Multiple Geophysical Surveys Research Articles

Delineating the Bonghwang earth castle and Royal Palace of Geumgwan Gaya Kingdom using multiple geophysical techniques

AbstractGeophysical techniques such as electrical resistivity, ground penetrating radar (GPR), gravity, magnetic, and seismic surveys are useful for prospecting archaeological remains. In this study, we delineated the domain and underground structure of the Bonghwang earth castle and the Royal Palace of the Geumgwan Gaya Kingdom, using multiple geophysical surveys (magnetic, electromagnetic, GPR, and electrical resistivity). Based on the results, the Bonghwang earth castle was extended from a small hill branching from the northern end of the Bonghwangdae hill with a width of 20 m to the hill on the southeast end with a width of slightly over 40 m. The Royal Palace inside the Bonghwang earth castle was further explored using magnetic and GPR surveys. As a result low magnetic values are surrounded radially by high magnetic values at multiple independent locations in an irregular shape in the centre of the Royal Palace. In contrast, the high anomaly zone near the centre of the Royal Palace had a rectangular or ellipsoidal shape, necessitating a clear need for archaeological investigation and excavation in the future.

Initiation and mobility of recurring loess flowslides on the Heifangtai irrigated terrace in China: Insights from hydrogeological conditions and liquefaction criteria

Heifangtai terrace is famous in China for its irrigation-induced loess landslides. The frequently recurring loess flowslides initiated along the platform margin of the irrigated Heifangtai terrace have caused 42 fatalities and significant economic losses due to their long-runout and high-speed mobility. Yet it is still unclear if the recurring loess flowslides almost always initiate in the same places, and their initiated conditions and subsequent mobility behaviors have not been fully evaluated. To better understand such under-researched questions, we selected three typically recurring loess flowslides on the Heifangtai irrigated area. We performed multiple geophysical surveys using electrical resistivity tomography (ERT) and multichannel analysis of surface waves (MASW). We tested water content, density, and strength of loess using in-situ profile sampling. In addition, we examined the steady-state shear behaviors of saturated loess utilizing a ring shear apparatus under undrained conditions. The geophysical signatures and in-situ loess property profiles showed that hydrogeological conditions are crucial to initiating the recurring loess flowslides. The results also demonstrated that the shear liquefaction behavior of saturated loess controls the mobility after the failure of the loess flowslides. Liquefaction potential was assessed based on a chart showing the liquidity and plasticity index, pore pressure ratio, and steady-state line, which were developed as new criteria of liquefaction susceptibility assessment. The novel criteria essentially contain general information about fine-grained soil's nature, state, and behavior. These findings provide a better understanding of the dynamic mechanisms of the loess flowslides and their implications for landslide hazard mitigation.

Comparison of novel semi-airborne electromagnetic data with multi-scale geophysical, petrophysical and geological data from Schleiz, Germany

In the framework of the Deep Electromagnetic Sounding for Mineral EXploration (DESMEX) project, we carried out multiple geophysical surveys from regional to local scales in a former mining area in the state of Thuringia, Germany. We prove the applicability of newly developed semi-airborne electromagnetic (EM) systems for mineral exploration by cross-validating inversion results with those of established airborne and ground-based investigation techniques. In addition, supporting petrophysical and geological information to our geophysical measurements allowed the synthesis of all datasets over multiple scales.An initial regional-scale reconnaissance survey was performed with BGR's standard helicopter-borne geophysical system deployed with frequency-domain electromagnetic (HEM), magnetic and radiometric sensors. In addition to geological considerations, the HEM results served as base-line information for the selection of an optimal location for the intermediate-scale semi-airborne EM experiments. The semi-airborne surveys utilized long grounded transmitters and two independent airborne receiver instruments: induction coil magnetometers and SQUID sensors. Due to the limited investigation depth of the HEM method, local-scale electrical resistivity tomography (ERT) and long-offset transient electromagnetic (LOTEM) measurements were carried out on a reference profile, enabling the validation of inversion results at greater depths.The comparison of all inversion results provided a consistent overall resistivity distribution. It further confirmed that both semi-airborne receiver instruments achieve the bandwidth and sensitivity required for the investigation of the resistivity structure down to 1 km depth and therewith the detection of deeply seated earth resources. A 3D geological model, lithological and geophysical borehole logs as well as petrophysical investigations were integrated to interpret of the geophysical results. Distinct highly-conductive anomalies with resistivities of less than 10 Ωm were identified as alum shales over all scales. Apart from that, the petrophysical investigations exhibited that correlating geophysical and geological information using only one single parameter, such as the electrical resistivity, is hardly possible. Therefore, we developed a first approach based on clustering methods and self-organizing maps (SOMs) that allowed us to assign geological units at the surface to a given combination of geophysical and petrophysical parameters, obtained on different scales.

