Dw. Redmayne et al., MINING-INDUCED EARTHQUAKES MONITORED DURING PIT CLOSURE IN THE MIDLOTHIAN COALFIELD, Quarterly Journal of Engineering Geology, 31, 1998, pp. 21-36
The British Geological Survey installed a seismometer network to monit
or earthquakes around Rosslyn Chapel in the Midlothian Coalfield from
November 1987 until January 1990. Accurate locations were obtained for
247 events and a close spatial and temporal association with concurre
nt coal mining, with a rapid decay of earthquake activity following pi
t closure, was demonstrated, indicating a mining-induced cause. Residu
al stress from past mining appears to have been an important factor in
generating seismicity, and observations indicate that limiting the wi
dth of the workings or rate of extraction may significantly reduce or
eliminate mining-induced earthquake activity, an extremely desirable p
rospect which warrants further investigation. A frequency-magnitude an
alysis indicates a relatively high abundance of small events in this c
oalfield area. The maximum magnitude of a mining-induced earthquake li
kely to have been experienced during the life of the coalfield (maximu
m credible magnitude) was 3.0 M-L, although an extreme event (maximum
possible magnitude) as large as 3.4 M-L was remotely possible. Signifi
cant seismic amplification was observed at Rosslyn Chapel, which is fo
unded on sand and gravel, compared with a nearby bedrock site. As a co
nsequence, relatively small magnitude events caused high, and occasion
ally damaging, seismic intensities at the chapel. This is likely to be
an important effect at similar sites elsewhere.