Le bassin de Tizi n'Test (Haut Atlas, Maroc) : exemple d'évolution d'un segment oblique au rift de l'Atlantique central au Trias

2003 ◽  
Vol 40 (7) ◽  
pp. 949-964 ◽  
Author(s):  
Abdelmounim Qarbous ◽  
Fida Medina ◽  
Christian Hoepffner
Keyword(s):  
Fault Zone ◽  
Inverse Analysis ◽  
Horizontal Stress ◽  
Strike Slip ◽  
High Atlas ◽  
State Of Stress ◽  
Minimum Stress ◽  
Maximum Horizontal Stress ◽  
Central Atlantic

Detailed mapping completed by a microtectonic study of the Tizi n'Test Triassic basin, located along the Tizi n'Test fault zone in the Moroccan High Atlas, has allowed us to improve the knowledge on the geometry of the structures and the activity of faults during the Triassic extensional events related to the rifting of the central Atlantic. The latter are reflected by the development of a rift, at present inverted and deformed by the collision of Africa and Europe, comprising kilometric-scale grabens and half-grabens bounded by major faults trending ENE–WSW, with a dip towards the NNW, and a dip-slip syndepositional motion. Inverse analysis of fault slickenside populations shows a heterogeneous Triassic state of stress. However, in the most significant measurement sites, the maximum horizontal stress σ1 is vertical, while the minimum stress σ3 is horizontal with a NW–SE trend. The strike-slip component appears to be very small during the Triassic, a noticeable fact because of the obliquity of the basin with respect to the Atlantic rift.

PRESENT-DAY STATE-OF-STRESS OF SOUTHEAST AUSTRALIA

2006 ◽  
Vol 46 (1) ◽  
pp. 283 ◽  
Author(s):  
E. Nelson ◽  
R. Hillis ◽  
M. Sandiford ◽  
S. Reynolds ◽  
S. Mildren
Keyword(s):  
Focal Mechanism ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Focal Mechanism Solutions ◽  
Southeast Australia ◽  
State Of Stress ◽  
Earthquake Focal Mechanism ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress ◽  
Gippsland Basin

There have been several studies, both published and unpublished, of the present-day state-of-stress of southeast Australia that address a variety of geomechanical issues related to the petroleum industry. This paper combines present-day stress data from those studies with new data to provide an overview of the present-day state-of-stress from the Otway Basin to the Gippsland Basin. This overview provides valuable baseline data for further geomechanical studies in southeast Australia and helps explain the regional controls on the state-of-stress in the area.Analysis of existing and new data from petroleum wells reveals broadly northwest–southeast oriented, maximum horizontal stress with an anticlockwise rotation of about 15° from the Otway Basin to the Gippsland Basin. A general increase in minimum horizontal stress magnitude from the Otway Basin towards the Gippsland Basin is also observed. The present-day state-of-stress has been interpreted as strike-slip in the South Australian (SA) Otway Basin, strike-slip trending towards reverse in the Victorian Otway Basin and borderline strike-slip/reverse in the Gippsland Basin. The present-day stress states and the orientation of the maximum horizontal stress are consistent with previously published earthquake focal mechanism solutions and the neotectonic record for the region. The consistency between measured present-day stress in the basement (from focal mechanism solutions) and the sedimentary basin cover (from petroleum well data) suggests a dominantly tectonic far-field control on the present-day stress distribution of southeast Australia. The rotation of the maximum horizontal stress and the increase in magnitude of the minimum horizontal stress from west to east across southeast Australia may be due to the relative proximity of the New Zealand segment of the plate boundary.

