scholarly journals Horizontal compressive stress regime on the northern Cascadia margin inferred from borehole breakouts

2016 ◽  
Vol 17 (9) ◽  
pp. 3529-3545 ◽  
Author(s):  
M. Riedel ◽  
A. Malinverno ◽  
K. Wang ◽  
D. Goldberg ◽  
G. Guerin
Keyword(s):  
Compressive Stress ◽  
Stress Regime ◽  
Cascadia Margin ◽  
Horizontal Compressive Stress ◽  
Borehole Breakouts

scholarly journals Regional tectonic stress near the San Andreas fault in central and southern California

2021 ◽  
Author(s):  
John Townend ◽  
M Zoback
Keyword(s):  
Compressive Stress ◽  
San Francisco ◽  
Southern California ◽  
San Andreas Fault ◽  
Horizontal Stress ◽  
Tectonic Stress ◽  
Bay Area ◽  
San Andreas ◽  
Regional Tectonic ◽  
Horizontal Compressive Stress

Throughout central and southern California, a uniform NNE-SSW direction of maximum horizontal compressive stress is observed that is remarkably consistent with the superposition of stresses arising from lateral variations in lithospheric buoyancy in the western United States, and farfield Pacific-North America plate interaction. In central California, the axis of maximum horizontal compressive stress lies at a high angle to the San Andreas fault (SAF). Despite relatively few observations near (±10 km) the fault, observations in the greater San Francisco Bay area indicate an angle of as much as 85°, implying extremely low fault strength. In southern California, observations of stress orientations near the SAF are rotated slightly counter-clockwise with respect to the regional field. Nevertheless, we observe an approximately constant angle between the SAF and the maximum horizontal stress direction of 68 ± 7° along ∼400 km of the fault, indicating that the SAF has moderately low frictional strength in southern California. Copyright 2004 by the American Geophysical Union.

Seismicity in South Carolina

1988 ◽  
Vol 59 (4) ◽  
pp. 165-171
Author(s):  
Kaye M. Shedlock
Keyword(s):  
South Carolina ◽  
Compressive Stress ◽  
Coastal Plain ◽  
Fault Plane ◽  
Strike Slip ◽  
Fault Plane Solutions ◽  
Reservoir Induced Seismicity ◽  
Southeastern Us ◽  
Horizontal Compressive Stress ◽  
Shallow Crust

Abstract The largest historical earthquake in South Carolina, and in the southeastern US, occurred in the Coastal Plain province, probably northwest of Charleston, in 1886. Locations for aftershocks associated with this earthquake, estimated using intensities based on newspaper accounts, defined a northwest trending zone about 250 km long that was at least 100 km wide in the Coastal Plain but widened to a northeast trending zone in the Piedmont. The subsequent historical and instrumentally recorded seismicity in South Carolina images the 1886 aftershock zone. Except for a few scattered earthquakes and a swarm of shallow (≤ 4 km deep), small (ML ≤ 2.5), primarily reverse faulting earthquakes that occurred along the flanks of a granite pluton about 60 km northwest of Columbia, the seismicity in the Piedmont province has been associated with water level changes in reservoirs. Reservoir induced seismicity (RIS) is shallow (≤ 6 km deep), primarily strike-slip or thrust faulting corresponding to an inferred maximum horizontal compressive stress oriented approximately N 60° E. Instrumentally recorded seismicity in the Coastal Plain province occurs in 3 seismic zones or clusters: Middleton Place-Summerville (MPSSZ), Adams Run (ARC), and Bowman (BSZ). Approximately 68% of the Coastal Plain earthquakes occur in the MPSSZ, a north trending zone about 22 km long and 12 km wide, lying about 20 km northwest of Charleston. The hypocenters of MPSSZ earthquakes range in depth from near the surface to almost 12 km. Thrust, strike-slip, and some normal faulting are indicated by the fault plane solutions for Coastal Plain earthquakes. The maximum horizontal compressive stress, inferred from the P-axes of the fault plane solutions, is oriented NE-SW in the shallow crust (< 9 km deep) but appears to be diffusely E-W between 9 to 12 km deep. Although there is localized variability, the current seismicity and associated faulting in South Carolina probably represent a regional response to the NE-SW maximum horizontal compressive stress prevalent throughout eastern North America.

