The USGS has updated its national seismic hazard maps for the first time since 2008, taking into account research from the devastating 2011 earthquake and tsunami off the Japanese coast and the surprise 2011 Virginia temblor. The new earthquake map turns up the shaking hazard just a bit for about one-third of the United States and lowers it for one-tenth.
The maps are used for building codes and insurance purposes and they calculate just how much shaking an area probably will have in the biggest quake likely over a building’s lifetime.
The highest risk places have a 2 percent chance of experiencing “very intense shaking” over a 50-year lifespan. Those with lower hazard ratings would experience less intense swaying measured in gravitational force. Parts of 16 states have the highest risk for earthquakes: Alaska, Hawaii, California, Oregon, Washington, Nevada, Utah, Idaho, Montana, Wyoming, Missouri, Arkansas, Tennessee, Illinois, Kentucky and South Carolina. With the update, new high-risk areas were added to some of those states. Colorado and Oklahoma saw increased risk in some parts and moved up to the second of the seven hazard classifications.
There are major faults and quake hazards along the entire west coast, with an increased concern in the Cascadia region around Oregon. Southern Alaska, the big island of Hawaii, the Missouri-Tennessee-Arkansas-Illinois New Madrid fault area and Charleston round out the biggest hazard areas.
The maps however did sidestep the issue of earthquakes created by injections of wastewater from oil and gas drilling in Oklahoma and other states, noting those extra quakes weren’t included in the analysis. So far this year, nearly 250 small to medium quakes have hit Oklahoma.