Basement Depth Research Articles

Using Multichannel Analysis of Surface Wave to Assess Bedrock Depth in Grand Aceh Baet Residential Area

Abstract Inadequate foundation studies had over time led to quite a number of mishaps, resulting in loss of lives and properties. To address this issue, a Multichannel Analysis of Surface Wave (MASW) survey was conducted at the proposed Grand Aceh Housing site to characterize the subsurface and determine the depth to the bedrock, ensuring a stable foundation for the Rusunawa construction. The survey was performed along four profile lines using a PASI 16S-24P seismograph. The acquired data were processed with Geopsypack Geopsy and Dinver version 2.5.0 and then modelled into 2D data using Surfer version 13. The results identified four distinct layers with varying depths and thicknesses: the first layer with shear wave velocity ≤175 m/s is classified as soft soil layer (SE), the second layer as medium soil (SD) with Vs 175-350 m/s, the third layer as solid soil and soft rock (SC) with Vs 350-750 m/s, and the fourth layer as rock layer (SB) with Vs 750-1200 m/s. The findings of this study suggest that the fourth layer is bedrock, capable of supporting the Rusunawa foundation.

Basement Configuration and Tectonic Evolution Beneath Zallah Trough, Western Sirt Basin, Libya, Obtained from Integrated Gravity, and Aeromagnetic Data

In this study, gravity and aeromagnetic datasets are analysed to map fault systems and the depth of the basement, which has hitherto been unknown. The gravity and magnetic data were provided by the Libyan Petroleum Institute. Low-pass filters separated local and regional components of gravity and aeromagnetic datasets, as well as the CET grid analysis filter, Euler deconvolution, Source Parameter Imaging (SPI) estimate of crystalline basement depth, Werner deconvolution, and 2D forward modelling. The results show the fault patterns, primarily trends, are NE-SW, N-S, and NW-SE, which define and constrain the trough. Some structural characteristics in the centre and southern trough have an NNE-SSW orientation with estimated depth ranging from (400 to 5350) m as resulted by Euler deconvolution. The SPI technique estimates the crystalline basement at about 5200 m. The Werner solution showed volcanic bodies in the form of sills; in addition, it approved that these volcanic bodies have depths of 4366m and 5067 m, respectively. Thle observed sill bodies may have been the result of the Sirt Basin rifting, causing a weakening of the crust to allow mantle flow. The 2D modelling showed that the depth of the basement ranges between (5100 and 5400) m beneath the depocenter of the study area.

Deep learning‐based inversion with discrete cosine transform discretization for two‐dimensional basement relief imaging of sedimentary basins from observed gravity anomalies

AbstractSedimentary basins, integral to Earth's geological history and energy resource exploration, undergo complex changes driven by sedimentation, subsidence and geological processes. Gravity anomaly inversion is a crucial technique offering insights into subsurface structures and density variations. Our study addresses the challenge of complex subsurface structure assessment by leveraging deep neural networks to invert observed gravity anomalies. Optimization approaches traditionally incorporate known density distributions obtained from borehole data or geological logging for inverting basement depth in sedimentary basins using observed gravity anomalies. Our study explores the application of deep neural networks in accurate architectural assessment of sedimentary basins and demonstrates their significance in mineral and hydrocarbon exploration. Recent years have witnessed a surge in the use of machine learning in geophysics, with deep learning models playing a pivotal role. Integrating deep neural networks, such as the feedforward neural networks, has revolutionized subsurface density distribution and basement depth estimation. This study introduces a deep neural network specifically tailored for inverting observed gravity anomalies to estimate two‐dimensional basement relief topographies in sedimentary basins. To enhance computational efficiency, a one‐dimensional discrete cosine transform based discretization approach is employed. Synthetic data, generated using non‐Gaussian fractals, compensates for the scarcity of true datasets for training the deep neural network model. The algorithm's robustness is validated through noise introduction with comparisons against an efficient and traditional global optimization‐based approach. Gravity anomalies of real sedimentary basins further validate the algorithm's efficacy, establishing it as a promising methodology for accurate and efficient subsurface imaging in geological exploration.

