Duplex kinematics reduces both frontal advance and seismic moment deficit in the Himalaya

Abstract

Abstract Duplexing plays important roles in the evolution of fold-and-thrust belts and accretionary wedges, and causes internal shortening of the system, which then impacts both rates of frontal advance and seismic-moment deficit. Nevertheless, the significance of this internal shortening has not yet been highlighted in previous studies in the Himalaya or elsewhere. We invoke geometric solutions to constrain the ratio of transferred slip (R; i.e., the ratio of updip slip to downdip slip) for the midcrustal ramp—the most active ramp within the midcrustal duplex—in the Himalayan wedge. We find that R is ~0.9, and then used this ratio to calculate the accumulating seismic moment. The reduction in seismic-moment accumulation over the past 1000 yr along the entire Himalayan arc (~2200 km) is equivalent to at least one ~Mw 8.72 earthquake, and potentially reduces the seismic moment deficit by ~23%–54%, which may reconcile the long-term unbalanced seismic moment in the Himalaya.