Basin Depth Research Articles

Extreme continental weathering in the northwestern Tethys during the end-Triassic mass extinction

The end-Triassic mass extinction (ETE) is thought to have been triggered by widespread eruption and emissions of volcanic and contact metamorphic carbon and sulfur gases from the Central Atlantic Magmatic Province (CAMP) flood basalts. Although palynological studies of shallow marine deposits in the basins of Denmark and Germany suggest that deforestation and catastrophic soil loss occurred during the CAMP volcanism and ETE interval, the intensity and timing of continental weathering in the region of northwestern Tethys Ocean remain unclear. Here we present Sr, C, and O isotope data, as well as multivariate statistical analyses of major element contents, for carbonate–clastic deposits in the Kardolína section, Slovakia, to develop a continental weathering record in the NW Tethys during the ETE event. This section consists of a shallow marine carbonate sequence in the Rhaetian Fatra Formation and the overlying Hettangian Kopieniec Formation. The Fatra Formation represents ramp facies deposits that formed in a restricted pull-apart basin of the Fatric Zone along the southern margin of the Bohemian Massif in the region of northwestern Tethys. Carbon isotope analysis of the limestones revealed two negative carbon isotope excursions (NCIEs) in the uppermost Fatra Formation. These two NCIEs occurred in the latest Rhaetian and can be compared to the “precursor” and “initial” NCIEs reported for the northwestern Tethys. Strontium isotope analysis of the limestones revealed an abrupt increase in Sr isotope ratios between the precursor and initial NCIEs, which indicates that continental weathering of the Bohemian Massif increased rapidly in the latest Rhaetian. Multivariate analysis of major element contents in the carbonate rocks also shows that intense chemical weathering of the hinterland was accelerated after the precursor NCIE, supporting the inferences drawn from Sr isotopes. Furthermore, our study reveals that the carbonate depositional environments of the Fatra Formation changed to the formation of specific Fe-rich oolites with increased continental weathering after the precursor NCIE. The concentrations of redox-sensitive major elements (e.g., Mn and Fe) and multivariate analysis of the major element data suggest that the Fe-rich oolites were formed by an influx of O-depleted water into the shallow water depositional environment of the Fatra Formation. A possible origin for this O-depleted water is the oxygen minimum zone (OMZ) that formed at intermediate water depths in European basins (e.g., the German and Eiberg basins) during the latest Rhaetian. Our results suggest that the marine environment in the European basins may have developed an OMZ due to the increase in continental weathering during the latest Rhaetian, and these environmental changes may have had an important role in the marine ETE event. • Sr, C, and O isotope data of the Rhaetian succession in Slovakia were determined. • Two negative carbon isotope excursions (NCIEs) were detected in latest Rhaetian. • Abrupt increase in Sr isotope ratios recognized between these two NCIEs. • Continental weathering was temporarily enhanced during the end-Triassic extinction. • Intense weathering led to development of oxygen minimum zone in NW Tethys.

An investigation on effect of variation of mass flow rate and number of collectors on yearly efficiency of single slope solar still by incorporating N similar photovoltaic thermal flat plate collectors

Abstract The effect of variation of mass flow rate and number of collectors (N) on the yearly efficiency of a single slope solar still by incorporating series connected N similar photovoltaic thermal flat plate collectors (NPVTFPCSS) has been investigated, keeping a constant water depth in basin as 0.14 m. The various parameters have been calculated, taking into account all four types of weather conditions for New Delhi using computing code developed in MATLAB-2015a. All equations and required data have been fed to the computing code for evaluating different relevant parameters. It has been concluded that the value of all types of annual efficiencies, except annual electrical efficiency, diminishes with increase in the value of at a selected value of N until = 0.10 kg/s and then becomes almost constant. Optimal values of N from annual overall exergy efficiency and annual overall thermal efficiency viewpoints have been found as four and ten respectively.

