SAN LUIS OBISPO – Four large trucks were staged in a San Luis Obispo parking lot on Wednesday (July 27) afternoon as PG&E held live demonstrations of ground-vibrating trucks to be used to help further understand earthquake faults in San Luis Obispo County.
The public demonstrations at the PG&E Energy Education Center were attended by about 70 people, most donning earplugs, and took about five minutes. The caravan of four, 65,000-pound Vibroseis trucks created a rumbling comparable to a large garbage truck rolling down a city street. The big trucks were displayed so the public would know what to expect when they hit nearby roadways later this year.
The trucks – to be teamed with up to 2,000 strategically-placed recording devices – will produce sound waves that can penetrate the earth’s crust up to 12 miles. When they complete the five-minute test in one section, they will drive up to 300 feet down the road and repeat the process. The recording devices, which are about 6 inches tall and wide and with a 5-inch spike to be planted in th
e ground, will record the echoes to create two-dimensional images, including seismic-reflection mapping, of the faults near Diablo Canyon Power Plant (DCPP). In tighter areas, a single and smaller weight-drop truck will be used.
The onshore seismic testing is part of PG&E’s increased efforts to analyze fault zones near its nuclear power plant and the greater San Luis Obispo area. PG&E has accelerated its ongoing seismic investigations in the wake of Japan’s March 11 earthquake and tsunamis that impacted the Fukushima Daiichi nuclear plant there. PG&E will be sharing all its seismic data with local, state and federal government institutions to ensure their facilities and emergency plans are based upon the most advanced understanding of the seismic characteristics of the region.
Dr. Stu Nishenko, PG&E senior seismologist, compared the advanced images PG&E expects to capture of the faults as upgrading from an X-ray to a detailed CT scan.
The demonstrations come nearly a week after PG&E presented public plans for offshore, three-dimensional seismic studies to further define the geophysical characteristics of the region off of the San Luis Obispo County coast. These meetings were held by the State Lands Commission, which is preparing an environmental impact report on the planned survey that will encompass several hundred square miles.
The Vibroseis trucks will hit the roadways later this year. Areas where some of the work will be conducted include Highways 101 and 1 near San Luis Obispo, Avila Beach, Grover Beach and Oceano as well as other roadways.
Just before the parking lot demo on Wednesday, members of the PG&E’s seismic team held two informational sessions for the general public and government officials. Among the questions raised were the affects the noise could have on animals and access to private property.
Nishenko said the goal is to keep noise and rattling to a minimum of less than .20 inches per second, which is just below the human nuisance threshold. “It doesn’t really cause that much ground vibration on the surface,” he said of the tests. And all residents in the affected areas will be notified prior of the testing, which will be done between the hours of 7 a.m. and 9 p.m., added Nishenko.
The offshore and onshore advanced seismic tests are part of the company’s ongoing Long Term Seismic Program at DCPP to ensure the safety of the plant. For more information about DCPP, visit www.diablocanyonpge.com.