New research investigates the impact of tidal pull on the San Andreas Fault Line.
Everyone knows the effect the gravitational pull of the Sun and Moon has on the ocean tides, but new research is looking at the impact the heavenly bodies may have on the San Andreas Fault Line that runs underneath California, according to LiveScience.com.
Nicholas van der Elst, a seismologist and geophysicist at the U.S. Geological Survey’s Earthquake Science Center in Pasadena, California, and lead author on a new study, said the research team focused on low-frequency quakes recorded between 2008 and 2015. Low-frequency quakes are described as small, deep seismic events, no larger than a magnitude 1 on the Richter Scale.
The gravitational pull of the moon and the sun varies over a two-week period, with the strongest pull being exerted during “spring” tides, as the objects are aligned, and the weakest during the “neap” tides, when the moon and sun are perpendicular to the Earth.
After analyzing the data from about 81,000 catalogued quakes in the region, the researchers noted the number of recorded quakes didn’t peak at the strongest part of the two-week cycle, but instead as the tidal pull was strengthening.
Van der Elst told Live Science the team looked at the part of the fault that was weak, and which responded to the tidal forces. The team’s findings show these types of quakes were more likely to happen on the days when the forces were the greatest difference from the previous day’s pull, and not on the days when the pull was the strongest, as would be expected.
“That tells you something about how fast the fault is loaded — how long it takes for the fault to recharge before you can trigger these earthquakes on it, how quickly this patch of fault is accumulating stress,” continued van der Elst.
The study author added the more we learn about the earthquake cycle and the better we understand the forces at work, the better we will be able to know when and where big earthquakes are likely to happen.
“The hope is that looking at low-frequency earthquakes that happen deep in the fault will ultimately shed light on how shallow parts of the fault accumulate stress.”
The findings from the study were published online in the journal Proceedings of the National Academy of Sciences.