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Context. Hot and warm Jupiters might have undergone the same formation and evolution path, but the two populations exhibit different distributions of orbital parameters. This challenges our understanding of their actual origin. Aims. We report the results of our warm Jupiters survey, which was carried out with the CHIRON spectrograph within the KESPRINT collaboration. We addressed the question of the population origin by studying two planets that might help to bridge the gap between the two populations. Methods. We confirm two planets and determine their mass. One is a hot Jupiter (with an orbital period shorter than 10 days), TOI-2420 b, and the other is a warm Jupiter, TOI-2485 b. We analyzed them using a wide variety of spectral and photometric data in order to characterize these planetary systems. Results. We found that TOI-2420 b has an orbital period of Pb=5.8 days, a mass of Mb=0.9 MJ, and a radius of Rb=1.3 RJ, with a planetary density of 0.477 g cm−3. TOI-2485 b has an orbital period of Pb=11.2 days, a mass of Mb=2.4 MJ, and a radius of Rb=1.1 RJ with a density of 2.36 g cm−3. Conclusions. With the current parameters, the migration history for TOI-2420 b and TOI-2485 b is unclear: Scenarios of a high-eccentricity migration cannot be ruled out, and the characteristics of TOI-2485 b even support this scenario. [ABSTRACT FROM AUTHOR]

We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a bright (V  = 12.6 mag, K  = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors 42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory, as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of 12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy. [ABSTRACT FROM AUTHOR]

We report the discovery of TOI-4641b, a warm Jupiter transiting a rapidly rotating F-type star with a stellar effective temperature of 6560 K. The planet has a radius of 0.73 R Jup, a mass smaller than 3.87 M Jup(3σ), and a period of 22.09 d. It is orbiting a bright star (V =7.5 mag) on a circular orbit with a radius and mass of 1.73 R ⊙ and 1.41 M ⊙. Follow-up ground-based photometry was obtained using the Tierras Observatory. Two transits were also observed with the Tillinghast Reflector Echelle Spectrograph, revealing the star to have a low projected spin-orbit angle (λ= |$1.41^{+0.76}_{-0.76}$| °). Such obliquity measurements for stars with warm Jupiters are relatively few, and may shed light on the formation of warm Jupiters. Among the known planets orbiting hot and rapidly rotating stars, TOI-4641b is one of the longest period planets to be thoroughly characterized. Unlike hot Jupiters around hot stars which are more often misaligned, the warm Jupiter TOI-4641b is found in a well-aligned orbit. Future exploration of this parameter space can add one more dimension to the star–planet orbital obliquity distribution that has been well sampled for hot Jupiters. [ABSTRACT FROM AUTHOR]

Among many agricultural practices proposed to cut carbon emissions in the next 30 years is the deposition of carbon in soils as plant matter. Adding rooting traits as part of a sequestration strategy would result in significantly increased carbon sequestration. Integrating these traits into production agriculture requires a belowground phenotyping method compatible with high-throughput breeding (i.e., rapid, inexpensive, reliable, and non-destructive). However, methods that fulfill these criteria currently do not exist. We hypothesized that ground-penetrating radar (GPR) could fill this need as a phenotypic selection tool. In this study, we employed a prototype GPR antenna array to scan and discriminate the root and rhizome mass of the perennial sorghum hybrid PSH09TX15. B-scan level time/discrete frequency analyses using continuous wavelet transform were utilized to extract features of interest that could be correlated to the biomass of the subsurface roots and rhizome. Time frequency analysis yielded strong correlations between radar features and belowground biomass (max R −0.91 for roots and −0.78 rhizomes, respectively) These results demonstrate that continued refinement of GPR data analysis workflows should yield an applicable phenotyping tool for breeding efforts in contexts where selection is otherwise impractical. [ABSTRACT FROM AUTHOR]

