Frequent Shallow Slow Slip Events along the Ecuadorian Subduction Zone

Abstract:

We use Continuous GPS data since 2008 to investigate the characteristics and frequency of Slow Slip Events (SSE) along the Andean Subduction Zone in Ecuador. Although the largest SSE are evident from a visual inspection of the time series, we show that expressing the time series with respect to an optimally defined local reference frame reduces the high frequency noise of GPS time series by a factor of two and enables us to detect and monitor the time evolution of many small SSEs. In central Ecuador, 6 events were detected since 2009. The two largest occurred at the downdip limit of a shallow (<20km), highly coupled local asperity near the La Plata Island (2010, 2013) and had durations of days and a moment release of M~6. SSE of duration of weeks to months with slightly larger moment are observed in northern Ecuador, in the rupture area of the Mw 8.8 1906 earthquake where the level of coupling is high. For both highly and weakly coupled areas, most of the SSE are synchronous to intense micro-seismicity occurring within or near the slip area, but no tremor have been detected so far. The seismicity tends to be clustered into families of repeating earthquakes, suggesting that the aseismic slip triggers the seismicity. Nonetheless, the associated seismicity accounts at most for a few percent of the total moment released during each episode. The frequency and size of the observed SSE suggest that transient aseismic slip contributes to release a significant fraction of the accumulating stress along the subduction interface.