Christchurch seismic activity

Fault ruptures associated with the Feb 2012 and June 2012 earthquakes

Key: colours  show the amount the two sides of the fault slipped past each other during the earthquake. Red = slip > 1.8m, yellow = slip > 1.2m, and green = slip > 0.6m.
The arrows show the direction of slip, with the length of the arrow proportional to the size of the slip.
The squares measure 1km by 1km.

The faults do not break through to the ground surface. Slip occurs down to about 7-8km depth and up to within about 1km of the surface.
Both earthquakes caused parts of the Port Hills to move south, or southwest, and up. Parts of the Port Hills have risen by more than 40 centimetres.
The magnitude 6.3 February earthquake had a slip > 2.5m between the two sides of the fault at 4km depth. The south side of the fault moved generally up and west while the north side moved the opposite way.
The fault trends in a WSW-ENE direction from about Cashmere to just offshore of the estuary, and it slopes towards the southeast.
It is not uncommon to have two nearby faults breaking in different orientations like this. Both the faults are responding to stresses in the ground that are oriented in a WNW-ESE direction, midway between the orientations of the two faults.

This Google map image shows the fault plane (rectangular area) across the southern part of Christchurch and northern Port Hills. Colours on the fault plane indicate the amount of slip between the two sides of the fault (see Fig. 2). The contour lines indicate the amount (in mm) the land has risen (blue contours) or subsided (red contours) due to the slip on the fault. The white line is the contour where there was no change in height. The red, green and yellow coloured symbols show some of the GPS stations whose displacements were used to derive the fault slip model

 Image indicating ground displacement made by combining satellite radar images taken before and after the earthquake. The coloured image shows an “interference pattern” derived from X-band radar images taken on 19 and 23 February 2011 by the Italian Cosmo-SkyMed satellite. Each colour cycle represents 1.5 centimetres of ground displacement, so the total displacement between the western edge of the image and central Christchurch is about 25 centimetres.