In ground penetrating radar (GPR) surveys of African‐American cemeteries suspected to contain unmarked graves, determining the proficiency of a new GPR practitioner is vital and perhaps even more fundamental than that of the GPR hardware, deployment configuration and software. Proficiency may be defined as the practitioner's true‐positive, true‐negative, false‐positive (i.e., false alarms) and false‐negative (i.e., misses) percentages. We embarked on this research as a means to improve our own proficiency in unmarked grave detection and to develop an algorithm by which to improve the proficiency of any new GPR practitioner. After surveying the Salem Cemetery in Brazos County, TX, and the Old Danville‐Shepherd Hill Cemetery in Montgomery County, TX, we first classified subsurface targets based on in‐field, visual inspection of the real‐time, onscreen, unprocessed (except for an automatic gain control) GPR B‐scans. We then developed a proxy for ground‐truthing that allowed us to calculate the proficiency of the in‐field classifications. From this proxy, we established a quantitative prevalence threshold for identifying or rejecting a subsurface object as a target of interest. Its quantitative nature allowed us to quantitatively control and adjust that threshold, a threshold we set at 70% likely to be to a specific target of interest. We show that our classification accuracy increased from 66.2% at the Salem Cemetery to 75.0% at the Old Danville‐Shepherd Hill Cemetery and, through use of diagnostic evaluations originally developed for medical imaging and herein applied to geophysics, showed that the accuracy improved due to increases in true‐negative classifications, that is, in examining real‐time, onscreen, mostly unprocessed GPR B‐scans, discerning a potential target and correctly concluding it was not an unmarked grave. This research outlines the procedure we developed to measure the proficiency of a new GPR practitioner. [ABSTRACT FROM AUTHOR]

Preferential flow between rivers and aquifers in alluvial floodplains may be a core component of shallow groundwater transport and, consequently, its understanding is key to modelling and managing groundwater resources. At a clay wedge separating present‐day streamflow and bank storage from an adjacent shallow aquifer, we image a suspected sand‐dominated structure. This structure cuts through the clay wedge and possesses temporally dynamic electrical resistivity as seen in time‐lapse electrical resistivity tomographic (ERT) images collected over a 61‐day study period. During days 11–12, following heavy rainstorms, the cross section of the electrically resistive sand fades into the background resistivity structure, reappearing the following day. This research shows that preferential flow can be imaged in time‐lapse ERT in buried sand‐dominated structures between a floodplain and the adjacent river. Our analysis demonstrates that sand conduits can transport infiltrated rainwater from the floodplain into the river as a bank spring and, hypothetically, at high‐stage streamflow, from the river into the adjacent shallow aquifer. In both directions, these conduits for preferential flow exert an important control on the regulation and distribution of water, sediments and contaminants. This phenomenon will help hydrological models to incorporate more real‐world phenomena and ultimately better prepare groundwater managers to sustainably steward shallow groundwater resources. [ABSTRACT FROM AUTHOR]

Many processes concerning below-ground plant performance are not fully understood, such as spatial and temporal dynamics and their relation to environmental factors. Accounting for these spatial patterns is very important as they may be used to adjust for the estimation of cassava fresh root yield masked by field heterogeneity. The yield of cassava is an important characteristic that every breeder seeks to maintain in their germplasm. Ground-Penetrating Radar (GPR) has proven to be an effective tool for studying the below-ground characteristics of developing plants, but it has not yet been explored with respect to its utility in normalizing spatial heterogeneity in agricultural field experiments. In this study, the use of GPR for this purpose was evaluated in a cassava field trial conducted in Momil, Colombia. Using the signal amplitude of the GPR radargram from each field plot, we constructed a spatial plot error structure using the variance of the signal amplitude and developed GPR-based autoregressive (AR) models for fresh root yield adjustment. The comparison of the models was based on the average standard error (SE) of the Best Linear Unbiased Estimator (BLUE) and through majority voting (MV) with respect to the SE of the genotype across the models. Our results show that the GPR-based AR model outperformed the other models, yielding an SE of 9.57 and an MV score of 88.33%, while the AR1 × AR1 and IID models had SEs of 10.15 and 10.56% and MV scores of 17.37 and 0.00%, respectively. Our results suggest that GPR can serve a dual purpose in non-destructive yield estimation and field spatial heterogeneity normalization in global root and tuber crop programs, presenting a great potential for adoption in many applications. [ABSTRACT FROM AUTHOR]

Selected results of complex geophysical surveys carried out on the Vistula river flood levee in Cracow are herein presented. Two complementary geophysical methods were applied for detection of potential unconsolidated zones in the body of the levee, i.e. microgravimetry and ground-penetrating radar (GPR). The surveys were carried out in 2D mode, along a profile at the crown of the flood levee. Microgravimetric data reveal anomalies showing zones of decreased bulk density. These zones provide information about poor quality of the levee. The main anomaly was interpreted in a quantitative manner using gravity modelling. Non-standard GPR processing and visualization of radargrams were employed to better extract information concerning the distribution of unconsolidated zones. High resolution GPR surveys allow to outline such zones which was the basis for construction of the 2D model used in the gravimetric modelling. Integration of these two geophysical methods provided important information about the spatial variations of mass density in several unconsolidated zones within the body of the flood levee.

