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Research Scientist Han Zhujun Found Evidence of Holocene Activity and Paleo-Earthquakes in Southern Section of the Xiaojiang Fault

2016/6/7 14:53:58

It is commonly thought that due to the impediment of NWW Qujiang Fault and Shiping-Jianshui Fault, the activity of the Xiaojiang Fault , the southern section of the Xianshuihe-Xiaojiang fault system is weak during the Late Quaternary Period. This recognition has influenced our understanding of current continental dynamic model for southeastern margin of Qinghai-Tibet Plateaufor a long time and also influenced the assessment of future seismic risk in the south section of Xiaojiang Fault. As a result, this section of the fault was not recognized as a potential seismic source zone in the 5thgeneration of Seismic Ground Motion Parameter Zonation Map of China (GB18306-2015).

Recently, with the support of NSFC and in reference to [J1] 1/50000 detailed map of active faults, research scientistsHan Zhujun of our institute and his team found evidence of Holocene activity and paleo-earthquake in the south section of Xiaojiang Fault.

On December 28-30, 2015, Deputy Director Ouyang Biao, the Institute of Geology, CEA lead a team of experts and held an on-site seminar to discuss the  activity of the south section of Xiaojiang Fault Zone in Late Quaternary Period in Jianshui County, Yunnan Province.

At the meeting, Han Zhujun first introduced the tectonic setting and recent work progresses of the south section of Xiaojiang Fault Zone, with a focus of their new findings on the fault geometry, landform signature and paleo-earthquake exploratory trench near the Longtan Village. Ran Yongkang, He Honglin, Zhou Bengang, Fu Bihong, Zhang Shimin, Zhou Rongjun, An Xiaowen and Chang Zufeng and other senior experts in the field of active tectonics from the Institute of Geology of CEA, the Institute of Remote Sensing and Digital Earth of CAS, the Institute of Crustal Dynamics of CEA, Earthquake Administration of Sichuan Province and Earthquake Administration of Yunnan Province studied the exposures in the exploratory trench near the Longtan Village, Jianshui County, Yunnan Province. The experts at the meeting engaged in heated and meticulous discussion on the expression of tectonic landform in the south section of Xiaojiang Fault and the evidence of paleo-earthquake events and stratigraphic and depositional characteristics exposed in the etrench. They unanimously concluded that  the excellent expression of fault landform and stratigraphic dislocation characteristics discovered in the field this time is a rare discovery in an area with widely outcropped limestone in the south section of Xiaojiang Fault. The multiple paleo-earthquake events revealed in the exploratory trench are significant contribution to renew our understanding on Late Quaternary activity of the faults in the south section Xiaojiang Fault Zone, while the deposition of fault-blocked ponding in the trench provides possibility for determining the occurrence times of paleo-earthquakes.

Xianshuihe-Xiaojiang Fault Zone is the largest active tectonic fault system  thein South-North Seismic Belt in central China and attracts great attention. The so obvious evidence of Holocene activity of this fault zone showed in the section near the NW-striking Honghe Fault Zone show that it is necessary to carry out further and detailed research of this fault section in order to ascertain the space distribution and activity stage of this fault, particularly the cutting relationship with the Honghe Fault Zone, and provide a scientific basis for assessing future seismic risk and seismic zoning. These studies have important theoretic and social significances to the establishment of a model of current deformation in the southeast margin of Qinghai-Tibet Plateau.