Geophysics Department Seminar: Jessica Hawthorne
Geophysics Department Seminar
Title: An investigation of aseismic slip associated with small earthquakes using strain and seismic data
We take two approaches to investigating aseismic slip associated with small earthquakes. First, we are motivated by the fact that the recurrence intervals of repeating earthquakes raise the possibility that much of the slip associated with small events is aseismic. To test this hypothesis, we examine the strain changes associated with M2 to 4 earthquakes near San Juan Bautista, CA. Most of the strain changes are below the noise level on a single record, so we bin the earthquakes into 4 groups according to their magnitude. We then invert for a time history of strain per seismic moment for each group. Each of the estimated strain time series displays a step at the time of the earthquakes. If we assume that the seismic moment scales as 101.0 M, the ratio of the strain step to seismic moment is approximately constant with magnitude. This would imply that the ratio of aseismic to seismic slip is approximately constant with magnitude.
In a second approach to looking for aseismic slip, we present a phase coherence approach to investigate seismic precursors to earthquakes. This method allows us to identify seismic signals coming from the earthquake location, even if those signals have complicated source-time functions. We confirm that a precursor to a M3.9 event in Nenana, AK originates near the earthquake location. Initial investigation of events on the San Jacinto Fault reveal no systematically occurring precursors.