Explore the vast range of titles available.

The study of ground resonances is important to assess seismic site amplification and to infer information on the geometrical and mechanical properties of the resonating structures. 1D- and 2D-type resonances imply different dynamic behavior that can be distinguished by inspecting the individual spectral components of single-station microtremor measurements. Typically, 2D resonance modes develop along cross-sections of deep sediment-filled valleys and consist of longitudinal, transverse and vertical modes that can be identified as spectral peaks when ground motion is recorded parallel to the axes of the valley. In the case of more complex geometries, such as sedimentary basins, resonance modes are more difficult to predict and depend on the unknown complexity of the buried bedrock geometry. We show how a simple signal rotation procedure applied to single-station microtremor recordings reveals the underlying 2D resonance pattern. The method allows assessing the axes of motion of buried geological structures and identifying 2D resonance modes along these axes. Their directionality, frequency and amplitude features are then analyzed to extract information on the bedrock geometry. We test our method in the Bolzano alluvial-sedimentary basin and we observe that apparently complicated resonance patterns may be simplified by locally referring to the simplest description of the phenomenon as 2D resonance of a valley slice. The bedrock morphology can be decomposed into 2D-like geometries, i.e., excavated channels, and the observed resonances develop within cross-sections of these channels.

The storage potential of hydrocarbon reservoirs in the central Gulf of Mexico (GOM) makes future development of CO[sub.2] storage projects in those areas promising for secure, large-scale, and long-term storage purposes. Focusing on the producing and depleted hydrocarbon fields in the continental slope of the central GOM, this paper analyzed, assessed, and screened the producing sands and evaluated their CO[sub.2] storage potential. A live interactive CO[sub.2] storage site screening system was built in the SAS[sup.®] Viya system with a broad range of screening criteria combined from published studies. This offers the users a real-time assessment of the storage sites and enables them to adjust the filters and visualize the results to determine the most suitable filter range. The CO[sub.2] storage resources of the sands were estimated using a volumetric equation and the correlation developed by the National Energy Technology Laboratory (NETL). The results of this study indicate that 1.05 gigatons of CO[sub.2] storage resources are available in the developed reservoirs at the upper slope area of the central GOM. The Mississippi Canyon and Green Canyon protraction areas contain the fields with the largest storage resources.

Stable carbon isotope ratios (δ13C values) of marine carbonates are widely used to infer the relative burial rates of organic carbon, a source of oxygen to the ocean‐atmosphere system. This inference, however, is based on the assumption that ocean‐atmospheric carbon is buried either as organic carbon or as marine carbonate minerals. The burial of authigenic carbonate minerals formed within sediments after deposition, with low δ13C values (i.e., similar to organic carbon), has been proposed to explain high δ13C values in marine carbonates without the need for high burial fluxes of organic carbon. To test this hypothesis, we focus on the Late Devonian, a time period with both pervasive ocean anoxia and a severe reduction in shallow‐water carbonate deposition—conditions hypothesized to promote authigenic carbonate formation. We present sedimentological and geochemical data from limestones and black shales of the Wabamun Group, Besa River and Exshaw formations of the Western Canada Sedimentary Basin. These data are compared to inorganic and organic weight percent measurements of North American shales acquired from the USGS National Geochemical Database (N = 4,437). Results show that basinal shale lack authigenic carbonate with low δ13C values and that the mean δ13C value of carbonate in these shales (−0.3‰) do not differ substantially from mean δ13C of carbonates in platform carbonates of a similar age (0.4‰). Furthermore, inorganic carbon content in Late Devonian shales (mean weight percent = 0.55%, N = 54) is lower than average Phanerozoic North American shale (mean of 1.95%, N = 4,055). Lastly, organic carbon‐to‐inorganic carbon ratios (OC:IC) of North American shales are well above 1 (mean = 3.72 for Late Devonian shales (N = 374), 2.25 for shales (N = 3,653) of all other ages). Therefore, even if the burial of fine‐grained siliciclastic formations carrying authigenic carbonates were to increase, the concomitant increase in organic carbon burial would be even larger. Together, data from this study do not provide evidence that the burial of authigenic carbonate would have a significant effect on global carbon isotope mass balance. Plain Language Summary Stable carbon isotope ratios (δ13C) of marine carbonate rocks are widely used as a proxy for estimating the relative amount of organic carbon buried throughout geological time. Certain instances in the geologic record indicate pronounced δ13C excursions for which there is no corroborating evidence for enhanced organic carbon burial. It has been proposed that these excursions may be the result of high burial rates of authigenic carbonate—carbonate minerals formed in situ within marine sediments. We test this hypothesis by analyzing the stable carbon isotope composition of Late Devonian limestones and shales of the Western Canada Sedimentary Basin. We also compare the organic and inorganic carbon compositions of shales from this field study with those from the USGS Geochemical database, an archive of North American shale geochemistry data from across the Phanerozoic. Results show that carbonates found in Devonian shales do not have low average δ13C values, and average organic carbon content was shown to be significantly higher than inorganic carbon in shale samples across the Phanerozoic. These results signify that authigenic carbonate burial had a negligible effect on the global carbon cycle, and furthermore, an increase in shale burial would result in a higher increase in organic carbon compared to authigenic carbonate. Key Points CaCO3 found in Late Devonian shales has average carbon isotope values similar to Late Devonian shallow marine carbonates Weight percent values of inorganic carbon content in Late Devonian shales are low compared to average North American shale The mass ratio of organic to inorganic carbon in Late Devonian shales is much higher than average North American shale

