Strain-rate estimation and focal mechanism stress inversion in Himalaya-Tibet region

The India-Eurasia collision zone is one of the most complex and destructive collisional zones globally. The Indian plate converges with the Tibetan Plateau to the north, exhibiting a convergence rate increasing from ~16.5 mm/yr (Kumar et al., 2023) in the west to ~21 mm/yr in the Bhutan region (Dal Zilio et al., 2020). Compression is primarily accommodated by the basal detachment commonly referred to as the Main Himalayan Thrust, whose surface expression is represented by the Main Frontal Thrust. To describe the destructiveness of this zone, historical and instrumental events such as the 1505 Lo Mustang earthquake (Mw 8.2-8.8), the 2015 Gorkha earthquake (Mw 7.8), and the 1714 Bhutan earthquake (Mw 8.1) are remembered. The Tibetan region, on the other hand, is primarily affected by extensional earthquakes that accommodate a west-east directed extension with moderate to high magnitude earthquakes, ranging between Mw 5.5 and Mw 6.8, such as the 2008 Xizang earthquake (Mw 6.7) and the 2008 Damxung earthquake (Mw 6.3) on the YadungGulu rift. Active strike-slip faults are also present, bordering much of the Tibetan plateau and intersecting its central zones (Wang & Barbot, 2023). Notable examples include the Altyn-Tagh fault, the Karakoram fault, and the Gyaring Co fault. Although the region is particularly affected by high rates of seismicity, seismic and geodetic networks are not well-distributed. In such cases, a multidisciplinary approach allows drawing from several data types to obtain a more comprehensive understanding of the seismotectonic setting. We have computed a new velocity field by processing continuous stations throughout the Tibetan-Nepal-Indian territory. Additionally, through Helmert transformations, all pre-existing velocity fields documented in the literature have been merged into a unified large-scale velocity field. This unified velocity field has been utilized to compute a fine strain rate map over the entire study area. A unified catalogue for instrumental seismicity and focal mechanisms, registered in the area since 1980, has also been collected. Such a unified catalogue is the outcome of a meticulous compilation of data sourced from various national and international catalogues aimed at improving the completeness magnitude of the area (approximately Mw 4.0). The same care has been applied to gather historical events preceding 1980, ensuring a comprehensive understanding of the seismic history (Cheng et al., 2017). The deformation pattern can be completely understood by comparing strain rate maps with focal mechanism inversions. This approach allows us to compare stress and strain and to discriminate the contributions of several sources of different kinematics.