Thermal modeling of the SW Ryukyu forearc (Taiwan): Implications for the seismogenic zone and the age of the subducting Philippine Sea Plate (Huatung Basin)

M. A. Gutscher*, F. Klingelhoefer, T. Theunissen, W. Spakman, T. Berthet, T. K. Wang, C.-S. Lee

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Subduction mega-thrust earthquakes in the SW Ryukyu trench pose a seismic and tsunami hazard. One of the objectives of this study is to estimate the downdip width of the seismogenic zone using numerical modeling to determine the temperature distribution along the plate interface. However, this approach depends strongly on the thermal parameters of the subducting slab. While the Philippine Sea plate (PSP) subducting beneath the central and eastern Ryukyu arc is of Eocene age (35-50. Ma), its age west of the Gagua Ridge is uncertain, with proposed ages ranging from Lower Cretaceous (140. Ma) to Upper Eocene (35. Ma). Since the sparse available heat flow data are insufficient to resolve this debate, both end-member hypotheses are tested as input parameters. We examined two transects at 122.5°E and 123.5°E on either side of the N-S trending, 4-km high, Gagua Ridge. The shallow forearc geometry is obtained from wide-angle seismic data. The deep slab geometry was obtained from hypocenter distribution and tomography. For an Eocene slab age, we obtain a 100. km and 110. km wide seismogenic zone (between the 150. °C and 350. °C isotherms) west and east of Gagua Ridge, respectively. This is in good agreement with the observed distribution of hypocenters. Using a Cretaceous slab west of Gagua Ridge predicts a deep seismogenic zone (25. km-60. km depth), inconsistent with observed thrust earthquakes. Tomographic images at 122.5°E and 123.5°E show a similar slab thickness of 70-80. km suggesting that the oceanic lithosphere has a young (Eocene) thermal age. The westernmost PSP (Huatung Basin) may have been thermally rejuvenated by mantle convection near the slab corner. The tectonic history since 6. Ma (transition from subduction to collision beneath Taiwan) may have also perturbed the thermal structure.

Original languageEnglish
Pages (from-to)131-142
JournalTectonophysics
Volume692
Issue numberPart B
Early online date4 Apr 2016
DOIs
Publication statusPublished - 5 Dec 2016

Keywords

  • Finite-element modeling
  • Forearc thermal structure
  • Seismogenic zone
  • Subduction

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