Assessing rainfall-triggered landslides considering small-scale depth to bedrock uncertainty: A random field approach

Depth to bedrock (DTB) is a critical factor for rainfall–induced slope failures. However, the influence of uncertainties in these measurements, particularly at a small–scale, has not been fully understood. Numerical modeling was conducted to assess the impact of a variable bedrock topography on the stability of a real–world unsaturated slope. The simulations included a three–dimensional pore–water pressure estimation, derived from the numerical solution of the Richards equation, coupled with a slope stability assessment using numerical limit analysis. The study explored the potential of incorporating random fields (RFs) into an established DTB model to improve the understanding of rainfall–triggered landslides. The proposed methodology was applied to the analysis of a small watershed within the Papagaio River basin in Brazil, an area historically subjected to landslides triggered by rainfall events. Our main findings reveal that small variations in DTB can significantly impact the safety factor and probability of failure estimations. Furthermore, they influence the shape, location and failure volume associated to predicted landslides. The incorporation of RFs effectively addresses small–scale uncertainty in DTB, controls bedrock morphology, and enhances the assessment of probabilistic numerical modeling for landslide susceptibility. This study highlights the importance of accurate and comprehensive DTB characterization for assessing rainfall–induced landslides at local slope scale.

Combining electrical resistivity tomography and passive seismic to characterise the subsurface architecture of a deeply weathered lateritic hill within the Avon River critical zone observatory

AbstractObserving the subsurface architecture of the deep Critical Zone (CZ), which lies beyond the uppermost layer of accessible soil, is a complex but crucial task. Near‐surface geophysics offers an alternative to accessing the deep CZ at scales relevant to fluid, nutrient and gas transport. As geophysical instruments are sensitive to different subsurface physical properties, their combination can enhance insight into CZ architecture. However, the agreement between and complementarity of multiple geophysical techniques has not been widely assessed for CZ‐related questions. This study employed geophysics to image a highly weathered lateritic hill rich in iron oxides developed from Archean granite within the Avon River Critical Zone Observatory, Western Australia. Data gathered from an electrical resistivity tomography (ERT) and horizontal‐to‐vertical‐spectral‐ratio (HVSR) passive seismic transect were used to visualise CZ architecture through specific resistivity values and ambient noise contrasts. Both techniques revealed a notable degree of lateral variability consistent with the formation of the ~3–4 m thick duricrust‐capped hilltop, the creation of gullies in the sodic material of the pallid zone exposed along the slope and the deposition of ~11 m thick colluvial sediment at the foot slope. Calculated bedrock depth was consistent between the HVSR and ERT instruments along the hilltop plateau but varied from ~23 m to 31 m on the slope and 32 m to 39 m at the foot slope, respectively. Overall, the vertical variation depicted by the ERT, including the differentiation of two layers within the lateritic weathering profile ‐ the pallid zone and saprolite – made up for the inaccuracy of the HVSR technique in depicting layers of similar composition. Moreover, the HVSR method clearly depicted bedrock depth, overcoming the partial masking of the bedrock by saline groundwater in the ERT model. The complementarity of these two methods allowed the development of a detailed conceptual model of subsurface CZ architecture within a saline lateritic weathering profile.

Qualitative and quantitative interpretations of high-resolution aeromagnetic data of Saki-East area, for basement and structural framework

Earth tremor is a small earthquake or seismic event that occurs in seismically unstable region. However there have been little information about the earth tremor before year 1987, but events between 1990 and 2000 have triggered further researches. This research work is aimed at qualitatively and quantitatively interpret high resolution aeromagnetic data of Saki-East area to provide basement and structural framework of the study area. The aeromagnetic data of the study area consisting of Igboho data sheet 200 and Lechilaku sheet 221 were processed using Oasis Montaj software and interpreted for mapping basement and structural stability in the area. Enhancement process was further carried out on the data to generate residual aeromagnetic data used in determining the lineament orientations in the study area. 3D Euler deconvolution and Source Parameter Imaging (SPI) techniques were implored to determine basement depth of subsurface geological structures. The result shows positive correlation with geologic structures, low magnetic anomalies revealed subsurface deformation of crystalline basement rocks. 3D Euler solutions for SI = 1 shows large clusters depicting geological bodies associating with faults. The magnetic basement depth from 3D Euler and SPI shows over 90% dominance of shallow depth range of 3-600 m in the study area, this revealed that the dominant shallow depth of magnetic basement causes the faulting system of the study area becoming weak zones through which tremor occurs. The lineaments in the study areas are classified into major and minor lineaments, the major lineaments are prominent within the basement rocks and are possibly produced by the regional historic orogenic movement that affected Nigeria basement.

