Geological Survey Updates Earthquake Threat Map

By: Stephen Bowers - Courtesy
By: Stephen Bowers - Courtesy

Following last week's earthquake in the Midwest, the U.S. Geological Survey has released a new set of maps and information with updated information regarding earthquake risk.

The changes on the USGS National Seismic Hazard Map indicate that earthquakes are still a threat for 46 states in the country. Western states, including Washington and Oregon, are shown to have higher ground shaking estimates and higher earthquake risks than they were shown to have on previous versions of the maps.

According to the U.S. Geological Survey, the following changes were made on the map:

Several new faults were included or revised as a source of earthquake ground shaking in California, the Pacific Northwest and the Intermountain West.

The Wasatch fault in Utah was modeled to include the possibility of a magnitude-7.4 earthquake, in addition to smaller earthquakes along the fault.

The model for earthquakes along the New Madrid Seismic Zone in the Central United States includes a wider range of possible magnitudes and return periods between major earthquakes. The model was also adjusted to allow for sequences of earthquakes to occur in groups of three within a few years time, similar to what occurred in 1811 - 1812.

Offshore faults were added as possible sources of earthquakes near Charleston, S.C.

For the Cascadia Subduction Zone, more weight was given to a magnitude-9 earthquake that ruptures the length of the subduction zone, versus multiple smaller magnitude-8 earthquakes that fill the zone over the same 500-year time period.

In the Eastern United States, the greatest threat is along the New Madrid Fault which runs along the Mississippi River from northeastern Arkansas through western Tennessee, southeastern Missouri, and western Kentucky into southern Illinois.

The map can be viewed on the U.S. Geological Survey's website. See below for the link.

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  • by Jerry Location: Belhaven on Apr 23, 2008 at 03:01 PM
    These changes are going to be modified I would think now that our global weather has changed. The United Staes is ongoing western and eastern changes since the past few years and with that would we conder more movement at the fault lines?

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