Science Made Simple: Laura Wallace on earthquakes

"Some of the toughest questions facing my field today are what causes earthquakes to happen?" says GNS Science geophysicist Dr Laura Wallace. Photo / File

Surveys have shown one third of Kiwis think science is too specialised to understand. In this series, scientists who tackle mind-bogglingly complex problems each day make it simple for us. Today, we talk to GNS Science geophyicist Dr Laura Wallace.

How would you describe what you do to a peer at a conference? And then how would you to a stranger at a barbecue?

When I'm at a conference and meet another Earth scientist for the first time, I usually say that "I do geodetic studies of plate boundary deformation with a focus on subduction zone interface processes, including locking and slow slip events."

That is a very jargony answer, but fortunately most other Earth scientists would know what I'm talking about.

To describe this to a non-scientist that I meet at a barbecue, I would say that "I use GPS technology to track millimeter-level movement of the land, to figure out where and how movement between the tectonic plates is accommodated. Some of my work also involves figuring out where fault lines are locked up and building up pressure that can be released in future earthquakes."

What project or projects are you currently working on at the moment and what's involved?

The Hikurangi subduction zone has totally taken over my life for the last decade.

The Hikurangi subduction zone is New Zealand's largest and most active plate boundary fault, and is where the Pacific Plate dives, or "subducts" beneath the North Island.

I am involved in a large number of projects using a variety of techniques to better understand the accommodation of plate motion at the subduction zone, and what this means for earthquake and tsunami hazard in New Zealand.

I am also involved in some projects to understand active tectonic plate boundaries in other parts of the western Pacific, such as Papua New Guinea, Japan, and the Solomon Islands.

What are the trickiest questions facing your field and why is solving them so difficult?

Some of the toughest questions facing my field today are what causes earthquakes to happen, and is there any way to better forecast when they might happen?

This is such a hard nut to crack because the part of a fault where earthquakes start is usually many kilometres beneath the Earth's surface.

Because the earthquake generating parts of faults are so deep, it is difficult to study them directly.

So, scientists have to get clever about how they study faults and earthquakes to be able to answer these questions.

What do you feel are the most interesting or fascinating aspects of your field?

One of the main things I have been studying for the last 15 years are these things called "slow slip events", or "slow slip earthquakes".

Their existence was first discovered less than 20 years ago, and since then they have blown open a huge new field of study in seismology.

Slow slip events are similar to earthquakes, because they involve faster than normal movement along a fault.

But, the slow slip events take weeks to months for this fault movement to occur.

This is very different from an earthquake, which are generated by fault movement that occurs over a matter of seconds.

I and many other scientists are fascinated by these slow slip events, because we don't yet understand the physical processes that cause faults to behave in such a way.

Why do you think the work is important and what could it help us understand?

Understanding why and where slow slip events happen is a key missing link in our understanding of how faults work.

A full understanding of the range of fault movements and their causes is also needed to understand how "fast slip" earthquakes are generated.

Slow slip events also have great potential to improve our ability to forecast earthquakes.

In New Zealand, we often see lots of small earthquakes during slow slip events on the Hikurangi subduction zone.

Once we can better understand this relationship between slow slip events and earthquakes - in space and time - we might be able to use slow slip events to do better earthquake forecasts.