A report published last year(1) includes recent analysis that dramatically expands the North American earthquake threat risk projections to now include almost half of the entire USA population and has also increased the severity projections for previously acknowledged regions. In many cases, those in these newly upgraded risk zones remain unaware and unprepared for earthquakes.
The report notes that a large portion of the population of the United States live in areas vulnerable to earthquake hazards although many of them are unaware of the risks and even more are unaware of the severity of some risks.
Using data collected in 2013 and 2014 as well as systematically analyzing the last four cycles of the U.S. Geological Survey's (USGS) National Seismic Hazard Models (published in 1996, 2002, 2008 and 2014), the report warns that the USA East Coast could be hit extra hard because of its dense populations and lack of earthquake prepared buildings and structures.
Also the upgraded risk warnings mentioned in the report include higher probabilities of catastrophic tsunamis that might hit coastlines of Alaska and the Pacific Northwest as well as repeats of historic catastrophic U.S. earthquakes, such as the 1906 San Francisco earthquake or the 1811-1812 New Madrid earthquakes. The report estimates that these repeat events could cause up to US$500 billion in damage. It also warns that there is a significant number of critical infrastructure facilities located in high earthquake-hazard areas and in many cases with insufficient earthquake risk mitigation efforts.
According to FEMA, the main factors that determine earthquake risk include:
- the level of seismic hazard in a geographical area;
- the number of people in the geographical area;
- the amount of property exposed to seismic hazards; and
- how vulnerable these people and property are to the hazards (mitigated vs. unmitigated risk vulnerability).
This new scientific analysis finds that there is greater seismic hazard than previously assumed, in denser population zones, and in areas where there are large percentages of unmitigated risk vulnerability. Hence, more people in more places are vulnerable to severe earthquake threat risks than had been previously known.
According to FEMA, geological seismic hazard levels differ significantly across the United States, both between and within states. (to compare the previously known risk levels in your region with these new calculations, go to Earthquake Hazard Maps on the FEMA website.)
Earthquake hazard map: SDC map of the Eastern United States for low-rise Occupancy Category I and II structures located on sites with average alluvial soil conditions.
Estimates of predicted earthquake casualties and fatalities correspond to the number of people present in the earthquake zone as well as the magnitude and intensity which the shake produces. Likewise, earthquake damages correspond to the quantity and value of the buildings, infrastructure and other property in those areas. According to FEMA, seismic risk increases as earthquake-prone regions become more densely populated and urbanized.
Since vulnerability of property damage is mitigated by the prevalence or lack of earthquake-resistant construction and best practices compliance the fact that large geographical areas are woefully unprepared and unmitigated suggests substantial damage potential exists. Buildings, infrastructure, and utilities that comply with the latest seismic building codes and standards should be more resistant to earthquake damage. Structures that do not comply are likely to sustain more damage.
According to FEMA, levels of earthquake preparedness and disaster resilience determine how vulnerable people are to seismic hazards. Businesses, schools, health care facilities, organizations, individuals and communities that have invested in assessing their risks and in formulating and implementing responsible preparedness and mitigation measures are likely to experience fewer casualties, less damage and less disruption from earthquakes. Earthquake-resistant construction is a preeminent example of such measures.
Brian Clark Howard, writing in the National Geographic about the 2013 and 2014 updated USGS data notes that the region’s most at risk are still the West Coast, the Intermountain West, and several known active regions in the central and eastern U.S., including near New Madrid, Missouri, and Charleston, South Carolina.
Howard writes that based on the new seismic data as well as improved computational modeling done at the University of California, Berkeley and elsewhere that the 16 states at highest risk of quakes are Alaska, Arkansas, California, Hawaii, Idaho, Illinois, Kentucky, Missouri, Montana, Nevada, Oregon, South Carolina, Tennessee, Utah, Washington, and Wyoming. In addition, the data suggests that there is an higher earthquake risk around the New Madrid Seismic Zone in southwestern Missouri; the zone stretches into Illinois, Indiana, Kentucky, Tennessee, Mississippi, and Arkansas. There is also higher risk than previously assumed across much of the West Coast, thanks to new data from California and theNorthwest's Cascadia Subduction Zone.
It may well be that for many of us, these new findings put us at risk or greater risk than we may have previously assumed based on our location and preparedness plans. This new report is a good “prompt” to revisit earthquake readiness for our businesses, homes, schools and not-for-profit organizations. You can learn more about earthquake readiness on the FEMA website. This may be a great wake-up call reminder for us to consider seriously our own revised exposure to earthquake risks.
There are specific steps that one can take to reduce the chances that earthquakes will injure employees, customers, or other workplace visitors, damage workplaces, or jeopardize the survival of your operations. Such steps include: assess your seismic risks and how to develop and implement a plan to cost-effectively mitigate those risks; educate your people with earthquake-related information resources, ranging from reports, handbooks, guides, and manuals to posters, software, web-based tools, and instructional materials; and implement training and readiness preparation focused on earthquake risk reduction, and managing an earthquake disaster. These efforts can supplement or be integrated with other training and preparation efforts to addresses mitigation, preparedness, and response subjects that are applicable to earthquakes and as well as other hazards.
 Kishor S. Jaiswal, Mark D. Petersen, Ken Rukstales, and William S. Leith (2015) Earthquake Shaking Hazard Estimates and Exposure Changes in the Conterminous United States Earthquake Spectra