Last night I was suddenly awakened by a jolt. I had just enough time to say to my better half “don’t panic – earthquake” before the surface waves hit. “How did you know?” she asked. “I felt the body waves first”* I replied. I was also able to assure her that it was a regional earthquake not a local one (our local events are much shorter and sharper) before turning the radio on to listen to the news. Five live’s up all night programme must have had the largest audience ever.The recording of the earthquake from Keele University is below:
The record is clipped in the middle as the seismometer was designed for fainter, more distant earthquakes.
The earthquake, about magnitude 5.2 according to the BGS, was centred on Market Rasen in Lincolnshire. It is the largest UK ‘quake since the Lleyn Peninsula earthquake of July 1984. The largest recorded UK earthquake , magnitude 6.1, was under the Dogger Bank, off Great Yarmouth in June 1931.
*Don’t believe this malarky about animals predicting earthquakes, they feel the smaller body waves first like I did, where has most humans are more likely to notice the later, larger surface waves.
Update:
As to the cause of this event, I’d rule out mine collapse as UK mining events rarely get above magnitude 3 and at magnitude 5.2 this is over a thousand times more powerful.
The UK is being compressed from the north-west (the mid-Atlantic Ridge) and the south-east (tail end of the Alpine orogeny). There are also vertical forces related to glacio-isostatic rebound (uplift) from the last ice age but most UK earthquakes are strike-slip with NW-SE compression.
The UK has a long and complex geological history. At England’s heart is a solid triangular Precambrian core – the Midlands Microcraton (with its upper apex somewhere near Manchester). Along the boundaries of the Midlands microcraton are a number of faults that have long and complex histories and tend to get reactivated by modern geological stresses.
To the west is the NE-SW trending Church Stretton / Pontisford Fault system (e.g. Bishop’s Castle 1990 earthquake), to the east is a NW-SE trending system (e.g. Market Rasen 2008, Dogger Bank Earthquake 1931). This triangle is also bisected by the N-S Malvern Line (e.g. Dudley Earthquake 2002)
So large earthquakes in the UK tend to be associated with lines of fundamental weaknesses in the English crust dating back to the Precambrian.
