Stress tensor orientation derived from fault plane solutions in the southwestern Alps

Stress tensor inversion has been applied to estimate principal stress axes orientations in Western Greece, from 178 earthquake fault plane solutions from the Kozani-Grevena May 13, 1995 sequence. All focal mechanisms were previously determined through the deployment of a dense portable array. The magnitude range is 2.7-6.5 and the depth range is 4.0-15 km. A single stress tensor with an average misfit of 6.5°, small enough to support the assumption of stress homogeneity, can describe the stress field. The maximum compressive stress, s1, has a NNE-SSW trend (N26°E) and a nearly vertical plunge (80°) while the minimum compressive stress, s3, has a NNW-SSE orientation (N159°E) and a shallow plunge (7°) southwards. The scalar quantity, R (stress ratio) was found equal to 0.4 suggesting a transtensional regime (normal faulting with strike-slip motions) in which s2 is compressional. The identification of the fault plane from the auxiliary plane was achieved for 99 fault plane solutions out of 178 in total (56%). Vertical cross sections support previous results concerning the north dipping main fault segments and the south dipping antithetic faulting. The strike-slip motion is mainly dextral, along NNE-SSW structures, which follow the direction of the main neotectonic faults while the scarce sinistral strike-slip motion is connected to NW-SE trending zones of weakness pre-existing the old phase of compression in the Aegean. The strong strike slip motion that supports the transtensional regime probably reflects the effect of the motions of the North Anatolian Fault, taken up by normal faulting in the area of Western Greece.

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The relation between fault plane solutions for earthquakes and the directions of the principal stresses

Bulletin of the Seismological Society of America ◽

10.1785/bssa0590020591 ◽

1969 ◽

Vol 59 (2) ◽

pp. 591-601

Author(s):

Dan P. McKenzie

Keyword(s):

Brittle Fracture ◽

Stress Tensor ◽

Principal Stress ◽

Fault Plane ◽

Triaxial Stress ◽

Homogeneous Material ◽

Principal Stresses ◽

Fault Plane Solutions ◽

Shallow Earthquakes ◽

Earthquake Zone

abstract The stresses involved in shallow earthquakes and their occurrence along fault planes suggest that they occur by failure on weak planes, rather than by brittle fracture of a homogeneous material. Possible orientations of the stress tensor are examined to determine what limits fault plane solutions can place on the orientation of the greatest principal stress. For the general case of a triaxial stress, the only restriction is that this stress direction must lie in the quadrant containing P, but may be at right angles to the P direction. Thus shallow earthquakes impose a few limitations on the orientation of the stress tensor. In contrast the fault plane solutions from deep earthquakes are best explained by fracture of a homogeneous material, with the greatest principal stress directed down the dip of the earthquake zone.

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Multiple Seismogenic Processes for High-Frequency Earthquakes at Katmai National Park, Alaska: Evidence from Stress Tensor Inversions of Fault-Plane Solutions

Bulletin of the Seismological Society of America ◽

10.1785/0120020113 ◽

2003 ◽

Vol 93 (1) ◽

pp. 94-108 ◽

Cited By ~ 28

Author(s):

S. C. Moran

Keyword(s):

Stress Tensor ◽

High Frequency ◽

National Park ◽

Fault Plane ◽

Fault Plane Solutions ◽

Katmai National Park

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Stress tensor computation from earthquake fault-plane solutions: an application to seismic swarms at Mt. Etna volcano (Italy)

Annals of Geophysics ◽

10.4401/ag-3867 ◽

1997 ◽

Vol 40 (5) ◽

Author(s):

S. Gresta ◽

C. Musumeci

Keyword(s):

Stress Tensor ◽

Fault Plane ◽

Local Stress ◽

Depth Range ◽

Etna Volcano ◽

Exact Methods ◽

Fault Plane Solutions ◽

Stress Regime ◽

Mt Etna ◽

Regional Tectonic

Fault-plane solutions of some tens of local earthquakes which occurred at Mt. Etna volcano during 1983-1986 have been inverted for stress tensor parameters by the algorithm of Gephart and Forsyth (1984). Three seismic sequences were focused on which respectively occurred during a flank eruption (June 1983), just after the end of a subterminal eruption (October 1984) and during an inter-eruptive period (May 1986). The application to the three sets of data of both the "approximate" and the "exact" methods evidenced the stability of results, and the stress directions are well defined in spite of the small number of events used for the inversion. The s1 obtained agrees with the regional tectonic framework, nearly horizontal and oriented N-S, only in the shallow crust, and just after the 1984 eruption. This supports the hypothesis of a tectonic control on the end of the eruptive activities at Mt. Etna. Conversely, results concerning the depth range 10-30 km are in apparent disagreement with other investigations (Cocina et al., 1997), as well as with the regional tectonics. The stress was here found homogeneous, but with s1 respectively trending ENE-WSW (June 1983) and E-W (May 1986). We suggest that the stress field could be temporarily modified by a local stress regime driven by the intrusion of uprising magma.

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A holistic seismotectonic model of Delhi region

Scientific Reports ◽

10.1038/s41598-021-93291-9 ◽

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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