Oblique subduction at a high rate of convergence along much of the Middle America Trench results in northwest-directed trench-parallel block motion. Accommodation of this motion along a northwest-striking dextral strike-slip fault has been postulated; however, in Nicaragua such faults are not well developed. We suggest instead that this motion is accommodated by bookshelf faulting involving north to northeast-striking left-lateral faults. We present earthquake epicenter and focal mechanism data and mapped fracture and fault data consistent with this model. Trenchward migration of the volcanic arc since the Miocene and reactivation of northeast-striking Miocene structures have led to the development of this arc- and trench-normal fault system.