NZ Herald: Hamish Campbell – Technically it’s just an aftershock

GNS Science geologist Dr Hamish Campbell explains why Tuesday’s earthquake is being classified as an aftershock of September’s Darfield earthquake.

The violence of the earthquake was due to a mixture of sideways and vertical movement, combined with accelerations of 1.8g or over (the greatest ground acceleration ever recorded in New Zealand)

An excerpt: (read in full here)

“The pattern of aftershocks following Tuesday’s big jolt has revealed yet another previously unidentified active fault. This is the culprit that has ruptured within the earth’s crust and which has given rise to the intense seismic shaking in the Christchurch region. However, it may also be thought of as a valve that has enabled pent-up energy to be released. In many ways faults actually focus and channel energy.

“It has ruptured over a length of about 17km on a near vertical plane slightly inclined to the south and between 3 and 12km in depth. It is more or less parallel to the E-W trending Greendale Fault that ruptured in the Darfield Earthquake. It may be thought of as an eastern extension but it is clearly dislocated from the trend of the Greendale fault and stepped to the south.”