Earth Planets Space, Vol. 56 (No. 12), pp. 1323-1330, 2004
Nobuhisa Matsuta1, Yasutaka Ikeda2, and Hiroshi Sato1
1Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
2Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033, Japan
(Received May 31, 2004; Revised November 22, 2004; Accepted December 6, 2004)
The slip-rates on the northern extent of Itoigawa-Shizuoka tectonic line (ISTL) are estimated based on seismic reflection profiles, drill core data and analysis of tectonic geomorphology. The ISTL is a major tectonic line that passes through the Honshu Island of Japan, and its northern and central segments form an active fault system characterized by high slip-rates. In the Kamishiro basin, near the northern end of the ISTL active fault system, the rate of net slip is estimated to be 4.4-5.4 m/kyr over the last 28 ka, with a vertical-separation-rate of 2.2-2.7 m/kyr. In the Omachi area, south of the Kamishiro basin, the Quaternary slip-rate is estimated to be at least 2.9 m/kyr based on the balanced cross-section derived from reflection profiles and surface geology. The dip angle of 30° determined from the Omachi seismic profile suggests a vertical-separation-rate of at least 1.5 m/kyr. Based on compiled evidence from the available geomorphological and paleo-seismological data, vertical-slip-rates of 1.0-2.9 m/kyr are inferred for the region between Hakuba and Toyoshina over the past 3 ka. The northern ISTL exhibits dip-slip-rate of at least 2.9 m/kyr, with a constant average slip-rate of 2.0-5.8 m/kyr since the Early Quaternary. A paleoseismological data and long-term slip-rate along the northern ISTL has potential for a large earthquake.
Key words: Northern Itoigawa-Shizuoka tectonic line, active fault, tectonic geomorphology, slip-rate.