HOLLISTER (CBS SF) — A new study that says there may be a link between earthquakes and the moon and sun could change the way scientists study tectonic plates.
Like most of California, Hollister is on shaky ground. And with a swarm of numerous small earthquakes over the last few days, the ground is shakier than normal.
“The internet said there were 18, but I only felt four,” said Hollister resident Rori Nelson. “They were short of rolling quakes, like someone was nudging you.”
But scientists with the U.S. Geological Survey say there is much more going on below the surface than just the earthquakes you can feel.
A new study says much smaller quakes are happening deep down below the earth’s crust almost on a regular schedule that are tied to the phases of the moon.
Just as the moon’s gravitational pull affects the ocean tides, scientists say they now have hard data to show how it has the same effect on hard ground.
“When the full moon is here, we are actually standing in relation to the center of the earth this much higher,” explained Research Geophysicist Dr. Malcolm Johnston.
Johnston says precise sensors located in Parkfield on the Central California Coast have been detecting deep tremors along an active section of the San Andreas Fault.
Scientists studied 81,000 of those tremors over a nine-year period and compared the data to tidal cycles.
They found these tiny earthquakes were much more likely to occur during the waxing period — when tides were getting higher — putting added pressure on the San Andreas.
“It applies a very, very small loading and unloading on the San Andreas fault,” said Johnston. “There are already great pressures on the San Andreas. This is many thousands of times smaller than that. This is a very small motivation, or loading if you like.”
Johnston says scientists will continue studying to see if the tidal cycles have any direct relationships larger earthquakes that reach the surface. But he says there’s no reason to believe the current swarm in Hollister is tied to our current full moon.
Scientists also say certain characteristics of faults such as orientation can affect the tidal response.