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Podcasts Take Two
Why 'trenching' quake zones isn't always conclusive
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Jun 18, 2014
Listen • 4:27
Why 'trenching' quake zones isn't always conclusive
The practice of digging deep holes to pinpoint evidence of past quakes — called trenching — isn't always conclusive.
Dr. Kate Scharer is a research geologist for the U.S. Geological Survey. State law requires developers to make sure they're not building directly on top of earthquake faults. Researchers like Scharer dig trenches to look for evidence of fault activity.
Dr. Kate Scharer is a research geologist for the U.S. Geological Survey. State law requires developers to make sure they're not building directly on top of earthquake faults. Researchers like Scharer dig trenches to look for evidence of fault activity.
(
Maya Sugarman/KPCC
)
Dr. Kate Scharer points to a thumbtack marking where she believes a geological event occurred. The difference in sediment is a sign that an earthquake may have occurred.
Dr. Kate Scharer points to a thumbtack marking where she believes a geological event occurred. The difference in sediment is a sign that an earthquake may have occurred.
(
Maya Sugarman/KPCC
)
Student Assistant Joseph Lucas, right, a geology student at University of Kentucky, is helping in the trench digging near Lake Elizabeth, Calif. at the San Andreas Fault. To study the sediment in the trenches, student assistants must scrape the walls flat to see the differences in each layer of sediment.
Student Assistant Joseph Lucas, right, a geology student at University of Kentucky, is helping in the trench digging near Lake Elizabeth, Calif. at the San Andreas Fault. To study the sediment in the trenches, student assistants must scrape the walls flat to see the differences in each layer of sediment.
(
Maya Sugarman/KPCC
)
Dr. Kate Scharer of the U.S. Geological Survey presents her findings on Thursday morning, June 12. The trenches tell the geological history of the area as far back as 1400 A.D.
Dr. Kate Scharer of the U.S. Geological Survey presents her findings on Thursday morning, June 12. The trenches tell the geological history of the area as far back as 1400 A.D.
(
Maya Sugarman/KPCC
)
Dr. Kate Scharer's black lab, Allie, lays in a trench at the San Andreas Fault as Scharer presents her findings on Thursday morning, June 12.
Dr. Kate Scharer's black lab, Allie, lays in a trench at the San Andreas Fault as Scharer presents her findings on Thursday morning, June 12.
(
Maya Sugarman/KPCC
)
Based on looking at these trenches near Lake Elizabeth, Calif., Dr. Kate Scharer estimates there were three to four penultimate events in this area.
Based on looking at these trenches near Lake Elizabeth, Calif., Dr. Kate Scharer estimates there were three to four penultimate events in this area.
(
Maya Sugarman/KPCC
)
Dr. Kate Scharer stands inside a 15-foot-deep trench along the San Andreas Fault near Lake Elizabeth, Calif.
Dr. Kate Scharer stands inside a 15-foot-deep trench along the San Andreas Fault near Lake Elizabeth, Calif.
(
Maya Sugarman/KPCC
)
Dr. Kate Scharer and her team currently have two open trenches near Lake Elizabeth, Calif.
Dr. Kate Scharer and her team currently have two open trenches near Lake Elizabeth, Calif.
(
Maya Sugarman/KPCC
)

The practice of digging deep holes to pinpoint evidence of past quakes — called trenching — isn't always conclusive.

California released a preliminary map of a seismic fault that runs through Hollywood earlier this year. 

It's thought to be capable of producing a magnitude 7 quake and developers looking to build in the area must prove they aren't directly on top of it. They typically do that by "trenching," or digging a deep hole and looking for evidence of past quakes.

But KPCC's Sanden Totten reports it's not always conclusive.