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 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.

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 Systematic Study of Earthquake Source Mechanism and Regional Stress Field in the Southern Montney Unconventional Play of Northeast British Columbia, Canada

2019 ◽  
Vol 91 (1) ◽  
pp. 195-206 ◽  
Author(s):  
Alireza Babaie Mahani ◽  
Fatemeh Esfahani ◽  
Honn Kao ◽  
Michelle Gaucher ◽  
Mark Hayes ◽  
...  
Keyword(s):  
British Columbia ◽  
Stress Field ◽  
Horizontal Stress ◽  
Strike Slip ◽  
P Wave ◽  
Source Mechanism ◽  
Induced Earthquakes ◽  
Nodal Plane ◽  
Reverse Faulting ◽  
Best Fitting

Abstract We provide a close look at the source mechanism of hydraulically fractured induced earthquakes and the in situ stress field within the southern Montney unconventional play in the northeast British Columbia, Canada. P‐wave first‐motion focal mechanisms were obtained for 66 earthquakes with magnitudes between 1.5 and 4.6. Results show that strike‐slip movement is the prevailing source mechanism for the events in this area, although reverse faulting is also observed for a few earthquakes. The best‐fitting nodal plane mostly strikes at ∼N60° E, with most events having dip angles of >60°. Using the Martinez‐Garzon et al. (2014) stress inversion module, we obtained the orientation of the three principal compressive stress (S1>S2>S3) and the relative intermediate principal stress magnitude (R) in five clusters. Assuming the best‐fitting nodal plane to be the causative fault, R values are mostly between 0.8 and 0.9 suggesting that the magnitude of S2 and S3 are similar, which is consistent with strike‐slip or reverse‐faulting regimes. The plunge of S1 varies between 1° and 3°, with its trend varying between N21°E and N34°E. On the other hand, the plunge of S3 varies between 22° and 50°, with its trend varies between N68°W and N58°W. Following Lund and Townend (2007), we calculated the trend of maximum horizontal stress to vary from N22°E to N33°E, in comparison with the average trend of N41°E from the World Stress Map (Heidbach et al., 2016). Through analysis of the Coulomb failure criterion and Mohr diagrams, we estimated the amount of pore‐pressure increase necessary to initiate shear slip to range between 4 and 29 MPa (average of 14±8  MPa) in the study area.

THE OTWAY BASIN: EARLY CRETACEOUS RIFTING TO NEOGENE INVERSION

1995 ◽  
Vol 35 (1) ◽  
pp. 494 ◽  
Author(s):  
A.J. Buffin ◽  
A.J. Sutherland ◽  
J.A. Gorski
Keyword(s):  
Stress Field ◽  
Normal Fault ◽  
Horizontal Wells ◽  
Horizontal Stress ◽  
Natural Fracture ◽  
Water Flooding ◽  
Hydraulic Fractures ◽  
Vertical Wells ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress

Borehole breakouts and hydraulic fractures in­ferred from dipmeter and formation microscanner logs indicate that the minimum horizontal stress (σh) is oriented 035°N in the South Australian sector of the Otway Basin. Density and sonic check-shot log data indicate that vertical stress (σv) increases from approximately 20 MPa at a depth of one km to 44 MPa at two km and 68 MPa at three km. Assum­ing a normal fault condition (i.e. σy > σH > σh), the magnitude of σh is 75 per cent of the magnitude of the maximum horizontal stress (σH), and the magni­tude of σH is close to that of av. Sonic velocity compaction trends for shales suggest that pore pressure is generally near hydrostatic in the Otway Basin.Knowledge of the contemporary stress field has a number of implications for hydrocarbon produc­tion and exploration in the basin. Wellbore quality in vertical wells may be improved (breakouts sup­pressed) by increasing the mud weight to a level below that which induces hydraulic fracture, or other drilling problems related to excessive mud weight. Horizontal wells drilled in the σh direction (035°N/215°N) should be more stable than those drilled in the σH direction, and indeed than vertical wells. In any EOR operations where water flooding promotes hydraulic fracturing, injectors should be aligned in the aH (125°N/305°N) direction, and off­set from producers in the orthogonal σh direction. Any deviated/horizontal wells targeting the frac­tured basement play should be oriented in the σh (035°N/215°N) direction to maximise intersection with this open, natural fracture trend. Hydrocar­bon recovery in wells deviated towards 035°N/215°N may also be enhanced by inducing multiple hydrau­lic fractures along the wellbore.Considering exploration-related issues, faults following the dominant structural trend, sub-paral­lel to σH orientation, are the most prone to be non-sealing during any episodic build-up of pore pres­sure. Pre-existing vertical faults striking 080-095°N and 155-170°N are the most prone to at least a component of strike-slip reactivation within the contemporary stress field.

