scholarly journals Seismicity and seismotectonics of the Albstadt Shear Zone in the northern Alpine foreland

Solid Earth ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 1389-1409
Author(s):  
Sarah Mader ◽  
Joachim R. R. Ritter ◽  
Klaus Reicherter ◽  
Keyword(s):  
Shear Zone ◽  
Fault Plane ◽  
Seismic Velocity ◽  
Driving Forces ◽  
Stress Component ◽  
Horizontal Stress ◽  
Fault Plane Solutions ◽  
Data Set ◽  
Velocity Models ◽  
Delay Times

Abstract. The region around the town Albstadt, SW Germany, was struck by four damaging earthquakes with magnitudes greater than 5 during the last century. These earthquakes occurred along the Albstadt Shear Zone (ASZ), which is characterized by more or less continuous microseismicity. As there are no visible surface ruptures that may be connected to the fault zone, we study its characteristics by its seismicity distribution and faulting pattern. We use the earthquake data of the state earthquake service of Baden-Württemberg from 2011 to 2018 and complement it with additional phase picks beginning in 2016 at the AlpArray and StressTransfer seismic networks in the vicinity of the ASZ. This extended data set is used to determine new minimum 1-D seismic vp and vs velocity models and corresponding station delay times for earthquake relocation. Fault plane solutions are determined for selected events, and the principal stress directions are derived. The minimum 1-D seismic velocity models have a simple and stable layering with increasing velocity with depth in the upper crust. The corresponding station delay times can be explained well by the lateral depth variation of the crystalline basement. The relocated events align about north–south with most of the seismic activity between the towns of Tübingen and Albstadt, east of the 9∘ E meridian. The events can be separated into several subclusters that indicate a segmentation of the ASZ. The majority of the 25 determined fault plane solutions feature an NNE–SSW strike but NNW–SSE-striking fault planes are also observed. The main fault plane associated with the ASZ dips steeply, and the rake indicates mainly sinistral strike-slip, but we also find minor components of normal and reverse faulting. The determined direction of the maximum horizontal stress of 140–149∘ is in good agreement with prior studies. Down to ca. 7–8 km depth SHmax is bigger than SV; below this depth, SV is the main stress component. The direction of SHmax indicates that the stress field in the area of the ASZ is mainly generated by the regional plate driving forces and the Alpine topography.

scholarly journals Seismicity and seismotectonics of the Albstadt Shear Zone in the northern Alpine foreland

2020 ◽  
Author(s):  
Sarah Mader ◽  
Joachim R. R. Ritter ◽  
Klaus Reicherter ◽  
Keyword(s):  
Shear Zone ◽  
Fault Plane ◽  
Seismic Velocity ◽  
Driving Forces ◽  
Horizontal Stress ◽  
Fault Plane Solutions ◽  
Velocity Models ◽  
Delay Times ◽  
Seismic Networks ◽  
Maximum Horizontal Stress

Abstract. The region around the town Albstadt, SW Germany, was struck by four damaging earthquakes with magnitudes greater than five during the last century. Those earthquakes occurred along the Albstadt Shear Zone (ASZ) which is characterized by more or less continuous microseismicity. As there are no surface ruptures visible which may be connected to the fault zone, its characteristics can only be studied by its seismicity. We use the earthquake data of the state earthquake service of Baden-Württemberg from 2011 to 2018 and complement it with additional phase picks beginning 2016 at the AlpArray and StressTransfer seismic networks in the vicinity of the ASZ. This extended dataset is used to determine new minimum 1-D seismic vp and vs velocity models and corresponding station delay times for earthquake relocation. Fault plane solutions are determined for selected events and the direction of the maximum horizontal stress is derived. The minimum 1-D seismic velocity models have a simple and stable layering with increasing velocity with depth in the upper crust. The corresponding station delay times can be well explained by the lateral depth variation of the crystalline basement. The relocated events align north-south with most of the seismic activity between the towns of Tübingen and Albstadt east of the 9° E meridian. The events can be separated into several subclusters which indicate a segmentation of the ASZ. The majority of the 36 determined fault plane solutions features a NNE-SSW strike, but also NNW-SSE striking fault planes are observed. The main fault plane associated with the ASZ is dipping steeply and the rake indicates mainly sinistral strike-slip, but we also find minor components of normal and reverse faulting. The determined direction of the maximum horizontal stress of 147° is in good agreement with prior studies. This result indicates that the stress field in the area of the ASZ is mainly generated by the regional plate driving forces as well as the Alpine topography.

