Question: What causes earthquakes?
The problem that we face as earthquake seismologists is that sticking and slipping is almost a chaotic process, not quite, but almost and so it’s very difficult to predict on a day-to-day basis. Over geologic time of course it’s very predictable. We can get an idea of where the active plate boundaries are. Those plate boundaries of course are major faults in the earth and we know where the earthquakes will occur, but because we can’t predict the stick and slip cycle very well, certainly over human timescales, we can’t really get what we call a prediction, but there is a deeper understanding of it that allows us to forecast instead of predict and by forecast I mean well first of all we know where they occur because we know where the plate boundaries are, but we can get a sense of what the probability of an earthquake might be in two ways. One, by looking at the past history and if we have enough earthquakes, we can sort of get a statistical model of when earthquakes might occur, and that gives us some probability, and the other is to actually do a bit of forward modeling and actually take the plate motions, take a model of the friction along the plate boundary, take a model of how the stress builds up and sort of predict when and where or I should say forecast when the next earthquake might occur, and it’s gotten to the point where we can probably do that over the span of a decade or two, perhaps 30 years, to the extent that we can sort of provide an actuarial table.
If you wanted to go out and buy insurance in California, as a matter of fact, there is such an actuarial table to help you determine what your rates are or I should help the insurance companies determine what they’re going to charge you. Of course we didn’t have that for Haiti. We barely had that for Chile, but the point is we’re getting better at it, so you know one of the exciting parts of earthquake seismology is that the better we get at forecasting earthquakes the closer we might actually come to a prediction that is useful on human timescales.