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Why 'trenching' quake zones 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 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 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
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.
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 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 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 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'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
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.
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 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 stands inside a 15-foot-deep trench along the San Andreas Fault near Lake Elizabeth, Calif.
Maya Sugarman/KPCC
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 and her team currently have two open trenches near Lake Elizabeth, Calif.
Maya Sugarman/KPCC


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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.