Overwash‐dominated stratigraphy of barriers with intermittent inlets

AbstractThe morphodynamics and structure of barriers with persistent tidal inlets have been well studied. In contrast the stratigraphy and functioning of barrier systems with ephemeral inlets is poorly understood. This article examines the barrier‐inlet systems of two intermittently closed open lagoons or temporarily open closed estuaries on the east coast of South Africa. Multiple geophysical surveys using ground‐penetrating radar (GPR) were correlated with exposed sections of the barrier where inlet formation revealed the internal stratigraphy. Stratigraphic observations were placed in the context of the contemporary wave dynamics and mesoscale geomorphic evolution. The integrated databases reveal an absence of migrating channel features. Instead the stratigraphy is dominated by landward dipping sheets of alternating high‐ and low‐amplitude reflectors. These correlate with gravel, shell debris and heavy mineral‐lined beds formed by overwash processes. Where ephemeral inlet structures are preserved in the stratigraphy, their fills comprise aggrading, high‐amplitude reflectors, linked to washover infilling of the inlet mouth. Multiple small channels in the more distal portions of the barrier in georadar stratigraphy are related to channelized washover flow.These barriers often breach during high swell and are subsequently sealed during fairweather wave conditions. Time series analysis of waves and satellite imagery shows a link between storms from the south and breach events. This is consistent with the truncations in subsurface images and inferred barrier lowering by overwash channelling. These barriers experience quasi‐stable oscillations in their landward and seaward shore position, punctuated by periods of barrier rollover associated with the most intense storms. As overwash is responsible in part for both the constructive and destructive phases of the barrier, these barriers have low preservation potential. Persistent rollover driven by overwashing will terminate once accommodation space is eliminated and the barriers are eroded by storm activity. © 2019 John Wiley & Sons, Ltd.

Multiple geophysical surveys for old landfill monitoring in Singapore.

One-dimensional boring presents limitations on mapping the refuse profile in old landfills owning to waste heterogeneity. Electrical imaging (EI) and multiple-analysis of surface wave (MASW) were hereby deployed at an old dumping ground in Singapore to explore the subsurface in relation to geotechnical analysis. MASW estimated the refuse boundary with a higher precision as compared to EI, due to its endurance for moisture variation. EI and MASW transection profiles suggested spots of interest, e.g., refuse pockets and leachate mounds. 3D inversion of EI and MASW data further illustrated the transformation dynamics derived by natural attenuation, for instance the preferential infiltration pathway. Comparison of geophysical surveys at different years uncovered the subterranean landfill conditions, indicating strong impacts induced by aging, precipitation, and settlement. This study may shed light on a characterization framework of old landfills via combined geophysical models, thriving landfill knowledge with a higher creditability.

Geological and geophysical integrated interpretation and modelling techniques

Exploration is becoming harder, at depth or under cover and decisions need to be made in model rather than data space; supported by multiple data sets. Geophysics plays an ever increasing role and integration of information from various geophysical data sets in tight collaboration with geological control is required to maximise the return from the individual data sets. In terms of integrating geological and geophysical data, the essential goal is to interpret the available geophysical data in terms of geological domains. The process requires a common sense approach to interpretation that is flexible, adaptive and objective driven. It is not an exact formula or procedure; particularly when multiple geophysical surveys are involved. Understanding the relationships between geology, geophysical responses and rock properties is the key to develop a geological basis for your integrated interpretation. Following this, rapid 3D geological modelling and geologically based forward modelling and inversion are essential for model validation and quantitative integration of data. An integrated interpretation is not necessarily the simplest approach, but does provide answers to geoscientific questions that are stronger than individual elements interpreted on their own. This paper presents a review of the mechanics involved in integrated interpretation and demonstrates the results with selected case study examples.

Long-term Geophysical Monitoring of Simulated Clandestine Graves using Electrical and Ground Penetrating Radar Methods: 4-6 Years After Burial.

This ongoing monitoring study provides forensic search teams with systematic geophysical data over simulated clandestine graves for comparison to active cases. Simulated "wrapped," "naked," and "control" burials were created. Multiple geophysical surveys were collected over 6 years, here showing data from 4 to 6 years after burial. Electrical resistivity (twin electrode and ERI), multifrequency GPR, grave and background soil water were collected. Resistivity surveys revealed that the naked burial had low-resistivity anomalies up to year four but then difficult to image, whereas the wrapped burial had consistent large high-resistivity anomalies. GPR 110- to 900-MHz frequency surveys showed that the wrapped burial could be detected throughout, but the naked burial was either not detectable or poorly resolved. 225-MHz frequency GPR data were optimal. Soil water analyses showed decreasing (years 4 to 5) to background (year 6) conductivity values. Results suggest both resistivity and GPR surveying if burial style unknown, with winter to spring surveys optimal and increasingly important as time increases.

