Thick Quaternary Sediments Research Articles

Unravelling the fragmented sediment–landform assemblage in an area of thick Quaternary sediment, western Hudson Bay Lowland, Canada

Laurentide Ice Sheet (LIS) reconstructions beyond the last glacial maximum (LGM) are difficult due to the incomplete stratigraphic record that has largely been eroded by the most recent glaciation. The Hudson Bay Lowland (HBL) is a key region to understanding the long-term evolution of the LIS, as it contains an extensive pre-LGM stratigraphic record of glacial and nonglacial events. This study uses a hybrid lithostratigraphy–allostratigraphy approach to decipher the stratigraphic record in the Kaskattama highland region of the western HBL, Manitoba, Canada. We identify five glacial (till) units and three nonglacial (sorted sediment) units that were deposited during at least three glacial–interglacial cycles, which are constrained by radiocarbon and optical ages. The provenance of till units is identified using clast-lithology and detrital hornblende 40Ar/39Ar ages and supported by matrix geochemistry. The new stratigraphic framework for this western HBL region indicates that the ice emanating from the Quebec–Labrador dome advanced into the region at the start of the last two glaciations, suggesting accelerated early growth of the Quebec–Labrador dome relative to the Keewatin Dome.

Fine interpretation of magnetic data for a concealed mineral deposit: A case study of the Fe-polymetallic deposit from Western China

We interpret the magnetic anomalies for exploration and characterization of the Galinge iron polymetallic deposit, which is the largest iron polymetallic deposit in Western China. This undeveloped deposit is completely concealed by the thick Quaternary sediments, presenting an exploration challenge. A lot of drillholes have been implemented focusing on the strong magnetic anomaly centers, while the relationship between magnetite-bearing and non-magnetite-bearing drillholes is unclear, and the metallogenic regularity in the whole area needs to be further studied. The edge detection is applied on the downward continued field to resolve individual magnetite ore bodies and enhance possible concealed ore bodies. Three anomaly belts trending NE-SW with a total extension length of ∼11 km are first revealed. Combining the sharper images from the enhanced magnetic anomaly and the drillholes, we infer that the deposits would be related to the syncline structure. Forward modeling confirms the inferred three belts of the ore bodies and also shows possibly two layers deposits in which the deep layer would be located at a depth of ∼1000 m. Although the deeper deposit results in a very smooth and low amplitude magnetic anomaly, the forward modeling shows that the anomalies from both the shallow magnetite and the inferred deep one fit the observed anomaly better. One deep drillhole reveals the fact that the magnetite is existed at a depth of ∼1000 m which highlights the interpretation of the deep deposit. The results show the contribution of the fine processing techniques which would be used to distinguish zones of potentially concealed mineralization.

Understanding land subsidence in the Pearl River Delta region of China based on InSAR observations

Land subsidence occurs in river delta areas. A comprehensive understanding of the factors contributing to land subsidence is crucial for effective geohazard mitigation and land planning. This study investigates the distribution characteristics and spatiotemporal evolution pattern of the land subsidence in the Pearl River Delta based on the InSAR-derived ground deformation data spanning 2016 to 2021; and, the effects of the influencing factors, including the Quaternary sediment thickness, land use classification, land reclamation, and subway construction and operation, on the subsidence are analyzed. The results unveil the presence of four major subsidence zones and several minor coastal subsidence bowls in the research area, with a total area of about 1100 km, all of which exhibit prolonged and intense subsidence. In the remaining regions, land subsidence predominantly exhibits weak and short-term occurrences. The subsidence in the study area follows a distinct linear evolutionary pattern with a slight rebound, potentially linked to the rise of groundwater levels. Regions with Quaternary sediment thickness surpassing 20 m, engaging in aquaculture or agricultural activities, and featuring reclaimed land are predisposed to prolonged and intense ground subsidence. In addition, the construction and operation of subway lines may induce ground subsidence, especially in geologically vulnerable areas. This study provides valuable insights into land subsidence research in delta regions.

