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Geophysical Techniques (geophysical + techniques)

Distribution by Scientific Domains

Earth and Environmental Science	100%

Selected Abstracts

Geophysical indicators of culturally emplaced soils and sediments

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 8 2002
Rinita A. Dalan
Archaeologists dealing with earthen forms must distinguish those constructed by humans from those with a natural origin. Geophysical techniques can help identify culturally loaded soils and sediments. We suggest that intrinsic changes in geophysical properties, due to cultural loading, can serve as fingerprints in determining whether a mound or other earthen form is natural or culturally constructed. Culturally emplaced soils might be identified through anomalous values in geophysical properties or through unusual spatial or stratigraphic complexity. The identification of this "lumpiness" in geophysical properties may involve geophysical techniques quite different from those employed in traditional archaeogeophysical surveys. Experiments at three prehistoric mound sites (the Cahokia Mounds State Historic Site, Effigy Mounds National Monument, and the Hopeton Earthwork) illustrate a number of these techniques including studies of the anisotropy (directionality) of geophysical properties, seismic Rayleigh (surface) waves, and magnetic susceptibility. © 2002 Wiley Periodicals, Inc. [source]

A comparison of cross-hole electrical and seismic data in fractured rock

GEOPHYSICAL PROSPECTING, Issue 2 2004
J.V. Herwanger
ABSTRACT Cross-hole anisotropic electrical and seismic tomograms of fractured metamorphic rock have been obtained at a test site where extensive hydrological data were available. A strong correlation between electrical resistivity anisotropy and seismic compressional-wave velocity anisotropy has been observed. Analysis of core samples from the site reveal that the shale-rich rocks have fabric-related average velocity anisotropy of between 10% and 30%. The cross-hole seismic data are consistent with these values, indicating that observed anisotropy might be principally due to the inherent rock fabric rather than to the aligned sets of open fractures. One region with velocity anisotropy greater than 30% has been modelled as aligned open fractures within an anisotropic rock matrix and this model is consistent with available fracture density and hydraulic transmissivity data from the boreholes and the cross-hole resistivity tomography data. However, in general the study highlights the uncertainties that can arise, due to the relative influence of rock fabric and fluid-filled fractures, when using geophysical techniques for hydrological investigations. [source]

A survey in the park: Methodological and practical problems associated with geophysical investigation in a late Victorian municipal park

ARCHAEOLOGICAL PROSPECTION, Issue 3 2010
Andrew Parkyn
Abstract The survey of Pudsey Park is a geophysical investigation of a late Victorian municipal park. The aim of the survey was to use geophysical techniques to identify the park's changing designs over a 120 year period. An initial design for the park was located during the desk-based assessment, however, it was unclear how much of the original plan had been implemented. It was suspected that Pudsey Park's design has been simplified over time. The project also aimed to identify a suitable sampling strategy for studying park and garden sites by using high-resolution surveys and multiple probe separations for varying depths of detection during earth resistance survey. It was hoped that multiple electrode separations combined with a high density survey could be used to differentiate the signal responses from the modern park designs and earlier design schemes. The choice of strategy is at a significantly higher resolution than guidelines for geophysical investigations for traditional archaeological features. The survey provided highly detailed but complicated data sets; areas of the park have had several redesigns, often where the modern scheme masks previous designs. A number of ,hard' and ,soft' landscaping features were identified including the foundations of the original bandstand (now replaced) and former flower beds. The 0.25,m probe separation surprisingly produced the most defined data with the greatest level of information due to the increased spatial resolution. The geophysical investigation is the first of its kind to investigate a Victorian municipal park in its entirety. The survey validates the importance of high-resolution survey in the study of parks and gardens and also provides a reference data set for future work where poorer documentation hinders interpretation. The geophysics data, together with the accompanying Geographical Information System database produce a unique and detailed picture of a Victorian park from its inception through 120 years of development. Copyright © 2010 John Wiley & Sons, Ltd. [source]

A geophysical investigation of subsurface structures and Quaternary geology at San Marcos Pueblo, New Mexico

ARCHAEOLOGICAL PROSPECTION, Issue 4 2008
Emily A. Hinz
Abstract San Marcos Pueblo site (LA 98), located in the Galisteo Basin south of Santa Fe, New Mexico, encompasses the remains of 43 identified room blocks, a Spanish mission and 20 middens. As part of ongoing field investigations at San Marcos, students and faculty from the Summer of Applied Geophysical Experience (SAGE) field programme are using multiple geophysical techniques to non-invasively investigate the site. Modelling of the underlying Quaternary stream terrace geology and the detection of subsurface Pueblo-era features were accomplished through the integrated interpretation of data from seismic refraction and reflection, electromagnetic, magnetic and ground-penetrating radar methods. Although to date only a targeted spatially small extent of the site has been explored using these methods, the SAGE field programme has been able detect a variety of anthropogenic structures and debris. The SAGE field programme validated the presence of excavations in the natural stream terrace sequence over areas believed to contain kivas, mapped the geometry of walls over a closed room block, and detected an area of magnetized debris associated with smelting operations. Collectively, the data from the SAGE field programme demonstrate the value of using multiple, complementary, geophysical methods for archaeological prospection. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Combined seismic tomographic and ultrashallow seismic reflection study of an Early Dynastic mastaba, Saqqara, Egypt

