Seismic zoning to consider in United Kingdom
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Reference peak ground acceleration on type A ground in m/s², by zone according to NA (2008) to BS EN 1998-1 are given for a 2500 years return period | Zones | 0 | 1 | 2 | 3 | 4 | 5 |
| Reference peak ground acceleration agr on type A ground in m/s² | 0,20 | 0,39 | 0,59 | 0,79 | 0,98 | 1,18 |
Additional advice specific to BS EN 1998‐1 from PD 6698:2009 § 4 and §7.4
As described in Clause 4, the whole of the UK is an area of very low seismicity, characterized by earthquakes of low energy release, short duration and relatively low amplitude of ground motions in the epicentral area:
"Comparison of the peak ground acceleration (PGA) values with PGA values found worldwide shows that seismic hazard in the UK is very low by international standards.
The recommended definition of a very low seismicity region in BS EN 1998-1 is an agR value of less than 0.04g for a 475 years return period; application of the Eurocode is not required in such regions.
It can be seen on the map that only a very small part of Wales exceeds this recommended value and studies found no values exceeding 0.08g. The zoning of the whole of the UK as an area of very low seismicity given in the UK National (forewords to BS EN 1998-1 and BS EN 1998-5) therefore essentially accords with the definition of very low seismicity recommended by the Eurocode.
It may be observed, however, that the Eurocode provides an alternative definition of very low seismicity regions as those where the product agRS (i.e. the design PGA on soil) exceeds 0.05 g; this represents the PGA at the reference return period after allowing for the amplifying effects of soil on the bedrock motions. It is likely that a rather larger area of the UK would exceed the “very low” seismicity threshold on this definition, but the area would still be relatively small."