Estimation of Groundwater in Tarim Basin from Three-dimensional Resistivity Model Constructed by Magnetotelluric Data

Groundwater is an important resource of irrigation and domestic water in Tarim Basin (TB), the largest arid inland basin in China. Hydrogeologic models and hydrogeochemical analysis have provided information of groundwater flow, salinity and hydrochemical type in TB. However, there is lacking in quantitative estimation of groundwater volume due to that the underground aquifer structure is unclear. To address the problem, magnetotelluric (MT) data were collected in TB and subsurface electrical resistivity were produced by MT inversion. To estimate the porosity of aquifers by resistivity, we should determine the resistivity of groundwater which is controlled by the Total Dissolved Solids (TDS) in water. From the previously published data, TDS increases from piedmont plain to alluvial plain along groundwater flow direction in TB and other similar settings. In terms of spatial distribution of TDS and 3-D resistivity model, the effective porosity of aquifers in the study area was calculated. Finally, by taking account of the water table and thickness of Quaternary sediments collected by BGP Inc., the total groundwater volume was estimated in northern parts of TB.

Co-seismic Ground Deformation Monitoring on Brebes-Segment of Baribis-Kendeng Fault Zone Based on Sentinel-1 Data

Co-seismic deformation is a sudden change in the earth’s surface in a fault zone. Therefore, with modern satellite imagery, it is possible to investigate. Synthetic Aperture Radar (SAR) data from Mission Sentinel-1 is one example of satellite imagery that can be used to identify deformation. We employ the interferometry method by utilizing the Interferometric synthetic aperture radar Scientific Computing Environment (ISCE) and another InSAR software to monitor the co-seismic ground deformation in the form of line-of-sight (LOS) displacement. This research focused on the Brebes Segment of the Baribis-Kendeng Fault Zone and applied the interferometry method for the March 22, 2015, Balapulang earthquake (M4.7) and December 11, 2020, Brebes earthquake (M4.2). The earthquake event choice is based on the shallow depth of the hypocenter, which represents the earthquake originating from the fault in the crustal, not the megathrust subduction. The results show that despite the earthquake occurring under the thick quaternary sediment of the north shore of Java Island, the deformation caused by the co-seismic is still emerging to the surface. The LOS displacement was detected within the range of 6 cm from the ascending and descending track of the satellite sensors. Furthermore, this result may provide new information on the Baribis-Kendeng Fault zone, specifically the Brebes Segment.

Improved 3D Shallow‐Deep Vs Structure in Tongzhou, Beijing (China), Revealed by Dense Array Ambient Noise Tomography

AbstractShear‐wave velocity (Vs) structures can reveal the shallow sediment thickness and deep tectonic features of buried faults and geological units. They are important for reducing seismic and geological disasters in urban areas. Based on ambient noise data from the Tongzhou dense array (919 seismographic stations), we obtain a fine shallow‐deep (0–5 km) 3D Vs model, by jointly inverting the phase‐velocity dispersions of Rayleigh waves, including short‐period (0.3–2 s) multimode dispersions using the frequency‐Bessel transform method and the long‐period (2–6 s) fundamental‐mode dispersions using the fast marching method. Our results show that the Vs inhomogeneities agree well with the distribution of geological units. We use the 1 km/s isodepth of Vs as the reference thickness of quaternary sediments. Fengbo sag (FBS) and Dachang sag (DCS), which mainly show low velocity and density, have thick sediment thicknesses (approximately 550–600 and 320–420 m, respectively). The NE high‐velocity belt in Daxing high (DXH) has a thinner sediment thickness (∼230 m). Thus, FBS and DCS have a greater risk of earthquake hazards owing to the strong amplification effects of ground motion. Additionally, Vs distribution in the FBS, DCS, DXH, and Yanshan Fold Belt are spatially related to the medium density and buried faults (Nanyuan‐Tongxian, Daxing, and Xiadian faults). We infer that the Vs structures are associated with the controlling effects of these large normal faults and inhomogeneous strata density. The discontinuity of the NE high‐velocity belt in DXH probably results from the intense tectonic activity of Nankou‐Sunhe fault.