Geodynamic evolution of the Tunisian margin during the Albian–Cenomanian: structural evidence of the Austrian orogenic phase and the early tectonic inversion of the Tunisian Atlas

2021 ◽  
pp. jgs2019-195
Author(s):  
Mohamed Ben Chelbi
Keyword(s):  
Atlantic Ocean ◽  
Compressive Stress ◽  
Lower Cretaceous ◽  
Geodynamic Evolution ◽  
Stress Regime ◽  
Alpine Orogeny ◽  
Excellent Opportunity ◽  
Test Models ◽  
Tunisian Atlas ◽  
Compressional Deformation

The Zebbag and Fahdene formations outcrop onshore Tunisia and provide an excellent opportunity to test models of the tectonosedimentary evolution of this region during the Albian–Cenomanian. A NW–SE compressive stress regime resulted in shortening of the Tunisian margin and this compressional tectonism defines the Austrian phase described in the surrounding margins. This event is not widely documented, but regionally extensive tectonism is suggested by NE–SW thrusting and folding, which produced an angular unconformity, active halokinetic diapirs and transpressional NW–SE pull-apart basins. The observed compressional deformation can be considered as a precursor to the Alpine Orogeny and led to the inversion of palaeoblocks inherited from Tethyan Jurassic and Lower Cretaceous rifting. A late Albian–Cenomanian onset of compressional deformation along the Tunisian margin may be intimately related to the drift of Africa with respect to Europe and to opening of the Atlantic Ocean.

Microseismicity and tectonics in northeast India

1991 ◽  
Vol 81 (1) ◽  
pp. 131-138
Author(s):  
J. R. Kayal ◽  
Reena De
Keyword(s):  
Spatial Variation ◽  
High Activity ◽  
Compressive Stress ◽  
Landsat Imagery ◽  
Northeast India ◽  
Focal Mechanisms ◽  
Shillong Plateau ◽  
The West ◽  
Tectonic Stresses ◽  
Horizontal Compressive Stress

Abstract Three microearthquake surveys were carried out in Shillong Plateau, Mikir Hills, and Assam valley areas during 1984 to 1986. Some 422 events are relocated by the Homogeneous Station Method. The microseismicity map reveals intense crustal (10 to 40 km) activity beneath the Tura area of Shillong Plateau. The areas to the west of Shillong and the area around Mikir Hills also show high activity. The microseismicity map further shows major tectonic lineaments that are compatible with the Landsat Imagery lineaments and the major faults. Composite focal mechanisms of the microearthquakes show spatial variation of the tectonic stresses in the region. An ENE-WSW horizontal compressive stress is dominant in the Tura area, whereas a SE-NW horizontal compressive stress is dominant in the Shillong and Mikir Hills areas.

Diapiric deformations in the Quaternary deposits of the central Ebro Basin, Spain

1986 ◽  
Vol 123 (1) ◽  
pp. 45-57 ◽  
Author(s):  
J. L. Simón ◽  
A. Soriano
Keyword(s):  
Compressive Stress ◽  
Plastic Flow ◽  
Plastic Material ◽  
Middle Pleistocene ◽  
Normal Faults ◽  
Ebro Basin ◽  
Quaternary Deposits ◽  
Horizontal Compressive Stress ◽  
Tension Cracks ◽  
Fluvial Sedimentation

AbstractFrom a study of 24 outcrops in Neogene and Quaternary deposits of the central Ebro Basin, a number of diapiric deformations have been recognized, two principal types being differentiated: domal or pillow structures, and piercement or intrusive structures. The former are incipient diapirs of gypsum. Piercing structures have reverse faulted contacts not caused by halokinesis; here Neogene marls are the active plastic material, contrasting with the competent behaviour of gypsum. These intrusive structures are viscous diapirs which easily pierce the non-consolidated, low strength Quaternary gravel overburden and submit it to a horizontal compressive stress. As a consequence, reverse faults and flexures develop in it. Generally normal faults and tension cracks do not appear. Underlying gypsum beds are frequently pulled up into diapirs and they constitute the structural core.Density contrast and conditions for plastic flow exist at the marl–gravel boundary. It seems to have been specially common at the time of Quaternary fluvial sedimentation, so that much deformation is synsedimentary. Diapiric phenomena have been very active during early to middle Pleistocene time, becoming weaker afterwards.

