Magnitude 2.9 earthquake Winchester, Hampshire, UK

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1 Magnitude 2.9 earthquake A magnitude 2.9 earthquake occurred close to the city of Winchester, in Hampshire, on 27th April The earthquake occurred at a depth of 3 km (~2 miles). Shaking was felt by people living in surrounding towns and villages. The earthquake was felt up to 60 km away from the epicentre. The UK typically experiences around 26 M earthquakes every year.

2 Where was the earthquake felt? Most shaking was felt within a km radius of the earthquake s epicentre. The furthest felt reports came from Southampton (20 km to the south), Newbury (30 km to the north) and Bournemouth (60 km to the southwest). The strongest recorded felt intensity was Intensity III (slight shaking). I. Instrumental II. Weak III. Slight IV. Moderate V. Rather Strong VI. Strong Not felt by many people unless in favourable conditions. Felt only by a few people at best, especially on the upper floors of buildings. Delicately suspended objects may swing. Felt quite noticeably by people indoors, especially on the upper floors of buildings. Many to do not recognise it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a truck. Duration estimated. Felt indoors by many people, outdoors by a few people during the day. At night, some awakened. Felt outside by most, may not be felt by some people in non-favourable conditions. Dishes and windows may break and large bells will ring. Vibrations like train passing close to house. Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken; books fall off shelves; some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight. VII. Very Strong VIII. Destructive IX. Violent Difficult to stand; furniture broken; damage negligible in building of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Noticed by people driving motor cars. Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture moved. General panic; damage considerable in poorly designed structures, well designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. X. Intense Some well build wooden structures destroyed; most masonry and frame structures destroyed with foundation. Rails bent. XI. Extreme XII. Cataclysmic Few, if any masonry structures remain standing. Bridges destroyed. Rails bent greatly. Total destruction everything is destroyed. Lines of sight and level distorted. Objects thrown into the air. The ground moves in waves or ripples. Large amounts of rock move position. Landscape altered, or leveled by several meters. In some cases, even the routes of rivers are changed. Location of shaking reports (image courtesy BGS) Modified Mercalli Intensity Scale

3 Past earthquakes in the region Small earthquakes in the UK are not unusual, although the south and south- east areas of the UK are historically some of the country s less seismically acuve regions. M3.0 earthquake, July 1982 The largest recorded earthquake in this region of was a magnitude 3.0 event in 1982, that occurred 30 km to the northeast of the January 2015 earthquake Historic seismicity (since 1970) recorded in the region. The earthquake epicentre is indicated by the red star. Earthquake locations from the BGS catalogue.

4 What caused this earthquake to occur? The UK does not lie on an acuve tectonic plate boundary (one of its nearest plate boundaries is the Mid- AtlanUc Ridge located some 2000 km to the west). However, the stresses from these plate boundaries can be transferred to the middle of the plates. This stress is someumes released along pre- exisung faults within the crust of the Eurasian tectonic plate. Earthquakes in the UK can also be caused by gradual upli[ of the crust since the last ice age. Many of the UK s ancient faults are not seen on the surface these are known as blind faults. The lack of large earthquakes in the UK also means we are unable to idenufy every fault in the UK that could cause an earthquake. Mid-Atlantic Ridge N. American plate Eurasian plate Alpine Pyrenees mountain belt Africa Eurasia collision zone Map of major tectonic boundaries in Western Europe

5 Recordings of the earthquake from the British Geological Survey seismometer network By finding the difference in arrival times between the P- and S-wave arrivals at different seismic stations, we can calculate the distance of the earthquake from each receiver (circles). If we do this for several stations (triangles), we can determine the approximate epicentre of the earthquake (red star) by finding the common intersection point of these circles.

6 Find out more BGS webpage for this earthquake html#page=summary BGS (British Geological Survey) seismology and earthquakes frequently asked questions BBC News article on this earthquake IRIS (Incorporated Research Institutions for Seismology) learning about earthquakes UK School Seismology Project classroom activities, videos and support documents USGS (United States Geological Survey) FAQs, glossary, posters, animations EMSC (European Mediterranean Seismological Centre)