A New Uniform Moment Tensor Catalog for Yunnan, China, from January 2000 through December 2014

2020 ◽  
Vol 91 (2A) ◽  
pp. 891-900
Author(s):  
Yan Xu ◽  
Keith D. Koper ◽  
Relu Burlacu ◽  
Robert B. Herrmann ◽  
Dan-Ning Li
Keyword(s):  
Stress Field ◽  
Seismic Hazard ◽  
Moment Tensor ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Moment Tensors ◽  
Yunnan Region ◽  
Seismic Waveforms ◽  
The Moment ◽  
Maximum Horizontal Stress

Abstract Because of the collision of the Indian and Eurasian tectonic plates, the Yunnan Province of southwestern China has some of the highest levels of seismic hazard in the world. In such a region, a catalog of moment tensors is important for estimating seismic hazard and helping understand the regional seismotectonics. Here, we present a new uniform catalog of moment tensor solutions for the Yunnan region. Using a grid-search technique to invert seismic waveforms recorded by the permanent regional network in Yunnan and the 2 yr ChinArray deployment, we present 1833 moment tensor solutions for small-to-moderate earthquakes that occurred between January 2000 and December 2014. Moment magnitudes in the new catalog vary from Mw 2.2 to 6.1, and the catalog is complete above Mw∼3.5–3.6. The moment tensors are constrained to be purely double-couple and show a variety of faulting mechanisms. Normal faulting events are mainly concentrated in northwest Yunnan, while farther south along the Sagaing fault the earthquakes are mostly thrust and strike slip. The remaining area includes all three styles of faulting but mostly strike slip. We invert the moment tensors for the regional stress field and find a strong correlation between spatially varying maximum horizontal stress and Global Positioning System observations of horizontal ground velocity. The stress field reveals clockwise rotation around the eastern Himalayan syntaxis, with northwest–southeast compression to the east of the Red River fault changing to northeast–southwest compression west of the fault. Almost 88% of the centroid depths are shallower than 16 km, consistent with a weak and ductile lower crust.

scholarly journals Microseismic Focal Mechanisms and Implications for Changes in Stress during the 2014 Newberry EGS Stimulation

2019 ◽  
Vol 109 (5) ◽  
pp. 1653-1660 ◽  
Author(s):  
Ana C. Aguiar ◽  
Stephen C. Myers
Keyword(s):  
Maximum Stress ◽  
Sequence Data ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Fluid Injection ◽  
Waveform Cross Correlation ◽  
Reference Event ◽  
Maximum Horizontal Stress ◽  
East West

Abstract We adapt the relative polarity method from Shelly et al. (2016) to compute focal mechanisms for microearthquakes associated with the 2014 hydroshearing stimulation at the Newberry volcano geothermal site. We focus the analysis on events relocated by Aguiar and Myers (2018), who report that six event clusters predominantly comprise the 2014 sequence. Data quality allows focal mechanism analysis for four of the six event clusters. We use Hardebeck and Shearer (2002, 2003; hereafter HASH) to compute focal mechanisms based on first‐motion polarities and S/P amplitude ratios. We manually determine P‐ and S‐wave polarities for a well‐recorded reference event in each cluster, then use waveform cross correlation to determine whether recordings of other events in the cluster are the same or reversed polarity at each network station. Most waveform polarities are consistent with the affiliated reference event, indicating similar focal mechanisms within each cluster. The deeper clusters are east–west‐striking normal faults, whereas the shallower clusters, close to the top of the open‐hole section of the borehole, are strike slip with east–west motion. Regional studies and prestimulation borehole breakouts find the maximum stress direction is vertical and maximum horizontal stress is approximately north–south. Fault geometry and focal mechanisms of microseismicity during the stimulation suggest that increased pressure from fluid injection predominantly caused changes in horizontal stress, consistent with predictions from numerical studies of stress change caused by fluid injection. At shallow depths, where previous studies suggest the difference between vertical and horizontal stress is lowest, injection appears to have rotated the direction of maximum stress from vertical to horizontal, resulting in strike‐slip motion. At greater depth, vertical stress continued to be the dominant direction during the stimulation, but fault orientation indicates either reactivation of pre‐existing fractures or rotation of the direction of maximum horizontal stress from approximately north–south to east–west.

scholarly journals Determination of horizontal stress orientation in the areas of the Tomsk region