Transport Processes of Seafloor Sediment From the Chukchi Shelf to the Western Arctic Basin

AbstractThe processes of seafloor sediment transport from the Chukchi shelf to the western Arctic basin were investigated using a pan‐Arctic sea ice‐ocean model and sediment‐trap measurements at four mooring stations: North of Barrow Canyon, North of Hanna Canyon, Northwind Abyssal Plain, and Chukchi Abyssal Plain. The available sediment‐trap data verified that the sinking flux of lithogenic material (LM) originally resuspended from the seafloor for 2010–2020 was simulated reasonably well in the four mooring areas. The model results were analyzed to quantify the spatiotemporal variability of LM and to reveal its background mechanisms. Analysis indicated that the Barrow Canyon throughflow, Chukchi Slope Current (CSC), and mesoscale eddies played important roles in LM redistribution. The CSC controlled the westward transport of LM from the mouth of Barrow Canyon to the Chukchi Borderland. The mesoscale eddies generated north of Barrow Canyon efficiently transported shelf‐origin LM toward the southern Canada Basin. The sinking flux of particulate organic carbon (POC) averaged from September 2010 to August 2020, which was estimated statistically from the simulated LM flux, was 0.13–0.30 gC m−2 yr−1 at 200‐m depth in the southern Canada Basin. This finding reveals that lateral transport of sediment from the Chukchi shelf bottom has a considerable effect on the sinking flux of POC in the western Arctic basin, and suggests that the western Arctic marine biogeochemical cycle is strongly influenced by shelf‐basin exchange that depends on the relative strength of the CSC and mesoscale eddy activity.

ON GOING COALBED METHANE (CBM) DEVELOPMENT IN THE SOUTH SUMATRA BASIN

Coalbed methane (CBM) is going to be an important facet of the nation’s energy mix. It is expected to contribute in importance energy back up for the future. CBM is natural gas, a clean-burning energy source that is reservoired in a coal seam. CBM is formed during the coal maturation process and may in a free or adsorbed state in coal seams in adjacent formations. CBM is dominantly methane but lesser concentrations of carbon dioxide and nitrogen, compare to conventional natural gas. However, in most cases, CBM is of sufficient quality for sale directly into natural gas transmission lines with a limited amount of moisture removal.CBM as natural gas has numerous benefits to include direct selling, well suited as city gas, electricity generation, boiler fuel, transportation fuel, and for many types of chemical industries feed. Beside CBM replaces coal to be greatly reduces the production of acid rain and other forms of air pollution, the development of CBM has benefitial for coal miners. It can contribute to improved mining safety as well as it can help reduce construction costs.CBM is probably one of the promising alternative fuel energy resources in Indonesia that its presence is actual and comparable with the existing coal resources in any potential basin. Unlike some well in developed countries where commercialization of methane production from coal seam has been developed, coals direct mined in Indonesia seem to be more attractive and preferable technique to supply the consumer demand of energy. This is because coal mines serve direct products, less complicated technology, low exploration risks, easy recovery, relatively low cost but quick yields and already have wide market. Consequently, people have overlooked the existence of consisting huge potential methane gas in coals.However, petroleum exploration data throughout Indonesia suggest that increasing coal rank occurs rapidly with depth in many basins and that gas kicks are almost common associated with some coal seams below 200 m depth. In addition, world CBM exploration now has shifted towards lower rank settings (i.e, vitrinite reflectance between 0.3% and 0.6% Ro). In Indonesia, thick coals generally are found at greater depth, higher in rank and therefore are expected to be more productive (Saghafi and Hadiyanto, 2000).LEMIGAS is currently conducting a drilling program to study the feasibility of CBM production in South Sumatra. The domain of the work is in the Muaraenim Formation (Upper – Middle Palembang). The coal sequences were deposited during Late Miocene. We believe that a big effort is extremely essential to establish the reserve and economic potential of CBM in South Sumatra to later extent to Indonesia.

