Source analysis of the March 7, 2019 $$\mathbf {M_L=4.0}$$ M L = 4.0 Somogyszob, Hungary earthquake sequence
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Source analysis of the March 7, 2019 𝐌𝐋 = 𝟒.𝟎 Somogyszob, Hungary earthquake sequence Zoltán Wéber1 · Barbara Czecze2 · Bálint Süle1 · István Bondár1 · AlpArray Working Group Received: 25 March 2020 / Accepted: 5 August 2020 / Published online: 18 August 2020 © The Author(s) 2020
Abstract Between February 16 and April 5, 2019, a series of earthquakes took place around the village of Somogyszob, Somogy county, Hungary. The mainshock occurred on March 7 with a local magnitude ML = 4.0 and epicentral intensity of 5 on the EMS scale. The main event was preceded by four foreshocks and followed by four aftershocks. The largest foreshock ( ML = 2.6 ) was also felt with maximum intensity of 4 EMS. This earthquake sequence is the first remarkable one in the region that was recorded by a significant number of highquality broadband digital seismographs. We have estimated the hypocenters of the 9 earthquakes using the hypoDD multiple-event location algorithm. The events occurred in a tight region around the mainshock at around 13–14 km depth. For the main event, we obtained an average moment magnitude of Mw = 3.75 , source radii of rP = 509 m and rS = 400 m, and static stress drops of 𝛥𝜎 P = 1.19 × 106 Pa and 𝛥𝜎 S = 4.00 × 106 Pa from the analysis of displacement P- and S-wave spectra, respectively. The resulting spectral source parameters for the investigated events agree well with the results of earlier research. We have also shown that our recently developed probabilistic waveform inversion techniques applied in this study are suitable to retrieve the source mechanism for weak local earthquakes. We have successfully estimated the focal mechanism for the mainshock, a foreshock and an aftershock. Each earthquake was a thrust faulting event with a sub-horizontal P-axis pointing towards N-NE, coinciding with the general trend of the compressional stress field in the epicentral region. Keywords Multiple-event earthquake location · Spectral source parameters · Earthquake source mechanism · Earthquake moment tensor · Bayesian waveform inversion · Tectonic stress
* Zoltán Wéber [email protected] 1
Geodetic and Geophysical Institute, Research Centre for Astronomy and Earth Sciences, Csatkai E. u. 6‑8., Sopron 9400, Hungary
2
Department of Geophysics and Space Science, Institute of Geography and Earth Sciences, Eötvös Loránd University, Pázmány Péter sétány 1/C, Budapest 1117, Hungary
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Vol.:(0123456789)
372
Acta Geodaetica et Geophysica (2020) 55:371–387
1 Introduction Between February 16 and April 5, 2019, an earthquake sequence took place in Somogy county, Hungary. During this 7 weeks, 9 earthquakes were recorded around the village of Somogyszob. The mainshock occurred on March 7 with a local magnitude ML = 4.0 and epicentral intensity of 5 on the European Macroseismic Scale (EMS). It was preceded by 4 foreshocks with 1.6 ≤ ML ≤ 2.6 , and followed by 4 aftershocks with 1.3 ≤ ML ≤ 2.3 . The largest foreshock ( ML = 2.6 ) was also felt in the epicentral region. Its macroseismic intensity was as large as 4 EMS. Seis
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