HR: 1330h
AN: S22A-0418    [PDF]
TI: Thermal Regime Inferred from Magnetic Anomaly Data in the Crust beneath the Japanese Islands, and its Relationship to Focal Depth
AU: * Tanaka, A
EM: akiko-tanaka@aist.go.jp
AF: Institute of Geoscience, Geological Survey of Japan/AIST, AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567 Japan
AU: Ishikawa, Y
EM: catfish@wa2.so-net.ne.jp
AF: Meteorological Research Institute, Japan Meteorological Agency, 1-1 Nagamine, Tsukuba, 305-0052 Japan
AB: One of the indicators of lithospheric strength is the focal depth distribution of earthquakes. Temperature has long been regarded as an important variable in determining the seismogenic portion of the lithosphere. The thickness of seismogenic crust layer correlates with surface heat flow in most interplate seismic areas of the world [e.g., Sibson, 1982]. However, heat flow measurements are often widely spaced, requiring an extrapolation of the data to estimate the thermal structure in the crust in some regions. The uncertainties associated with these extrapolations preclude improving on the general correlation between heat flow and depth of seismicity. We used another approach to estimate the thermal structure in the crust. The bottom of the magnetized crust determined from the spectral analysis of residual magnetic anomalies is generally interpreted as the level of the Curie point isotherm. We estimate the bottom of the magnetized crust, Z$_{b}$, of squares of 2.125$^{o}$ subregions using the magnetic anomaly map of the Japanese Islands [Makino et al., 1992]. At the same region, the thickness of seismogrnic crust is estimated as the depth above which 90 percent of the earthquakes occur, D$_{90}$, using good quality hypocenters by JMA (Japan Meteorological Agency) data. Z$_{b}$ and D$_{90}$ range from about 11 to 32 km and 12 km to 28 km, respectively. This suggests that our analysis cannot catch a locally shallow depth. And it is consistent with the expected inverse relation between Z$_{b}$ and the minimum heat flow values [Yamano et al., 1997] within the subregions. The inverse relation between Z$_{b}$ and D$_{90}$ suggests that this analysis is useful to estimate the regional thermal structure.
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 5104 Fracture and flow
DE: 5120 Plasticity, diffusion, and creep
DE: 7218 Lithosphere and upper mantle
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting