Near-trench coupling conditions offshore the Nicoya Peninsula, Costa Rica and Southern Nicaragua.

Subduction zones host the largest earthquakes of any tectonic setting and can produce large tsunamis. The occurrence of tsunamis depends on the amount of co-seismic slip in the shallow, offshore portion of the plate interface near the trench and may be related to the degree of coupling along the interface. Tsunamis have been observed in Nicaragua as a result of large earthquakes with the latest occurring in 1992 after a Mw 7.7 earthquake. In 2012, a Mw 7.6 earthquake occurred offshore the Nicoya Peninsula but did not generate a tsunami. The disparate behavior between these two adjacent segments of the Central American megathrust is enigmatic. We apply the stress-constrained model of slip deficit from Lindsey et al., 2021 on the interseismic velocities of Nicoya to estimate the slip deficit in the updip portion of the megathrust, and create locking models from the earthquake rupture models of the 1992 Mw 7.7 earthquake. Between 0.8-8.5 cm/yr of strain accumulation is occurring at the trench offshore Nicoya, suggesting that large earthquake and tsunamis are possible offshore Nicoya. Limited available geodetic data in Nicaragua are consistent with a tsunami rupture model, but uncertainties are large. Sea-floor geodesy would allow much better constraints on slip deficit in both regions.