Where Does Water Go During Hydraulic Fracturing?

During hydraulic fracturing millions of gallons of water are typically injected at high pressure into deep shale formations. This water can be housed in fractures, within the shale matrix, and can potentially migrate beyond the shale formation via fractures and/or faults raising environmental concerns. We describe a generic framework for producing estimates of the volume available in fractures and undamaged shale matrix where water injected into a representative shale site could reside during hydraulic fracturing, and apply it to a representative site that incorporates available field data. The amount of water that can be stored in the fractures is estimated by calculating the volume of all the fractures associated with a discrete fracture network (DFN) based on real data and using probability theory to estimate the volume of smaller fractures that are below the lower cutoff for the fracture radius in the DFN. The amount of water stored in the matrix is estimated utilizing two distinct methods—one using a two‐phase model at the pore‐scale and the other using a single‐phase model at the continuum scale. Based on these calculations, it appears that most of the water resides in the matrix with a lesser amount in the fractures.     

Can Hydraulic Conductivity of Fluvial Sediments be Informed by Spectral Reflectance?

Water Resources - This study explores the statistical relationship between spectral reflectance and hydraulic conductivity (K) of fluvial sediments in two Nebraska rivers. The spectral reflectance...     

Why meter-wide dikes at oceanic spreading centers?

Numerical models show that maximum dike width at oceanic spreading centers should scale with axial lithospheric thickness if the pre-diking horizontal stress is close to the Andersonian normal faulting stress and the stress is fully released in one dike intrusion. Dikes at slow-spreading ridges could be over 5 m wide and maximum dike width should decrease with increasing plate spreading rate. However, data from ophiolites and tectonic windows into recently active spreading ridges show that mean dike width ranges from 0.5 m to 1.5 m, and does not clearly correlate with plate spreading rate. Dike width is reduced if either the pre-diking horizontal stress difference is lower than the faulting stress or the stress is not fully released by a dike. Partial stress release during a dike intrusion is the more plausible explanation, and is also consistent with the fact that dikes intrude in episodes at Iceland and Afar. Partial stress release can result from limited magma supply when a crustal magma chamber acts as a closed source during dike intrusions. Limited magma supply sets the upper limit on the width of dikes, and multiple dike intrusions in an episode may be required to fully release the axial lithospheric tectonic stress. The observation of dikes that are wider than a few meters (such as the recent event in Afar) indicates that large tectonic stress and large magma supply sometimes exist.     

Experiment on Hydraulic Fracturing in Rock and Induced Earthquake

Experiment on rock hydraulic fracturing strength under different confining pressures was conducted on a series of test specimens with various pre-cracks prepared from 7 types of rock, Combining the data of an actual reservoir-induced earthquake with the experimental results of the contemporary tectonic stress field according to the theory of rock strength and the principle and method of rock fracture mechanics, the authors tentatively investigated the earthquakes induced by pore-water pressure in rock and obtained the initial results as follows： （1） One type of induced earthquake may occur in the case of larger tectonic stress on such weak planes that strike in similar orientation of principle tectonic compressional stress in the shallows of the rock mass; the pore-water pressure σp may generate tensile fracture on them and induce small earthquakes; （2） Two types of induced earthquake may occur in the case of larger tectonic stress, i, e,, ①on such weakness planes that strike in similar orientation of principle tectonic compressional stress, σ1, in the shallows of the rockmass, the pore-water pressure, σp, may generate tensile fracture on them and induce small earthquakes; ②When the tectonic stress approximates the shear strength of the fracture, the pore-water pressure σp may reduce the normal stress, σn, on the fracture face causing failure of the originally stable fracture, producing gliding fracture and thus inducing an earthquake. σp may also increase the fracture depth, leading to an induced earthquake with the magnitude larger than the previous potential magnitude; （3） There is a depth limit for each type of rock mass, and no induced earthquake will occur beyond this limit.     

Why does the Kuroshio northeast of Taiwan shift shelfward in winter?

Observations indicate that off the northeastern coast of Taiwan a branch of the Kuroshio intrudes farther northward in winter onto the shelf of the East China Sea. We demonstrate that this seasonal shift can be explained solely by winter cooling. Cooling produces downslope flux of dense shelf water that is compensated by shelfward intrusion. Parabathic isopycnals steepen eastward in winter and couple with the cross-shelf topographic slope (the “JEBAR” effect) to balance the enhanced intrusion. The downslope flow also increases vortex stretching and decreases the thickness of the inertial boundary layer, resulting in a Kuroshio that shifts closer to the shelf break.     

