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Q&A: A geophysicist talks about the recent spate of earthquakes, lessons from Charles Darwin and the possibility of volcanoes erupting.
There are a few cases that we know of where human activity causes small earthquakes – like oil fields where they inject water or steam into the ground to get the oil out more effectively. That can trigger very small earthquakes, on the Richter scale of 1 or 2. Other cases are very large dams where the weight of the water has caused enough stress on the nearby rocks to trigger small earthquakes. But very large earthquakes start at great depths in the earth. And at those depths it's impossible for humans to have any effect. It's just too deep in the ground. The Chile earthquake started 40 miles beneath the surface.
What are scientists looking into with regard to ecosystem relationships? How about atmospheric pressures?
There was a recent study published a few months ago that showed that some very small earthquakes in the San Andreas Fault were related to changes and stress due to the tides. The gravity of the moon pulls on the oceans but the solid part of the earth moves up and down by a tiny amount too. You don't normally detect it with your eye, but sensitive instruments can measure what we call earth tides. Small earthquakes on the San Andreas Fault strongly correlate with these solid earth tides. But that area on the San Andreas has special characteristics. So far we haven’t found that tides correlate to most regular earthquakes.
Is the timing of earthquake activity related to volcanic activity?
Well actually, people are very interested in looking at the volcanoes that are close to the large earthquake in Chile because of Charles Darwin.
Charles Darwin observed the volcanoes erupting in that same part of Chile not long after a large earthquake in 1835. In fact we believe that this year's earthquake could be a repeat of the earthquake that Charles Darwin observed then. He was on the Beagle and he wrote about it in his book. The observations he made were in exactly the same section of the coast near Concepcion, Chile. He was nearby on the ground at the time of the earthquake. He noted the uplift of the coastline, quite similar to what we observed in the earthquake this year.
And people are looking at the volcanoes near Chile now?
I'm sure the Chileans have people monitoring them on the ground, but there are people studying them remotely, using radar interferometry. We can see that some of the volcanoes have some deformation. People are still working on this so these are still preliminary results.
Last question: What's the big question? What's the most important thing that geophysicists like yourself want to know about earthquakes?
The question of how activity on one fault affects activity on nearby faults is one that I've been working on for quite a while. The North Anatolian fault in Turkey fits the theory that faults occur in a sequence, but there are lots of places where the faults don't occur in a sequence. So we'd really like to know more about how that process works. That would give us a much better way to evaluate seismic risk.