sentences:  Wales is not a particularly seismically active country, nevertheless earthquakes of lesser magnitude occur from time to time.Ground stability is more of an issue due both to natural causes and, in former areas of coal and other mineral exploitation, due to mining, surface excavation and spoil deposition.Deep-mining of coal in particular has led to reactivation of pre-existing landslips, notably in the steeply-sided valleys of the South Wales Coalfield.