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.

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.

scholarly journals Seismic evidence for the tectonics of Central and Western Asia

1959 ◽  
Vol 49 (4) ◽  
pp. 369-378
Author(s):  
A. E. Scheidegger
Keyword(s):  
Fault Plane ◽  
Stress System ◽  
Motion Direction ◽  
Fault Plane Solutions ◽  
Small Areas ◽  
Mountain Ranges ◽  
Central Asian ◽  
Western Asia ◽  
Tectonic Motion

Abstract A statistical analysis of the null axes of the fault-plane solutions of earthquakes in any one area permits determination of the average tectonic motion direction of that area. In the present paper this method has been applied to areas in central and western Asia for which several hundred fault-plane solutions are readily available in the literature. The investigation yields the result that (seismically) calculated tectonic motion directions in a series of small areas that are part of a larger unit are consistent with each other and that there is in every case an excellent correlation with the tectonic motion of the area as postulated from geological studies. This appears to justify completely the seismic method. The seismically determined tectonic motion in central Asia appears to be mainly in a north-south direction. The motion refers to the present time (since the earthquakes occur at the present time), but it is the same as that postulated in geology for an explanation of the folding of the central Asian mountain ranges. This demonstrates that the stress system which created the central Asian mountains is active at the present time.

An eigenvalue method for the statistical evaluation of fault plane solutions of earthquakes

1963 ◽  
Vol 53 (4) ◽  
pp. 811-816 ◽  
Author(s):  
H. D. Fara ◽  
A. E. Scheidegger
Keyword(s):  
Input Data ◽  
Fault Plane ◽  
Test Case ◽  
Eigenvalues And Eigenvectors ◽  
Motion Direction ◽  
Fault Plane Solutions ◽  
A Value ◽  
Eigenvalue Method ◽  
Tectonic Motion ◽  
First Time

Abstract A method for the calculation of the tectonic motion direction in an area from fault plane solutions of earthquakes is presented. This method is similar to an earlier one described in the literature, but with an improved weighting procedure of the input data. The problem then reduces to that of calculating the eigenvalues and eigenvectors of a certain matrix. The new method enables one for the first time to get easily a value for the scattering of the input data. The method is first applied to a test case, and then to a series of earthquakes that occurred in the vicinity of the Marianas Islands.

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.

Fault imaging at Mt Pollino (Italy) from relative location of microearthquakes

2020 ◽  
Vol 224 (1) ◽  
pp. 637-648
Author(s):  
Ferdinando Napolitano ◽  
Danilo Galluzzo ◽  
Anna Gervasi ◽  
Roberto Scarpa ◽  
Mario La Rocca
Keyword(s):  
Fault Plane ◽  
Active Faults ◽  
Local Stress ◽  
Tectonic Stress ◽  
Relative Location ◽  
Fault Plane Solutions ◽  
Stress Regime ◽  
Main Fault ◽  
Detailed Imaging ◽  
Good Agreement

SUMMARY Relative location of microearthquakes that occurred at Mt Pollino (Italy) from 2011 to 2013 have been analyzed with the aim of a detailed imaging of the geometry of active faults. We identified 27 clusters composed of a number of earthquakes from 9 to 33, with local magnitude in the range 0.6–2.7. The relative location shows that the distribution of hypocentres in each cluster is characterized by extension from few tens of meters to at most 350 m. For each cluster the hypocentre distribution was fitted by a plane to infer the fault orientation, and results were compared with the fault plane solutions corresponding to the focal mechanism of earthquakes of the same cluster. The comparison shows a good agreement in most of the cases. The relative location analysis, generally applied to earthquakes with similar waveform, has been improved to permit also the relative location of earthquakes characterized by not similar signals. To achieve this purpose a modified procedure that overcome the condition of very similar waveforms has been applied to estimate the time delay between first pulses of the master events. The relative location of master events of all clusters shows a precise imaging of the relative position of all analysed sources and allows also to follow with high accuracy the evolution in time of the seismic swarm within the selected periods. The hypocentre position of master events and the nearly parallel fitting planes of any clusters suggest that most of the analyzed earthquakes were produced by different patches of the same fault. The final results depict a main fault plane characterized by NW–SE strike, dip of about 35–45° and depth between 4.5 and 6.5 km b.s.l. Focal mechanisms, used also to evaluate the local stress field, are mostly of normal type with few strike slip solutions for the shallowest events. This result is in good agreement with the local tectonic stress regime that is characterized by predominant NE–SW transtension, as inferred from structural, seismological and geophysical data.

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.

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.

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 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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