Challenges to Understanding Seismic Observations of Fast and Slow Slip Phenomena in Multiple Tectonic Environments

Abstract:

Faults prone to rupture do so in various ways. Some demonstrate fast ruptures, some exhibit slow ruptures and other faults are (seemingly) dormant. In multiple tectonic regimes around the world, the interplay of fast vs. slow rupture remains unclear, especially with respect to the plethora of seismic observations streaming in near-real-time. With the onset of improved seismic instrumentation, observations of what represent a signature of fast vs. slow slip remain a challenge. This is particularly true with respect to events less than < Mw 2 that could be considered fast and/or slow.

In Southwest Japan, large historical fast ruptures are updip on the primary plate boundary whereas slow ruptures are at the downdip extent. Observations of recent seismicity in Costa Rica, Alaska, Mexico and Cascadia suggest otherwise where an intermingling of fast vs. slow rupture is unclear. Swarms of small earthquakes in the Virginia Seismic Zone are not indicitave of a slow slip event, whereas swarms of small earthquakes in transform boundary environments could be. Geodetic observations of slow rupture along the San Jacinto fault in Southern California are encouraging of detecting an observational seismic sibling, however an ambient signal has yet to be verified despite the instrumentation there. Likewise, analyzing and comparing these signals warrants a fruitful discussion.

This study provides a tour of seismograms recorded around the world of documented tremor, low frequency earthquakes, and low magnitude earthquakes in order to understand what we as seismologists are observing with respect to fault rupture.