SPATIAL AND TEMPORAL RELATIONSHIP OF SLOW-SLIP AND NON-VOLCANIC TREMOR IN CASCADIA

The relationship of geodetically-detected slow-slip to seismologically-detected non-volcanic tremor is being investigated by inverting GPS time series from the PANGA and PBO continuous networks. The specific aim is to see whether or not these two phenomena are coincidental in space and time. We first examine the 2008 episodic-tremor-and-slip (ETS) event from the Puget region in May 2008. Wech and Creager (GRL, L20302, 2008) located non-volcanic tremor (NVT) at depths of 28 to 50 km from about 47N to 49N. Inverting daily position time series from PANGA and PBO continuous GPS sites and limiting slip to occur only within the portion of the plate interface where NVT occurred results in a slip distribution that overestimates the vertical signal at sites up-dip of the slip patch. This result and subsequent inversions indicate that some slow-slip occurred well up-dip of the NVT. Looking at the April-June 2008 ETS event from Oregon shows that NVT occurred from 30 to 45 km depth and from 42N to 45N (Boyarko and Brudzinski, AGU abstract U33A-0020, 2008). Inversion of GPS time series from the same period of time shows slow-slip in the same depth range but shifted northward, i.e, between 42.5N to 46N. It is well known that significant NVT at Cascadia can occur without detectable slow-slip. Cascadia, like other subduction zones, can also have detectable slow slip without accompanying tremor.