Forward modeling plays a key role in both the creation of predictive models and the study of the surrounding environment through inversion methods. Due to their competitive computational cost and modest algorithmic complexity, finite difference methods (FDM) are commonly used to model the acoustic wave equation. An algorithm has been developed to decrease the computational cost of acoustic-wave forward modeling that can be applied to most finite difference methods. An important feature of the algorithm is the calculation, at each time step, of the pressure in only a moving subdomain which contains the grid points across which waves are passing. The computation is skipped at grid points at which the waves are negligibly small or non-existent. The novelty in this work comes from flexibility of the subdomain and its ability to closely follow the developing wavefield. To demonstrate the efficacy of the algorithm, it is applied to a standard finite difference scheme and validated against 2-D modeling results. The algorithm herein can play an important role in the reduction in computation time of seismic data analysis as the volumes of seismic data increase due to developments in data acquisition technology. [ABSTRACT FROM AUTHOR]

The controlled source electromagnetic (CSEM) geophysical method is used for a number of purposes, including exploration and characterization of oil and geothermal deposits. Here, based on idealized modeling scenarios, we explore an adaptation of the method to remotely inspect shallow buried pipelines and determine its suitability for monitoring corrosion because of the sensitivity of CSEM responses to electrical conductivity contrasts within the subsurface. We show that the electric field response from an in-line transmitter-receiver configuration provides more diagnostic information than the broadside configuration while both are likely to detect the pipeline response in the presence of ambient noise. The presence of a conductive pipeline is considerably easier to detect in sandy soils than in clays and there is a reduction in amplitude and response shape when the pipeline is resistive. In-line responses can diagnose the level of corrosion, although it is difficult to distinguish between a highly corroded pipeline and one with a break. In cases where a pipeline break is present, some data processing may be required to precisely locate the break. [ABSTRACT FROM AUTHOR]

A finite-element analysis of electromagnetic induction (EMI) in the presence of multiple buried metal targets is undertaken for the purpose of unexploded ordnance (UXO) detection and discrimination. The effects of mutual coupling between metal targets and the host conductivity are shown to be important. At high frequencies, mutual coupling is strong, and effects of host conductivity are relatively minor. At lower frequencies near the resistive limit, EMI responses are very small, but the effect of host conductivity becomes important. This is due to the galvanic current flow in the host medium that dissipates charge accumulations on the host/target interfaces. Qualitative analysis of induced current patterns in metal targets demonstrates that mutual coupling is strongly affected by target orientation and skin depth. Rigorous forward modeling of EMI responses is essential to understanding UXO sensor signatures so that discrimination between live UXO items and harmless fragments and clutter may become possible. Index Terms--Eddy currents, electromagnetic induction (EMI), finite-element methods (FEMs), geophysics, mutual coupling.

Electromagnetic instrument responses suffer from signal drift that results in a variable response at a given location over time. If left uncorrected, spatiotemporal aliasing can manifest and global trends or abrupt changes might be observed in the data, which are independent of subsurface electromagnetic variations. By performing static ground measurements, we characterized drift patterns of different electromagnetic instruments. Next, we performed static measurements at an elevated height, approximately 4 metre above ground level, to collect a data set that forms the basis of a new absolute calibration methodology. By additionally logging ambient temperature variations, battery voltage and relative humidity, a relation between signal drift and these parameters was modelled using a machine learning (ML) approach. The results show that it was possible to mitigate the effects of signal drift; however, it was not possible to completely eliminate them. The reason is three‐fold: (1) the ML algorithm is not yet sufficiently adapted for accurate prediction; (2) signal instability is not explained sufficiently by ambient temperature, relative humidity and battery voltage; and (3) the black‐box internal (factory) calibration impeded direct access to raw data, which prevents accurate evaluation of the proposed methodology. However, the results suggest that these challenges are not insurmountable and that ML can form a viable approach in tackling the drift problem instrument specific in the near future. [ABSTRACT FROM AUTHOR]

