The Oklahoma Department of Transportation is relieved by the results of a recent scientific analysis showing it’s unlikely that a 4.6 or less magnitude earthquake will damage transportation infrastructure in the state, including bridges. The department plans to incorporate this new information into its bridge inspection protocol starting in April.
“This is great news for Oklahomans concerned with the long-term effects of increased earthquakes in our state,” said Mike Patterson, ODOT executive director. “Our department has aggressively inspected bridges and infrastructure for the past few years and learned a great deal through this process about this relatively new phenomenon in our state.”
Infrastructure Engineers Inc., a team of consultants that worked closely with researchers from the University of Oklahoma, validated ODOT’s inspection process. Additionally, the year-long study of earthquake data revealed there is no structural damage occurring on bridges after tremors below magnitude 4.7, indicating that bridge inspections are unnecessary below this level. The department will continue to inspect bridges after earthquakes, but starting at a threshold of 4.7 magnitude events.
The magnitude of an earthquake will determine how wide an area from the epicenter will be inspected. Starting in April, crews will respond immediately to earthquakes at these new levels:
- 4.7 to 4.8 magnitude — 5-mile inspection radius;
- 4.9 to 5.3 magnitude — 15-mile inspection radius;
- 5.4 to 5.8 magnitude — 30-mile inspection radius;
- 5.9 to 6.2 magnitude — 60-mile inspection radius; and
- 6.3-plus magnitude — 120-mile inspection radius.
ODOT previously checked bridges after almost every earthquake, then adjusting later to inspect after every 3.0-magnitude event. After consulting national experts, including the California Department of Transportation, the U.S. Geological Survey and Oklahoma Geological Survey, that protocol changed in mid-2014 to inspections after every 4.0-magnitude event within a 5-mile radius of the epicenter.
“We were conservative in our approach to bridge inspections, but now we have the science to know with more certainty that 4.0- to 4.6-magnitude earthquakes present no danger to transportation infrastructure in the state,” said Casey Shell, ODOT chief engineer. “This change in protocol allows the department to better focus its resources.”
Shell said ODOT has never found any structural bridge damage in the state related to earthquakes since inspections began in 2013. Oklahoma’s bridges meet federal design standards, meaning they are meant to safely withstand some degree of vibrations and movement.
Another component of the current $575,000 study was the creation of a post-earthquake bridge inspection manual that describes best practices in detail as well as providing a step-by-step inspection guide. This comprehensive document will be used by all ODOT bridge inspectors statewide, and will be shared with other state agencies and government entities such as the Oklahoma National Guard and with counties and municipalities. Additionally, the study provided training to ODOT personnel that also will be shared with other agencies, as well as detailed structural analysis on three bridges representing those typically used in Oklahoma.
A second phase of the Infrastructure Engineers Inc. study is planned to begin next fiscal year, which will create an analytical program combining ODOT bridge data and earthquake data to help plan a localized inspection route. This will help inspectors respond even more quickly and be more cost effective while ensuring safety for motorists.