Fault Geometry Control on Earthquake Segmentation and Locking Transition on Mid‐Crustal Ramp in Kumaun‐Garhwal, Central Himalaya: Implications for Regional Tectonics and Seismic Hazard

Abstract The Himalayan arc experiences numerous earthquakes that rupture its different segments at different times. Considerable attempts have been made to find discernible patterns and understand the underlying physics that can enable reliable forecasting of these earthquakes and precise seismic hazard assessment. We use a dense cGPS network, regional seismicity and topography to investigate the fault geometry variations in the ∼300 km long Kumaun‐Garhwal Himalaya and their implications for future earthquake hazard. We further assess the influence of ramp‐flat structural transition on the seismic‐aseismic slip transition at the mid‐crustal ramp. We find that the Garhwal megathrust accommodates a higher convergence rate (∼18.5 mm/yr) and exhibits a gently dipping (∼12°) and wider (30–40 km) mid‐crustal ramp than the Kumaun segment with ∼16.5 mm/yr convergence rate, ∼35° ramp‐dip and 7–10 km ramp‐width. A prominent lateral ramp, causing megathrust segmentation, is located between the Garhwal and Kumaun Himalaya, which can hinder the propagation of earthquake ruptures. The interseismic slip decay at the locking transition zone is found to be strongly controlled by the ramp‐flat structural transition and shares the characteristics of exponential slip decay on the mid‐crustal ramp. The Garhwal megathrust is vulnerable to intermittent small‐magnitude earthquakes with ramp confined partial ruptures. The wider decoupling zone in Garhwal suggests a larger recurrence interval between great earthquakes. The Kumaun megathrust can display seismic quiescence between through‐going ruptures, most likely nucleating at the updip edge of the mid‐crustal ramp. Such earthquakes can displace multiple fold‐accommodating hinterland faults in Kumaun, causing events with higher seismic intensity.