Great earthquake and tsunami potential in the eastern Makran subduction zone: New insights from geodetic and structural constraints

The Makran subduction zone ranks one of the highest potentials for seismic and tsunami hazards. However, the rupture style and tsunami-wave dynamics remain ambiguous due to incomplete historical recordings and the lack of modern seismo-geodetic measurements. In this study, we integrate geomorphological, seismic structural models based on seismic images, InSAR measurement, high-resolution multibeam bathymetry, and the Slab-2 model of the subducted oceanic lithosphere to propose a series of geodetic-structural-constrained slip deficit models for tsunami hazard assessment in the northwestern Indian Ocean with a focus on Gwadar port in Pakistan. We show that the accumulated strain on the megathrust could generate an M-w 8.1-8.4 earthquake assuming current steady-state coupling ratio and a 30 GPa rigidity. We reveal the imbricate thrusts of the outer wedge are more efficient to excite tsunamis than the sub-horizontal megathrust (reference model) by increase in wave height at least 1 m (50%) when included, and these have not been considered in tsunami hazard assessments previously. In the worst-case of M-w 9 megathrust model, can occur waves >5 m, strong currents reaching 6 m/s, and inundation distance (>1 km) in the Gwadar port when rupturing to the trench. Additionally, if the updip area of the 1945 event source region ruptured, it could amplify wave height by 0.2-1 m in the Gwadar port and generate a strong tsunami current (>2 m/s) compared with the reference model. These new findings are crucial for seismic and tsunami hazard mitigation and preparedness in the northwestern Indian Ocean. We also demonstrate that modeled maximum tsunami wave heights based on the multibeam, SRTM15+ and GEBCO_2020 bathymetry differ by 0.2-1 m in the source and by 0.1-0.3 m in the far-field. Our study provides better-constrained source models for inundation studies at coastal mega-cities for hazard preparedness and highlights that the tsunami hazard potential is notably higher than previously recognized in this region.