The tectonic stress and tectonic motion direction in the Pacific and Adjacent areas as calculated from earthquake fault plane solutions

1965 ◽  
Vol 55 (1) ◽  
pp. 147-152 ◽  
Author(s):  
A. E. Scheidegger
Keyword(s):  
Fault Plane ◽  
Horizontal Stress ◽  
Tectonic Stress ◽  
Pacific Basin ◽  
Motion Direction ◽  
Fault Plane Solutions ◽  
Earthquake Fault ◽  
The Pacific ◽  
Tectonic Motion ◽  
Consistent Picture

Abstract The best P and T axes as well as the best normals to the null directions were calculated for groups of earthquake fault plane solutions belonging to 29 areas of the Pacific Basin and vicinity. The method employed was one developed in an earlier paper of the writer; it is based on a calculation of the eigenvectors of a quadratic form. It is shown that the principal horizontal stress (PHS) directions obtained in this fashion are in excellent agreement with those obtained from other evidence. In the Western Pacific Basin and vicinity the calculations were sufficiently dense to determine PHS trajectories; the latter are shown and yield a consistent picture of the area in question.

Aftershocks of an M = 4.2 earthquake in Hawaii and comparison with long-term studies of the same volume

1985 ◽  
Vol 75 (3) ◽  
pp. 759-777
Author(s):  
Martha Kane Savage ◽  
Robert P. Meyer
Keyword(s):  
Main Shock ◽  
Rift Zone ◽  
Fault Plane ◽  
Linear Region ◽  
Fault Plane Solutions ◽  
One Dimensional ◽  
Delay Times ◽  
The Relationship ◽  
Long Term Studies

Abstract Study of the aftershocks recorded in a 3-hr period after a 4.2 magnitude event on the East Rift Zone of Kilauea volcano, Hawaii, on 12 April 1982 shows that the aftershocks occurred on different planes than the main shock, probably as a result of stress redistribution; the aftershock locations are probably controlled by preexisting structures. This study also suggests that these relatively small aftershocks occurred in the same seismicity patterns as larger events recorded in the same volume over a period of 10 yr. Slips on most of the aftershocks and the main shock are in the same direction, perpendicular to the East Rift Zone, as has been found in studies of other, larger earthquakes. However, fault-plane solutions varied more, as did the tensional axes, and several of the smaller events showed movement in the opposite direction from the main shock and the rest of the aftershocks, suggesting some rebound was occurring near the edges of the aftershock zone. Because ten times as much energy was released in the aftershocks in a narrow linear region as elsewhere, and since the main shock epicenter was oceanward of all the aftershocks, we suggest that rupture began at the main shock hypocenter and propagated landward, implying an almost “one-dimensional” fault. For the aftershocks, the relationship between moment and magnitude was: log M0 = (1.18 ± 0.17) ML + (17.3 ± 0.17). Differences in amplification lead to site differences of up to 0.8 units in local magnitude and 1.5 orders of magnitude in energy release. These correlated somewhat with station time corrections in that the stations with the longest delay times also had greatest amplification.

Determining contemporary stress directions from neotectonic joint systems

1991 ◽  
Vol 337 (1645) ◽  
pp. 29-40 ◽  
Keyword(s):  
Stress Field ◽  
Fault Plane ◽  
Horizontal Stress ◽  
Tectonic Stress ◽  
Stress Fields ◽  
Ebro Basin ◽  
Fault Plane Solutions ◽  
Near Surface ◽  
Initiation And Propagation

A neotectonic joint is a crack which propagated in a tectonic stress field that has persisted with little or no change of orientation until the present day. Investigating neotectonic joints is of value because the approximate orientation of the contemporary stress field can be inferred from them. Although exposed neotectonic joints in the flat-lying sedimentary rocks of some cratons are related to regional stress fields, their initiation and propagation occurred close to the Earth’s surface. For example, neotectonic joints in the centre of the Ebro basin (N. Spain) preferentially developed in a thin, near-surface channel sited within a sequence of weak Miocene limestones underlying the upper levels of plateaux. The Ebro basin joints strike uniformly NNW-SSE throughout an area of at least 10 000 km 2 and they are parallel or subparallel to the direction of greatest horizontal stress extrapolated from in situ stress measurements and fault-plane solutions of earthquakes.

Relocation of Koyna earthquakes

1980 ◽  
Vol 70 (5) ◽  
pp. 1849-1868
Author(s):  
B. K. Rastogi ◽  
P. Talwani
Keyword(s):  
Fault Plane ◽  
Seismic Velocity ◽  
Landsat Imagery ◽  
Velocity Model ◽  
Strike Slip ◽  
Normal Faulting ◽  
Large Area ◽  
Fault Plane Solutions ◽  
Lateral Strike Slip ◽  
Induced Earthquake

