Fifteen Years of Slow Slip and Tremor Observations at the Northern Costa Rica Subduction Zone

Abstract:

Coordinated long-term geophysical observations at the northern Costa Rica seismogenic zone, facilitated by NSF’s MARGINS program, have greatly expanded our understanding of its megathrust behavior. Here 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 deep (~30-40 km), large slow slip events that occur about every 2 years, smaller events that locate at more intermediate depth (10-15 km) and occur more frequently (~1 per year), and very shallow events at the toe of the margin wedge that produce no discernible GPS signal on land but are detected on seafloor pressure sensors. Most of these slow slip events at the toe are accompanied by seismic tremor. Short-term, GPS only observations might have detected a few of these slow slip events; however, the longer more diverse instrument deployment was necessary to reveal their greater complexity. This demonstrates the need for a sustained, multi-instrument deployment and off-shore instrumentation at several different subduction zones, like that proposed for the Subduction Zone Observatory (SZO), to significantly advance our understanding of slow slip at convergent boundaries. Similar instrumentation to what exists in Nicoya is presently being established in the Osa-Burica region of southern Costa Rica to capture earthquake cycle deformation there. These two installations can provide a good nucleus for a larger circum-Pacific SZO effort.