The macroseismic survey of the 27 February 2008 Market Rasen earthquake

Immediately following the occurrence of the Market Rasen earthquake on 27 February 2008 (5.2 ML, 4.5 Mw), an online questionnaire was opened on the BGS web site to collect felt reports. In addition, questionnaire data were collected automatically by USGS as part of the “Did You Feel It?” (DYFI) programme (Wald et al. 1999), and also by EMSC as part of its European monitoring. Some additional data were also gathered by agencies on the fringe of the felt area, notably ROB in Brussels, and DIAS in Dublin. This report summarises the findings

UK seismic hazard assessments for strategic facilities: a short history

The UK is a country with only low to moderate seismicity, and the long intervals between significant earthquakes in Britain results in people forgetting they occur. As a result, seismic hazard was only thought of for the first time in Britain in 1976. For ordinary construction, it is true that seismic hazard can be considered insignificant in the UK, but for strategic facilities, especially those with a high consequence of failure, such as nuclear power plants (NPPs), seismic hazard is important. This paper traces the history of such studies, with emphasis on those for the nuclear industry. The UK seismological community saw major investment from the nuclear industry after 1980. There was a cessation of NPP construction in Britain after 1995, but in recent years steps have been taken towards a resumption of NPP building, which will see a need for new seismic hazard studies

Eurocode 8 seismic hazard zoning maps for the UK

The earliest attempt to map seismic activity, and hence hazard, in the UK was made by O’Reilly (1884), and the (perhaps better known) map of Ballore (1896) does show a division of the British Isles into distinct zones. However, at this early date, hazard could only be expressed in terms of simple distinctions between levels of frequency of earthquake occurrence, usually subjectively assessed, and not as ground motion, which is how seismic hazard is expressed today. The first true hazard map (in the modern understanding of the word) for Great Britain was thus that of Lilwall (1976), which expressed hazard in terms of intensity with a 200-year return period, using an extreme-value technique based on the work of Milne and Davenport (1969). A subsequent study by Ove Arup (1993) used true probabilistic seismic hazard assessment (PSHA) to calculate hazard at selected points in the UK, but these points were too few to be contoured. The first contour maps of hazard on the UK territory produced using PSHA were therefore those of Musson and Winter (1996), prepared for the then Department of Trade and Industry (DTI). The UK was, of course, also covered in two major international seismic hazard mapping projects, the Global Seismic Hazard Assessment Programme (GSHAP) and SESAME (Grünthal et al 1996, Jiménez et al 2001). Both these studies used a common source model for the UK, which was derived from a simplified version of the Musson and Winter (1996) model. The results are in conformity with those of Musson and Winter (1996), although different ground motion models were used. An updated hazard map for the UK was published by Jackson (2004), but only for intensity. This is described in Musson (2004a). A specific zoning map for the UK was produced for a report on dam safety for the UK, and has since been widely circulated (Halcrow 1990). This map assesses hazard in a completely subjective way into high, medium and low classes, which are to be understood as entirely relative terms. Despite its informal nature, it proved to be a reasonable depiction of relative hazard levels when compared to later quantitative maps

Macroseismic estimation of earthquake parameters

The derivation of earthquake parameters from macroseismic (intensity) data is an inveterate problem. Yet for earthquakes in the pre-instrumental period (roughly, before 1900) intensity data points (IDPs) are the only form of numerical data available to the seismologist. In order to produce a numerate, consistent catalogue of historical earthquakes that can be combined in a compatible way with modern instrumental data requires some system for estimating what instrumental parameters would have been obtained had seismometers been in operation. Successive catalogue authors have had to deal with this problem as they saw fit; but as most earthquake catalogues have been compiled as national initiatives, one finds that one type of method has been used in one country, something else in another, and so on. This leads to obvious problems of inconsistency when it comes to studies that need to transcend national borders. A major aim of the NA-4 module of the European Framework project NERIES is to produce a catalogue of European earthquakes before 1900 in which there is the greatest possible level of internal consistency in the determination of earthquake parameters. This means the use of uniform procedures for determining earthquake parameters over the whole of Europe. Finding suitable procedures that can be used for this is a difficult task, and is the subject of this report. The parameters to be determined are essentially the location and the size of each earthquake. Precisely how one defines location in this context is arguable – one speaks of the “macroseismic epicentre”, but this is not necessarily exactly the same as an epicentre in the sense of the surface projection of the point where an earthquake rupture initiates. Where an earthquake rupture is large, while the distribution of high intensities may delineate its extent, there is no possibility to determine the initiating point – and probably not a lot of interest in doing so either. The co-ordinates that will be used will be those of the centre point of the rupture; something approximating to the focus from which the seismic energy radiated. For this reason, the term barycentre is sometimes preferred (Cecić et al 1996). From the point of view of seismic hazard, arguably such a point is of greater interest, in terms of reconstructing the seismic field. Since earthquakes occur in three dimensions, as well as the latitude and longitude co-ordinates, one needs also some sort of depth of focus. This is evidently more meaningful for smaller earthquakes of limited rupture dimensions. “Size” has to be considered here to mean “magnitude”; whereas many earlier historical earthquake catalogues were content to use epicentral intensity, Io, as a size measure, for modern applications, and for consistency with modern data sets, this is not enough, and magnitude, preferably moment magnitude, Mw, has to be estimated