Evidence of karstification in chalk and limestone aquifers connected with stream systems and possible relation with the fish ecological quality ratio in Denmark

Although chalk aquifers are not too often associated with conduit flow, they are highly productive groundwater systems and, like limestone aquifers, they can be vulnerable to contamination when exposed to land use activities. The Danish carbonate rocks are generally recognized to be highly fractured and covered by thick Quaternary sediments. Fissure flow is pronounced, occurring in the upper 50–100 m due to Pleistocene glaciations. According to recently published maps of the distribution of karst in Europe, Denmark has no karst. However, this study concludes that karstified chalk and limestone aquifers are an important source of freshwater in Denmark. Four national datasets on karst features, groundwater flow, groundwater chemistry, and fish ecological quality ratio (EQR) data now indicate more heterogeneous structures and preferential flow pathways in the chalk and limestone aquifers than had been conceptualized and modelled with a national water resources groundwater/surface-water model in the recent past. This study provides new qualitative evidence that rapid and preferential flow of water and agrochemicals from the surface through thinner parts of the Quaternary cover layers, sinkholes and solution-enlarged fractures may likely impact the vulnerability of chalk and limestone aquifers. Additionally, due to the preferential flow system, some gaining streams discharged by karstified chalk and limestone aquifers show increased fish EQR values when using observed river daily discharge data instead of simulated daily discharge.

Radiocarbon and OSL dating on cores from the Chaoshan delta in the coastal South China Sea

Accurate chronology plays a crucial role in reconstructing delta evolution. Radiocarbon (14C) and optically stimulated luminescence (OSL) dating are widely used to establish a stratigraphic chronology of the late Quaternary sediments. The Chaoshan plain is located on the southern coast of China and borders the South China Sea. The thickness of Quaternary sediments in this area extends to a depth of 140 m and is considered a valuable archive for studying the evolution of the delta in response to climate and sea-level changes. However, reliable chronological data are still very limited. In this paper, eighteen accelerator mass spectrometry (AMS) 14C and thirteen quartz OSL ages were obtained from two cores from the Rongjiang plain, the middle part of the Chaoshan plain: ZK001 (90.85 m in depth) and ZK002 (100 m in depth). The present study aims to provide a reliable chronology of the Chaoshan plain based on OSL and 14C dating methods and examine the upper limit of the 14C dating on plant remains. Our results show that (1) OSL ages of cores ZK001 and ZK002 range from 56 to 1.7 ka and from 177 to 15 ka, respectively; (2) 14C ages of core ZK002 range from 8.8 to 41 cal ka BP, showing that all 14C ages below ca. 30 m depth are younger than OSL ages and that the upper limit of plant remains is around 35 cal ka BP. OSL ages are consistent with stratigraphic order within uncertainties. The oldest OSL age obtained from core ZK002 is 177 ± 20 ka at a depth of 93 m, and is considered a minimum age. This indicates that the Quaternary deposition in the Rongjiang plain can trace back to at least the marine isotope stage (MIS) 6 during sea-level lowstand, during which the plain is mainly influenced by the fluvial process. The comparison between 14C and OSL ages in the Chaoshan plain suggests that 14C ages older than 35 cal ka BP need to be re-evaluated. However, the OSL dating method proves reliable for establishing a comprehensive chronological framework for the late Quaternary sediments in this area.

