Seismic Profiles Research Articles

The latest activity of the slope fault zone (Pearl River Mouth) in northern South China Sea and implications for earthquake hazard assessments

In the northern region of the South China Sea, located at the intersection of the continental shelf and slope, there have been recorded four earthquakes with magnitudes M ≥ 6.0. This pattern of seismic activity suggests the presence of a previously unidentified active submarine fault. Notably, no active faults have been documented in this area prior to our investigation, with earlier studies predominantly focusing on the structural morphology and sedimentary basin evolution associated with the South China Sea's spreading phenomenon. Through the examination of seismic profiles and historical earthquake records, we have identified a newly discovered fault, termed the Slope Fault Zone (SFZ). The SFZ exhibits diverse structural components, including a listric normal fault in the western sector and a strike-slip fault zone in the eastern sector. Analysis of shallow seismic profiles and borehole data has revealed that the SFZ intersects with strata from the late Pleistocene epoch, confirming its classification as an active fault. The derived fault parameters indicate that the western segment of the SFZ has the potential to generate earthquakes of considerable magnitude, ranging from M 6.7 to 7.2. Furthermore, given the significant occurrence of submarine landslides along the southern boundary of the SFZ, there exists a risk that such seismic events could trigger slope failures and subsequent tsunamis. In summary, our research has unveiled the presence of an active fault capable of precipitating submarine earthquakes, landslides, and tsunamis.

Applying seismic sedimentology to characterize the architecture of a fan delta complex: Triassic Baikouquan formation, Mahu Sag, Junggar Basin, western China

Reservoir architecture is often heterogeneous and can affect the migration and accumulation of hydrocarbons. The Triassic Baikouquan Formation in the Mahu oilfield presents a unique opportunity to use seismic data for fan delta channel and lobe belt characterization in an area with a sparse well spacing of about 800–1200 m. The Baikouquan Formation comprises coarse-grained lacustrine fan delta units deposited by traction and debris flows. The occurrence, distribution, and morphology were investigated using petrography, frequency spectrum decomposition, stratal slices, seismic forward modeling, and wireline logs. Fan-shaped lobe complexes and distributary channel complexes (sixth-order architectural units) exhibiting relatively large lateral and vertical variation were identified from 45- and 60-Hz seismic profiles. Channel and fan-shaped lobe belts (fifth-order architectural units) were investigated by integrating provenances, architectural elements from individual wells, the ratio of conglomerate to formation, cross section analysis, and seismic stratal slices. Four channel belts and three fan-shaped lobe belts were recognized, occurring in six evolutionary stages. It was discovered that these channel and lobe belts had distinct geomorphological traits. Reservoir architecture and distribution was governed by paleogeomorphology, fluctuations in accommodation space, and sediment supply. The identified fifth-order architectural units are useful for reservoir modeling and contribute to remaining oil development. This study indicates the suitability of seismic sedimentology for characterizing reservoir architecture in areas with sparse well spacing.

Sound velocities in lunar mantle aggregates at simultaneous high pressures and temperatures: Implications for the presence of garnet in the deep lunar interior

Recent experimental and theoretical studies on lunar magma ocean crystallisation have suggested the presence of significant proportions of garnet in the deep lunar interior. While phase relation studies indicate a deep lunar mantle consisting of olivine, pyroxene, and garnet, the compatibility of such an assemblage with seismic models of the lunar interior is yet untested. In this study we report compressional and shear wave velocities in an iron-rich assemblage consisting of olivine, orthopyroxene, clinopyroxene, and garnet up to ∼8 GPa and 1300 K, by means of ultrasonic interferometry measurements combined with synchrotron techniques using the multi-anvil press apparatus. Sound velocity and density models of lunar mantle rocks along a selenotherm based on our experimental results find good agreement with the seismic and density profiles at lunar interior depths of 740–1260 km. Further models are constructed, allowing for the variation of chemical composition, phase proportion, and temperature; these suggest that a garnet-rich deep lunar mantle is compatible with present-day lower lunar mantle temperatures of between 1400–1800 K. Our results show that lunar mantle rocks with up to 33 wt.% garnet may provide an explanation for the observed high velocities of the lower lunar mantle. The presence of garnet in the lowermost part of the Moon's mantle has significant implications for the depth and temperature of the Moon's magma ocean as well as the composition, structure and internal dynamics of the solid Moon.

