Vertically Inhomogeneous Models of the Upper Crustal Structure in the West-Bohemian Seismoactive Region Inferred from the Celebration 2000 Refraction Data

Málek, Jiří; Janský, Jaromír; Novotný, Oldřich; Rössler, Dirk

doi:10.1023/b:sgeg.0000045478.42945.6a

Cited by 13 publications

(9 citation statements)

References 10 publications

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“…The differences are mostly larger in the upper parts, down to depths of about 4 km. Málek et al (2004) and Novotný et al (2004) found that characteristic features of 1D models of the region under study are relatively low P-wave velocities close to the surface and prominent velocity increases within the uppermost crust down to depth of about 1 km.…”

Section: Introductionmentioning

confidence: 83%

One-Dimensional qP-Wave Velocity Model of the Upper Crust for the West Bohemia/Vogtland Earthquake Swarm Region

Málek

Horálek²,

Janský

2005

Stud Geophys Geod

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The western part of the Bohemian Massif (West Bohemia/Vogtland region) is characteristic in the relatively frequent recurrence of intraplate earthquake swarms and in other manifestations of past-to-recent geodynamic activity. In this study we derived 1Danisotropic qP-wave model of the upper crust in the seismogenic West Bohemia/Vogtland region by means of joint inversion of two independent data sets -travel times from controlled shots and arrival times from local earthquakes extracted from the WEBNET seismograms. We derived also simple 1-D P-wave and S-wave isotropic models. Reasons for deriving these models were: (a) only simplified crustal velocity models, homogeneous half-space or 1D isotropic layered models of this region, have been derived up to now and (b) a significant effective anisotropy of the upper crust in the region which was indicated recently by S-wave splitting. Both our anisotropic qP-wave and isotropic P-and S-wave velocity models are constrained by four layers with the constant velocity gradient. Weak anisotropy for P-waves is assumed. The isotropic model is represented by 9 parameters and the anisotropic one is represented by 24 parameters. A new robust and effective optimization algorithm -isometric algorithm -was used for the joint inversion. A two-step inversion algorithm was used. During the first step the isotropic P-and S-wave velocity model was derived. In the second step, it was used as a background model and the parameters of anisotropy were sought.Our 1D models are adequate for the upper crust in the West Bohemia/Vogtland swarm region up to a depth of 15 km. The qP-wave velocity model shows 5% anisotropy, the minimum velocity in the horizontal direction corresponds to an azimuth of 170°. The isotropic model indicates the V P /V S ratio variation with depth. The difference between the hypocentre locations based on the derived isotropic and anisotropic models was found to be several hundreds of meters. K e y w o r d s : West Bohemia/Vogtland region, earthquake swarm, anisotropy, 1D velocity model, inverse problem, earthquake location Stud. Geophys. Geod., 49 (2005), 501−524 501 © 2005 StudiaGeo s.r.o., Prague J. Málek et al.

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Section: Introductionmentioning

confidence: 83%

One-Dimensional qP-Wave Velocity Model of the Upper Crust for the West Bohemia/Vogtland Earthquake Swarm Region

Málek

Horálek²,

Janský

2005

Stud Geophys Geod

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“…Several homogeneous and inhomogeneous isotropic velocity models were proposed for the focal area in West Bohemia (see e.g. Novotný, 1996;Málek et al, 2004). Three anisotropic/isotropic models used in this study and referred to as Models I-III, see Fig.…”

Section: Source Retrieval Formentioning

confidence: 99%

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

Rössler

Pšenčı́k²,

Rümpker

2007

Stud Geophys Geod

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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. 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

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“…More complicated velocity models did not give significantly smaller travel time residuals for the whole network. Recent 2D velocity models from refraction seismic experiment CELEBRATION 2000 also confirm crustal velocities with a rather small gradient below the sedimentary layer (e.g., Málek et al, 2004).…”

Section: Seismicity Of West Saxony and The Leipzig-regensburgmentioning

confidence: 78%

Seismicity and seismotectonics of West Saxony, Germany — new insights from recent seismicity observed with the Saxonian seismic network

2008

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A new network of permanently recording seismic stations in West Saxony has considerably improved detection threshold, location accuracy and depth determination in this seismically active region. Between 2001 and 2007 more than 900 events have been located. Seismicity mainly occurred along a band stretching north-south between Leipzig and Vogtland/NW Bohemia area with local magnitudes ranging between 0.8 and 2.8. Seismicity clearly delineates the Leipzig-Regensburg (L-R) fault zone striking N-S, and theGera-Jachymov (G-J) fault zone striking roughly NNW-SSE. The hypocentral depths can be divided into two depth ranges, one at depths below 10 km, and a second at less than 10 km depth that only extends S-N from the Vogtland until the crossing between L-R and G-J fault zones. A small earthquake sequence that occurred near Werdau/Zwickau in August 2006 at almost the same epicenters as an earlier sequence 1997/98 seems to confirm this finding: a relative localization of 15 events with the double-difference technique clearly reveals two distinct subclusters at about 6 and 1214 km depth. With the improved station coverage 33 new fault plane solutions from events along the L-R fault zone north of the swarmquake area could be determined from P-polarities and P/S ratios. They do not differ significantly from solutions in the Vogtland/NW-Bohemia area and are mostly compatible with a N-S oriented fault plane. Strike slip mechanisms with or without a dip slip component dominate.

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Vertically Inhomogeneous Models of the Upper Crustal Structure in the West-Bohemian Seismoactive Region Inferred from the Celebration 2000 Refraction Data

Abstract: As part of the international refraction measurements in Central Europe in the year

Cited by 13 publications

References 10 publications

One-Dimensional qP-Wave Velocity Model of the Upper Crust for the West Bohemia/Vogtland Earthquake Swarm Region

One-Dimensional qP-Wave Velocity Model of the Upper Crust for the West Bohemia/Vogtland Earthquake Swarm Region

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

Seismicity and seismotectonics of West Saxony, Germany — new insights from recent seismicity observed with the Saxonian seismic network

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