Post-earthquake seismic reflection survey, Christchurch, New Zealand

Donald C. Lawton, Malcolm B. Bertram, Kevin W. Hall, Kevin L. Bertram, Jarg Pettinga

Approximately 50 line-km of high-fold reflection seismic data were recorded in and around the city of Christchurch, New Zealand, following a devastating Mw 6.3 earthquake in this area on February 22, 2011 that resulted in the loss of 182 lives. The recording system used was the 600-channel Aram Aries system and Envirovibe belonging to the Department of Geoscience at the University of Calgary. The goal of the seismic program was to map previously unknown faults in and around the city for hazard assessment and to assist in the post-earthquake recovery effort. Equipment preparation and field recording in New Zealand was undertaken by CREWES staff on a full cost-recovery basis.

Seismic data were collected along six 2D lines, two of which were within the Christchurch metropolitan area and four were in rural areas west of the city. Recording conditions were challenging within the city, but good quality images were obtained along all of the seismic lines, with events interpretable to a depth of approximately 1.5 km. Numerous faults were imaged along the lines and these were interpreted in two groups - older faults that showed clear offsets in deep (> 1 km) reflections and younger faults that showed displacement in shallow reflections. Some faults in the latter group were interpreted to be directly associated with hypocentres of shallow after-shocks in the region. Figure 1 is an interpreted section from across a fault that ruptured to surface during the Mw 7.1 Darfield Earthquake that struck west of Christchurch on September 2010 but caused no loss of life. The seismic interpretations are now being incorporated into a risk assessment for further possible shallow earthquakes in the region.