab earthquakes, that there appears to be a break in self-similarity in the source parameters for the Hokkaido region, which suggests that different mechanisms may be important in the two subduction zones. However, we note that the observable magnitudes of the earthquakes in each region is limited by the cropped bandwidth at which data has good signal quality. We hence supplement our study by performing source inversions of larger events in each region, to better understand what possible differences in the source model can be observed in the data.

Presenting Author: Shanna Chu

Additional Authors