SUMMARY We present new methods for the interpretation of 3‐D seismic wide‐angle reflection and refraction data with application to data acquired during the experiments CELEBRATION, 2000 and ALP 2002 in the area of the Eastern Alps and their transition to the surrounding tectonic provinces (Bohemian Massif, Carpathians, Pannonian domain, Dinarides). Data was acquired on a net of arbitrarily oriented seismic lines by simultaneous recording on all lines of seismic waves from the shots, which allows 2‐D and 3‐D interpretations. Much (80%) of the data set consists of crossline traces. Low signal to noise (S/N) ratio in the area of the young orogens decreases the quality of travel time picks. In these seismically heterogeneous areas it is difficult to assign clearly defined arrivals to the seismic phases, in particular on crossline record sections. In order to enhance the S/N ratio, signal detection and stacking techniques have been applied to enhance the Pg‐, Pn‐ and PmP phases. Further, inversion methods have been developed for the interpretation of WAR/R‐data, based on automated 1‐D inversion (Pg) and the application of the delay time concept (Pn). The results include a 3‐D velocity model of the crust based on Pg waves, time and depth maps of the Moho and a Pn‐velocity map. The models based on stacked data are robust and provide a larger coverage, than models based on travel time picks from single‐fold (unstacked) traces, but have relatively low resolution, especially near the surface. They were used as the basis for constructing models with improved resolution by the inversion of picks from single‐fold data. The results correlate well with geological structures and show new prominent features in the Eastern Alps area and their surrounds. The velocity distribution in the crust has strong lateral variations and the Moho in the investigation area appears to be fragmented into three parts.

Results from geophysical explorations of three deep valleys, selected from different tectonic regimes in the Eastern Alps (Ö tz-, Oichten-, and Drau Valley), are presented and discussed. Ongoing tectonic deformation may use tectonic structures related to these valleys. However, seismic activity is low there. During the Würm ice age, the thickness of the ice cover ranged between 300 and 1,500 m above present ground elevation. The geophysical investigations comprised reflection seismology, gravityand resistivity surveys. The maximum depth down to the erosional base of the valleys varies from *340 to 700 m. Distinct layer packages of the valley-infill at depths greater than 250 m were termed ''old valley-fill''. Geophysical parameters and a comparison with the reflection seismic image of an intermediate layer at the recent Pasterze glacier suggest that the top of the ''old valley-fill'' represents the glacier bed during the decay of the Würm glaciation. Deep erosion is not related to high basal shear stress. The confluence of tributary glaciers is apparently not a significant factor for deep erosion in our examples of deep alpine valleys. We conclude that deep erosion may be related to high water pressure at the glacier bed, supported by specific processes of tectonic weakening.

No abstract

Geological and geophysical investigations, as well as drilling have brought the quality of geotechnical prognosis for tunnels to a high standard. However, the remaining risk during tunnel construction is still considerable, especially in case of construction by a tunnel boring machine (TBM). Seismic imaging of faults and other geological features affecting the construction ahead of a tunnel face can supply valuable information to reduce this risk. These methods are based on Vertical Seismic Profiling (VSP) locating sources and receivers in the tunnel and generating seismic waves by small blasts or mechanical devices. A fundamental problem in the application of this method is that reflectors (fault zones, petrologic boundaries, or similar) are imaged at their intersection with the tunnel axis only in case they are orthogonal to this axis. Reflectors oriented obliquely to the tunnel axis may be imaged perfectly. However, they must be extrapolated to their intersection with the tunnel axis, thus imposing major uncertainties on prediction.Therefore it was decided to concentrate on Tunnel Seismic While Drilling (TSWD), an alternative method, which uses the vibrations produced by the cutting head of the TBM as seismic source. Continuous monitoring is possible by this method and the above mentioned problem may be overcome. Conventional seismic traces are extracted from the recordings by the use of a pilot signal recorded near the cutting head of the TBM. First results from a pilot study accompanying the construction of a gallery in the Gesäuse mountain range, Styria, Austria are presented. The bandwidth of the seismic signals is >200 Hz, a high signal to noise ratio is achieved, and excellent conventional seismic traces are extracted. Thus the most important component of the whole method has been realised successfully. Additional aspects of the method are discussed and an outlook to the continuation of the pilot study is given.

No abstract

A part of the IUGS-UNESCO research project "Landslide Hazard Assessment and Cultural Heritage" includes testing the application of geophysical methods for assessing hazard risks to people and cultural assets. In this work, Austria contributed with a study on the assessment of rock-fall hazards. As the Old Town of Salzburg is a prime example of such hazards, systematic GPR-measurements were made on major rock surfaces. The aim of the exploration with GPR was to assess the potential of the method for monitoring rock walls. That is, whether structures in the rock mass which could become important when considering the risk of a rock fall, can be imaged. To manage this problem successfully, moving the antenna over the rough rock surface was made as regular as possible. The effects of vegetation lifting the antenna from the rock surface and of overhanging regions could not be avoided. Due to the loss of coupling of the antenna and the change of radiation pattern, some interference of the records occurred. Thus, only after processing could it become clear which reflections came from within the rock. A three-dimensional survey of discontinuities in the rock requires accurate mapping of the rock surface by photogrammetric methods, to get a digital terrain model for the analysis of the GPR records. The results of repeated measurements have proved to be of essential relevance. They have shown that it is possible to reveal changes with time. For the interpretation of such observations, modeling is a very useful tool.

No abstract

No abstract