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 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.

Hydroselsmicity: A Hypothesis for The Role of Water in the Generation of Intraplate Seismicity

1987 ◽  
Vol 58 (3) ◽  
pp. 41-64 ◽  
Author(s):  
John K. Costain ◽  
G. A. Bollinger ◽  
J. Alexander Speer
Keyword(s):  
Fluid Pressure ◽  
Tectonic Stress ◽  
Surface Flow ◽  
Intraplate Seismicity ◽  
Fracture Permeability ◽  
Intraplate Earthquakes ◽  
Near Surface ◽  
Gravity Driven ◽  
Groundwater Basins

Abstract A new hypothesis termed Hydroseismicity that has hydrologic (diffusion of pore pressure transients from recharge areas of groundwater basins), geologic (rifted, fractured crust), and chemical (solubility of minerals) elements is proposed to explain the role of water in the generation of intraplate seismicity. Its basis is a spatial correlation in the southeastern U. S. between 1) seismogenic crustal volumes of high seismicity, 2) large gravity-driven river basins that can provide an adequate supply of water to the upper- and mid-crust, and 3) a permeable crust that is tectonically stressed close to failure. It is suggested that in crustal volumes with a combination of connected fractures and adequate groundwater, natural transient increases in hydraulic head in recharge areas of groundwater basins can be transmitted to depths of 10–20 km, and thereby trigger earthquakes, via a flow-path geometry that resembles except for scale the model familiar to groundwater hydrologists for near-surface flow. Possible trigger mechanisms for Hydroseismicity include small increases in fluid pressure at hypocentral depths caused by such transient increases, and hydrolytic weakening of minerals that leads to structural weakening. Implicit in the model is a diffuse distribution of epicenters (as is observed in the region) rather than concentrations along discrete geologie (faults) or geomorphic (rivers) elements. Open fractures imply fracture roughness, i.e., asperities under a higher stress that keep fractures open even in an ambient tectonic stress field. Intraplate earthquakes in a fractured crust prestressed to near-failure are thus postulated to be triggered by small transient increases in fluid pressure transmitted along preexisting fractures in a rock fabric weakened by stress corrosion of asperities. Abundant petrologic evidence is available to justify an assumption of fracture permeability to depths of 20 km near passive rifted margins. All four principal seismogenic volumes in the southeastern U. S. are within gravity-driven groundwater basins that can provide an abundant supply of water to the ernst, and that intersect known or suspected Eocambrian or Mesozoic rifted crust. The host basins have the largest surface recharge areas and contain rivers with the highest average stream gradients as measured from their headwaters to the Fall Line. Seismicity in the region is characterized by steeply dipping focal mechanism nodal planes and diffuse alignments and/or clusters of epicenters. These characteristics are compatible with a steep to vertical fracture fabric currently being reactivated by porc pressure diffusion from surface recharge of groundwater basins.

TECTONIC STRESS REGIME RECORDED IN ZIRCON TH/U

2017 ◽  
Author(s):  
Matthew P. McKay ◽  
◽  
William T. Jackson
Keyword(s):  
Tectonic Stress ◽  
Stress Regime

Present-day tectonic stress regime in Egypt and surrounding area based on inversion of earthquake focal mechanisms

2013 ◽  
Vol 81 ◽  
pp. 1-15 ◽  
Author(s):  
H.M. Hussein ◽  
K.M. Abou Elenean ◽  
I.A. Marzouk ◽  
I.M. Korrat ◽  
I.F. Abu El-Nader ◽  
...  
Keyword(s):  
Tectonic Stress ◽  
Focal Mechanisms ◽  
Surrounding Area ◽  
Stress Regime ◽  
Earthquake Focal Mechanisms

Recruitment of the barnacle Balanus amphitrite in a tropical estuary: implications of environmental perturbation, reproduction and larval ecology

2005 ◽  
Vol 85 (4) ◽  
pp. 909-920 ◽  
Author(s):  
Dattesh V. Desai ◽  
A.C. Anil
Keyword(s):  
Temporal Variations ◽  
Larval Abundance ◽  
Balanus Amphitrite ◽  
Larval Ecology ◽  
The West ◽  
Environmental Perturbation ◽  
Recruitment Failure ◽  
Acorn Barnacle ◽  
New Recruits ◽  
Impulsive Release

Phytoplankton blooms are known to influence barnacle recruitment and in boreal regions spring blooms work as an important trigger. Close to the west coast of the sub-continent of India, blooms tend to be triggered by breaks in the monsoon and the recurrence of the monsoon after a short break can stress the new recruits. The recruitment of Balanus amphitrite, an acorn barnacle, at Dona Paula Bay at the mouth of Zuari estuary, Goa, India was studied. Observations included variations in recruitment, larval abundance, development and reproduction. Adult conditioning and inter-brood variations were important factors in the larval ecology of this organism. The results indicate that the impulsive release of larvae during breaks between monsoons could be a short-sighted luxury for Balanus amphitrite in these waters. Temporal variations or recruitment failure in such environments can be attributed to inappropriate cue synchronization.