Land subsidence and its affecting factors in Cangzhou, North China Plain

Land subsidence is a typical geo-hazard in Cangzhou, North China Plain, having caused severe damages to transportation networks, public utilities, and other civil infrastructures. The mechanism of land subsidence and its affecting factors were revealed by theoretical model analysis, and doing geotechnical tests and monitoring of soil deformation as well as groundwater level. Theoretical analysis shows that groundwater withdrawal from both unconfined and confined aquifers can lead to land subsidence. Land subsidence of the Cangzhou Plain is mainly caused by the exploitation of deep confined groundwater. Geotechnical tests show a general trend that the compressive modulus increases with the increase of soil depth. The strata of the Upper Pleistocene and Holocene are mostly normally consolidated and partially under-consolidated, which are prone to produce large compression after pumping. Land subsidence in the Cangzhou Plain has a strong hysteresis because of seepage consolidation and creep. The deformation characteristics of strata change at different depth. The shallow aquifers are mainly elastic deformation. The area of severe land subsidence in the Cangzhou Plain is closely related to rainfall, mainly because the large amount of water are used for agricultural irrigation. InSAR results show a sudden change in regional subsidence across the Cangdong fault, which is caused by the difference in the thickness of Quaternary sediments and the difference in the deep confined groundwater level.

Hydrogeological structure modelling based on an integrated approach using multi-source data

The simulation of groundwater flow is widely used to understand dynamic groundwater processes and frequently serves as the basis for quantitative analysis and management of groundwater resources. Reliable groundwater flow simulations require a sound understanding of the hydrogeological structure of the subsurface materials. However, a detailed model of the hydrological structure of thick unconsolidated basin sediments is often limited by their inaccessible nature, especially in the deep domain. As a result, deep regional flow is generally neglected in traditional groundwater flow simulations. This study presents an integrated approach for developing a model of hydrogeological structures using multiple data sources, including audio-magnetotelluric data (AMT), borehole data, and the interpreted lower boundary of Quaternary sediments. The approach overcomes the disadvantages of using the depth of boreholes as the lower boundary of the hydrogeological system and may be used to analyse the effects of hydrogeological structures on groundwater flow simulations. The model, which utilized sequential Gaussian simulation (SGS) and natural neighbor interpolation (NNI), was evaluated by application to a typical cross-section through the Yinchuan Basin, China, to a depth of 1,700 m. The horizontal hydraulic conductivity (Kx) field was calibrated using observation wells and the PEST pilot points (PPP) method. The effects of the developed hydrogeological structure on groundwater flow simulations were evaluated for the entire thickness of Quaternary sediments (complete-domain model, CDM) as well as for sediments above the maximum depth of the boreholes (shallow-domain model, SDM). In addition, the sensitivity of the Kx field on groundwater flow patterns was analysed. The results show that the proposed approach can characterize the spatial distribution of lithologic units and the heterogeneity of hydrogeological parameters in the deep domain (>300 m), as well as avoid the multi-solution problem of inferring hydrogeological parameters from geophysical data. It can also improve the accuracy of the hydrogeological structure model and the reliability of groundwater flow simulations. The adjustment of the hydrogeological structure affects the flow budget as well as the pattern of the groundwater flow systems (including the type of system, and their number, location, and extent). Changes in the Kx field affect the local flow field, whereas adjustment of the hydrogeological structure model affects the global flow field.

Preliminary Map Showing Quaternary Geology of the Franklin 7.5-Minute Quadrangle, Indiana

