Magnitude 4.2 earthquake Ramsgate, Kent, UK

1. Magnitude 4.2 earthquake Ramsgate, Kent, UK Friday, 22 May, 2015 at 01:52:19 UTC A magnitude 4.2 earthquake occurred near Ramsgate, Kent, in southeast England 22nd May 2015. The earthquakes occurred at a depth of 15 km (~9 mile). Shaking was felt by people living in surrounding towns and villages. The strongest ground shaking was felt up to around 25 km away from the epicentre. The UK typically experiences around 3 earthquakes of this size every year.

2. Magnitude 4.2 earthquake Ramsgate, Kent, UK Friday, 22 May, 2015 at 01:52:19 UTC Where was the earthquake felt? Most shaking was felt within a 20 km radius of the earthquake’s epicentre. Farther afiled, shaking was reported in Faversham, Chatham, Basildon and Southend-on-Sea areas. The most distant reports have been received from Norwich, North Walsham and Cromer. The strongest recorded felt intensity was Intensity IV(moderate shaking). Location of shaking reports (image courtesy BGS) Modified Mercalli Intensity Scale

3. Magnitude 4.2 earthquake Ramsgate, Kent, UK Friday, 22 May, 2015 at 01:52:19 UTC Past earthquakes in the region Small-moderate sized earthquakes in the UK are not unusual. South-east England has experienced moderate earthquakes in the past. In April 2007, a magnitude 4.3 earthquake occurred just 25 km to the southwest of the May 2015 event, close to the town of Folkstone. Historical evidence also suggests magnitude 5 earthquakes in 1382 and 1580 struck the region. Historic seismicity (since 1970)recorded in the region. The earthquake epicentre is indicated by the red star. Earthquake locations from the BGS catalogue.

4. Magnitude 4.2 earthquake Ramsgate, Kent, UK Friday, 22 May, 2015 at 01:52:19 UTC What caused this earthquake to occur? The UK does not lie on an active tectonic plate boundary (one of its nearest plate boundaries is the Mid-Atlantic 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 sometimes released along pre-existing faults within the crust of the Eurasian tectonic plate. Earthquakes in the UK can also be caused by gradual uplift 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 identify every fault in the UK that could cause an earthquake. N. American plate Eurasian plate Alpine – Pyrenees mountain belt Mid-Atlantic Ridge Africa – Eurasia collision zone Map of major tectonic boundaries in Western Europe

5. Magnitude 4.2 earthquake Ramsgate, Kent, UK Friday, 22 May, 2015 at 01:52:19 UTC What was the mechanism of this earthquake? Fortunately, due to the rather large size of this event compared to most UK earthquakes, faulting mechanisms are available that are based on seismic data. Although there are some discrepancies between the ‘beach ball’ patterns, they seem to indicate a mechanism of reverse faulting with a slightly oblique (horizontal) component. Reverse faulting is where the hanging wall moves up relative to the foot wall block. Hanging wall Foot wall

6. Magnitude 4.2 earthquake Ramsgate, Kent, UK Friday, 22 May, 2015 at 01:52:19 UTC 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.

7. Magnitude 4.2 earthquake Ramsgate, Kent, UK Friday, 22 May, 2015 at 01:52:19 UTC Find out more … • BGS webpage for this earthquake http://www.earthquakes.bgs.ac.uk/earthquakes/recent_events/20150522015216.html#page=summary • BGS (British Geological Survey) – seismology and earthquakes – frequently asked questions http://www.earthquakes.bgs.ac.uk/education/faqs/faq_index.html • BBC News article on this earthquake http://www.bbc.co.uk/news/uk-england-32840579 • IRIS (Incorporated Research Institutions for Seismology) – learning about earthquakes http://www.iris.edu/hq/programs/education_and_outreach/students • UK School Seismology Project – classroom activities, videos and support documents http://www.bgs.ac.uk/schoolseismology/home.html • USGS (United States Geological Survey) – FAQs, glossary, posters, animations http://earthquake.usgs.gov/learn/ • EMSC (European Mediterranean Seismological Centre) http://www.emsc-csem.org/