FAQs on Seismicity Near Yucca Mountain

Yes, we record about 10 micro-earthquakes per day within roughly 50 km (30 mi) of the proposed repository. At a closer range, we see about 20 per year within 15 km (10 mi). Our network is sensitive enough to detect earthquakes to M 0 and below in this inner range. Typically, none of these events are felt.

Yes, in 1992 the M 5.6 Little Skull Mt. Earthquake shook and damaged the Field Operations Center near the actual epicenter, but there was no damage at facilities at Yucca Mountain itself. In almost every year since then, there have been mild earthquake felt reports for smaller shocks from personnel working at the Yucca Mountain site. This is not unusual, as the same would occur for nearly any place in Nevada.

Yes, and we tend to divide the past into geologic, historic, and instrumental time. "Historic" time starts in the middle of the 1800's and "instrumental" time starts with the monitoring network in 1978. During instrumental time, there was the M 5.6 Little Skull Mountain about 25 km (15 mi) from Yucca Mountain. In this same time period, there have been no earthquakes >= 4 within 15 km (10 mi) of it. In historic time, earthquake locations are somewhat fuzzy; but we believe the Little Skull Mt. earthquake was the largest within 25 km (15 mi). In geologic time, it has been over 50,000 years since an event of at least M 6.5 has occurred within this range.

During the monitoring period, we believe that the level of seismic activity in the vicinity of Yucca Mountain has stayed about the same, except for a few years following the 1992 Little Skull Mt. earthquake which had thousands of aftershocks, but confined to a relatively small area. The current level seems consistent with the historical level and probably with the level over the past few thousand years. Continued monitoring is important in verifying that this level stays nearly constant. The appearance of many earthquakes near Yucca Mountain on some NSL maps of seismic activity is, in large part, due to the dense and sensitive network that NSL operates there.

Again, this is the responsibility of the DOE engineers. Possible damage to stored waste canisters and potential effects on the long-term storage barriers will be addressed by the DOE. The largest earthquake at the repository itself, as known from geologic evidence, had a slip of about 1 meter; earthquakes of this size appear to recur at intervals like tens of thousands of years there. The possibility of strong ground motion from faults outside the immediate area exists at a much smaller recurrence interval, but their ground motion is predicted to be less and is being considered in the seismic design.

Again, the DOE will design the transportation casks with many hazards in mind, including earthquake effects. Derailment of train cars or overturning of trucks are possible, but very unlikely, due to an earthquake. Even in such cases, the transportation casks are designed to withstand much larger impacts than these accidents might lead to.

The ground motion from such an earthquake at Yucca Mountain would be felt as a slow-moving wave, with an amplitude too small to be damaging. Similar waves have already been felt at the proposed site from the 1992 M 7.3 earthquake at Landers, California.

The DOE has funded the lab for about the last ten years to monitor seismicity in the area around Yucca Mountain and to do research on this topic at the level of about $1M per year. This funding amounts to about half of the lab's external funding. There are 5-6 Ph. D. level personnel at the lab involved with the Yucca Mountain seismic studies and several more support personnel. The task of monitoring seismic activity in the rest of the state has benefited from sharing of the communication and computer infrastructure emplaced at the lab with Yucca Mountain funding.