Abstract
We have developed an automated procedure to resolve fault-plane ambiguity for small to medium-sized earthquakes (2.5 ≤ M L ≤ 5) using synthetic Green’s tensors computed in a 3-D earth structure model and applied this procedure to 35 earthquakes in the Los Angeles area. For 69 per cent of the events, we resolved fault plane ambiguity of our CMT solutions at 70 per cent or higher probability. For some earthquakes, the fault planes selected by our automated procedure were confirmed by the distributions of relocated aftershock hypocentres. In regions where there are no precisely relocated aftershocks or for earthquakes with few aftershocks, we expect our method to provide the most convenient means for resolving fault plane ambiguity. Our procedure does not rely on detecting directivity effects; therefore it is applicable to any types of earthquakes.
Highlights
A fundamental ambiguity of the most general point-source representation of an earthquake, the centroid moment tensor (CMT), is that it does not specify which of the two nodal planes is the actual fault plane (Aki & Richards 2002)
The lowest-order representation of a finite rupture is the finite moment tensor (FMT, Chen et al 2005), which contains the secondorder polynomial moments of the source–space–time function in addition to the zeroth- and first-order polynomial moments included in the CMT parameters (Backus & Mulcahy 1976; McGuire et al 2001)
In Chen et al (2005) we demonstrated the feasibility of full Finite moment tensor (FMT) inversion for regional medium-sized earthquakes (4.5 ≤ ML ≤ 6) using highfrequency (∼2.5 Hz) waveform data
Summary
A fundamental ambiguity of the most general point-source representation of an earthquake, the centroid moment tensor (CMT), is that it does not specify which of the two nodal planes is the actual fault plane (Aki & Richards 2002). The lowest-order representation of a finite rupture is the finite moment tensor (FMT, Chen et al 2005), which contains the secondorder polynomial moments of the source–space–time function in addition to the zeroth- and first-order polynomial moments included in the CMT parameters (Backus & Mulcahy 1976; McGuire et al 2001). In previous studies that derive finite source properties for small to medium-sized earthquakes, empirical Green’s functions (EGF) were often employed to account for propagation path-effects (Mori 1996; Hellweg & Boatwright 1999; McGuire 2004). We corrected the propagation path-effects in the observed data using synthetic Green’s functions computed in path-averaged 1-D Earth structure models and a ‘denuisancing’ technique, which is similar to, but more flexible than traditional EGF techniques
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