12 January 2012, 17:38

Can cyclones, hurricanes and typhoons 'predict' earthquakes?

Can cyclones, hurricanes and typhoons 'predict' earthquakes?
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Folk legends say that if you hear a dog whining a storm might be on the way. But recent studies conducted by the University of Miami indicate that tropical cyclones, hurricanes and typhoons could be far better predictors of earthquakes.

Folk legends say that if you hear a dog whining a storm might be on the way. But recent studies conducted by the University of Miami indicate that tropical cyclones, hurricanes and typhoons could be far better predictors of earthquakes. We are joined by Shimon Wdowinski, Associate Professor of Marine Geology and Geophysics, to discuss the effect of storms on tectonic plates and earthquakes.

How strong is this correlation – the relationship between hurricanes or cyclones and future tectonic activity?

The correlation is found to be very good only in certain areas, where we have a lot of seismic activities and also where tropical cyclones occur, like in Taiwan. That’s the area that we studied the most.

So, the results of your study do not hold true in other geographic regions or the relationship is not quite as strong statistically?

We also found some indication in Haiti but we didn’t study other areas. We mostly concentrated in these two study areas. But it has to be both a mountainous area where a lot of seismic activity occurs and where tropical cyclones pour a lot of rain.

So, it’s not the wind, it’s the rain. How deep must the rain penetrate or what degree of saturation is necessary to cause plate instability?

It occurs after a very rainy cyclone. For example, in Taiwan in 2009 there was a very wet typhoon – in this part of the world it’s called typhoon – that poured almost three meters of rain within five days, which is a huge amount of rain. As a result of rains, there is a lot of erosion because the earth cannot sustain all of this water, it washes and there are many landslides and debris flow that carry mountain material down to the ocean.

15 feet of rain is a tremendous amount of rain. Does this also mean that areas that have been heavily deforested are under greater danger of earthquakes?

It’s hard to predict. But, since the mechanism is erosion, there is some likelihood that areas where there was deforestation can be subjected to a higher level of erosion and other results can help trigger the earthquake. Let me explain that the cause of the earthquake is not the rain but tectonic motions when tectonic plates move with respect to one another and exert forces, which, every once in a while, maybe a hundred, maybe two hundred years, will rupture and releases all the energy that has accumulated along the plate boundaries. The energy is accumulated there because of the motion but also the timing, when the earthquake occurs, can vary from one area to another and there are many things that can trigger this effect at a particular time. What I’m suggesting is that the timing, when this event occurs, in the mountainous area is affected by this heavy rain from these cyclones.

And the timing is an interesting question.  How closely are they related in terms of time? How long after a typhoon or hurricane delivering this amount of rain might an earthquake occur?

What we studied in Taiwan, where we have the best record – we have a record for the past 50 years, the ten wettest typhoons over there and hundreds of earthquakes – we studied the most significant earthquakes and saw that 85% of the largest earthquakes with magnitude 6 and above occurred within four years after the very wet typhoons.

In this region that you were studying, how often did the earthquakes occur without a typhoon or this kind of weather?

Earthquakes of the magnitude 6 and above mostly occurred right within 1-4 years after wet typhoons. We studied the most significant typhoons. There were three of them: one occurred in 2009, one in 1996 and one in 1969. These are the three wettest typhoons and most of these earthquakes occurred either within a few months after the wet typhoon or within 2-3 years.

So, the typhoons are a good indicator, we believe, for larger earthquakes and maybe not as good a predictor for smaller tremors?

That’s right. We see that there is a dependency of the magnitude, not only the timing but the magnitude. A larger event occurs after a wet typhoon – but only in this particular area that we studies in Taiwan.

What are the implications of this work? Does this give us a possibility of preventing future earthquakes if we know that there is this kind of activity? Can we sandbag fold-lines or areas of weakness?

No, the thing is that there is a lot of energy accumulated along these folds due to the tectonic motion. We cannot prevent that from happening. It will occur one way or the other. What we can forecast is the probability that it might happen after a very wet typhoon, a hurricane and not at any particular time, so there is more likelihood that this bigger earthquake will occur after wet typhoons.

So, it’s a domino effect and we might not be able to use this as an emergency warning system, although I suppose that, if you are having this kind of weather, you should move much more inland regardless.

Yes, the typhoon we studies in Taiwan is a huge system that covers the entire island and it rains. For the first time people have to prepared for floods and erosion and all of that. But you should know that there is likelihood there is going to be an earthquake after that, within a few months or a few years.

I guess that means that we should listen to the dogs whine and also keep a track of rains that are falling down.

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