Near-trench coupling conditions offshore the Nicoya Peninsula, Costa
Rica and Southern Nicaragua
Abstract
Subduction zone tsunamis require significant co-seismic slip in the
shallow, offshore plate interface near the trench, possibly related to
the degree of prior interseismic coupling. In Nicaragua, a large tsunami
was associated with the1992 Mw 7.7 earthquake. To the
south, the 2012 Mw 7.6 earthquake in the Nicoya
peninsula of Costa Rica did not generate a tsunami. The disparate
behavior between these two adjacent segments of the Central American
megathrust remains unexplained. A stress-constrained model of slip
deficit applied to the interseismic surface velocity field in Nicoya
suggests a slip deficit rate in the updip portion of the megathrust
between 0.8-8.5 cm/yr, suggesting that large tsunamis are possible here.
Limited GPS data in Nicaragua can be reconciled by an offshore locked
zone that matches the shallow rupture defined by the model of the 1992
tsunami. Sea-floor geodesy would allow much better near-trench
constraints on slip deficit in both regions.