Font ResizeRUSSIAN RIDGE — At the summit of Rolph Hill, in a corner of the Russian Ridge Open Space Preserve closed to the public, stands an alien-looking machine — a small white dome balanced on three long "legs" sunk deep into moss-covered bedrock.
Inside is a small, powerful GPS receiver that's measuring the movement of the earth via satellite every 15 seconds and a cellular modem that sends the data hundreds of miles away. Scientists are using it to calculate earthquake hazards across the San Andreas Fault, which lies a few miles to the east.
"My co-worker always says it looks like a droid, like R2-D2," joked Erica Simmons, a planner with the Midpeninsula Regional Open Space District, as she touched the immaculate white dome that holds the GPS data receiver and antenna.
Three fellow 'droids,' identical in every aspect, have also been installed at key locations on Midpeninsula Regional Open Space District properties, including Rancho San Antonio, Mills Creek and La Honda Creek open space preserves.
They are among 220 Plate Boundary Observatories installed in Northern California and 1,050 such stations across the Western U.S., and together they form a comprehensive picture of the strain and stress occurring deep in the earth as the North American and Pacific tectonic plates grind against each other.
Geophysicists and other earthquake experts, as well as the public, can now access a database with all the information for
The view from the peak of Rolph Hill is deceptively serene, considering the San Andreas fault runs under Portola Valley and up through Crystal Springs Reservoir down in the valley below. Both areas were swathed in fog clear out to Mt. Diablo on Wednesday morning. Another fog bank covered the Pacific ocean to the west, leaving the impression of living in a sunny island above the clouds.
It doesn't feel like it, but this area is moving — faster than most other earthquake zones in the Western U.S.
Scientists estimate movement between the two tectonic plates at an average of 2 inches per year, but the Russian Ridge GPS device showed that the area moved approximately 1.2 inches to the north and 0.8 inches west in the past year, as well as gaining 0.3 inches in elevation, according to the Midpeninsula Open Space District.
"It's your classic San Andreas Fault motion, where the areas to the west are moving north relative to the areas to the east," said Simmons.
Or, more specifically, the Pacific plate is moving northwest while the North American plate moves southwest.
They meet at the fault lines, bending and warping the crust where they meet. Enough pressure can cause an earthquake.
"The most damaging earthquakes we're likely to have are at plate boundaries, and that's why people study the plate boundaries very carefully," said Jessica Murray-Moraleda, a GPS expert and member of an earthquake hazards team with the U.S. Geological Survey in Menlo Park.
Murray-Moraleda says the new technology is a great improvement over a seismometer, the tool traditionally used to record ground motion, because it transmits information every 15 seconds and sometimes as quickly as every second. It also records post-earthquake movement, which is too slow for a seismometer to catch.
"You can use it to estimate, 'How much did the crust move underground?' And it's useful in understanding where stress has been released and where it has been increased because of that earthquake," she explained.
To learn more about the Plate Boundary Observatory project or download data compiled by the project, visit pboweb.unavco.org/
Staff writer Julia Scott can be reached at (650) 348-4340 or at julia.scott@bayareanewsgroup.com.