Deepwater regions have emerged as pivotal domains for global oil and gas exploration and development, serving as strategic alternatives to conventional resources. The Silk Road region is distinguished by its abundant oil and gas reserves and stands as a leading arena for worldwide exploration and development in the oil and gas sector. Since 2012, a series of atmospheric fields have been discovered in the deep sea of the Luwuma Basin and the Tanzania Basin, with cumulative recoverable reserves reaching 4.4 × 1012 and 8.3 × 1011 m3, including multiple oil and gas fields ranking among the top ten global discoveries at that time. Profound advancements have been achieved in the exploration of deepwater oil and gas reserves along the Silk Road. However, deepwater oil and gas exploration presents challenges, such as high development costs and risks, leading to certain areas remaining underexplored and exhibiting a relatively low level of exploration activity, thereby hinting at considerable untapped potential. Deepwater sedimentary basins along the Silk Road predominantly adhere to a distribution pattern characterized as “one horizontal and one vertical”. The “horizontal” dimension refers to the deepwater basin grouping within the Neo-Tethys tectonic domain, primarily extending from east to west. Conversely, the “vertical” dimension denotes the deepwater basin grouping along the East African continental margin, predominantly extending from north to south. Recent discoveries of deepwater oil and gas reserves validate the presence of foundational elements within Silk Road basins conducive to the formation of substantial oil and gas reservoirs and the establishment of efficient migration pathways. Despite these achievements, exploration activities in deepwater oil and gas resources along the Silk Road remain relatively limited. Future exploration endeavors in deepwater regions will predominantly focus on identifying structural and lithological traps. In the deepwater areas of the Bay of Bengal, the emphasis is on lithological traps formed by Neogene turbidite sandstone deposits. In the deepwater regions of Pakistan, the focus shifts to lithological traps emerging from Neogene bio-reefs and river-channel sandstone accumulations. Along the deepwater coastline of East Africa, the focus is on lithological traps formed by nearshore Mesozoic–Cenozoic bio-reefs and seafloor turbidite sandstone formations. Within the deepwater regions of Southeast Asia, the primary objective is to locate large structural-type oil and gas fields. Analyzing the characteristics of oil and gas discoveries in deepwater areas aims to enhance the theory of the control of the formation of deepwater oil and gas, providing valuable insights for predicting future exploration directions.

We decomposed complex synthetic wavefields in an inhomogeneous sedimentary basin into P-, SV-, and SH-wavefields, and quantitatively evaluated the amplitude, propagation velocity, and propagation direction of coherent waves in each decomposed wavefield within the 0.125–1 Hz frequency band. In sedimentary basins with irregular subsurface structures, P-, SV-, and SH-waves can coexist at the same location and time, propagating as either body waves or surface waves, where SH-waves manifest as Love waves and P- and SV-waves combine to form Rayleigh waves. The relative amplitudes of these wave types depend on both the source radiation pattern and the subsurface geometry. To accurately evaluate the propagation characteristics, such as amplitude and directional variation, of each wave type, it is necessary to first decompose the wavefield by wave type. To date, no studies have addressed this issue from such a perspective. We fully decomposed the reproduced strong-motion waveforms from the 2018 Mw 5.6 earthquake beneath the margin of the Osaka sedimentary basin in Japan—the target event of this study—into P-, SV-, and SH‑wave components using Helmholtz decomposition. By applying semblance analysis to the decomposed wavefields, we quantitatively evaluated the propagation processes of each wave type in the three-dimensional sedimentary basin. Using the derived propagation characteristics, we conducted pseudo-trajectory analysis (PTA) to visualize wave propagation paths, analogous to streamlines in fluid dynamics. We noted spatial differences in the SH‑ and SV‑wavefields. For example, during an early time window, ground motions were oriented northwest–southeast on both sides of the north–south fault zone in the Osaka Plain. These motions result from southwestward-propagating SH-waves in the western region and southeastward-propagating SV-waves in the eastern region. Later, in the western region, Love waves dominated in the 0.125–0.25 Hz band, while Rayleigh waves dominated in the 0.25–0.5 Hz band. The spatiotemporal amplitude variations of these wave types depend on the combined effects of the source radiation pattern and the subsurface structure as noted above. The proposed method can also be applied to identify, where and what types of waves are likely to be generated. Graphical Abstract

