Palaeoseismicity studies on end-Pleistocene and Holocene lake deposits around Basle, Switzerland

Abstract

Summary Palaeoseismological investigations in the lakes of Seewen and Bergsee in the Basle region, Switzerland and southern Germany, revealed characteristic event horizons in an otherwise uniform background sedimentary record. Dated and correlated based on radiocarbon ages, palynostratigraphy and sedimentation rates, some of these event horizons show soft‐sediment deformation features and fractures that can be interpretated as being the result of earthquake shaking. Two of the event horizons with clear indications for earthquake deformation were detected in both lakes, showing approximately the same age as indicated by radiocarbon dating. A third event horizon with fractures of apparent seismogenic origin, was detected at several drill sites in only one lake (Bergsee). Three further event horizons, two in the Bergsee and one in Lake Seewen, are of uncertain origin, though they show some characteristics that could well be caused by earthquakes. Based on the observations in both lakes, five events were detected of which three are most probably related to earthquakes which occurred between 180 BC–1160 BC, 8260 BC–9040 BC and 10 720 BC–11 200 BC, respectively. The Basle region is well known for the strongest historical earthquake north of the Alps, the AD 1356 Basle earthquake. Based on combined historical and palaeoseismological data, it has been inferred that earthquakes with size comparable to the AD 1356 Basle earthquake have occurred several times within the last 12 000 yr and that the recurrence time for such strong earthquakes are in the range of 1500–3000 yr.

Earthquake-induced deformation structures in lake deposits: A Late Pleistocene to Holocene paleoseismic record for Central Switzerland

“…Earthquake-induced faulting has been observed by several authors (Seilacher et al 1969;Ringrose 1989;Becker et al 2002). It occurs within more consolidated lake sediments stiff enough to show brittle failure, such as buried sediments in a few dm depth, fast consolidating carbonate-rich mud or jelly-like gyttja (e.g.…”

“…It occurs within more consolidated lake sediments stiff enough to show brittle failure, such as buried sediments in a few dm depth, fast consolidating carbonate-rich mud or jelly-like gyttja (e.g. Becker et al 2002). Soft-sediment deformations like load casts and pseudonodules are generated by cyclic loading during earthquake shaking and subsequent liquefaction and reorganization of a gravitational unstable succession of layered lake sediments (Allen, 1982;Anketell, 1970).…”

“…As the northern study area can be influenced by large earthquakes in the Basel region (Mayer-Rosa & Cadiot 1979), we include also paleoseismic data from on-fault surface mapping and lake deposits in the Basel area (Becker et al 2002(Becker et al , 2005Ferry et al 2005). In this region a five-stage scale of probability of earthquake-triggering ranging from very high to very low is proposed for the different events.…”

“…Paleoseismic studies have been successfully carried out in outcrops of lacustrine sediments (for example Sims 1973 and1975;Marco et al 1996;Ringrose 1989;Rodriguez-Pascua et al 2000;Hibsch et al 1997). In modern lakes, investigations are based on high-resolution seismic data (Shilts & Clague 1992;Chapron et al 1999) and more rarely on sediment cores (Doig 1986;Becker et al 2002, Migowski et al 2004.…”

Origins of Soft-Sediment Deformation Structures from the Batang Paleodammed Lakes in the Upper Jinsha River, SE Tibetan Plateau

“…Soft sediment deformation structures (SSDS) are features occurring in unconsolidated sediment. SSD can be induced by many natural processes, including gravity acting, overloading, unequal loading, wave-induced cyclical or impulsive stresses, shear by aqueous or other currents, storms, sudden changes in groundwater level, or earthquakes [2][3][4][5][6][7][8][9]. SSD features are known from a wide variety of depositional environments, both terrestrial: fluvial, aelolian or volcanic [9][10][11], or marine: shore, turbiditic, subglacial [12][13][14], but they are particularly well-reported from lacustrine depositional environments [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”