THE CANTERBURY, NEW ZEALAND EARTHQUAKE SEQUENCE: LESSONS FROM A YEAR OF EARTHQUAKES

In the year since the September 2010 earthquake in Canterbury, the lives of New Zealanders have been changed forever. The main sequence of earthquakes led after almost 6 months to the deadly and damaging Christchurch Earthquake of February 22, 2011 (23:51, 21/02/11 UTC); a critically important event, but only one part of the Canterbury earthquake sequence started by the Mw 7.1 Darfield Earthquake in September of 2010. These earthquakes have occurred on previously unrecognized fault(s) and significantly distant from the main components of the plate boundary system through South Island, New Zealand. The initial rupture pattern of the September event and subsequent aftershocks have delineated a linear (nearly east-west in orientation) trend of seismicity extending from the foothills of the Southern Alps to the Pacific coast to the east of the city of Christchurch. Understanding the relationships among the various fault segments, the regional geologic structure, and crustal stresses associated with regional plate interactions (further modified by the earthquakes) is key to placing these events into a context allowing their lessons to be applied elsewhere. Here we focus on the seismo-tectonics of the sequence in the year following the initial event to address the following: 1) How does the February 22 event’s fault relate to the September 3 fault system both physically and through stress conditions; 2) Where do the other larger aftershocks fit into the overall sequence; 3) Are there gaps in moment release between main rupture segments and what role have aftershocks played in modifying any gaps; 4) Are there other faults capable of hosting moderate but damaging earthquakes in the region and have the year of aftershocks identified these faults; and 5) Can we say anything about the potential for future events such as the February 22 earthquake; both nearby to Christchurch and regionally? This last point is the fundamental question that Christchurch residents would like answered and is diagnostic of the issues that mark the global significance of this and similar events.