Venue & Other Technical Information

Technical Site Visit Locations: 

NUMO Site

Jardines de San Juan Restuarant  

DeRose Vineyards (features outside that show shearing) 9970 Cienega Rd, Hollister, CA 95023

The first stop of the technical site visit will take attendees to the NUMO field site in California where

Berkeley Lab has instrumented a dedicated in-situ borehole observatory to study the effects of dynamic

stressing on faults. The field test is motivated by the challenge of safe nuclear waste disposal in

seismically active regions, common in Japan, the United States, and other countries worldwide. There is

a concern that traveling seismic waves produced by major earthquakes may significantly affect the

hydromechanical properties of the host rocks used for disposal.

The site is located atop the San Andreas fault (SAF) zone 4 km northwest of San Juan Bautista, about

120 km southeast of San Francisco. The area features regular local earthquakes with magnitudes of 3.5-

4.5 as well as strong earthquakes of magnitude ~7 originated within 500 km from the site. Berkeley Lab

drilled three dedicated boreholes hosting pressure and strain monitoring sensors as well as distributed

acoustic sensing and optical seismometers for characterization of the incident signals. The boreholes are

equipped with a novel tool, DORSA (Downhole Robotic Stress Analyzer), dedicated to the long-term

monitoring of fault deformation, pressure, and seismicity. The group will be led by Dr. Craig Ulrich on a

tour of the borehole installation and view active road deformations which show how sagging can occur

in a strike slip fault zone on a small scale.

The group will then have lunch in San Juan Bautista and participate in a discussion about the measured

SAF deformations at the NUMO field site. Participants will make a short stop after lunch at the San Juan

Bautista Mission – although there is no obvious trace of damage related to earthquakes (due to the

many repairs made over the years), the eastern side of the building shows the 19th century earthquake

scarp that is quite impressive.

The final stop will be at nearby DeRose Winery where the group will visit a building on the property to

observe another example of shear deformations from damage during a recent earthquake. Although

some repairs have been made to the structure, the fault is more actively creeping in this area and

participants will be able to see new aspects of damage. The return trip to Berkeley will include some

nice views of SAF geomorphology that can be seen from the shuttle along the road.

Some participants of the technical site visit will remember that the topic of fault slip and its potential for

creating permeable pathways for radionuclide transport was at the center of Task B in the previous

DECOVALEX-2019 phase.