Basin Depth Research Articles

Effects of Pressure on Nitrogen Content and Solidification Structure during Pressurized Electroslag Remelting Process with Composite Electrode

The nitrogen content and solidification structure of the 1Mn18Cr18N ingots produced by the customized laboratory‐scale vacuum induction melting furnace and the pressure electroslag remelting furnace (PESR) with novel composite electrode under different pressure and the same power consumption are compared and studied. The results show that there are perfectly uniform radial chromium and nitrogen profiles during the PESR process. The nitrogen uptake reaction in the PESR process with composite electrode takes place on the liquid metal film on the electrode. Nitrogen uptake could be improved by increasing the nitrogen partial pressure. In addition, the basin depth at a pressure of 0.1 and 1.22 MPa is about 41 and 38 mm, the angle of the grains with respect to the vertical axis is 35° and 31°, respectively. The flat metal basin profile resulted from the thermal resistance at the slag–mold interface decreasing with increasing pressure. Primary and secondary dendritic arm spacing (PDAS and SDAS) variations exhibit an increasing and subsequently decreasing the trend as they move further away from the center in a horizontal direction. Both PDAS and SDAS decrease with increasing pressure from 0.1 to 1.22 MPa.

Revisiting the 1934 Mw 8.2 Bihar–Nepal earthquake—Simulation of broadband ground motions

SUMMARY The 1934 Mw 8.2 Bihar–Nepal earthquake was one of the devastating earthquakes, which made seismologists realize the importance of proper seismic hazard analysis and design aspects in India. The event occurred way before proper seismic networks were implemented and hence there are no recorded ground motions available for this event. This study, thus aims to generate possible ground motions for the 1934 Mw 8.2 Bihar–Nepal event. The complex geographical features, ambiguous source information and lack of ground motion data make the simulation and validation of ground motions very difficult. In this regard, the broad-band (BB) ground motions are simulated and validated for the most recent well-documented Himalayan event, that is, the 2015 Mw 7.9 Nepal earthquake in order to calibrate the model and simulation methodology. For this purpose, the computational model is presented for a region of 1000 km × 670 km (longitude 80–89 °E and latitude 23–30 °N) in the Indo-Gangetic Basin to simulate the low-frequency (LF) ground motions using spectral element method. These deterministically simulated LF ground motions are combined with stochastically simulated high-frequency (HF) ground motions based on an improved seismological model . The seismic moment and dimensions of the rupture plane are used to generate ten samples for the finite fault source model having different slip distribution along the rupture plane as a random field. The BB ground motions (0.01–25 Hz) are obtained by merging LF and HF ground motions in the time domain by matching them at a frequency of ∼0.3 Hz. Such BB results are simulated at a grid of stations and at locations where modified Mercalli intensity (MMI) values are available. The estimated MMI values and the observed MMI values are compared to emphasize the efficacy of the model. The maximum PGA estimated from the simulated ground motions in horizontal and vertical directions are observed to be 0.48 g and 0.4 g. Further, 5 per cent damped response spectra and spectral amplification are analysed concerning the sediment depth of the Indo-Gangetic Basin. The results from the study can serve as inputs for dynamic analysis and the design of earthquake-resistant structures across different locations in the Indo-Gangetic Basin.

Mapping Los Angeles Basin Depth With Sp Converted Phases

Mapping Los Angeles Basin Depth With Sp Converted Phases

The Styrian Basin: an overview with new insights from seismic data

The Neogene Styrian Basin is the westernmost subbasin of the Pannonian Basin System. The last comprehensive studies on the basin were published in the last millennium. This overview of the current understanding of basin evolution is based on the re-interpretation of partly unpublished reflection seismic data and a wealth of sedimentological and stratigraphic studies performed during the last 25 years. Reflection seismic data indicate the presence of a major E to SE dipping detachment horizon within the pre-Neogene basement reflecting high-strain upper crustal extension during the early Miocene syn-rift stage of basin evolution. Fault block rotations caused subsidence in several subbasins, which developed often with marked asymmetric geometry. The maximum basin depth exceeds 4 km (Gnas Basin). Syn-rift deposits include thick alluvial fan and fan delta sediments overlain in the basin center by deeper marine pelitic rocks. Subduction-related magmatic activity commenced during the syn-rift stage and continued into the middle to late Miocene post-rift stage. Syn- and post-rift sediments are separated by the middle Miocene “Styrian Unconformity”. Shallow marine sedimentation, controlled by third- and fourth-order sea-level variations, prevailed during the early post-rift stage. The final stage of basin evolution was characterized by differential surface uplift, erosion, and Pliocene-Pleistocene basaltic magmatism.

