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1.
We present an efficient methodology for assessing leakage detectability at geologic carbon sequestration sites under parameter uncertainty. Uncertainty quantification (UQ) and risk assessment are integral and, in many countries, mandatory components of geologic carbon sequestration projects. A primary goal of risk assessment is to evaluate leakage potential from anthropogenic and natural features, which constitute one of the greatest threats to the integrity of carbon sequestration repositories. The backbone of our detectability assessment framework is the probability collocation method (PCM), an efficient, nonintrusive, uncertainty-quantification technique that can enable large-scale stochastic simulations that are based on results from only a small number of forward-model runs. The metric for detectability is expressed through an extended signal-to-noise ratio (SNR), which incorporates epistemic uncertainty associated with both reservoir and aquifer parameters. The spatially heterogeneous aquifer hydraulic conductivity is parameterized using Karhunen–Loève (KL) expansion. Our methodology is demonstrated numerically for generating probability maps of pressure anomalies and for calculating SNRs. Results indicate that the likelihood of detecting anomalies depends on the level of uncertainty and location of monitoring wells. A monitoring well located close to leaky locations may not always yield the strongest signal of leakage when the level of uncertainty is high. Therefore, our results highlight the need for closed-loop site characterization, monitoring network design, and leakage source detection. 相似文献
2.
Patrick Allard 《Journal of Volcanology and Geothermal Research》2010,189(3-4):363-374
In addition to rhythmic slug-driven Strombolian activity, Stromboli volcano occasionally produces discrete explosive paroxysms (2 per year on average for the most frequent ones) that constitute a major hazard and whose origin remains poorly elucidated. Partial extrusion of the volatile-rich feeding basalt as aphyric pumice during these events has led to consider their triggering by the fast ascent of primitive magma blobs from possibly great depth. Here I examine and discuss the alternative hypothesis that most of the paroxysms could be triggered and driven by the fast upraise of CO2-rich gas pockets generated by bubble foam growth and collapse in the sub-volcano plumbing system. Data for the SO2 and CO2 crater plume emissions are used to show that Stromboli's feeding magma may originally contain as much as 2 wt.% of carbon dioxide and early coexists with an abundant CO2-rich gas phase with high CO2/SO2 molar ratio (≥ 60 at 10 km depth below the vents, compared to ～ 7 in time-averaged crater emissions). Pressure-related modelling indicates that the time-averaged crater gas composition and output are well accounted for by closed system decompression of the basalt–gas mixture until the volcano–crust interface (～ 3 km depth), followed by open degassing and crystallization in the volcano conduits. However, both the low viscosity and high vesicularity of the basaltic magma permit bubble segregation and bubble foam growth at deep sill-like feeder discontinuities and at shallower physical boundaries (such as the volcano–crust interface) where the gas-rich aphyric basalt interacts with the unerupted crystal-rich and viscous magma drained back from the volcano conduits. Gas pressure build-up and bubble foam collapse at these boundaries will intermittently trigger the sudden upraise of CO2-rich gas blobs that constitute the main driving force of the paroxysms. Deeper-sourced gas blobs, driving the most powerful explosions, will be the richest in CO2 and have highest CO2/SO2 ratios. This mechanism is shown to account well for the dynamic, seismic and petrologic features of Stromboli's paroxysms and, hence, to provide a potential alternative interpretation for their genesis and their forecasting. Enhanced bubble foam leakage prior to a paroxysm, or foam emptying in several steps, should lead indeed to precursory upstream of CO2-rich gas and increasing CO2/SO2 ratio in crater plume emissions. The recent detection of such signals prior to two explosions in December 2006 and March 2007 strongly supports this expectation and the model proposed in this study. 相似文献
3.
Carbon dioxide injection into deep saline formations may induce large‐scale pressure increases and migration of native fluid. Local high‐conductivity features, such as improperly abandoned wells or conductive faults, could act as conduits for focused leakage of brine into shallow groundwater resources. Pressurized brine can also be pushed into overlying/underlying formations because of diffuse leakage through low‐permeability aquitards, which occur over large areas and may allow for effective pressure bleed‐off in the storage reservoirs. This study presents the application of a recently developed analytical solution for pressure buildup and leakage rates in a multilayered aquifer‐aquitard system with focused and diffuse brine leakage. The accuracy of this single‐phase analytical solution for estimating far‐field flow processes is verified by comparison with a numerical simulation study that considers the details of two‐phase flow. We then present several example applications for a hypothetical CO2 injection scenario (without consideration of two‐phase flow) to demonstrate that the new solution is an efficient tool for analyzing regional pressure buildup in a multilayered system, as well as for gaining insights into the leakage processes of flow through aquitards, leaky wells, and/or leaky faults. This solution may be particularly useful when a large number of calculations needs to be performed, that is, for uncertainty quantification, for parameter estimation, or for the optimization of pressure‐management schemes. 相似文献
4.