A shallow crustal velocity structure (above 10 km depth) is essential for understanding the crustal structures and deformation and assessing the exploration prospect of natural resources, and also provides priori information for imaging deeper crustal and mantle structure. Passive-source seismic methods are cost-effective and advantageous for regional-scale imaging of shallow crustal structures compared to active-source methods. Among these passive methods, techniques utilizing receiver function waveforms and/or body-wave amplitude ratios have recently gained prominence due to their relatively high spatial resolution. However, in basin regions, reverberations caused by near-surface unconsolidated sedimentary layers often introduce strong non-uniqueness and uncertainty, limiting the applicability of such methods. To address these challenges, we propose a two-step inversion method that uses multi-frequency P-RF waveforms and P-RF horizontal-to-vertical amplitude ratios. Synthetic tests indicate that our two-step inversion method can mitigate the non-uniqueness of the inversion and enhance the stability of the results. Applying this method to teleseismic data from a linear seismic array across the sedimentary basins in Northeast China, we obtain a high-resolution image of the shallow crustal S-wave velocity structure along the array. Our results reveal significant differences between the basins and mountains. The identification of low-velocity anomalies (≤2.8 km s −1 ) at depths less than 1.0 km beneath the Erlian Basin and less than 2.5 km beneath the Songliao Basin suggests the existence of sedimentary layers. Moreover, the high-velocity anomalies (∼3.4–3.8 km s −1 ) occurring at depths greater than 7 km in the Songliao Basin may reflect mafic intrusions emplaced during the Early Cretaceous. Velocity anomaly distribution in our imaging result is consistent with the location of the major faults, uplifts, and sedimentary depressions, as well as active-source seismic results. This application further validates the effectiveness of our method in constraining the depth-dependent characteristics of the S-wave velocity in basins with unconsolidated sedimentary cover.

This study focuses on the post-Miocene neotectonic evolution of the slope-perched sedimentary basins around the Eastern Korean Continental Margin and which category these basins could be classified into. The Hupo Basin, the largest neotectonic sedimentary basin on the Eastern Korean Continental Margin, comprises three key geological components: 1) Neotectonic Sequence, which has divergently filled the Hupo Basin since the Early Pliocene, 2) Hupo Fault, a N-S striking, high-angle thrust (or reverse) fault that bounds the Hupo Basin to the east, and 3) Hupo Bank, a N-S elongated submarine wave-cut platform that sits on top of the uplifted eastern Hupo Fault block. On the basis of stratigraphic and structural restoration, we conclude that the Hupo Basin was formed by the compressional uplift of the Hupo Bank during the incipient subduction of the Ulleung Basin crust after the Miocene. Given the morphostructural features of the Hupo Basin and its host incipient subduction system, we categorize it as a sort of piggyback basins. The basin-forming process shown in this study is commonly found in numerical models that simulate modern cases of subduction initiation around the world.

This study proposes using a two-dimensional nonlinear gravimetric inversion methodology based on the regularized Quasi-Newton method to infer the geometry of the boundary between the sedimentary deposit and its basement and to define the simulated lateral density contrast in a sedimentary basin environment. The interpretation model consists of a set of rectangular prisms in 2D space. The parameters estimated in this inversion proposal are the thickness of each prism and its density contrast, interpreted in terms of the depth of the basement and the lateral variation of contrast between the basement and the basin sediment. While most commonly used inversion programs neglect lateral density contrast to estimate basement depth, resulting in algorithms that overlooks much of the lateral geological complexity present in the subsurface, the proposal of this work encompasses such complexities more generically. In this research, the initial analysis involved tests with gravimetric anomalies generated by two synthetic models that exhibited variations in basement depth and lateral density contrast. Subsequently, the methodology developed was applied to data from the high-resolution Earth gravity field model, SGG-UGM-2, along a profile crossing the central part of the Tucano Basin, Bahia, Brazil.

Fluids in sedimentary basins exert a crucial influence on various geological phenomena including natural resource formation. Worldwide drilling projects have revealed that the salinity of sedimentary basinal fluids generally increases with depth, irrespective of lithology, age of sediments, or the presence of a halite bed. However, how these vertical salinity variations are produced and what controls the salinity remain unclear. This work examines a new hypothesis that downward‐increasing salinity variations are a natural outcome of the constant chemogravitational potential condition. In a static environment, the salinity is distributed such that the chemogravitational potential of the solute is constant with depth. Once formed, such a distribution would be maintained because no further migration of the solute would occur. To test the hypothesis, a constant chemogravitational potential distribution model was constructed for NaCl–H2O fluids in the sediment column, and NaCl content at each depth was calculated. The results showed that NaCl content monotonically increases with depth, and the variations are similar to the trend of measured data. However, the data were not necessarily completely reproduced by the model, and deviated in some parts from the calculated profile. Such deviation may indicate fluxing of external fluid occurring in these parts, as the constant chemogravitational potential is vulnerable to an advective flow. Therefore, it is proposed that the constant chemogravitational potential condition is a possible endmember theory, influencing natural salinity variations in a static environment. Key Points Vertical variations in salinity of sedimentary basinal fluid were simulated under constant chemogravitational potential conditions The simulation showed that the salinity increases with depth and the salinity gradient is positively dependent on the geotherm The constant chemogravitational potential distribution is roughly coincident with the data of natural sedimentary basinal fluids