Using GPS Data To Study The Distribution Of Fault Slip And Stress Changes In Nepal Mw 7.8 Earthquake

On April 25,2015,a strong earthquake occurred in the central Himalayas,about 80 km northwest of the capital city of Kathmandu,Nepal.The moment magnitude was Mw 7.8,and the focal depth was about 15 km.Seismological and geodetic research results show that this earthquake is a low dip event with unbroken surface.The thrust is dominated by slip,with a small amount of right-lateral components,and the maximum slip is mainly concentrated in 10-15 km,depth.This paper uses GPS continuous observation data to study the crustal deformation characteristics of the pre-seismic,co-seismic and post-seismic,and investigates the temporal and spatial distribution pattern of fault slip in the coseismic and post-earthquake.Evaluates the earthquake risk in Nepal based on the coseismic and post-seismic stress changes.By studying the surface deformation in the epicentral area,fault slip distribution after the earthquake,and distribution of stress changes,it provides reasonable basis and scientific guidance for the earthquake rupture model,stress transmission mechanism and earthquake disaster assessment in Nepal.The main results as follows:?1?Using the GPS observation data from Nepal and southern Tibet,the least squares parameter fitting method was used to obtain the near-field and far-field coseismic and post-earthquake surface displacements of the Nepal Mw 7.8 earthquake.Nepal is moving southwards due to the earthquake,the maximum horizontal co-seismic displacement is 1.88m at the KKN4 station located in the northeastern direction of the source of the earthquake,and in southern Tibet to reach millimeter to centimeter level deformation.Large surface deformation mainly occurs in the east direction of the epicenter,revealing the eastward propagation of the coseismic rupture.After the earthquake,the postseismic displacement continued to decay,the maximum horizontal postseismic displacement occurred at CHLM and DNC4 stations at about 100 km east of the epicenter,reaching 6.37 cm and 5.80 cm,respectively.?2?To calculate the coseismic faults slips induced by this earthquake we use the model of dislocation sources embedded in an elastic layered half-space,and employ SDM?Steepest Decent Mothod?code.The results show that the rupture of the Gorkha earthquake does not reach the surface,average slip is 0.62 m,the maximum slip is 4.82 m,The maximum slip occurs along the strike 122.5 km,depth 13.0 km.The moment tensor released is6.76?10²⁰N·m,and the corresponding moment magnitude is Mw 7.8.?3?Basing on the elastic dislocation theory,we use the Principal Component Analysis-based Inversion Method?PCAIM?to study the time-and space-dependent evolutions of afterslip on fault using 531-day observations of 16 GPS stations.The results show that the postseismic afterslip obeys the logarithmic decay patterns;the fault slip is mainly concentrated in the northern part of the mainshock rupture zone,with the maximum slip of 20.6 cm located at 26.7 km depth;The inverted seismic moment is 3.36×10²00 N·m,equivalent to a moment magnitude?Mw?of 7.6.The fault slides after the earthquake did not reach the surface,mainly in the east direction of the main shock.?4?In this paper,PSGRN/PSCMP and fault slip results are used to calculate Coulomb stress changes produced by coseismic and post-seismic dislocations.The maximum Coulomb stress caused by the coseismic occurred at the depth of 7 km,reaching 3 MPa,causing a stress increment of 0.04 MPa-0.06 MPa in the maximum aftershock?Mw 7.3?region.The maximum stress change of the afterslip occurred at the depth of 15 km,reaching 1 MPa.The Coulomb stress in the eastern of the mainshock increases more than in the west,indicating that the earthquake ruptures to the east.Aftershocks of the earthquake are mainly distributed in the Coulomb stress enhancement area in the eastern region of the main earthquake,and the subsequent aftershocks are induced by the strengthening of the Coulomb stress.The stress in the shallow and western regions has not been released and there is a large earthquake risk.