Seismicity and stress field in the vicinity of the KTB location

Dahlheim, H.-A.; Gebrande, H.; Schmedes, E.; Soffel, H.

doi:10.1029/96jb02812

Cited by 23 publications

(8 citation statements)

References 15 publications

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“…Some parts of the medium are in direct vicinity to failure, suggesting that already very small stress or pore pressure perturbations may cause brittle failure in rocks. This finding is confirmed by observed fluid‐injection‐induced seismicity [see Baisch et al , ] and natural seismic activity in the vicinity of the KTB [see Dahlheim et al , ]. Nevertheless, in the most stable parts of the model CFS perturbations of up to 20MPa are needed to initiate failure.…”

Section: Fluctuations Of Rock Strengthmentioning

confidence: 58%

Gutenberg-Richter relation originates from Coulomb stress fluctuations caused by elastic rock heterogeneity

Langenbruch

Shapiro

2014

J. Geophys. Res. Solid Earth

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Based on measurements along boreholes, a characterization of the Earth's crust elastic heterogeneity is presented. We investigate its impact on Coulomb stress distribution and earthquake magnitude scaling. The analysis of elastic modulus distribution at various borehole locations in different regions reveals universal fractal nature of elastic heterogeneity. By applying a homogeneous far‐field stress to a representative model of elastic rock heterogeneity, we show that it causes strong Coulomb stress fluctuations. In situ fluctuations of Coulomb stress are mainly controlled by in situ elastic moduli. Fluctuations caused by surrounding heterogeneities are only of minor importance. Hence, the fractal nature of elastic heterogeneity results in Coulomb stress fluctuations with power law size distribution. As a consequence, fault sizes and magnitudes of earthquakes scale according to the Gutenberg‐Richter relation. Due to the universal fractal nature of elastic heterogeneity, the b value should be universal. Deviation from its universal value of b≈1 occurs due to characteristic scales of seismogenic processes, which cause limitations or changes of fractal scaling. Scale limitations are also the reason for observed stress dependency of the b value. Our analysis suggests that the Gutenberg‐Richter relation originates from Coulomb stress fluctuations caused by elastic rock heterogeneity.

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Section: Fluctuations Of Rock Strengthmentioning

confidence: 58%

Gutenberg-Richter relation originates from Coulomb stress fluctuations caused by elastic rock heterogeneity

Langenbruch

Shapiro

2014

J. Geophys. Res. Solid Earth

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“…Open question has been a cause of the anisotropy. The stress tensor estimations by means of the focal mechanism inversion show the NW-SE (Wirth et al, 2000;Havíř, 2000;Plenefisch and Klinge, 2003) or NNW-SSE (Sonnleitner, 1993;Dahlheim et al, 1997;Havíř, 2000) orientation of the maximum horizontal axis of compression in the upper crust in the West Bohemia/Vogtland region. A uniform NNW-SSE maximum horizontal stress orientation was also found in the KTB deep borehole based on the breakouts and drilling induced fractures (Brudy et al, 1997).…”

Section: Discussionmentioning

confidence: 99%

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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“…Natural seismicity is sparse in the area. Dahlheim et al [1997] operated a local network over a period of 5 years consisting of four stations. About 80 local earthquakes were detected with the majority (73) belonging to earthquake swarms near Marktredwitz at 20 km distance to the KTB site.…”

Section: Introductionmentioning

confidence: 99%

“…Location map of the German Continental Deep Drilling Program (KTB) superdeep drill hole in southeast Germany, fault plane solutions of natural seismicity [ Dahlheim et al , 1997], and the local stress field after Brudy et al [1997]. The size of the beachballs is scaled to the largest event of M l = 2.8 being recorded during a 5 year period by a local network.…”

Section: Introductionmentioning

confidence: 99%

“…A significant change in the stress field orientation was observed below a major fault zone (the so called SE1 reflector at 6.8–7.2 km depth [see Harjes et al , 1997]). Furthermore, Barton and Zoback [1994] found a stress field heterogeneity at 5.4 km depth that is limited to a vertical extent of only 4 m. Interestingly, determination of the local stress field using various data sets and methods such as borehole breakouts, earthquake focal mechanism data, overcoring, hydraulic fracturing and analysis of geological stress indicators [e.g., Müller et al , 1992; Zoback , 1992; Dahlheim et al , 1997] revealed comparatively large variations for the average trend of σ 1 of up to 60° in the vicinity of the KTB. It is of interest whether these variations are due to local stress field heterogeneities (as the different studies might look at different depth levels and/or different scales of the stress field) or whether they reflect uncertainties in the applied methods.…”

Section: Introductionmentioning

confidence: 99%

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Fault mechanisms of induced seismicity at the superdeep German Continental Deep Drilling Program (KTB) borehole and their relation to fault structure and stress field

2004

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[1] One hundred twenty-five fault plane solutions for microearthquakes induced during a long-term fluid injection experiment at the German Continental Deep Drilling Program (KTB) boreholes (Germany) in 2000 are investigated. A predominant strike-slip mechanism is observed, partly with components of normal but also with reverse faulting. Adding 54 fault plane solutions of an earlier injection experiment at the KTB, we determine the local stress field and find a subhorizontal north-south orientation for the maximum principal stress and a near-vertical orientation for the intermediate principal stress. The stress field exhibits no temporal or spatial variations within the resolved accuracy of ±15°. However, the results of the stress tensor inversion point to heterogeneities of second order. On the basis of the hypocentral distribution of the induced microearthquakes and the similarity of fault mechanisms, we relate our data to the fault structure at the KTB. We find that the larger faults act as pathways for the injected fluid, whereas the brittle failure occurs on fault asperities of the larger mapped faults and nearby smaller faults, both in agreement with the local stress field. Applying a thorough error analysis of the individual fault plane solutions, we correlate the diversity of mechanisms with their strength and find that the strongest events tend to a representative mechanism that is in good correspondence with the stress field. In contrast, the diversity of fault mechanisms is larger for the smaller events, indicating local stress perturbations.

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Seismicity and stress field in the vicinity of the KTB location

Cited by 23 publications

References 15 publications

Gutenberg-Richter relation originates from Coulomb stress fluctuations caused by elastic rock heterogeneity

Gutenberg-Richter relation originates from Coulomb stress fluctuations caused by elastic rock heterogeneity

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

Fault mechanisms of induced seismicity at the superdeep German Continental Deep Drilling Program (KTB) borehole and their relation to fault structure and stress field

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