Fiber optic networks do more than just ride out major earthquakes without dropping a bit. They can also detect and collect data on the quakes themselves. Two major quakes – magnitude 6.4 and 7.1 – hit eastern California on 4 and 5 July 2019 respectively, in the high desert of Kern and San Bernardino counties, where seismometers aren’t thick on the ground. To understand what happened, and what continues to happen, Caltech scientists needed to quickly get more sensors into the field.
Fortunately, the eastern slope of the Sierra Nevada – Mono, Inyo, Kern and San Bernardino counties in California, and Washoe and Douglas counties and Carson City in Nevada – has fast, earthquake ready fiber connectivity.
The Digital 395 open access fiber optic network, which links Reno to Barstow along the eastern Sierra, runs right through the area that was hardest hit. By connecting “surveillance technology initially developed for military and general security applications that can detect ground movement” to a single fiber strand, an underground fiber route – or sections of it, at least – can be used for “pre-shock detection of P and S waves across the fibers”, according to Michael Ort, CEO of Praxis Associates/Inyo Networks, which built and operates Digital 395. In other words, fiber optic networks can be used detect the big incoming shockwaves a few critical seconds before they hit, as well as provide valuable scientific data about the event.
Preliminary discussions about installing distributed acoustic sensing equipment had been held with Caltech, but everything went into high gear when the quakes began hitting Ridgecrest. Zhongwen Zhan, a Caltech scientist, asked about using one of Digital 395’s strands, and got a quick yes from Ort.
He hooked up his instruments on 9 July 2019, four days after the 7.1 quake and while the ground was still shaking with aftershocks. The results were immediate, with multiple (mostly small) quakes detected every minute, beginning as soon as the equipment was turned on.
“The fiber gave them about 5,000 sample points over 10km of fiber. Before they had only a handful of sample points in the area. So you got only “discrete points” of these, not the overall picture”, Ort said.
“This first time ever use of fiber has given us many data points, making our observations more complete and natural”, said Mark Simons, JPL chief scientist and CalTech professor of geophysics. “It’s a true breakthrough that will revolutionise our perspective and help with early warning”.
Digital 395 was built with money from the 2009 federal stimulus program and from the California Advanced Services Fund (CASF). It was the first and the longest of the open access middle mile fiber routes funded by CASF, before the California legislature bowed to pressure (and money) from incumbent telephone and cable companies and banned those types of projects.