BUENOS AIRES, Argentina — The quake that hit China Wednesday was the latest in a string of earthquakes in the news lately. Many people are wondering what's going on, so we decided to ask NASA. Eric Fielding is a geophysicist who uses satellites to study earthquakes at the Jet Propulsion Laboratories in California.
GlobalPost: So first question is the one on everybody's mind. What on earth, literally, is going on? What's up with the earthquakes?
Eric Fielding: The most important thing to remember is there are earthquakes all the time, someplace in the world. In a normal year, there are around 16 earthquakes with magnitudes 7 or higher. So far this year we've had six earthquakes like that. So we're well within the expected range for a three or four month period. (See a list of the earthquakes so far this year.)
Is there ever a pattern to a series of earthquakes?
There are certainly cases where one area experiences a sequence of earthquakes over time. The most famous and well studied are the sequences that occurred on the North Anatolian Fault in Turkey. The first one was in 1939 and there was a series of seven major earthquakes, the most recent being the 1999 earthquake that destroyed Izmit, Turkey. They were all along the same fault; each one increased the stress on another section of the fault and caused the next section to go. That's the classic example people use of one earthquake triggering another. There were two earthquakes in 1999, about a month and a half apart.
There was an earthquake that happened in Salta, Argentina, right after the one in Chile. Was that related? The seismic waves would have had to travel through the Andes.
I'd say that was a little further distance than we'd expect. We want to find out more about exactly what happened during that earthquake and how it might be related. We're hoping to get some radar data from that earthquake but we're still waiting for the satellites.
There’s a lot of new information to analyze then?
Lately there's a lot to look at. People like me, who study earthquakes, are getting a little overwhelmed this year. I almost don't want to turn on the news. But the ones we've had this year are more newsworthy. The one in Haiti caused a lot of devastation, the one in Mexico was very close to California. We even felt it here in Los Angeles. The Sumatra earthquake is more expected, they have a magnitude 7 or 8 earthquake every two to three years. The Chile fault line had been identified as overdue for an earthquake and it happened this year.
Are there any lingering questions in your mind with regard to the recent activity? Or do you think it's completely expected, completely normal?
These earthquakes in general are sort of random — sometimes by chance you're going to get a coincidence of several earthquakes in a region like the Pacific Rim in a few months. It's like flipping a coin and getting heads four times in a row. It happens.
Do humans do anything that causes instability or triggers earthquakes?
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.