Spatial variation in seismic anisotropy beneath the eastern and northeastern Iranian plateau and its geodynamic implications

2021 ◽  
Author(s):  
Yifan Gao ◽  
Ling Chen ◽  
Morteza Talebian ◽  
Zimu Wu ◽  
Xu Wang ◽  
...  
Keyword(s):  
Large Scale ◽  
Seismic Anisotropy ◽  
Strike Slip ◽  
Surface Strain ◽  
Deformation Pattern ◽  
Strain Rates ◽  
Lithospheric Deformation ◽  
Iranian Plateau ◽  
Lut Block ◽  
Imaging Results

<p>The Iranian plateau is a natural laboratory for studying the early stage of continental collision and plateau development. The collisional front and northern plateau are the major areas accommodating the Arabia-Eurasia convergence. GPS observations suggest that the blocks of central Iran with minor shortening may be relatively rigid. However, recent seismic imaging results suggest that the lithosphere in this region might not be rigid for it is thin and not seismically fast. Widespread mantle-derived magmatism since Middle Miocene also lends support to a relatively hot and weak lithosphere. It may raise a question of why these blocks could behave rigidly when transmitting stresses to the north.</p><p>Deformation patterns of the lithosphere and asthenosphere in the northeastern and eastern Iranian plateau, which can be constrained by seismic anisotropy, may help to understand the nature of the lithosphere within the continental interior and its responses to the Arabia-Eurasia collision. We studied the seismic anisotropy of the region via teleseismic shear-wave splitting analysis on dense array data and compared the new results with multidisciplinary observations, particularly the surface strain rates and the structure of the lithosphere-asthenosphere system. In northeastern Iran around the Paleo-Tehtys suture, the dominant fast polarization direction (FPD) is NW-SE, subparallel to the strikes of thrust faults and orogenic belts. This combined with the relatively higher strain rates and thicker crust and lithosphere suggests that northeastern Iran with pre-existing weakness may have experienced considerable lithospheric shortening. The Lut block, which is a major block of eastern Iran bounded<strong> </strong>by large-scale strike-slip faults and previously assumed rigid, shows a complex anisotropic structure. In its northern part where the strain rates are low, the average NE-SW FPD has no obvious link to active faults but is roughly parallel to the collision-induced asthenospheric flow. The area to the south around the Dasht-e-Bayaz fault shows high strain rates and a complex structure of Moho. The generally NW-SE FPDs are subparallel to the direction of the surface right-lateral shear, possibly reflecting a fault-controlled lithospheric deformation pattern. Further south is the central Lut area with moderate strain rates. It is characterized by a two-layer structure of anisotropy, with the FPDs in the upper and lower layers being similar to those of the area around the Dasht-e-Bayaz fault and the northern Lut block, respectively. This feature indicates that the anisotropy and deformation of the central Lut area could be affected by both large-scale strike-slip faults and collision-induced mantle flow.</p><p>Collectively, our observations suggest that both the collisional processes at the plate boundary and the nature and structural heterogeneities of the continental lithosphere may control the intracontinental deformation of the Iranian plateau. The observed minor deformation of the Lut block and also other blocks within this young plateau does not necessarily mean that these blocks are rigid, but is probably because of significant deformation preferentially taking place at not only the collision front but also mechanically weak zones in the hinterland, which may have accommodated most of the Arabia-Eurasia convergence.</p>

scholarly journals Cenozoic stress field in the southwestern Antarctic Peninsula from brittle mesostructures in Wright Peninsula, Adelaide Island