Effects of upstream and downstream boundary conditions on lacustrine shallow-water delta morphologies: A numerical modeling approach

Lacustrine shallow-water deltas exhibit highly variable morphologies, owing to their high sensitivity to changes in the upstream and downstream boundary conditions, where a small change significantly alters their morphology. In this study, we present the results from a numerical model (DELFT3D) used to explore the mechanism of distributary network amalgamation and delta evolution under various boundary conditions. We established a reference case to model the delta building-out process considering the basin water depth difference (shallow and deep). Geological and hydrodynamic models were established by varying the water level under a steady river discharge and sediment supply. Despite similar initial conditions, each modeled delta exhibits a unique morphological evolution, progressing through distinct stages: (i) formation of unstable, narrow channels with quasi-radial shapes; (ii) channel development, shaping the delta based on controlling factors; (iii) reduction of deltaic activity and increased channel avulsion due to delta submergence, and; (iv) new channels emerging, paving the way for reshaping and migration towards new paths, resulting in fewer bifurcations and straighter channels. Quantitative relationships characterizing delta morphology and distributary channels were established, and the following results were noted: (i) a positive correlation between active and abandoned channels, distributary channel network opening angle, and delta area with discharge and sediment grain size, and negative correlation with basin depth and falling water level; (ii) a positive correlation of lobe elongation with basin depth and discharge, and a negative correlation with sediment grain size; and (iii) roughness and length-to-width ratio emerging as key predictors of delta shape. By applying the model predictions to real-world scenarios, including modern deltas (Sile and Chiemsee) and ancient systems (Bohai Bay Basin), this study can provide valuable insights into the dynamics of lacustrine deltaic systems and their responses to changing boundary conditions. This highlights the importance of understanding deltaic systems for both theoretical research and practical applications.

Performance optimization and comparative study of a conical solar distiller with optimized construction of aluminium balls as energy storage materials

This study seeks to find the ideal size of aluminum balls to improve the effectiveness of conical solar stills for storing energy, due to the increasing demand for drinking water and the high costs of getting portable drinking water. To achieve this, three comparable conical solar distillers were made using aluminum balls of various diameters (1 cm, 1.5 cm, 2 cm, and 2.5 cm) at a 4 cm center spacing. Two days were spent on the experiments. The first distiller had no metal balls on the first day, whereas the second and third had 41 1 cm and 1.5 cm aluminum balls uniformly dispersed at the bottom. On the second day, the first distiller had no metal balls, but the second and third had 41 2 cm and 2.5 cm balls. The water basin depth was consistently maintained at 2.5 cm. The results revealed that the distiller with 2 cm diameter aluminum balls achieved the highest productivity, yielding 840 mL/m2, compared to the distillers with aluminum balls of 1 cm, 1.5 cm, and 2.5 cm diameter, as well as the conventional distiller without any storage materials, which yielded 645 mL/m2, 695 mL/m2, 755 mL/m2, and 570 mL/m2, respectively. The ideal diameter for the aluminum balls was found to be 2 cm, leading to a significant 47.37 % enhancement in water productivity. Conical solar stills using 2 cm diameter aluminum balls as an economical energy storage material provide the best answer.

The significance of basin slope for curve number estimation and the impact on flood prediction in arid basins

ABSTRACT The Natural Resources Conservation Service Curve Number (NRCS-CN) method was developed in agricultural basins with slopes less than or equal to 5%. This research investigates the relationship between the basin slope and runoff depth in arid basins by the NRCS-CN method. The results show that there is a clear effect of the proposed curve number equation with slope (the slope adjusted CN, CN IIα ) on the runoff depth in the studied basins, and this is consistent with the literature. However, large basin areas with a high percentage of alluvium area and vegetation, and high infiltration rates, counteract the slope of the basin, and consequently the basin slope will not have a significant effect on runoff. The correlation coefficient of various developed equations varies between 0.89 and 0.93 and the root mean square error of runoff depth varies between 11 mm for λ = 0.2 and 5.2 mm for λ = 0.01.

