Old Zircons provide Insights into Earthquakes of the Past
New study might develop understanding of how today’s tremors release energy
Earthquakes have rocked the planet for ages. Studying the quakes of old could aid scientists in better understand recent tremors, but tools to perform such work are scarce.
Enter zircons. Scientists utilized the gemstones to home in on the temperatures reached within a fault during earthquakes countless years ago. The technique provides insights into the intensity of long-ago quakes and could enhance understanding of how today’s tremors launch energy, the scientists report in the April Geochemistry, Geophysics, Geosystems.
“The more we understand the past, the more we can comprehend what could occur in the future,” claims Emma Armstrong, a thermochronologist at Utah State University in Logan.
Armstrong and coworkers concentrated on California’s Punchbowl Fault. That now-quiet portion of the larger San Andreas Fault was probably active between 1 million to 10 million years ago, Armstrong claims.
The process of zircon formation
Warm from the friction is created in a fault when it slides and sets off an earthquake. Previous analyses of kept organic material indicated that temperatures within the Punchbowl Fault peaked between 465°C and 1065°C. The researchers suspected that zircons in rocks from the fault might narrow that vast window.
Zircons often contain uranium and thorium’s radioactive chemical elements, which decay to helium at a predictable rate (SN: 5/2/22). That helium then accumulates in the crystals. However, when a zircon is warmed past a temperature threshold– the magnitude of which depends on the zircon’s composition– the accumulated helium gets out.
Measuring the amounts of the three elements in zircons from the fault suggests that one of the most extreme earthquakes created temperatures lower than 800°C. That roughly halves the array formerly reported. The discovery supplies hint for warm launched by quakes, something hard to gauge for modern-day tremors because they frequently happen at excellent depths.
Armstrong plans to continue examining zircons in the hopes of finding more means to exploit them for details about ancient quakes.
Read the original article on Science News.
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