Лечебные грязи на побережье Тауйской губы Охотского моря

The article describes the results of studying the conditions of occurrence and composition of sulphide muds on the coast of the Tauysk Bay in the Sea of Okhotsk. Bacterial oxidation of methane, that migrated from the depths of aquatic sedimentary basins (catagenetic methane), plays a leading role in the formation of sulfide silty pelites. A genetic relationship was noted between the accumulations of therapeutic mud on the Tauysk Bay coast and possibly oil-and-gas- and coal-bearing depressions in the Yama-Tauy sedimentary basin. An environmentally safe method of extracting muds from the ice of reservoirs in the cold season is recommended.

Basin Effects on the Seismic Fragility of Steel Moment Resisting Frames Structures: Impedance Ratio, Depth, and Width of Basin

Deep sedimentary basins often increase the intensity of ground motions, but this effect is not considered explicitly in most codal provisions. The effect of basin amplification on structures to the fragility level is significant to study. For the first time, the effect of basin amplification on Steel Moment Resisting Frames (SMRF) is presented as a function of the basin material and geometry. This paper evaluates the effect of basin material, basin depth, and basin width on Peak Ground Velocity (PGV), Spectral Acceleration (Sa), and fragility of 4, 8, 12, and 20 story steel structures using synthetic ground motions simulated in SPECFEM3D. It has been found that the variation in basin width and impedance ratio can increase the spectral acceleration by a factor of 4 and 2.5, respectively. The response of SMRF is computed by incremental dynamic analysis, and fragility curves are derived for the collapse limit state. Results of fragility analysis reveal that SMRF structure is more fragile to variation in impedance contrast between basin-bedrock. It has been observed from the results that the collapse intensity measure for impedance ratio variation is 40% and 19% lesser on average than the width and depth variation, respectively. Comparison between the present fragility analysis results and HAZUS fragility parameters indicates that the vulnerability of structure located in the basin is underestimated in its current provisions, and the SMRF would need to increase its strength two times to account for basin amplification.

Basement structure investigation using 3-D forward modeling and inversion of geomagnetic data of the Zeit basin area, Gulf of Suez, Egypt

The Zeit basin is located on the western coast of the Gulf of Suez. It is a major, elongated half-graben structure with faults dipping steeply to the southwest. The Zeit basin contains the thickest Miocene sediments and evaporites in the Gulf of Suez. Many exploration activities have been conducted in and around the study area due to the known presence of hydrocarbon resources. In petroleum exploration, the estimation of basement depth (or sedimentary thickness) is a primary exploration risk parameter, in particular, for estimation of heat flow. The magnetic method is one of the few methods that can be used to study the basement structure and estimate the top basement depth. In this paper, the top basement geometry, distribution of the magnetic susceptibility and the basement depth of the Zeit basin were investigated using 3-D forward magnetic modeling and the 3-D inversion of geo-magnetic data. The 3-D forward modeling of the aeromagnetic field data from the Zeit basin area revealed a NW-SE trending half-graben structure, consistent with the known geology of the study area. Magnetic susceptibility cutoff 0.005 SI was applied to show the subsurface relationships among the basement sedimentary units. The calculated depth of the Zeit basin is around 4–5 km. The magnetic field data, calculated using the Gauss Legendre quadrature method, generally agree with the measured data as well as data calculated using the inversion process. The depth and magnetization intensity values used in the 3-D forward modeling, as well as petroleum borehole data, provide a structural basis for the 3-D inversion process.

