Is it just me, or is it quiet? A seismically uneventful year for Long Valley
The beginning of a new year is often a time for reflection about the highlights of the previous one. Seismologists reflect on large or impactful earthquakes, volcanologists on the highest ash plumes or lava fountains… but those of us at CalVO are marveling at just how uneventful 2025 was, at least as far as earthquakes near our volcanoes are concerned.
The California Volcano Monitor is a weekly column written by scientists and collaborators of the California Volcano Observatory. This week's contribution is from Alicia Hotovec-Ellis and Josh Crozier, geophysicists with the U.S. Geological Survey.
As part of our routine monitoring, we define boxes around our volcanoes, count the earthquakes that happened within the bounds of those boxes, and report on those counts each week. It’s a simple exercise, but an important one. Knowing what’s typical for the day-to-day earthquake rate lets us compare it to our records from the start of modern seismic monitoring in the 1980s. That, in turn, allows us to quickly decide how unusual any current observations are compared to what was observed in the past.
We found that 2025 was an average year for earthquakes at California’s volcanoes… except at Long Valley. This was the first year since 1980 that there were fewer than 10 located M≤1 earthquakes. Sometimes, a year will appear quiet because a seismic network outage reduced the ability to detect earthquakes, but the network in Long Valley is in excellent shape thanks to our partners at the Northern California Seismic Network. So, why was this year different?
Looking at the plot in the third image, which summarizes numbers of earthquakes by bar height and their cumulative magnitude by color, we see that 2025 is part of a longer trend in the last half decade of fewer earthquakes each year in Long Valley. The nearby Sierra Block area to the south of Long Valley has also been on the quieter side the last few years, though not to the same degree. It could be the crustal stress in the broader region surrounding Long Valley is changing and as a result the faults aren’t producing as many earthquakes as before. But then what’s causing that stress change? Stay tuned next week as we dig into another clue. Don’t worry, though, we don’t think this is a quiet before the storm—just a normal fluctuation in the life cycle of our volcano.