Comparison of Tremor and Slow Slip Behavior Before and After the 2012 Mw 7.6 Nicoya Costa Rica Earthquake

Abstract:

Subduction beneath the Nicoya Peninsula, Costa Rica generates the largest underthrusting earthquakes in the country with a recurrence interval of about 50 years. The most recent of these events occurred on September 5th 2012 (Mw 7.6). This event occurred directly beneath a network of seismic and continuous GPS stations and within an area of focused geophysical research. This provides an opportunity to study slow slip and tremor behavior in the decade before, and years after a large megathrust event to track changes in the mechanics of the plate interface through the earthquake cycle. We review fifteen years of seismic, geodetic, ocean bottom fluid flow and pressure sensor data collected on or near the Nicoya Peninsula, above the shallow thrust interface that document a variety of slow slip behaviors. These include relatively large slow slip events that occur about every 2 years and have both deep (25-40 km) and shallow slip (5-15), smaller events with only shallow slip that occur more frequently (~1 per year), and events that occur at the toe of the margin wedge that are detected on seafloor pressure sensors. All of these slow slip events are accompanied by seismic tremor. We focus on changes in slow slip and tremor characteristics following the 2012 Nicoya earthquake.