Monday, August 10, 2015

USGS: Nearly Half Of U.S. Population Exposed to Potentially Damaging Earthquakes


2014 Update of the United States National Seismic Hazard Maps


# 10,403


In 2006 the USGS calculated that earthquakes posed a significant risk to 75 million Americans living in 39 States.  Since then, populations have changed and/or shifted and ongoing research has uncovered new seismic risks (see USGS: Updated U.S. Seismic Risk Hazard Maps), and geologists have a better understanding of the extent of ground shaking from these quakes.

A new study, published today in the journal Earthquake Spectra, nearly doubles – to 143 million - the number of Americans who live or work in areas susceptible to potentially damaging ground shaking.

First a link and excerpts from a USGS science brief on the paper, after which I’ll be back with a little more.  Follow the link below for additional details, along with  more maps and charts.


Nearly Half of Americans Exposed to Potentially Damaging Earthquakes

Categories: Featured, Natural Hazards
Posted on August 10, 2015 at 9:30 am
Last update 11:44 am By: Kishor Jaiswal, 303-273-8584, and Jessica Robertson, 703-648-6624,

More than 143 million Americans living in the 48 contiguous states are exposed to potentially damaging ground shaking from earthquakes. When the 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.

Scientists with the USGS published this research online today in the journal Earthquake Spectra.

“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, who is the USGS senior science advisor for earthquake and geologic hazards and a co-author of this study. “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.”

High Versus Some Potential for Damage

About 143 million people live and work in areas with some potential for damaging shaking, a level that could at least lead to damage in structures. 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 USGS shaking calculations consider the chance of an earthquake occurring in a 50-year time frame, as that is the typical lifetime of a building. This time frame is thought to be reasonable for life-safety considerations when designing buildings and other structures.

Which States Have the Strongest Shaking Potential?

When one considers very strong ground shaking levels, the 10 states with the highest populations exposed (in descending order) are 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 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.

Start with Science

These new estimates are derived 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. The population data are from LandScan, and the infrastructure data are from the Homeland Security Infrastructure Program (HSIP) database.

(Continue . . . )


Of particular note, since research is still ongoing, this study didn’t consider earthquakes due to human activity – such as `Fracking’ - nor does it take into consideration the amplification of ground shaking due to soil type, which could exacerbate the effects of some earthquakes.


Even though the half of all Americans live in a seismically active region of the country, few are really prepared to deal with the aftermath of a major quake.  As a bare minimum, everyone should have a well thought out disaster and family communications plan, along with a good first aid kit, a `bug-out bag’, and sufficient emergency supplies to last at least 72 hours.


In When 72 Hours Isn’t Enough, I highlighted  a colorful, easy-to-follow, 100 page `survival guide’ released by Los Angeles County, that covers everything from earthquake and tsunami preparedness, to getting ready for a pandemic.


The guide may be downloaded here (6.5 Mbyte PDF).

While designed specifically for the nearly 10 million residents of Los Angeles County, this guide would be a valuable asset for anyone interested in preparing for a variety of hazards. And in Los Angeles, the advice is to have emergency supplies (food, water, etc) to last up to 10 days. In my humble opinion, 2-weeks in an earthquake zone isn’t overkill.

Working to improve earthquake awareness, preparation, and safety is, which promotes yearly earthquake drills and education around the country (see NPM13: A Whole Lotta Shakeouts Going On).  If you live in one of these seismically active areas, I would encourage you to take part in these yearly drills.


The start of National Preparedness Month is only three weeks away, so now is an opportune time to become better prepared as an individual, family, business owner, or community to deal with all types of disasters   I would invite you to visit the following preparedness sites.






And for some recent blogs on earthquake hazards in the United States, you may wish to revisit:

OSU: Pragmatic Action - Not Fatalism - In Order To Survive The `Big One’
USGS: New Madrid Simulation Shows Risks For Memphis & Little Rock
USGS: Eastern Earthquakes - Rare But Powerful
Estimating The Economic Impact Of A San Andreas Quake)
Revised Risk Of `The Big One’ Along San Andreas Fault

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