Updated attenuation tomography of Japan subduction zone

Zewei Wang, Dapeng Zhao

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

We determine an updated model of P- and S-wave attenuation (Qp, Qs) tomography of the Japan subduction zone using an improved inversion scheme, and derive the first Qp/Qs model of the study region.We establish a system of observation t? equations by taking 1/Qvalues at 3-D grid nodes arranged in the study volume as unknown parameters. This scheme can eliminate model errors caused by ignoring high-order terms of the Taylor expansion in the Q-format scheme adopted by previous studies. The inversion problem is considered as a quadratic programming problemwith bound constraints for best fitting the observed t? data in a least-squares sense. The 3-D attenuation model is obtained by using a limited-memory Broyden-Fletcher-Goldfarb-Shanno algorithm for bound constrained optimization. Because this inversion scheme uses bound constraints to avoid negative Q values, damping regularization is not needed, hence the ranges of Qp and Qs values obtained are less affected by human subjectivity. The subducting Pacific and Philippine Sea slabs exhibit high-Q and high Qp/Qs, whereas the mantle wedge beneath the volcanic front and back-arc area shows low-Q and low Qp/Qs. Both Qp and Qs vary in a range of 10-2000, and the Qp/Qs ratio changes from 0.4 to 1.4. Our results reveal a narrow high-Qp/Qs belt that is coincident with the distribution of volcanic and non-volcanic low-frequency micro-earthquakes (M 0.0-2.5), which may reflect high watersaturation anomalies that are probably associated with slab-derived fluids and responsible for the generation of low-frequency micro-earthquakes.

Original languageEnglish
Pages (from-to)1679-1697
Number of pages19
JournalGeophysical Journal International
Volume219
Issue number3
DOIs
Publication statusPublished - 2019 Aug 30

Keywords

  • Inverse theory
  • Seismic attenuation
  • Seismic tomography
  • Subduction zone processes

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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