Applicability of 1D site response analysis to shallow sedimentary basins: A critical evaluation through physics‐based 3D ground motion simulations

AbstractOne‐dimensional site response analysis (1D SRA) remains the standard practice in considering the effect of local soil deposits and predicting site‐specific ground motions, although its range of applicability to realistic seismic wavefields is still in question. In this 1D approach, horizontal and vertical ground shaking are assumed to be induced by vertically propagating shear and compressional waves, respectively. A recent study based on analytical two‐dimensional (2D) plane waves and simple point source earthquake simulations has shown two mechanistic limitations in this 1D modelling technique for general inclined seismic waves, that is, systematic over‐prediction of the vertical motion and wave trapping in the 1D soil column. In this article, we evaluate in detail the applicability of this 1D modelling approach to realistic three‐dimensional (3D) simulated seismic wavefields in shallow sedimentary basins. Linear‐viscoelastic 1D SRA predictions using two types of input motions that are commonly used in practice—rock outcrop and in‐column motions, are compared with the reference true site response results from 3D earthquake simulations in terms of various measures in the frequency and time domain. It is shown that the horizontal motion in the 3D seismic wavefield exhibits dominant shear wave propagation phenomenon, while the vertical motion is a combined effect of compressional and shear waves and can be over‐predicted by the 1D approach when the incident seismic waves are inclined. Direct evidence of the wave refraction process that leads to the vertical motion over‐prediction is provided. 1D SRA with in‐column inputs can yield motions that have significantly longer duration compared to the true 3D site response solution due to trapped waves, casting in doubt the frequent need for increased soil damping in existing site studies to compensate for wave attenuation due to scattering alone. Sensitivity investigation on the increase of soil profile damping by a multiplier Dmul shows Dmul values compatible with those found in the literature for both horizontal and vertical motions. It is shown that the level of Dmul optimized for a best match of the spectral acceleration is dependent on the characteristic of the input motion and a larger Dmul is typically required for the vertical component. In contrast, 1D SRA with outcrop motions predicts motions with shorter significant duration due to its inability to capture the basin‐edge generated surface waves. A suite of ground motion simulations was performed to assess the sensitivity of the observations to the basin geologic structure including the velocity gradient, rock‐basin impedance contrast and basin depth. The analysis results show that the accuracy of the simplified 1D procedure is dependent on the wavefield composition of both the input motions and the true 3D site response solution. While the horizontal motions in shallow sedimentary basins can, to the first order, be reasonably captured by the simplified 1D approach, 1D SRA for the vertical component is in general not reliable and contributions from inclined shear waves should be accounted for in site‐specific evaluation of the vertical design ground motion.

Lithofacies Characteristics of Continental Lacustrine Fine-Grained Sedimentary Rocks and Their Coupling Relationship with Sedimentary Environments: Insights from the Shahejie Formation, Dongying Sag

Lacustrine fine-grained sedimentary rocks in the Dongying Sag of the Bohai Bay Basin in China exhibit significant potential for hydrocarbon exploration. This study investigates the lithofacies types and sedimentary evolution of the Paleogene Shahejie Formation’s lower third member (Es3l) and upper fourth member (Es4u), integrating petrological and geochemical analyses to explore the relationship between lithofacies characteristics and sedimentary environments. The results show that the fine-grained sedimentary rocks in the study area can be classified into 18 lithofacies, with seven principal ones, including organic-rich laminated carbonate fine-grained mixed sedimentary rock lithofacies and organic-rich laminated limestone lithofacies. In conjunction with analyses of vertical changes in geochemical proxies such as paleoclimate (e.g., CIA, Na/Al), paleoproductivity (e.g., Ba), paleosalinity (e.g., Sr/Ba), paleo-redox conditions (e.g., V/Sc, V/V + Ni), and terrigenous detrital influx (e.g., Al, Ti), five stages are delineated from bottom to top. These stages demonstrate a general transition from an arid to humid paleoclimate, a steady increase in paleoproductivity, a gradual decrease in paleosalinity, an overall reducing water body environment, and an increasing trend of terrestrial detrital input. This study demonstrates that the abundance of organic matter is primarily influenced by paleoproductivity and paleo-redox conditions. The variations in rock components are predominantly influenced by paleoclimate, and sedimentary structures are affected by the depth of the lake basin. Special depositional events, such as storm events in Stage II, have significantly impacted the abundance of organic matter, rock components, and sedimentary structures by disturbing the water column and disrupting the reducing conditions at the lake bottom. The present study offers crucial insights into the genesis mechanisms of continental lacustrine fine-grained sedimentary rocks, facilitates the prediction of lithofacies distribution, and advances the exploration of China’s shale oil resources in lacustrine environments.

