Preprints
https://doi.org/10.5194/nhess-2021-281
https://doi.org/10.5194/nhess-2021-281

  19 Oct 2021

19 Oct 2021

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

Magnitude and source area estimations of severe prehistoric earthquakes in the western Eastern Alps

Patrick Oswald1, Michael Strasser1, Jens Skapski2, and Jasper Moernaut1 Patrick Oswald et al.
  • 1Department of Geology, University of Innsbruck, Innsbruck, 6020, Austria
  • 2Risklayer GmbH, Karlsruhe, 76131, Germany

Abstract. In slowly deforming intraplate tectonic regions such as the Alps only limited knowledge exists on the occurrence of severe earthquakes, their maximum possible magnitude and their potential source areas. This is mainly due to long earthquake recurrence rates exceeding the time span of instrumental earthquake records and historical documentation. Lacustrine paleoseismology aims at retrieving long-term continuous records of seismic shaking. A paleoseismic record from a single lake provides information on events for which seismic shaking exceeded the intensity threshold at the lake site. In addition, when positive and negative evidence for seismic shaking from multiple sites can be gathered for a certain time period, minimum magnitudes and source locations can be estimated for paleo-earthquakes by a reverse application of an empirical intensity prediction equation in a geospatial analysis. Here, we present potential magnitudes and source locations of four paleo-earthquakes in the western Eastern Alps based on the integration of available and updated lake paleoseismic data. The paleoseismic records at Plansee and Achensee covering the last ~10 kyrs were extended towards the age of lake initiation after deglaciation to obtain the longest possible paleoseismic catalogue at each lake site. Our results show that 25 severe earthquakes are recorded in the four lakes Plansee, Piburgersee, Achensee and potentially Starnbergersee over the last ~16 kyrs, from which four earthquakes are interpreted to left imprints in two or more lakes. Earthquake recurrence intervals range from ca. 1,000 to 2,000 years with a weakly periodic to aperiodic recurrence behavior for the individual records. We interpret that relatively shorter recurrence intervals in the more orogen-internal archives Piburgersee and Achensee are related to enhanced tectonic loading, whereas a longer recurrence rate in the more orogen-external archive Plansee might reflect a decreased stress transfer across the current-day enhanced seismicity zone. Plausible epicenters of paleo-earthquake scenarios coincide with the current enhanced seismicity regions. Prehistoric earthquakes with a minimum moment magnitude (MW) 5.8–6.1 might have occurred around the Inn valley, the Brenner region and the Fernpass-Loisach region, and might have reached up to MW 6.3 at Achensee. The paleo-earthquake catalogue might hint at a shift of severe earthquake activity near the Inn valley from east to west to east during Postglacial times. Shakemaps highlight that such severe earthquake scenarios not solely impact the enhanced seismicity region of Tyrol, but widely affect adjacent regions like southern Bavaria in Germany.

Patrick Oswald et al.

Status: open (until 18 Dec 2021)

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Patrick Oswald et al.

Patrick Oswald et al.

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Short summary
This study provides the first regional earthquake catalogue of the Eastern Alps spanning 16,000 years by using three lake paleoseismic records. Recurrence statistics reveal that earthquakes recur every 1,000-2,000 years in an aperiodic pattern. The magnitudes of paleo-earthquakes exceed the historically documented values. This study estimates magnitude and source areas for severe paleo-earthquakes and their shaking effects are explored in the broader study area.
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