abstract The Koyna earthquake of December 10, 1967 was the most damaging reservoir-induced earthquake. It was followed by a long sequence of earthquakes which is still continuing. Precise locations of the Koyna earthquakes have been very much disputed as different locations of the main earthquake and stronger aftershocks were obtained by various workers. Over 1,500 epicenters of Koyna earthquakes through 1973 were obtained by Guha et al. (1974). They cover a large area in a diffused pattern. In view of the continuing seismicity and a recently obtained seismic velocity model, the larger events (ML ≧ 4.0) and about 300 selected smaller events (ML < 4.0) were relocated. The relocated epicenters show some concentration and suggest the possibility of two trends in the NNE and NW directions. There is a NNE trend of epicenters near the dam and another about 20 km west of the reservoir. The NW trend cuts through these NNE trends. The events were grouped to obtain their composite fault-plane solutions which indicate left-lateral strike-slip faulting along the NNE faults and normal faulting in the NW direction. Faults observed in the LANDSAT imagery match with these trends.

The tectonic stress and tectonic motion direction in Europe and Western Asia as calculated from earthquake fault plane solutions

1964 ◽  
Vol 54 (5A) ◽  
pp. 1519-1528 ◽  
Author(s):  
A. E. Scheidegger
Keyword(s):  
Fault Plane ◽  
Horizontal Stress ◽  
Tectonic Stress ◽  
Motion Direction ◽  
Fault Plane Solutions ◽  
Plane Normal ◽  
Western Asia ◽  
Best Fitting ◽  
Tectonic Motion ◽  
Vector Sum

Abstract The statistics of fault plane solutions of earthquakes is further analyzed and it is shown that, to find a best axis or best plane to a set of axes, the eigenvectors of a certain matrix must be calculated. The justification for this procedure follows from the same argument as that of Fisher who showed that the best of a series of directions is obtained by forming the vector sum. The eigenvector technique is then applied to the pertinent axes of fault plane solutions of earthquakes that occurred in Europe and Western Asia. It is shown that, in this region, the focal mechanisms of the earthquakes tend to orient themselves in such a fashion that the P axes coincide with the principal horizontal stress directions, the latter being normal to the geographically prominent features. The null axes tend to lie in a plane normal to the best fitting P axes. The chief random element enters into the orientation of the T axes. All this is in conformity with the predictions of theory.

scholarly journals 20 July 2017 Bodrum-Kos Earthquake (Mw:6.6) in southwestern Anatolia, Turkey

2021 ◽  
Vol 25 (3) ◽  
pp. 309-321
Author(s):  
Semir Över ◽  
Süha Özden ◽  
Esra Kalkan Ertan ◽  
Fatih Turhan ◽  
Zeynep Coşkun ◽  
...  
Keyword(s):  
Fault Plane ◽  
Regional Scale ◽  
Aegean Sea ◽  
Horizontal Stress ◽  
Focal Mechanisms ◽  
Stress Axis ◽  
Small Scale ◽  
Normal Type ◽  
Fault Plane Solutions ◽  
Stress Regime

In the Aegean Sea, the western part of Gökova Gulf, Kos and Bodrum were struck by a 6.6 (Mw) earthquake on July 20, 2017. The fault plane solution for the main shock shows an E-W striking normal type fault with approximately N-S (N4°E) tensional axis (T-axis). Fault plane solutions of 33 aftershocks show two groups of normal type fault with E-W and NE-SW to ENE-WSW orientations. The inversion of the focal mechanisms of the aftershocks yields two different normal faulting stress regimes: one is characterized by an approximately N-S (N5°E) σ3 axis (minimum horizontal stress axis). This extension is obtained from 13 focal mechanisms of aftershocks with approximately E-W direction. The other is characterized by approximately NW-SE (N330°E) σ3 axis. The latter is calculated from 21 seismic faults of aftershocks with approximately NE-SW direction. These aftershocks occurred on relatively small-scale faults that were directed from NE-SW to ENE-WSW, and possibly contributed to expansion of the basin in the west. The 24 focal mechanisms of earthquakes which occurred since 1933 in and around Gökova Basin are introduced into the inversion analysis to obtain the stress state effective in a wider region. The inversion yields an extensional stress regime characterized by an approximately N-S (N355°E) σ3 axis. The E-W directional metric faults, measured in the central part of Gökova Fault Zone bordering the Gökova Gulf in the north, also indicate N-S extension. The NE-SW extension obtained from NE-SW aftershocks appears to be more local and is responsible for the expansion of the western part of the asymmetric Gökova Basin. This N-S extension which appears to act on a regional-scale may be attributed to the geodynamic effects related to the combined forces of the southwestward extrusion of Anatolia and the roll-back process of African subduction beneath Anatolia.