Subsurface Imaging in Urban Areas With Ambient Noise Using DAS and Seismometer Data Sets: Granada, Spain

AbstractDistributed acoustic sensing (DAS) is an innovative technology with great potential for acquiring seismic data sets in urban areas. In this work, we check the suitability of a DAS data set acquired in Granada (Spain) for retrieving subsurface reflectivity from ambient noise. The fiber‐optic is a pre‐existing underground telecommunication cable that crosses the city from Northwest to Southeast. We use a 10 hr recording of strain rate from a 2020 experiment to obtain seismic reflections using the autocorrelation method. We compare the DAS results with reflections obtained from seismic ambient noise recorded in nine seismometers deployed close to the fiber‐cable for 7 days in November 2022. The novel approach proposed in this study for the identification of the reflections is to use autocorrelations after bandpass filtering for specific central frequencies and to check the stability of the signals over a broad frequency band. Microtremor Horizontal to Vertical Spectral Ratio (MHVSR) measurements at a total of 14 stations, five of them outside the city, help to constrain the reflection interpretation. These include one station at the borehole that reaches the basement in the Granada Basin crossing all the Cenozoic units. We use the legacy sonic log to obtain a relationship between frequencies of MHVSR peaks and depth. Autocorrelation and MHVSR methods give consistent results delineating bedrock depth deeper than 1,000 m in Granada. These results confirm that DAS can provide valuable subsurface information in urban areas.

Crustal structure and tectonic evolution of the Pranhita-Godavari Rift: A comprehensive study using edge enhancement techniques and 2D gravity modeling

The Pranhita-Godavari Rift basin is a significant tectonic feature in peninsular India. The Bouguer gravity anomaly digital grids from the gravity map of India (after NGRI-GSI, 2006) were analyzed to present a detailed discussion of the Pranhita-Godavari rift basin’s crustal structure and contribute to understanding its regional geology (i.e., Sediment thickness, depth of the basement, Conrad, and Moho) and tectonics. Using advanced techniques like the horizontal gradient method (HGM), first vertical derivative (FVD), and tilt derivative (TDR), we successfully mapped the regional tectonic features. The identified key lineaments and faults have trends primarily in NW-SE, WNW-ESE, NNE-SSW to N-S, and NE-SW directions.The depth of the Moho, Conrad, and basement was computed using 2D gravity modeling. The modeling reveals significant findings, including substantial crustal thickening within the rift, with Moho depths ranging from 38.6 km to 41 km, indicating considerable tectonic subsidence and sediment accumulation. Conrad discontinuity depths vary between 18 km and 26 km, reflecting complex crustal deformation associated with rifting processes. Basement depths range from 3.5 km to 6.2 km; the Alluvium, Barakar, Sullavai, and Pakhal sediments are deposited over the Archean basement, highlighting differential subsidence within the rift compared to adjacent cratonic regions. Additionally, several major and newly observed faults were mapped using 3D Euler deconvolution and 2D gravity modeling. The Ahiri-Tippapuram, Godavari Valley, Kinnerasani Godavari, Koddam, and Kolleru Lake faults were identified, extending to the Moho with significant downthrows, indicating varied tectonic activity. These findings provide valuable insights into the tectonic evolution and structural dynamics of the PGR, offering a deeper understanding of rift-related processes and aiding future research in the region.

