Two Decades of Geodetic and Seismological Insight into the Seismogenic Zone: A View from Nicoya, Costa Rica

The Nicoya Peninsula in Costa Rica has major magnitude ~7.5 earthquakes about every 50 years, with the prior event occurring in 1950. With the initiation of a major NSF-MARGINS project " Imaging the Seismogenic Zone with Geodesy and Seismology" at the turn of the century, and continuing with a number of projects that followed, we have obtained the most complete set of observations available on any seismogenic megathrust. The team from Univ. South Florida, UC Santa Cruz, Georgia Tech, and the Observatorio Vulcanológico y Sismológico de Costa Rica, collectively called the Nicoya Seismic Cycle Observatory (NSCO), captured detailed seismic and geodetic recordings of transient, late-interseismic, coseismic, afterslip, recoupling, and renewed interseismic deformation around a magnitude 7.6 earthquake directly beneath the network in 2012. Major seismogenic zone discoveries include: 1) geometric, seismogenic, and frictional shifts are associated with changes in incoming plate origin; 2) episodic slow-slip events (SSE) can recur in both shallow (possibly to the trench) and deep environments; 3) pre-earthquake coupling and SSE behavior are indicative of future coseismic slip magnitude and spatial limits; 4) seismicity rates identify locked zones that failed during the earthquake; 5) the future slip could be described by dynamic rupture modeling stress buildup during interseismic coupling; 6) rupture can focus along a subducted topographic high; 7) aftershocks dominate around the edges of afterslip and are a fraction of the size; 8) seismic velocity changes reveal pressurized pore fluids in the forearc; 9) during recoupling, the forearc sliver displays punctuated along-trench translations; 10) interseismic coupling can recur within 4 years; 11) recurrence times of SSEs do not vary between large earthquakes.