Source Parameters of the Shallow 2012 Brawley Earthquake , Imperial Valley

Resolving earthquake parameters, especially depth, is difficult for events occurring within basins because of issues involved with separating source properties from propagational path effects. Here, we demonstrate some advantages of using a combination of teleseismic and regional waveform data to improve resolution following a bootstrapping approach. Local SS-S differential arrivals from a foreshock are used to determine a local layered model which can then be used to model teleseismic depth phases: pP, sP, and sS. Using the cut-and-paste (CAP) method for which all strike (θ), dip (δ), rake (λ), and depth variations are sampled for several crustal models. We find that regional data prove the most reliable at fixing the strike, whereas the depth is better constrained by teleseismic data. Weighted solutions indicate a nearly pure strike-slip mechanism (θ 59° 1°) with a centroid depth of about 4.0 km and an Mw of 5.4 for the mainshock of the 2012 Brawley earthquake. Online Material: Figures showing examples of waveform fits, comparison of synthetic teleseismic waveforms using different grid sizes in the FD calculation, effect of soft sediment on teleseismic Green's functions, and sensitivity of regional and teleseismic data on the focal mechanisms.