I had not been a member of the Black Country Geological Society (BCGS) for long and was enjoying my first Dudley rock and fossil fair on the weekend of the 21st / 22nd September 2002. However, what happened as Sunday night passed into Monday morning made the weekend most memorable.
During the night I sensed a deep rumbling noise and was jolted awake to the sound of falling plaster behind the cavity wall of the flat, I was renting at the time in Tettenhall, Wolverhampton. At first I thought the next door boiler had blown up, but I soon realised that in actual fact I had probably just witnessed my third ‘earthquake’. Next morning the radio confirmed my suspicions that indeed an earthquake had struck the Black Country.
Occurring at 23:53 Universal Time Coordinated (UTC), on Sunday 22nd September 2002 (or 00:53 local time, Monday 23rd September 2002) the earthquake measured 4.7 magnitude. A small 2.7 magnitude aftershock was also felt locally throughout Dudley and in Birmingham on 23 September at 03:32 UTC (04:32 local time).
During the earthquake seismograph stations belonging to the British Geological Survey (BGS) and scattered throughout the UK gathered data. This showed that the epicentre was at mid-crustal depth (approximately 14km down) and at approximately 1km west of the Western Boundary Fault. On the ground surface this placed the epicentre approximately 3km northwest of Dudley town centre, at the junction of High Arcal and Himley Road.
The Western Boundary Fault is a major north–south striking fault zone, which has downthrown Triassic rocks to the west, against older Upper Carboniferous rocks, belonging to the South Staffordshire Coalfield, to the east. The fault zone stretches from the Bristol Channel to Lancashire passing to the west of Dudley and to the east of Stourbridge.
The BGS data indicated that the source of the earthquake was due to strike-slip movements along the Western Boundary Fault zone. These movements were probably a response to regional stresses built up through dominant northwest compressional forces from the spreading of the Mid-Atlantic Ridge. Earthquakes of such magnitude are not uncommon in the UK, which experiences around 300 earthquakes every year, with one around 5.0 magnitude occurring approximately every ten years.
Before the Dudley earthquake I had experienced two others, which included the Llyn Peninsula earthquake of 1984 and the Bishops Castle earthquake of 1990, both of which measured 5.4 and 5.1 magnitude, respectively.
The next day and over the following weeks the Dudley earthquake was on the lips of most people and the brunt of several humorous e-mails.
Many BGS accounts collected after the event spoke of objects, such as CDs, books, plant pots, candlesticks, picture frames, mirrors and clocks, being thrown about. Other accounts spoke of violently shaking furniture, children and parents being thrown out of bed or off chairs. There were no recorded major injuries and only three minor ones involving banged heads and a broken toe. Minor structural damage was also reported to buildings including cracks in walls, plasterwork, mortar and window sills and dislodged roof tiles.
The event was felt mostly across the West Midlands, but also over an area of 260,000 square kilometres (100,387 square miles), reaching as far as Wales and Southern Ireland, Liverpool, Carlisle, Durham, Yorkshire, Wiltshire, Cornwall, London and The Netherlands.
Next time we will investigate the personal stories of local people who may or may not have experienced the quake.
By Andrew Harrison
BCGS Field Secretary