広帯域MT観測及び重力測定による北海道東部弟子屈地域の地殻構造

概要

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Wide-band magnetotelliric and gravity surveys were conducted at the Teshikaga area, located in eastern Hokkaido, Japan, where intra-plate earthquakes had teken place. We inferred shallower (<2-Km depth) crustal density structur using the gravity and borehole data, and then compared it with resistivity structure revealed by two-dimensional MT inversions. The results show that the density and resistivity structures are closely correlated with each other. The resistivity profiles and Bouguer anomaly map indicate that the high density and high resistivity zone, which presumably represents Miocene volcanic and sedimentary rocks is apparently cut by a major dextral strike slip fault. Location and strike of the apparent dextral strike slip fault closely match those of the inferred earthquake fault formed by the 1938's earthquake estimated from surface displacement. However, the dextral strike slip movement is not the result of recent crustal movement, because sinistral movement has been documented for the earthquake faults. Preexisting dextral strike slip fault was presumably reactivated to cause present-day earthquakes.
北海道大学大学院理学研究科地球惑星科学専攻（地球物理学）の論文
2006-03-15