Identification of Peridotite Bedrock using Resistivity Geoelectric Method in Lapao Pao Estuary Area, Kolaka District

Ultramafic rocks are the main source of nickel laterite deposits. One of the areas that has an ultramafic complex is located in Muara Lapao Pao Village, Kolaka Regency. The research was conducted in the mining area of PT Tri mitra Babarina Putra using the resistivity geoelectric method of the Wenner - Schlumberger configuration, In the area it is not yet known exactly how much peridotite bedrock is present in the subsurface. Therefore, it is necessary to conduct a geophysical survey in identifying the occurrence of peridotite bedrock, and can determine the depth and thickness of peridotite bedrock in the research area. the occurrence of peridotite bedrock in the mining area of PT Tri Mitra Babarina Putra has a resistivity value between 3000 – 17984 Ohm-meters. Peridotite bedrock in the research area on all four tracks has a depth and thickness that is almost uniform. lines 1 and 2 and 4 are at a depth of 34.5 - 39.6 meters with a thickness of up to 5.1 meters. and line 3 peridotite bedrock is at a depth of 40 m to more. There are 3 layers in the study area, namely, soil/overburden layer with a resistivity value of 16.5 – 122 Ohm-meters, serpentinite rock layer with a resistivity value of 200 – 2438 Ohm-meters and peridotite bedrock layer with a resistivity value of 3000 – 17984 Ohm-meters.

Magnetometric and seismic investigation of the Nova Colinas impact structure, Parnaíba Basin, Brazil

Nova Colinas (NC) is a complex-type impact structure located in the northeast region of Brazil. It was formed in the volcano-sedimentary strata of the Parnaíba Basin, in the northern part of Western Gondwana. With an apparent diameter of approximately 6.5–7 km, its rim exhibits a distinctive magnetic signal, likely associated to basic volcanic rocks from the Mosquito Formation. These rocks present shock deformation, bracketing the maximum age of the impact event to 197 Ma. We use the magnetometric and seismic methods to establish the geophysical signature of NC and it is the structural framework in subsurface, as well as for characterizing the occurrence and extent of the volcanics. The magnetometric maps present two distinct magnetic domains in the region of NC: (i) the northern area is characterized by short-wavelength magnetic anomalies related to the basaltic flows of the Mosquito Formation; and (ii) the southern region, where sedimentary rocks from the Sambaiba Formation occur, which lacks significant magnetic anomalies, a typical pattern of siliciclastic sedimentary strata. The magnetic sources at the structure's rim reach an estimated depth of ∼250 m, and the position of the rim itself has been effectively established by the total horizontal derivative of the tilt derivative (THDR_TDR) technique. The regional magnetic anomaly suggests a deeper source at the center of the structure, possibly caused by strata with high magnetic susceptibility uplifted in the modification stage of crater formation. Magnetometric modeling using the magnetization vector inversion (MVI) method allowed detailed mapping of the volcanic rocks that form NC's rim. Additionally, analysis of the seismic data allowed the identification of two well-marked horizons, interpreted as diabase sills, located at depths of 600 m and 1200 m, respectively. Impact-related deformation represented by structures such as fractures, a central uplift, and reflector discontinuities associated with faulting, fracturing, and brecciation, were also unveiled by the seismic data, as well as the establishment of the depth of the crystalline basement at ca. 2200 m.

Ice-sheet burial and erosion inferred from cosmogenic nuclide bedrock depth profiles: Implications for the glaciation history of northeastern Fennoscandia

In this study, we evaluate the application of shallow (<2.5 m) cosmogenic depth profiles in bedrock to constrain long-term ice-burial and erosion histories. Using Markov Chain Monte Carlo inversion modelling on a series of synthetic scenarios, we demonstrate that cosmogenic 10Be and 26Al profiles provide more robust constraints on ice-burial duration and erosion histories than surface samples alone, particularly when erosion rates are low (<5–10 m Myr−1) and/or non-steady. We apply this method to new depth profiles of 10Be and 26Al measurements from two tors in the Parkajoki region in northeastern Sweden. Our results indicate erosion depths of ∼2–10 m and ice burial for ∼20–35% of the time since 500 ka. These estimates imply more erosion and less ice burial than previously inferred from the same tors. However, by re-assessing the extent of ice cover during the Weichselian from existing records, we show that some cosmogenic nuclide inheritance predates the penultimate glacial maximum (Late Saalian), implying limited glacial erosion in the Parkajoki region during the last glacial cycle.