Since late 2002, a continuous automatic monitoring network is operating in Tuscany, Central Italy, to investigate the geochemical response of selected aquifers to local seismic activity. The monitoring is aimed at identifying possible earthquake geochemical precursors. The network is currently constituted by six stations, all equipped with sensors for the measurement of temperature, pH, redox potential, electrical conductivity, CO2 and CH4 dissolved concentration, that have been installed in the areas of highest seismic risk of the region. By combining geochemical data gathered from the automatic station of Gallicano (Garfagnana, Northern Tuscany), and obtained via chemical analyses of spring water samples collected during periodic field surveys in the area surrounding this station, the most significant aspects of the deep fluid circulation paths feeding the Gallicano thermo-mineral system have been investigated, and the geochemical baseline of the Gallicano spring defined. The CO2 continuous signal recorded by the Gallicano automatic station has been then processed over the period 2003–2013 in the search for anomalies possibly related to local seismic activity. A substantial anomaly in CO2 content has been observed at Gallicano in conjunction with the Alpi Apuane earthquake (M = 5.2) of 21 June 2013. 相似文献
5.
In general, the rate and timing of calcite precipitation is in part affected by variations in cave air CO2 concentrations. Knowledge of cave ventilation processes is required to quantify the effect variations in CO2 concentrations have on speleothem deposition rates and thus paleoclimate records. In this study we use radon-222 (222Rn) as a proxy of ventilation to estimate CO2 outgassing from the cave to the atmosphere, which can be used to infer relative speleothem deposition rates. Hollow Ridge Cave, a wild cave preserve in Marianna, Florida, is instrumented inside and out with multiple micro-meteorological sensor stations that record continuous physical and air chemistry time-series data. Our time series datasets indicate diurnal and seasonal variations in cave air 222Rn and CO2 concentrations, punctuated by events that provide clues to ventilation and drip water degassing mechanisms. Average cave air 222Rn and CO2 concentrations vary seasonally between winter (222Rn = 50 dpm L? 1, where 1 dpm L? 1 = 60 Bq m? 3; CO2 = 360 ppmv) and summer (222Rn = 1400 dpm L? 1; CO2 = 3900 ppmv). Large amplitude diurnal variations are observed during late summer and autumn (222Rn = 6 to 581 dpm L? 1; CO2 = 360 to 2500 ppmv).We employ a simple first-order 222Rn mass balance model to estimate cave air exchange rates with the outside atmosphere. Ventilation occurs via density driven flow and by winds across the entrances which create a ‘venturi’ effect. The most rapid ventilation occurs 25 m inside the cave near the entrance: 45 h? 1 (1.33 min turnover time). Farther inside (175 m) exchange is slower and maximum ventilation rates are 3 h? 1 (22 min turnover time). We estimate net CO2 flux from the epikarst to the cave atmosphere using a CO2 mass balance model tuned with the 222Rn model. Net CO2 flux from the epikarst is highest in summer (72 mmol m? 2 day? 1) and lowest in late autumn and winter (12 mmol m? 2 day? 1). Modeled ventilation and net CO2 fluxes are used to estimate net CO2 outgassing from the cave to the atmosphere. Average net CO2 outgassing is positive (net loss from the cave) and is highest in late summer and early autumn (about 4 mol h? 1) and lowest in winter (about 0.5 mol h? 1). Modeling of ventilation, net CO2 flux from the epikarst, and CO2 outgassing to the atmosphere from cave monitoring time-series can help better constrain paleoclimatic interpretations of speleothem geochemical records. 相似文献
6.