DTI Strategic Environmental Assessment Area 4 (SEA4) : sub seabed geology

The SEA 4 region is underlain by continental crust situated on the north-western part of the Eurasian tectonic plate. The oldest continental crust >590Ma (Pre-Cambrian) of interest to oil production, it is divided by a major fault, the Moine Thrust, into ages ranging in age from >2500Ma (Archaean) to the west in which potentially commercial hydrocarbons been discovered and 2500 - 590 Ma (Proterozoic) to the east which is not currently prospective for commerciallyproduced hydrocarbons. The <590Ma sedimentary basins and intervening highs have evolved from pre-, syn- and postdepositional responses to deformation during crustal compression and extension. Many of the modern regional crustal structures retain a NE-SW trend, inherited from events 440-410Ma year ago (Caledonian Orogeny). The results from <65Ma regional NW-SE trending deformation events are also included within the major basin structural configurations. During 60-50 Ma (Late Paleocene to Early Eocene) the region was affected by uplift and in the NW by extrusion of thick volcanic lavas and intrusion of igneous sills. Interactions between historically significant shifts of long-term global climate cooling, an increase in the short-term periodicity and intensity of global climate change and changes to the rates and orientation of crust deformation have been particularly important from 25Ma to the present day (Neogene to Quaternary). These interactions have driven global-to-local changes to basin geological structure, marine circulation, sea level and sediment supply and removal rates and have resulted in the evolutionary changes to submarine basin geometries and lithologies. The modern seabed habitat has thus resulted from the remoulding of inherited basin geometries and lithologies by the processes affecting seabed. The structural history of the region has created a wide variety of potential hydrocarbon trapping mechanisms. The 154-136Ma (Late Jurassic, Kimmeridgian to Ryazanian) Kimmeridge Clay Formation is the principal source rock of the area. The Foinaven and Schiehallion oilfields started production in late 1997 and 1998 respectively both from 60-55Ma (Upper Paleocene) sandstone reservoirs. Geological and technical problems have so far prevented the development of the massive 440-390Ma (Devono-Carboniferous) Clair Field which is the largest undeveloped oilfield on the UK continental shelf. Other hydrocarbon accumulations have been discovered in 245-208Ma (Triassic), 208-146Ma (Jurassic) and 146-65Ma (Cretaceous) intervals in the West Shetland area in the most prospective parts of the SEA 4 region

National seismic hazard maps for the UK: 2020 update

This report is the published product of a study by the British Geological Survey (BGS) to update the national seismic hazard maps for the UK. This is to take account of advances in seismic hazard methodology since the last seismic hazard maps were developed by Musson and Sargeant (2007) and present the results in a format that will be compatible with the future Eurocode 8 revisions

The 2020 national seismic hazard model for the United Kingdom

We present updated seismic hazard maps for the United Kingdom (UK) intended for use with the National Annex for the revised edition of Eurocode 8. The last national maps for the UK were produced by Musson and Sargeant (Eurocode 8 seismic hazard zoning maps for the UK. British Geological Survey Report CR/07/125, United Kingdom, 2007). The updated model uses an up-to-date earthquake catalogue for the British Isles, for which the completeness periods have been reassessed, and a modified source model. The hazard model also incorporates some advances in ground motion modelling since 2007, including host-to-target adjustments for the ground motion models selected in the logic tree. For the first time, the new maps are provided for not only peak ground acceleration (PGA) but also spectral acceleration at 0.2 s (SA0.2s) and 1.0 s for 5% damping on rock (time-averaged shear wave velocity for the top 30 m Vs30 ≥ 800 m/s) and four return periods, including 475 and 2475 years. The hazard in most of the UK is generally low and increases slightly in North Wales, the England–Wales border region, and western Scotland. A similar spatial variation is observed for PGA and SA0.2s but the effects are more pronounced for SA0.2s. Hazard curves, uniform hazard spectra, and disaggregation analysis are calculated for selected sites. The new hazard maps are compared with the previous 2007 national maps and the 2013 European hazard maps (Woessner et al. in Bull Earthq Eng 13:3553–3596, 2015). There is a slight increase in PGA from the 2007 maps to this work; whereas the hazard in the updated maps is lower than indicated by the European maps

Updated intensity attenuation for the UK

For many purposes, including seismic hazard and risk calculations, it is useful to be able to estimate the expected intensity value at a place as a function of magnitude and distance. Such a model was published by Musson (2005), relating intensity to local magnitude and hypocentral distance, based on a dataset comprising 727 isoseismals from 326 British earthquakes, including both modern and historical events, up to 1 October 2002, though for the preferred equation only a subset of this dataset was used. This update adds more data from earthquakes that have occurred since then, up to 1 June 2013. More importantly, the model is recast in terms of moment magnitude. The preferred result is I = 3.50 + 1.28 Mw – 1.18 ln R This is derived from a subset of the total dataset, discarding data for intensity 2 (poorly constrained) and using only earthquakes with at least two isoseismals

The macroseismic survey of the 27 February 2008 Market Rasen earthquake

This report is the published product of a study by the British Geological Survey (BGS) into the effects of the 27 February 2008 Market Rasen (or Lincoln) earthquake, magnitude 5.2 ML, 4.5 Mw. In contrast to former BGS practice (since 1974), in the last few years macroseismic data (i.e. reports on earthquake effects) have been collected over the internet through a page on the BGS web site (http://www.earthquakes.bgs.ac.uk/index.html). Formerly, questionnaires were published in local newspapers, and the task of sifting and interpreting the replies was immense. Data of this sort is also gathered routinely by USGS as part of their “Did You Feel It?” programme, and also by EMSC. Data from all three agencies, plus data from local agencies in Belgium and Ireland, have been merged in this study