Abstract
Lianfeng Fault Zone (LFZ) in Southwest China has great significance for understanding the seismogenic environment, but its activity is still poor constrains. The Qiaojia-Jinyang segment (QJS) of LFZ intersects with Jinsha River; Here well developed river terraces provide a potential Spatiotemporal constrains for faulting. Based on investigation of the terrace deposits along river, this paper makes a detailed logging and dating of the faulting and liquefaction of QJS. Combined previous data, the spatiotemporal sequence of the Late Quaternary river terraces in the area was redetermined. It is considered that the first and second grade river terraces at QJS (~10-20m and 60-70m, respectively, above the local river level) are roughly developed in the middle Holocene and the late Late Pleistocene, indicating that the valley along QJS was strongly undercut since the Late Pleistocene. Based on the analysis of the morphological characteristics, spatial distribution, material composition and intersecting relationship between the sand veins and the layers, the cause of the ground motions is preliminarily determined, which indicates the strong seismic activity of the LFZ during the Quaternary. Combined with the faulting characteristics within the profiles of terrace deposits and the dating data of the overlying strata, it is considered that the LFZ is active at least at QJS, and the latest active time is not earlier than the early-middle Holocene. These understandings provide a clear geological evidences for the seismicity assessment at LFZ, and help to the understanding of regional tectonic environment and the prevention of earthquake disasters.
Geomorphological And Sedimentary Records of Late Quaternary Activities of Qiaojia-Jinyang Segment of Lianfeng Fault Zone, Southwest China
