On June 17, 2013, the Tianshui Central Seismological Station submitted an earthquake prediction based on the anomalies of our downhole ground resistivity, Wushan No. 22 well radon, Wushan No. 1 spring radon, and the tilt observation of the Wushan vertical pendulum boreholes, and then an earthquake of M_S6.6 occurred on July 22, 2013 in the Minxian-Zhangxian junction of Gansu Province. Therefore, it can be assumed that the above four geophysical field data from Tianshui Station truly reflect the changes of the underground medium in the region before the earthquake. Based on the anomaly analysis of the raw data of the above four data, this paper extracts the anomalies with normalized variation rate, subordinate function, and tidal factor, respectively, and summarizes the relationship between the anomalous characteristics of each measured item and the Minxian-Zhangxian earthquake. Finally, the geophysical field anomalous changes in spatial and temporal characteristics are explored by using the fault virtual dislocation model in combination with the seismic source mechanism solution.

The pre-earthquake anomalies of Tianshui apparent resistivity are located in Yawan Village, Ma paoquan Town, Maiji District, and the current downhole observation system was officially put into operation as a post-disaster reconstruction project in January 2012, with the electrode buried at a depth of 100 m. The hourly values of the NS, EW, and N45W orientations of Tianshui Station have shown synchronized high-frequency disturbance anomalies since April 9, 2013 to May 9, 2013, with the maximum magnitude of disturbance being 1.83%, 1.00%, and 4.28%, respectively. during which the April 20, 2013 Lushan, Sichuan M_S7.0 earthquake occurred. Synchronized high-frequency disturbance anomalies occurred again from June 12, 2013 to August 8, 2013, with maximum disturbance amplitudes of 1.41%, 0.85%, and 0.94%, respectively, during which the July 22, 2013 Minxian-Zhangxian M_S6.6 earthquake occurred. And the high-frequency disturbance amplitude of the Lushan earthquake is more obvious, which is related to the different deep structures and seismogenic environments of the two earthquakes. The change of the daily average value of Tianshui apparent resistivity is basically consistent with the resistivity change process in the seismic source area described by the DD model Pore fluid plays a central role in this model.

Wushan Spring No. 1, Well No. 22, and vertical pendulum borehole tilt are all located in Wushan Seismic Station, Hot Spring Town, Wushan County, Tianshui City, China. The observation point of Wushan No.1 spring is a natural outcrop spring, and Wushan No.22 well belongs to a fully pressurized well, and the distance between them is about 100 m. The background radon value of Wushan No.22 well is 240 （Bq/L）, and the background radon value of No.1 spring is 470 （Bq/L）, and the radon value of the two measurement points basically changes in a synchronized manner, and it rises since April 2012, with the overall trend of “low value-high value-low value”, and the high value anomaly lasts for about 1 year. The seismic change started from June 25, 2012, and the whole process is “uplift-seismic-decline”. 22 wells and No.1 spring radon values before the quake had the maximum variation of 6.36% and 9.59%, respectively, and the radon values decreased after the quake but did not restore the original background values. The tilt of the Wushan vertical pendulum borehole shows a decreasing and increasing trend of NS and EW components, respectively, since the observation. The rate from July 2012 to February 2013 is 3.11×10⁻³/day, and the rate from February 2013 to June 2013 is 5.66×10⁻³/day, and the post-earthquake aberration is in the co-seismic strain order.

Minxian-Zhangxian M_S6.6 earthquake was preceded by a synchronous rising anomaly in three normalized rate curves, and the anomaly threshold was determined to be 0.8. Monthly mean values of Wushan well No. 22 increased from March 2012 to August 2012 with a maximum variation of 13.6%; 13-point sliding values increased from February 2012 to September 2012 with a maximum variation of 8.7%. μ values showed three anomalies larger than the threshold before the earthquake （14 months before the earthquake）. The monthly mean value of Wushan Spring No. 1 increased since March 2012, with a maximum variation of 15.7%; the 13-point sliding value increased from February 2012 to November 2012; μ values showed three anomalies larger than the threshold value before the earthquake （14 months before the earthquake）, and μ values recovered since August 2013 after earthquakes. The Minxian-Zhangxian M_S 6.6 earthquake was preceded by a significant change in the tidal factor, i.e., the γ values of the north-south and east-west components showed a significant step-down from April 2012 to January 2013, which is a medium- to long-term trend change, and the earthquake occurred 6 months after the γ values rebounded.

The following conclusions can be drawn from the above analysis: （1） All four measurements are located in the stress extrusion region. （2） The geophysical field anomalies of Tianshui station are mainly concentrated within 200 km from the epicenter, and the anomaly evolution and anomaly amplitude show the characteristic anomalous changes of “long-mid-short-proximity” with the change of distance from the epicenter, which is corresponding to the Minxian-Zhangxian earthquakes in time and space. （3） The breeding of earthquakes involves the long-trend background, medium-term anomalies and short-term changes of the geophysical field. After the occurrence of regional earthquakes, we should analyze and summarize the data anomalies and accurately identify the anomalies based on the spatial and temporal strength and morphological characteristics of the precursor anomalies, and set up a database of typical regional seismic examples.