甘肃岷县漳县M_S6.6地震与甘肃形变异常情况探讨

Analysis of the Relationship between Abnormal Ground Deformation of Gansu and the Minxian-Zhangxian M_S6.6 Earthquake

对岷县漳县MS6.6地震震中附近的甘肃省形变观测资料进行了初步分析,发现了一些异常情况,总结出来供大家讨论。

Minxian, located in southwestern Dingxi City of southern Gansu in the eastern region of the Qinghai Tibet Plateau, borders on Longnan and the West Qinling Mountains and is the geo- metric center of Dingxi, Tianshui, Longnan, and Gannan. The geological structure of Minxian belongs to the Qinling Mountains Hercynian geosyncline fold belt at the north branch of the Western Qinling Mountains fold belt. At 7：45 CST on July 22, 2013, an Ms6.6 earthquake oc- curred at the junction of Minxian and Zhangxian with a focal depth of 20 km. The earthquake oc- curred along the north branch Lintan--Dangchang fracture, 126 km from Dingxi and 17 km from Minxian County. Strong tremors were felt by residents in Dingxi, Tianshui, Longnan, and Gan- nan; those in Lanzhou and Baiyin also detected movement. The Earthquake Administration of Gansu province operates 8 deformation observation stations and 15 deformation observation pro- jects situated within 300 km of the earthquake focus that include DSQ and SSY at Tanchang sta- tion; CZB at Wushan station; CZB and YRY at Linxia station; YZ--1 at Liujiaxia station; CZB at Lanzhou station; DSQ, SSY, SSY-- II, SSQ, and PET at Lanzhou Shilidian station; and DSQ and SSY at Baiyin station. This study focuses on the data of 15 observation projects to conduct preliminary analysis, through which abnormal variation was detected in the data of 10 projects. Moreover, DSQ and SSY at Tanchang station and CZB at Lanzhou station showed obvious/？, [72, and Yl stages, and CZB at Wushan and Liangshui exhibited obvious/71 and/？2 stages. Therefore, deformation anomalies were present prior to the Ms6. 6 earthquake. Although the distance be- tween Lanzhou and Shilidian stations is less than 10 kin, only DSQ, SSY, and SSY--II at Shilidi- an exhibited a significant bulge anomaly; SSQ of Shilidian showed no obvious abnormalities. Such a huge discrepancy in such a close proximity required further explanation. It was determined that the CZB component at Linxia station began to increase rapidly in January 2011 and entered a de- clining trend in August. At the same time, the EW component began to alter from a normal de-cline, which resulted in significant deformation. These changes are unrelated to the NS compo- nent. Therefore, further research is needed to determine the reason for such anomalies.