Empirical ground-motion basin response in the California Great Valley, Reno, Nevada, and Portland, Oregon

We assess how well the Next-Generation Attenuation-West 2 (NGA-West2) ground-motion models (GMMs), which are used in the US Geological Survey’s (USGS) National Seismic Hazard Model (NSHM) for crustal faults in the western United States, predict the observed basin response in the Great Valley of California, the Reno basin in Nevada, and Portland and Tualatin basins in Oregon. These GMMs rely on site parameters such as the time-averaged shear-wave velocity ( VS) in the upper 30 m of Earth’s crust ( VS30) and depths to 1.0 and 2.5 km/s shear-wave isosurfaces ( Z1.0 and Z2.5) to capture basin effects and were developed using observations and simulations primarily from the Los Angeles region in southern California. Using ground-motion records from mostly small-to-moderate earthquakes and mixed-effects regression analysis, we find that the GMMs perform well with our local basin-depth models for the California Great Valley. With our local basin-depth models for Reno, the GMMs do not perform as well for this relatively shallow basin and exhibit little sensitivity to the basin parameters used in the NGA-West2 GMMs. We also find good performance for the local Z1.0 model across the Portland region, whereas the local Z2.5 model provides little predictive power except at sites in the deepest part of the Tualatin basin. Additional work could improve the performance of the site and basin terms in the NGA-West2 GMMs for regions with geologic structure different than the deep basins in southern California and the Great Valley. In addition, we find significant discrepancies among the GMMs in how the uncertainty in the ground motion varies with basin depth and pseudospectral period. Our results can help guide seismic hazard analyses on whether to include these local basin-depth models.

Basin effects from 3D simulated ground motions in the Greater Los Angeles region for use in seismic hazard analyses

We develop basin-depth-scaling models (i.e. “basin terms”) from the long-period ([Formula: see text]) simulated ground motions of the Southern California Earthquake Center (SCEC) CyberShake project for use in seismic hazard analyses at sites within the sedimentary basins of southern California. Basin terms use the Next Generation Attenuation (NGA)-West-2 ground-motion models (GMMs) as reference models and use their functional forms with slight modifications. We investigate the use of two approaches to incorporate the time-averaged shear-wave velocity in the upper 30 m ([Formula: see text]) in these calculations and find that the use of site-specific and uniform [Formula: see text] has minor effects on the resulting basin terms for this data set. By centering the simulated ground motions on the basin terms, we separate the information from the simulations about absolute ground-motion level from information relating to the relative amplifications, such as the differences between shallow- and deep-basin sites. Recent observations from sedimentary basins of southern California indicate that additional amplification effect may persist at relatively shallow basin depths (i.e. the GMM basin terms should have positive values when differential depths, [Formula: see text], are near zero), and we present models for “centered” and “adjusted” basin-depth scaling models that reflect this potential. The simulation-modified GMMs are appropriate for crustal sources and for deep-basin sites ([Formula: see text]) within basins of the Greater Los Angeles region, for the magnitudes and distances defined by each of the reference NGA-West-2 GMMs.

Trends in the ocean mixed‐layer depth in the western North Pacific tropical cyclone basin

AbstractThe upper ocean mixed‐layer depth (MLD) has been recognized as a crucial factor in understanding the impact of climate change on tropical cyclone (TC) intensity, while the specific MLD variations in the western North Pacific (WNP) basin have received comparatively little attention. Using two ocean reanalysis datasets and the output of 28 CMIP6 models, the climatological mean MLD and its trend in the TC active region are examined. Compared to the ORAS4 and EN4 datasets, the spatial pattern of the climatological mean MLD can be well simulated in the multi‐model ensemble (MME). The mean MLD decreases with increasing latitude and maintains the maximum in the equatorial region. The spatial patterns of MLD long‐term (1958–2017) and short‐term (1979–2017) trends are deepening in the TC active region, with the relatively large positive trends occurring to the southeastern WNP primarily between 5°N and 15°N. However, the simulated trend in the MME is dominant with shoaling MLD, and the shoaling of the MLD is also projected under the SSP5‐8.5 scenario. It is suggested that the bias on the simulated shoaling of the MLD in CMIP6 models may result from the overestimated enhancement of the upper‐ocean stratification. Thus, there is a discrepancy between the observed and simulated MLD trends in the WNP basin, which may have implications for TC intensity change under global warming scenarios.

