Benjamin Bellwald

Modeling potential paleoearthquakes based on results from subaquatic mass movements in Western Norway

During my PhD as a Quaternary geologist, I did quite some work on turbidite paleoseimology in west- and mid-Norway, with some very interesting outcomings. I was further involved in a study in the Alps where we have been modeling the magnitudes and epicenters of potential paleoearthquakes in the last 10000 years. In the upcoming seminar, I would like to introduce my results and discuss the potential for modeling paleoearthquake magnitudes and epicenters offshore Norway and along the western Norwegian coast.

Benjamin Bellwald

Please find attached the abstract covering part of the seminar (AGU 2016).

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Holocene Mass Transport Deposits in Western Norwegian fjords and lakes revealing prehistoric earthquake history of Scandinavia

Bellwald, B.¹, Hjelstuen, B.O.¹, Sejrup, H.P.¹, Stokowy, T.², Kuvås, J.¹

¹Department of Earth Science, University of Bergen, Norway
²Department of Clinical Science, University of Bergen, Norway

The sensitivity of fjord sediments to seismic shaking makes fjord systems appropriate study sites when extending regional earthquake catalogs back in time and when estimating recurrence rates of prehistoric earthquakes in intraplate settings. In this study we compiled evidence of 140 postglacial mass movement events and their associated mass transport deposits (MTDs) from previously analyzed and new sediment cores and high-resolution seismic profiles from 22 fjord systems and six lakes in Western Norway. Evaluation of trigger mechanisms make us infer that most of these mass movement events were initiated by regional earthquakes, and that both climate-related processes and tsunamis most likely can be excluded as trigger mechanism for most of the events.  A total of 33 individual earthquakes has been identified, which most likely outbalance the historically recorded events in magnitude, thus indicating magnitudes >6. Frequency plots of MTDs suggest high seismic activity in the early Holocene (11000-9700 cal. yrs BP), followed by seismic quiescence in the mid-Holocene before a seismic reactivation took place at ~4000 cal. yrs BP. Coevally-triggered MTDs at ~8100 cal. yrs BP are identified in all the archives, and are correlating with the age of the offshore Storegga slide. We estimate earthquake recurrence rates of 1/80 years directly after the last deglaciation of Western Norway (12800-11600 ca. yrs BP), 1/200 years for the early Holocene and 1/300 years for the last 4000 years. Our compilation suggests that the mid-Holocene is characterized by low seismic activity, suggesting recurrence rates of 1/1300 years. Comparisons of the Western Norwegian dataset with paleoseimologic studies of other previously glaciated intraplate settings indicate that both Scandinavia and the Alps show similar trends as Western Norway, whereas Eastern Canada is not correlating with the paleoseismologic trend of this study, which could be explained by different deglaciation histories.