Melton Mowbray Earthquake Macroseismic

The earthquake of the 28 October 2001 occurred at 16:25 local time, with an epicentre 4 km east of Long Clawson, 9 km north of Melton Mowbray. The instrumental magnitude was determined at 4.1 ML, and initial reports suggested that the earthquake had been felt throughout Lincolnshire, Leicestershire, Warwickshire, Yorkshire, Shropshire and Nottinghamshire. A questionnaire survey was launched using the usual BGS methodology as described in Musson and Henni (1999). Questionnaires were placed in the following newspapers giving extensive coverage over the felt area:

Additionally, an electronic questionnaire was made available from the BGS ‘Earthquakes’ web site, promoted on the main BGS web site, the BBC news site and, also, in the above newspapers as part of editorials and with the web address given at the bottom of the published questionnaires. Approximately 1900 emailed responses were received.

The total number of usable replies received was approximately 6500, of which 3267 were used, 3134 of which were positive and 133 were negative. From the larger settlements sufficient replies were received to allow the assignment of intensities, but many small hamlets and isolated farms contributed single questionnaires, from which it is more difficult to establish reliable values, and which were given ‘F’ to denote ‘felt’. The total number of places from which replies were received was 482 (after amalgamating replies from very close settlements less than 2 km apart). The large number of replies received is partly a function of the strength of shaking in the most affected area, but is also influenced by the fact that the shock occurred in the heart of the English Midlands, in a quite well-populated area. Of the approximate 3200 replies not used, these mainly covered the LE and NG postcode areas. An overwhelming number of responses were received from these areas due to their proximity to the earthquake's epicentre and being highly populated. Therefore, it was decided that the results for these areas obtained from the preliminary macroseismic survey would have remained relatively unchanged. A preliminary macroseismic map was produced and put online by mid-December 2001.

The highest intensity experienced was 5 EMS (European Macroseismic Scale), which was observed quite widely over an area around and south of Newark-on-Trent, and east of Loughborough. In this area there was a certain amount of mingling of places where the intensity was 4 and where it was 5, and borderline cases. Intensity 5 was generally distinguished by an increased number of reports of objects thrown down, a greater level of alarm, and a greater tendency for the shaking to be described as strong. Objects thrown down included a large model boat falling off a shelf, books thrown from shelves, candlesticks falling from a windowsill, a picture thrown off a wall, small ornaments and children's toys being knocked over, and so on. In a number of cases alarms were set off, and in one case a traveller on the Loughborough train reported passengers screaming simultaneously as the train momentarily lurched on the railtracks, evidently denoting of quite strong shaking. In some places (e.g. Belvoir, Leicestershire) the shock was perceptible out of doors. There were a few reports of people running out in fright, and many reports of people going outside to investigate. Animals (pets, cage birds, horses) were alarmed in many cases. A very few reports mentioned people falling off their chair or over-balancing. A very common report was the creaking of house joists.

A number of reports of extremely minor damage were received, not all of which can be authenticated (it is common that after an earthquake householders believe their pre-existing cracks have widened, but unless measurements before and after have been made, this could be put down to imagination much of the time). The following reports more or less sum up all the damage:

Coventry South East - "… cement pointing fell out of roof - not there day before …"

Carlton Scoop - "…slight cracks in wall plaster surrounding door and window frames…"

Keyworth - "… long stepped cracks have appeared in the mortar in a wall … rendering bowed away from bricks on a neighbour's wall… a little mortar and brickwork loosened under a window … a piece of cement about 6" long fell off the gable end of the house …"

Long Eaton - "… a chimney stack on some old terraced houses nearby collapsed …"

The most distant reports were from the following places: in the west, the earthquake was felt near Chester. In the east, the earthquake was reported from Great Ryburgh, 5 km south east of Fakenham, Norfolk. In the north, the limit of observation was marked by Knaresborough. In the south, the shock was felt as far as Bedford, with also a very distant observation from Salisbury. The total felt area is over 51,300 sq km.

The distribution of intensity points is shown in Figure 1 with an inset map of the epicentral area shown as Figure 2 . Isoseismal lines have been drawn for intensity 5, 4, 3 and 2 EMS, as shown in Figure 3. As is usual, not many places can be assigned an unqualified intensity 2 observation, but the scarcity of reports from heavily populated areas such as South Yorkshire and the Thames Valley indicates that the intensity was probably generally 2 EMS in these areas. The isoseismals show an elongation in the NE-SW azimuth, especially those for intensity 3 and 4. The areas within each isoseismal (rounded to the nearest 100 sq km) were as follows:

Isoseismal	Area (sq km)
2	57,000
3	25,000
4	8,000
5	1,000

Macroseismic parameters were calculated according to the procedures described in Musson (1996). The magnitude was consistently calculated to be 4.1 ML from either the 3 or 4 isoseismal. The macroseismic depth is around 12-13 km. These values (for both magnitude and depth) are within the error margins of the instrumental determinations, showing that both methods of calculation are in good agreement.

Musson, R.M.W., 1996. Determination of parameters for historical British earthquakes, Annali di Geofisica, vol 39, no 5, pp 1041-1048.

Musson, R.M.W. and Henni, P.H.O., 1999. From questionnaires to intensities – Assessing free-form macroseismic data in the UK, Phys. Chem. Earth (A), vol 24 no 6, pp 51

Melton Mowbray Earthquake Survey Results