2011 ◽  
Vol 32 (1) ◽  
pp. 39-58 ◽  
Author(s):  
Adolfo Maestro ◽  
Jerónimo López-Martínez
Keyword(s):  
Stress Field ◽  
Antarctic Peninsula ◽  
Bimodal Distribution ◽  
Horizontal Stress ◽  
Early Miocene ◽  
Western Antarctic Peninsula ◽  
Compressional Stress ◽  
Stress States ◽  
Maximum Horizontal Stress ◽  
Adelaide Island

Cenozoic stress field in the southwestern Antarctic Peninsula from brittle mesostructures in Wright Peninsula, Adelaide IslandPalaeostresses inferred from brittle mesostructures in the southern Wright Peninsula show a stress field characterized by compressional, strike-slip and extensional regime stress states. The compressional stress (σ1) shows a main NW-SE direction and the extensional stress (σ3) shows a relative scattering with two main modes: NE-SW to E-W and NW-SE. The maximum horizontal stress (σy) has a bimodal distribution with NW-SE and NE-SW direction. The compressional orientation is related to subduction of the former Phoenix Plate under the Antarctic Plate from the Early Jurassic to the Early Miocene. Extensional structures within a broad-scale compressional stress field can be related to both the decrease in relative stress magnitudes from active margins to intraplate regions and stretching processes occurring in eastern Adelaide Island, which develop a fore-arc or intra-arc basin from the Early Miocene. Stress states with NW-SE-trending σ1are compatible with the dominant pattern established for the western Antarctic Peninsula. NW-SE orientations of σ3suggest the occurrence of tectonic forces coming from fore-arc extension along the western Antarctic Peninsula.

Stress magnitudes in the crust: constraints from stress orientation and relative magnitude data

1991 ◽  
Vol 337 (1645) ◽  
pp. 181-194 ◽  
Keyword(s):  
Stress Field ◽  
Plate Boundary ◽  
Horizontal Stress ◽  
Crustal Thickening ◽  
Viscous Drag ◽  
Stress Orientation ◽  
Relative Stress ◽  
Stress Orientations ◽  
Intraplate Stress

The World Stress Map Project is a global cooperative effort to compile and interpret data on the orientation and relative magnitudes of the contemporary in situ tectonic stress field in the Earth's lithosphere. Horizontal stress orientations show regionally uniform patterns throughout many continental intraplate regions. These regional intraplate stress fields are consistent over regions 1000-5000 km wide or ca . 100 times the thickness of the upper brittle part of the lithosphere ( ca . 20 km) and about 10-15 times the thickness of typical continental lithosphere ( ca . 150-200 km). Relative stress magnitudes or stress regimes in the lithosphere are inferred from direct in situ stress measurements and from the style of active faulting. The intraplate stress field in both the oceans and continents is largely compressional with one or both of the horizontal stresses greater than the vertical stress. The regionally uniform horizontal intraplate stress orientations are generally consistent with either relative or absolute plate motions indicating that plate-boundary forces dominate the stress distribution within the plates. Since most regions of normal faulting occur in areas of high elevation, the extensional stress régimes in these areas can be attributed to superimposed bouyancy forces related to crustal thickening and/or lithosphere thinning; stresses derived from these bouyancy forces locally exceed mid-plate compressional stresses. Evaluating the effect of viscous drag forces acting on the plates is difficult. Simple driving or resisting drag models (with shear tractions acting parallel or antiparallel to plate motion) are consistent with stress orientation data; however, the large lateral stress gradients across broad plates required to balance these tractions are not observed in the relative stress magnitude data. Current models of stresses due to whole mantle flow inferred from seismic tomography models (and with the inclusion of the effect of high density slabs) predict a general compressional stress state within continents but do not match the broad-scale horizontal stress orientations. The broad regionally uniform intraplate stress orientations are best correlated with compressional plate-boundary forces and the geometry of the plate boundaries.

