Researchers determined from GPS analysis that there are new areas of motion near the San Andreas Fault System. The data was identified and understood due to new approaches that diminished the inevitable statistical noise.
125-mile-wide “lobes” of uplift and subsidence were determined by the team of researchers, who used the data collected by the EarthScope Plate Boundary Observatory GPS array. The lobes, which straddle the fault line, had had a few millimeters of annual movement according to the recent findings, as reported by UPI.
Previous models have identified the possible action, although without precision and any particular location. The team used advanced statistical modeling to determine the source of the possible change and avoid the noise that comes with monitoring minute movements in the Earth’s crust.
“While the San Andreas GPS data has been publicly available for more than a decade, the vertical component of the measurements had largely been ignored in tectonic investigations because of difficulties in interpreting the noisy data,” said lead author Samuel Howell, a researcher at the University of Hawaii at Manoa, in a press release. “Using this technique, we were able to break down the noisy signals to isolate a simple vertical motion pattern that curiously straddled the San Andreas fault.”
The validity of the vertical patterns found by the team was confirmed because similar motions were predicted by an earthquake model designed at the University of Hawaii’s School of Ocean, Earth Science and Technology. This previous work suggested a precedent in the work and more accurate way to determine the movements in the area.
According to researcher Bridget Smith-Konter, associate professor at SOEST, the team was surprised and thrilled when the statistical method produced a velocity field similar to the one predicted by their physical earthquake cycle model.
The powerful combination of prior model predictions and a unique analysis of vertical GPS data led them to confirm that the buildup of century-long earthquake cycle forces within the crust is a dominant source of the observed vertical motion signal, he wrote in a press release from the university.
With the new methodology created by the team, researchers can use GPS vertical motion measurements better to understand the structure and behaviors of faults, even in times of earthquake quiescence, when no major ruptures have occurred since a very long time.
The results from a specialized search and analysis within the San Andreas Fault System, could help constrain seismic hazard estimates and allow for a more careful mapping of the large-scale motion resulting from the next significant rupture of the system.
San Andreas in a critical stage?
Last month, the director of the Southern California Earthquake Center, Thomas Jordan, made a troubling announcement. He assured that the San Andreas Fault appeared to be in critical conditions, and a massive earthquake was imminent.
This was related to the lack of activity of the fault over the last few years. There have been no major release of stress in the southern portion of the San Andreas fault system since 1857, as reported by UPI.
Currently, the plates are moving in an approximately northerly direction, even though the Pacific plate is moving faster that the North American tectonic plate, which means that the stresses between both of them are always building up.
In 1906, this level of stress resulted in a major release in the San Francisco Bay area of 7.8, and another one in 1989 of 6.9 in northern California. Earthquakes of such proportion have not occurred along the San Andreas fault in the south of the state, which leads to the suggestion that one is imminent, and this will probably be a big one.
According to the predictions from the U.S. Geological Survey, the possible maximum earthquake magnitude along the San Andreas fault system is 8.0, although this came with a seven percent probability estimate that such event could occur within the next 30 years.
However, within the same period of 30 years, there is a likelihood of 75 percent that an earthquake of a magnitude of 7.0 could happen. The difference between this two sizes could be seen as small, but an earthquake of a magnitude of 8.0 unveils 1,000 times more energy than one of 7.0 does.
For a better understanding of the possible damages that such event could produce, the USGS modeled a 7.8 magnitude event, with slippage of 2-7 meters, to represent the catastrophic repercussions this could have in California.
It was determined that the damage from a 7.8 earthquake would be most severe to constructions straddling the fault. This kind of properties is few and far from the expected area of impact. The most affected by the possible event were the 996 roads, 90 fiber optic cables, 39 gas pipes and 141 power lines across the fault zone.
“Simple safeguards include practicing ‘drop, cover, and hold on,’ securing items in your home and workplace that could fall during an earthquake, and storing seven days worth of food and water,” the report from the USGS stated. “Homeowners can also consider structural retrofits, such as bolting the house to its foundation, as well as earthquake insurance options.”
Source: University of Hawaii