Correlation between tectonic stress regimes and methane seepage on the west of west-Svalbard margin

2018 ◽  
Author(s):  
Anonymous
Keyword(s):  
Tectonic Stress ◽  
The West ◽  
Methane Seepage

scholarly journals Correlation between tectonic stress regimes and methane seepage on the west-Svalbard margin

2018 ◽  
Author(s):  
Andreia Plaza-Faverola ◽  
Marie Keiding
Keyword(s):  
Fluid Pressure ◽  
Tectonic Stress ◽  
Temporal Variations ◽  
Passive Margin ◽  
Morphological Evidence ◽  
Glacial Cycles ◽  
The West ◽  
Stress Regime ◽  
Near Surface ◽  
Methane Seepage

Abstract. Methane seepage occurs across the west-Svalbard margin at water depths ranging from the upper shelf at  1000 m. The Vestnesa sedimentary ridge, located on oceanic crust between 1000–1700 m water depth, hosts a perennially stable gas hydrate system with evidence of both past and present-day seepage. On the ridge, an eastward transition from a zone with clear morphological evidence of past seepage to a zone of active present-day seepage coincides with a change in the faulting pattern of near-surface strata. We modelled the tectonic stress regime due to oblique spreading along the Molloy and Knipovich spreading ridges to investigate whether spatial and temporal variations in the regional stress field may explain patterns of seepage distribution. The model reveals a zone of tensile stress that extends northward from the Knipovich Ridge and encompasses a zone of active seepage and extensional faulting. A zone of past seepage is presently located in a strike-slip regime. Our modelling results suggest that seepage is promoted by opening of faults and fractures in a tensile regime. We develop a conceptual model to describe how seepage may be controlled by an interplay between tectonic stresses and pore fluid pressure within shallow gas reservoirs across the passive margin off west-Svalbard. Glacio-isostatic flexural stresses may have influenced fluid dynamics along the Vestnesa Ridge in the past, explaining the presence of dormant pockmarks outside the ridge segment that is under a tensile regime at present and reconciling formerly suggested models of seepage periodicity linked to glacial cycles.

scholarly journals Study on the relationship between multi-stage strike-slip mechanism and basin evolution in Fangzheng fault depression

2018 ◽  
Vol 22 (4) ◽  
pp. 335-339
Author(s):  
Jingfeng Wu ◽  
Qi'an Meng ◽  
Xiaofei Fu ◽  
Yuling Ma ◽  
Meifeng Sun ◽  
...  
Keyword(s):  
Seismic Data ◽  
Structural Characteristics ◽  
Stage Structure ◽  
Tectonic Stress ◽  
Strike Slip ◽  
The West ◽  
Lateral Strike Slip ◽  
Slip Mechanism ◽  
Pull Apart Basin ◽  
Multi Stage

Fangzheng fault depression is controlled by the northern of the Tan-Lu fault zone. It undergoes multi-stage strike-slip, extrusion modification, and erosion of the thermal uplift, forming a tectonic pattern of uplifts connected with sags. Through the regional dynamic analysis, the study of the activity law of the western Pacific plate has clarified the formation and transformation of the regional tectonic stress field. Under the background of the multi-stage of the strike-slip mechanism in the northern part of the Tan-lu fault, the Fangzheng fault depression has a characteristic of the “left-lateral strike-slip pull-apart basin, right-lateral strike-slip extrusion transformation.” According to the difference of the strike-slip, the Fangzheng fault depression has divided into two parts: the East fault depression and the West fault depression. The seismic data, seismic attribute analysis, and geological modeling techniques have applied to analyze the two fault depressions, the East fault depression has actively controlled by the strike-slip activity, and the structure is complex. The seismic data quality is poor; the structure of the West Fault Depression is the opposite and structural characteristics of asymmetrical difference strike-slip in the East and West fault depressions. Interpretation of seismic sections through a slippery background, the strike-slip attributes of the whole fault depression from south to north are segmented, and the strike-slip mechanism from east to west is different. Under the control of the multi-stage strike-slip mechanism, the Fangzheng fault depression is divided into six stages of strike-slip evolution, corresponding to the six different stages of the strike-slip control basin, the formation process of the asymmetric difference strike-slip fault basin is clarified, which provides a reference for the study of the strike-slip pull-apart basin with multi-stage structure.