Influence of Degree of Saturation in the Electric Resistivity–Hydraulic Conductivity Relationship

The relationship between aquifer hydraulic conductivity and aquifer resistivity, either measured on the ground surface by vertical electrical sounding (VES) or from resistivity logs, or measured in core samples have been published for different types of aquifers in different locations. Generally, these relationships are empirical and semi-empirical, and confined in few locations. This relation has a positive correlation in some studies and negative in others. So far, there is no potentially physical law controlling this relation, which is not completely understood. Electric current follows the path of least resistance, as does water. Within and around pores, the model of conduction of electricity is ionic and thus the resistivity of the medium is controlled more by porosity and water conductivity than by the resistivity of the rock matrix. Thus, at the pore level, the electrical path is similar to the hydraulic path and the resistivity should reflect hydraulic conductivity. We tried in this paper to study the effect of degree of groundwater saturation in the relation between hydraulic conductivity and bulk resistivity via a simple numerical analysis of Archie’s second law and a simplified Kozeny-Carmen equation. The study reached three characteristic non-linear relations between hydraulic conductivity and resistivity depending on the degree of saturation. These relations are: (1) An inverse power relation in fully saturated aquifers and when porosity equals water saturation, (2) An inverse polynomial relation in unsaturated aquifers, when water saturation is higher than 50%, higher than porosity, and (3) A direct polynomial relation in poorly saturated aquifers, when water saturation is lower than 50%, lower than porosity. These results are supported by some field scale relationships.     

Depth-Recursive Tomography of the Bohemian Massif at the CEL09 Transect—Part B: Interpretation

In the accompanying paper (Part A), depth-recursive tomography was applied to the CEL09 refraction data. A deblurred P-wave velocity image was obtained down to a depth of 20 km. This paper (Part B) is devoted to the interpretation of the upper- and middle-crustal structures of the Bohemian Massif imaged in the CEL09 section. Because of inherent ambiguity of the refraction method in imaging low-velocity zones, other well-known results based on other geophysical data sets are also used to independently verify the interpreted velocity features. Comparison with the density and velocity models previously obtained indicates that the presented P-wave velocity image has superior resolution revealing or verifying a number of geological features. The prominent lateral velocity changes encountered in the CEL09 pattern across the imaged crustal section were used to delineate the main terranes and deep regional fault zones such as the Kru?né hory Fault, the SW continuation of the Litomě?ice Fault Zone, the West and Central Bohemian Shear Zones, the Blanice-Rodl Fault, the P?ibyslav-Vitis Fault and the Boskovice-Diendorf Fault. The 450-km-long CEL09 transect reveals seven major deeply rooted high-velocity (HV) anomalies identified as Variscan massifs intruded near or within these deep fault zones. They form buried ridges mostly parallel to the SW-NE trending Variscan strike. Their discovery allows new insights into a number of phenomena such as the West Bohemian earthquake swarms, the Saxothuringian paradox, the character of the Saxothuringian-Barrandian contact zone, the detachment surface due to the slab of the Saxothuringian crust subducting beneath the Teplá-Barrandian zone in the Devonian, the depth extent of the Mariánské-Lázně Complex (MLC) as an equivalent unit of the Zone Erbendorf-Vohenstrauss (ZEV), the subsidence of the Barrandian syncline, the root zones of the Central and South Bohemian Plutons, the accretionary wedge formed along the Moravo-Moldanubian suture and its link with the Gföhl terrane, the Carpathian foreland relief and the subsidence observed in the Vienna Basin.     

Why a new journal like Earthquake Research Advances(ERA)?

正In these difficult and hard times of pandemic, why another new journal, like ERA, should come out?What is ERA? It is a journal sponsored by the China Earthquake Networks Center and co-sponsored by the School of Earth and Space Sciences, University of Science and Technology in China. The reason for establishing this journal is to start something innovative and forge a path to a new leaf in earthquake-related research.     

