Earthquake weather: Is there such a thing?
Over the past month, the Asia-Pacific region has seen a sudden spike in major earthquakes. They include the deadly West Sumatra quake on Sept. 30, and one the day before near the Samoan Islands, which triggered a devastating tsunami.
During the same general time period (beginning mid-September) four tropical storms and five typhoons (the name used for hurricanes that form over the Pacific Ocean) passed close to the region that experienced the earthquakes (see map of storm paths). Moreover, the tropical Pacific has transitioned to El Nino conditions over the past summer.
Coincidence? Maybe, maybe not!
Geologists generally assume that earthquakes occurring in clusters are unrelated and reflect nothing more than a startling coincidence. However, for some geologists the recent spate of quakes challenges this assumption.
Could weather and climate contribute to the occurrence of earthquakes? At first glance, a connection seems rather far-fetched considering that earthquakes originate miles underground seemingly beyond the influence of wind, temperature, barometric pressure, precipitation or ocean conditions. In fact, scientists have long maintained that the idea that earthquakes are associated with certain kinds of weather is a myth and nothing more.
However, New Scientist reports that "even slight changes in weather and climate can rip the planet's crust apart, unleashing the furious might of volcanic eruptions, earthquakes and landslides," according to conclusions reached in London at a September conference on Climate Forcing of Geological and Geomorphological Hazards.
The basis of the argument is that changes in the mass of ice and water can affect the stresses and strains on Earth's crust, which in turn can trigger seismic activity leading to earthquakes, as well as initiating the eruption of volcanoes. In the context of long-term climate change, alternating colder and warmer periods over thousands of years inevitably cause fluctuations in the weight of ice covering land masses, and in the pressure water exerts on the ocean floor as sea levels rise and fall in response to temperature changes.
On a much shorter time scale, NASA and U.S. Geological Survey scientists believe that retreating glaciers in southern Alaska over the last hundred years or so led to the magnitude 7.2 St. Elias earthquake in 1979. Additionally, increased levels of volcanic activity have been recorded as ice cover decreases over volcanoes in the Cascades Range of the U.S. and in the Andes. The growth and retreat of glaciers and ice cover is highly dependent on year-to-year variability in temperature and precipitation.
So far, so good. But while it seems reasonable that forces felt by the Earth's crust from massive changes in ice and sea level can affect seismic activity, the idea that "even slight changes" could have a major impact sounds more dubious, though seemingly plausible.
Indeed, scientists at the London meeting are confident that even subtle rises in local sea level (several inches) associated with El Nino can precipitate earthquakes. They argue that the increased weight of the water can increase the pressure on the pores between rocks below the seabed, which could be enough to counteract the frictional forces holding slabs of rock together, thereby making it easier for faults to slip. In other words, a small additional perturbation can have a substantial effect. Sound familiar?
And, it's argued that small changes in rainfall can trigger volcanic eruptions by destabilizing the volcano's dome enough for it to collapse and unleash the magma within. "It wouldn't have to be spectacularly heavy rainfall. ... You don't have to have a hurricane," according to the lead author of a recent study written up in New Scientist.
Case closed?... Nope. Not by a long shot. But the recent cluster of deadly earthquakes across Asia-Pacific does have some scientists shaking their heads and questioning long-held assumptions.
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