Accelerated sliver transport during transition from postseismic to interseismic conditions

Developing a detailed spatiotemporal characterization of the period between a large earthquake and the quasi-stable interseismic period is critical to understanding the mechanics of seismic cycle behavior. Particularly, understanding how faults heal and how stresses realign as the interface begins to recouple. Detailed surface deformation data prior to and during this time are scarce, however.For the 2012 Mw 7.6 Nicoya, Costa Rica earthquake, we evaluate 4.5 years of continuous and campaign GPS observations from up and down dip of the coseismic rupture area. This complex dataset shows initially postseismic seaward motion from afterslip, short-lived very rapid sliver transport, and finally a return to landward motion near pre-seismic rates. While afterslip for this event has been considered previously, we invert subsets of the 4.5-year window to show a late postseismic burst of slip at 25-40 km depth in mid-2015. After this period, the sense of slip begins reversing, for diminishing cumulative slip as relocking becomes dominant. The most surprising signal is the excessive and near-exclusive trench-parallel sliver motion across the entire region, that is observed between early 2015 and early 2016. This motion hits a maximum of near 27 mm/yr, much greater than the 11mm/yr interseismic average [Feng et al., JGR, 2012], and occurs shortly after locking reinitiates near the coast (and immediately updip of the 2012 rupture). We will present the results of detailed kinematic processing of the evolution of the spatial deformation observed through the postseismic period. We use these data to also model the locking behavior along the megathrust and accommodating transform system. Identifying and understanding this process is important as it give insight into far-field fault `communications' and short-term hazard mitigation following a major earthquake, given that most earthquake risk in Central America is due to smaller crustal events associated with strike-slip faulting that accommodate such sliver transport.