Determination for 3D sedimentary basin depths from gravity anomaly data using steepest descent method

In solving the gravity exploration inverse problems, determining the depth of the sedimentary basin played an important role in the petroleum exploration. In this paper, the depth to the basement of 3D sedimentary basin was calculated from the gravity anomaly using the steepest descent method. This method allowed minimizing the objective function based on the first derivative and adjusting the step length by the iterative method; using the variable is the depth of adjacent rectangular prism in the x, y directions with parabolic function between density contrast and the depth. The parameters in the parabolic function were determined by the nonlinear regression method based on the information of deep borehole in the Mekong Delta. This parabolic function was used to calculate the theoretical gravity anomaly for the sedimentary basin and solve the 3D inverse gravity problem on the model and on the real data. The used objective function was the mean square error function between the measured gravity anomaly and the calculated anomaly. The proposed method was tested on the model, showing that the calculated sedimentary basin depth almost coincides with the original model depth; then the method was applied to calculate the depth of 3D sedimentary basin from the local gravity anomaly in Bac Lieu province. The analysis results were consistent with previous publications, but the calculation time was significantly shortened, so this method can be extended to analyze data on a large area.

Ergodic site response model for subduction zone regions

We present an ergodic site response model with regional adjustments for use with subduction zone ground-motion models. The model predicts site amplification of peak ground acceleration, peak ground velocity, and 5% damped pseudo-spectral accelerations of the orientation-independent horizonal component for oscillator periods from 0.01 to 10 s. The model depends on the time-averaged shear-wave velocity in the upper 30 m ( VS30), basin depth, and region and is independent of subduction earthquake type. It has three components: a linear site-amplification term in the form of VS30-scaling, a nonlinear term that depends on VS30 and shaking intensity parameterized by peak ground acceleration at the reference-rock velocity condition of 760 m/s, and a basin sediment-depth term for Japan and Cascadia conditioned on the depth to the 2.5 km/s shear-wave velocity isosurface ( Z2.5). A global VS30-scaling model is provided along with regional adjustments for Japan, Taiwan, South America, Alaska, and Cascadia. The nonlinear model is global, with a functional form that has often been used to fit nonlinear responses inferred from simulations, but here we calibrate it empirically. Relative to a prior model for shallow earthquakes in active tectonic regions, our subduction zone global VS30-scaling is comparable at short periods (<1.0 s) but weaker at long periods, while the nonlinear site response is generally less pronounced but extends to lower levels of shaking. Basin depth models are conditioned on the difference of the actual Z2.5 and a VS30-conditioned mean Z2.5. Sites with positive differential depths have increased long-period site responses and decreased short-period responses, with the opposite occurring for negative differential depths.

Degradation of dam reservoirs under the influence of mining subsidence in Upper Silesian Coal Basin, South Poland

AbstractExploitation of mineral resources can result in dramatic multidirectional changes in the natural environment in mining areas, with the changes being particularly evident in the form of land degradation. One of the consequences of underground mining is subsidence of the overlying surface of the land area. The greatest subsidence typically occurs when the mining operation is carried out with a longwall top coal caving process, which can result in subsidence basin deformation developing on the surface. This development can lead to a change in natural landforms. As a consequence of the development of subsidence basins in the present study, the maximum depth in the Upper Silesian Coal Basin may exceed 30‐m, which can also change the hydrological conditions of the area. Development of subsidence basins can often lead to changes in the morphometric parameters of the existing hydrographic objects, a phenomenon that also applies to dam reservoirs. As a result of land subsidence, the depth and surface area of hydrographic objects can increase, with the maximum depth point moving deeper into the reservoir outside the frontal barrage zone, with changes also occurring in the reservoir tank morphometry. In extreme cases, the barrage may stop water damming, being located outside the reservoir zone, meaning the tank's water management function is lost. All the reservoirs in the current study are located in the Upper Silesian Coal Basin in southern Poland, which is currently the only significant coal‐mining centre in Europe, with the surface area of the basin being 7490 km2.

