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Temperature distribution and focal depth in the crust of the northeastern Japan

Abstract

The thickness of seismogenic crust layer correlates with surface heat flow in most interplate seismic areas of the world (e.g., Sibson, 1982). Although the inverse relationship between heat flow and the base of seismogenic zone is obvious, the quantitative relationships are less certain and there should be variability of the focal depths among different tectonic settings. Comparisons of the heat flow (Yamano et al., 1997), thermal gradient (Tanaka et al., 1999) and earthquake (Japan Meteorological Agency, JMA) databases for the northeastern Japan provide detailed geologic and geophysical information about the earthquake process of island arc. Temperatures in the crust were calculated using a steady-state, one-dimensional, heat conductive transport model with heat generation as a function of heat flow and thermal gradient. The evaluated temperatures for D90, the depth above which 90% of earthquakes occur, range between 200°C and 500°C except for high heat flow and thermal gradient data. The consistency of temperature for D90 over a large depth interval supports that the temperature is the dominant factor governing the focal depth in the crust.

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Correspondence to Akiko Tanaka.

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Keywords

  • Thermal Gradient
  • Focal Depth
  • Thermal Structure
  • Seismogenic Zone
  • Japanese Island