scholarly journals Velocity structure and the role of fluids in the West Bohemia Seismic Zone

2014 ◽  
Vol 6 (1) ◽  
pp. 511-534
Author(s):  
C. Alexandrakis ◽  
M. Calò ◽  
F. Bouchaala ◽  
V. Vavryčuk
Keyword(s):  
Velocity Structure ◽  
Weighted Average ◽  
Tectonic Stress ◽  
Double Difference ◽  
Seismic Zone ◽  
The West ◽  
Fluid Concentration ◽  
West Bohemia ◽  
Basic Characteristics ◽  
Tomography Method

Abstract. In this study, we apply the double-difference tomography method to investigate the detailed 3-D structure within and around the Nový Kostel seismic zone, an area in the Czech Republic known for frequent occurrences of earthquake swarms. We use data from the extensively analyzed 2008 swarm, which has known focal mechanisms, principal faults, tectonic stress, source migration and other basic characteristics. We selected about 500 microearthquakes recorded at 22 local seismic stations of the West Bohemia Network (WEBNET). Applying double-difference tomography, combined with Weighted Average Model post-processing to correct for parameter dependence effects, we produce and interpret 3-D models of the Vp-to-Vs ratio (Vp/Vs) in and around the focal zone. The modeled Vp-to-Vs ratio shows several distinct structures, namely an area of high Vp-to-Vs ratio correlating with the microearthquakes, and a layer of low values directly above it. These structures may reflect changes in lithology and/or fluid concentration. The overlaying low Vp-to-Vs ratio layer coincides with high density metamorphic unit associated with the Fichtelgebirge (Smrčiny) granitic intrusion. It is possible that the base of the layer acts as a fluid trap, resulting in the observed periodic swarms.

scholarly journals Correlation between tectonic stress regimes and methane seepage on the western Svalbard margin

Solid Earth ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 79-94 ◽  
Author(s):  
Andreia Plaza-Faverola ◽  
Marie Keiding
Keyword(s):  
Gas Hydrate ◽  
Surface Deformation ◽  
Tectonic Stress ◽  
Maximum Principal Stress ◽  
Stress Regime ◽  
Near Surface ◽  
Ocean Ridges ◽  
Methane Seepage ◽  
Lithospheric Flexure ◽  
State Of Stress

Abstract. Methane seepage occurs across the western Svalbard margin at water depths ranging from < 300 m, landward from the shelf break, to > 1000 m in regions just a few kilometres from the mid-ocean ridges in the Fram Strait. The mechanisms controlling seepage remain elusive. The Vestnesa sedimentary ridge, located on oceanic crust at a depth of 1000–1700 m, hosts a perennial gas hydrate and associated free gas system. The restriction of the occurrence of acoustic flares to the eastern segment of the sedimentary ridge, despite the presence of pockmarks along the entire ridge, indicates a spatial variation in seepage activity. This variation coincides with a change in the faulting pattern as well as in the characteristics of the fluid flow features. Due to the position of the Vestnesa Ridge with respect to the Molloy and Knipovich mid-ocean ridges, it has been suggested that seepage along the ridge has a tectonic control. We modelled the tectonic stress regime due to oblique spreading along the Molloy and Knipovich ridges to investigate whether spatial variations in the tectonic regime along the Vestnesa Ridge are plausible. The model predicts a zone of tensile stress that extends northward from the Knipovich Ridge and encompasses the zone of acoustic flares on the eastern Vestnesa Ridge. In this zone the orientation of the maximum principal stress is parallel to pre-existing faults. The model predicts a strike-slip stress regime in regions with pockmarks where acoustic flares have not been documented. If a certain degree of coupling is assumed between deep crustal and near-surface deformation, it is possible that ridge-push forces have influenced seepage activity in the region by interacting with the pore-pressure regime at the base of the gas hydrate stability zone. More abundant seepage on the eastern Vestnesa Ridge at present may be facilitated by the dilation of faults and fractures favourably oriented with respect to the stress field. A modified state of stress in the past, due to more significant glacial stress for instance, may explain vigorous seepage activity along the entire Vestnesa Ridge. The contribution of other mechanisms to the state of stress (i.e. sedimentary loading and lithospheric flexure) remain to be investigated. Our study provides a first-order assessment of how tectonic stresses may be influencing the kinematics of near-surface faults and associated seepage activity offshore of the western Svalbard margin.

