[J06-2] The spectrum of fault-zone deformation processes (from slow slip to earthquake) II

[J06-2-01] Completing the Seismic Cycle: Approaching 100% slip recovery along the subduction megathrust beneath Nicoya Peninsula, Costa Rica

^○Andrew Newman¹, Christodoulos Kyriakopoulos², Tiegan Hobbs¹ (1.Georgia Institute of Technology, Atlanta, Georgia, USA, 2.University of California Riverside, Riverside, California, USA)

The seismogenic megathrust beneath the Nicoya Peninsula exhibits magnitude 7.5+ earthquakes approximately every 50 years directly under land. Because of this, there have been numerous geophysical studies there including the Nicoya Seismic Cycle Observatory (NSCO) consisting of dense seismic and GPS networks cooperatively operated by UC Santa Cruz, Georgia Tech, U. South Florida, and OVSICORI. As detailed by a recent high-resolution 3D slab interface model by Kyriakopoulos et al. [JGR, 2015], the megathrust environment below Nicoya has strong along-strike transitions in oceanic crust origin and geometries, including massive subducted seamounts, and a substantial crustal suture. Using GPS data collected from campaign and continuous sites over the past two decades numerous studies have imaged components of the seismic cycle, including late-interseismic coupling, frequent slow-slip events, coseismic rupture of a moment magnitude 7.6 earthquake in 2012, and now several years of postseismic response. We report on a reanalysis of all slip behavior measured through this time, using the 3D geometry and consistent inversion methods to reveal a unified analysis of the full continuum of slip. We find that the late-interseismic locking that was observed in the decade prior to the major earthquake, accurately reflects the combination of episodic slow slip (contributing to weak to low-coupling zones), major coseismic rupture (contributing dominantly to the strongly locked patch), and afterslip (contributing to a combination of strongly locked zone transitioning to intermediately weak behavior). After accounting for all slip observed, little energy is left for significant earthquake behavior, suggesting that the fault has indeed released nearly its full potential, and likewise adding additional credence to the hypothesis that the megathrust environment is weak. Without the long-term and continuous geodetic observations made by the NSCO, this work would not have been possible.