Ground-penetrating radar has emerged as a prominent non-destructive evaluation tool for the study of inaccessible subsurface elements of cultural heritage structures. Often of central interest is the desire to image the remains of a pre-existing historic structure that is located directly beneath a more recently built one. The interpretation of GPR images in such cases is usually difficult due to ambiguities caused by the presence of pervasive clutter, environmental noise, and overlapping target signatures. Sites with abundant ground truth allow for more confident interpretations and serve as a useful testbed to assist similar studies at other places, where little or no ground truth is available. This study reports GPR interpretations of structures belonging to the 19th century Citadel beneath the main prison cellhouse at Alcatraz. At this site, lidar scans, direct observations, and historical documents are available to facilitate identification of radar target signatures. A general interpretation of the acquired radargrams is made in this paper, while the companion paper presents more advanced analysis of target signatures based on curvelet image processing. This study points to the development of a radar facies classification scheme that is specific to cultural heritage investigations. [ABSTRACT FROM AUTHOR]

The Khorat plateau covers most of northeast Thailand along with parts of southern Laos. Recent earthquake hazard assessment and other studies of the regional Thakek fault have rarely appeared in publications and reports. The Thakek fault zone in the Laos region includes three main principal fault planes, but it rapidly fades out when the fault passes through Thailand. A geophysical hidden fault study in the Khorat plateau is herein performed in Bung Kan and Nakhon Phanom provinces, Thailand, where the surface expression is difficult to document through conventional geological surveys. Some fault traces have been identified by satellite image interpretation and digital elevation model analysis. Geological field investigation and electrical resistivity tomography surveys were carried out in order to determine an optimal site for trenching. The electrical resistivity tomography results show zones of high and low resistivity interpreted as coarse sediment layers and mudstone, respectively. The maximum vertical fault offset occurring along the fault trace interpreted from the three‐dimensional electrical resistivity tomographic slices is 40 ± 5 m. Based on the electrical resistivity tomography results, a trench was excavated to directly investigate patterns of faulting and deformation. Based on structural geological observations at the trench wall, indications of faulting have been tentatively identified. In particular, faulting appears to have displaced mudstone over Quaternary sediments with vertical offsets >3.5 m cutting the youngest unit. The result has implications for seismic hazard assessment in northeast Thailand. [ABSTRACT FROM AUTHOR]

Seismic data provides integral information in geophysical exploration, for locating hydrocarbon rich areas as well as for fracture monitoring during well stimulation. Because of its high frequency acquisition rate and dense spatial sampling, distributed acoustic sensing (DAS) has seen increasing application in microseimic monitoring. Given large volumes of data to be analyzed in real-time and impractical memory and storage requirements, fast compression and accurate interpretation methods are necessary for real-time monitoring campaigns using DAS. In response to the developments in data acquisition, we have created shifted-matrix decomposition (SMD) to compress seismic data by storing it into pairs of singular vectors coupled with shift vectors. This is achieved by shifting the columns of a matrix of seismic data before applying singular value decomposition (SVD) to it to extract a pair of singular vectors. The purpose of SMD is data denoising as well as compression, as reconstructing seismic data from its compressed form creates a denoised version of the original data. By analyzing the data in its compressed form, we can also run signal detection and velocity estimation analysis. Therefore, the developed algorithm can simultaneously compress and denoise seismic data while also analyzing compressed data to estimate signal presence and wave velocities. To show its efficiency, we compare SMD to local SVD and structure-oriented SVD, which are similar SVD-based methods used only for denoising seismic data. While the development of SMD is motivated by the increasing use of DAS, SMD can be applied to any seismic data obtained from a large number of receivers. For example, here we present initial applications of SMD to readily available marine seismic data. [ABSTRACT FROM AUTHOR]

This paper underscores the importance of spatially dense geophysical data sets for making informed decisions in water management strategies. Such decisions may require understanding how site‐specific subsurface architecture – especially hydraulic connectivity – impacts the response of a shallow aquifer to anthropogenic hydrologic disturbances (e.g. over‐pumping of a shallow aquifer). At a 0.2‐km2 alluvial floodplain site characterized by thick clay over fine sand to gravel and shale bedrock in the subtropical, sub‐humid belt of the Gulf Coast of the United States, we image an asymmetrically shaped, compartmentalized, sand‐dominated channel‐belt using electrical resistivity tomography and 31 time‐domain electromagnetic soundings probing to depths of ∼40 m and ∼90 m, respectively. Lithological interpretation and a hydrological model are developed based on the geophysical data and nearby sediment cores, where the resistivity of the groundwater is 9.1 Ωm. In a modelling scenario wherein the compartmentalized sand channel‐belt starts out dry (i.e. an over‐pumped shallow aquifer), we simulate 26 weeks of infiltration due to flooding of the surface. Preferential filling of the channel‐belt occurs through its sides rather than from above, generating a new understanding of the hydraulic connectivity around and into asymmetrically shaped, sand‐dominated channel‐belts. This insight can inform decisions about the optimal placement of shallow water wells in a heterogeneous alluvial floodplain aquifer system and also highlights the dangers of over‐pumping. [ABSTRACT FROM AUTHOR]