Effects of changing adjacent building conditions on ground settlement profiles around deep excavation construction

ABSTRACT This study investigates the impact of deep excavation on ground settlement under various adjacent building conditions using the finite element method. It simulates diaphragm wall earth retention systems with plate elements and uses H-beam assemblies with preloaded anchors to represent temporary earth retention and ensure safety measures. Adjacent structures are also modeled with plate elements. Unlike traditional methods that often overestimate settlement by simulating only ground loads, this research includes the effects of neighboring basements and validates the model using field data. The study employs the HSS model, which provides a more accurate representation of soil deformation compared to the Mohr-Coulomb model. Findings indicate that ground settlement significantly increases when the adjacent building’s basement depth is about half the excavation depth, stabilizing as it approaches 1.6 times the excavation depth. Settlement is more pronounced for buildings closer to the diaphragm wall and decreases with distance. The relationships are described by normalized curves, and y = 1.9x−0.4 and 2.5/√x, representing the behavior of ground settlement in response to varying building conditions.

Basement Depth Map Estimation and Linear Features Detection Depending on Interpretation of Magnetic Data at Qarun Oil Field and Surrounding Areas, North Western Desert, Egypt

This investigation primarily targets a specific area situated in the northeastern Western Desert and northwest Beni-Suef, covering Wadi Al Rayan area, Gindi basin, Kattaniya inversion, and El-Fayum depression. It extends to the east of the river Nile. This study aims to Evaluate the depth of the basement complex in the area under investigation. The total aeromagnetic intensity data was reduced to the north pole (RTP) for clarity. 2D modeling of this RTP data was then used to evaluate the basement depth. The analysis of basement depth maps revealed significant variations in the subsurface structure of the study area, showing both elevated features (horsts) and depressed areas (grabens). The elevated basement (horsts) was found to be at a depth of approximately 813 meters, while the deepest depression (grabens) reached down to 7600 meters. Based on magnetic data combined with eight wells drilled into the basement complex, a basement lineament map of the area is delineated as a result of the investigation. This map shows a series of large alternating highs and valleys in ENE-WSW, NE-SW and E-W trending bands. Together with other minor trends, these major trends have shaped the basement surface into several tilted fault blocks, creating anticlinal and syncline zones of different depths and directions to form the Qattrani-El Gindi low trends. Whereas the high trend is located in El Fayum, El-Sagha, and Abu Rawash areas. The study helped to re-evaluate the subsurface structures affecting the Qarun oil field's hydrocarbon accumulation.

Novel method to determine bedrock from a single sensor based seismic reflection signal using Haar wavelet transform

The determination of bedrock depth is crucial across various earth sciences and related fields. Geophysical techniques, notably the continuous wavelet transform, are increasingly employed to map subsurface bedrock structures. This method allows the transformation of 1D time domain seismic reflection signals into a 2D image, providing time–frequency representations for feature extraction. Leveraging the advantages of wavelet theory, particularly the Haar wavelet known for its simplicity and compact support, this study utilizes continuous Haar wavelet local maxima lines to enhance bedrock analysis. Seismic reflection data is acquired using an extremely sensitive geophone as a receiver along with a high dynamic range data logger. The Common Midpoint (CMP) approach, coupled with optimized offset distances, is utilized to ensure robust data quality and signal strength. Simple sources, such as a sledgehammer, generate sound waves for data collection prior to borehole drilling, correlating acquired data with lithogeological information. This research emphasizes the significance of adjusting parameters like sampling frequency, choice of wavelet, and optimal offset distances. The methodology employed, involving a single geophone, a one-channel data recorder, and a basic sledgehammer as a sound source, offers an inexpensive, straightforward, and non-invasive approach. The study demonstrates the effectiveness of Haar wavelet local maxima lines in accurately determining bedrock depth, producing results closely aligned with both predicted and actual depths.