Using δ18O and δ2H to Detect Hydraulic Connection Between a Sinkhole Lake and a First-Magnitude Spring

Oxygen and hydrogen isotopes were used in this study to detect a hydraulic connection between a sinkhole lake and a karst spring. In karst areas, surface water that flows to a lake can drain through sinkholes in the lakebed to the underlying aquifer, and then flows in karst conduits and through aquifer matrix. At the study site located in northwest Florida, USA, Lake Miccosukee immediately drains into two sinkholes. Results from a dye tracing experiment indicate that lake water discharges at Natural Bridge Spring, a first-magnitude spring 32 km downgradient from the lake. By collecting weekly water samples from the lake, the spring, and a groundwater well 10 m away from the lake during the dry period between October 2019 and January 2020, it was found that, when rainfall effects on isotopic signature in spring water are removed, increased isotope ratios of spring water can be explained by mixing of heavy-isotope-enriched lake water into groundwater, indicating hydraulic connection between the lake and the spring. Such a detection of hydraulic connection at the scale of tens of kilometers and for a first-magnitude spring has not been previously reported in the literature. Based on the isotope ratio data, it was estimated that, during the study period, about 8.5% the spring discharge was the lake water that drained into the lake sinkholes.     

Depth-Recursive Tomography of the Bohemian Massif at the CEL09 Transect—Part A: Resolution Estimates and Deblurring Aspects

The refraction CEL09 profile from the CELEBRATION 2000 project intersects the main terranes of the Bohemian Massif in the NW–SE direction: the Saxothuringian, the Teplá-Barrandian, the Moldanubian and the Moravo-Silesian. In its easternmost part, it crosses the Western Outer Carpathians overthrust westward onto the Bohemian Massif. Only the first 450 km were surveyed with the densest deployment of shot points providing data suitable for a reliable geological interpretation. The first-arrival depth-recursive tomography was applied here to derive a P-wave velocity image of the upper and middle crust (Part A). The proper interpretation of the obtained velocity features is the subject of the accompanying paper (Part B). The attained resolution in the velocity image is shown to be superior as compared with the previous CEL09 models based also on the more uncertain later arrivals of reflection waves. The applied DRTG (depth-recursive tomography on grid) method is based on a regular network of refraction grid rays generated for iteratively updated starting models. Only the distinct first arrivals with minimum uncertainty are used for the DRTG inversions to yield the maximum resolution. Thanks to the full control of the data fit by the grid rays used, the statistical lateral resolution could be determined at single grid depths for the chosen confidence levels. Thus, the lateral sizes of the anomalies that can be yet resolved are determined in dependence on their depths and their velocity excesses. The defocusing of the imaged features is studied on the basis of the spatial responses to spike excitation. The calculated spatial responses also allowed the edge smearing of the velocity anomalies to be assessed. Special attention is paid to the imaging of low-velocity zones that are usually suppressed by the smoothing measures used in standard tomographic methods. An improvement was achieved if the smoothing was suggested with regard to the occurrence of the low-velocity zones repeatedly appearing in higher iterations. The gained deblurring effect concerns both the negative and positive anomalies as documented on the velocity features interpreted in the accompanying paper.     

Why are hatching and emergence success low? Mercury and selenium concentrations in nesting leatherback sea turtles (Dermochelys coriacea) and their young in Florida

Leatherback sea turtles (Dermochelys coriacea) have low hatching and emergence success compared to other sea turtle species. Postmortem examinations of hatchlings showed degeneration of heart and skeletal muscle that was similar to that found in other neonates with selenium deficient mothers. Selenium deficiency can result from elevated concentrations of bodily mercury. Ingested mercury is detoxified by the liver through mercury-selenium compound formation. In animals persistently exposed to mercury, the liver’s ability to detoxify this element may decrease, especially if dietary selenium is insufficient. We measured mercury and selenium concentrations in nesting female leatherbacks and their hatchlings from Florida and compared the levels to hatching and emergence success. Both liver selenium and the liver selenium-to-mercury ratio positively correlated with leatherback hatching and emergence success. This study provides the first evidence for the roles of mercury and selenium in explaining low reproductive success in a globally imperiled species, the leatherback sea turtle.     

Discussion on Deep Tectonic Background of Moderately Strong Earthquake in Anhui Province and Its Neighboring Areas Using Results of Seismic Tomography

INTRODUCTIONThe studied areaislocated mostlyinthe southeastern part of the North Chinafault block provinceat 28°~39°N, 112°~124°E, where the geologic tectonics is complex with frequent historicalmoderate-strong earthquakes .The 3Dvelocity images derived fromseismic tomography have enrichedthe knowledge about the deep structures of the crust and the upper mantle ,and by combining thespatial distribution of seismicity patterns ,we canfurther studythe relations of velocitystructure toth…