The increasing demand for gypsum as a raw material for construction projects motivates exploration for additional reserves. Electrical resistivity tomography (ERT) and seismic refraction geophysical methods, augmented with borehole and laboratory measurements on core samples, are used here to delineate the top, bottom and lateral boundaries of an important gypsum ore deposit in Thailand, an economically developing region. The gypsum-bearing formation is found throughout the study area to have an irregular upper boundary on account of karstic dissolution processes. The deeper transition from gypsum to anhydrite, however, is not constrained by the measurements. The P-wave velocity measured in the field is consistent with the core specimen measurements. The electrical resistivity of the core specimens, however, is substantially higher than the values measured in the field. The specimen measurements may depend on the presence of micro cracks, whereas electrical resistivity in the field may be affected by the enclosing clay-rich materials. [ABSTRACT FROM AUTHOR]

Gully formation has been associated to groundwater seepage in unconsolidated sand- to gravel-sized sediments. Our understanding of gully evolution by groundwater seepage mostly relies on experiments and numerical simulations, and these rarely take into consideration contrasts in lithology and permeability. In addition, process-based observations and detailed instrumental analyses are rare. As a result, we have a poor understanding of the temporal scale of gully formation by groundwater seepage and the influence of geological heterogeneity on their formation. This is particularly the case for coastal gullies, where the role of groundwater in their formation and evolution has rarely been assessed. We address these knowledge gaps along the Canterbury coast of the South Island (New Zealand) by integrating field observations, luminescence dating, multi-temporal unoccupied aerial vehicle and satellite data, time domain electromagnetic data and slope stability modelling. We show that gully formation is a key process shaping the sandy gravel cliffs of the Canterbury coastline. It is an episodic process associated to groundwater flow that occurs once every 227 d on average, when rainfall intensities exceed 40 mm d -1. The majority of the gullies in a study area southeast (SE) of Ashburton have undergone erosion, predominantly by elongation, during the last 11 years, with the most recent episode occurring 3 years ago. Gullies longer than 200 m are relict features formed by higher groundwater flow and surface erosion >2 ka ago. Gullies can form at rates of up to 30 m d -1 via two processes, namely the formation of alcoves and tunnels by groundwater seepage, followed by retrogressive slope failure due to undermining and a decrease in shear strength driven by excess pore pressure development. The location of gullies is determined by the occurrence of hydraulically conductive zones, such as relict braided river channels and possibly tunnels, and of sand lenses exposed across sandy gravel cliffs. We also show that the gully planform shape is generally geometrically similar at consecutive stages of evolution. These outcomes will facilitate the reconstruction and prediction of a prevalent erosive process and overlooked geohazard along the Canterbury coastline. [ABSTRACT FROM AUTHOR]

We analysed the photometry of 20 038 cool stars from campaigns 12, 13, 14, and 15 of the K2 mission in order to detect, characterize, and validate new planetary candidates transiting low-mass stars. We present a catalogue of 25 new periodic transit-like signals in 22 stars, of which we computed the parameters of the stellar host for 19 stars and the planetary parameters for 21 signals. We acquired speckle and AO images, and also inspected archival Pan-STARRS1 images and Gaia DR2 to discard the presence of close stellar companions and to check possible transit dilutions due to nearby stars. False positive probability (FPP) was computed for 22 signals, obtaining FPP < |$1{{\ \rm per\ cent}}$| for 17. We consider 12 of them as statistically validated planets. One signal is a false positive and the remaining 12 signals are considered as planet candidates. 20 signals have an orbital period of P |$_{\rm orb} \lt 10\,\mathrm{ d}$|⁠ , 2 have |$10\, \mathrm{ d} \lt $|   P |$_{\rm orb} \lt 20\, \mathrm{ d}$|⁠ , and 3 have P |$_{\rm orb} \gt 20\, \mathrm{ d}$|⁠. Regarding radii, 11 candidates and validated planets have computed radius R < 2R⊕, 9 have 2R⊕ < R < 4R⊕, and 1 has R  > 4R⊕. Two validated planets and two candidates are located in moderately bright stars (⁠|$\rm \mathit{ m}_{kep}\lt 13$|⁠) and two validated planets and three candidates have derived orbital radius within the habitable zone according to optimistic models. Of special interest is the validated warm super-Earth K2-323 b (EPIC 248616368 b) with T |$_{\rm eq} = 318^{+24}_{-43} \, \mathrm{ K}$|⁠ , S |$_{\rm p} = 1.7\pm 0.2 \, \mathrm{ S}_{\oplus }$|⁠ , and R |$_{\rm p} = 2.1\pm 0.1 \, \mathrm{ R}_{\oplus }$|⁠ , located in an m |$\rm _{kep}$| = 14.13 star. [ABSTRACT FROM AUTHOR]

