Earthquake swarms driven by aseismic creep in the Salton Trough, California

Abstract

In late August 2005, a swarm of more than a thousand earthquakes between magnitudes 1 and 5.1 occurred at the Obsidian Buttes, near the southern San Andreas Fault. This swarm provides the best opportunity to date to assess the mechanisms driving seismic swarms along transform plate boundaries. The recorded seismicity can only explain 20% of the geodetically observed deformation, implying that shallow, aseismic fault slip was the primary process driving the Obsidian Buttes swarm. Models of earthquake triggering by aseismic creep can explain both the time history of seismic activity associated with the 2005 swarm and the ∼1 km/h migration velocity exhibited by this and several other Salton Trough earthquake swarms. A combination of earthquake triggering models and denser geodetic data should enable significant improvements in time‐dependent forecasts of seismic hazard in the key days to hours before significant earthquakes in the Salton Trough.

Report on the August 2012 Brawley Earthquake Swarm in Imperial Valley, Southern California

“…Nevertheless, alignments of earthquakes from previous swarms (Shearer et al, 2005;Lin et al, 2007;Lohman and McGuire, 2007), fumarolic vents (Lynch and Hudnut, 2008), and faults displacing sedimentary layers in and around the southern Salton Sea (Brothers et al, 2009;Rymer et al, 2011) suggest that the modern deformation is controlled by a complex set of intersecting northeast-, north-, and northwesttrending faults whose surface expression has been masked by agricultural activity and repeated basin flooding events.…”

“…1). The sequence exhibited swarm-like behavior, and Lohman and McGuire (2007) attributed its migration pattern to a slow aseismic slip event at depth.…”

“…Nonetheless, surface fractures that are related to the swarm were identified both from InSAR images and field observations. Prior occurrences of surface faulting in association with swarm activity within the BSZ activity include the 2005 swarm (Lohman and McGuire, 2007;Rymer et al, 2011). The largest event of the 2005 swarm was M w 5.1, yet surface rupture was up to 20 cm in that case.…”

Rate‐Dependent Incompleteness of Earthquake Catalogs

“…Such high seismicity rates occur, for example, during aftershock sequences triggered by earthquakes that are much larger than the basic detection threshold of the seismic network (i.e., the mainshocks). Furthermore, aseismic processes such as slow-slip events (Lohman and McGuire, 2007) and rapid magma (Toda et al, 2002) or fluid intrusion (Miller et al, 2004) can also cause earthquake swarms with high temporal earthquake clustering. Those seismicity phenomena are usually not only temporally, but also spatially, densely clustered and thus usually are recorded by the same seismic stations.…”

Statistic analysis of swarm activities around the Boso Peninsula, Japan: Slow slip events beneath Tokyo Bay?

“…Slow slip events, SSE, are another kind of the swarm driving mechanism. Recently, SSE induced swarms have been discovered in various geological environments, such as near the San Andreas Fault, California (Lohman and McGuire, 2007), beneath Kilauea volcano (Montgomery-Brown et al, 2008), Hawaii (Segall et al, 2006), and in subduction zones in Japan (Ozawa et al, 2007;NIED, 2007) and New Zealand (Reyners and Bannister, 2007).…”