scholarly journals Сollision deformations of the Dnieper-Donets Depression. Article 2. Kinematic mechanisms of tectonic inversion

2019 ◽  
Vol 4 (181) ◽  
pp. 32-44
Author(s):  
Оleksiy BARTASHCHUK
Keyword(s):  
Tectonic Stress ◽  
Geological Mapping ◽  
Donets Basin ◽  
The West ◽  
Late Mesozoic ◽  
Left Hand ◽  
Folded Structure ◽  
Tectonic Inversion ◽  
Kinematic Mechanisms ◽  
Kinematic Mechanism

The second article is devoted to the investigation of the natural mechanisms of tectonic inversion of the Dnieper-Donets depression. Using the materials of geological mapping of the territory of the West-Donetsk graben, structural proofs of the destruction of the riftogenic structure by collision tectonic movements of Hercinian and Alpic tectogenesis were obtained. The consequence of the inversion deformations is the formation of the West Donets cover-folding tectonic region within the Lugansk-Komyshuvasky tectonic area of the uplift-folding and the Kalmius-Toretsky region of the scalloped thrust covers, which are divided by the Main anticline. For the diagnosis of kinematic mechanisms of tectonic inversion, the data of reconstruction of tectonic stress fields and quantitative modeling of deformations of the southern outskirts of the Eastern European Platform were used. It is assumed that the tectonic inversion of the Dnieper-Donets basin began in the Zaal and Pfalz phases of orogenesis due to the collision motions of the compression orogen at the outskirts of Paleotetis. The formation of linear folding occurred in the uplifting-thrust mode in the field of stresses of the oblique left-hand compression of the sub-meridional directions. The kinematic mechanism of the folded deformations determined the longitudinal bending of the layers due to the extrusion of sedimentary geomas from the zone of maximum compression in the axial part to the zones of “geodynamic shadow” – in the direction of the sides of the depression. In the late Mesozoic and Cenozoic, uplifting-thrust and strike-slip stresses formed echeloned cover-thrust and coulisse-jointed uplift-folded structural paragenesis. According to the results of tectonophysical diagnostics of deformation structures, it was found that under geodynamic conditions of clustering of compression axes in the central part of the West-Donets graben against the reduction of the geological space horizontally and extension of the section due to the formation of the cover-folded allochthon, there were flexural deformations of the primary linear Hercinian folded forms. Such data can be considered as a kinematic mechanism of tectonic inversion of the invasion of the “tectonic stamp” by the Donets folded structure. Under its influence, the wedge-shaped segment of the tectonic thrust, which was diagnosed by the orcline of the transverse extension of the shallow type, was formed by the repeatedly deposited folds of sedimentary geomas in the articulation zone between the depression and the folded structure. In the front of the thrusted were formed folded zones of extrusion of geomas, which consist of coulisse-jointed uplift-anticlines and folded plates-coverings of tectonic thrusted. At the apex of the orocline, at the end of the dynamically coupled main thrusts, an advanced tectonic fan of compression is formed. In the rearward of the oraclline formed sutures – the roots of folded cover.

scholarly journals Velocity structure and the role of fluids in the West Bohemia Seismic Zone

