Preprints
https://doi.org/10.5194/se-2021-13
https://doi.org/10.5194/se-2021-13

  16 Feb 2021

16 Feb 2021

Review status: this preprint is currently under review for the journal SE.

Regional centroid MT inversion of small to moderate earthquakes in the Alps using the dense AlpArray seismic network: challenges and seismotectonic insights

Gesa Maria Petersen1,2, Simone Cesca1, Sebastian Heimann1, Peter Niemz1,2, Torsten Dahm1,2, Daniela Kühn1,3, Jörn Kummerow4, Thomas Plenefisch5, and the AlpArray Working Group Gesa Maria Petersen et al.
  • 1GeoForschungsZentrum Potsdam, Potsdam, Germany
  • 2University of Potsdam, Institute of Geosciences, Potsdam, Germany
  • 3NORSAR, Applied Seismology, Kjeller, Norway
  • 4Freie Universität Berlin, Berlin, Germany
  • 5Federal Institute for Geosciences and Natural Resources (BGR), Hanover, Germany
  • For further information regarding the team, please visit the link which appears at the end of the paper.

Abstract. The Alpine mountains in central Europe are characterized by a heterogeneous crust accumulating different tectonic units and blocks in close proximity to sedimentary foreland basins. Centroid moment tensor inversion provides insight into the faulting mechanisms of earthquakes and related tectonic processes, but is significantly aggravated in such an environment. Thanks to the dense AlpArray seismic network and our flexible bootstrap-based inversion tool Grond we are able to test different set-ups with respect to the uncertainties of the obtained moment tensors and centroid locations. We evaluate the influence of frequency bands, azimuthal gaps, input data types and distance ranges and study the occurrence and reliability of non-DC components. We infer that for most earthquakes (Mw ≥ 3.3) a combination of time domain full waveforms and frequency domain amplitude spectra in a frequency band of 0.02–0.07 Hz is suitable. Relying on the results of our methodological tests, we perform deviatoric MT inversions for events with Mw > 3.0. We present here 75 solutions and analyse our results in the seismo-tectonic context of historic earthquakes, seismic activity of the last three decades and GNSS deformation data. We study regions of high seismic activity, namely the western Alps, the region around Lake Garda, the SE Alps, besides clusters further from the study region, in the northern Dinarides and the Apennines. Seismicity is particularly low in the eastern Alps and in parts of the central Alps. We apply a clustering algorithm to focal mechanisms, considering additional focal mechanisms from existing catalogs. Related to the NS compressional regime, E-W to ENE-WSW striking thrust faulting is mainly observed in the Friuli area in the SE Alps. Strike-slip faulting with a similarly oriented pressure axis is observed along the northern margin of the central Alps and in the northern Dinarides. NW-SE striking normal faulting is observed in the NW Alps showing a similar strike direction as normal faulting earthquakes in the Apennines. Both, our centroid depths as well as hypocentral depths in existing catalogs indicate that Alpine seismicity is predominantly very shallow; about 80 % of the studied events have depths shallower than 10 km.

Gesa Maria Petersen et al.

Status: open (until 30 Mar 2021)

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Gesa Maria Petersen et al.

Gesa Maria Petersen et al.

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Short summary
The Alpine mountains are known for a complex tectonic history. We shed light onto ongoing tectonic processes by studying rupture mechanisms of small to moderate earthquakes between 2016 and 2019 observed by the temporary AlpArray seismic network. The rupture processes of 75 earthquakes were analyzed along with past earthquakes and satellite deformation data. Our observations point at variations in the underlying tectonic processes and stress regimes across the Alps.