Liquefaction Structures from a High-Magnitude Paleoseismic Event at about 12,400 C14-Years BP in Southern Sweden

Nils-Axel Mörner

doi:10.4236/ojer.2017.64014

Abstract

The Swedish catalogue of paleoseismic events includes 64 separate events. The seismic activity was especially high, in magnitude and frequency, in the Late Glacial with peak rates of glacial isostatic uplift. At about 12,400 C14-years BP (14,600 cal?yrs BP), there was a very strong event on the Swedish west coast. The magnitude was estimated at M > 8. It was linked to intensive liquefaction and a major tsunami event. In this paper we describe sedimentological structures of liquefaction, ground shaking and tsunami wave actions from the Hunnestad gravel pits, to the east of the city of Varberg on the Swedish West Coast. The liquefaction structures documented offer impressive and educational insight into the process of liquefaction at high-magnitude earthquakes.

Highlights

Sweden has turned out to have been an area of high seismicity in magnitudes as well as in frequency [1] [2]
In this paper we describe sedimentological structures of liquefaction, ground shaking and tsunami wave actions from the Hunnestad gravel pits, to the east of the city of Varberg on the Swedish West Coast
In the Båstad region, huge earth slides have been recorded along the Mt Hallandsåsen fault zone. These slides go down to the 12,400 C14-yrs BP shoreline [9] and were interpreted as co-incidental to this shore position. This implies that they are of the same age as the liquefaction structure and tsunamite recorded in Hunnestad gravel pit

Summary

Introduction

Sweden has turned out to have been an area of high seismicity in magnitudes as well as in frequency [1] [2]. This paper will focus on the deformational structures of the 12,400 C14-years BP (14,600 cal∙yrs BP) paleoseismic event [2] observed in gravel pits at Hunnestad located 9 km east of the city of Varberg This site was the target for a paleoseismological excursion in 2008 [8] and a seismological excursion in 2013 [9] because of its excellent records of liquefaction structures, ground-shaking deformations and tsunami effects [2] [9]

Previous Work

Structures Observed

Additional Seismotectonic Structures

Possible Magnetic Grain Rotation

Conclusions