The history of subsidence, fires, flooding and other kinds of environmental hazards related to shallow coal workings in India goes back to colonial times some 300 years ago. As coal production accelerated in modern times, so did the environmental and socio‐economic drawbacks related to exploitation. In the mid‐1980s, a hydropneumatic sand‐stowing method was developed to fill in abandoned galleries but their exact location had to be known. Unfortunately, most of these old workings are uncharted and consequently large tracts of land cannot be stabilized. A research programme making use of integrated surface, borehole and cross‐hole geophysical methods was undertaken over a five‐year span to try to solve this problem. Surface geophysical methods, being cheaper and faster than their cross‐ and downhole counterparts, were used to cover larger areas on an exploratory basis, while cross‐hole methods were employed to locate more accurately one or a network of galleries to be perforated by drillhole(s) and used as a conduit for sand stowing. We report the results of one of the cross‐hole geophysical methods: electrical resistivity tomography (ERT). A pole–dipole configuration is used and both cross‐hole and surface‐borehole methodologies are tested. Forward modelling and inversion of synthetic data making use of downhole and surface physical and geometrical parameters are presented first. This phase is followed by the inversion of real data. It is concluded that ERT is not applicable for the detection of dry voids, but is effective in a waterlogged environment which is estimated to represent 85–90% of the cases. In waterlogged galleries, ERT is applicable in both cross‐hole and surface‐downhole modes, the latter allowing a larger surface coverage at low cost. ERT is thus a reliable geophysical tool to image water‐filled voids and an adequate technique to address environmental and geotechnical problems.

A ground-penetrating radar (GPR) survey was conducted at the site of the first to fourth century AD Roman villa of Tourega, near E ¤ vora, Alentejo region, Portugal.This site has been partially excavated, revealing a bathhouse complex consisting ofa tank reservoir, multiple bathingrooms and a major corridor.The excavated portion of Tourega provides direct archaeological feedback as to the size, shape, depth and orientation of structures revealed by GPR surveys. A 4500 m 2 area surrounding the known site was surveyed using common-offset 500 MHz and 200 MHz pseudo-three-dimensional acquisition. Amplitude time-slice analysis reveals a large numberof well-defined additional structures confirming a much broader extension of the site. For shallow buried rectilinear structural targets, the high frequency 500 MHz common-offset data provide excellent imaging. However, limited depth penetration at 500 MHz necessitated a lower frequencyofinvestigation; therefore 200 MHz commonoffset and multi-offset data were also acquired.Two 200 MHz multi-offset GPR profiles were obtained over the large double-walled structure identified on the time-slices, acquired using a newly proposed multi-offset acquisition technique^rapid multi-offset acquisition. This acquisition technique uses the existing single-channel GPR system, is extremely cost-effective, and easily acquires a high fold. Rapid multi-offset acquisition provides an average time saving up to five times that of stationary multioffset profiling. The 200 MHz multi-offset profiles provide a greater depth penetration and enhanced structural detail (i.e. improved imaging of dipping structures) than comparable 200 MHz common-offset profiles. Post-stack, inverse-Q filtering increases vertical resolution and interpretability of the multi-offset sectionsvia removalof wavelet dispersion.Althoughmulti-offset data arelessfeasible for characterizing this site in three dimensions because of the large time commitment in data collection, two multi-offset profiles over key structures of interest improved the final site interpretation, with enhanced image quality and higher resolution than comparable common-offset profiles. The combined results of the multi-offset survey with a common-offset grid should encourage a more frequent use of multi-offset data at archaeological sites when the depth extent of the archaeological site is uncertain.

No abstract

Samples spanning 66 m of Permian redbeds were collected from a vertical, but azimuthally unoriented, drill core obtained during a uranium exploration programme in the L o d h e Basin of southern France. Inclinations are well grouped @= -6.5", k = 121.5) and consistent with the known Permian palaeolatitude of Europe. Declinations have been estimated by using a sedimentological model involving tectonically-rotated cross-bed laminations. The results are very encouraging and suggest a pole at 151°E, 53"N ( 6 p = lo, 6m = 2", N = 43), which agrees well with the Eurasian apparent polar wander curve. The small polar discrepancy could well be due to secular variation, which is consistent with the small variance and presumed short time spanned by the sequence. Fully oriented surface samples confirm these findings, and support the validity of the orientation model. Temporal variations revealed by the stratigraphic ordering can be interpreted as slow dipole wobble, on a time-scale of lo5 yr or more, on which is superimposed a more rapid nondipole secular variation. It appears that the core stores of the world could become -at least under favourable circumstances -an important source of palaeomagnetic information.

Varios autores han propuesto que el Bloque de Jalisco del oeste de México ha sido sometido a deformaciones internas asociadas con un movimiento hacia el noroeste con respecto a la placa Norteamericana. Estas deformaciones habrían resultado en la formación de varias fosas tectónicas dentro de la parte norte del Bloque. Dos de estas fosas son la de Mascota y la de Talpa Allende. Los análisis datos paleomagnéticos de seis distintos flujos de lava recientes encontraos en las fosas de Mascota y Talpa no indican movimientos estadísticamente significativos en la zona. Mas precisamente, la dirección esperada (campo dipolar axial, D=0°, I=37°) se encuentra dentro del cono de confianza de 95% de la dirección paleomagnética promedia (D=352.2°, I=24.0°,α95=16.8°). Sin embargo, la proximidad del polo de referencia Norteamericano y del limite de confianza a 95% del polo paleomagnético indica que datos adicionales podrían permitir la definición de un movimiento significativo hacia el Norte, de la parte de Bloque de Jalisco, o la definición de un basculamiento local de la zona.