6600 years of earthquake record in the Julian Alps (Lake Bohinj, Slovenia)

Abstract : Sequences of lake sediments often form long and continuous records thatmay be sensitive recorders of seismic shaking. A multi-proxy analysis ofLake Bohinj sediments associated with a well-constrained chronology wasconducted to reconstruct Holocene seismic activity in the Julian Alps (Slovenia).A seismic reflection survey and sedimentological analyses identified 29homogenite-type deposits related to mass-wasting deposits. The most recenthomogenites can be linked to historical regional earthquakes (i.e. 1348 AD,1511 AD and 1690 AD) with strong epicentral intensity [greater than ‘damaging’(VIII) on the Medvedev–Sponheuer–Karnik scale]. The correlationbetween the historical earthquake data set and the homogenites identified ina core isolated from local stream inputs, allows interpretation of all similardeposits as earthquake related. This work extends the earthquake chronicleof the last 6600 years in this area with a total of 29 events recorded. Theearly Holocene sedimentary record is disturbed by a seismic event(6617 94 cal yr BP) that reworked previously deposited sediment and ledto a thick sediment deposit identified in the seismic survey. The periodbetween 3500 cal yr BP and 2000 cal yr BP is characterized by a major destabilizationin the watershed by human activities that led to increases in erosionand sedimentation rates. This change increased the lake’s sensitivity torecording an earthquake (earthquake-sensitivity threshold index) with theoccurrence of 72 turbidite-type deposits over this period. The high turbiditefrequency identified could be the consequence of this change in lake earthquakesensitivity and thus these turbidites could be triggered by earthquakeshaking, as other origins are discarded. This study illustrates why it is notacceptable to propose a return period for seismic activity recorded in lakesediment if the sedimentation rate varies significantly.
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Submitted on : Wednesday, July 25, 2018 - 10:46:03 AM
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  • HAL Id : hal-01848777, version 1

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William Rapuc, Pierre Sabatier, Maja Andric, Christian Crouzet, Fabien Arnaud, et al.. 6600 years of earthquake record in the Julian Alps (Lake Bohinj, Slovenia). IPA-IAL Stockholm 2018 conference, Jun 2018, Stockholm, Sweden. ⟨hal-01848777⟩

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