Faulting and Fore-arc Sliver Transport in the Nicaraguan Subduction Zone

Abstract:

Strain partitioning and the migration of fore-arc terranes due to oblique convergence occur in numerous subduction zones around the globe, yet the mechanisms that accommodate the motion of these terranes in the upper plate remain uncertain. In the Nicaraguan segment of the Central American subduction zone, GPS-derived surface velocities provide evidence for northwest-directed Central American fore-arc sliver transport, parallel to the Cocos and Caribbean plate boundary, with much of the deformation occurring in a region surrounding the volcanic arc. Focal mechanisms from upper-crustal earthquakes in this zone are consistent with margin-parallel dextral strike-slip faults or margin-normal sinistral strike-slip faults. For many larger events, surface deformation and aftershock relocation have shown that the active fault is margin-normal, indicating that bookshelf faulting plays a role in enabling fore-arc transport. To investigate the implications of the April 2014 Mw6.1 Lake Managua earthquake for these processes, we relocated its aftershocks. Using data from broadband stations of the INETER seismic network, we measured P wave differential times for aftershocks spanning a three month period, and relocated the events using the GrowClust algorithm (Trugman and Shearer, 2017). The relocated aftershocks define a NW-striking, nearly vertical, fault plane. This strike is consistent with the conclusions of Suarez et al. (2015), although the fault is now more clearly delineated. Combined with the April 2014 mainshock focal mechanism, the fault plane indicates margin-parallel dextral strike-slip motion. The April 2014 earthquake fault lies within 50 km of the well-documented left-lateral margin-normal fault that ruptured in the 1972 Managua earthquake, indicating that margin-parallel shear and bookshelf faulting can occur in close proximity within the deformation zone that accommodates fore-arc sliver transport.