scholarly journals EARTHQUAKES FELT IN MOLDOVA 2014: March, 29 with КP=12.5, Mw=4.7, September, 10 with КP=12.4, Mw=4.5 and November 22 with КP=14.3, Mw=5.8 (Romania–Moldova)

2020 ◽  
pp. 288-297
Author(s):  
N. Stepanenco ◽  
V. Cardanets ◽  
N. Simonova
Keyword(s):  
Compressive Stress ◽  
Main Shock ◽  
Southwestern Part ◽  
Republic Of Moldova ◽  
The North ◽  
Horizontal Compressive Stress ◽  
Isoseismal Maps ◽  
The Republic ◽  
Largest Aftershock ◽  
Observation Period

All earthquakes felt in 2014 on the territory of Moldova occurred outside its borders, in the Vrancea and Pre-Carpathian regions (Romania). In 2014, the population of Moldova felt 13 earthquakes. The article discusses in detail the most powerful events, occurred on March 29, September 6, and November 22. The March 29 earthquake, Mw=4.7, hрР=136 km was felt in the eastern and southern counties of Romania (in 41 settlements), in the Odessa region of Ukraine, and also in the central and southern regions of the Republic of Moldova (22 points). The epicenter was situated in a bend of the Vrancea mountains. The earthquake on Sep-tember 10, Mw=4.5, hрР=108 km was felt in the eastern and southern counties of Romania (in 27 settlements), in the central and southern parts of Moldova (22 points), in the north of Bulgaria and in the Odessa region of Ukraine. Both earthquakes, March 29 and September 10, occurred under the action of prevailing near-horizontal compressive stress. The November 22 earthquake, Mw=5.8, hрР=37 km occurred in the southwestern part of Romania and turned out to be the most significant crust event for the instrumental observation period. Movement in the source occurred under the action of tensile stresses. Earthquakes in this zone continued until January 19, 2015. The largest aftershock was on December 7 with МwMED=4.4. Foci are associated with the activation of the Peceneaga-Camena fault. The main shock was felt in Romania (in 66 settlements) and neighboring countries: Bulgaria, Moldova (23 settlements), Ukraine (18 settlements). The isoseismal maps were constructed for all three earthquakes considered in detail in this work. The intensity at the epicenter of the November 22 earthquake reached I0=6, for other two events I0=5.

scholarly journals Dike Propagation During Global Contraction: Making Sense of Conflicting Stress Histories on Mercury

2021 ◽  
Vol 9 ◽  
Author(s):  
Kelsey Crane ◽  
Allison Bohanon
Keyword(s):  
Physical Model ◽  
Compressive Stress ◽  
Propagation Distance ◽  
Flood Basalt ◽  
Horizontal Stress ◽  
Principal Stresses ◽  
Stress Regime ◽  
Making Sense ◽  
Griffith Criterion ◽  
Uppermost Layer

Thrust fault-related landforms, smooth plains units, and impact craters and basins have all been observed on the surface of Mercury. While tectonic landforms point to a long-lived history of global cooling and contraction, smooth plains units have been inferred to represent more punctuated periods of effusive volcanism. The timings of these processes are inferred through impact cratering records to have overlapped, yet the stress regimes implied by the processes are contradictory. Effusive volcanism on Mercury is believed to have produced flood basalts through dikes, the propagation of which is dependent on being able to open and fill vertical tensile cracks when horizontal stresses are small. On the contrary, thrust faults propagate when at least one horizontal stress is very large relative to the vertical compressive stress. We made sense of conflicting stress regimes through modeling with frictional faulting theory and Earth analogue work. Frictional faulting theory equations predict that the minimum and maximum principal stresses have a predictable relationship when thrust faulting is observed. The Griffith Criterion and Kirsch equations similarly predict a relationship between these stresses when tensile fractures are observed. Together, both sets of equations limit the range of stresses possible when dikes and thrusts are observed and permitted us to calculate deviatoric stresses for regions of Earth and Mercury. Deviatoric stress was applied to test a physical model for dike propagation distance in the horizontally compressive stress regime of the Columbia River Flood Basalt Province, an Earth analogue for Borealis Planitia, the northern smooth plains, of Mercury. By confirming that dike propagation distances from sources observed in the province can be generated with the physical model, we confidently apply the model to confirm that dikes on Mercury can propagate in a horizontally compressive stress regime and calculate the depth to the source for the plains materials. Results imply that dikes could travel from ∼89 km depth to bring material from deep within the lithosphere to the surface, and that Mercury’s lithosphere is mechanically layered, with only the uppermost layer being weak.

