Slow slip beneath the Nicoya Peninsula, Costa Rica and its effect on the interseismic cycle.

摘要

The close proximity of the Nicoya Peninsula to the Cocos-Caribbean Subduction zone plate boundary makes it a prime location to use GPS to study episodic tremor and slip. Nicoya Peninsula currently has operating networks of both continuous GPS (CGPS) and seismic stations designed to identify and characterize the pattern of episodic tremor and slip (ETS) events along the seismogenic zone under Costa Rica's Pacific Margin. The occurrence of slow slip events has been previously postulated in this region based on correlated fluid flow and seismic tremor events recorded near the margin wedge in 2000 and from sparse GPS observations in 2003. Paucity of data prevented details of these events from being resolved. In May 2007 a slow slip event was recorded on our densified GPS network. This slow slip event was also accompanied by seismic tremor, worked up by colleagues at the University of California-San Diego. I will present the GPS time series, correlated with the seismic tremor for the event in May 2007. I will also present the inferred pattern of slip on the plate interface from elastic half space inversion modeling compared with the tremor and Low Frequency Earthquake (LFE) locations. The geodetic slip and seismic tremor co-locate temporally very well. Spatially the seismic tremor and LFE locations are offset but not independent of both the up dip and down dip patches of geodetic slip.;The identification of these slow slip events enhances our understanding of the nuances of the interseismic period. Previous studies of the interseismic strain accumulation patterns in the region of the Nicoya Peninsula have not accounted for the occurrence of slow slip, thus underestimating the magnitude of locking on the fault plane. My study resolves this bias by using our CGPS network to estimate the interseismic surface velocity field, accounting for the May 2007 slow slip event. I will present the results of this velocity field estimation and the results of inversions for locking patterns on the fault plane. My study has also elucidated a potential temporal variability in the locking pattern on the fault plane beneath Nicoya.