CORONA画像の実体視判読に基づく1957年 Gobi-Altay地震の地表地震断層の認定

抄録

The 1957 M8.3 Gobi-Altay, Mongolia, earthquake was caused by the rupture of the eastern part of the Gobi-Altay active fault zone and produced 260-km-long surface ruptures with maximum horizontal and vertical displacement of 7 m and 5 m, respectively. We mapped these rupture traces based on geomorphic stereo analysis of CORONA satellite imagery and compared our map with the previously-reported detailed distribution map of the ruptures. We identified active fault traces that moved during the 1957 earthquake based on displacement of modern river beds or very young fluvial surfaces adjacent to them. We conclude that 1) we are able to identify the 1957 surface ruptures using CORONA imagery, 2) we are able to clearly interpret branch directions along surface ruptures. However, we are occasionally not able to detect the surface ruptures because of a) small vertical displacement of less than 1 m that is less than the threshold to identify any surface ruptures using CORONA imagery, b) distortion that impedes stereo analysis itself as well as scale reduction in the edge portion of CORONA imagery, and c) weak geomorphic expression due to small amounts of both coseismic and cumulative displacement. This study demonstrate that geomorphic stereo analysis using CORONA satellite imagery enables us to reconstruct details of recent surface ruptures that appeared several-ten years before the imagery was taken during AD 1959 and 1972, or perhaps several-hundred years before that period in arid areas where external geomorphic processes do not work so frequently.