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As Hurricane Hilary approached the southern California coast, I had a lot of questions about the amount of rain in the desert; some areas might receive a year’s worth of rain in one storm, with devastating consequences. But one question haunted me: can hurricanes cause earthquakes?
The answer was a quick no. I’ve never been presented with any scientific evidence that this was possible, but we have seen earthquakes and hurricanes occur at similar times and locations.
Looking back at 2011, Hurricane Irene (one of the retired hurricane names) came with a 5.8 magnitude earthquake in Virginia. There have been others as well.
I’ve seen it with just enough frequency to wonder if anyone has really looked at this question seriously. When the 5.1 magnitude quake struck California as Hilary was raining down, many scientists did a double take. Immediately, I wondered if there was a connection, and was it just correlation or causation?
Correlation or Causation
A correlation between two things means there is a statistical association between these things, but they don’t cause one another. Like ice cream sales and shark attacks. There is a strong correlation between them, rate graphs nearly match every year, both low in the winter and peak in the summer. But one does not cause another. It’s just a correlation.
Causation means that a change in one thing will cause a direct change in another thing. That they are tied together, one causes another. Like the sun causes sunburns, and we see more of those in the summer. Winter means less sun, less sunburns.
So do hurricanes cause earthquakes, or do they just happen at the same time? And with Lee affecting New England and Atlantic Canada at the moment, I wonder if it will happen again.
Why Earthquakes Happen
Earthquakes happen because of underground faults. Tectonic plates are always slowly moving under our feet, but sometimes, they get stuck at their edges due to friction. The meeting places between plates is a fault. When the stress on the fault overcomes the friction and moves again, there is an earthquake that releases energy in waves that travel through the earth’s crust and cause the shaking that we feel.
Zhigang Peng, a seismologist at the Georgia Institute of Technology, compared the time of aftershocks to atmospheric pressure, testing their hypothesis that lower pressure caused by the storm may have reduced forces on the fault enough to allow it to slip and cause an earthquake. But they didn’t find the biggest increase in aftershocks when air pressure was at its lowest. Instead, a spike came a few hours later, as the storm was moving away. This research was looking at just one storm and, while interesting, doesn’t have a lot of statistical significance on its own.
Shimon Wdowinski, a seismologist at the Florida International University, says he found a strong correlation between extremely wet tropical cyclones (Hurricanes that take place in the western Pacific) and big earthquakes that occur up to three years later. His hypothesis is that a storm’s landslides trigger a change in fault loading, eventually producing an earthquake. His research says that earthquakes may be inevitable but happen sooner due to storms. “The main engine that’s actually responsible for the earthquake is not the wet typhoon,” Wdowinski said. “The wet typhoon just determines the timing.”
I often wonder about the weight of the water rained down from the atmosphere onto the land. Considering the average hurricane drops 2.4 trillion gallons of water per day, or 20 trillion pounds (or 10 billion tons), that is a significant weight change in a short period of time. Could that be enough to cause an earthquake?
The U.S. Geological Survey (USGS) has said, “It’s unlikely that seismic hazard is affected by precipitation. This makes sense as rainwater cannot easily percolate several kilometers below the earth’s surface to the depths where most earthquakes occur.” Most earthquakes do happen far below the surface, and such a correlation would be a stretch, like ice cream sales and shark attacks.
However, The USGS continues to say, “periods of heavy precipitation or of drought might indirectly affect earthquake-prone faults.” Annual variations in stress on California’s faults, which correlate to seismic activity, are larger during years of unusually heavy precipitation or drought, according to Researchers at Stony Brook University.
Wenyan Fan, a Florida State University assistant professor, wasn’t looking for this specific correlation when he found an annual cycle of seismic signals that correlated to hurricane season, and even individual storms.
The varying pressure on the sea floor by hurricane waves produces seismic activity that scientists are calling “stormquakes.” In the Gulf of Mexico, deep shudders equal to a 3.5 magnitude earthquake were found to coincide with hurricanes. Most of these are not felt by people.
There is some evidence out there that Nor’easters have been tied to seismic activity, which was measured near New England, Nova Scotia, Newfoundland, and British Columbia.
Most of the case studies and peer-reviewed journal articles focus on a single or subset of storms. More data and analysis need to be completed before this question can be really answered.