Estimating the upper limit of prehistoric peak ground acceleration using an in situ, intact and vulnerable stalagmite from Plavecka priepast cave (Detrekoi-zsomboly), Little Carpathians, Slovakia-first results

Earthquakes hit urban centres in Europe infrequently, but occasionally with disastrous effects. Obtaining an unbiased view of seismic hazard (and risk) is therefore very important. In principle, the best way to test probabilistic seismic hazard assessments (PSHAs) is to compare them with observations that are entirely independent of the procedure used to produce PSHA models. Arguably, the most valuable information in this context should be information on long-term hazard, namely maximum intensities (or magnitudes) occurring over time intervals that are at least as long as a seismic cycle. The new observations can provide information of maximum intensity (or magnitude) for long timescale as an input data for PSHA studies as well. Long-term information can be gained from intact stalagmites in natural caves. These formations survived all earthquakes that have occurred over thousands of years, depending on the age of the stalagmite. Their 'survival' requires that the horizontal ground acceleration (HGA) has never exceeded a certain critical value within that time period. Here, we present such a stalagmite-based case study from the Little Carpathians of Slovakia. A specially shaped, intact and vulnerable stalagmite in the Plavecka priepast cave was examined in 2013. This stalagmite is suitable for estimating the upper limit of horizontal peak ground acceleration generated by prehistoric earthquakes. The critical HGA values as a function of time going back into the past determined from the stalagmite that we investigated are presented. For example, at the time of Joko event (1906), the critical HGA value cannot have been higher than 1 and 1.3 m/s(2) at the time of the assumed Carnuntum event (similar to 340 AD), and 3000 years ago, it must have been lower than 1.7 m/s(2). We claimed that the effect of Joko earthquake (1906) on the location of the Plavecka priepast cave is consistent with the critical HGA value provided by the stalagmite we investigated. The approach used in this study yields significant new constraints on the seismic hazard, as tectonic structures close to Plavecka priepast cave did not generate strong earthquakes in the last few thousand years. The results of this study are highly relevant given that the two capitals, Vienna and Bratislava, are located within 40 and 70 km of the cave, respectively.Web of Science2151130111

Topography effects on displacements and gravity changes due to magmatic intrusions

The paper describes a method for including topographic effects in a thermo-visco-elastic model. An approximate methodology for the consideration of topography in the computation of thermo-viscoelastic displacement and gravity changes was used. It gave us a relatively general and simple solution useful for solving the inverse problem. Our results show that for volcanic areas with an important relief, the perturbation of the thermo-viscoelastic solution (deformation and total gravity anomaly) due to topography can be quite significant. In consequence, neglect of topographic effects can give a rise to significant errors in the estimation of surface displacements and gravity changes, and therefore in the estimation of the intrusion characteristics obtained solving the inverse problem.Peer reviewe

3D analytical and numerical modelling of the regional topography influence on the surface deformation due to underground heat source

Thermo-elastic strains and stresses play a considerable role in the stress state of the lithosphere and its dynamics, especially at pronounced positive geothermal anomalies. Topography has a significant effect on ground deformation. In this paper we describe two methods for including the topographic effects in the thermo-viscoelastic model. First we use an approximate methodology which assumes that the main effect of the topography is due to distance from the source to the free surface and permits to have an analytical solution very attractive for solving the inverse problem. A numerical solution using Finite Element Method (FEM) is also computed. The numerical method allows to include the local shape of the topography in the modelling. In the numerical model the buried magmatic body is represented by a finite volume thermal source. The temperature distribution is computed by the higher-degree FEM. For analytical as well as numerical model solution only the forces of thermal origin are considered. The comparison of the results obtained using both analytical and numerical techniques shows the qualitative agreement of the vertical displacements. In the numerical values small differences were obtained. The results show that for the volcanic areas with an important relief the perturbation of the thermo-viscoelastic solution (deformation and total gravity anomaly) due to the topography can be quite significant. In consequence, neglecting topography could give erroneous results in the estimated source parameters.Peer reviewe

Efectos del modelo de tierra en cálculos teóricos de de formación del terreno

[ES] En este ai-tículo se estudian los efectos del modelo de Tierra empleadoen los cálculos teóricos de deformación y variaciones de gravedad causados en campo cercano por una intrusión magmática considerada puntual. Para ello se revisan los resultados obtenidos en medios elásticos y elástico-gravitatorios, así como homogéneos y estratificados. Se comparan también los resultados obtenidos considerando modelos de Tierra elástico-gravitatoria y termo-elástica en los modelos teóricos de deformación.[EN] In this paper we study the efi’ects of the Earth model used in theoretical computations of gravity changés and deformation in the near field dne to a magmatie intrusion which is assumed as a point source. To carry out this we summarized te previous results obtained using elastic and elastic-gravitational media as well as homogeneous and layered ones. Wc also compare the obtained results considering a elastie-gravitational and thermo-elastic Earth models in deformation modelling.Los autores estamos agradecidos a la Siovak Graní Agency for Science (grant N0 2/1063) por la financiación parcial de este trabajo. La investigación de 1. Fernández y R. d. R. Granelí se sufragó con cargo al proyecto EV5VCT93- 0283 dentro del Programa de Medioambiente de la Unión Europea.Peer reviewe