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Researchers develop method for estimating ancient earthquake temperatures

Fault lines visible from sky.
An aerial image of a San Andreas fault section

“If you take just even the magna earthquake down near Salt Lake. We all know the Wasatch fault is there, but it took some time for geophysicists to sort of figure out exactly what structure the earthquake even happened on. My point is that at all scales fault zones are complicated. And there are a lot of them.“

That’s Associate Professor Alexis Ault of Utah State University’s Department of Geosciences. Along with PhD graduate student, Emma Armstrong, Ault and colleagues published a paper last month using a technique that allows geoscientists to measure the temperatures of fault slips during ancient earthquakes. Armstrong said when an earthquake happens, heat is produced.

“So, when an earthquake happens friction generated heat is produced. And so, if you can detect evidence of that friction generated heat, you can detect an earthquake in the past and get an understanding of the intensity of that earthquake. And so, in this case, the past is the key to the present,” Armstrong said.

Ault and Armstrong used a technique called low temperature thermochronology to measure the Uranium, Thorium and Helium content of tiny zircon grains, barely visible to the naked eye, along the Punchbowl fault in Southern California. Punchbowl is a part of the San Andreas fault system and is inactive today, but prior research showed that it had past earthquakes along it. In these Punchbowl samples less Helium in the grains suggests a high temperature event in the past.

Ault and Armstrong compared their zircon analyses with previous estimates of earthquake temperatures from another method to more accurately estimate earthquake heat.

Ault stressed that slip rate, fault material properties and fault displacement are all important factors in what determines earthquake temperatures and ultimately intensity. And that being able to accurately measure the temperature of past earthquakes will give us a clearer understanding of how today’s earthquakes propagate beneath the Earth’s surface.