Estimation Of Sediment Thickness Research Articles

Assessing Shallow Soft Deposits through Near-Surface Geophysics and UAV-SfM: Application in Pocket Beaches Environments

This study employs a multimethod approach to investigate the sediment distribution in two pocket beaches, Ramla Beach and Mellieha S Beach, in Malta. Both study sites were digitally reconstructed using unmanned aerial vehicle (UAV) photogrammetry. For each case, an ERT and a dense network of ambient seismic noise measurements processed through a horizontal-to-vertical spectral ratio (HVSR) technique were acquired. Electrical resistivity tomography (ERT) analysis enables the estimation of sediment thickness in each beach. HVSR analysis revealed peaks related to beach sediments overlying limestone rocks in both sites and also indicated a deeper stratigraphic contact in Mellieha S Beach. Based on ERT measurements, sediment thickness is calculated for each HVSR measurement. Interpolation of results allows for bedrock surface modelling in each case study, and when combined with digital terrain models (DTMs) derived from photogrammetric models, sediment volumes are estimated for each site. The geometry of this surface is analyzed from a geological perspective, showing structural control of sediment distribution due to a normal fault in Mellieha S Beach and stratigraphic control facilitated by a highly erodible surface in Ramla Beach. The results emphasize the importance of adopting a three-dimensional perspective in coastal studies for precise sediment volume characterization and a deeper understanding of pocket beach dynamics. This practical multimethod approach presented here offers valuable tools for future coastal research and effective coastal management, facilitating informed decision making amidst the growing vulnerability of coastal zones to climate change impacts.

Evaluation of Lake Sediment Thickness from Water-Borne Electrical Resistivity Tomography Data.

Lakes are integrators of past climate and ecological change. This information is stored in the sediment record at the lake bottom, and to make it available for paleoclimate research, potential target sites with undisturbed and continuous sediment sequences need to be identified. Different geophysical methods are suitable to identify, explore, and characterize sediment layers prior to sediment core recovery. Due to the high resolution, reflection seismic methods have become standard for this purpose. However, seismic measurements cannot always provide a comprehensive image of lake-bottom sediments, e.g., due to lacking seismic contrasts between geological units or high attenuation of seismic waves. Here, we developed and tested a complementary method based on water-borne electrical-resistivity tomography (ERT) measurements. Our setup consisted of 13 floating electrodes (at 5 m spacing) used to collect ERT data with a dipole–dipole configuration. We used a 1D inversion to adjust a layered-earth model, which facilitates the implementation of constraints on water depth, water resistivity, and sediment resistivity as a priori information. The first two parameters were readily obtained from the echo-sounder and conductivity-probe measurements. The resistivity of sediment samples can also be determined in the laboratory. We applied this approach to process ERT data collected on a lake in southern Mexico. The direct comparison of ERT data with reflection seismic data collected with a sub-bottom profiler (SBP) showed that we can significantly improve the sediment-thickness estimates compared to unconstrained 2D inversions. Down to water depths of 20 m, our sediment thickness estimates were close to the sediment thickness derived from collocated SBP seismograms. Our approach represents an implementation of ERT measurements on lakes and complements the standard lake-bottom exploration by reflection seismic methods.

Data set | Evaluation of Lake Sediment Thickness from Water-Borne Electrical Resistivity Tomography Data

Lakes are integrators of past climate and ecological change. This information is stored in the sediment record at the lake bottom, and to make it available for paleoclimate research, potential target sites with undisturbed and continuous sediment sequences need to be identified. Different geophysical methods are suitable to identify, explore, and characterize sediment layers prior to sediment core recovery. Due to the high resolution, reflection seismic methods have become standard for this purpose. However, seismic measurements cannot always provide a comprehensive image of lake-bottom sediments, e.g., due to lacking seismic contrasts between geological units or high attenuation of seismic waves. Here, we developed and tested a complementary method based on water-borne electrical-resistivity tomography (ERT) measurements. Our setup consisted of 13 floating electrodes (at 5 m spacing) used to collect ERT data with a dipole–dipole configuration. We used a 1D inversion to adjust a layered-earth model, which facilitates the implementation of constraints on water depth, water resistivity, and sediment resistivity as a priori information. The first two parameters were readily obtained from the echo-sounder and conductivity-probe measurements. The resistivity of sediment samples can also be determined in the laboratory. We applied this approach to process ERT data collected on a lake in southern Mexico. The direct comparison of ERT data with reflection seismic data collected with a sub-bottom profiler (SBP) showed that we can significantly improve the sediment-thickness estimates compared to unconstrained 2D inversions. Down to water depths of 20 m, our sediment thickness estimates were close to the sediment thickness derived from collocated SBP seismograms. Our approach represents an implementation of ERT measurements on lakes and complements the standard lake-bottom exploration by reflection seismic methods.