Introduction to special section: Monitoring reservoir and overburden changes

Time-lapse geophysical technologies, including 4D seismic methods, are key enablers for improved hydrocarbon recovery and more cost-effective field operations. By analyzing differences in multiple geophysical surveys and by integrating those analyses with conventional reservoir monitoring data, time

3D joint inversion of geophysical data with Gramian constraints: A case study from the Carrapateena IOCG deposit, South Australia

Explorers are moving to increase the “discovery space” by exploring under cover and to greater depths, e.g., subsalt and sub-basalt exploration for oil and gas, and beneath transported cover for minerals. With this shift, there becomes an increased reliance on geophysical methods to delineate resources with no recognized geological or geochemical expressions. Different geophysical fields provide information about different physical properties of the Earth. Multiple geophysical surveys spanning gravity, magnetic, electromagnetic, and seismic methods are often interpreted to infer geology from models of different physical properties. In many cases, the various geophysical data are complementary, making it natural to consider a formal mathematical framework for their joint inversion to a shared Earth model. There are different approaches to joint inversion. The simplest case of joint inversion is where the physical properties are identical between different geophysical methods (e.g., Jupp and Vozoff, 1975). In other cases, joint inversion may infer theoretical, empirical, or statistical correlations between different physical properties (e.g., Hoversten et al., 2003, 2006). In cases where the physical properties are not correlated but, nevertheless, can be assumed to share a similar structure, joint inversions have been formulated as a minimization of the cross-gradients between different physical properties (e.g., Haber and Oldenburg, 1997; Gallardo and Meju, 2003, 2004). The latter has now been widely adopted by joint inversion practitioners as the de facto standard (e.g., Colombo and De Stefano, 2007; Hu et al., 2009; Jegen et al., 2009; De Stefano et al., 2011).

Geophysical characterization of hydrothermal systems and intrusive bodies, El Chichón volcano (Mexico)

[1] The 1982 explosive eruptions of El Chichón volcano (Chiapas, Mexico) destroyed the inner dome and created a 1-km-wide and 180-m-deep crater within the somma crater. A shallow hydrothermal system was exposed to the surface of the new crater floor and is characterized by an acid crater lake, a geyser-like Cl-rich spring (soap pool), and numerous fumarole fields. Multiple geophysical surveys were performed to define the internal structure of the volcanic edifice and its hydrothermal system. We carried out a high-resolution ground-based geomagnetic survey in the 1982 crater and its surroundings and 38 very low frequency (VLF) transects around the crater lake. A 3-D inversion of the ground-based magnetic data set highlighted three high-susceptibility isosurfaces, interpreted as highly magnetized bodies beneath the 1982 crater floor. Inversion of a digitized regional aeromagnetic map highlighted four major deeply rooted cryptodomes, corresponding to major topographic highs and massive lava dome outcrops outside and on the somma rim. The intracrater magnetic bodies correspond closely to the active hydrothermal vents and their modeled maximum basal depth matches the elevation of the springs on the flanks of the volcano. Position, dip, and vertical extent of active and extinct hydrothermal vents identified by VLF-EM surveys match the magnetic data set. We interpret the shallow lake spring hydrothermal system to be mostly associated with buried remnants of the 550 BP dome, but the Cl-rich soap pool may be connected to a small intrusion emplaced at shallow depth during the 1982 eruption.

Resolution and quality assurance in near-surface geophysical surveys: A multimethod field trial and results

Characterization of subsurface materials almost always requires the measurement of multiple physical parameters, and therefore involves multiple geophysical surveys. The integration of the multiple data sets is the key to detailed interpretations. Following this logic, the key elements of a near-surface survey become the ability to make multiple precise survey measurements and integrate them. Technological developments in precise positioning, data logging, and GIS data manipulation provide the potential for major advances in near-surface surveys in both areas.

ABANDONED DEEP MINE SUBSIDENCE INVESTIGATION AND REMEDIAL DESIGN, INTERSTATE 70, GUERNSEY COUNTY, OHIO

A two thousand linear foot, undermined section of Interstate 70 in Guernsey County, Ohio experienced settlements due to pothole type subsidence events within the travel lanes, shoulders and adjacent right-of-way areas. Potholes measured approximately ten feet in depth and width. The subsidence occurred after the dewatering of the abandoned deep mine during auger mining operations west of the site. A two-phase emergency investigation was undertaken by the Ohio Department of Transportation (ODOT) and Gannett Fleming Cord dry and Carpenter (GF). The purpose of the investigation was to assess the immediate danger of potholes occurring in the traveled lanes and paved shoulders, to identify the subsidence mechanisms, and to design a remediation program. Phase one investigations involved the review of existing subsurface data, the advancement of shallow borings and the performance of multiple geophysical surveys including ground penetrating radar, seismic refraction and electromagnetic terrain conductivity. The Phase one investigations did not reveal the presence of subsidence voids. Phase two investigations included borings to the mine level and videotaping of mine conditions. The mine was found to be completely flooded. Based upon the collected data, two mechanisms of failure, localized roof fall and piping of overburden soils into the mine void, weremore » identified. Two remedial alternatives, (1) the filling of the mine void, and (2) the reinforcement of the highway using geotextiles, were evaluated, Filling of the mined interval and grouting of overburden bedrock fractures and voids, within a limited area, were selected. Construction plans, specifications and cost estimates were prepared for bidding and award. During the bidding process, a catastrophic, pothole type failure of the I-70 travel lanes occurred. The interstate was closed and the planned remediation activities were performed as an emergency project. The mine interval was grouted and portions of the highway pavement were replaced. The highway was reopened within 180 calendar days of the failure.« less