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New Map Fingers Future Hot Spots For U.S. Earthquakes
sciencehabit writes Earthquake risk assessments can seem pretty abstract at first glance, with their "percent probabilities" and "peak ground accelerations." But the U.S. Geological Survey's (USGS's) national hazard maps, updated periodically, pack a powerful punch: Insurance companies and city planners rely heavily on the maps, which influence billions of dollars in construction every year. Today, USGS scientists released the most recent earthquake hazard assessments for the country. Although the picture hasn't changed much on a national scale since the last report in 2008, the devil is in the details, the report's authors say—and some areas in the country are now considered to be at higher risk for powerful quakes than once thought.
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California
California has some pretty big earthquakes but for the really big quakes you need a subduction zone like the Cascadia that covers from just south of the Oregon border up to southern British Columbia or the Aleutian Megathrust zone off of southern Alaska. Those produce magnitude 9+ quakes like the one off of Indonesia a few years ago. Fortunately they don't happen that often.
Starting on page 12 of the report is a series of maps showing the changes since the 2008 report. Of note:
* The South Carolina seismic zone has been displaced southward by about 50 miles.
* The New Madrid zone has changed shape, with some areas seeing a substantial reduction in estimated earthquake risk.
* The risk zones in California are more sharply defined.
* The risk for the central Rocky Mountains area is higher, but still relatively low.
* The earthquake risk estimate for coastal Oregon has been reduced.
* A new seismic zone is present in Oklahoma, reflecting whatever is causing the massive increase in earthquake rates there.
"They redundantly repeated themselves over and over again incessantly without end ad infinitum" -- ibid.
Why - we had our seismic events millions of years ago. That's why. Big old mountains to my north and the city I live in is comprised of many hills.
On occasion we do get little 2-4 range tremblors though. Back in 2011 or so we were in the office and all felt a swaying sensation. We all noticed but after noticing just went back to what we were doing.