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During the heat wave in early June, a lot of people were calling it “earthquake weather” and felt a little more cautious moving around the Bay Area.
Hiro Sato of San Mateo has heard people in the Bay Area talk about earthquake weather. He asked Bay Curious, "Is there actually any correlation between weather and earthquakes?"
In short, no. There's no such thing as earthquake weather. The idea goes all the way back to Aristotle in ancient Greece, but it's just not a thing.
Bay Curious asked KQED Science editor Craig Miller to unpack the meteorological myth.
The following interview has been edited for clarity.
BC: What is earthquake weather?
CM: I think it may depend on where you live. There are different notions of it around the world. In California, the notion of earthquake weather is typically warmer than usual and still. There's a lack of wind. It's almost kind of like this eerie calm before the storm feeling. If you look back at the Loma Prieta earthquake, for example, in October 1989, I recall the weather was kind of like that.
BC: Spooky. Is it true then?
CM: No. A couple of years ago a contributing geologist to KQED wrote a piece on this, postulating that the stillness in a place that is usually pretty breezy can give one a sense that the earth is holding its breath. So it might cause us to hold our collective breaths, to wait and wonder what's next.
But no, earthquakes are a geological thing and not a meteorological thing, and there is no known connection between the weather and earthquakes themselves.
BC: However, in your reporting you've found an interesting twist on this myth. Can you talk about that?
CM: This dates back to the 6.0 earthquake in Napa five years ago. A scientist at the University of Nevada started looking at [earthquakes] and comparing them to the location of groundwater reserves and the natural fluctuations in the earth.
Seasonally, groundwater aquifers fill up in the winter and spring, and then get depleted later in the season. This might be especially true in agricultural areas.
What happens is the reduced weight of that water pressure underground might release or unlock faults so that they're more likely to slip. The study even suggests that this may have played a role in the Napa earthquake. So while there's no earthquake weather, there could be an earthquake season in the late summer or early fall.
BC: That is wild.
CM: And if you go back and you look at when the Napa quake happened, it was late summer, in August. The Loma Prieta was in October during that time of year when the groundwater is lessening in its pressure.