Deep saline aquifers are commonly used for disposal and storage of various surface fluids. The target injection zone must be hydraulically isolated from overlying zones in order to ensure containment of the injected fluids. Improperly plugged nonoperational abandoned wells that penetrate the injection zone are the main potential leakage pathways. Leakage through such wells may cause an observable pressure signal in a zone overlying the injection zone; such a signal can be used to detect the leakage. In this paper we develop an analytical model to evaluate the pressure change induced by leakage through a well in a multilayer system. Unlike previous analytical models on the topic, our model uses a closed system, which may significantly affect the strength and behavior of the pressure signal induced by leakage. The analytical model is first presented for a two-layer system centered at the leaky well location. We evaluate the leakage-induced pressure change using the Laplace transform of Duhamel’s superposition integral, yielding the solution in the Laplace domain. We then derive a late-time asymptotic solution using the final value theorem, which suggests that the leakage rate becomes constant after sufficient time. We then obtain the multilayer solution by extending the two-layer solution and presenting it in matrix form in the Laplace domain. We apply the solution to three examples. In the first example, we apply the analytical model to a two-layer system, investigating its behavior and comparing the results with a numerical solution. In order to demonstrate behavior and potential applications of the multilayer analytical model, we present two multilayer examples: one with identical layers and another, replicating a CO2 storage site, with dissimilar layers. The leakage-induced pressure change does not necessarily decrease as the distance increases from the injection zone toward the surface. 相似文献
7.
The Oligocene to present evolution of the North Patagonian Andes is analyzed linking geological and geophysical data in order to decipher the deformational processes that acted through time and relate them to basin formation processes. Seismic reflection profiles reveal the shallow structure of the retroarc area where contractional structures, associated with Oligocene to early Miocene inverted extensional depocenters, are partially onlapped by early to late Miocene synorogenic deposits. From the construction of five structural cross sections along the retroarc area between 40° and 43°30′ S, constrained by surface, gravity and seismic data, a shortening gradient is observed along Andean strike. The highest shortening of 18.7 km (15.34%) is determined near 41°30′ S coincidentally with maximum mean topographic values on the eastern Andean slope, where basement blocks were uplifted in the orogenic front area, and the deepest and broadest synorogenic depocenters were formed towards the foreland. Additionally, eastward shifting of Miocene calc-alkaline rocks occurred at these latitudes, which is interpreted as indicative of a change in the subduction parameters at this time. Deep crustal retroarc structure is evaluated through inversion of gravity models that made possible to infer Moho attenuated zones. These coincide with the occurrence of younger than 5 Ma within-plate volcanics as well as with crustal thermal anomalies suggested by shallowing of the Curie isotherm calculated from magnetic data. Younger volcanism and thermal anomalies are explained by slab steepening since early Pliocene, after a mild-shallow subduction setting in the middle to late Miocene, age of the main compressive event. 相似文献
8.
The selection and the subsequent design of a subsurface CO2 storage system are subject to considerable uncertainty. It is therefore important to assess the potential risks for health, safety and environment. This study contributes to the development of methods for quantitative risk assessment of CO2 leakage from subsurface reservoirs. The amounts of leaking CO2 are estimated by evaluating the extent of CO2 plumes after numerically simulating a large number of reservoir realizations with a radially symmetric, homogeneous model. To conduct the computationally very expensive simulations, the ‘CO2 Community Grid’ was used, which allows the execution of many parallel simulations simultaneously. The individual realizations are set up by randomly choosing reservoir properties from statistical distributions. The statistical characteristics of these distributions have been calculated from a large reservoir database, holding data from over 1200 reservoirs. An analytical risk equation is given, allowing the calculation of average risk due to multiple leaky wells with varying distance in the surrounding of the injection well. The reservoir parameters most affecting risk are identified. Using these results, the placement of an injection well can be optimized with respect to risk and uncertainty of leakage. The risk and uncertainty assessment can be used to determine whether a site, compared to others, should be considered for further investigations or rejected for CO2 storage. 相似文献
9.
