The use of varved clay chronology for dating paleoseismic events: the Erstavik record in the Stockholm area, south Sweden

Geological structures suggest that the Fennoscandian Shield was subjected t o a higher seismicity at the end of the last glaciation than today. This ar ticle demonstrates the use of varved clay chronology for dating paleoseismi c events. It is argued that the deposited annually layered, glacial varves were sensitive to past ground movements. In the Stockholm area, the Erstavi k varved clay chronology suggests four paleoseismic events: a first (I) dat ing 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 totall y different seismic regime at the time of deglaciation than what exists tod ay. It coincided with the period of maximum isostatic uplift. The complexit y of the varved clay response to seismic events is also discussed. (C) 2000 Elsevier Science B.V, All rights reserved.