Assessing the seismic hazard of the central eastern United States

Dec 10, 2010
Virginia Tech associate professor of civil and environmental engineering Russell Green focuses on the study of paleoseismology to achieve a greater understanding of the probability of seismic events. Credit: Provided by Virginia Tech

As the U.S. policy makers renew emphasis on the use of nuclear energy in their efforts to reduce the country's oil dependence, other factors come into play. One concern of paramount importance is the seismic hazard at the site where nuclear reactors are located.

Russell A. Green, associate professor of civil and environmental engineering at Virginia Tech, spent five years as an earthquake engineer for the U.S. Defense Nuclear Facilities Safety Board in Washington, D.C., prior to becoming a university professor. Part of his responsibility at the safety board was to perform seismic safety analyses on the nation's defense nuclear facilities.

"I found the greatest uncertainty in seismic analyses was related to the ground motions used in the analyses... Many of the facilities being analyzed were already built and operating, and the facilities were already heavily contaminated with radioactive material," Green said.

An immediate concern then became how and which buildings to retrofit. The balance in the decision-making process was between using overly conservative ground motions and potentially wasting "hundreds of millions of dollars in unnecessary retrofits" versus using less demanding motions and potentially "placing facility workers, neighboring towns, and cities at risk," Green added.

Green's concerns and expertise in earthquake engineering earned him a National Science Foundation CAREER Award in 2006 valued at more than $400,000. He has used this support for the development of procedures for collecting and analyzing data required for assessing the seismic hazard in regions where moderate to large earthquakes would have significant consequences, yet they remain low probability events.

Green said a "huge shift" in the engineering profession's approach to reducing has occurred during the past decade. Building codes have been modified to include performance-based earthquake engineering (PBEE) concepts. This differs from the previous traditional design approach that used "life safety as the primary design goal," Green explained. "PBEE is based on the premise that performance can be predicted and evaluated with quantifiable confidence, allowing the engineer, together with the client, to make intelligent and informed trade-offs based on life-cycle considerations rather than construction costs alone."

To implement PBEE and to calculate the annual probability of specific losses due to seismic events, engineers need to know the fragility of structural systems and the probabilistically quantified seismic hazard.

To conduct his research, Green is focusing on paleoseismology, the study of the timing, location, and size of prehistoric/pre-instrumental earthquakes, ranging from those that occurred hundreds to tens of thousands of years ago.

"I believe that encompasses geology, seismology, geotechnical engineering, structural engineering, urban planning, and emergency response, " Green said.

"The appropriate selection of ground motions is particularly difficult because many critical facilities are located in the central and eastern U.S. and in the Pacific Northwest," Green said. "We know moderate to large earthquakes have occurred in these regions. We just do not know how large the events were, how often they occurred, or the characteristics of the associated ground shaking, such as duration, amplitude, and frequency content."

Unlike many places in the western U.S. where excavations can be used to determine the past movement on earthquake faults, in the central-eastern U.S. the locations of most faults are unknown and/or the faults are too deep to excavate. As a result, Green is concentrating his work on the development and validation of paleoliquefaction procedures. Soil liquefaction is the transition of soil from a solid to a liquefied state. Earthquakes are one cause of liquefaction, with the evidence of liquefaction often remaining in the soil profile for many thousands of years after the earthquake.

"Paleoliquefaction investigations are the most plausible way to determine the recurrence time of moderate to large earthquakes in the central-eastern U.S. ," Green said. "By extending the earthquake record into prehistoric times, paleoseismic investigations remove one of the major obstacles to implementing PBEE across the U.S."

To determine the age of a paleoliquefaction feature, researchers might use any one of a number of techniques, including: radiocarbon dating, optically stimulated luminescence, or archeological evidence.

Green said his work will address the "gaps in knowledge that typically stem from uncertainties related to analytical techniques used in back-calculations, the amount and quantity of paleoliquefaction data, and the significance of changes in the geotechnical properties of post-liquefied sediments such as aging and density changes."

In addition to his work studying paleoearthquakes, Green has also been involved in performing field studies of several recent earthquakes. He has performed post-earthquake field studies of the 2008 Mt. Carmel, Ill., magnitude 5.2 earthquake, the 2008 Iwate Miyagi-Nairiku, Japan, magnitude 6.9 earthquake, the 2010 Haiti, magnitude 7.0 earthquake, and the 2010 Darfield, New Zealand, magnitude 7.1 earthquake. The latter two field studies were National Science Foundation sponsored Geo-Engineering Extremes Events Reconnaissance (GEER) investigations, with Green serving as the US Team leader for the Darfield study.

Explore further: Synchronization of North Atlantic, North Pacific preceded abrupt warming, end of ice age

add to favorites email to friend print save as pdf

Related Stories

Ill. earthquake a wake-up call

Apr 20, 2008

A U.S. seismologist said the earthquake that jolted the Midwest Friday is a reminder of the risks seismic events pose outside familiar quake areas.

Earthquakes: Bracing against the shaking

Oct 08, 2010

(PhysOrg.com) -- An Arizona State University geotechnical engineer says the U.S. should learn from what New Zealanders did to withstand a recent powerful quake – and how they could have prepared even ...

US ports vulnerable to devastating earthquake damage

May 23, 2006

If a repeat of the 1906 San Francisco earthquake were to occur, and the Port of Oakland were so severely damaged that it took as long as two years to resume full operations, what would be the impact on the U.S. economy?

Recommended for you

Fires in Central Africa During July 2014

10 hours ago

Hundreds of fires covered central Africa in mid-July 2014, as the annual fire season continues across the region. Multiple red hotspots, which indicate areas of increased temperatures, are heavily sprinkled ...

NASA's HS3 mission spotlight: The HIRAD instrument

20 hours ago

The Hurricane Imaging Radiometer, known as HIRAD, will fly aboard one of two unmanned Global Hawk aircraft during NASA's Hurricane Severe Storm Sentinel or HS3 mission from Wallops beginning August 26 through ...

Fires in the Northern Territories July 2014

Jul 23, 2014

Environment Canada has issued a high health risk warning for Yellowknife and surrounding area because of heavy smoke in the region due to forest fires. In the image taken by the Aqua satellite, the smoke ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

Raveon
3 / 5 (2) Dec 10, 2010
What about the reactors near the shore? There are quite a few at sea level and they are going to be a major headache when the sea level rises. The stuff inside other than the fuel is all radioactive as well. Every containment building (the reactor housing) is full of tons of metal and other stuff that is all now radioactive. Since our one true god is money, my bet is that they will seal them up, wave a wand and declare it safe, then let them just sit there and go under water. stoopid monkeys
neiorah
not rated yet Dec 11, 2010
I once read about a nuclear power plant in a mid western state that was built along a fault line. All I could think was "how stupid are these people". I am glad someone is looking into the risk that these less well known faults carry, especially when it comes to nuclear power.
Nik_2213
not rated yet Dec 12, 2010
One problem is that there may not be a single, clear surface fault trace in a potentially active area. Instead, there can be a complex web of smaller, buried faults, wriggling and writhing, transferring tensions to and fro. Some may only shift significantly once in a millenium, some may now have been unloaded by isostasis following the last ice age. Until and unless there's a minor tremblor on a fault, it can require luck and inspired deduction to locate such. IIRC, a recent seismic survey across the continental US found a lot of surprises. New Madrid isn't the only contender...