The S-19 Cave was with its explored depth of 177 m one of the most important caves of the Mt. Kanin massif, but after its discovery in 1974, a huge snow avalanche protection dyke was constructed ...across the cave entrance. To excavate the buried cave, the accurate location of the cave had to be determined first. Since the entrance coordinates were incorrect and no markers were available, application of geophysical techniques was necessary to do this. A Ground Penetrating Radar (GPR) with special 50 MHz rough terrain antennas was selected as the single suitable geophysical method for the given conditions where thick debris overlay a rugged limestone surface. Nevertheless, it was not possible to directly detect the relatively narrow cave entrance itself due to data resolution limits. However, a historical photo of the area showed that the cave entrance was located in a local depression, which therefore represented the main target of the GPR survey. Seven GPR profiles were measured across the rough and steep surface causing difficulties in traversing the area with sensitive research equipment. In all recorded radargrams a small depression was clearly imaged under debris, and recognized as a topographic feature with the cave entrance. Based on the GPR data interpretation, the exact location for digging was determined and the thickness of debris assessed at 6.5–7 m. A massive excavation by a dredger resulted in a successful opening of the cave entrance, confirming both its geophysically determined location and its estimated depth. The application of an advanced geophysical method was therefore proven successful in providing a solution to this specific case in karst exploration and an important cave was saved.
Alp01 and Alp02 are the longest profiles recorded during ALP 2002, a large international seismic refraction and wide‐angle reflection experiment undertaken in the Eastern Alps in 2002. Alp01 crosses ...the Alpine orogen from north to south, thus providing a cross section mainly affected by the collision between Europe and the Adriatic microplate. Alp02 extends from the Eastern Alps to the Pannonian basin, supplying evidence on the relation between Alpine crustal structure and tectonic escape to the Pannonian basin. During this experiment, 363 single‐channel recorders were deployed along these profiles with an average spacing of 3.2 km. Recordings from 20 inline shots were used in this study. Two‐dimensional forward modeling using interactive ray‐tracing techniques produced detailed P wave velocity models that contain many features of tectonic significance. Along Alp01, the European Moho dips generally to the south and reaches a maximum depth of 47 km below the transition from the Eastern to the Southern Alps. The Adriatic Moho continues further south at a significantly shallower depth. Moho topography and a prominent south‐dipping mantle reflector in the Alpine area support the idea of southward subduction of the European lithosphere below the Adriatic microplate. The most prominent tectonic feature on the Alp02 profile is a vertical step of the Moho at the transition between the Alpine and Pannonian domains, suggesting the existence of a separate Pannonian plate fragment. The development of the Pannonian fragment is interpreted to be a consequence of crustal thinning due to tectonic escape from the Alpine collision area to the Pannonian basin.
Breginjski kot is among the most endangered seismic zones in Slovenia with the seismic hazard assessed to intensity IX MSK and the design ground acceleration of 0.250 g, both for 500-year return ...period. The most destructive was the 1976 Friuli Mw = 6.4 earthquake which had maximum intensity VIII-IX. Since the previous microzonation of the area was based solely on the basic geological map and did not include supplementary field research, we have performed a new soil classification of the area. First, a detailed engineering geological mapping in scale 1 : 5.000 was conducted. Mapped units were described in detail and some of them interpreted anew. Stiff sites are composed of hard to medium-hard rocks which were subjected to erosion mainly evoked by glacial and postglacial age. At that time a prominent topography was formed and different types of sediments were deposited in valleys by mass flows. A distinction between sediments and weathered rocks, their exact position, and thickness are of significant importance for microzonation. On the basis of geological mapping, a soil classification was carried out according to the Medvedev method (intensity increments) and the Eurocode 8 standard (soil factors) and two microzonation maps were prepared. The bulk of the studied area is covered by soft sediments and nine out of ten settlements are situated on them. The microzonation clearly points out the dependence of damage distribution in the case of 1976 Friuli earthquake to local site effects.
The region of Ilirska Bistrica is one of the most seismically active areas of Slovenia, where 15 damaging earthquakes with maximum intensity equal or greater than V EMS-98 have occurred in the last ...100 years. These earthquakes have shown that strong site effects are characteristic of the parts of the town that are built on soft Pliocene clay and sand overlain by Quaternary alluvium. Since there is a lack of boreholes and geophysical and earthquake data, the microtremor horizontal-to-vertical spectral ratio (HVSR) method was applied to a 250 m dense grid of free-field measurements over an extended area and to a 200 m dense grid in the town area in order to assess the fundamental frequency of the sediments. Measurements were additionally performed in ten characteristic houses to assess the main building frequencies. The effects of wind and artificial noise on the reliability of the results were analyzed. The map of the fundamental frequencies of sediments shows a distribution in a range of 1-20 Hz. The lower frequency range (below 10 Hz) corresponds to the extent of Pliocene clays and sand overlain by alluvium, which form a small basin, and the higher frequencies to flysch rocks, but variations within short distances are considerable. The measurements inside the buildings of various heights (2-6 stories) showed main longitudinal and transverse frequencies in the range 3.8-8.8 Hz. Since this range overlaps with the fundamental frequency range for Pliocene and Quaternary sediments (2-10 Hz), the danger of soil-structure resonance is considerable, especially in the northern part of the town. Soil-structure resonance is less probable in the central and southern part of the town, where higher free-field frequencies prevail. These observations are in agreement with the distribution of damage caused by the 1995 earthquake (M
L
= 4.7, I
max
= VI EMS-98), for which a detailed damage survey data is available.
Ground penetrating radar (GPR) named "Roteg" was used to detect known and unknown passages of Divaška Jama and Trhlovca caves in SW Slovenia. "Roteg's" main characteristics are an extraordinary high ...power output (20 MW) and high voltage on antennas (up to 20 kV), which allows penetration more than ten times deeper than common GPRs. During the measurement we used 3-m long antennas (50 MHz) with a central frequency of 50 MHz and we clearly detected the reflections from the depth of200 m after data processing. During field survey 22 profiles were completed with a total length of 4487.97 m. Pretnerjeva and Žibernova Dvorana chambers in Divaška Jama were well visible on radarograms. New big cavities, which were detected below profiles P18, P21 and P22, are almost all at the same level of 350 - 400 m a.s.l. There is another group of cavities at a level of 420 - 450 m a.s.l., which corresponds to Trhlovca. Both cave groups are separated by the gap which extends in the vertical direction, and probably presents a tectonic zone, which is as well visible on the radarograms. By the use of "Roteg" at the karst surface we were able to detect known caves, new - unknown caves and tectonic zones up to 200 m below the surface.
PDF
