- © 2008 by the Seismological Society of America
Earthquakes in Britain are usually minor with respect to damage. However, the Folkestone earthquake (ML 4.3, Mw 4.0), which occurred on the southeastern coast of England (Figure 1) on 28 April 2007 at 07:18 UTC (08:18 BST) caused significant damage. One person was injured by falling masonry, and the Shepway District Council invoked emergency procedures to deal with the effects of the earthquake. This is the first time that emergency procedures have been invoked for a British earthquake. Approximately 60,000 homes lost power for 85 minutes due to tripping of two high-voltage transformers.
The epicenter of the earthquake, latitude 51.102°N and longitude 1.169°E (Ottemöller et al. forthcoming), locates very close to Folkestone (Figures 1A–C). Ottemöller et al. (forthcoming) determine a depth of around 6 ± 3 km from United Kingdom (UK) and European short-period and broadband data. The focal mechanism, shown in Figure 1C, indicates normal faulting with a significant component of strike-slip on either a north-northwest to south-southeast trending or east-northeast to west-southwest trending plane (Ottemöller et al. forthcoming). The earthquake was followed by nine after-shocks (ML 1.0–1.8), which occurred up to 5 May 2007. None of these were felt.
A compendium of observations from the Folkestone earthquake is presented here. This includes analysis of the first “strong-motion” record from a British earthquake, a description of the damage, an investigation of how the distribution of damage may relate to the distribution of unconsolidated deposits, and the results of the macroseismic survey for the earthquake. Assignment of maximum intensity, and its spatial extent, provoked a lively debate among the authors, which is also documented here.
SEISMICITY OF THE FOLKESTONE AREA
There is a distinct east-west divide in terms of the distribution of seismicity in the UK. Most activity is concentrated in western Scotland, northwestern England, Wales, the Midlands and Cornwall (Figure 1A …