scholarly journals Crustal stress regime in Italy

1997 ◽  
Vol 40 (3) ◽  
Author(s):  
P. Montone ◽  
A. Amato ◽  
A. Frepoli ◽  
M. T. Mariucci ◽  
M. Cesaro
Keyword(s):  
Horizontal Stress ◽  
Focal Mechanisms ◽  
Plate Motion ◽  
Stress Regime ◽  
Deep Wells ◽  
Stress Directions ◽  
Geothermal Wells ◽  
Borehole Breakouts ◽  
Well Data ◽  
Messina Strait

In order to obtain a reliable map of the present-day stress field in Italy, needed to better understand the active tectonic processes and to contribute to the assessment of seismic hazard, in 1992 we started to collect and analyze new data from borehole breakouts in deep oil and geothermal wells and focal mechanisms of earthquakes (2.5 < M <5) occurred in Italy between 1988 and 1995. From about 200 deep wells and 300 focal mechanisms analyzed to date, we infer that: the internal (SW) sector of the Northern Apenninic arc is extending with minimum compressional stress (Shmin) oriented ? ENE, while the external front is thrusting over the Adriatic foreland (Shmin ? NW-SE). The entire Southern Apennine is extending in NE direction (from the Tyrrhenian margin to the Apulian foreland) and compression (in the foredeep) is no longer active at the outer (NE) thrust front. Between these two arcs, an abrupt change in the tectonic regime is detected with directions of horizontal stress changing by as much as 90º in the external front, around latitude 430N. Along the Ionian side of the Calabrian arc the stress directions inferred from breakouts and focal mechanisms are scattered with a hint of rotation from N-S Shmin close to the Southern Apennines, to ~ E-W directions in the Messina Strait. In Sicily, a NW-SE direction of SHmax is evident in the Hyblean foreland, parallel to the direction of plate motion between Africa and Europe. A more complex pattern of stress directions is observed in the thrust belt zone, with rotations from the regional trend (NW í directed SHmax) to NE oriented SHmax. A predominant NW direction of SHmax is also detected in mainland Sicily from earthquake focal mechanisms, but no well data are available in this region. In the northern part of Sicily (Aeolian Islands) a ~N-S direction of SHmax is observed.

scholarly journals Evolution of the geological structure and mechanical properties due to the collision of multiple basement topographic highs in a forearc accretionary wedge: insights from numerical simulations

2022 ◽  
Vol 9 (1) ◽  
Author(s):  
Ayumu Miyakawa ◽  
Atsushi Noda ◽  
Hiroaki Koge
Keyword(s):  
Numerical Simulations ◽  
Pore Pressure ◽  
Compressive Stress ◽  
Plate Boundary ◽  
Structural Features ◽  
Geological Structure ◽  
Accretionary Wedge ◽  
Rapid Reduction ◽  
Compressive Stresses ◽  
Horizontal Compressive Stress

AbstractWe propose a conceptual geological model for the collision of multiple basement topographic highs (BTHs; e.g., seamounts, ridges, and horsts) with a forearc accretionary wedge. Even though there are many BTHs on an oceanic plate, there are few examples of modeling the collision of multiple BTHs. We conducted numerical simulations using the discrete element method to examine the effects of three BTH collisions with forearcs. The typical geological structure associated with a BTH collision was reproduced during the collision of the first BTH, and multiple BTH collisions create a cycle of formation of BTH collisional structures. Each BTH forces the basal décollement to move up to the roof décollement, and the roof décollement becomes inactive after the passage of the BTH, and then the décollement moves down to the base. As the active décollement position changes, the sequences of underthrust sediments and uplifted imbricate thrusts are sandwiched between the décollements and incorporated into the wedge. At a low horizontal compressive stress, a “shadow zone” is formed behind (i.e., seaward of) the BTH. When the next BTH collides, the horizontal compressive stress increases and tectonic compaction progresses, which reduce the porosity in the underthrust sediments. Heterogeneous evolution of the geological and porosity structure can generate a distinctive pore pressure pattern. The underthrust sediments retain fluid in the “shadow” of the BTH. Under the strong horizontal compressive stresses associated with the next BTH collision, pore pressure increases along with a rapid reduction of porosity in the underthrust sediments. The distinctive structural features observed in our model are comparable to the large faults in the Kumano transect of the Nankai Trough, Japan, where a splay fault branches from the plate boundary and there are old and active décollements. A low-velocity and high-pore-pressure zone is located at the bottom of the accretionary wedge and in front (i.e., landward) of the subducting ridge in the Kumano transect. This suggests that strong horizontal compressive stresses associated with the current BTH collision has increased the pore pressure within the underthrust sediments associated with previous BTHs.