Identifying imaging challenges for 1D and 3D geometric complexity (LG space)

In some situations, it is difficult to image seismic data even when factors such as illumination, anisotropy, and attenuation are resolvable. An often-overlooked but dominant factor affecting imaging is the geometric complexity of subsurface reflectors. In some of these settings, we propose that geometric complexity plays a dominant role in the quality of seismic imaging. This has been documented in subsalt regions with poor image quality where 3D vertical seismic profiles (VSPs) are available. VSPs often demonstrate that there is good illumination below salt, but the complexity of the observed downgoing wave and diffractions cannot be simulated with smooth earth models. We use synthetic examples with high geometric complexity and no other complications to analyze the imaging process: a 2D sediment-salt model with rough salt-top topography, and a 1D model with complex reflectivity. In these models, it is difficult to estimate velocity, and it is challenging to image the data. These synthetic examples are useful to understand the limitations of imaging with smooth models, to create guidelines to identify geometric complexity in field data, and to develop possible mitigations to improve imaging. Further real data examples will be needed to test geometric complexity.

Kinematic Evolution of the Santa Bárbara System in the Foreland of the Central Andes of Northwestern Argentina (26°S)

AbstractCompared to the thin‐skinned Subandean foreland fold‐and‐thrust belt of northern Argentina and Bolivia, the tectonically active morphotectonic province of the Santa Bárbara System in the Andean broken foreland of northwestern Argentina is characterized by a temporally and spatially disparate deformation style. Although there is no well‐defined orogenic deformation front associated with the uplift of these basement‐cored, reverse‐fault bounded mountain ranges, there has been an overall eastward trend in Andean compressional deformation since the Miocene. While reactivation of basement anisotropies, such as early Paleozoic metamorphic fabrics and Cretaceous normal faults, has been proposed to have profoundly affected deformation processes in the Santa Bárbara System, other mechanisms involving Mesozoic and Cenozoic cover rocks may also have played an important role in orogenic deformation in this sector of the Andean foreland. We present structural field observations, interpretations of seismic reflection profiles, and kinematic modeling from the basins bordering the Candelaria Range in the southern sector of the Santa Bárbara System at 26°S. Our analysis features a 110‐km‐long structural cross section that images and links deep‐seated structures with shallow neotectonic faults. We find that regional shortening has been facilitated by several faults associated with a regional detachment at a depth of 23 km, resulting in total horizontal shortening of about 17% (18.4 km). While the deep‐seated first‐order structures seem closely linked to seismogenic processes in the Andean foreland, shallow second‐order structures within the sedimentary cover modify the intermontane landscapes and appear to be associated with aseismic creep.

Seismogenic Structure of the 1605 Qiongshan M7½ Earthquake and Its Holocene Activity History in Northern Hainan Island, China: Evidence from Cross-Section Drilling and Shallow Seismic Profile

Seismogenic Structure of the 1605 Qiongshan M7½ Earthquake and Its Holocene Activity History in Northern Hainan Island, China: Evidence from Cross-Section Drilling and Shallow Seismic Profile

Acid-Extracted Hydrocarbon Anomalies and Significance in the Chaoshan Depression of the Northern South China Sea

To predict the favorable zones and the types of reservoirs, acid extraction has been used in the Chaoshan depression to detect trace amounts of light hydrocarbons, heavy hydrocarbons, and the δ 13C (‰) of methane. As a result, two integration anomalous zones for exploration activity were blocked out in the northeastern and southwestern parts of the Chaoshan Depression, respectively. By analyzing the differentiation law and structural characteristics of hydrocarbon gases, as well as the stable carbon isotope ratio of methane, the underlying reservoirs were predicted to be gas reservoirs, and the seismically interpreted Dongsha-A (DS-A) structure was predicted to be a gas-rich structure. By correlating the seismic profile and geochemical anomalies, it was determined that fault planes and micro-fractures are the main controlling factors for the occurrence of the seabed’s geochemical anomalies. A composite formation mechanism of “lower generation, upper accumulation and micro fractures leaking” is proposed for the control of the underlying petroleum reservoirs, as well as for the micro-fracture control of permeability and surface adsorption control. Acid-extracted hydrocarbon anomalies have favorable indicating significance for exploration activity.

