We describe here the results of the characterization of subsurface structures in an area of the south-eastern edge of the Bohemian Massif, in Austria by high-resolution geophysical survey techniques ...and advanced analysis methods of potential fields. The employed methods included potential field multiscale techniques for source-edge location and characterization of sources at depth. Our results confirmed the presence of already known structures: the location of the Diendorf Fault and the Moldanubian Shearzone are clearly recognized in the data at the same location as on the geological maps, even where the Diendorf fault is covered with sediments of the Molasse Basin. In addition, we detected several geological contacts between different rock types in the Bohemian Massif west of the Diendorf Fault. From our results, we were also able to quickly identify and image, without a priori information, previously unknown structures, such as faults with-depth-to-the top of about 500 m and magmatic intrusions about 400 m deep.
The reuse of vintage datasets which were acquired in the 20th century can pose challenges for modern geophysical modeling due to missing detailed preprocessing information, significant uncertainties, ...or lack of precise tracking, etc. Nevertheless, they are often the only available datasets in a target region. We explore here the potential of such vintage airborne geophysical datasets (magnetics, AEM, radiometrics) to detect the location and dip direction of geological faults, using a non-modeling interpretation approach based on multiple GIS tools. We apply our approach in a geologically well-known region where four different types of faults are mapped. The applicability of the tools used in this study depend on the geological setting of each fault and is evaluated based on the comparison with geological and—where available—with modeling data. In general, the GIS tools, especially used on a combination of datasets, show reliable results concerning the location and strike of faults, and even seem to be able to predict the dip direction of a fault.
The Vienna Basin Transfer Fault System (VBTFS) is the most active fault system in the region between the Eastern Alps, the western Carpathians and the Pannonian Basin. The spatial and temporal ...distribution of earthquakes along the fault system shows a heterogeneous pattern including a long-time decay of seismicity at the northern part of the VBTFS, which was interpreted to result from a long aftershock sequence subsequent to the 1906 Dobrá Voda earthquake (M=5.7). In this paper we investigate if other segments of the VBTFS display similar long-term declines of seismicity that might indicate long aftershock sequences following strong, yet unrecorded, earthquakes in historical times.
In order to analyse the distribution of seismicity, the VBTFS is divided into arbitrary segments of about 50 km length each. The segments are chosen to overlap each other to avoid missing information from neighbouring segments due to arbitrarily selected segment boundaries. For each segment we analyse the temporal evolution of seismicity and calculate the parameters of the corresponding Gutenberg-Richter (GR) relation.
The temporal seismicity patterns revealed from the segments covering the Dobrá Voda area confirm the protracted aftershock sequence following the 1906 earthquake. All but one of the other segments do not show temporal changes of seismicity comparable to the long-term Dobrá Voda aftershock sequence. Seismicity patterns, however, include short-term Omori-type aftershocks following moderate earthquakes such as the 2000 Ebreichsdorf earthquake (M=4.8). The segment covering the SW tip of the VBTFS revealed a 200 years long gradual decrease of the largest observed magnitudes starting with the 1794 Leoben (M=4.7) earthquake. The 1794 event is the oldest earthquake listed in the catalogue for the region under consideration. It therefore remains open if the recorded decay of seismicity results from the 1794 event, or a stronger earthquake before that time. The latter is corroborated by the low magnitude of the 1794 earthquake which would typically not be considered to cause long aftershock sequences.
GR a- and b-values, calculated for the individual segments, vary significantly along the VBTFS. Values range from 0.47 to 0.86 (b-values) and 0.81 to 2.54 (a-values), respectively. Data show a significant positive correlation of a- and b-values and a coincidence of the lowest b-values with fault segments with large seismic slip deficits and very low seismicity in the last approximately 300 years. These parts of the VBTFS were previously interpreted as “locked” fault segments, which have a significant potential to release future strong earthquakes, in spite of the fact that historical and instrumentally recorded seismicity is very low. We find this interpretation corroborated by the low b-values that suggest high differential stresses for these fault segments.
