image: Figure 1. Model showing the crustal structure and stress field of the Eastern Himalayas. Two vertical faces are receiver function images across-strike and along-strike of the Himalayas. There is a north-south compressional stress field in the Tibetan crust and low-angle subduction of the Indian crust.
Credit: ©Science China Press
Complex Faulting in the Eastern Himalayas
The Eastern Himalayas are a region of both intercontinental convergence and strike-slip faulting. The area produces large earthquakes that threaten population centers of millions of people. However, there is no accepted explanation for the combined strike-slip and thrust faults that cause the frequent earthquakes.
New Seismic Data
In a recent study by Bai et al. (2025), new data recorded on a recently deployed broadband seismic array in the region was analyzed. Installing instruments in this largely inaccessible area is often difficult so there are few previous data from this area. Using earthquake focal mechanisms, the regional stress field is found to be dominantly north-south horizontal compression, which is consistent with both the thrust and strike-slip faulting. Also, details of the structure of the Moho and the geometry of subducting Indian plate are clarified from earthquake relocation and receiver function analyses of the seismic data.
Proposed Tectonic Model
Using the results from the new seismic data, a tectonic model (Figure 1) was proposed for the region. The model shows that the generation of megathrust earthquakes and the uplift of the broad mountains in the Eastern Himalayas can be explained by low-angle subduction of the crust-mantle boundary (Moho) and flat-ramp geometry of the Indian plate beneath the Eurasian plate. The subduction interface is termed the Main Himalayan Thrust (MHT), which is well recognized in the western and central Himalaya but more complicated in the eastern Himalaya.