Finite element modelling of the 2015 Gorkha earthquake through the joint exploitation of DInSAR measurements and geologic-structural information

We investigate the co-seismic effects of the Mw 7.8 Gorkha earthquake through a Finite Element modelling approach that jointly exploits space-borne DInSAR deformation measurements and geologic-structural information. Our model permits to retrieve the coseismic displacements with a very good accuracy and to confirm the finding of earlier studies suggesting that the slip reaches a maximum value of about 7 m at a depth of 7-15 km along the Main Himalayan Thrust (MHT) and occurs in an area about 30 km northern of Kathmandu. In particular, the main-shock ruptured the deep part of the seismogenic zone of MHT, with rather small displacement values retrieved along the splay faults (Main Frontal Thrust - MFT; Main Boundary Thrust - MBT) in the southern region. A relevant aspect of our results is the imaging of about 3 m of displacement in correspondence to the shallow portion of the Main Central Thrust (MCT) to the north and of the Munsiari/Mahabharat Thrust (MT) to the south; this finding may be associated to a possible mechanism for accommodating the MHT-sourced deformation on the adjacent thrusts, highlighting a passive role of the hinterland structures as receiver faults of the displacements transferred from earthquakes originating on the MHT. In addition, the proposed model allow us to map the stress field distribution (evaluated through von Mises failure criteria) associated to the main seismic event; this result is in good agreement with the hypocentral distribution and mechanism of the investigated aftershocks.