Estimation of sediment thickness by solving Poisson's equation with bedrock outcrops as boundary conditions

AbstractSediment thickness and bedrock topography are vital for the terrestrial hydrosphere. In this study, we estimated sediment thickness by using information from digital elevation models, geological maps, and public databases. We discuss two different approaches: First, the horizontal distances to the nearest bedrock outcrop were used as a secondary function in kriging and cokriging. Second, we applied Poisson's equation to estimate the local trend of the sediment thickness where bedrock outcrops were used as boundary conditions. Differences between point observations and the parabolic surface from Poisson's equation were minimized by inverse modelling. Ordinary kriging was applied to the residuals. These two approaches were evaluated with data from the Øvre Eiker, Norway. Estimates derived from Poisson's equation gave the smallest mean absolute error, and larger soil depths were reproduced better if the local trend was included in the estimation procedure. An independent cross-validation was undertaken. The results showed the best accuracy and precision for kriging on the residuals from Poisson's equation. Solutions of Poisson's equation are sensitive to the boundary conditions, which in this case were locations of the bedrock outcrops. Bedrock outcrops are available for direct observations; hence, the quality of the estimates can be improved by updating input from high-resolution mapping.

Investigation of Site Condition Using Elliptical Curve Inversion from Horizontal-to-Vertical Spectral Ratio (HVSR)

This study aims to investigate site conditions based on the dominant period and elliptical curve inversion of Horizontal-to-Vertical Spectral Ratio (HVSR). The data were taken using a seismometer portable short period in the minimum time span of data retrieval for 30 minutes. The Nakamura method as known as Horizontal-to-Vertical Spectral Ratio (HVSR) is used to obtain the value of the dominant frequency and amplification factor. The dominant frequency is changed to the dominant period which can indicate the type of soil. HVSR processing use Geopsy software with a guide from the SESAME Project. The results of processing show that the dominant frequency and the amplification factor. In Geopsy there are several modules and packages. This processing uses TFA Module and Max2curve Package and Dinver Package. Waveform can be inversed based on the elliptical curve of HVSR model to produce a shear wave velocity model (Vs) uses that modules and packages. From the velocity model, we can know Vs30 to determine the type of soil layer. The shear wave velocity model obtained can show the estimation of sediment thickness in the area under investigation.

Estimation of sediment thickness (including Mesozoic) in the western central part of Kachchh Basin, Gujarat (India) using Magnetotellurics

The Magnetotellurics (MT) survey has been conducted along a North-South profile having a length of 55 km with the station spacing of 2–3 km in the western central Kachchh, from Shervo village in the north to Dujapar village in the south for estimation of Mesozoic sediment thickness. A total of 18 MT stations have been acquired. The three different 1D inversion techniques (Occam inversion, Bostick inversion and Least square inversion (ZondMT1D)) have been applied to the data, which reveals three different types of subsurface layer sequences by averaging result from all the methods. In the northern part of the profile, ~1000 m thick Mesozoic sediments with resistivity in the range of 2–15 Ω.m is present beneath the ~700–800 m conductive (from 0.5 Ω.m to 2.0 Ω.m) recent (Quaternary-Tertiary) sediments whereas, in the southern part of the profile ~1500 m thick Mesozoic sediments are inferred to be rested under ~400–500 m thick resistive (from 50 Ω.m to 90 Ω.m) Deccan basalt. The ~1800–2000 m thick Mesozoic sediments are imaged as a shallow conductive layer overlying the resistive crystalline basement rocks in the middle of the profile. The Mesozoic sediment thickness ~1500–2000 m is computed in the study area which correlates well with the lithology from a borehole drilled nearby. The dimensionality of the data has suggested a 1D structure <10 s. The 1D forward modeling has also been conducted to verify the results. The obtained model has also been compared with the drilled borehole in the area and they are in good agreement with it.