2021 ◽  
Vol 1 (7) ◽  
pp. 16-24
Author(s):  
Anton E. Antonov ◽  
◽  
Andrei S. Shadrin ◽  
Dmitrii V. Konoshonkin ◽  
Valerii S. Rukavishnikov ◽  
...  
Keyword(s):  
Horizontal Stress ◽  
Summary Table ◽  
Average Value ◽  
The North ◽  
Stress Orientation ◽  
Tomsk Region ◽  
Stress Orientations ◽  
Borehole Breakouts ◽  
Minimum Stress ◽  
Maximum Horizontal Stress

Introduction. The World Stress Map project proves that horizontal stress orientation determination is a global task essential for the majority of geomechanical calculations. However, there is scant data on stress orientations in the territory of Russia at the moment. The task is therefore highly relevant. Research objective is to determine the orientations of maximum and minimum horizontal stresses by separate areas of the Tomsk region and build a map of horizontal stresses. Method of research. The basis for determining the orientations of horizontal stresses is the theory of drilling-induced fracture and borehole breakouts occurrence. The maximum stress orientation coincides with the drilling-induced fracture orientation, whereas the minimum stress orientation coincides with the borehole breakouts orientation or is perpendicular to the maximum stresses. Results. Research results are compiled in a summary table containing mean orientations of horizontal stresses by areas and a map of horizontal stress orientations. Conclusions. A summary map of maximum horizontal stress strike azimuths has been constructed. The stresses are of similar orientation in every well under consideration, except for a well in the North-Shingin area. The average value of maximum horizontal stress orientation has made up 337° northwest and 157° southeast.

scholarly journals Crustal Strain and Stress Fields in Egypt from Geodetic and Seismological Data

2021 ◽  
Vol 13 (7) ◽  
pp. 1398
Author(s):  
Mohamed Rashwan ◽  
Rashad Sawires ◽  
Ali M. Radwan ◽  
Federica Sparacino ◽  
José Antonio Peláez ◽  
...  
Keyword(s):  
Stress Field ◽  
Large Scale ◽  
Nile Delta ◽  
Plate Boundary ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Surface Strain ◽  
Gulf Of Aqaba ◽  
Seismological Data ◽  
Maximum Horizontal Stress

The comparison between crustal stress and surface strain azimuthal patterns has provided new insights into several complex tectonic settings worldwide. Here, we performed such a comparison for Egypt taking into account updated datasets of seismological and geodetic observations. In north-eastern Egypt, the stress field shows a fan-shaped azimuthal pattern with a WNW–ESE orientation on the Cairo region, which progressively rotated to NW–SE along the Gulf of Aqaba. The stress field shows a prevailing normal faulting regime, however, along the Sinai/Arabia plate boundary it coexists with a strike–slip faulting one (σ1 ≅ σ2 > σ3), while on the Gulf of Suez, it is characterized by crustal extension occurring on near-orthogonal directions (σ1 > σ2 ≅ σ3). On the Nile Delta, the maximum horizontal stress (SHmax) pattern shows scattered orientations, while on the Aswan region, it has a WNW–ESE strike with pure strike–slip features. The strain-rate field shows the largest values along the Red Sea and the Sinai/Arabia plate boundary. Crustal stretching (up to 40 nanostrain/yr) occurs on these areas with WSW–ENE and NE–SW orientations, while crustal contraction occurs on northern Nile Delta (10 nanostrain/yr) and offshore (~35 nanostrain/yr) with E–W and N–S orientations, respectively. The comparison between stress and strain orientations over the investigated area reveals that both patterns are near-parallel and driven by the same large-scale tectonic processes.

