Nearly half of Americans exposed to potentially damaging earthquakes: journal article

Nearly half of Americans are exposed to potentially damaging ground shaking from earthquakes, said a research report published in the journal Earthquake Spectra this week.

The report, from scientists at the U.S. Geological Survey (USGS), found that more than 143 million Americans (about 46% of the U.S. population) living in the 48 contiguous states are exposed to the potentially damaging ground shaking. When people living in the earthquake-prone areas of Alaska, Hawaii and U.S. territories are added, this number rises to nearly half of all Americans.

“The new exposure estimate is nearly double the previous 2006 estimate of 75 million Americans in 39 states, and is attributed to both population growth and advances in science,” said William Leith, the USGS senior science advisor for earthquake and geologic hazards and a co-author of the study, in a blog posting on the USGS website. “Populations have grown significantly in areas prone to earthquakes, and USGS scientists have improved data and methodologies that allow for more accurate estimates of earthquake hazards and ground shaking.”

The USGS reported that about 143 million people live and work in areas with some potential for damaging shaking, a level that could at least lead to structural damage. “Approximately 57 million people are in areas with a moderate chance of such shaking, and 28 million people in areas that have a high potential to experience damaging shaking,” the blog said. The USGS shaking calculations consider the chance of an earthquake occurring in a 50-year time frame, the typical lifetime of a building.

The researchers estimated the number of people exposed to peak ground accelerations at or above 0.1 g. At least 28 million (about 9% of the population) may experience “0.1 g level of shaking at relatively frequently intervals (annual rate of 1 in 72 years or 50% probability of exceedance (PE) in 50 years).” About 18% of the total population (57 million) may experience this level of shaking at moderately frequent intervals (annual rate of 1 in 475 years or 10% PE in 50 years), and 143 million (46% of the total population) may experience such shaking at relatively infrequent intervals (annual rate of 1 in 2,475 years or 2% PE in 50 years).

Earthquakes due to human activity—or induced seismicity—were not accounted for in the estimations. [click image below to enlarge]

According to the USGS, the 10 states with the highest populations exposed to “very strong ground shaking levels” are, in descending order: California, Washington, Utah, Tennessee, Oregon, South Carolina, Nevada, Arkansas, Missouri and Illinois. “Although this level of shaking is estimated to occur relatively infrequently, it could cause significant damage and causalities,” the blog noted. “The difference between those areas at risk from moderate versus strong shaking depends on a variety of factors, including the location of fault lines and the seismicity rates of the area.”

To determine the strongest ground shaking potential, USGS researchers used estimates from the recently updated U.S. National Seismic Hazard Maps, which identify where future earthquakes will occur, how often they will occur, and how strongly the ground will likely shake as a result. Researchers analyzed high-resolution population data and infrastructure data to determine populations exposed to specific levels of earthquake hazard.

“This new research helps us better understand the scale of earthquake hazards and ultimately strengthen the nation’s ability to protect Americans against future events,” said Kishor Jaiswal, a USGS research structural engineer and lead author of the study, in the blog. “Of particular concern is the significant amount of critical infrastructure located in high earthquake-hazard areas, ranging from private and public schools to health care facilities and fire stations.”