Pre-2010 historical seismicity near Christchurch, New Zealand: the 1869 M sub(W) 4.7-4.9 Christchurch and 1870 M sub(W) 5.6-5.8 Lake Ellesmere earthquakes

The 5 June 1869 (NZMT), 4 June 1869 (UT) Christchurch earthquake has long been known to have caused chimney and structural damage, to Modified Mercalli intensity MM7, in central Christchurch. On 31 August 1870, another strong earthquake shook the city causing widespread contents damage and the cracking and fall of a few chimneys. These two events represent the most significant near-field earthquakes in Christchurch's historical record prior to the 2010 M sub(W) 7.1 Darfield and 2011 M sub(W) 6.2 Christchurch earthquakes. Comprehensive data on the effects of 1869 and 1870 events now provide reasonable constraint on their locations and magnitudes. The 1869 earthquake, known as the New Brighton earthquake prior to 1999, occurred at shallow depth (upper crustal) about 3 kilometres southwest of Christchurch Central Business District, within the aftershock zone of the 2010 and 2011 events. The 1870 Lake Ellesmere earthquake had a larger magnitude, was deeper and was about 30 km south of Christchurch.