Earthquakes, Tsunamis And Pakistan
Chris - So Tiziana, can scientists use other people's misfortune when having an earthquake in order to learn more about what's happening inside the Earth and the structure of the Earth?
Tiziana - Strangely enough, it's already been done. There are two main types of wave that are generated when you have an earthquake. They're called primarya nd secondary waves, mainly because primary waves arrive first and secondary waves arrive second. Through the monitoring these waves around the globe, we can basically see how long they've taken to reach various locations around the Earth. They travel different speeds through different chemicals. We also found that part of the core is liquid because S-waves, which are compression waves a bit like sound waves, can't travel through liquids, and therefore aren't visible on the other side of the planet.
Chris - So that's how we know what bits are liquid and which bits are solid.
Tiziana - Yes, it's surprising.
Kat - So earthquakes only travel around the surface. If there was an earthquake in Australia now, we wouldn't feel it because we're on the other side of the planet.
Tiziana - Well another type of wave released when you have an earthquake is a P-wave. When the P-waves and S - waves hit the Earth's surface, they set up vibrations. This is what we feel as the strong ground motion. It's also what causes the most damage to buildings and causes panic among populations. They attenuate quite rapidly with distance from where the earthquake has happened.
Chris - Are we any closer to predicting when an earthquake is going to happen?
Tiziana - Unfortunately not. I think the greatest progress that has been made so far is to monitor the relative strains along faults.
Chris - Why is it so difficult to do an earthquake forecast, just like we have weather forecasts? What are the difficulties that scientists encounter?
Tiziana - An earthquake will generally occur along a fault and we don't always know where the faults are. We only have about 10 years worth of instrumental data on which to base our predictions. People have made studies of historical data by looking at old news cuttings and historical records to try and find out where earthquakes have occurred and assigning sizes to those earthquakes, but essentially we don't have enough data. We don't understand the Earth as well as we might and we can't predict what amount of time will lapse between one earthquake and the next. That's our main problem.
Chris - Now tell us a bit about what you've been up to in Pakistan. You work as a structural engineer, and as the old saying goes, it's not earthquakes that kill people, it's the buildings.
Tiziana - It is. If an earthquake happens in the middle of the desert, no-one will get killed. Even if a person is standing there they won't fall into the rupture even though people think that they would after seeing films. What happens in cities is that buildings that aren't built to resist the earthquake loads, which is the majority of buildings, will collapse and be damaged. This causes life loss and economic loss to the city or the country. I was in Pakistan after the Kashmir earthquake that occurred in October last year. I looked at the different types of building there and the different materials being used, and tried to work out why different buildings collapsed.
Kat - So what can you do to make a building earthquake-safe?
Tiziana - If you're building a new building, you can apply seismic codes, which will tell you what kind of structural forms will resist the lateral loads imposed by buildings. But if you have an existing structure, you have to see how strong it is, what size earthquake it can resist, and whether or not someone should intervene with a strengthening of that structure.
Kat - Can you make springy buildings? Aren't there some that have big springs up the inside?
Tiziana - Yes, these are called base isolation systems. They look like gum drops except they have steel plates between them. What they do is isolate the building above from the ground motion, so that when the ground shakes, these gum drops absorb all the energy and the structure above will stay relatively still.
Chris - Roughly how many earthquakes are going on around the world today?
Tiziana - Oh gosh, hundreds probably. Some are too small to be detected by humans, and some occur under the oceans or elsewhere.
Chris - Why is it that we can have an earthquake in Dundee or Dudley, as happened recently in this country, but we're not near any plate boundaries. How does that happen?
Tiziana - Well there are deformation stresses that build up within plates themselves and we don't fully understand how these events happen. You do sometimes have small earthquakes happening in places that have never experienced earthquakes before, or at least we don't think they have.