scholarly journals Microseismicity in the central Southern Alps, Westland, New Zealand

2021 ◽  
Author(s):  
◽  
Carolin Boese
Keyword(s):  
Stress Field ◽  
Surface Waves ◽  
Compressive Stress ◽  
Tectonic Stress ◽  
Southern Alps ◽  
Focal Mechanisms ◽  
Tectonic Stress Field ◽  
Nodal Plane ◽  
Alpine Fault ◽  
Horizontal Compressive Stress

<p>Present-day seismicity associated with the central Alpine Fault and the zone of active deformation and rock uplift in the central Southern Alps is reported in this thesis. Robust hypocentre locations and magnitude estimates for ~2300 earthquakes have been obtained analysing 18 months of data from the Southern Alps Microearthquake Borehole Array (SAMBA), designed for this study. The earthquakes are distributed between the Alpine Fault and the Main Divide Fault zone and confined to shallow depths (90% of events ≤12.2 km). The thickness of the seismogenic zone follows lateral variations in crustal resistivity: earthquake hypocentres are restricted to depths where resistivities exceed 390 Ω m. Rocks at greater depth are interpreted to be too hot, too fluid-saturated, or too weak to produce detectable earthquakes. A low-seismicity zone extends between the Whataroa and Wanganui rivers at distances 15–30 km southeast of the fault, which is concluded to be a relatively strong, unfractured block that diverts deformation around it. A new magnitude scale is developed incorporating the effects of frequency-dependent attenuation, which enables magnitudes to be calculated consistently for earthquakes of different sizes and frequency contents. Focal mechanism solutions for 379 earthquakes exhibit predominantly strike-slip mechanisms. Inversion of these focal mechanisms to determine the prevailing tectonic stress field reveals a maximum horizontal compressive stress direction of 115±10°, consistent with findings from elsewhere in South Island. The 60° angle between the strike of the Alpine Fault and the direction of maximum horizontal compressive stress suggests that the Alpine Fault is poorly oriented in an Andersonian sense. Earthquake swarms of at least 10 events with similar waveforms frequently occur within the region, of which some were remotely triggered by two major South Island earthquakes. Focal mechanisms of the largest event in each swarm (ML≤2.8) reveal at least one steeply-dipping nodal plane (≥50°) and one well-oriented nodal plane in the tectonic stress field. The swarms exhibit a distinctly different inter-event time versus duration pattern from that of typical mainshock-aftershock sequences. The triggered seismicity commences with the passage of the surface waves, continues for ~5 and ~2 days, and is followed by a quiescence period of approximately equal length. Remotely triggered swarms occur delayed by several hours and their delay and locations are consistent with fluid diffusion from a shallow fluid reservoir. Estimated peak dynamic stresses (≥0.09 MPa) imposed by the surface waves are comparable to observations of triggering thresholds (>0.01 MPa) elsewhere. The triggered swarms have no apparent differences from the background swarms, and appear to have been clock-advanced. Tectonic tremor in the vicinity of the Alpine Fault coincides with a low-velocity, high-attenuation zone at depth. The tremor occurs at the downdip extension of the Alpine Fault and in the region where bending of the Australian and Pacific plates is largest at depths spanning 12–49 km. Similarities with tremor occurring on the San Andreas Fault near Cholame in terms of tremor duration, depth, spatial extent and amplitude distribution, imply property variations in the lower crust and upper mantle along the strike of the Alpine Fault.</p>

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