Translating Megathrust Behavior Into the Nicoya Crust, Revealing a Dynamic Dance Across the Seismic Cycle

Date: 4/24/2019

Time: 04:30 PM

Room: Cascade II

The relatively unique geometry of the Nicoya Peninsula directly over the seismogenic megathrust in northwestern Costa Rica has allowed a unique opportunity for the development of a rich 20-year geodetic time history of behavior. The geodetic and seismic network operated in the region is jointly operated by University of South Florida, University of California Santa Cruz, and Georgia Tech, and is called the Nicoya Seismic Cycle Observatory (NSCO). Starting in the 1990s, we’ve observed approximately 15 years of interseismic strain accumulation centered beneath the peninsula, with frequent, nearly biennial slow-slip events outlining the locked regions. These events varied in size occurring both down-dip and up-dip, going offshore and becoming difficult to constrain. We then captured the 2012 Mw 7.6 Nicoya earthquake, which we anticipated, having ruptured the area previously locked. The afterslip and aftershocks tell a story of coexistence, but not colocation, with most aftershocks occurring at the periphery of afterslip, and not account their cumulative moment not accounting for the geodetic one of afterslip. Finally, following afterslip, we then see a very strange postseismic sliver transient during the recoupling period. This sliver transient is concurrent, but not necessarily dependent on transient locking near the coastline. Finally, the interface completely relocks itself, making it hardly distinguishable from the pre-2012-event. We will explain the totality of the locking in relationship to other behaviors over time, and discuss the relative similarities between relocking and old locking. By completing the cycle, we are getting at understanding the complete geodetic moment budget allowable from tectonic convergence rather than the 10-20% allowable from seismic only estimates.

Presenting Author: Andrew Newman

Authors