Pantelleria Island, located in the Sicily Channel Rift Zone (Italy), is the type locality for the peralkaline rhyolitic rocks called pantellerites. In the last 50 ka, after the large Green Tuff caldera-forming eruption, volcanic activity at Pantelleria has consisted of effusive and explosive eruptions mostly vented inside and along the rim of the caldera and producing silicic lava flows, lava domes and poorly dispersed pantelleritic pumice fall deposits. Basaltic cinder cones and lava flows are only present outside the caldera in the NW sector of the island. The most recent basaltic (Cuddie Rosse, ～ 20 ka) and pantelleritic (Cuddia Randazzo and Cuddia del Gallo, ～ 6 ka) pyroclastic products were sampled to investigate magmatic volatile contents through the study of melt inclusions.The melt inclusions in pyroxene and olivine phenocrysts of Cuddie Rosse scoriae have an alkali basalt composition. The dissolved volatiles comprise 0.9–1.6 wt.% H2O, several hundred ppm of CO2, 1600–2000 ppm of sulphur and 500–900 ppm of chlorine. The water–carbon dioxide couple gives a confining pressure ～ 2 kbar prior to the eruption. This result indicates that episodes of magma ponding and crystallization occurred in the upper crust prior to eruption. The melt inclusions in feldspar, fayalite and aenigmatite phenocrysts of Cuddia del Gallo and Cuddia Randazzo pumice have a pantelleritic composition (Agpaitic Indices 1.3–2.1), up to 4.4 wt.% H2O, 8700 ppm Cl, 6000 ppm F, and CO2 below the detection limit. Sulphur averaging 420 ppm has been measured in Cuddia Randazzo melt inclusions. These data indicate relatively high volatile contents for these low-energy Strombolian-type eruptions. Melt inclusions in Cuddia del Gallo pumice show the most evolved composition (Agpaitic Indices 2–2.1) and the highest volatile content, in agreement with fluid saturation conditions in the magma chamber prior to the eruption. This implies a confining pressure of ～ 1 kbar for the top of the pantelleritic reservoir. The composition of melt inclusions and mineralogical assemblage of Cuddia Randazzo pumice indicate that it has a lower evolutionary degree (Agpaitic Indices 1.3–1.8) and lower pre-eruptive Cl and H2O contents than Cuddia del Gallo pumice. An increase in pressure due to the exsolution of volatiles in the upper part of the pantelleritic reservoir may have triggered the Cuddia del Gallo explosive eruption. Evidence of widespread pre-eruptive mingling between trachytes and pantellerites suggests that the intrusion of trachytic magma into the pantelleritic reservoir likely played a major role in destabilizing the magma system just prior to the Cuddia Randazzo event. 相似文献
10.
John A. Becker Mike J. Bickle Albert Galy Tim J.B. Holland 《Earth and Planetary Science Letters》2008,265(3-4):616-629
Hot springs in the Marsyandi Valley, Nepal, vent CO2 sourced from metamorphic fluids that mix with shallow groundwaters before degassing near the Earth's surface. The δ13C of spring waters ranges up to + 13‰, while that of the coexisting free gas phase is close to ? 4‰. Empirical and thermodynamic modelling of this isotopic fractionation suggests > 97 ± 1% CO2 degassing. The calculated minimum total CO2 degassing in the Marsyandi catchment is 5.4 × 109 mol/yr from a Cl-based estimate of the spring water discharge to the Marsyandi River and the fraction of CO2 degassed. Extrapolated to the whole of the Himalayas, this implies a probable minimum metamorphic CO2 flux of 0.9 × 1012 mol/yr, or ～ 13% of solid Earth CO2 degassing. The calculated flux is a factor of three greater than the estimated CO2 drawdown by silicate weathering in the Himalayas. Himalayan metamorphic degassing contributes a significant fraction of the global solid Earth CO2 flux and implies that metamorphism may cause changes in long-term climate that oppose those resulting from the orogenic forcing of chemical weatherability. 相似文献
11.
Evangelia Krasakopoulou Spyridon Rapsomanikis Anastasios Papadopoulos Evangelos Papathanassiou 《Continental Shelf Research》2009,29(11-12):1477-1488
Data on the distribution of fCO2 were obtained during a cruise in the Aegean Sea during February 2006. The fCO2 of surface water (fCO2sw) was lower than the atmospheric fCO2 (fCO2atm) throughout the area surveyed and ΔfCO2 values varied from ?34 to ?61 μatm. The observed under-saturation suggests that surface waters in the Aegean represent a sink for atmospheric CO2 during the winter of 2006. Higher fCO2sw values were recorded in the ‘less warm’ and ‘less saline’ shallow northernmost part of the Aegean Sea implying that the lower seawater temperature and salinity in this area play a crucial role in the spatial distribution of fCO2sw.A first estimate of the magnitude of the air–sea CO2 exchange and the potential role of the Aegean Sea in the transfer of atmospheric CO2 was also obtained. The air–sea CO2 fluxes calculated using different gas transfer formulations showed that during February 2006, the Aegean Sea absorbs atmospheric CO2 at a rate ranging from ?6.2 to ?11.8 mmol m?2 d?1 with the shipboard recorded wind speeds and at almost half rate (?3.5 to ?5.5 mmol m?2 d?1) with the monthly mean model-derived wind speed. Compared to recent observations from other temperate continental shelves during winter period, the Aegean Sea acts as a moderate to rather strong sink for atmospheric CO2.Further investigations, including intensive spatial and temporal high-resolution observations, are necessary to elucidate the role of the Aegean Sea in the process of transfer of atmospheric CO2 into the deep horizons of the Eastern Mediterranean. 相似文献
12.