Unexpectedly High Magma Productivity Inferred From Crustal Roughness and Residual Bathymetry on the Eastern Part of the Ultra‐Slow Spreading Gakkel Ridge Since ∼45 Ma, Eurasian Basin, Arctic Ocean

AbstractThe Gakkel Ridge in the Eurasian Basin has the slowest seafloor spreading worldwide. The western Gakkel Ridge (3°W–85°E; 14–11 mm/a) alternate between magmatic and sparsely magmatic zones, while the eastern Gakkel Ridge (85–126°E; 11–6 mm/a) appears to be dominated by magmatic zones despite ultraslow spreading. Little is known about the seafloor spreading conditions in the past along the entire ridge. Here, we exploit the residual bathymetry and basement roughness to assess the crustal accretion process of the Gakkel Ridge over time using 23 published regional multichannel seismic reflection profiles. Full seafloor spreading rates were faster (20–24 mm/a) up to ∼45 Ma, and residual bathymetry for the older crust is deeper than the world average in the entire Eurasian Basin. There is a sharp transition to 300–400 m shallower residual bathymetry for seafloor <45 Ma in the eastern Eurasian Basin. The crustal roughness versus spreading rate of the western Eurasian Basin is on the global trend, while that of the eastern is significantly below. Both low roughness and shallow residual bathymetry of the eastern Eurasian Basin is close to that of oceanic crust for spreading rates above 30 mm/a, demonstrating increased magmatic production of the eastern Gakkel Ridge since ∼45 Ma. A recent mantle tomography model predicts partial melting in the upper mantle based on the low Vs anomaly underneath. The sedimentary pattern toward the Lomonosov Ridge indicates that this hot mantle anomaly started to cause dynamic uplift of the area at ∼45 Ma.

Seismo-Stratigraphic Data of Wave-Cut Marine Terraces in the Licosa Promontory (Southern Tyrrhenian Sea, Italy)

Some seismo-stratigraphic evidence on the occurrence of wave-cut marine terraces in the Licosa promontory (Southern Tyrrhenian Sea, Italy) based on Sub-bottom Chirp seismic sections is herein presented. Such evidence is provided by marine terraced surfaces situated at various water depths below sea level and etched into the rocky acoustic basement, which are extensively extending in the seaward extension of the Licosa promontory. It is possible that the isotopic stratigraphy and the terraced marine surfaces are connected, so they can be attributed and dated indirectly. The geologic study of seismic profiles has pointed to the prominence of the acoustic basement, extending to the seabed close to the coast and subsiding seawards under the Quaternary marine succession. Ancient remains of marine terraces, found at a range of water depths between 5 m and 50 m, have documented the major morphological changes of the acoustic basement during the Late Quaternary.

Migration and controls of Shenhu submarine canyons in the upper continental slope of northern South China Sea: Insights from three‐dimensional seismic data mapping

AbstractSubmarine canyons, prominent features on continental margins, hold significant scientific and engineering implications. Despite extensive research on various types of submarine canyons, current understanding of those canyons developed on the upper continental slope, recognized as the most common type globally, remains limited. The Shenhu Canyons on the upper continental slope of the northern South China Sea, comprising over 19 subparallel features persistently developed from the Late Miocene to Quaternary, offer an excellent opportunity for in‐depth study. Previous assumptions suggested a unidirectional eastward migration of these canyons parallel to the host margin, primarily based on observations from two‐dimensional transverse seismic profiles. However, this study's analysis using three‐dimensional seismic data mapping reveals that not all canyons have migrated eastward; 28% display an opposite or a zigzag patterned migration, challenging previous assumptions. The eastward migration of the Shenhu Canyons on the eastern slope of the palaeo‐Pearl River shelf‐edge delta can be linked to the south‐east–southward progradation of the host margin and the palaeo‐shelf‐edge delta. However, the overall eastward migration pattern is complicated by submarine landslides and turbidity current processes. Landslides can influence the direction and magnitude of canyon migration through four mechanisms: turbidity current diversion; retrogressive development of canyon‐wall landslides; retrogressive landslides on surrounding open slopes; and emplacement of landslides in canyon thalwegs. These mechanisms may result in widening, bifurcation, confluence or obstruction of canyons, contributing to canyon migration. Erosion by turbidity currents can trigger canyon‐wall failures, which in turn promote the lateral migration of the canyons. If overspilled turbidity currents lead to the growth of levées in the lower reaches, canyon confinement increases, suppressing lateral migration. The inherited high‐gradient Palaeogene syn‐rift tectonic slope, combined with the depositional delta‐front slope of the palaeo‐shelf‐edge delta, creates favourable conditions for the initiation and persistent development of the straight Shenhu Canyons. This comprehensive analysis provides valuable insights into the complex dynamics and factors influencing the migration of upper continental slope submarine canyons.

