Abstract: Using the GPS horizontal movement data during 1999—2007, 2009—2015 and 2015—2017 before and after the Menyuan M_S6.4 earthquake in January 21, 2016, as well as the mobile short-leveling observational data of cross-fault within the radius of 200 km around the epicenter, aid by the calculation of GPS apparent strain field, negative dislocation inversion of Lenglongling fault profile and the extraction of new index of cross-fault deformation intensity, the medium-long term locking background of related fault and medium-short term dynamic evolution process of fault activities were comprehensively analyzed. The results show that: ① the differential movement and compression variation between GPS stations in the middle-eastern Qilian Mountains tectonic area increased during 2009—2015 compared with 1999—2007; the short-leveling observation of cross-faults also showed similar acceleration characteristics of fault activity or deformation-strain in about 2 years before this earthquake. ② Layered non-uniform negative dislocation inversion revealed that the Lenglongling faults related to this earthquake were locked for a long time in 1999—2007, more than ten years before this earthquake; and locking degree increased in the depth of 0~15.6 km below the surface during 2009—2015, six and a half years before this earthquake. ③ The new index of cross-fault deformation intensity in the range of 200 km radius around the epicenter showed that accelerating of variation amplitude which slightly displayed thrust feature in half a year before the earthquake, reflecting medium-short-term precursors.

Key words: Negative dislocation inversion, GPS, Cross-fault leveling, The Menyuan strong earthquake