Faisal Alonaizi Roman Pevzner Andrej Bóna Mohammad Alshamry Eva Caspari Boris Gurevich 《Geophysical Prospecting》2014,62(2):197-209
Time‐lapse seismic analysis is utilized in CO2 geosequestration to verify the CO2 containment within a reservoir. A major risk associated with geosequestration is a possible leakage of CO2 from the storage formation into overlaying formations. To mitigate this risk, the deployment of carbon capture and storage projects requires fast and reliable detection of relatively small volumes of CO2 outside the storage formation. To do this, it is necessary to predict typical seepage scenarios and improve subsurface seepage detection methods. In this work we present a technique for CO2 monitoring based on the detection of diffracted waves in time‐lapse seismic data. In the case of CO2 seepage, the migrating plume might form small secondary accumulations that would produce diffracted, rather than reflected waves. From time‐lapse data analysis, we are able to separate the diffracted waves from the predominant reflections in order to image the small CO2 plumes. To explore possibilities to detect relatively small amounts of CO2, we performed synthetic time‐lapse seismic modelling based on the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) Otway project data. The detection method is based on defining the CO2 location by measuring the coherency of the signal along diffraction offset‐traveltime curves. The technique is applied to a time‐lapse stacked section using a stacking velocity to construct offset‐traveltime curves. Given the amount of noise found in the surface seismic data, the predicted minimum detectable amount of CO2 is 1000–2000 tonnes. This method was also applied to real data obtained from a time‐lapse seismic physical model. The use of diffractions rather than reflections for monitoring small amounts of CO2 can enhance the capability of subsurface monitoring in CO2 geosequestration projects. 相似文献
13.
Surface partial pressure of CO2 (pCO2), dissolved inorganic carbon (DIC), temperature, salinity and chlorophyll a (Chl a) at grid stations were measured in the southern Yellow Sea (SYS; 32–37°N to 120–125°E) during four cruises conducted in March 2005 (winter), April 2006 (spring), May 2005 (late spring), and July 2001 (summer). Factors influencing pCO2 spatial and seasonal variations are explored.Surface seawater pCO2 during winter was oversaturated with respect to the atmosphere in the entire study area (380–606 μatm), primarily due to the complete mixing of the water column in winter which brought CO2-enriched bottom water to the surface. However, during spring, surface pCO2 in the central SYS was undersaturated relative to the atmosphere with a low range between 274 and 408 μatm. The net CO2 sink in the central SYS was mainly due to the consumption of CO2 by the strong phytoplankton activity and to the weak water stratification, whereas surface pCO2 in the nearshore area was oversaturated for the atmosphere owing to vertical mixing and terrestrial inputs. During summer, surface pCO2 varied between 125 and 599 μatm over the entire sampling area. In the Changjiang (Yangtze River) Diluted Water (CDW) area, surface pCO2 was undersaturated because of the nutrient inputs via the Changjiang, triggering strong phytoplankton activity, whereas surface pCO2 was oversaturated in other areas. We conclude that the nearshore area behaves as a source of atmospheric CO2 during the entire investigated periods owing to vertical mixing and terrestrial inputs as well as upwelling, whereas the central region generally shifts from a source of CO2 in March to a sink in the remaining time of the investigation. 相似文献
14.
