Geothermal gradient and heat flow data in and around Japan (II): Crustal thermal structure and its relationship to seismogenic layer

Abstract

The high-quality database of seismicity of Japan (JMA, Japan Meteorological Agency) and an extensive compilation of thermal measurements (Tanaka et al., 2004a) are used to quantify the concept of temperature as a fundamental parameter for determining the thickness of the seismogenic zone. Qualitative comparisons between each data of heat flow and geothermal gradient, and the lower limit of crustal earthquake hypocentral distributions beneath the Japanese Islands show that, as expected, the lower limit of seismicity is inversely related to heat flow and geothermal gradient. However, the density of the data is not uniform but highly clustered and spatially concentrated instead. To fill the data gaps, the available data were interpolated onto regular grids of points with a spacing of 0.25• × 0.25• . Gridded heat flow or geothermal gradient and D 90 , the depth above which 90% of earthquakes occur, correlated well with each other. The evaluated temperatures for D 90 range between 250• C and 450• C except for higher heat flow data. The consistency of temperature for D 90 over a large depth interval almost all over the Japanese Islands support the concept that the temperature is the dominant factor governing the focal depth in the crust. A comparison of our results with other tectonic regions could provide evidence for variations in temperatures for D 90 .

Geothermal gradient and heat flow data in and around Japan (I): Appraisal of heat flow from geothermal gradient data

“…In the following paper (Tanaka, 2004b), we will discuss how the lower cutoffs in seismicity vary with the thermal field.…”

The effect of obliquity on temperature in subduction zones: insights from 3D numerical modeling

“…In any case, the simple numerical modeling performed in this contribution positively tests our hypothesis that along-strike variation in subduction obliquity may have a first-order control on the temperature at the subduction interface, and may help us to understand the variation of geothermal gradient along strike of subduction zones, such as predicted by surface heat flow, for example below Japan (Tanaka, 2004). In light of the presented numerical models we argue that the plate boundary configuration may play a prime role in inducing strong lateral variations in geotherm within subduction systems, e.g.…”

Combination of Well-Logging Temperature and Thermal Remote Sensing for Characterization of Geothermal Resources in Hokkaido, Northern Japan

“…In general, temperatures in the western region are higher than in the other two regions, which agrees with the large distribution frequency of Quaternary volcanoes. As shown in Figure 9, high SST zones mostly overlapped with the distribution of Quaternary volcanic rocks areas (Figure 2 [48,49] (at 1100 m), and their contour map by weighted kernel density (at 1500 m). Purple at depths deeper than 1100 m b.s.l indicates that the area is outside the calculation region due to insufficient temperature data for KED.…”

“…The SST model is harmonious with the terrestrial heat flow map retrieved from the database of geothermal gradients and heat flow data in and around Japan [48,49], with the highest temperature zones at 1500 m b.s.l. being found in the western region (Figure 10), which is consistent with the extremely high heat flow region ( Figure 9).…”