Depth-to-Basement Estimates Using Magnetic Data of the Iraqi Southern Desert: A Statistical Approach

Regions characterized by a considerable thickness of sedimentary cover situated on a basement complex are always interesting. These regions require accurate basement data that includes defining the locations of high thicknesses in sedimentary beds (the basins). The Southern Desert of Iraq is one of these regions that is still subject to more detailed studies concerning basement geology. Utilizing the magnetic data, we present five depth-to-basement maps using techniques that hold different theoretical assumptions and model characterizations. Further, we have obtained a sixth map using a statistical approach which is built on the selection of depth-position points that have depths confirmed from the five maps. These points are chosen along depth profiles whenever the depth curves, of the depth-to-basement maps, are met or clustered referring to close depth estimations. The derived map could be more reliable than the other five maps and may be used to suggest drilling boreholes in areas of shallow basement. The minimum estimated depth-to-basement is ~4.5 km. Moreover, the derived map shows the locations and depths of deep sedimentary basins that reach 10 km deep.

Application of GK17 Ground-Motion Model to Preliminary Processed Turkish Ground-Motion Recordings Dataset and GK Model Adjustment to the Turkish Environment by Developing Partially Nonergodic Model

Abstract The global ergodic GK17 (Graizer, 2018) ground-motion model developed using the Next Generation Attenuation-West2 database (Ancheta et al., 2014) for the active crustal regions (ACRs) was applied to the dataset of recordings from the two largest moment magnitude Mw 7.8 and 7.5 earthquakes in Türkiye (Buckreis et al., 2023a). The GK17 model demonstrates acceptable performance while mostly underpredicting spectral accelerations (SAs) at near-fault up to ∼100 km and far-field more than ∼400 km rupture distances for periods T < 1 s. The GK17 model was modified by applying additional Rrup distance and VS30 residuals corrections, creating an updated GK nonergodic model tuned for Türkiye called the GK_T model. After varying anelastic attenuation of SAs QSA, it was concluded that the average for the ACRs value of QSA=120 produces the best results. Comparisons of the model site amplification functions (SAFs) show that the GK_T SAFs are lower compared to the GK17 model. The Türkiye-specific GK_T partially nonergodic model shows better agreement with the recorded data than the ergodic GK17 model, especially at short periods and short rupture distances. As expected, application of the Türkiye-specific model results in a lower sigma. It is also lower than the within-event sigma of the GK17 model, except for the period range of 1.5 < T < 3 s. Improvements to the GK_T model can be expected with an addition of deep sediment (basin depth) information to the current dataset and other earthquakes in the region.

Green Heat and Wind Factors in Sustainable Urban Development of Mountain-Basin Relief

The article studies mountain basin relief’s influence on the heat and wind regime organization when developing it for sustainable urban planning purposes. Each time a unique relief is identified, it requires an individual design approach taking into account the identification of the aesthetic expressiveness of green settlement development. Depending on the slope, there may be different options for using the site. The article presents the features of the geometry of the mountain-basin space associated with the relative depth of the mountain basin. The thermal field of the mountain-basin space, which is formed due to the energy of incoming solar radiation and the internal heat of insolated urban development, is analyzed. The city’s mountain-basin terrain requires an individual design approach, taking into account the identification of the aesthetic expressiveness of green settlement development. Based on the generalization and analysis of studies of air flows’ structure, their direction, velocity, and temperature fields, as well as the characteristics of the microclimate in the development of the mountain-basin space, an aerodynamic picture of air movement arising under the influence of natural thermal forces was obtained. The thermal field of the mountain-basin space has been established, which is formed due to the energy of incoming solar radiation and the internal heat of insolated urban development. The proposed methodology for calculating the heat and wind conditions of development is the basis for preliminary forecasting, assessment, and regulation of heat and wind parameters, as well as optimization of the sustainable development planning of mountain-basin relief.