Effect of soil-building interaction on dynamic earth pressure on basement walls

This study investigates dynamic earth pressure on basement walls by considering soil-structure interaction, a factor that is often overlooked by conventional methods like Mononobe-Okabe, Seed and Whitman, and Wood. Superstructure, basement, and soil were numerically simulated in a single model to evaluate the inertial and kinematic effects of buildings on dynamic earth pressure on the basement walls. The numerical model was validated using data from a centrifuge test and an instrumented building. Then, a parametric study was performed, with the height, width, and basement depth of the building varied with six input motions. The results showed that the inertia of the building increased dynamic thrust. Furthermore, the dynamic thrust showed a similar trend with the displacement response spectrum curve of the ground surface acceleration as the building height increased, while the distribution shape transitioned from triangular to inverted triangular. Additionally, wider buildings had increased dynamic earth pressure, while deeper buildings exhibited smaller normalized dynamic thrust.

Fuzzy c-mean (FCM) integration of geophysical data from an iron-oxide copper gold (IOCG) deposit under thick cover

Geophysical methods depend on a range of physical and chemical mechanisms, and each method has different sensitivities and resolution of Earth parameters, and over different scale lengths. Additionally, such geophysical methods will also have their own statistical characteristics. Thus, it is a significant challenge to combine different methods through a single inversion framework. Rather than attempting to find an optimal and single model for different geophysical responses, an alternative approach is to use FCM clustering to identify clusters of parameters from two or more different geophysical data sets or models that have similar statistical properties. In this paper, we apply the FCM approach to integrate data and model sets for an array of 100 broadband magnetotelluric (MT) and 100 passive seismic receivers spaced 1 km apart on a 10 by 10 grid above the Vulcan IOCG prospect in the Olympic Cu–Au Province, southern Australia. The challenge for exploration of the Vulcan prospect is that it lies beneath 750 m of regolith sedimentary cover, no single geophysical method provides a unique characterization of the deposit geometry, and drilling is very expensive. Fuzzy c-mean cluster analyses are undertaken in 2D for gravity data and shear-wave velocity model data for basement depths beneath cover and in 3D for shear-wave velocity and electrical resistivity model data. Fuzzy c-mean clustering is shown to provide a simple and efficient method of integrating different geophysical measurements to produce a geological framework that can be verified with drilling information.

Testing the Efficacy of Indirect Methods on Characterization of Sedimentary Basins by Correlation of Direct Data and Geophysical Techniques

The information obtained from direct data (geological mapping and boreholes) and indirect techniques (reflection seismology, time-domain electromagnetics and magnetometry) is combined to analyse the northern limit of the Bailén basin (southeastern Spain). This Triassic–Neogene basin is confined by a graben-type structure, limited by two normal faults in the SW–NE direction (the Baños de la Encina-La Carolina fault and Guarromán fault). The movement of these faults was complex, with different pulses occurring over time. Therefore, the subsidence of the basin and the sedimentary filling of the graben were different, giving rise to lateral changes in the facies and thicknesses. This study focuses on the Baños de la Encina fault, chosen as the experimental site to analyse the effectiveness and accuracy of these geophysical techniques to reveal the basement structure and geometry. Seismic reflection allows to detect two faults that caused the subsidence of the eastern sector of the graben. The TDEM method made it possible to calculate the depth of the Palaeozoic basement, as well as reveal the presence of the two aforementioned faults. Magnetic total field data highlight variations in the basement depth that can be used to infer previously unknown fractures, in this case, in the NW–SE direction.

Earth's longest lava flows erupted from its largest igneous province: The submarine Ontong Java Plateau

