Regional crustal deformation characteristic before 2016 Yuncheng M4.4 earthquake swarm based on CMONOC continuous GPS data

To further study regional deformation characteristic in the southeast margin of Ordos Block during the period between the Alanshan M5.8 and Yuncheng M4.4 earthquake swarm,we analyze continuous GPS sites around the study area.The time-varying strain parameters removed a linear trend deviated from the background state in varying degrees since April,2015,and began to turn back at the end of the year 2015,meanwhile,the maximum extension strain and shear strain have the bigger variation relative to others.The GPS measurement also shows that the eastward displacement rate of the stations decreases during 2015e2016 in varying degrees compared to 2011e2015,and the variation is closely related to its geologic structural location.The differential movement between the stations is converted into regional strain accumulation due to the fault locking.Furthermore,during 2015e2016,the maximum extension rate oriented at near NS direction obviously increased,and the maximum contraction strain direction is changed from NW to EW direction,which contributes to strengthen extension and shear strain of the NEstriking faults,it’s consistent with the regional background strain state of Shanxi seismic zone,this may be an important contributor to occurrence of M4.4 earthquake swarm in Yuncheng basin.