[Rockhounds] Scientists stumble across rare evidence that Earth is peeling underneath the Sierra Nevada

[Kreigh Tomaszewski]

Seismologist Deborah Kilb was wading through California earthquake records
from the past four decades when she noticed something odd — a series of
deep earthquakes that had occurred under the Sierra Nevada at a depth where
Earth’s crust would typically be too hot and high pressure for seismic
activity.

“In Northern California usually the (earthquake) data goes down to about 10
kilometers (6 miles). In Southern California, they’ll go down a little bit
deeper into 18 kilometers (11 miles),” said Kilb, a researcher at the
Scripps Institution of Oceanography at the University of California, San
Diego, referring to the depths at which earthquakes usually occur in those
regions.

But the earthquakes she found taking place near the central region of the
mountain range were up to twice as deep — and appear to be ongoing.

“The fact that we see some seismicity that’s below 20 kilometers (12.4
miles) — like 20 kilometers to 40 kilometers (25 miles) — is very odd,”
Kilb said. “It’s not something you would typically see in crustal
earthquakes.”

Kilb flagged the data to Vera Schulte-Pelkum, a research scientist at the
Cooperative Institute for Research in Environmental Sciences and an
associate research professor of geological sciences at the University of
Colorado Boulder. Schulte-Pelkum was already studying the Sierra Nevada’s
peculiar rock footprint, which had shown deep rock deformations within the
same area.

Using the newfound data, the researchers imaged the Sierra Nevada through a
technique known as receiver function analysis, which uses seismic waves to
map Earth’s internal structure. The scientists found that in the central
region of the mountain range, Earth’s crust is currently peeling away, a
process scientifically known as lithospheric foundering. Kilb and
Schulte-Pelkum reported the findings in December in the journal Geophysical
Research Letters
<https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024GL111290>.

https://www.cnn.com/2025/04/18/science/lithospheric-foundering-earth-peeling-sierra-nevada/index.html