Abstract
Rapid and accurate source characterizations of large, shallow subduction earthquakes are key for improved tsunami warning efforts. We assess the quality of source parameters of large magnitude (Mw ≥ 7.5) shallow subduction earthquakes of the past 20 yr determined using SCARDEC, a recent fully automated broad-band body-wave source inversion technique for the fast estimation of the moment magnitude, depth, focal mechanism and source time functions of global events. We find that SCARDEC source parameters agree well with those reported in the global centroid moment tensor (GCMT) catalogue, with only the fault dip angle showing a tendency for steeper SCARDEC dip values than GCMT. We investigate this discrepancy through independent validation tests of the source models by: (i) testing how well they explain data not used in their construction, notably low-frequency normal mode data; and, (ii) assessing the data fit using 3-D forward modelling tools more sophisticated than those used to build the source models; specifically, we use a spectral element method for a 3-D earth model. We find that SCARDEC source parameters explain normal mode data reasonably well compared to GCMT solutions. In addition, for the 3-D earth model used in our experiments, SCARDEC dip angles explain body-wave data similarly or slightly better than GCMT. Moreover, SCARDEC dip angles agree well with results from individual earthquake studies in the literature and with geophysical constraints for different subduction zones. Our results show that SCARDEC is a reliable technique for rapid determinations of source parameters of large (Mw ≥ 7.5) subduction earthquakes. Since the SCARDEC method provides realistic source time functions allowing the fast identification of long-duration tsunami earthquakes, it is complementary to existing methods routinely used for earthquake monitoring and suitable for ocean-wide tsunami warning purposes
Highlights
Fast, automated and reliable earthquake source parameter determinations are of critical importance for rapid seismic hazard assessment and relief response efforts
The largest differences are observed at SBA station on the vertical component and TAM station on the transverse component, where the SCARDEC dip angle leads to an improved body-wave data fit
The general agreement between SCARDEC and global centroid moment tensor (GCMT) source parameters is encouraging, with the only clear systematic discrepancy occurring for fault dip angle estimates, where SCARDEC dip angles tend to be larger than GCMT
Summary
Fast, automated and reliable earthquake source parameter determinations are of critical importance for rapid seismic hazard assessment and relief response efforts. Ray theory is used to calculate double couple point-source body-wave signals in the 1-D IASP91 earth model (Kennett & Engdahl 1991), for a given source depth, fault geometry and mechanism (strike, dip and rake) By deconvolving these point source signals from real data, and taking into account some physical constraints on the resulting relative source time functions (see Vallee et al 2011, for details), the SCARDEC method retrieves the optimal set of source parameters. Finding objective strategies to benchmark, compare and independently test the quality of earthquake source models, as done in this study, is a crucial step for the rigorous quantification of seismic source processes and associated uncertainties in future earthquake studies
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