A 2500 year paleoseismic record of the Húsavík-Flatey Fault inferred from the sediments of Botnsvatn Lake (North Iceland)

Avşar, Ulaş
Jonsson, Sigurjon
Geirsdttir, Aslaug
Thordarson, Thor
The Mid-Atlantic-Ridge formed by the divergent movement of the North American and Eurasian plates is offset towards east in Iceland, which results in a dextral transform zone just north of the island. The strain accommodated along this dextral transform zone is released mainly by the Húsavík-Flatey Fault (HFF) and Grímsey Oblique Rift (GOR) in magnitude 6-7 earthquakes. However, historical accounts of past major earthquakes are inaccurate and incomplete and primarily provide information for only the last 300 years. The GOR does not allow paleoseismological trenching since it is completely offshore, but a ~20 km-long southeastern part of the HFF is onshore. Still, the number of sites that are favorable for paleoseismic trenching is limited. We have therefore carried out lacustrine paleoseismological investigations in Botnsvatn Lake, which is located in a pull-apart basin of the HFF, that may provide crucial information about the past seismic activity of the HFF. We collected five sediment cores from the lake to investigate possible sedimentary traces of past earthquakes of the HFF. We detected a total of eleven earthquake-triggered ice-rafted debris deposits (IRD) during the last 1800 years of the Botnsvatn record, four of which are temporally correlated to the known historical earthquakes. On the other hand, the IRDs become highly frequent (40-50 years apart) during the period between 1800 BP and 2400 BP, which corresponds to significantly warmer climatic conditions compared to the rest of the record. Hence we believe that the oldest 600 years of the Botnsvatn record probably contains non-seismic origin IRDs, which prevents revealing paleoseismic information. According to the last 1800 years of the record, the recurrence interval of the earthquake-triggered IRDs is 140±35 years.
Citation Formats
U. Avşar, S. Jonsson, A. Geirsdttir, and T. Thordarson, “A 2500 year paleoseismic record of the Húsavík-Flatey Fault inferred from the sediments of Botnsvatn Lake (North Iceland),” presented at the International Workshop on Earthquakes in North Iceland, (31 Mayıs - 03 Haziran 2016), Húsavík, North Iceland, 2016, Accessed: 00, 2021. [Online]. Available: https://hdl.handle.net/11511/75173.