Salinization is a growing concern of global proportions. In urban settings effective salinity management strategies must be adopted to ensure environmental sustainability in the face of rapid development. Geophysical methods, particularly electrical methods, can be used to non-invasively map the spatial distribution of subsurface groundwater salinity over wide areas at reasonable cost. In this paper, electrical resistivity tomography and vertical electrical sounding geophysical methods were used to determine the electrical resistivity structure of the subsurface beneath the rapidly developing Khon Kaen University campus in NE Thailand. The geophysical results were combined to generate a contour map of depth to saline groundwater beneath the campus. Saline groundwater was present in shallow strata in the southern part of the campus but is not indicated beneath the northern half, so that drilling for groundwater wells is recommended there. The map can be used by campus planners to inform their salinity management strategies, including the siting of groundwater wells, the design of potential soil reclamation schemes, and the location and design of buried infrastructure according to indications of soil corrosivity. The method can be applied at other urban sites located on salt-affected lands and, in general, provides a valuable supplement to costly traditional geotechnical testing. [ABSTRACT FROM AUTHOR]

Soil and groundwater salinity poses a serious problem in Khon Kaen Province of Thailand and causes major reductions to crop productivity. In this study, aerial photo interpretation, field studies, and borehole lithology log data were analyzed to explore the spatial relationship between geological structure and the distribution of salinity. The results show that geological structures play an important role in determining the salinity distribution. Slight and moderate salinity are generally found over syncline structures and rock formation boundaries, whereas severe salinity is generally found over anticline structures and around depressions containing rock salt. All three categories of salinity (slight, moderate, and severe) are encountered along fractures associated with braided streams and faults associated with meandering streams. The electrical resistivity tomography results showed that the depth of saline groundwater was between 5 and 30 m and its distribution was related to geomorphology. Salinity distributions are natural occurrences controlled by subsurface geological structures and geomorphology. [ABSTRACT FROM AUTHOR]

In the northeast of Thailand, many swamps and lakes show evidence of rock salt dissolution, with attendant environmental problems due to saline groundwater and soil salinization. The knowledge of the depth and structure of the rock salt would be useful to achieve a better understanding of the impact of its dissolution on the environment and to facilitate effective land management strategies. Geophysical methods can provide key subsurface information. Four seismic refraction profiles and three electrical resistivity tomography profiles were carried out between Nong Bo and Nong Pong reservoirs in the salt‐affected Borabue district of Maha Sarakham province. The seismic results indicate the top of shallow rock salt beneath Nong Bo reservoir as a diagnostic zone of high P‐wave velocity >3400 m/s at depths >20 m. The electrical resistivity tomography investigation shows electrical resistivity values ≳5 Ωm at similar depths, indicative also of shallow rock salt. Zones interpreted to be saline groundwater are electrically conductive, identified by electrical resistivity values ≲5 Ωm in the electrical resistivity tomography images. The combined seismic–electrical resistivity tomography interpretation suggests that shallow rock salt lies beneath the reservoirs and ponds in the Borabue district but does not appear to form a continuous body between the two largest reservoirs. [ABSTRACT FROM AUTHOR]

A good understanding of the subsurface geological conditions at proposed construction sites is a fundamental requirement to design appropriate building foundations. In this study, the 2D electrical resistivity tomography (ERT) method was used to characterize the subsurface geology at three active construction sites located on or near exposed bedrock in northeast Thailand. The resistivity tomograms proved useful for determining the thickness of intact bedrock overlying a potentially weaker weathered rock of variable saturation. The wide-area information provided by the ERT method should be helpful to foundation design engineers assuming they have confidence in the geophysical results. Geophysics was also useful to guide suitable locations for ongoing geotechnical tests at a given construction site especially if difficult ground conditions exist. [ABSTRACT FROM AUTHOR]