Petroleum Potential Prospectivity of Muglad Basin, South Sudan: A Case of Source Rocks Characterisation in the Drilled Kaikang West-1 Well

This study focuses on Prospectivity of Petroleum Potential of Muglad basin, South Sudan, with the help of petroleum source rocks characterisation in the drilled Kaikang West-1 Well based on the organic matter quantity, quality, and the thermal maturation generation capability of the organic matter disseminated in the analysed rock samples. Muglad basin is a major petroliferous Western and Central African Rifts System (WCARS) member, with estimated reserves of 2,053 mm bbl. Muglad Basin comprises thick sandstones of Aradeiba and Bentiu Formations, considered to be the main petroleum prospectivity targets, with trapping mechanism being structural faults and lithological anticlines. The organic matter contents were determined directly from laboratory analyses of the source rock samples with the help of seismic and gamma ray profiles, total organic carbon (TOC wt %), maturity indices (OI, HI and PI), temperature maximum (Tmax °C), porosities and other sedimentological parameters. This study involved a series of analytical geochemistry and petro-physical studies to ascertain a number of effective source rock samples from the well cores which were then analysed in terms of TOC, OI, PI, HI, S2, S1 and Tmax to determine oil/gas prone samples (resource areas). These were then distinguished from strata with very high organic matter samples as well as very high TOC to help identify for possible source rock characterizations within the lithology pertaining to the well in terms of potential source-reservoir-seals combinations. The Rock-Eval pyrolysis data were useful in assessing and evaluating the type of organic matter, thermal maturity, and the generation capability of source rocks for hydrocarbon exploration rationale. The analyses revealed that some strata, within the sampled well data, have high hydrocarbon generation potential with the existence of commercial hydrocarbon production

Tectonic influence on the evolutionary dynamics of deep-water channel systems along the active accretionary prism margin in the Rakhine Basin, Myanmar: A high-resolution 3d seismic analysis

This study reveals the morphological transformations of a deep-water channel system within the Rakhine Basin in the northeastern Bay of Bengal through a comprehensive analysis of high-resolution 3D seismic data integrated with drilling logs. Employing the “source-channel-sink” paradigm, this investigation examined the impact of various factors, including tectonic transformations, sediment influx, slope dynamics, climatic changes, and relative sea-level fluctuations, on the evolutionary trajectory of these channel systems. Applying precise time-slicing techniques integrating root-mean-square amplitude attributes, coherent amplitude attributes, and horizontal amplitudes on seismic profiles, this investigation recognized three distinct stages in the evolution of channel-levee complexes (CLCs): the Middle Miocene erosional deep-water channel-levee complex (CLC-1), the Pliocene erosional-depositional deep-water channel-levee complex (CLC-2), and the Pleistocene depositional deep-water channel-levee complex (CLC-3). Comparative analysis revealed that the CLC-3 exhibits unique characteristics, including shallower channel depth (D), wider channel width (WC), extensive U-shaped cross-sectional area (S), broader natural levee width (WL) and height (H), and the highest tortuosity coefficient (LC/LS) when contrasted with the other two CLCs. Furthermore, this study substantiated how tectonic processes, primarily the collision between the Indo-Eurasian plates, resulting in the Himalayan and Indo-Burma Range orogenies, have shaped the region's geological and climatic framework, thereby influencing monsoon circulation and precipitation patterns, which in turn augmented detrital material influx into the basin. Moreover, this tectonic collision has led to gradual changes in the slope gradient of the Rakhine Basin and its deep-water areas, impacting internal flow velocities and channel curvature, thus governing deep-water channel systems' development and spatial distribution. Also, episodic sea level fluctuations were identified as significant contributors to sediment transport from shelves to deep-water regions and sediment deposit reworking. Overall, this study underscores the role of tectonic changes after the Eocene in driving the evolutionary dynamics of the deep-water channel system within the Rakhine Basin, Myanmar.

