The Case for Large Earthquakes Felt in the UK in Historical Times - Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes - page 194

Fig. 5 Sketch showing a notional (and not very likely) reconstruction of the 23 May 1847 event.
Stippled area is the continental slope; lozenges indicate earthquake felt reports
with what one expects from a tsunami and suggests instead some meteorological
phenomenon. In this case, both earthquake reports are coincidences.
What happened on 23 May 1847 is thus enigmatic.
6 Discussion and Conclusions
From what is known about patterns of intraplate seismicity, the possibility of a large
earthquake on the passive margin of north-west Europe has to be considered. Phys-
ical evidence on the sea floor suggests that such events have occurred in the past, at
least in geologically recent time, since it may be the case that at least some of the
observed slides were earthquake-triggered.
Asking the question as to whether such an event could have occurred in historical
time without this having been recognised from existing reports, the answer appears
to be yes. There exist poorly documented earthquakes that were widely felt with no
evidence that they were strong or damaging in what might be the epicentral area.
Until now, the question as to whether any of these might be a large passive margin
earthquake has not been raised. There is no conclusive evidence that any of these
earthquakes are passive margin events; one can only say that it is conceivable that
they might be. The best candidate is probably the earthquake of 19 September 1508;
but even with this one there are alternative interpretations that are also consistent
with the evidence.