Source-rock seismic-velocity models: Gassmann versus Backus

Geophysics ◽  
2011 ◽  
Vol 76 (5) ◽  
pp. N37-N45 ◽  
Author(s):  
José M. Carcione ◽  
Hans B. Helle ◽  
Per Avseth
Keyword(s):  
Oil And Gas ◽  
Seismic Velocity ◽  
Transversely Isotropic ◽  
Source Rocks ◽  
Seismic Velocities ◽  
Fluid Mixture ◽  
Data Set ◽  
Velocity Models ◽  
The North ◽  
Anisotropic Case

Source rocks are described by a porous transversely isotropic medium composed of illite and organic matter (kerogen, oil, and gas). The bulk modulus of the oil/gas mixture is calculated by using a model of patchy saturation. Then, the moduli of the kerogen/fluid mixture are obtained with the Kuster and Toksöz model, assuming that oil is the inclusion in a kerogen matrix. To obtain the seismic velocities of the shale, we used Backus averaging and Gassmann equations generalized to the anisotropic case with a solid-pore infill. In the latter case, the dry-rock elastic constants are calculated with a generalization of Krief equations to the anisotropic case. We considered 11 samples of the Bakken-shale data set, with a kerogen pore infill. The Backus model provides lower and upper bounds of the velocities, whereas the Krief/Gassmann model provides a good match to the data. Alternatively, we obtain the dry-rock elastic moduli by using the inverse Gassmann equation, instead of using Krief equations. Four cases out of 11 yielded physically unstable results. We also considered samples of the North Sea Kimmeridge shale. In this case, Backus performed as well as the Krief/Gassmann model. If there is gas and oil in the shale, we found that the wave velocities are relatively constant when the amount of kerogen is kept constant. Varying kerogen content implies significant velocity changes versus fluid (oil) saturation.

scholarly journals Relocation and seismotectonic interpretation of the seismic swarm of August - December of 2012 in the Linares area, northeastern Mexico

2016 ◽  
Vol 55 (2) ◽  
Author(s):  
Carmen M. Gómez-Arredondo ◽  
Juan C. Montalvo-Arrieta ◽  
Arturo Iglesias-Mendoza ◽  
Victor H. Espíndola-Castro
Keyword(s):  
Fault Plane ◽  
Horizontal Stress ◽  
Nodal Plane ◽  
Fault Plane Solutions ◽  
Focal Mechanism Solutions ◽  
Reverse Faulting ◽  
Northeastern Mexico ◽  
Time Periods ◽  
Maximum Horizontal Stress ◽  
Seismotectonic Interpretation

We relocated 52 events of 2.5 ≤ Mc ≤ 3.6 from a seismic sequence of over 250 events that occurred during July-December 2012 southwest of the Linares area, northeastern Mexico. To examine this swarm four seismic stations were installed in the region and operated during different time periods from September to December. Relocation of the swarm showed that the earthquake hypocentral depths were at 8 (±5) km, and the time residuals had values ≤ 0.38 s. The fault plane solutions were generated for individual earthquakes and through the use of the composite mechanism technique. The focal mechanism solutions show pure reverse faulting; the SW dipping NNW - SSE trending nodal plane is the inferred fault plane (strike ~150°, dip ~50° and rake ~67°), which reveals that maximum horizontal stress (SHmax > Shmin > Sv) predominates in the area.

scholarly journals A holistic seismotectonic model of Delhi region

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Brijesh K. Bansal ◽  
Kapil Mohan ◽  
Mithila Verma ◽  
Anup K. Sutar
Keyword(s):  
Strain Energy ◽  
Fault Plane ◽  
Near Field ◽  
Energy Estimates ◽  
The West ◽  
Fault Plane Solutions ◽  
Northern India ◽  
Structural Environment ◽  
Reverse Faulting ◽  
Using Data

AbstractDelhi region in northern India experiences frequent shaking due to both far-field and near-field earthquakes from the Himalayan and local sources, respectively. The recent M3.5 and M3.4 earthquakes of 12th April 2020 and 10th May 2020 respectively in northeast Delhi and M4.4 earthquake of 29th May 2020 near Rohtak (~ 50 km west of Delhi), followed by more than a dozen aftershocks, created panic in this densely populated habitat. The past seismic history and the current activity emphasize the need to revisit the subsurface structural setting and its association with the seismicity of the region. Fault plane solutions are determined using data collected from a dense network in Delhi region. The strain energy released in the last two decades is also estimated to understand the subsurface structural environment. Based on fault plane solutions, together with information obtained from strain energy estimates and the available geophysical and geological studies, it is inferred that the Delhi region is sitting on two contrasting structural environments: reverse faulting in the west and normal faulting in the east, separated by the NE-SW trending Delhi Hardwar Ridge/Mahendragarh-Dehradun Fault (DHR-MDF). The WNW-ESE trending Delhi Sargoda Ridge (DSR), which intersects DHR-MDF in the west, is inferred as a thrust fault. The transfer of stress from the interaction zone of DHR-MDF and DSR to nearby smaller faults could further contribute to the scattered shallow seismicity in Delhi region.

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