Seismically induced land damage on Whitewash Head, Christchurch, New Zealand

On 14 February 2016 a M5.7 earthquake, now commonly referred to as the Valentine’s Day Earthquake, struck off the coast of Christchurch city causing land damage in the Port Hills. This earthquake follows almost five years after the M6.3 earthquake that struck the city on 22 February 2011 that caused extensive cliff retreat and ground cracking near the cliff edges. Another significant earthquake with a magnitude of 6.3 struck the same year on 13 June. This caused the cliffs at Whitewash Head in the east of the Port Hills to retreat along already mapped tension cracks and created new cracks up to 10m from the cliff edge. Currently, the structures on ‘red-zoned’ properties on Whitewash Head are being demolished as part of the land clearance works undertaken by Land Information New Zealand. The demolitions are in geotechnically high risk areas and strict monitoring controls are in place. The recent Feb 14 earthquake was the largest since monitoring was installed, thus enabling the engineering geologists to observe how these monitoring systems performed during a significant seismic event. This paper presents the response of the monitoring networks and aerial photograph review following the 2016 Valentine’s Day earthquake; discusses possible failure modes and implications of further land deformation in the Port Hills and concludes by providing options for management of future land clearance sites affected by geotechnical hazards.