Alison M. Shaw Mark D. Behn Susan E. Humphris Robert A. Sohn Patricia M. Gregg 《Earth and Planetary Science Letters》2010,289(3-4):311-322
We present new analyses of volatile, major, and trace elements for a suite of glasses and melt inclusions from the 85°E segment of the ultra-slow spreading Gakkel Ridge. Samples from this segment include limu o pele and glass shards, proposed to result from CO2-driven explosive activity. The major element and volatile compositions of the melt inclusions are more variable and consistently more primitive than the glass data. CO2 contents in the melt inclusions extend to higher values (167–1596 ppm) than in the co-existing glasses (187–227 ppm), indicating that the melt inclusions were trapped at greater depths. These melt inclusions record the highest CO2 melt concentrations observed for a ridge environment. Based on a vapor saturation model, we estimate that the melt inclusions were trapped between seafloor depths (～ 4 km) and ～ 9 km below the seafloor. However, the glasses are all in equilibrium with their eruption depths, which is inconsistent with the rapid magma ascent rates expected for explosive activity. Melting conditions inferred from thermobarometry suggest relatively deep (25–40 km) and cold (1240°–1325 °C) melting conditions, consistent with a thermal structure calculated for the Gakkel Ridge. The water contents and trace element compositions of the melt inclusions and glasses are remarkably homogeneous; this is an unexpected result for ultra-slow spreading ridges, where magma mixing is generally thought to be less efficient based on the assumption that steady-state crustal magma chambers are absent in these environments. All melts can be described by a single liquid line of descent originating from a pooled melt composition that is consistent with the aggregate melt calculated from a geodynamic model for the Gakkel Ridge. These data suggest a model in which deep, low degree melts are efficiently pooled in the upper mantle (9–20 km depth), after which crystallization commences and continues during ascent and eruption. Based on our melting model and the assumption that CO2 is perfectly incompatible, we show that the highest CO2 concentrations of the melt inclusions (～ 1600 ppm) are consistent with the calculated CO2 concentrations of primary undegassed melts. The highest measured CO2/Nb ratio (443) of Gakkel Ridge melt inclusions predicts a mantle CO2 content of 134 ppm and would result in a global ridge flux of 2.0 × 1012 mol CO2/yr. 相似文献
15.
16.
This study presents a new unsteady-state method for measuring two-phase relative permeability by obtaining local values of the three key parameters (saturation, pressure drop, and phase flux) versus time during a displacement. These three parameters can be substituted to two-phase Darcy Buckingham equation to directly determine relative permeability. To obtain the first two, we use a medical X-ray Computed Tomography (CT) scanner to monitor saturation in time and space, and six differential pressure transducers to measure the overall pressure drop and the pressure drops of five individual sections (divided by four pressure taps on the core) continuously. At each scanning time, the local phase flux is obtained by spatially integrating the saturation profile and converting this to the flux using a fractional flow framework. One advantage of this local method over most previous methods is that the capillary end effect is experimentally avoided; this improvement is crucial for experiments using low viscosity fluids such as supercritical and gas phases. To illustrate the new method, we conduct five CO2-brine primary drainage experiments in a 60.8 cm long and 116 mD Berea sandstone core at 20 °C and 1500 psi. In return, we obtain hundreds of unsteady-state CO2 and brine relative permeability data points that are consistent with steady-state relative permeability data from the same experiments. Due to the large amount of relative permeability data obtained by the new unsteady-state method, the uncertainties of the exponents in the Corey-type fits decrease by up to 90% compared with the steady-state method. 相似文献
17.
Vincent Famin Satoru Nakashima Anne-Marie Boullier Koichiro Fujimoto Tetsuro Hirono 《Earth and Planetary Science Letters》2008,265(3-4):487-497
Fourier transform infrared (FTIR) microanalysis of pseudotachylytes (i.e. friction-induced melts produced by seismic slip) from the Nojima fault (Japan) reveals that earthquakes almost instantaneously expel 99 wt.% of the wall rock CO2 content. Carbon is exsolved because it is supersaturated in the friction melts. By extrapolation to a crustal-scale fault rupture, large events such as the M7.2 Kobe earthquake (1995) may yield a total production of 1.8 to 3.4 × 103 tons CO2 within a few seconds. This extraordinary release of CO2 can cause a flash fluid pressure increase in the fault plane, and therefore enhance earthquake slip or trigger aftershocks; it may also explain the anomalous discharge of carbon monitored in nearby fault springs after large earthquakes. Because carbon saturation in silicate melts is pressure-dependent, FTIR can be used as a new tool to constrain the maximum depth of pseudotachylyte formation in exhumed faults. 相似文献
18.