Active tectonics and seismicity in the Calabrian Arc subduction complex (Ionian Sea)

2020 ◽  
Author(s):  
Alina Polonia ◽  
Sgroi Tiziana ◽  
Artoni Andrea ◽  
Barberi Graziella ◽  
Billi Andrea ◽  
...  
Keyword(s):  
Source Parameters ◽  
Plate Boundary ◽  
Strike Slip ◽  
Accretionary Wedge ◽  
Ionian Sea ◽  
Tectonic Structures ◽  
Fault Systems ◽  
Seismological Data ◽  
Subduction System ◽  
Historic Earthquakes

<p>The Calabria Arc (CA) is the narrowest subduction-rollback system on Earth, and it has been struck repeatedly by destructive historical earthquakes often associated with tsunamis. In spite of the detailed earthquake catalogue, the source parameters of most historic earthquakes are still debated, especially for earthquakes that may have been generated offshore.</p><p>The subduction system is characterized by an irregular plate boundary reflecting the presence of continental blocks, indenters, and different rates of continental collision. Convergence between Eurasia and Africa produces both compressive and transtensional deformation in the offshore accretionary complex. Shortening occurs along the outer deformation front and along splay faults accommodating differences in rheology and basal detachment depth. Two oppositely dipping strike-slip/transtensional fault systems, i.e., the Ionian (IF) and Alfeo-Etna (AEF) faults produce deep fragmentation of the subduction system and the collapse of the accretionary wedge, in agreement with geodetic models suggesting plate divergence in this region. Transtensional lithospheric faults segmenting the subduction system are punctuated by mantle-rooted diapirism driven by arc orthogonal rifting, collapse of the accretionary wedge, and deep fragmentation of the subduction system along pre-existing Mesozoic transform faults.</p><p>Seismological observations in the Western Ionian Sea highlight the presence of earthquake clusters along wide and deep-seated active tectonic structures, which were proposed as likely seismogenic sources for large magnitude historic earthquakes/tsunamis in the region. Low to moderate magnitude earthquakes occurring offshore were relocated using a new 1D velocity model for the Ionian Sea, constrained by geological and geophysical observations, which included data collected by NEMO-SN1 seafloor observatory. Seismological data from NEMO-SN1 were integrated with observations carried out by over 100 land stations of the INGV network, and led us to compile a map of 3D distribution for over 2600 events. 3D locations and focal mechanism analyses allowed us to highlight local lithospheric structure. Although seismicity appears scattered in a wide corridor of deformation within the subduction system, we observe alignments of events along main fault systems with strike-slip and extensional mechanisms. Moreover, results from seismological data analysis, i.e., misfits in the 3D distribution of hypocenters and tomographic maps, could be explained by the presence of an anomalous area between the two structures, characterized by thinned lithosphere probably caused by incipient rifting, as suggested by seismic reflection images and geodynamic interpretations.  </p>

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 FE model of the Suez rift basin and its geodynamic implications

2013 ◽  
Vol 46 ◽  
Author(s):  
Sunil Kumar Dwivedi ◽  
Daigoro Hayashi Hayashi
Keyword(s):  
Stress Field ◽  
Red Sea ◽  
Horizontal Stress ◽  
Dead Sea ◽  
Gulf Of Aqaba ◽  
Rift System ◽  
Fe Model ◽  
Gulf Of Suez ◽  
Rift Basin ◽  
Dead Sea Transform

Northeast Africa forms the northernmost extension of the East African Rift System and is considered one of the geodynamically active regions in the Earth. The Red Sea, Gulf of Suez, Gulf of Aqaba, and Dead Sea transform are the most prominent tectonic features in the region. Despite the motion of African and Arabian Plates being well-established, contribution of these plates to the origin of stress field in the Gulf of Suez has been under discussion. The main debate is on the controlling factors for the geodynamic origin of the Suez rift basin. The factors, either the present-day stress field is originated due to the Gulf of Suez rift itself or due to the influence of nearby tectonic boundaries, is under question. An attempt has been made to model the stress field of the area by 20 plane stress finite-element (FE) modeling incorporating realistic rock parameters and velocities for African and Arabian Plates. The modeled maximum horizontal stress (σHmax and minimum horizontal stress (σHmin) directions correlate well with observed stress indicators from the world stress map (WSM), focal mechanism solutions (FMS) of earthquakes, in-situ stress measurements, and geological stress information; and displacement field correlate well with GPS data of the region. Modeling result reveals that the present-day stress field in the Gulf of Suez is emerged from coeval influence of superimposed forces acting from rifting processes in the Red Sea, Gulf of Aqaba, and Dead Sea transform.

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