Stable and clumped isotopes in desert carbonate spring and lake deposits reveal palaeohydrology: A case study of the Lower Jurassic Navajo Sandstone, south‐western USA

AbstractCarbon, oxygen and clumped isotope (Δ47) values were measured from lacustrine and tufa (spring)‐mound carbonate deposits in the Lower Jurassic Navajo Sandstone of southern Utah and northern Arizona in order to understand the palaeohydrology. These carbonate deposits are enriched in both 18O and 13C across the basin from east to west; neither isotope is strongly sensitive to the carbonate facies. However, 18O is enriched in lake carbonate deposits compared to the associated spring mounds. This is consistent with evaporation of the spring waters as they exited the mounds and were retained in interdune lakes. Clumped isotopes (Δ47) exhibit minor systematic differences between lake and tufa‐mound temperatures, suggesting that the rate of carbonate formation under ambient conditions was moderate. These clumped isotope values imply palaeotemperature elevated beyond reasonable surface temperatures (54 to 86°C), which indicates limited bond reordering at estimated burial depths of ca 4 to 5 km, consistent with independent estimates of sediment thickness and burial depth gradients across the basin. Although clumped isotopes do not provide surface temperature information in this case, they still provide useful burial information and support interpretations of the evolution of groundwater locally. The findings of this study significantly extend the utility of combining stable isotope and clumped isotope methods into aeolian environments.

A passive seismic approach to estimating the thickness of sedimentary cover on the Nullarbor Plain, Western Australia

ABSTRACTPassive seismic approaches, using a single-station, enable rapid, cost-effective and non-invasive estimates of the thickness of sedimentary rocks overlying crystalline basement. This approach was applied to estimate the Cenozoic and Cretaceous succession beneath the Nullarbor Plain in southeastern Western Australia. Passive seismic data acquired at the majority of the 94 sites show a single, strong resonance frequency peak between 0.4 and 0.6 Hz suggesting an impedance contrast of a single subsurface layer. Modelling these resonance frequencies against known stratigraphy at 12 drill holes shows that this impedance contrast corresponds to the contact of the base of the Cenozoic–Cretaceous sedimentary succession of the Eucla and Bight basins with the crystalline basement. Data from the remaining sites produced sediment thickness estimates ranging from only tens of metres near the western edge of the Nullarbor Plain to over 860 m near its southern margin. Near this margin, rapid thickening of the sedimentary cover is coincident with an interpreted paleosea-cliff or indicative of localised faulting. Beneath the Western Australian portion of the Nullarbor Plain the sedimentary cover is on average 320 m thick with the succession thinning gradually towards the margins of the basin. A passive seismic approach is thus seen as a useful screening tool for the mineral exploration industry in areas that are under cover allowing for better targeting and cost-reduction in greenfields exploration.

CIGN, A Strong‐Motion Seismic Network in Central Indo‐Gangetic Plains, Foothills of Himalayas: First Results

Online Material: Table of PGAs and PGVs during the 21 May 2014 ( M w 6.1) Bay of Bengal earthquake at Central Indo‐Gangetic Plains network (CIGN) stations. The arcuate shape Himalayan collision zone is one of the most seismically active regions of the world. Five M ∼8 earthquakes have occurred in the last 120 years: 1897 Meghalaya, 1905 Kangra, 1934 Bihar–Nepal border, 1950 Arunachal Pradesh, and 2015 Gorkha. Several workers (e.g., Bilham et al. , 2001; Lave et al. , 2005; Hough and Bilham, 2008) recomputed magnitudes of the older earthquakes in the Himalayas, estimated present‐day seismic moment deficit, and reported earthquakes of M w∼8.8 along the arc in the past. These earthquakes have caused extensive damage in the region (Ambraseys, 2000). Seismicity along the Himalayan collision zone is due to the movement of the Indian plate in a north‐northeast direction at a rate of ∼5 cm/yr of which 2 cm/yr is accommodated through stick and slip manner on a seismically active detachment under the outer and lesser Himalayas (Molnar, 1990; Bilham et al. , 1997; Seeber and Armbruster, 1981). The Indo‐Gangetic Plains (IGP) is a foredeep basin that follows the trend of the Himalayan collision zone. The basin is filled with thick alluvium deposits of varying degrees of compaction overlying the basement faults, ridges, and other tectonic features, obliterating their surface expression. Estimates of sediment thickness in the IGP, varying between 0.5 and 3.9 km, have been reported from gravity and borehole data (Sastri et al. , 1971; Rao, 1973; Srivatsava, 2001) and receiver function analysis (Srinivas et al. , 2013), with maximum thickness observed along the foothills of Himalayas. The near‐surface geologic structures, especially soft soils in basins, are known to dramatically amplify seismic waves and cause great damage and deaths, even at sites relatively far from the epicenter …