The Franklin 7.5-minute quadrangle is situated near the maximum limit of Wisconsin Episode glacial deposits insoutheastern Johnson County. Till of Wisconsin Episode age (Trafalgar Formation) dominates the surficial geology of thequadrangle. Areas of Wisconsin Episode outwash (Atherton Formation) are found in the Sugar Creek, Youngs Creek, andHurricane Creek valleys and within former meltwater pathways not occupied by modern streams. Kame deposits (sand andgravel) are found in the northern half of the quadrangle and are part of a larger kame complex present in central JohnsonCounty. Holocene (post-glacial) alluvium is found in the valleys of Sugar, Youngs, Nineveh, Buckhart, and Ray Creeks andtributaries. Unconsolidated sediment thickness generally increases from southwest to northeast across the quadrangle, fromless than 15 ft along the southwestern margin of the quadrangle to over 200 ft thick in the far northeastern corner of thequadrangle. This transition of bedrock topography represents the buried northern end of the Knobstone Escarpment. Twosignificant bedrock paleovalleys exist in the quadrangle, one in the south-central part of the quadrangle which parallels theburied Knobstone Escarpment and one in the northeast corner of the quadrangle which is part of a large bedrock valleyextending north into Marion County. The Quaternary sediments in the western half of the quadrangle are underlain byMississippian Borden Group siliciclastic rocks. In the eastern half of the quadrangle, the Devonian New Albany Shale andMuscatatuck Group carbonate rocks subcrop under thick Quaternary sediment cover. The Wisconsin Episode maximumlimit is located within one mile south of the southern boundary of the quadrangle. Radiocarbon ages from the adjacentTrafalgar 7.5-minute quadrangle indicate the Laurentide Ice Sheet reached its maximum extent just after 23,700 years ago. Asecond glacial limit, marked by the Crawfordsville Moraine in the adjacent Trafalgar 7.5-minute quadrangle,crosses the southern end of the Franklin 7.5-minute quadrangle, albeit diffuse. The Crawfordsville Moraine represents thelimit of a readvance which occurred 21,700 years ago. This preliminary geologic map is an interim geologic map product thatdocuments progress in mapping the Quaternary geology of Johnson County, Indiana. The lithologic classification of theQuaternary units of Indiana was used in assigning map units.

Sediment Structures Constrained by Converted Waves From Local Earthquakes Recorded by a Dense Seismic Array in the Tangshan Earthquake Region

To investigate the sediment structures within the Tangshan earthquake region in North China, we developed an effective and inexpensive method for reliably detecting the thickness of Quaternary sediments by using converted waves from local, small earthquakes recorded by a dense seismic array. From January to March 2017, we deployed 145 three-component seismographs with inter-station distances ranging between 1 and 4 km throughout the Tangshan earthquake region. Tens of local events with magnitudes between ML 0.1 and ML 2.4 were adequately recorded by the Tangshan dense seismic array and were accurately relocated. A synthetic seismogram analysis clearly showed that the travel-time differences between direct S and Sp converted waves or between direct P and Ps converted waves were almost linearly correlated with the sediment thicknesses, providing tight constraints on the basement depth. With this method, we generated a sediment thickness map of the Tangshan earthquake region. Overall, the measurements from the local converted wave method are consistent with those of previous microtremor horizontal-to-vertical spectral ratio studies. The sediment thicknesses indicate that the subsurface sedimentary structure throughout the Tangshan earthquake region has experienced significant transformations over time, partially controlled by the NE–SW-trending Tangshan Fault. The obtained sediment thickness map provides beneficial information for ensuring the safe construction of infrastructure in Tangshan city and can serve as an important model for simulating earthquake strong ground motions in the Tangshan earthquake region. Our study suggests that the proposed simple and efficient method of using converted waves could be applied to other populous plains or basins with high seismic activity and could be used to determine the general characteristics of the sediment structures in a given study area.

A reactivated cave system induces rapidly developing cover-collapse sinkholes in Tasmania, Australia

The reasons of rapid development of cover-collapse sinkholes near Railton, Tasmania were investigated after sinkholes first appeared in a mature pine plantation in 2011. Sinkhole monitoring, dye tracing, chemical analyses of stream water and field observations indicated that large sinkholes in Quaternary alluvium overlying Ordovician limestone resulted from deepening of a limestone quarry south of the plantation. Intersection of a cave system during quarrying lowered the local water table, initiated streamsinks, and caused streams that previously flowed north towards the Mersey River to flow south to the quarry, via streamsinks and reactivated subsurface channels. Concurrently, the thickness of the vadose zone in thick Quaternary sediments overlying the limestone increased, hydraulic support for the sediments decreased, and numerous cover-collapse sinkholes formed. Chemical data including isotope analyses confirmed that the local aquifer is mainly recharged after high winter rainfall during high stream flow, when a proportion of the water in surface streams also flows directly northwards to the Mersey River. During low (summer) flow most water in surface streams flows into streamsinks and south into the quarry via the cave system. It is then pumped to a surface stream running north through the area in question, returns into the cave system via streamsinks and sinkholes, and finally returns to the quarry. The study demonstrates that water-table lowering by quarrying in limestone is not confined to cones of depression but may extend for kilometres if relict subsurface stream channels are intersected. In this area, the rapid development of cover-collapse sinkholes presents risks to infrastructure (a railway line, an electricity transmission line, and roads); to stream biodiversity because of altered water flow duration and water quality; to the safety of forest contractors, particularly those using heavy machines; and to the future use of presently productive land for economic return.

