| 研究実績の概要 |
In the past year, we start our study on the active tectonics and earthquake hazard of the Longmen Shan fold-and-thrust belt and Sichuan basin in western China, which is proposed in our previous JSPS research plan. We have conducted multi-disciplinary geological and geophysical investigations on the Longquan fault (LQF) and Range front blind thrust (RFBT) system, as summarized below:
1). The LQF fault defines the east boundary of the Longmen Shan fold-and-thrust belt, with the total length of about 230 km. By using high-resolution satellite images combined with the field observations, we mapped the fault traces of the active back-thrust of the LQF, and excavated a trench across the ~5 m high fault scarp that formed on the alluvial fan. Based on the indentification of the colluvial wedges and the C14 dating ages, we infer that there are at least two paleoearthquake events are recorded in the trench wall. These findings confirm the cumulative of uplift of river terraces are produced by the LQF through repeated paleoearthquake events.
2). Our study shows that the 2013 Mw 6.6 Lushan, China, earthquake ruptured a small segment of the fault on the RFBT. We found the 2008 Wenchuan and 2013 Lushan earthquakes, along with results from this new study, demonstrate that the Longmen Shan and western Sichuan basin are underlain by an active, imbricate thrust system. Because of these fault are close to large cities, and the prospect for basin amplification of seismic waves, these newly discovered faults represent significant hazards.
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