This week, the largest typhoon to hit Japan since 1993, killed at least 6 people. A news report cited the strength of the typhoon, but then made note of the fact that, less than a day after, the country was rocked by two major earthquakes. Fortunately, there was no tsunami generated by the quakes. Even so, the news got me thinking about the links between the two disaster events and whether or not one could be considered as "causing" the other. Surprisingly, evidence is mounting that this is so.
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An article in Smithsonian Magazine notes that, a few days after an unusual earthquake of 5.8 magnitude rocked Virginia, causing damage to landmarks in Washington DC, "Hurricane Irene moved into the region, wiping out power, downing trees and, according to new research presented at the meeting of Seismological Society of America, says Nature, triggering more small earthquakes in the recently ruptured fault. 'The rate of aftershocks usually decreases with time, says study leader Zhigang Peng, a seismologist at the Georgia Institute of Technology in Atlanta. But instead of declining in a normal pattern, the rate of aftershocks following the 23 August, 2012 , earthquake near Mineral, Virginia, increased sharply as Irene passed by.'"
Hurricanes are known to produce seismic waves on their own. Smithsonian notes that Hurricane Sandy produced seismic activity as far away as Seattle, but the aftershocks that hit Virginia were not the same sort of waves. But how would a storm cause the earth to move? The article offers an explanation and an eerie warning:
“Scientists did not initially notice the
unusual pattern, Peng said, because the aftershocks were small (many
below magnitude 2) and the hurricane itself produced a lot of seismic
noise.” A careful analysis of the data, however, revealed that the
aftershock activity actually rose around the time of the hurricane’s
passing.
The scientists, says Nature, argue that “a decrease in pressure caused by the storm’s travel up the East Coast might have reduced forces on the fault enough to allow it to slip.” More research will be needed to definitively pin down the proposed tie between the hurricane and the earthquake. But the suggestion that the Virginia fault system would have been susceptible to the stresses caused by the hurricane aligns well with the idea that big natural systems, sometimes treated as if they act independently of the world around them, might actually all be connected.
The Irene-triggered aftershocks could have happened because the fault system that had ruptured in Virginia has memory—that is, the fact that it slipped so recently makes it easier for it to do so again. The idea of a natural system having memory is one that is becoming increasingly important for scientists trying to understand natural disasters. The idea is important to the field of complexity science. In a previous interview by this author with Surjalal Sharma, the University of Maryland astronomer explains this idea of memory:
“Memory is, essentially, a correlation in time or space. My memory of past events affects what I do now; that’s long range or long-term correlation. The bunching or clustering of events is, as we understand it, due to the memory of the events in a system. That is, a sequence of natural disasters may not be just a coincidence. If we look at the data for floods, earthquakes, or solar storms, we see that their distributions are ... not random events. Rather, these systems have long-term memory."
More research is needed, but if it turns out to be the case that hurricanes really can cause earthquakes, then (the earth) just got a whole lot more dangerous.
MORE READING
More about the concept of geologic "memory" and some other reasons these events might be related are discussed in a Newsweek article on the subject and in this article by a researcher at Florida International University who suggests understanding the link might help better predict such events.
The scientists, says Nature, argue that “a decrease in pressure caused by the storm’s travel up the East Coast might have reduced forces on the fault enough to allow it to slip.” More research will be needed to definitively pin down the proposed tie between the hurricane and the earthquake. But the suggestion that the Virginia fault system would have been susceptible to the stresses caused by the hurricane aligns well with the idea that big natural systems, sometimes treated as if they act independently of the world around them, might actually all be connected.
The Irene-triggered aftershocks could have happened because the fault system that had ruptured in Virginia has memory—that is, the fact that it slipped so recently makes it easier for it to do so again. The idea of a natural system having memory is one that is becoming increasingly important for scientists trying to understand natural disasters. The idea is important to the field of complexity science. In a previous interview by this author with Surjalal Sharma, the University of Maryland astronomer explains this idea of memory:
“Memory is, essentially, a correlation in time or space. My memory of past events affects what I do now; that’s long range or long-term correlation. The bunching or clustering of events is, as we understand it, due to the memory of the events in a system. That is, a sequence of natural disasters may not be just a coincidence. If we look at the data for floods, earthquakes, or solar storms, we see that their distributions are ... not random events. Rather, these systems have long-term memory."
More research is needed, but if it turns out to be the case that hurricanes really can cause earthquakes, then (the earth) just got a whole lot more dangerous.
MORE READING
More about the concept of geologic "memory" and some other reasons these events might be related are discussed in a Newsweek article on the subject and in this article by a researcher at Florida International University who suggests understanding the link might help better predict such events.
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