The Case for Large Earthquakes Felt in the UK in Historical Times - Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes - page 179

TheCaseforLarge ( M 7 ) Earthquakes Felt

in the UK in Historical Times

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R. M. W. Musson

Abstract Evidence from seismic and bathymetric surveys along the passive margin
of NW Europe indicates that there are a number of features suggestive of large
earthquakes having occurred in geologically recent times, although the exact timing
of these events is difficult to establish. It might be thought that, although such large
earthquakes may have occurred, for example, in immediate post-glacial times in
response to rapid isostatic readjustment, no earthquake in the UK area in historical
times has exceeded a value of around 5.7 Mw. However, in past interpretations of
regional seismicity, the possibility that some known historical earthquakes were in
fact passive margin events has not really been canvassed. A large, distant, offshore
earthquake is likely to be felt only at moderate strength over well-populated areas
without any observable damage concentration. In a period when documentation of
earthquakes is always sparse, such an occurrence is likely to lead to vague reporting
that will not be easily interpretable. Looking at the historical record with this in
mind, it is possible to identify some earthquakes that are at least compatible with
an offshore interpretation, as shown in a series of case studies. However, in no case
is such an interpretation the only one viable. Also, some cases that initially appear
to be potentially passive margin events can in fact be discounted. While there is no
unequivocal evidence for large earthquakes having occurred on the NW European
passive margin in historical times, neither can the possibility be rejected, and ex-
amination of the record shows one event in particular (in 1508) which may be a
large passive margin event. Thus the regional maximum magnitude could possibly
be larger than has hitherto been assumed.

Keywords Passive margins · historical earthquakes · maximum magnitude ·

seismic hazard · offshore earthquakes · water fluctuations.