Solid Earth ◽  
2014 ◽  
Vol 5 (2) ◽  
pp. 863-872 ◽  
Author(s):  
C. Alexandrakis ◽  
M. Calò ◽  
F. Bouchaala ◽  
V. Vavryčuk
Keyword(s):  
Velocity Structure ◽  
Weighted Average ◽  
Monitoring Network ◽  
Tectonic Stress ◽  
Double Difference ◽  
Seismic Zone ◽  
The West ◽  
Fluid Concentration ◽  
West Bohemia ◽  
Weighted Average Model

Abstract. In this study, we apply the double-difference tomography to investigate the detailed 3-D structure within and around the Nový Kostel Seismic Zone, an area in the Czech Republic known for frequent occurrences of earthquake swarms. We use data from the 2008 swarm since it has already been analysed in terms of earthquake focal mechanisms, principal faults, tectonic stress and foci migration. We selected about 500 microearthquakes recorded at 22 local seismic stations of the West Bohemia seismic monitoring network (WEBNET). Applying double-difference tomography, combined with weighted average model (WAM) post-processing to correct for parameter dependence effects, we produce and interpret 3-D models of the Vp-to-Vs ratio (Vp/Vs) in and around the focal zone. The modelled Vp/Vs ratio shows several distinct structures, namely an area of high Vp/Vs ratio correlating with the foci of the microearthquakes, and a layer of low values directly above it. These structures may reflect changes in lithology and/or fluid concentration. The overlaying low Vp/Vs ratio layer coincides with the base of the Fichtelgebirge (Smrčiny) granitic intrusion. It is possible that the base of the layer acts as a fluid trap and an upper limit to the seismicity, resulting in observed periodic swarms.

scholarly journals New data on the latest stress state of the earth’s crust on Sakhalin Island (based on structural and geomorphological indicators of tectonic stress)

2020 ◽  
Vol 4 (4) ◽  
pp. 372-383
Author(s):  
L.A. Sim ◽  
◽  
P.A. Kamenev ◽  
L.M. Bogomolov ◽  
◽  
...  
Keyword(s):  
Stress State ◽  
Crustal Deformation ◽  
Field Measurements ◽  
Field Work ◽  
Tectonic Stress ◽  
Strike Slip ◽  
The West ◽  
North Eastern ◽  
Central Sakhalin Fault ◽  
Entire Island

To verify the ideas about neotectonic and modern stresses of Sakhalin, we analyze structural and geomorphological signs of the stress state of this region, discovered during field work in 2019–2020. Along with updated field measurements using the structural-geomorphological method, data on crustal deformation based on GPS/GLONASS measurements are presented. Data from geophysical studies (seismological and borehole methods) are given. The identification of three types of areas with different geodynamic regime: transtension, transpression and strike – slip (simple shift) is confirmed. Variations of the current stress field at the boundaries of regions with different geodynamic regime for the formation of new faults are noted. Northern Sakhalin has specific directions of compression axes of neotectonic stresses, expressed in North-Eastern orientations, in contrast to the prevailing sublatitudinal orientations on the entire island. Studies have shown that in the south of Sakhalin, the border between the Amur and Okhotsk microplates runs along the West Sakhalin fault rather than the Central Sakhalin fault.

Enumeration and Identification of Asbestos Fibres in Water

1974 ◽  
Vol 32 ◽  
pp. 526-527 ◽  
Author(s):  
O. Mudroch ◽  
J. R. Kramer
Keyword(s):  
Water Supply ◽  
Water Samples ◽  
Drainage Basin ◽  
Lake Superior ◽  
Research Work ◽  
List Type ◽  
The West ◽  
Asbestos Fibre ◽  
Amphibole Asbestos

Approximately 60,000 tons per day of waste from taconite mining, tailing, are added to the west arm of Lake Superior at Silver Bay. Tailings contain nearly the same amount of quartz and amphibole asbestos, cummingtonite and actinolite in fibrous form. Cummingtonite fibres from 0.01μm in length have been found in the water supply for Minnesota municipalities.The purpose of the research work was to develop a method for asbestos fibre counts and identification in water and apply it for the enumeration of fibres in water samples collected(a) at various stations in Lake Superior at two depth: lm and at the bottom.(b) from various rivers in Lake Superior Drainage Basin.

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