Anomalous South Pacific lithosphere dynamics derived from new total sediment thickness estimates off the West Antarctic margin

Paleotopographic models of the West Antarctic margin, which are essential for robust simulations of paleoclimate scenarios, lack information on sediment thickness and geodynamic conditions, resulting in large uncertainties. A new total sediment thickness grid spanning the Ross Sea–Amundsen Sea–Bellingshausen Sea basins is presented and is based on all the available seismic reflection, borehole, and gravity modeling data offshore West Antarctica. This grid was combined with NGDC's global 5 arc minute grid of ocean sediment thickness (Whittaker et al., 2013) and extends the NGDC grid further to the south. Sediment thickness along the West Antarctic margin tends to be 3–4km larger than previously assumed. The sediment volume in the Bellingshausen, Amundsen, and Ross Sea basins amounts to 3.61, 3.58, and 2.78millionkm3, respectively. The residual basement topography of the South Pacific has been revised and the new data show an asymmetric trend over the Pacific–Antarctic Ridge. Values are anomalously high south of the spreading ridge and in the Ross Sea area, where the topography seems to be affected by persistent mantle processes. In contrast, the basement topography offshore Marie Byrd Land cannot be attributed to dynamic topography, but rather to crustal thickening due to intraplate volcanism. Present-day dynamic topography models disagree with the presented revised basement topography of the South Pacific, rendering paleotopographic reconstructions with such a limited dataset still fairly uncertain.

LAKE SEDIMENT THICKNESS ESTIMATION USING GROUND PENETRATING RADAR

The objective of the study is to provide estimates of sediment thickness in Punem Lake, which is a shallow perennial lake in Manipur, India. Radar profiles are obtained in the lake with Mala GPR using 100 MHz RTA (Rough Terrain Antenna). The average depth of the lake is found to be around 2.2 m with the total sediment thickness ranging from 2.2 m to 3.8 m. For the present study two sediment layers are identified that can be easily differentiated from the GPR radargram and the thickness as well as the volume is calculated using ArcGIS. Minimum, maximum, and an average thickness of 0.02m, 1.16m and 0.50m respectively is observed in the first layer with the majority of the thickest sediment deposits towards the North, Northeast and Eastern side of the lake. In the second layer a minimum, maximum, and an average thickness of 0.08m, 0.99m and 0.37m respectively is observed with the majority of the thickest sediment deposits towards the North, Northeast and Western parts of the lake. Sediment volume of about 260303.33 cubic meters of deposit is estimated in the first layer of the lake bottom whereas that of the second layer is estimated to be about 188171.51 cubic meters only.

Global sediment thickness data set updated for the Australian‐Antarctic Southern Ocean

We present a new, 5 min sediment thickness grid for the Australian‐Antarctic region (60°E–155°E, 30°S–70°S). New seismic reflection and refraction data have been used to add detail to the conjugate Australian and Antarctic margins and intervening ocean floor where regional sediment thickness patterns were poorly known previously. On the margins, sediment thickness estimates were computed from velocity‐depth functions from sonobuoy/refraction velocity solutions ground‐truthed against seismic reflection data. For the Southeast Indian Ridge abyssal plains, sediment thickness contours from Geli et al. (2007) were used. The new regional minimum sediment thickness grid was combined with the global National Geophysical Data Center (NGDC) sediment grid to create an updated global grid. Even using the minimum estimates, sediment accumulations on the extended Australian and Antarctic continental margins are 2 km thicker across large regions and up to 9 km thicker in the Ceduna Basin compared to the global NGDC compilation of sediment thickness data.

