Abstract
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 Plavecká 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 Jókő event (1906), the critical HGA value cannot have been higher than 1 and 1.3 m/s2 at the time of the assumed Carnuntum event (∼340 AD), and 3000 years ago, it must have been lower than 1.7 m/s2. We claimed that the effect of Jókő earthquake (1906) on the location of the Plavecká 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 Plavecká 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.
Highlights
Damaging earthquakes in Central Europe are infrequent, but do occur
Our research focused on the effect of earthquakes on intact and vulnerable stalagmites; it is worth to mention Šmída’s (2010) work in Plavecká priepast cave
An intact and vulnerable stalagmite (IVSTM) from the Plavecká priepast cave with a candlestick shape, tall, slim, cylindrical with a large height– diameter ratio, was examined to estimate the upper limit of horizontal peak ground acceleration generated by prehistoric earthquakes
Summary
Damaging earthquakes in Central Europe are infrequent, but do occur. This raises the important issue for society of how to react to this hazard: Potential damages are enormous, and infrastructure costs for addressing these hazards are huge as well. There is a critical need for additional observations that constrain the occurrence of the largest earthquakes and/or the maximum seismic acceleration over timescales of thousands of years Fragile geologic features such as precariously balanced rocks at Yucca Mountain, Nevada, have been used to quantitatively estimate the ground acceleration required to topple such boulders (Brune and Whitney 2000; Anderson et al 2011). The ‘survival’ of vulnerable stalagmites requires that horizontal ground accelerations have never exceeded a certain critical value over time periods of thousand years or more Such speleoseismological studies have been performed in several caves using an in situ approach (Lacave et al 2000, 2004; Becker et al 2006; Szeidovitz et al 2005, 2008a, 2008b; Paskaleva et al 2008; Gribovszki et al 2008, 2013a, 2013b; Shanov and Kostov 2015) complemented by laboratory studies (Cadorin et al 2001; Paskaleva et al 2006; Bednárik 2009). We compare our results to ground motion estimates from the 10 January 1906 Jókő earthquake
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