Spatial and temporal dynamics of near-bottom dissolved oxygen in the central basin of Lake Erie

Abstract Eutrophication continues in Lake Erie and low oxygen concentration remains a concern in the central basin of the lake. Summertime dissolved oxygen concentrations can be hypoxic (low dissolved oxygen) and anoxic (dissolved oxygen <1 mg l-1) in the hypolimnion. We examined the spatial and temporal patterns of hypoxia in the central basin along a ∼ 26 km west-east station transect in the western portion of the central basin (depth gradient from 11.4 m in the west to 20 m in the east). Water column properties were monitored using moored instruments (dissolved oxygen, temperature, turbidity, Chlorophyll a fluorescence) and instrument profiling during cruises in 2008 and 2009. Hypoxia was examined using a biologically relevant value of 40% dissolved oxygen saturation (i.e. ∼4 mg l-1) and 25% dissolved oxygen saturation (i.e. ∼2.5 mg l-1) as used by government agencies. Our goals were to determine the onset and location of hypoxia, as well as the frequency of hypoxic events. We observed differences in the spatial and temporal patterns between the two years, related potentially to different water levels, stronger winds, and a smaller hypolimnion and lower thermocline depth in 2009. Near-bottom hypoxia occurred in the east at the end of June and extended westward by the end of July 2008 using 40% saturation; in early July to mid-August using 25% saturation. The onset of hypoxia (40% sat) occurred earlier in the west in 2009 but was similar to 2008 using 25% saturation. Hypoxia was not static, rather there were a total of ∼100 events of both levels of hypoxia, which were of different duration, noted across the transect in both years. Both the frequency and duration of hypoxic events (> 1 min) were higher and longer in 2008, perhaps related to water circulation and the resuspension of bottom sediment by synoptic-scale storms, which coincided with low oxygen events. Understanding the spatial and temporal patterns of hypoxia provides insight into their effects on habitat quality as well as biogeochemical processes in benthic and hypolimnetic environments in Lake Erie.

Preliminary analysis of amplified ground motion in Bangkok basin using HVSR curves from recent moderate to large earthquakes

BackgroundThe Bangkok Basin has been known from non-instrumental observations of the local population to be subject to ground motion amplification due to the deep alluvial sediments and basin geometry. This study analyzes available seismic data to confirm that basin effects are significant in the Bangkok Basin. The paper contributes to the evaluation of basin effects by characterizing the engineering ground motion parameters and HVSR curves for the Bangkok basin which produce lengthening of ground motion duration with respect to nearby rock sites, albeit with very low ground motions. For this purpose, we analyzed ground motion records from seismic stations located within the Bangkok alluvial basin from 2007 to 2021. Recorded peak horizontal ground acceleration (PGA) for seismic stations inside the basin always exceeded 1 cm/s2 during eight earthquakes with Mw ≥ 5.5. Of these, two were intraslab events and six were shallow crustal earthquakes. These recorded ground motions shook high-rise buildings in Bangkok even though their epicentral distance exceeded 600 km.MethodsSeveral time and frequency domain analyses (such as analysis of residual, HVSR, Hodogram plots, etc.) are used on the ground motion records in the Bangkok basin to determine the frequency content of recorded ground motion and to demonstrate the significance of surface waves induced by the deep basin in altering the engineering ground motion amplitudes. In addition, centerless circular array microtremor analysis is used to determine the depth of sedimentary basin to the bedrock.ResultsBased on comparisons from those stations located outside the Bangkok basin, we observed the capability of alluvial deposits in the Bangkok basin to amplify ground motion records by about 3 times. We observed that there is a unique site amplification effect between 0.3 and 0.1 Hz due to local surface waves and other moderate amplifications between 2 and 0.5 Hz due to a soft layer like other deep alluvial basins in other metropolitan areas.ConclusionWe noticed that there is a unique site amplification effect between 0.1 and 0.3 Hz and smaller peaks around 2 and 0.5 Hz consistent with expectations for site amplification effects associated with deep basins. Moreover, we noticed the presence of low frequencies content of the surface wave generated within the basin which deserved further studies using the 2D/3D ground motion modelling through basin topography and velocity models.