Depth to magnetic sources in the offshore northern Perth Basin

During 2009-11 Geoscience Australia completed a petroleum prospectivity study of the offshore northern Perth Basin. Basement in the northern Perth Basin is deep and generally not resolved in the reflection seismic data. Recent improvements to the magnetic ship-track database and magnetic anomaly grid allowed an assessment of depth to magnetic sources, and estimation of sediment thickness, providing new insight into basement depth and trends. 2D models along seismic transects and analysis using spectral methods indicate that penetration of the deepest sediments by high-susceptibility bodies is probable. The reflection seismic evidence for these bodies is not clear, though in some cases they may be associated with faults and structural highs. Where the modelled bodies penetrate the sediments they are mostly below or within the Permian strata. A moderate positive magnetic anomaly (the Turtle Dove Ridge) is modelled by massive bodies whose tops are 5-15 km below sea floor. The depth to magnetic basement map highlights sub-basins and structural highs within the northern Perth Basin, with up to 12 km of sediment in the Zeewyck sub-basin.

Preliminary results from marine seismic survey GA302 over Capel and Faust Basins

Data from 50 sonobuoys were recorded over the Capel and Faust Basins, 800 km to the east of mainland Australia in water depths 1500?2000 m, during a 2006 seismic survey for Geoscience Australia. These data were interpreted and forward modelled by ray-tracing to provide an estimate of P-wave velocities in the upper sedimentary section, and hence constrain estimates of sediment thickness. Also recorded were gravity and magnetic anomaly data which, in conjunction with the very high quality seismic reflection data, provided additional constraints upon the velocity models. Typical ranges in four model layers below water were: 1.9, 2.3?3.0, 3.6?4.7, 5?5.3 km/s. Gravity models based on these results were compared to features identified on depth converted seismic reflection lines and indicate that sediment thickness at densities approximating 2.3 t/m3 may reach 5 km in several localities.

Towards remote sensing of sediment thickness and depth to bedrock in shallow seawater using airborne TEM

Following a successful bathymetric mapping demonstration in a previous study, the potential of airborne EM for seafloor characterisation has been investigated. The sediment thickness inferred from 1D inversion of helicopter-borne time-domain electromagnetic (TEM) data has been compared with estimates based on marine seismic studies. Generally, the two estimates of sediment thickness, and hence depth to resistive bedrock, were in reasonable agreement when the seawater was ~20 m deep and the sediment was less than ~40 m thick. Inversion of noisy synthetic data showed that recovered models closely resemble the true models, even when the starting model is dissimilar to the true model, in keeping with the uniqueness theorem for EM soundings. The standard deviations associated with shallow seawater depths inferred from noisy synthetic data are about ± 5% of depth, comparable with the errors of approximately ± 1 m arising during inversion of real data. The corresponding uncertainty in depth-to-bedrock estimates, based on synthetic data inversion, is of order of ± 10%. The mean inverted depths of both seawater and sediment inferred from noisy synthetic data are accurate to ~1 m, illustrating the improvement in accuracy resulting from stacking. It is concluded that a carefully calibrated airborne TEM system has potential for surveying sediment thickness and bedrock topography, and for characterising seafloor resistivity in shallow coastal waters.

Seismic Microzonation and Damage Assessment of Bam City, Southeastern Iran

This article aims to study the dynamic characteristics of soil in Bam, southeastern Iran. Fundamental frequency and amplification factor of soil sediment were estimated by microtremor measurement. This procedure was performed at 49 sites in the city. Two 120-second data were recorded at each site. Segmental cross spectra were applied to calculate spectrum, Nakamura's method (H/V) was used for analyzing data and fundamental frequency and amplification factor values were derived. Iso-frequency and iso-amplification maps of the city were prepared. Results show that soil type in Bam city is mainly stiff, although amplification factor is relatively large. There is a short period zone in northwest to southeast direction. Sediment depth was estimated using a correlation between fundamental frequency and sediment thickness. Results obtained from microtremors were compared to the geotechnical boreholes and it was shown that microtremors can be used for a rough estimation of sediment thickness. Damage distribution map of Bam due to the Bam earthquake on December 26, 2003 was prepared by both field and aerial investigation. Quality of buildings in Bam was evaluated, as a result a crude zoning map on the building quality was prepared. Finally, it was concluded that several factors have contributed to damage intensity variation; earthquake characteristics, local site effect, and buildings' quality. All mentioned parameters affected the damage variation.