Deep Blind Fault Activity—A Fault Model of Strong Mw 5.5 Earthquake Seismogenic Structures in North China

North China is one of the high-risk areas for destructive and strong earthquakes in mainland China and has experienced numerous strong historical earthquakes. An earthquake of magnitude MW 5.5 struck Pingyuan County, Dezhou city, in Shandong Province, China, on 6 August 2023. This earthquake was the strongest in the eastern North China Craton since the 1976 Tangshan earthquake. Since the earthquake did not produce surface ruptures, the seismogenic structure for fault responsible for the Pingyuan MW 5.5 earthquake is still unclear. To reveal the subsurface geological structure near the earthquake epicenter, this study used high-resolution two-dimensional (2D) seismic reflection profiles and constructed a three-dimensional (3D) geometric model of the Tuqiao Fault by interpreting the faults in the seismic reflection profiles. This study further combined focal mechanism solutions, aftershock clusters, and other seismological data to discuss the seismogenic fault of the Pingyuan MW 5.5 earthquake. The results show that the Tuqiao Fault is not the seismogenic fault of the MW 5.5 earthquake. The actual seismogenic structure may be related to the NE-oriented high-angle strike-slip blind fault developed in the basement. We further propose three possible fault models for the strong seismogenic structure in North China to discuss the potential seismotectonics in this region.

Submarine morphology of Pantelleria volcano: The interplay between volcanic and erosive-depositional processes modulated by sea-level fluctuations.

High-resolution multibeam data integrated with seismic reflection profiles are used to identify and characterize the main primary volcanic and erosive-depositional features along the submarine part (about the 80%) of the active Pantelleria volcano located in the Sicily Channel. Volcanic features include lava flows, cones and elongated ridges. Lava flows are mainly recognized over the insular shelf, while volcanic cones and ridges are mostly concentrated along the steep submarine flanks, especially along the wider SE and NW ones. A strong volcano-tectonic interaction is envisaged for their formation, as indicated by their preferential elongation or alignment along the (main) SE-NW and (secondary) SW-NE directions that have controlled the evolution of the whole volcanic edifice. Erosive-depositional features mainly include small-scale landslide scars and narrow gullies affecting the edge of the insular shelf and overlying submarine depositional terraces. Gullies sometimes merge downslope in larger channels, whose formation is primarily controlled by the distribution of volcanic features and/or shelf sectors characterized by different age or lithologies. Based on the marked morphological differences between the different flanks of the Pantelleria volcano, we infer an overall migration of the volcanic activity from SE to NW over time. This migration is apparently in contrast with the presence of a much wider but shallower NW insular shelf with respect to the SE one. This anomaly can be explained through a two-stage model, with the formation, in the NW sector, of a polygenic shelf rejuvenated by volcanic progradation during the last eustatic hemicycle. The different depths of the insular shelf edge around the island also provide insights on vertical deformations that affected the Pantelleria volcano during the Late-Quaternary.

A speculative ridge within the Kidson Sub-basin – integrated interpretation from geophysical data

This paper presents an analysis of the basement geometry and its implications on the Kidson Sub-basin in the southern Canning Basin. Integration of seismic data primarily near the rim of the sub-basin with airborne electromagnetic data across its central portion reveals an east-northeast oriented ridge at Permian level, suggesting a possible elevated structure in the Ordovician and basement. The proposed ridge effectively separates the Kidson Sub-basin into two distinct parts, providing an explanation for facies and thickness variations observed in the Nambeet and Goldwyer formations, as well as the absence of the Willara Formation in the southeastern portion of the sub-basin. The presence of shallowing trends observed in seismic profiles along the southern flank of the ridge suggests the proximity of the basement high. The ridge is speculative and requires further work to verify its existence, potentially including passive and reflection seismic surveys across the structure. If confirmed, it might be a significant feature with far-reaching implications for the prospectivity of resources in the Kidson Sub-basin. The hydrocarbon sourced from the Nambeet, Goldwyer and Bongabinni formations in the NNW depocentre may have migrated via the extension of the Parallel Range Fault and be trapped in the footwall block over the ridge. Compared to the structures in the Fitzroy Trough, the traps within the Kidson Sub-basin are expected to maintain reasonable integrity and have good potential for petroleum accumulation and carbon sequestration in the thick Paleozoic succession.