2D seismic response of shallow sandy basins subjected to obliquely incident waves

Under the effects of the near-field earthquakes, the change in the incident angle of the incoming wave changes the symmetric response of basins to asymmetric. This paper investigates the 2D response of shallow trapezoidal sandy basins to incident plane SV waves. To attain this goal, a trapezoidal basin with 100 m depth, as the representative of shallow sedimentary basins, with an inclined bedrock angle of 10° was selected. These values fall inside of the ranges of the shallow basin depth and bedrock angle of several real basins. To make the results useful in engineering affairs, three different sand types belonging to the different class of soils, with respect to the soil classification codes, were selected. The constructed models were subjected to the collection of 24 earthquakes with different PGA's of 0.1, 0.2, 0.3 and 0.4 g using a fully nonlinear method. The results showed that the change in the incident angle of the motions not only affects the response at two basin edges but also influences the response of the central part. Among different sandy basins, the behavior of the basin with medium dense sand is less affected by the change in the wave incident angle. For basin with loose sand, while greater maximum spectral amplifications happen at the backward direction of the basin, the forward direction is less affected by the change in the wave incident angle. A different pattern was seen for basin with dense sand. Greater maximum spectral amplifications were seen at the forward direction of the basin. Regarding the effect of motion incident angle on the amplification frequency of shallow basins, it was seen that in case of the obliquely incident waves the spectral amplification curves of the points close to the edges have more than one (generally two) maximum points. Besides, unlike the vertical incident wave case that the SAF curves tend to almost one curve at the distant points from edges, no convergence among the SAF curves of the surface points was seen for the obliquely incident wave condition.

A new basin depth map of the fault-bound Wellington CBD based on residual gravity anomalies

ABSTRACT A new basin depth map for the Wellington Central Business District shows a maximum depth of 540 m near the Wellington Stadium. Our new basin geometry constraints are from a residual gravity anomaly study, based on ∼600 new gravity observations. Residual gravity anomalies are as large as −6.2 mGal with uncertainties <0.1 mGal. Two-dimensional gravity models constrained by boreholes that intersect basement are used to generate the basin depth map. Our maximum depth is twice that previously estimated from other geological and geophysical criteria. An onshore extension of the recently discovered Aotea Fault on the western side of Mt Victoria, is also interpreted from the gravity data. A maximum basement offset of up to 130 m and gravity anomaly gradients up to 8 mGal/km are observed across the fault. A secondary splay off the main Aotea Fault is identified in the NW corner of Mt Victoria, and a possible extension to the Lambton Fault is identified beneath the Wellington Railway Station. This new basin depth and fault trace data provide valuable constraints to models of seismic hazard assessment for Wellington City.

Shallow S-Wave Velocity Structure in the Middle-Chelif Basin, Algeria, Using Ambient Vibration Single-Station and Array Measurements

In order to better assess the seismic hazard in the northern region of Algeria, the shear-wave velocity structure in the Middle-Chelif Basin is estimated using ambient vibration single-station and array measurements. The Middle-Chelif Basin is located in the central part of the Chelif Basin, the largest of the Neogene sedimentary basins in northern Algeria. This basin hosts the El-Asnam fault, one of the most important active faults in the Mediterranean area. In this seismically active region, most towns and villages are built on large unconsolidated sedimentary covers. Application of the horizontal-to-vertical spectral ratio (HVSR) technique at 164 sites, and frequency–wavenumber (F–K) analysis at 7 other sites, allowed for the estimation of the ground resonance frequencies, shear-wave velocity profiles, and sedimentary cover thicknesses. The electrical resistivity tomography method was used at some sites to further constrain the thickness of the superficial sedimentary layers. The soil resonance frequencies range from 0.75 Hz to 12 Hz and the maximum frequency peak amplitude is 6.2. The structure of the estimated shear-wave velocities is presented in some places as 2D profiles to help interpret the existing faults. The ambient vibration data allowed us to estimate the maximum depth in the Middle-Chelif Basin, which is 760 m near the city of El-Abadia.

