Source Estimation from Broadband Regional Seismograms

Recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms. The reason is that Green's functions generated from flat-layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure. The inversion is usually performed by removing short periods and inverting only selected portions of the records. In this article, we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect Green's function are available. The procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the Green's functions independently. The preferred source is the orientation that minimizes the average L1 and L2 norms in term of the four parameters, M₀, strike, dip, and rake. The L2 error emphasizes the longer period surface waves while the L1 error weights the shorter period body waves. We obtain estimates of duration by modeling long period and broadband signals. The depth determination can be obtained directly from the surface reflected phases sPₘP or sSₘS or by cycling through the depth-dependent Green's functions. In addition to the source parameters, we obtain “δt” phase alignments shifts that can be used as Green's function corrections for relocating other events or as a guide to deriving new crustal models.