Abstract:An earthquake of MS5.4 occurred at the boundary between Jinta County, Jiuquan City, Gansu Province and Ejina County, Alashan City, Inner Mongolia Autonomous Region in the north Jinta-Huahai Basin(south margin of Beishan) of the active Altun fault belt on May 3, 2012. We found that the values of groundwater radon from Jiayuguan, Lanzhou, Wushan, and Pingliang stations exhibit synchronous abnormal variations before and after April 22 within 90~900 km from the epicenter by time-space scanning of the observed data from the Gansu precursor network and calculating the slip change rate of groundwater radon and variation rate of base value. These abnormal variations were mainly presented as increasing groundwater radon value from 5.6% to 37%. From April 22, 2012, the daily measured water level parameter increased a step with the amplitude increasing initially from 0.36% to 1% and then decreasing. The relationship between the abnormal variations in groundwater radon values observed from the Wushan, Pingliang, and Shilidian stations far from the epicenter and this earthquake must be further studied; however, this phenomenon is objective.Deformation anomaly information from the observatory primarily indicates that the ground tilt in the EW and SN directions measured at the Gaotai station, 170 km from the epicenter, decreases rapidly after April 11, 2012. The value of ground tilt in both the SN and EW directions increases abruptly from April 19 and April 24, respectively, and the amplitude reaches 100% at 11:38 a.m. on April 30 and continues until 10:07 a.m. on May 2. In the EW direction, the value decreases rapidly to the minimum value from 10:00 a.m. on May 2 to 11:39 a.m. on May 3 and then increases rapidly and recovers to the level measured on May 2, which is contrary to the trend observed in the SN direction. The ground tilt values in both the EW and SN directions reach the maximum value after 11:39 a.m. on April 3 and stay out nearly 6 hours; subsequently, Jinta, Jiuquan experienced an earthquake of MS5.4 at 18:19. The increase in Dingxin-Delingha baseline shortening velocity in 2010 indicates that the northeastern Qinlian Structure Belt was squeezed and the baseline shortened by 5 mm in two and a half years before the Jinta MS5.4 earthquake.A series of abnormal variations occurred 10 days prior to the Jinta MS5.4 earthquake. The short-impending anomaly primarily appeared at the stations at a distance of 200 km from the epicenter from mid-March to late April. The impending earthquake anomaly occurred primarily between April 28 and May 1. The Gaotai station recorded the ground tilt data and the complete rock stress change process during the occurrence of the Jinta, Jiuquan MS5.4 earthquake, thus providing complete evolution data with earthquake development and occurrence and has significant research value for the developing a perfect seismic theoretical model and earthquake prediction.
