SLEUTHING SLOW SLIP PHENOMENA

Slow slip phenomena refer to transient aseismic slip and the variety of sources that emit lower frequency seismic signals than earthquakes (e.g. tremor, low frequency earthquakes, etc.). Understanding the requirements for the generation of slow slip phenomena requires observation of them and their absence, in multiple environments where the posited relevant conditions and processes differ. For example, thermal structure as a key controlling parameter can be ruled out from observations of slow slip and tremor in the subduction zones of southwest Japan and northern Cascadia, where predicted thermal structures vary significantly. Another comparison reveals the coincidence of very low seismic velocities and slow slip phenomena in multiple subduction zones, strongly suggesting the importance of specific material properties (e.g. fluids at near lithostatic pore pressures). In all comparisons, variability in detection thresholds and resolution must be considered.

We extend this approach to other scales and settings where slow slip phenomena have been observed or postulated. We consider glaciers, landslides, shallow fault creep, and laboratory experiments documented in the published literature. We also present preliminary results from two of our own observational studies of slow slip phenomena. The first study examines regional seismic network data for tremor within a few tens of kilometers of a transform fault with documented shallow creep events, along the San Juan Bautista section of the San Andreas fault in California. In the second study we search for tremor signals from the Slumgullion landslide in Colorado, which is known to exhibit slip at steady and episodically higher rates and that has been explained using frictional models that are nearly identical to those applied to subduction zones.