The hydrostatic corer Selcore—a tool for sediment sampling and geophysical site characterization

Hydrostatic energy is used to power an active device for sediment sampling and geophysical site characterization. In the Selcore design, a steel tank with built-in drive unit constitutes the core head. The difference between ambient water pressure and atmospheric pressure in the tank provides the energy. The Selcore prototype enters the seabed as a gravity corer and automatically shifts into pile driving mode with up to 52 duty cycles without the need for an external trigger mechanism. The corer has operated in water depths from 300 to 3500 m. Operation at depths shallower than 300 m including on dry land can be facilitated using auxiliary water pressure. Penetration and recovery is generally more than two times the performance of a gravity corer of equivalent weight. The added utilization of hydrostatic energy has particular advantage in cases of relatively high shear strength sediments as well as attempts to core shallow bedrock below a sediment cover . Selcore has potential as a seabed seismic hammer source and initial land tests show good signal repeatability. Estimates of sediment thickness and seismic velocity obtained from the inversion and interpretation of the dominant Rayleigh surface waves corresponds closely to the shallow borehole stratigraphy at a land test site.

Bathymetry, depth to magnetic basement, and sediment thickness estimates from aerogeophysical data over the western Weddell Basin

We estimated the bathymetry and sediment thickness of a remote and difficult to access portion of the Antarctic continental margin using aerogeophysical surveying techniques. The U.S., Argentina, Chile aerogeophysical survey collected magnetic and gravity data over the basins surrounding the Antarctic Peninsula. Thirty‐seven of these flight lines were used to estimate bathymetry and depth to magnetic basement for the western Weddell Basin. A wavenumber technique was applied to individual magnetic anomaly profiles in an automated fashion to obtain estimates of the depth to magnetic basement. The bathymetric estimates were obtained by admittance inversions of the gravity field. The results were then gridded at a 40‐km interval for the region 64°W, 44°W, 73°S, and 62°S. Bathymetric estimates and depth to magnetic basement estimates were differenced at each grid point to obtain a regional estimate of the thickness of nonmagnetic overburden (assumed to be sediment). Subsequent spot measurements of topography in the estimated region of the continental margin generally agree to about 52 m. The estimated magnetic basement deepens from the Antarctic Peninsula margin eastward to a maximum of 10–12 km near 54°W. We also postulate the existence of two moderately large basins flanking the eastward continuation of the Jason Peninsula. Farther east, the basement steps upward, with a correspondent thinning of the sedimentary layer. Along the east coast of the peninsula, results agree well with seismic studies on James Ross Island and magnetotelluric studies on Marambio Island and the Larsen nunatak, as well as the British Antarctic Survey basement estimates from aeromagnetic data. This study further demonstrates the utility of combined application of airborne and satellite geophysical techniques in the study of structure and tectonic evolution of continental margins and marine basins.

Sediment volume in the north polar sand seas of Mars

Data from studies of the cross‐sectional area of terrestrial transverse dunes have been combined with maps of dune morphometry derived from Viking orbiter images to generate new estimates of sediment thickness and dune sediment volume in the north polar sand seas of Mars. A relationship between dune spacing and equivalent sediment thickness (EST) was developed from field data on Namibian and North American dunes and was applied to data on dune spacing and dune cover measured on Viking orbiter images to generate maps of dune sediment thickness for Martian north polar sand seas. There are four major sand seas in the north polar region of Mars, covering an area of 6.8×105 km2. Equivalent sediment thickness ranges between 0.5 and 6.1 m with a mean of 1.8 m. The sand seas contain a total of 1158 km3 of dune sediment, which may have been derived by erosion of polar layered deposits and concentrated in its present location by winds that change direction seasonally.