Constraints on crustal compositional architecture across the North China-Altaids transition and implications for craton margin reworking

Abstract The phase of secular evolution of continents is manifested as the degree of compositional differentiation, modification, and maturation of continental crusts, which is vital in understanding the mechanism of continental evolution but is difficult to quantify. Here we use integrated passive- and active-source seismic profiling to conduct joint analysis and inversion and derive Vs and Vp/Vs section models across the North China craton (NCC) to southeastern Altaids boundary zone that bears a tectonic transition from a reworked ancient craton margin to a Phanerozoic accretionary orogen. We systematically exploited the imaged multiple physical properties as precise and delicate proxies to constrain the compositional architecture in the crust across this important tectonic transition subject to various crustal evolutional phases. Our Vs and Vp/Vs imaging, together with the existing isotopic data, characterizes the Yin Shan-Yan Shan belt as the northern NCC margin with layered homogeneous compositions that point to an evolved crust. However, the lower-crustal low-Vs/high-Vp/Vs signature that overlaps the shallowly dipping to horizontal reflective fabrics suggests the crust of the northern NCC margin has undergone considerable reworking through lower-crustal-stretching assisted melt migration and mixing since the late-Paleozoic to Mesozoic era. The process probably involved crust-mantle interaction and thus resulted in a compositionally modified ancient crustal basement. On the contrary, the southeastern Altaids domain manifests crustal complexity in compositions and structures inferred to be indicative of a juvenile crust of the Phanerozoic accretionary orogen. Our results provide deep physical-property constraints that shed new light on the crustal evolution of a complex craton margin.

Fault structure and hydrocarbon prospects of the Palawan Basin on the southeastern margin of the South China Sea based on gravity, magnetic, and seismic data

To study the structural features and hydrocarbon prospects of the Palawan Basin in the South China Sea (SCS), the authors collect and collate the existing gravity and magnetic data and obtain edge recognition information from the potential fields. Combined with the seismic profile data, this paper analyzes the features of the gravity and magnetic anomalies and the edge recognition information of the potential fields, determines the fault system, and delineates favorable areas for oil and gas exploration in the Palawan Basin. The results indicate that four main groups of faults with northeast, northwest, near east–west, and near south–north trends developed in the Palawan Basin and adjacent areas in the SCS. The northeast-trending fault is the regional fault, whereas the northwest-trending fault is the main fault. The northwest-trending fault often terminated at the northeast-trending fault, indicating that the northwest-trending fault is formed subsequently. This investigation has characterized two different types of exploration favorable areas (type I and type II) based on the characteristics observed. The most notable characteristic of these exploration favorable areas is that they are located in the high-value zones of the local anomaly of the Bouguer gravity anomaly and their development is obviously controlled by the faults. The amplitude of the gravity anomalies is higher and the gradient of the gravity anomalies is steeper, and there are oil and gas wells and fields distributed in the type I favorable areas for exploration. Compared with the type I favorable areas, the amplitude of gravity anomalies is relatively small, and the gradient of the gravity anomalies is relatively gentle, corresponding to the type II favorable areas.

3D VSP Imaging Using DAS Recording of P- and S-Waves in Vertical and Lateral Well Sections in West Texas.