Geomorphologic and infilling characteristics of the slope-confined submarine canyons in the Pearl River Mouth Basin, northern South China Sea

Submarine canyons, classified as shelf-incision and slope-confined types, are considered as the most important sediment transportation conduits in the continental margins. Being one of the obvious submarine landforms in the northern continental slope of the Pearl River Mouth Basin (PRMB) in the northern South China Sea, the Shenhu Submarine Canyon Group (SSCG) is composed of 17 NW-SE oriented slope-confined submarine canyons. The SSCG serves as a routing system for delivering large volume of terrestrial sediments, which generate canyon infillings and was deposited further toward the basin. Using the high-resolution bathymetric and seismic data, the geomorphologic features and internal architectures of these slope-confined submarine canyons have been quantitatively analyzed and described in this study. Based on the differentiations in geomorphologies, four canyon segments could be divided from north to south, including upper, middle and lower reaches, and the canyon mouth area. Corresponding to the geomorphological segmentation of these submarine canyons, the variations in the Quaternary infillings were also interpreted clearly downstream, revealing the interaction between gravity flows along the canyon axis and lateral sediment transportation by mass movements. Supported by variation in geomorphologies, infilling characteristics and thickness of the Quaternary sediments from north to south, the sedimentary processes in the different segments of the slope-confined submarine canyons could be documented as erosional-dominant processes in the shelf-edge to the upper slope and depositional-dominant processes in the toe area. The head area of the Pearl River Canyon (PRC) is characterized by the thinner Quaternary strata and shallow-incised small-scale channels. In addition, no considerable change of Quaternary sediment thickness is observed from upper-middle reach of the PRC in other large-scale submarine canyon in the PRMB, indicating lower rate of sediment accumulation and limited sediment redistribute to deep-water basinfloor. Previous study envisaged by Ding et al. (2013) demonstrated the main contribution of the SSCG to deep-sea basins. In this study, we confirm that the SSCG were proposed as the major sediment routing system within the PRMB, which transport abundant terrestrial sediments from the Pearl River Delta via shelf and upper slope in the north to the deep-sea environments in the south.

Diagnosing the landslide areas of Angren open pit marginal mass according to the data of seismo- and electrical prospecting