Particulate biogenic barium tracer of mesopelagic carbon remineralization in the Mediterranean Sea (PEACETIME project)

Abstract. We report on the sub-basin variability in particulate organic carbon (POC) remineralization in the western and central Mediterranean Sea in late spring during the PEACETIME (ProcEss studies at the Air–sEa Interface after dust deposition in the MEditerranean sea) cruise. POC remineralization rates were estimated using the excess biogenic particulate barium (Baxs) inventories in the mesopelagic layers (100–1000 m depth) and compared with prokaryotic heterotrophic production (PHP). Baxs-based mesopelagic remineralization rates (MRs) ranged from 25±2 to 306±70 mgCm-2d-1. MRs were larger in the Algero-Provençal (ALG) Basin than in the Tyrrhenian (TYR) and Ionian (ION) basins. Our Baxs inventories and integrated PHP data also indicated that significant mesopelagic remineralization occurred down to 1000 m depth in the ALG Basin in contrast to the ION and TYR basins, where remineralization was mainly located above 500 m depth. We propose that the higher and deeper MRs in the ALG Basin were sustained by an additional particle export event driven by deep convection. The TYR Basin (in contrast to the ALG and ION basins) presented the impact of a previous dust event, as reflected by our particulate Al water column concentrations. The ION and TYR basins showed small-scale heterogeneity in remineralization processes, reflected by our Baxs inventories and integrated PHP data at the Tyrr long-duration station. This heterogeneity was linked to the mosaic of blooming and non-blooming patches reported in this area during the cruise. In contrast to the western Mediterranean Sea (ALG Basin), the central Mediterranean Sea (ION and TYR basins) showed lower remineralization rates restricted to the upper mesopelagic layer during the late spring PEACETIME cruise.

Diversity and Biogeography of Bathyal and Abyssal Seafloor Bacteria and Archaea Along a Mediterranean-Atlantic Gradient.

Seafloor sediments cover the majority of planet Earth and microorganisms inhabiting these environments play a central role in marine biogeochemical cycles. Yet, description of the biogeography and distribution of sedimentary microbial life is still too sparse to evaluate the relative contribution of processes driving this distribution, such as the levels of drift, connectivity, and specialization. To address this question, we analyzed 210 archaeal and bacterial metabarcoding libraries from a standardized and horizon-resolved collection of sediment samples from 18 stations along a longitudinal gradient from the eastern Mediterranean to the western Atlantic. Overall, we found that biogeographic patterns depended on the scale considered: while at local scale the selective influence of contemporary environmental conditions appeared strongest, the heritage of historic processes through dispersal limitation and drift became more apparent at regional scale, and ended up superseding contemporary influences at inter-regional scale. When looking at environmental factors, the structure of microbial communities was correlated primarily with water depth, with a clear transition between 800 and 1,200 meters below sea level. Oceanic basin, water temperature, and sediment depth were other important explanatory parameters of community structure. Finally, we propose increasing dispersal limitation and ecological drift with sediment depth as a probable factor for the enhanced divergence of deeper horizons communities.

Profiling the Quito basin (Ecuador) using seismic ambient noise

SUMMARY Quito, the capital of Ecuador, with more than 2.5 M inhabitants, is exposed to a high seismic hazard due to its proximity to the Pacific subduction zone and active crustal faults, both capable of generating significant earthquakes. Furthermore, the city is located in an intermontane piggy-back basin prone to seismic wave amplification. To understand the basin’s seismic response and characterize its geological structure, 20 broad and medium frequency band seismic stations were deployed in Quito’s urban area between May 2016 and July 2018 that continuously recorded ambient seismic noise. We first compute horizontal-to-vertical spectral ratios to determine the resonant frequency distribution in the entire basin. Secondly, we cross-correlate seismic stations operating simultaneously to retrieve interstations surface-wave Green’s functions in the frequency range of 0.1–2 Hz. We find that Love waves travelling in the basin’s longitudinal direction (NNE–SSW) show much clearer correlograms than those from Rayleigh waves. We then compute Love wave phase-velocity dispersion curves and invert them in conjunction with the HVSR curves to obtain shear-wave velocity profiles throughout the city. The inversions highlight a clear difference in the basin’s structure between its northern and southern parts. In the centre and northern areas, the estimated basin depth and mean shear-wave velocity are about 200 m and 1800 ms−1, respectively, showing resonance frequency values between 0.6 and 0.7 Hz. On the contrary, the basement’s depth and shear-wave velocity in the southern part are about 900 m and 2500 ms−1, having a low resonance frequency value of around 0.3 Hz. This difference in structure between the centre-north and the south of the basin explains the spatial distribution of low-frequency seismic amplifications observed during the Mw 7.8 Pedernales earthquake in April 2016 in Quito.

