Imaging Slow-slip Events in Costa Rica

Faults slip varies in duration ranging from a fraction of a second to multiple years. The longer duration end of this spectrum exists the slow-slip events (SSEs). These SSEs do not radiate seismic waves and hence are not destructive, but they contribute significantly to moment budget and therefore need to be considered for seismic hazard assessments. In this study, we utilize the time series of the surface displacements measured by GPS stations around Nicoya peninsula in Costa Rica. We start our analysis by using the secular linear motion to determine the interseismic coupling along the Costa Rica subduction zone and subtracted it from the GPS time series along with the co-seismic and instrumental offsets. We then apply the modified variational Bayesian Independent Component Analysis (vbICA) on the GPS time series data to separate the geodetic strain signal due to tectonic sources from non-tectonic sources. Concentrating on the tectonic strain signals, we ignore the postseismic afterslip and select only those that are related to the SSEs. From that, we perform an inversion with the Independent Component Analysis-based Inversion Method (ICAIM) to obtain the time evolution of the slip on the fault associated with the SSEs. Using the catalog obtained, we explore the characteristics of SSEs in Costa Rica, particularly the scaling law between moment and duration. We then compare the behaviors of SSEs from Costa Rica with regular earthquakes and SSEs from other regions to elucidate some underlying mechanics of SSEs.