Several kinds of geochemical anomaly before strong earthquakes have been observed in China since 1966. They include changes in groundwater radon levels, ion content of water (Ca+2, Mg+2, Cl–, SO
4
–2
, F–), dissolved gases (H2, CO2), and gases escaping from the aeration zone through abandoned dry wells (Ar, N2, CO2). The radon anomalies may be grouped as long-term and short-term anomalies. Most of the geochemical anomalies observed are characterized by a pattern of increase. The largest amplitude recorded was 37 times the base level. Preliminary study indicates that the types of seismogeochemical anomaly observed prior to strong earthquakes depend on tectonic, geologic, lithologic, and hydrogeological conditions at the monitoring station. Results obtained from modelling experiments on the mechanisms of some anomalies are given. 相似文献
19.
Weekly surface loading variations are estimated from a joint least squares inversion of load-induced GPS site displacements, GRACE gravimetry and simulated ocean bottom pressure (OBP) from the finite element sea-ice ocean model (FESOM).In this study, we directly use normal equations derived from reprocessed GPS observations, where station and satellite positions are estimated simultaneously. The OBP weight of the model in the inversion is based on a new error model, obtained from 2 FESOM runs forced with different atmospheric data sets.Our findings indicate that the geocenter motion derived from the inversion is smooth, with non-seasonal RMS values of 1.4, 0.9 and 1.9 mm for the X, Y and Z directions, respectively. The absolute magnitude of the seasonal geocenter motion varies annually between 2 and 4.5 mm. Important hydrological regions such as the Amazon, Australia, South-East Asia and Europe are mostly affected by the geocenter motion, with magnitudes of up to 2 cm, when expressed in equivalent water height.The chosen solar radiation pressure model, used in the GPS processing, has only a marginal effect on the joint inversion results. Using the empirical CODE model slightly increases the annual amplitude of the Z component of the geocenter by 0.8 mm. However, in case of a GPS-only inversion, notable larger differences are found for the annual amplitude and phase estimates when applying the older physical ROCK models. Regardless of the used radiation pressure model the GPS network still exhibits maximum radial expansions in the order of 3 mm (0.45 ppb in terms of scale), which are most likely caused by remaining GPS technique errors.In an additional experiment, we have used the joint inversion solution as a background loading model in the GPS normal equations. The reduced time series, compared to those without a priori loading model, show a consistent decrease in RMS. In terms of the annual height component, 151 of the 189 stations show a reduction of at least 10% in seasonal amplitude.On the ocean floor, we find a positive overall correlation (0.51) of the inversion solution with time series from globally distributed independent bottom pressure recorders.Even after removing a seasonal fit we still find a correlation of 0.45. Furthermore, the geocenter motion has a significant effect on ocean bottom pressure as neglecting it causes the correlation to drop to 0.42. 相似文献
20.
Paula M. Carreira José M. Marques M. Rosário Carvalho Giorgio Capasso Fausto Grassa 《Journal of Volcanology and Geothermal Research》2010,189(1-2):49-56
Na–HCO3–CO2-rich thermomineral waters issue in the N of Portugal, within the Galicia-Trás-os-Montes region, linked to a major NNE-trending fault, the so-called Penacova-Régua-Verin megalineament. Along this tectonic structure different occurrences of CO2-rich thermomineral waters are found: Chaves hot waters (67 °C) and also several cold (16.1 °C) CO2-rich waters. The δ2H and δ18O values of the thermomineral waters are similar to those of the local meteoric waters. The chemical composition of both hot and cold mineral waters suggests that water–rock reactions are mainly controlled by the amount of dissolved CO2 (g) rather than by the water temperature. Stable carbon isotope data indicate an external CO2 inorganic origin for the gas. δ13CCO2 values ranging between ? 7.2‰ and ? 5.1‰ are consistent with a two-component mixture between crustal and mantle-derived CO2. Such an assumption is supported by the 3He/4He ratios measured in the gas phase, are between 0.89 and 2.68 times the atmospheric ratio (Ra). These ratios which are higher than that those expected for a pure crustal origin (≈ 0.02 Ra), indicating that 10 to 30% of the He has originated from the upper mantle. Release of deep-seated fluids having a mantle-derived component in a region without recent volcanic activity indicates that extensive neo-tectonic structures originating during the Alpine Orogeny are still active (i.e., the Chaves Depression). 相似文献