Retrieval of source parameters of an event of the 2000 West Bohemia earthquake swarm assuming an anisotropic crust

Abstract

In the recent publication (Rössler et al., 2007) we reported on small, but significant, non-shear components for one M L 3.1 earthquake in West Bohemia on 15 October 2000, which persisted even if an anisotropic crust was considered. For data analysis we used P waves recorded at temporary and permantent stations of the WEBNET of the Institute of Geophysics AS CR and of other networks. Unfortunately, only after publication of the results, we were informed that the vertical components of three stations, LBC, STC and VAC, were distorted by clipping (J. Horálek, personal communication) and thus should not be used for source retrieval. Clipping of P-wave forms was invisible at STC and VAC and difficult to detect at LBC. It could be found from an analysis of S waves, which we, unfortunately, did not study. Neither did we know the clipping level. We have therefore repeated calculations ignoring the three clipped traces. Despite omitted traces, the newly obtained source parameters did not differ much from the previous ones (see Table 1). The main differences with results published by Rössler et al., (2007) consist in the reduction of data residual by 0.01, in a small rotation of the rupture plane, and in a small decrease of non-shear components. Nevertheless, the non-shear components remain non-negligible, indicating existence of a crack opening during rupture process. Following our previous argumentation, jackknife (see Fig. 1) and bootstrap (not Table 1. Data residual R, slip inclination δ as well as mean slip inclination δ and standard deviation σ(δ) (the latter two result from bootstrap tests), rupture plane orientation, seismic moment M T (M T = M × 10 14 Nm), and moment-tensor components retrieved by using velocity Model II. Upper line: results from Rössler et al., (2007), lower line: results with the three clipped traces omitted during inversions. Slip Inclination [°] Rupture Plane [°] Moment Tensor [%] Model R δ δ σ(δ) Strike Dip Rake M DC ISO CLVD II 0.06 86.8 86.9 1.2 166 76 −40 3.6 82.0 +4.9 +13.1 II (this paper) 0.05 88.2 88.6 1.1 169 76 −39 3.5 91.4 +5.7 +2.8

Retrieval of source parameters of an event of the 2000 West Bohemia earthquake swarm assuming an anisotropic crust

“…Despite omitted traces, the newly obtained source parameters did not differ much from the previous ones (see Table 1). The main differences with results published by Rössler et al, (2007) consist in the reduction of data residual by 0.01, in a small rotation of the rupture plane, and in a small decrease of non-shear components. Nevertheless, the non-shear components remain non-negligible, indicating existence of a crack opening during rupture process.…”

“…Data residual R, slip inclination δ as well as mean slip inclination δ and standard deviation σ(δ) (the latter two result from bootstrap tests), rupture plane orientation, seismic moment M T (M T = M × 10 14 Nm), and moment-tensor components retrieved by using velocity Model II. Upper line: results from Rössler et al, (2007) shown here, but with comparable outcome as the jackknife test) tests seem to indicate that the non-shear components are significant. Rössler et al, (2007) using the vertically inhomogeneous anisotropic Model II.…”

“…Upper line: results from Rössler et al, (2007) shown here, but with comparable outcome as the jackknife test) tests seem to indicate that the non-shear components are significant. Rössler et al, (2007) using the vertically inhomogeneous anisotropic Model II. In 500 realisations, a) 10% and b) 25% of all available traces are randomly excluded from the inversions.…”

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In the recent publication (Rössler et al, 2007) we reported on small, but significant, non-shear components for one M L 3.1 earthquake in West Bohemia on 15 October 2000, which persisted even if an anisotropic crust was considered. For data analysis we used P waves recorded at temporary and permantent stations of the WEBNET of the Institute of Geophysics AS CR and of other networks.

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Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array

“…Between August and December 2000, more than 10,000 events, M L,max = 3.4, could be detected (Tittel and Wendt 2003;Fischer 2003). Evidences for tensile components with spatiotemporal variations were found (Roessler 2006;Roessler et al 2007Roessler et al , 2008. Fischer and Horálek (2003) have further identified 27 microswarms and solitary events (M L,max < 2) between 1991 and 2001.…”