Short- / Long-Term Deformation of Upper Crust: Integrated and Quantitative Approach for Neotectonics

The Japanese Islands are facing active convergent margin, and have suffered intense deformation. On 11 March 2011, accumulated stress on the Japan Trench was released as a catastrophic earthquake (Mw 9.0), and the number of casualties are still increasing during preparation of this manuscript. The authors offer our deepest condolences on the loss of human lives, and dedicate this paper to the deceased hoping that our research can contribute to the advancement of integrated evaluation of seismic hazards. The islands are divided into northeast and southwest Japan at the Itoigawa-Shizuoka Tectonic Line (ISTL; Figure 1), which is a remarkable geological break and a zone of highly active reverse faults. An area of extremely high strain rate is conventionally named as Central Japan, which is a mountainous province associated with a number of active faults/volcanoes. Based on geomorphological studies, distribution of active faults in Central Japan has been clarified in detail (Research Group for Active Faults, 1991). Countless Quaternary tephra are precisely correlated (Machida & Arai, 2003), and serve to monitor subtle neotectonic deformation as explained in the following sections. It is an example of a junction of arcs (northeast Japan, southwest Japan and Izu-Bonin arcs), and an intensive collision zone. Remarkable bent of geologic belts, caused by collision of the Izu-Bonin arc, has been studied from the viewpoint of paleomagnetism / structural geology. Itoh & Ito (1989) clarified process of ductile deformation of the crust since the Miocene on the basis of spatial distribution of vertical-axis rotation deduced from paleomagnetic data. Long-term deformation in Central Japan is accommodated by conjugate strike-slip fault system; the NE-SW Atotsugawa fault system and NW-SE Atera fault system (Figure 1). Huzita (1980) proposed that they have been activated under an E-W compressive stress regime provoked during the Quaternary. Recently, paleomagnetic studies (Kimura et al., 2004; Itoh et al., 2008) revealed that rotation pattern around the active faults is simulated as deformation of continuous medium. Although temporal fluctuation of geomagnetic field (secular variation) generally hinders us from precise determination of tectonic rotation