A 3D vertical seismic profiling (VSP) survey was acquired using a distributed acoustic sensing (DAS) system in the Permian Basin, West Texas. In total, 682 shot points from a pair of vibroseis units were recorded using optical fibers installed in a 9000 ft (2743 m) vertical part and 5000 ft (1524 m) horizontal reach of a well. Transmitted and reflected P, S, and converted waves were evident in the DAS data. From first-break P and S arrivals, we found average P-wave velocities of approximately 14,000 ft/s (4570 m/s) and S-wave velocities of 8800 ft/s (3000 m/s) in the deep section. We modified the conventional geophone VSP processing workflow and produced P-P reflection and P-S volumes derived from the well's vertical section. The Wolfcamp formation can be seen in two 3D volumes (P-P and P-S) from the vertical section of the well. They cover an area of 3000 ft (914 m) in the north-south direction and 1500 ft (460 m) in the west-east direction. Time slices showed coherent reflections, especially at 1.7 s (~11,000 ft), which was interpreted as the bottom of the Wolfcamp formation. Vp/Vs values from 2300 ft (701 m) -8800 ft (2682 m) interval range were between 1.7 and 2.0. These first data provide baseline images to compare to follow-up surveys after hydraulic fracturing as well as potential usefulness in extracting elastic properties and providing further indications of fractured volumes.

Combined onshore and offshore wide-scale seismic data acquisition and imaging for carbon capture and storage exploration in Havnsø, Denmark

Strong global actions for climate change include carbon capture and storage (CCS) as a feasible solution to reach carbon neutrality and raise opportunities for detailed subsurface investigations. An acquisition set-up designed for onshore-offshore zones was maximized for wide-scale high-resolution structural imaging and implemented to cover a domal structure of interest for CCS utilization close to the town of Havnsø (Denmark). The challenges of the combined acquisition and processing of land and marine multisensor data along a 42 km seismic profile are analyzed, the suggested solutions are applied, and the limitations are discussed. On the onshore side, a nodal array and a seismic landstreamer system were simultaneously used, whereas along the transition zone, a marine seismic streamer and ocean-bottom seismometers were added to record the seismic response generated by two seismic vibrator sources. The adopted sensing domains (velocity, acceleration, and pressure) were studied, and different processing steps were evaluated to enable their processing and subsequent data set merging. Results suggest, as the best approach, a separate prestack processing of the different data sets and the computation of new geometries and new surface-consistent residual static correction after their merging. The data acquired in the transition zone illuminate, for the first time, the subsurface geology of the region, delineating an expected domal closure. The final seismic section shows high continuity of the reflections with good resolution along the entire profile, identifying the main reservoir structure and the surrounding areas, which are important to ensure reservoir integrity and safe exploitation over longer time scales. Shallow and deep reflections are consistent with the stratigraphic column from a well log near the profile. The presented study shows a comprehensive workflow for processing such a multisensor data set in onshore and transition zone settings.

Contrasting sedimentary and long-lasting geochemical imprints of seismic shaking in a small, groundwater-fed lake basin (Klopeiner See, Eastern European Alps)

In slowly deforming tectonic settings (e.g., European Alps), large earthquakes occur too infrequently to be adequately represented in instrumental and historical records. This leads to uncertainties and inaccuracies of seismic hazard estimations. To extend the seismic record, lacustrine paleoseismologists usually resort to the sedimentary archive of large lakes where earthquakes can be recorded as mass-transport deposits and associated turbidites. The imprint of seismic shaking is generally more subtle and poorly understood in small lakes (<2 km2) with small catchments and therefore such sediment-starved basins are often neglected for paleoseismology. However, these basins might harbour additional information about past earthquakes, thus constituting a valuable supplement to other paleoseismic data. Here, we present the 18 ka-long paleoseismic record of Klopeiner See, a small and rather shallow groundwater-fed lake in the Eastern European Alps. Reflection seismic profiles and sediment cores reveal that several large earthquakes led to extensive mass-wasting in early Late-Glacial times when sedimentation rates were very high (~10 mm/yr). In the Early and Middle Holocene, low sedimentation rates (~0.2-0.5 mm/yr) may have decreased the lake´s sensitivity for recording seismic shaking and no imprints were found for paleo-earthquakes inferred from other records in the region. A short succession of turbidites at ca. 3160 cal BP suggests a burst of strong paleoseismic activity. This may have caused permanent modifications of inflowing ground water systems, archived as a permanent shift in the geochemical signal of the sediment. Such a period of enhanced paleoseismic activity was also inferred from the nearby Lake Wörthersee, but it remains unclear whether these represent the same earthquakes or migrating paleoseismicity. This study highlights the unexpected potential and peculiarities of paleoseismology on small ground-water fed lakes.