 Sunday afternoon a couple of reasonably large earthquakes jolted and rolled their way through Christchurch reminding us all that earthquakes aren't going away they occur all the time all over the world and that they can be quite scaring. Like many things in nature there's a silver lining. Actually earthquakes are a very useful tool for scientists to learn about the internal structure of the earth. If you've ever wondered how we could possibly know that some 3,000 kilometers beneath our feet is a layer of liquid molten iron it was actually earthquakes detected all around the world that we could discover this. So I like to make little earthquakes in the lab to work out the internal properties of a whole range of different materials from ice and wood and rocks to fruit. You've actually already heard of this before in medical imaging we call it an ultrasound scan and when you go for an ultrasound the doctor has little wand that emits waves into the body kind of like earthquakes except here instead of seeing a core of liquid molten iron maybe we can see a unborn baby. The goal of my research is to use quakes to measure the internal properties of materials without ever coming into contact with the sample and I can do it using lasers. So instead of having a contacting wand like a doctor I can use high energy pulses of light which I focus onto the surface of my sample. When all that energy from the light pulses absorbed by the material the rapid increase in temperature generates a shockwave just like an earthquake. This shockwave propagates through the material to where I detect it using a laser detector that I designed. One of the most successful applications that I've been applying this technique to is measuring the firmness or ripeness of apples. An apple is kind of like a little earth it has a core it has a crust it's kind of round and I can use laser generated apple quakes to measure the ripeness of an apple. I do this by comparing the waves that travel around the surface of the apple those are called Rayleigh waves they're the ones that knock your buildings over in the earth to the waves that travel directly through the apple flesh. So you can imagine that I can measure the ripeness of an apple completely non-contacting so I could measure every single apple coming off an orchard. So one day in the future you may see in your local supermarket and bright lights laser-certified apples. $50 a kilo.