Aftershock identification plays an important role in the assessment and characterization of large earthquakes. Especially, the length of the aftershock sequence is an important aspect of declustering ...earthquake catalogues and therefore impacts the frequency of earthquakes in a certain region, which is important for future seismic hazard assessment. However, in intraplate regions with low deformation rates and low to moderate seismicity, it is still questionable if aftershocks after a major event may continue for much longer time. In this study, we use one of the earliest instrumentally recorded earthquakes, the 1906 Dobrá Voda earthquake (Ms/I
=5.7/VIII-IX), to compare different approaches of aftershock determination and their suitability for understanding the recorded earthquake sequence. The Dobrá Voda segment of the Vienna Basin Transfer Fault System is one of the seismically most active zones in Slovakia with the 1906 earthquake as the strongest recorded earthquake. We first assess the epicentral intensity of the earthquake according to the Environmental Intensity Scale (ESI2007) using contemporary descriptions of earthquake effects. This additional information leads to constrain the maximal intensity to IESI2007=IX. This result agrees well with first the assessment of Imax in 1907 and indicates the reliability of this intensity data. In the second step, earthquake data are plotted for two spatial windows extending 13 km and 26 km from the epicenter of the mainshock, respectively. Despite uncertainties regarding the completeness of data due to war times and lack of nearby seismic stations, the overall temporal evolution of seismicity can apparently not be described as an Omori-type aftershock sequence following the event in 1906. Instead, earthquake occurrence within 13 km of the mainshock shows elevated earthquake activity right after the 1906 event that only decays to a lower level of activity within decades after the mainshock. The decline of seismicity therefore occurs over time scales which are much longer than those predicted by the Omori relation. We conclude that today’s seismic activity may still be affected by the 1906 earthquake.
Burial dating with terrestrial cosmogenic nuclides and luminescence dating techniques have become two powerful tools to temporally constrain Quaternary deposits. A combination of both methods at the ...same geological setting has rarely been realized to date, although their viable time frames overlap by several tens of thousands of years. When Middle Pleistocene sediments with depositional ages ranging around ca. 120 ka to ca. 300 ka are targeted, both methods are employed, but come towards their lower and upper limits, respectively. A combined dating approach can be worthwhile at this age range and allows not only exploring the edges of both methods, but holds the opportunity to do a cross-check of results at an age spectrum, where both dating techniques are at risk to become fuzzy.
Here we present a case study where numerical ages of two Middle Pleistocene terraces located in the Vienna Basin were generated by combining burial and luminescence dating. A variety of processes, such as changing sediment input rates, erosion, and tectonics controlled the formation of fluvial terraces in the basin and shaped its complex modern surface. Age correlation of the evolved mosaic of blocks and dislocated sediment bodies is challenging and requires quantitative geochronological information in order to establish a coherent terrace stratigraphy. Luminescence and burial samples originating from two fluvial terraces, the lower Gaenserndorf terrace (GDT) and the higher Schlosshof terrace (SHT), were analyzed and evaluated. Luminescence and burial ages at the GDT site are in good agreement and suggest a depositional age of 140 ± 170 ka bracketed by pIRIR225 luminescence ages ranging from 120 ± 10 ka to 260 ± 30 ka. Luminescence samples at the SHT site are in saturation, but provide minimum ages, which are coherent with the burial dating result of 340 ± 170 ka. The new numerical ages indicate that the vertical offset between the GDT site and the SHT site was not purely caused by fault activity, but suggest two independent episodes of sediment accumulation.
Besides providing new insights into the stratigraphic and morphological configuration of the central Vienna Basin area, the cosmogenic nuclide data set is compelling from a methodological point of view. At the GDT site, several samples exhibited 26Al/10Be nuclide ratios exceeding the surface production ratio of 6.75. Even though affected samples were excluded from burial age calculations, a detailed investigation on possible scenarios, which could have caused an upwards shift of 26Al/10Be ratios, was carried out.
A new guideline for geological maps with QGIS Erharter, Georg H.; Steinbichler, Mathias; Eder, Markus ...
Austrian journal of earth sciences,
01/2023, Letnik:
116, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Being able to create digital geological maps has become a basic requirement for the skillset of today’s geologists. QGIS is a geographical information system that receives increasing popularity due ...to its user-friendliness and the fact that it is an open access software. This contribution provides an update and extension to a previously published software guideline that gives a stepwise explanation on how to create a geological map with QGIS. The article serves as a brief overview of the guideline through an illustrated example. The guideline itself is published as a supplement to this paper. Within six sections, the guideline explains how to create a geological map with QGIS: 1. Introduction, 2. Download and installation, 3. Basemaps, 4. Map drawing, 5. Plugins, 6. Layouts. The aim is to instruct geologists who are completely inexperienced with digital map creation as well as provide specific information for more advanced users. In general, providing software guidelines for the geological community is an important step towards increasing geologists’ digital proficiency and to keep up with today’s fast paced developments in digitalization.
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