Sediment thickness map of United States Atlantic and Gulf Coastal Plain Strata, and their influence on earthquake ground motions

With the recent successful accounting of basin depth ground-motion adjustments in seismic hazard analyses for select areas of the western United States, we move toward implementing similar adjustments in the Atlantic and Gulf Coastal Plains by constructing a sediment thickness model and evaluating multiple relevant site amplification models for central and eastern United States seismic hazard analyses. We digitize and combine existing sediment thickness data sets into a composite surface that delineates the base of Cretaceous sediments under the Atlantic Coastal Plain and the base of Mesozoic sediments under the Gulf Coastal Plain. Amplification models dependent on sediment thickness, site natural period, and source-to-site path length are compared with data sets of observed ground motions to evaluate the ability of the new models to improve ground motion estimates. We find that the amplification models can account for observed trends in sediment-thickness and period-dependent residuals, but some tuning is required. For example, the model of Chapman and Guo requires a reference VS30, the time-averaged shear-wave velocity within 30 m of the Earth’s surface, for non-Coastal Plain sites, which we estimate to be between about 1 and 2 km/s. Along with our sediment thickness model, we estimate a velocity profile for application to the Harmon et al. site-natural-period-based model in order to best match the Chapman and Guo period dependence for a broad range of sediment thicknesses. The Next Generation of Attenuation models for the eastern United States Gulf Coast path-based adjustment models can also account for seismic attenuation in the Coastal Plain sediments and reduce the standard deviation of total residuals. If enacted in the U.S. Geological Survey National Seismic Hazard Model, these amplification models will reduce predicted short-period (<1 s) and increase predicted long-period (>1 s) ground motions in the Coastal Plains appreciably.

Salinization, warming, and loss of water clarity inhibit vertical mixing of small urban ponds

AbstractUrbanization drives multiple environmental changes that influence critical ecosystem processes. Factors such as salinization by deicing road salts, reduced water clarity (and greater light attenuation) from eutrophication and sediment loading, and warming constrain not only the biodiversity of ponds, but also their physical mixing (with consequences for oxygen availability and the provision of ecosystem services). Leveraging an extensive urban gradient in the Greater Toronto Area, we collected summertime depth profiles from 50 stormwater retention ponds to investigate their vertical stratification. We found that water columns were generally stratified but contrary to expectations, we found relatively minor roles of basin area and depth. Instead, we discovered an overwhelming effect of salinity along with significant impacts of temperature and water clarity on water density gradients. Findings extend our fundamental understanding of mixing regimes in small, shallow waterbodies and indicate increasing risks to pond functioning in a warmer and saltier future.

Terrestrial heat flow and subsidence of the Eastern Mediterranean Sea

We analysed the bathymetry and both marine and continental heat-flow data of the Eastern Mediterranean Sea basins. Bathymetry was corrected for the subsidence caused by sediment deposition to obtain the water-loaded seafloor depth. The thermal measurements were critically reviewed and corrected for sedimentation by 1–13 mW m−2 and for climatic changes by 4–5 mW m−2 to infer the purely conductive terrestrial heat flow. The seafloor depths and thermal data of the Ionian, Herodotus and Levantine basins were compared to reference models of continental lithosphere stretching and ocean plate cooling. In the Levantine Basin, the seafloor depth of 5.0 km argues for a continental crust that thinned ∼100 Ma ago by a factor of 2.7. The seafloor depth of the Herodotus and Ionian basins (7.5 and 6.3 km, respectively) does not match the continental stretching model predictions, suggesting they are floored by oceanic lithosphere. The reference models for the plate cooling and subsidence only partly account for the seafloor depth of the Eastern Mediterranean Sea basins. The seafloor of the Ionian agrees or is slightly deeper than the reference models, while in the Herodotus, it may exceed the expected subsidence of about 1 km. Compared to the reference models of plate cooling, the heat flow of the Herodotus and Ionian basins is lower by about 10 mW m−2. Together with the seafloor depth and gravity anomaly pattern, this argues for a cold and thick lithosphere beneath the Ionian and Herodotus basins. The lower heat flow may suggest that the basins escape from classical schemes of oceanic lithosphere cooling or that the reference models cannot be used for such old seafloors.