Slow eathquakes below Alpine Fault

Researchers monitoring seismic activity under the Southern Alps have reported ‘slow’ and ‘creeping’ earthquakes occurring deep under the mountain range.

A team of researchers from Victoria University of Wellington have recorded a number of prolonged bursts of low-strength seismic energy, termed tectonic tremor, on the southern alpine fault-line. Their findings were published in the journal Geophysical Research Letters this week

The research focused on an area in the mid-section of the South Island’ s Southern Alps, near Fox Glacier. The scientists installed 11 seismic sensors over a 60km area to get high resolution data of ground shaking activity in the area, which has an unusually low level of  earthquake activity.

Between March 2009 and October 2011, the researchers detected 65 individual tectonic tremor bursts.

It’s only the second time that this type of seismic activity has been recorded on a strike-slip fault, which are those with walls that move sideways rather than up or down. The other is the San Andreas Fault in California.

A member of the team, Dr Aaron Wech, said in a media release that these slow earthquakes don’t cause damage but knowing they are happening sheds new light on activity in the Alpine Fault.

“Our research shows that between large earthquakes, the fault is still moving. It’s not yet clear what this means for future earthquakes – it could be that constant tremor builds up stress and may trigger a major fault movement or, alternatively, the activity may decrease the likelihood of a major quake by acting as a release valve for stress.

“What’s important is that we find out more about these tremor events, such as where they happen and how often, so we can better predict the hazard the Alpine Fault poses.”

The research has been covered by the media. Examples include:

World News Australia: Long, slow quakes shaking NZ Alpine Fault

MSN News: Long, slow quakes shaking Alpine Fault

NZ Herald: 30 min quakes common in Southern Alps Slow Moving Quakes Beneath Alpine Fault

Radio New Zealand: Creeping quakes found beneath alpine fault