The 4.2 ML Warwick earthquake of 23 September 2000

On 23 September 2000, many residents of Warwick were awoken by an earthquake of local magnitude (ML) 4.2, at 05:25 am (04:25 UTC). It was felt up to a maximum intensity of about 5 on the European Macroseismic Scale (EMS) (Grünthal, 1998) in Warwick, Leamington Spa and Stratford-Upon-Avon, close to the epicentre, and was felt over a total area of about 50,000 km2 (Isoseismal 2). The earthquake was located about 2 km west of the city of Warwick at a depth of 14.4 km. This is the largest earthquake to occur in the UK since the 5.1 ML Bishops Castle earthquake of 2 April 1990, which was located near the Welsh border, about 100 km WNW of Warwick. The well-constrained focal mechanism for the Warwick earthquake indicates almost pure normal faulting on a NW-striking fault plane, either dipping moderately to the NE or to the SW. The T-axis is horizontal and strikes NESW and the P-axis is vertical. The location and orientation of one of the possible fault planes is consistent with the strike and dip of the SW-dipping Whitnash fault, which lies 5 km east of the earthquake epicentre. However, seismic lines reveal many similarly oriented buried faults in the region, and so the earthquake could equally have occurred on a buried fault parallel to the Whitnash fault.