Time Constraints on Seepage Through Fractured Regions on the Vestnesa Ridge off the W-Svalbard Coast

2021 ◽  
Author(s):  
Hariharan Ramachandran ◽  
Andreia Plaza-Faverola ◽  
Hugh Daigle ◽  
Stefan Buenz
Keyword(s):  
Fluid Flow ◽  
Effective Stress ◽  
Gas Hydrate ◽  
Fluid Pressure ◽  
Fracture Network ◽  
The Arctic ◽  
Stability Zone ◽  
Methane Seepage ◽  
Carbonate Formation ◽  
Hydrate Stability

&lt;p&gt;Evidences of subsurface fluid flow-driven fractures (from seismic interpretation) are quite common at Vestnesa Ridge (around 79&amp;#186;N in the Arctic Ocean), W-Svalbard margin. Ultimately, the fractured systems have led to the formation of pockmarks on the seafloor. At present day, the eastern segment of the ridge has active pockmarks with continuous methane seep observations in sonar data. The pockmarks in the western segment are considered inactive or to seep at a rate that is harder to identify. The ridge is at ~1200m water depth with the base of the gas hydrate stability zone (GHSZ) at ~200m below the seafloor. Considerable free gas zone is present below the hydrates. Besides the obvious concern of amount and rates of historic methane seeping into the ocean biosphere and its associated effects, significant gaps exist in the ability to model the processes of flow of methane through this faulted and fractured region. Our aim is to highlight the interactions between physical flow, geomechanics and geological control processes that govern the rates and timing of methane seepage.&lt;/p&gt;&lt;p&gt;For this purpose, we performed numerical fluid flow simulations. We integrate fundamental mass and component conservation equations with a phase equilibrium approach accounting for hydrate phase boundary effects to simulate the transport of gas from the base of the GHSZ through rock matrix and interconnected fractures until the seafloor. The relation between effective stress and fluid pressure is considered and fractures are activated once the effective stress exceeds the tensile limit. We use field data (seismic, oedometer tests on calypso cores, pore fluid pressure and temperature) to constrain the range of validity of various flow and geomechanical parameters in the simulation (such as vertical stress, porosity, permeability, saturations).&lt;/p&gt;&lt;p&gt;Preliminary results indicate fluid overpressure greater than 1.5 MPa is required to initiate fractures at the base of the gas hydrate stability zone for the investigated system. Focused fluid flow occurs through the narrow fracture networks and the gas reaches the seafloor within 1 day. The surrounding regions near the fracture network exhibit slower seepage towards the seafloor, but over a wider area. Advective flux through the less fractured surrounding regions, reaches the seafloor within 15 years and a diffusive flux reaches within 1200 years. These times are controlled by the permeability of the sediments and are retarded further due to considerable hydrate/carbonate formation during vertical migration. Next course of action includes constraining the methane availability at the base of the GHSZ and estimating its impact on seepage behavior.&lt;/p&gt;

scholarly journals Absorption coefficient of urban aerosol in Nanjing, west Yangtze River Delta, China

2015 ◽  
Vol 15 (23) ◽  
pp. 13633-13646 ◽  
Author(s):  
B. L. Zhuang ◽  
T. J. Wang ◽  
J. Liu ◽  
Y. Ma ◽  
C. Q. Yin ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Urban Area ◽  
Yangtze River ◽  
Temporal Variations ◽  
Yangtze River Delta ◽  
River Delta ◽  
Near Surface ◽  
Absorbing Aerosols ◽  
The Impact ◽  
532 Nm

Abstract. Absorbing aerosols can significantly modulate short-wave solar radiation in the atmosphere, affecting regional and global climate. The aerosol absorption coefficient (AAC) is an indicator that assesses the impact of absorbing aerosols on radiative forcing. In this study, the near-surface AAC and absorption Ångström exponent (AAE) in the urban area of Nanjing, China, are characterized on the basis of measurements in 2012 and 2013 using the seven-channel Aethalometer (model AE-31, Magee Scientific, USA). The AAC is estimated with direct and indirect corrections, which result in consistent temporal variations and magnitudes of AAC at 532 nm. The mean AAC at 532 nm is about 43.23 ± 28.13 M m−1 in the urban area of Nanjing, which is much lower than that in Pearl River Delta and the same as in rural areas (Lin'an) in Yangtze River Delta. The AAC in the urban area of Nanjing shows strong seasonality (diurnal variations); it is high in cold seasons (at rush hour) and low in summer (in the afternoon). It also shows synoptic and quasi-2-week cycles in response to weather systems. Its frequency distribution follows a typical log-normal pattern. The 532 nm AAC ranging from 15 to 65 M m−1 dominates, accounting for more than 72 % of the total data samples in the entire study period. Frequent high pollution episodes, such as those observed in June 2012 and in winter 2013, greatly enhanced AAC and altered its temporal variations and frequency distributions. These episodes are mostly due to local emissions and regional pollution. Air masses flowing from northern China to Nanjing can sometimes be highly polluted and lead to high AAC at the site. AAE at 660/470 nm from the Schmid correction (Schmid et al., 2006) is about 1.56, which might be more reasonable than from the Weingartner correction (Weingartner et al., 2003). Low AAEs mainly occur in summer, likely due to high relative humidity (RH) in the season. AAC increases with increasing AAE at a fixed aerosol loading. The RH–AAC relationship is more complex. Overall, AAC peaks at RH values of around 40 % (1.3 < AAE < 1.6), 65 % (AAE < 1.3 and AAE > 1.6), and 80 % (1.3 < AAE < 1.6).

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