Facies architecture, modal analysis and geochemistry of the Early Ediacaran turbiditic series in the Skoura inlier (Central High Atlas, Morocco): Implications for provenance and geotectonic setting.

A multidisciplinary approach based on lithostratigraphy, petrography, modal composition and geochemistry was performed for the first time, to study the Early Ediacaran Skoura Turbidites (EEST) of the Skoura inlier, Central High Atlas. It represents widely distributed turbidite successions up to 8 km in thickness. A total of twelve lithofacies types have been distinguished, spread in four profiles, and grouped in three major depositional environments: shallow delta complex (FA1), submarine channel (FA2), and deep-sea fan (FA3). The paleogeographic distribution of the EEST may indicate basin depth changes related to the onset of convergence.Petrographic and modal analyses of EEST reveal greywacke and lith-arenite lithologies displaying similar clast composition, mainly comprising quartz and lithic fragments. Volcanic, plutonic, and metamorphic rocks have been exposed in the source areas feeding the Skoura basin. On Q-F-L diagram, EEST have characteristics of a recycled orogen, suggesting their derivation from an active arc setting. Geochemical data of EEST samples display similar SiO2 and Al2O3 abundances, with relatively intermediate compositions. Most of the studied samples demonstrate their derivation from a composite of oceanic island and continental arc systems providing felsic and mafic to intermediate detritus to the Skoura basin. Rare-earth element patterns show features similar to those of sandstones in modern active margin zones. The EEST rocks are similar with other Early Ediacaran sediments of the Saghro Group in the Anti-Atlas belt. This architecture suggests deposition of the EEST in an orogenic basin developed in a back-arc setting during the Early Ediacaran time.

Spatial-temporal variation patterns of groundwater tables in the middle section of the Hexi Corridor

It is of great significance to research spatial-temporal variations of groundwater tables from the perspective of the whole groundwater variable field in a basin. In this study, the original observation matrix was constructed using 38 monitoring wells data from 1984 to 2019 in the Heihe River Basin in the middle section of the Hexi Corridor and processed to be centered and standardized, respectively. The empirical orthogonal function (EOF) method was used to decompose the transformed matrices to obtain spatial and temporal variation patterns of groundwater tables which were represented by the spatial weights of typical uncorrelated modes with the corresponding temporal functions (TF). The resulting main variation pattern showed general drops in regional groundwater tables for both centered and standardized cases, especially in the southeast regions when using centered EOF modes. The second to fifth modes presented reverse distribution characteristics from the northwest to southeast directions. The downward trend in the first TF series indicated that the groundwater depth of the whole basin varied to be deeper. The local rise occurring at some sites demonstrated the positive effects of continuous ecological water delivery since 2000, but was still not recovered to the previous level due to long-term serious groundwater overdrawing.

