The use of varved clay chronology for dating paleoseismic events: the Erstavik record in the Stockholm area, south Sweden |
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| Authors: | Per-Einar Trften |
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| Institution: | Paleogeophysics and Geodynamics, Kräftriket 24, Stockholm University, 10691 Stockholm, Sweden |
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| Abstract: | Geological structures suggest that the Fennoscandian Shield was subjected to a higher seismicity at the end of the last glaciation than today. This article demonstrates the use of varved clay chronology for dating paleoseismic events. It is argued that the deposited annually layered glacial varves were sensitive to past ground movements. In the Stockholm area, the Erstavik varved clay chronology suggests four paleoseismic events: a first (I) dating from varve year 10,473 to 10,468 BP; a second (II) 10,451 to 10,445 BP; a third (III) 10,429 to 10,425 BP; and a fourth (IV) 10,409 to 10,404 BP. In De Geer's ‘old' (1940) chronology the first (I) dating corresponds with ?1117 to ?1112, the second (II) with ?1095 to ?1089, the third (III) with ?1073 to ?1069, and the fourth (IV) with ?1053 to ?1048. The most pronounced event was the one at around varve year 10,429 BP (varve ?1073 in De Geer's ‘old' chronology). The recurrence time of about 20 years suggests a totally different seismic regime at the time of deglaciation than what exists today. It coincided with the period of maximum isostatic uplift. The complexity of the varved clay response to seismic events is also discussed. |
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| Keywords: | Sweden varved clay chronology paleoseismic events earthquakes clay deglaciation |
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