Discrimination of earthquakes and quarry blasts in Mecsek Mountain region (Hungary) and its vicinity by using a linear discrimination function

<p>Contamination of earthquake catalogues with anthropogenic events largely complicates seismotectonic interpretation. It is especially true for relatively low seismicity areas, such as Hungary. In the present study, we analyze the characteristics of earthquakes and blasts of quarries occurred between 2015 and 2020 in the Mecsek Mountains in southern Hungary within 120 km to MORH and KOVH stations.</p><p>The objective of this study was to determine the linear discrimination line between the two classes earthquakes and explosions. We investigated the effectiveness of P/S amplitude ratios using filtered waveforms at different ranges of frequencies. We applied waveform cross-correlation to build correlation matrices at both stations and performed hierarchical cluster analysis to identify event clusters. Because most of the quarry blasts were carried out by ripple-fire technology, we computed spectrograms and examined the spectral ratio between low and high frequencies and the steepness of spectra.</p><p>Classes of earthquakes and quarry blasts have separated well from each other by combining the amplitude ratio, waveform similarity and the different spectral methods. We compare the discrimination parameters and capability of both stations to identify the explosions in analyzed quarries that were misclassified as earthquakes in the Hungarian National Bulletins.</p>

Focal mechanisms for small to intermediate earthquakes in the northern part of the Alps and their seismotectonic interpretation

<p>In the framework of the AlpArray project more than 600 broadband stations have been installed and operated in the Alps and the surroundings. Together with the permanent stations in the area it is one of the most densely spaced seismic networks worldwide. Thereby, it offers an excellent opportunity to investigate the seismicity and seismotectonics of the Alpine chain. Due to the huge number of stations focal mechanisms can be calculated even for small magnitude earthquakes with high accuracy. The focal mechanisms are one important key to reveal the contemporary stress field and thus contribute to a better understanding of the geodynamic processes of the Alps.</p><p>In our study we focus on small to intermediate earthquakes in the Northern Alps, namely on four distinct sub-regions. These are from West to East the Lake Constance, the Arlberg region, the area of Garmisch-Partenkirchen and the broader region of Innsbruck. In order to calculate the focal mechanisms, we apply the FOCMEC program (Snoke, 2003), which inverts for a pure double-couple source. P-polarities as well as amplitude ratios of SH to P are used as input parameters for the inversion. Thanks to the dense network a good coverage of the focal sphere is achieved in most cases.</p><p>Altogether, we calculated focal mechanisms for 25 earthquakes in the magnitude range between 2.5 and 3.5 from the time period 2016 to 2019. Most of the focal mechanisms represent reverse or strike-slip faulting, normal faulting events are rather rare. The mechanisms are analysed with respect to lateral changes along the Northern Alpine. On one hand we compare the mechanisms with mechanisms of older studies as well as with moment tensors of events of slightly larger magnitudes. Those events are the scope of another subproject in the framework of the AlpArray (Petersen et al., 2019). On the other hand, we compare our mechanisms with geological indicators, namely orientation of faults. Finally, the focal mechanisms are used as input to invert for the stress field.</p>

Discrimination between earthquakes and quarry blasts in the Vertes Hills, Hungary using a correlation detector

<p>Contamination of earthquake catalogues with anthropogenic events largely complicates seismotectonic interpretation. It is especially true for relatively low seismicity areas, such as Hungary. In the present study, we analyze the characteristics of the waveforms of earthquakes and quarry blasts that occurred in the close vicinity of Csokako (CSKK) station between 2017 and 2019 in the Vértes Hills, Hungary.</p><p>The objective of this study was to determine the linear discrimination line between the of earthquake and explosion populations. We investigated the effectiveness of P/S amplitude ratios using filtered waveforms at different frequency bands. We applied waveform cross-correlation to build correlation matrices at CSKK and performed hierarchical cluster analysis to identify event clusters. Because most of the quarry blasts were carried out by ripple-fire technology, we computed spectrograms and examined the spectral ratio between low and high frequencies and the steepness of spectra.</p><p>Overall, classes of earthquakes and quarry blasts have separated well from each other by combining the amplitude ratio, waveform similarity and the different spectral methods. We created a set of master events for individual quarries to run correlation detectors on past waveforms and identify the explosions of analyzed quarries that were misclassified as earthquakes in the annual Hungarian National Seismological Bulletins.</p>

Relocation and seismotectonic interpretation of the seismic swarm of August - December of 2012 in the Linares area, northeastern Mexico

We relocated 52 events of 2.5 ≤ Mc ≤ 3.6 from a seismic sequence of over 250 events that occurred during July-December 2012 southwest of the Linares area, northeastern Mexico. To examine this swarm four seismic stations were installed in the region and operated during different time periods from September to December. Relocation of the swarm showed that the earthquake hypocentral depths were at 8 (±5) km, and the time residuals had values ≤ 0.38 s. The fault plane solutions were generated for individual earthquakes and through the use of the composite mechanism technique. The focal mechanism solutions show pure reverse faulting; the SW dipping NNW - SSE trending nodal plane is the inferred fault plane (strike ~150°, dip ~50° and rake ~67°), which reveals that maximum horizontal stress (SHmax > Shmin > Sv) predominates in the area.