Relations between deep temperatures and other geophysical characteristics in Central Honshu, Japan

Abstract

The area of interest, Central Honshu, represents a complicated knot of triple junction of the North American plate, the Eurasian plate and the Izu-Bonin arc of the Philippine Sea plate. Due to complicated geological-structural characteristics of the crust and specific plate tectonic features of the lithosphere, this region has been extensively investigated by different geophysical methods for decades. Beside seismic studies (yielding detailed information on the crustal structure and providing models for seismic velocity perturbations and seismic-wave attenuation in the area), particularly measurements of three-component geomagnetic variations, magnetic anomalies, studies of seismicity, etc., were made. This paper presents the results of a search for correlations between the thermal field in the region and other geophysical parameters. To specify the thermal regime of the crust and the uppermost mantle, a quantitative geothermal model of Central Honshu for six seismic profiles with a total length of some 1500 km was used. No correlation is indicated between Curie-point depth from magnetic data and that inferred by thermal modeling. Moderate but significant correlations are found between heat flow and depths to the Conrad and the Moho discontinuities. Strong correlations were found between temperature and seismic-wave attenuation, and also between fractional velocity perturbations and temperature in the uppermost mantle. Again, the correlation is strong and highly significant between electrical conductivity and temperature in the lower crust-upper mantle.