ARCHAEOLOGICAL PROSPECTION, Issue 4 2005
Mohamed Metwaly
Abstract Mastabas were large rectangular structures built for the funerals and burials of the earliest Pharaohs. One such mastaba was the basic building block that led to the first known stone pyramid, the,>4600-year old Step Pyramid within the Saqqara necropolis of Egypt. We have tested a number of shallow geophysical techniques for investigating in a non-invasive manner the subsurface beneath a large Early Dynastic mastaba located close to the Step Pyramid. After discovering that near-surface sedimentary rocks with unusually high electrical conductivities precluded the use of the ground-penetrating radar method, a very high-resolution seismic data set was collected along a profile that extended the 42.5,m length of the mastaba. A sledgehammer source was used every 0.2,m and the data were recorded using a 48-channel array of single geophones spaced at 0.2,m intervals. Inversions of the direct- and refracted-wave travel times provided P-wave velocity tomograms of the shallow subsurface, whereas relatively standard processing techniques yielded a high-fold (50,80) ultrashallow seismic reflection section. The tomographic and reflection images were jointly interpreted in terms of loose sand and friable limestone layers with low P-wave velocities of 150,650,m,s,1 overlying consolidated limestone and shale with velocities,>,1500,m,s,1. The sharp contact between the low- and high-velocity regimes was approximately horizontal at a depth of ca. 2,m. This contact was the source of a strong seismic reflection. Above this contact, the velocity tomogram revealed moderately high velocities at the surface location of a friable limestone outcrop and two low-velocity blocks that probably outlined sand-filled shafts. Below the contact, three regularly spaced low velocity blocks probably represented tunnels and/or subsurface chambers. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Electrical and magnetic response of archaeological features at the early neolithic site of Movila lui Deciov, western Romania

ARCHAEOLOGICAL PROSPECTION, Issue 4 2004
J. M. Maillol
Abstract An archaeological geophysics survey was conducted on the early neolithic site of Movila lui Deciov, in the Province of Banat, Romania. Magnetometry and electromagnetic terrain conductivity were used for the main prospection effort, and a test of electrical resistivity imaging was conducted on a selected profile. In addition, magnetic susceptibility measurements were obtained from excavation pit samples. The magnetic survey was successful in determining the extent of the site, in delimiting zones rich in structures and artefacts, and in confirming the presence of a ditched enclosure that could be the earliest known in the region. The electromagnetic survey was limited by a lack of resolution of electrical property contrast. Detailed joint modelling of the magnetic and electrical response of the subsurface was used to confirm that electrical resistivity imaging can provide depth information to complement magnetic mapping. One of very few reported in Romania, this survey paves the way for an increased use of geophysical techniques in the cultural heritage management of this country. From a methodological viewpoint, this work further demonstrates the potential of electrical resistivity imaging in archaeology Copyright © 2004 John Wiley & Sons, Ltd. [source]

Comparison of geophysical techniques for investigating an infilled ditch at Bury Walls hill fort, Shropshire

ARCHAEOLOGICAL PROSPECTION, Issue 4 2003
R. E. Murdie
Abstract Five geophysical survey techniques were used to investigate the infilled section of the outer ditch at the Iron Age hill fort of Bury Walls, Shropshire. The techniques were resistance mapping and four profiling methods: resistivity sounding, ground-penetrating radar (GPR), P-wave seismic refraction and S-wave seismic refraction. The ditch was clearly visible on the resistance map and on GPR profiles, but no depth estimate was obtainable from these surveys. The most successful survey technique was S-wave seismic refraction, both for determining whether the ditch was present on a profile and for obtaining an estimate of its depth. A key factor for the success of S-wave seismic refraction profiling was that the ditch had been excavated into the sandstone bedrock. Copyright © 2003 John Wiley & Sons, Ltd. [source]

The geophysical evaluation of British lead and copper working sites.

ARCHAEOLOGICAL PROSPECTION, Issue 3 2002
Comparisons with iron working
Abstract Recent research at the University of Bradford has been very effective in evaluating early iron-working sites using geophysical techniques. In addition, lead and copper smelting sites have been surveyed with a fluxgate gradiometer. Although the fluxgate gradiometer readings from these sites are lower than those from iron-smelting sites it is possible to identify anomalies related to the different smelting methods. The paper provides details of some of the surveys and the different features that may be identified. Magnetic susceptibility measurements of selected slag samples provided additional information. Copyright © 2002 John Wiley & Sons, Ltd. [source]