Diurnal and nocturnal scavenger communities differ at two shallow-water depths in an Irish marine lough

We report on still/video photographic studies in 2018/9 of diurnal and nocturnal benthic scavenging on carrion in shallow water (2 m and 12 m depths) within Lough Hyne (a biodiverse Irish sea lough) using natural light during replicated 6 h daytime deployments and dim red light (630 nm) during 6 h deployments at night. In 2018 at 2 m depth in the North Basin, bait was present throughout day-time deployments, showing little evidence of scavenging; scavenger species' richness and abundance were low. At night, baits disappeared or were skeletonised; they were scavenged by a significantly more abundant and species-rich scavenger guild. At 12 m depth in the same basin, baits were removed or skeletonised during day and night. This confirmed our hypothesis that scavengers avoid well-lit very shallow water during the day, probably to avoid predation. Multivariate analysis of 2018/19 still photo data (12 m depth) revealed pronounced and statistically significant separate clustering of day, night and basin abundance/species data, although overall species' richness values did not differ significantly. These analyses together reflected differences in species’ compositions associated with contrasting sediments, flow regimes and night/day. Nephrops norvegicus, Pagurus bernhardus and Crangon crangon were only found in the low flow rate North Basin; Homarus gammarus, Trigla sp., Callionymus lyra, Agonus, Tritia reticulata and Marthasterias glacialis were only found in the high flow rate South Basin. Most scavenger species foraged in both day and night (though in different proportions). However, prawns (Palaemon serratus) only appeared at night. Small mobile scavenging fish, small crabs and prawns arrived at baits within seconds to minutes, as did locally-abundant slow movers (e.g. anemones (Anthopleura ballii), whelks (T. reticulata)). These times are shorter than recorded in earlier studies in deeper water. Larger crustaceans (e.g. Cancer pagurus, H. gammarus) took tens of minutes to hours before arrival; similar times have previously been recorded in deeper water. Large crustacean scavengers (C. pagurus, Maja squinado, H. gammarus) took substantial quantities of bait during long feeding bouts, but catsharks (Scyliorhinus canicula) often took similar quantities in a few seconds. All of the dominant scavenger species are broad-spectrum omnivores; only one obligate scavenger species (Tritia reticulata) was present (only in South Basin) and consumed negligible quantities of bait.

Basin and Site Effects in the U.S. Pacific Northwest Estimated from Small-Magnitude Earthquakes

ABSTRACTEarthquake hazards in the U.S. Pacific Northwest (PNW) are increased by the presence of deep sedimentary basins that amplify and prolong ground shaking. To better understand basin and site effects on ground motions, we compile a database of recordings from crustal and intraslab earthquakes. We process 8028 records with magnitudes from 3.5 to 6.8 and hypocentral depths up to 62 km to compute Fourier amplitude spectra of ground acceleration for frequencies of 0–20 Hz. We compute residuals relative to the Bayless and Abrahamson (2019; hereafter, BA18) ground-motion model and perform a series of linear, crossed, mixed-effects regressions. In addition to estimating the bias, event, and site terms, we incorporate groupings for broad regionalized site response in three different regions (Seattle basin, Puget Lowland, non-Puget Lowland), for effects from seismotectonic regime (crustal and intraslab sources), and for interactions between the regions and seismotectonic regimes. We find that the scaling of site response with respect to VS30 (time-averaged shear-wave velocity from the surface to a depth of 30 m) and to basin depth indicators Z1.0 and Z2.5 (depths to the 1.0 and 2.5 km/s shear-wave velocity horizons) is generally consistent with BA18; however, the region terms display strong spatial amplification patterns. For frequencies less than 5 Hz, the Seattle basin amplifies ground motions up to a factor of four, relative to the non-Puget Lowland, with a maximum amplification around near 0.5 Hz. Sites in the Puget Lowland amplify low frequencies up to a factor of 2.5. At higher frequencies (f&amp;gt;5 Hz), the Puget Lowland and Seattle basin show regional deamplification of ground motions, with the smallest average amplification factor of 0.65 occurring at 10.0 Hz. Although we observe slight differences in the seismotectonic regime terms, we find that the region terms are significantly more important for modeling earthquake hazard in the PNW.