We use high-precision analyses of fresh basalt glasses from the submarine, Cretaceous Ontong Java Plateau (OJP) recovered by the Ocean Drilling Programs (ODP) to test for long submarine lava flows. Major elements and Cl show that glasses from ODP Holes 1185B and 1186A, which are 200 km apart, are compositionally identical and must have erupted simultaneously from the same well-mixed magma chamber. Identical CO2 contents show they erupted at the same water depth, but 1185B is directly downslope from 1186A and has a corrected basement depth that is >700 m deeper. Remarkably, <2 °C cooling took place over 200 km, requiring a cooling rate <0.01 °C/km.Further evidence of long flows is the lack of vesicles in OJP's glasses, in contrast to mid-ocean ridge basalt glasses that almost always contain vesicles and are often oversaturated in dissolved CO2. We propose that OJP's lavas degassed to saturation levels of dissolved CO2 +H2O and lost all bubbles because they remained liquid for much longer periods during long distance flow. Dissolved CO2+H2O are used to estimate paleoeruption depths which are compared to current corrected basement depths. Using a fixed value of plateau subsidence (500 m) we reconstruct flow distances of 0 to 900 km for eight lava groups from six drill sites. Eruption depths in Hole 807 C are 3040 m for Kwaimbaita-type lavas but 1110 m for Singgalo-type lavas that directly overlie them suggesting that the Singgalo lavas erupted 900 km away (near Site 1183).Paleoeruption depths for Cretaceous glasses from the Jurassic East Mariana and Nauru Basins adjacent to OJP are shallower than most glasses recovered from OJP even though their reconstructed basement depths are 1500–3800 m deeper. It is very likely that the basins’ lavas were erupted on OJP and flowed up to 1600 km: longer than any lava flow known on Earth. Flow distances are shorter (≤1000 km) if a plateau subsidence of 1500 m is used in the calculations. Extremely high Cl in Nauru Basin glasses also supports eruption from OJP. Long distance flow with minimal cooling was facilitated on OJP by favorable slopes, lack of barriers, insulation of rapidly forming glass, and possibly by flow within lava tubes. Lava effusion rates were probably >100 m/sec and flow rapid: >1 m/sec.

An assessment of prospects of geothermal energy in India for energy sustanability

The search for indigenous, renewable, environment-friendly, and sustainable energy resources has increased globally during the past few decades. Geothermal energy is one such ubiquitous source of energy, having the potential to become an alternate energy resource with a reduced carbon footprint. In this study, eight crucial characteristic parameters, i.e., heat flow, thermal gradient, Curie point depth, lithology, basement depth, crustal thickness, and seismicity, were integrated into a multi-criteria decision model framework to identify areas that may have the potential for geothermal energy in India. The weights of various parameters estimated using AHP are in the order of heat flow (∼ 0.252), followed by the Curie point depth (∼ 0.195), thermal gradient (∼ 0.173), and crustal thickness. Our analysis indicates that the geothermal province in the Himalayas (including the NW and NE regions), SONATA lineaments, central parts, and some parts of the west coasts and Mahanadi graben may have better prospects of geothermal energy compared to other tectonic provinces. We find that ∼14.86%, and ∼21.98 % of the study region have extremely high to high geothermal potential. About ∼ 27.18 % of the region have medium geothermal prospects, whereas ∼ 11.78 % and 24.20 % of the region have very low to low potential for geothermal energy.

Ambient noise tomography of an iron-oxide copper–gold (IOCG) deposit under thick cover

As most outcropping and shallow mineral deposits have been found, new technology is imperative to finding the hidden critical mineral deposits required for the renewable energy transition. One such seismic technique, called ambient noise tomography (ANT), has shown promise in recent years as a low cost and low environmental impact passive method of three-dimensional (3D) imaging of shear-wave velocity structure of the Earth. Over the last twenty years the method has been well-established in academia to image crustal and regional scale geological features but has seldom been used at the mineral exploration deposit-scale. In this paper we show the application of seismic ANT at an IOCG deposit in South Australia under more than 750 m of sedimentary cover. A 100-site survey in a 10 by 10 grid with site spacing of 1 km, using 3-component nodal seismometers with a natural-frequency of 5 Hz, was conducted over a two-week period. Data were inverted to generate a 3D velocity model to a depth of 2 km. When compared to drillholes in the survey area, the tomographic model delineates cover sequence lithologies and the depth of crystalline basement. A velocity anomaly in the basement has characteristics of a potential IOCG deposit and is aligned with a gravity anomaly due to brecciated haematite. The results of the paper indicate that ANT is a useful tool for deep cover mineral exploration that can potentially expedite the discovery of new deposits.