Introduction. Sloping structures (quarry sides, dumps, banks, cuts, dams, etc) stability forecasting accuracy improvement requires detailed elaboration of physical-mechanical properties of the rock mass under consideration. Traditional methods of well engineering-geological exploration and hydrogeological monitoring are therefore supplemented by geophysical study. Research aim is to diagnose unstable deconsolidated and wetted zones in marginal masses for the purpose of further forecast of quarry sides stability. Methodology. Databases of geophysical studies obtained by the expeditions of the services of the Republic of Uzbekistan at Angren open pit. Results. For the test area represented by 11 seismic stations at the southern side of the quarry, the criterion assessing the state of the site as potentially landslide hazardous according to the results of circular seismic sounding has been experimentally obtained. With the use of this criterion, in the plan of the landslide zone the borders have been established. For the test area represented by 16 geophysical profiles at the northers side, by electrical profiling graphs and geological sections for the corresponding profiles, 58 "Izvestiya vysshikh uchebnykh zavedenii. Gornyi zhurnal". No. 1. 2020 ISSN 0536-1028 the following regularities have been found: at profile areas adjacent to the runs (rivers), local negative anomalies of effective resistivity up to 20–50 Ohm ∙ m are observed connected with soils wetting; between the anomalous areas the alternation of effective resistivity qualitatively coincides with the alternation of the thickness of a layer of loose deposits. By the arrangement of the negative anomalies borders at the graphs pf effective resistivity dependence on the spread of the profile along all profiles (PR1–PR16), the borders of the wetted zones were established in the plan of the test area. Summary. For geomechanical processes monitoring in the landslide zones it is advisable to apply the method of circular seismic sounding determining the value and the anisotropy coefficient according to the extreme values of compressional arrival time. For the conditions of the Angren open pit, the criterion of potential hazard of landslide development is the value of the anisotropy coefficient higher than 1.6. When elaborating the detailes of the physical properties of landslide zones in quarry sides which are weakened by sand-clay Quaternary sediments, by the method of electrical profiling it is advisable to use: the linear dependence on the thickness of Quaternary sediments on the value of the effective resistivity; hyperbolic dependence of soils relative wetness within the water saturation zones on the value of the effective resistivity ascribed to the reference value defined in the site of soil samples collection, and the borders of wetting zones are to be established by the negative anomalies at electrical profiling graphs. In order to construct the solid geologicalgeophysical models of the landslide zones of the sides, in addition to the geological sections data, the following results of geophysical sounding should be used: the boundaries of landslide zones in the plan, detailed contact geometry of loose Quaternary sediments with bedrock; soil properties modified by wetting

Ground-motion site effect in the Beijing metropolitan area

In the past 500 years, many moderate to strong earthquakes have occurred in or near the Beijing metropolitan area, which is underlain by thick Quaternary and Tertiary sediments. Therefore, the area is susceptible to damage associated with ground-motion site effect, particularly for the large number of high-rise buildings. In order to understand the earthquake site effect potential, particularly in the context of the high-rise buildings, we are undertaking an effort to construct a 3-D shear-velocity model of the Quaternary and Tertiary sediments for the Beijing metropolitan area. In this paper, we present an integrated method of deriving shear-wave velocity profiles at sites across the Beijing metropolitan area using shear-wave velocity and ambient-noise measurements. Our results demonstrate that this method is practical for obtaining shear-wave velocity profiles.We performed 1-D site response analyses at six sites in the Beijing metropolitan area. The results show that the site resonant periods vary between 0.1 s at shallow sites in the west and 4.0 s for deep sites in the east. Moreover, this range of resonant periods coincides with the fundamental periods of many buildings between one to 40 stories. In other words, earthquake site effect could generate a double resonance in a significant number of buildings in the Beijing area. Results also show that the average shear-wave velocity of the top 20 or 30 m, Vs20 or Vs30, does not correlate with site resonance, and is therefore not an appropriate parameter to account for site effect in earthquake engineering.

Geophysical methods for mapping Quaternary sediment thickness: Application to the Saint-Lary basin (French Pyrenees)

This study aims at mapping the sediment infill thickness in the Saint-Lary basin (Aure valley, French Pyrenees). For this purpose, we combine passive seismic and gravity surveys. The resonance frequencies of the sediment body are retrieved from seismic ambient measurements, while the gravimetric survey shows negative residual anomaly of about −3 mGal in the basin. Both methods reveal unexpected but consistent bedrock shape. The southern Saint-Lary basin appears deeper than its northern part, with maximal infill thickness of about 300 m and 150 m, respectively. Valley cross sections show regular and smooth “U”-shape in the southern Saint-Lary basin, in contrast to an irregular and asymmetric pattern in the northern basin. This basin shape may be related to Quaternary fluvio-glacial carving processes especially controlled by a regional fault (the Soulan fault), variations in bedrock hardness, and preferential ice flow paths.

