9th EAGE/EEGS Meeting

By decree of the Minister of Environment of the Czech Republic the organization of the Czech Geological Survey consists of two organizations under the direction of the Ministry of Environment: the Czech Geological Survey (CGS), and the Czech Geological Survey - Geofond (Geofond).

In boom-mounted magnetometer systems, the primary noise falls into two main categories: maneuver noise and rotor noise. The forrner is relatively low Frequency, while the latter is relatively high frequency. Frequency filters of various types have been used with success, but fall short where the noise is within the bandwidth of the signal. Such is often the case when searching for unexploded ordnance (UXO) and other shallow targets at rapid flight speeds. Under these conditions, helicopter noise can be reduced by making use of the fact that much of it is coherent between sensors. In this paper, we examine the coherence of various types of helicopter noise and demonstrate that measured vertical gradients can offer raw signal-tonoise improvements of 4:1 or more over comparable total field measurements.

In 2001, two high-resolution airbome geophysical surveys were flown in West Texas using Fugro's MEGATEM II system to acquire time-domain EM (TDEM) and magnetic field data. One survey, flown at 100-m line spacing on the Edwards Plateau, identified and assessed groundwater salinization in an oil-field area. The second survey, flown at 400-m line spacing over a West Texas basin, identified favorable areas for groundwater exploration.

Results of the geophysical data for in-situ evaluation of the physical-mechanical properties of the rocks in the unstable slopes in Albania are presented.

Among many natural hazards, rock falls are a very frequent phenomenon in mountainous areas, characterized by its suddenness and its difficulty to predict. The growing urbanisation in these areas implies-to better assess this hazard, and consequently to determine the location and volume of a rock mass which could fall. The stability assessment of a rock mass is generally based on surface observations (slope morphology, structural properties of the massif, deformation measurements). Even if these studies are necessary, the lack of information within the rock mass and, particularly, on discontinuities (geometry, properties) leads to major problems in hazard assessment.

Due to deep coal mining activities dwing the years from 1980 to 2000 in depths between 700 and 1000 m a local stress systcm was induced in the northern part of the Ruhr Area in Germany. Atter strong rainfall in November 2002 this stress system leads to visible clefts at the earth's surface (Figure 1) with a lateral extension of the cleft zone of more than 250 m over arable soil along a country road and directly below a house. To explore the cleft zone below the house the seismic tomography was used to detemine it's extension and dip and additionally to investigate if the cleft zone may have significant influence on the stability of the underground below the house fundaments.

The purpose of this study is to implement a new technique for monitoring the abandoned mines subjected to flooding: it consists of a hydroacoustic monitoring (sensor placed in water filling the mining cavity) in a broad frequency bandwidth (30 Hz-1 80 kHz). GISOS, a French scientific interest group concerned with the impact and the safety of the underground works in the field of the post-mining, aims amongst other at understanding the phenomena occurring in the old mining cavities in order to forecast their evolution. A very significant research effort is put on the monitoring methods for assessing degradation of the mining works, as they directly threaten the infrastructures located on the ground surface. One of the parameters, which have a significant role in the stability of the underground works, is water.

The hot and wet condition are the main factor in speeding-up the physical and chemical weathering process, as well as creating fractures on the rock. Further erosion and weathering will cause the rock to break into boulders, and eventually form a thick blanket of soil. The occurrence of landslide in Malaysia is believed primarily due to the unusual thick soil profile and high rainfall. Buried boulders can also disrupt civil engineering projects especially piling and hill cutting.

Determination of the mechanical parameters of rocks and soil are very useful for building and other civil engineering purposes, but the mechanical properties of sedimentary rocks have wide range of values and are much influenced by lithological factors. These parameters are usually measured in the laboratory from some collected samples. These samples not reflect the mechanical behavior of the whole rocks. In this work a comparative study for measuring the mechanical properties of some Eocene Limestone rocks along four selected sites by using the shallow refraction seismic method and the laboratory method had been carried out for judging which one is suitable for this purpose.

On the basis of the decision of the Ministry of Transport and Communications of the Czech Republic on the provision of financial resources, the following grant was commenced in 2001 and will be completed in 2003: "Application of Geophysical Methods for Checking the Condition of Czech Railway Tracks".