Earthquake threat remains high in US

Earthquakes remain a serious threat in 46 States in America, according to the latest version of the US Geological Survey’s (USGS) national seismic hazard maps.

For some areas such as western Oregon and Washington, the new maps contain higher estimates for how hard the ground will shake compared to earlier versions of the maps released in 1996 and 2002. In most of the US, the ground shaking estimates are lower.

The timing of the release of the new maps is tied to the schedule for revising model building codes. Cities and counties rely on seismic design provisions in building codes to ensure that structures such as buildings, bridges, highways and utilities are earthquake resistant.

USGS director Mark Myers said: ‘The hazard maps released today incorporate more than a century of seismic monitoring and decades of research. These maps help policymakers and engineers make all of our structures — from our homes to our hospitals to the utilities that run beneath our feet — better able to withstand the earthquakes of tomorrow.’

Last week the USGS and its partners released a new earthquake rupture forecast for California, the first ever such forecast done statewide. That forecast focused on the likelihood of earthquakes happening on specific faults. The National Seismic Hazard Maps take the information about those faults and calculate the intensity of shaking that a given location could potentially experience over a 50-year period. These shaking estimates combine the effects from all possible earthquakes, both nearby and distant.

The USGS said the changes in earthquake ground shaking estimates are due principally to the incorporation of new models on the strength of earthquake shaking near faults, and the manner in which shaking decreases with distance.

The maps are done at a national scale and do not take into account local soil conditions and the depth of sedimentary basins, which can significantly amplify shaking relative to bedrock, added the USGS.