3D upper crustal density structure of the Deccan Syneclise, Central India

ABSTRACTA constrained 3D density model of the upper crust along a part of the Deccan Syneclise is carried out based on the complete Bouguer anomaly data. Spectral analysis of the complete Bouguer gravity anomaly map of the study region suggests two major sources: short wavelength anomalies (<100 km) caused primarily due to the density inhomogeneities at shallow crustal level and long wavelength anomalies (>100 km) produced due to the sources deeper than the upper crust. A residual map of the short wavelength anomalies is prepared from the complete Bouguer anomaly using Butterworth high‐pass filter (100 km cut‐off wavelength). Utilizing the constraints from deep resistivity sounding, magnetotellurics and deep seismic sounding studies, 2.5D density models have been generated along 39 profiles of this region. The mismatch between the calculated response of the a priori 2.5D model with the residual (short wavelength) gravity anomalies is minimized by introducing high‐density intrusive bodies (≥2.81 g/cm3) in the basement. With these 2.5D density models, the initial geometry of our 3D density model, which includes alluvium, Deccan trap, Mesozoic sediment and high‐density intrusive bodies in the basement up to a depth of 7 km (upper crust), is generated. In the final 3D model, Deccan trap extends from 200 m to nearly 1700 m below the 90–150 m thick Quaternary sediment. Further down, the sub‐trappean Mesozoic sediment is present at a depth range of 600–3000 m followed by the basement. The derived 3D density model also indicates six intrusive bodies of density 2.83 g/cm3 in the basement at an average depth of about 4–7 km that best fits the residual gravity anomaly of the study area.

Geoelectric structure of northern Cambay rift basin from magnetotelluric data

Broadband and long-period magnetotelluric data were acquired over the northern part of the Cambay rift zone along an east–west profile ~ 200 km in length. The decomposed TE- and TM-mode data were inverted using a 2-D nonlinear conjugate gradient algorithm to obtain the lithospheric structure of the region. A highly conductive (~ 1000 S) layer was identified within the Cambay rift zone and interpreted as thick Quaternary and Tertiary sediments. The crustal conductors found in the profile were due to fluid emplacement in the western part, and the presence of fluids and/or interconnected sulfides caused by metamorphic phases in the eastern part. The demarcation of the Cambay rift zone is clearly delineated with a steeply dipping fault on the western margin, whereas the eastern margin of the rift zone gently dips along the NE–SW axis, representing a half-graben structure. A highly resistive body identified outside the rift zone is interpreted as an igneous granitic intrusive complex. Moderately conductive (30–100 Ω-m) zones indicate underplating and the presence of partial melt due to plume–lithosphere interactions.

The Last Glacial aeolian record of the Island of Susak (Croatia) as seen from a high-resolution grain–size and rock magnetic analysis

The loess-palaeosol record on the island of Susak in Croatia is a unique archive of Late Glacial climate changes in the Adriatic region, possibly even in the wider area. On Susak up to 90 m of thick Quaternary sediments were deposited, and are accessible for detailed palaeoclimate reconstructions. In this paper, the results of a high-resolution grain-size and rock magnetic investigation on the Last Glacial (Upper Pleniglacial) Sand Pit section from Susak are presented. In spite of its significant thickness, the Sand Pit section does not represent a continuous record; it is a result of a very dynamic environment. There, the deposition of dust and formation of loess has been interrupted by pedogenesis, periods of increased sand accumulation, erosion due to slope wash and water activity, redeposition and wildfires, and all in the time period of about 10.000 years of the Upper Pleniglacial, as seen from the IRSL dating results. The grain-size data clearly show a shift towards coarser grain sizes which differs from typical loess regions. Such predominance of the coarser-grained over the fine-grained fraction, very likely resulted from the predominance of deposition over pedogenesis, increased wind activity and proximal source of material. The rock magnetic signal preserved in the sediment also differs compared to loess-palaeosol records from other regions. The susceptibility values are several times higher than in the records from the Pannonian basin and from typical Eurasian loess. Both the increased susceptibility values and the grain-size are very likely the result of a significant proximal material input from the Po River plain.