Woods Hole Oceanographic Institution

Jeffrey J Mcguire

»Gofar Transform Earthquakes

The Network Strain Filter - A New Tool for Monitoring and Detecting Transient Deformation Signals in GPS Arrays


Scaling Relations for Seismic Cycles on Mid-Ocean Ridge Transform Faults

»Earthquake Swarms on Transform Faults
»Modeling Seismic Swarms Triggered by Aseismic Transients
»Analysis of Seafloor Seismograms of the 2003 Tokachi­Oki
  Earthquake Sequence for Earthquake Early Warning

»Seismic Cycles
»Fore-arc structure and subduction zone earthquakes
»Salton Trough Swarms
»Earthquake Predictability
»SEAJADE Experiment

Emily Roland and Jeff McGuire , Earthquake Swarms on Transform Faults , submitted to GJI, 2008

Swarm-like earthquake sequences are commonly observed in a diverse range of geologic settings including volcanic and geothermal regions as well as along transform plate boundaries. They typically lack a clear mainshock, cover unusually large regions relative to their total seismic moment release, and fail to decay in time according to standard aftershock scaling laws. Swarms often result from a clear driving phenomenon, such as a magma intrusion, but most lack the necessary geophysical data to constrain their driving process. To identify the mechanisms that cause swarms on strike-slip faults, we use relative earthquake locations to quantify the spatial and temporal characteristics of a set of swarms along Southern California and East Pacific Rise transform faults. Swarms in these regions exhibit distinctive characteristics, including a relatively narrow range of hypocentral migration velocities, on the order of a kilometer per hour. This rate corresponds to the rupture propagation velocity of shallow creep transients that are sometimes observed geodetically in conjunction with swarms, and is significantly faster than the earthquake migration rate associated with fluid diffusion. The uniformity of migration rates and low effective stress drops observed here suggest that shallow aseismic creep transients are the primary process driving swarms on strike-slip faults. Moreover, the migration rates are consistent with laboratory values of the rate-state friction parameter b (0.01) as long as the Salton Trough faults fail under hydrostatic conditions.

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