Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Assessing the seismic hazard of the central eastern United States

13.12.2010
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 seismic risk 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 earthquake engineering 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 earthquake study.

Lynn Nystrom | EurekAlert!
Further information:
http://www.vt.edu

More articles from Earth Sciences:

nachricht Climate satellite: Tracking methane with robust laser technology
22.06.2017 | Fraunhofer-Gesellschaft

nachricht How reliable are shells as climate archives?
21.06.2017 | Leibniz-Zentrum für Marine Tropenforschung (ZMT)

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>