Friday, July 18, 2014

USGS: Updated U.S. Seismic Risk Hazard Maps



# 8846


Yesterday the USGS released a 243 page PDF report outlining the revised seismic hazard risks for the United States – their first major update since 2008 – and among its findings it reports a higher risk of strong quakes in the Eastern United States than previously appreciated. 


Be warned, with hundreds of maps and graphics, this is a very large (113mb) download.




Documentation for the 2014 Update of the United States National Seismic Hazard Maps

By Mark D. Petersen, Morgan P. Moschetti, Peter M. Powers, Charles S. Mueller, Kathleen M. Haller, Arthur D. Frankel, Yuehua Zeng, Sanaz Rezaeian, Stephen C. Harmsen, Oliver S. Boyd, Ned Field, Rui Chen, Kenneth S. Rukstales, Nico Luco, Russell L. Wheeler, Robert A. Williams, and Anna H. Olsen

The national seismic hazard maps for the conterminous United States have been updated to account for new methods, models, and data that have been obtained since the 2008 maps were released (Petersen and others, 2008). The input models are improved from those implemented in 2008 by using new ground motion models that have incorporated about twice as many earthquake strong ground shaking data and by incorporating many additional scientific studies that indicate broader ranges of earthquake source and ground motion models. These time-independent maps are shown for 2-percent and 10-percent probability of exceedance in 50 years for peak horizontal ground acceleration as well as 5-hertz and 1-hertz spectral accelerations with 5-percent damping on a uniform firm rock site condition (760 meters per second shear wave velocity in the upper 30 m, VS30). In this report, the 2014 updated maps are compared with the 2008 version of the maps and indicate changes of plus or minus 20 percent over wide areas, with larger changes locally, caused by the modifications to the seismic source and ground motion inputs.



Although earthquakes in the Eastern half of the United States have been recorded in the past (including the Charleston, SC earthquake of 1886), the August 2011 5.8 earthquake that rocked Virginia and the Nation’s capital (see USGS Statement On The Virginia Earthquake) provided fresh evidence not only of their potential to occur,  but also how widely felt they may be (see USGS: Eastern Earthquakes - Rare But Powerful).


Another strong quake a few months later in the Heartland (see 5.6 Mag Quake Rattles Oklahoma), has been followed by hundreds of additional quakes in a region not expected to produce that much seismic activity. 


Additional earthquake research has turned up new fault lines in California, and perhaps most worrisome of all, found the potential for a much larger quake from the Cascadia Fault in the Pacific Northwest than previously estimated (see Just A Matter Of Time for more on this threat)

While all 50 states have at least some seismic potential (yes, even Florida), 42 states are viewed as having a reasonable chance of seeing a damaging quake in the next 50 years, and 16 states in particular are considered at highest risk.  The USGS press release states:


The hazard is especially high along the west coast, intermountain west, and in several active regions of the central and eastern U.S., such as near New Madrid, MO, and near Charleston, SC. The 16 states at highest risk are Alaska, Arkansas, California, Hawaii, Idaho, Illinois, Kentucky, Missouri, Montana, Nevada, Oregon, South Carolina, Tennessee, Utah, Washington, and Wyoming.


While they acknowledge the risks of man-made earthquakes – due primarily to fracking and injection wells – research into these hazards is just getting started.  The USGS states:


Induced Earthquakes … Research Underway

Some states have experienced increased seismicity in the past few years that may be associated with human activities such as the disposal of wastewater in deep wells.

One specific focus for the future is including an additional layer to these earthquake hazard maps to account for recent potentially triggered earthquakes that occur near some wastewater disposal wells. Injection-induced earthquakes are challenging to incorporate into hazard models because they may not behave like natural earthquakes and their rates change based on man-made activities.


While it may not be predictive of future events, so far 2014 has provided a major uptick in seismic activity in the United States, and around the globe.  Southern California, Alaska, and California have all reported increased activity (see LA Times Quakes are increasing, but scientists aren't sure what it means).


Last December, in Dr. Lucy Jones: `Imagine America Without Los Angeles’, we looked at a presentation given by Dr. Jones at the  annual meeting of the American Geophysical Union (held this year in San Francisco),  that emphasized that should the `big one’ hit Southern California, we could literally `lose’ Los Angeles.


She warned that the damage could be far greater, and last much longer, than most people believe.  While 99 out of 100 modern buildings might remain standing, the (often buried) infrastructure needed to provide water, electricity, internet connectivity, and natural gas – the lifeblood -  to the region could be devastated (see CBS News report).


If this sounds like hyperbole, in 2010 (see Revised Risk Of `The Big One’ Along San Andreas Fault) we looked at a study that suggested that Southern California may be more overdue for another major quake than previously thought, and in the following year (see Estimating The Economic Impact Of A San Andreas Quake) we looked at a report from the U.S. Bureau of Labor Statistics that endeavored to gauge the crippling impact that a highly feasible (and long overdue) 7.8 magnitude Southern California earthquake would have on jobs and local businesses.


Download PDF file

A quake of this magnitude, they estimate, could affect  430,000 businesses and 4.5 million workers and deliver a devastating – and prolonged – blow to the local (and national) economy.


While attempts at predicting earthquakes have met with little success, we do know that over time, seismically active regions will be hit again and again, and that the only defense is to be prepared for when that happens.


Seismic threats extend beyond earthquakes, as they encompass volcanic eruptions (see Washington State: Volcano Awareness Month) - and Tsunamis – both of which have the ability to affect both people and property thousands of miles away from the originating event  (see The USGS West Coast Tsunami Scenario Report & East Coast Tsunami Threats).


Which is why everyone should have a disaster plan, not just those who live in an earthquake zone.


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.


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 lastly, in NPM13: The Greatest Prep Of All,  I wrote about what I consider to be the most important preparedness step you can take – having, and being,  a disaster buddy.  Cultivating a network of family and friends to whom you can turn for help in a disaster, to who can turn to you for aid,  if they need it.


Because no matter where you live, its just a matter of time before the next disaster strikes.

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