A comparative study of the anisotropic dynamic and static elastic moduli of unconventional reservoir shales: Implication for geomechanical investigations

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. D245-D261 ◽  
Author(s):  
Jaime Meléndez-Martínez ◽  
Douglas R. Schmitt
Keyword(s):  
Bedding Plane ◽  
Horizontal Stress ◽  
Pressure Sensitivity ◽  
S Wave ◽  
Fracture Pressure ◽  
Highly Nonlinear ◽  
Rock Anisotropy ◽  
Minimum Stress ◽  
Sonic Logging ◽  
Static Elastic Moduli

We obtained the complete set of dynamic elastic stiffnesses for a suite of “shales” representative of unconventional reservoirs from simultaneously measured P- and S-wave speeds on single prisms specially machined from cores. Static linear compressibilities were concurrently obtained using strain gauges attached to the prism. Regardless of being from static or dynamic measurements, the pressure sensitivity varies strongly with the direction of measurement. Furthermore, the static and dynamic linear compressibilities measured parallel to the bedding are nearly the same whereas those perpendicular to the bedding can differ by as much as 100%. Compliant cracklike porosity, seen in scanning electron microscope images, controls the elastic properties measured perpendicular to the rock’s bedding plane and results in highly nonlinear pressure sensitivity. In contrast, those properties measured parallel to the bedding are nearly insensitive to stress. This anisotropy to the pressure dependency of the strains and moduli further complicates the study of the overall anisotropy of such rocks. This horizontal stress insensitivity has implications for the use of advanced sonic logging techniques for stress direction indication. Finally, we tested the validity of the practice of estimating the fracture pressure gradient (i.e., horizontal stress) using our observed elastic engineering moduli and found that ignoring anisotropy would lead to underestimates of the minimum stress by as much as 90%. Although one could ostensibly obtain better values or the minimum stress if the rock anisotropy is included, we would hope that these results will instead discourage this method of estimating horizontal stress in favor of more reliable techniques.

scholarly journals Kinematic partitioning in the Southern Andes (39° S–46° S) inferred from lineament analysis and reassessment of exhumation rates

2021 ◽  
Author(s):  
Paul Leon Göllner ◽  
Jan Oliver Eisermann ◽  
Catalina Balbis ◽  
Ivan A. Petrinovic ◽  
Ulrich Riller
Keyword(s):  
Fault Zone ◽  
Vertical Displacement ◽  
Strike Slip ◽  
Structural Studies ◽  
Southern Andes ◽  
Plate Convergence ◽  
Exhumation Rates ◽  
Lineament Analysis ◽  
Dextral Strike Slip ◽  
Data Call

AbstractThe Southern Andes are often viewed as a classic example for kinematic partitioning of oblique plate convergence into components of continental margin-parallel strike-slip and transverse shortening. In this regard, the Liquiñe-Ofqui Fault Zone, one of Earth’s most prominent intra-arc deformation zones, is believed to be the most important crustal discontinuity in the Southern Andes taking up margin-parallel dextral strike-slip. Recent structural studies, however, are at odds with this simple concept of kinematic partitioning, due to the presence of margin-oblique and a number of other margin-parallel intra-arc deformation zones. However, knowledge on the extent of such zones in the Southern Andes is still limited. Here, we document traces of prominent structural discontinuities (lineaments) from the Southern Andes between 39° S and 46° S. In combination with compiled low-temperature thermochronology data and interpolation of respective exhumation rates, we revisit the issue of kinematic partitioning in the Southern Andes. Exhumation rates are maximal in the central parts of the orogen and discontinuity traces, trending predominantly N–S, WNW–ESE and NE–SW, are distributed across the entire width of the orogen. Notably, discontinuities coincide spatially with large gradients in Neogene exhumation rates and separate crustal domains characterized by uniform exhumation. Collectively, these relationships point to significant components of vertical displacement on these discontinuities, in addition to horizontal displacements known from published structural studies. Our results agree with previously documented Neogene shortening in the Southern Andes and indicate orogen-scale transpression with maximal vertical extrusion of rocks in the center of the transpression zone. The lineament and thermochronology data call into question the traditional view of kinematic partitioning in the Southern Andes, in which deformation is focused on the Liquiñe-Ofqui Fault Zone.

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