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Redwood Tree Stumps Offer Clues to Past Earthquakes

By Communications and Publishing September 23, 2022

Researchers are studying slices of tree stumps to study past earthquakes.

A team of researchers from the USGS and a university partner collected slices from 23 redwood tree stumps along the north coast section of the San Andreas Fault near Gualala, California in late August 2022.  

The tree stumps were several hundred years old when they were cut down in the late 19th and early 20th centuries. Their rings store their growth histories and possibly the effects of earthquakes prior to the magnitude 7.9 San Francisco earthquake in 1906.  

The team, including Belle Philibosian, Nick Cunetta, and Austin Elliott, researchers with the USGS Earthquake Science Center, and Allyson Carroll, a researcher at Cal Poly Humboldt, plan to analyze the tree ring records at Humboldt. They will also collect cores of living redwoods and compare the two datasets to search for evidence of, and precisely date, past San Andreas Fault earthquakes.  

Here’s a pictorial tour of their fieldwork, from climbing massive tree stumps to observing sawyers cutting into the stumps to preparing the stump slices for analyses.  

A massive tree stump takes up most of the frame while a scientist poses on the side.
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Belle Philibosian with the USGS Earthquake Science Center examines a redwood stump along the north coast section of the San Andreas Fault near Gualala, California in late August 2022.  
Researchers stand around as they watch sawyers cutting into a leaning redwood snag.
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Belle Philibosian, Nick Cunetta, and Allyson Carroll watch sawyers cutting into a leaning redwood snag. The snag is located directly on the San Andreas fault scarp (slope down to the right) and the leaning may have occurred during an earthquake.
two tree cutters stand among skinny trees and a tree stump
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Sawyers cutting into a leaning redwood snag. The snag is located directly on the San Andreas fault scarp (slope down to the left) and the leaning may have occurred during an earthquake.
A tree stump with a rectangle box removed from the middle.
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Wedge sample removed from a redwood stump at the base of the San Andreas fault scarp (slope up in the background).
a man stands among skinny redwood trees with green leaves in the background
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Nick Cunetta stands between two sampled redwood stumps on a pressure ridge between two strands of the San Andreas fault
a couple rectangle blocks of redwood stumps on top of mulch
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Sample removed from a redwood stump, displaying annual rings. The sample will help researchers determine past earthquakes in the area. 
a man wearing a grey shirt and green hat squats next to a bag of tree stump samples
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Austin Elliott with the USGS Earthquake Science Center prepares to carry Redwood stump samples out to the road.
tree stump samples of varying sizes with blue tapped labels sit on the floor
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Labeled stump samples sit on the floor awaiting analysis in the laboratory at Cal Poly Humboldt.

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