On Wednesday, a major improvement of the earthquake early-warning system was revealed in California. This system will now provide residents with more timely alerts concerning incoming megaquakes. It is also being deployed in Oregon and Washington to offer basic features for the “Big One” alert.
This upgrade suggests that Californians could be given earlier and more accurate estimates of the magnitude of the quake before motion is felt. For instance, if a magnitude 7. 8 earthquake begins on the San Andreas fault near the Mexican border and moves toward Los Angeles County, the new system would alert residents sooner. The update is paramount for the Pacific Northwest and California’s North Coast, which are at risk of tsunamis resulting from quakes along the Cascadia subduction zone.
The enhanced system was unveiled by the U. S. Geological Survey (USGS) and a nonprofit organization called EarthScope on Wednesday. Another ShakeAlert System operations team leader, Robert de Groot, highlighted the need for the upgrade in relation to strong earthquakes. He said that these enhancements enable estimating the size of major earthquakes more rapidly. For smaller quakes, the older system was adequate enough, but for the large quakes it frequently underestimated the magnitude. This meant residents had less time to prepare for the maximum ground movement.
For example, let there be an earthquake originating at the Mexican border in the southern part of San Andreas fault and initially assumed to have a magnitude of 6. 5 but turns out to be magnitude 8, the delay in accurate information could affect how people react. According to David Mencin, the vice-president of data services for EarthScope, it is critical that the data be correct for the worst earthquakes. He pointed out that this upgrade addresses the issue of underestimating magnitudes, which is fundamental.
A significant underestimation occurred in 2011 with the magnitude 9. 1 severe earthquake off eastern Japan. Earlier assessments put it at 7. 9 indicating that actual quake was much stronger. This underestimation led to a misjudgment of the actual height of the Tsunami and the initial alerts provided were extremely low estimates of the Tsunami. Therefore, many individuals were given false alerts on evacuation and this made many feel safe.
Earlier, Japan’s experience showed that using GPS data, it is possible to obtain more accurate quake magnitudes without delay. The USGS West Coast earthquake early-warning system has used seismographs installed beneath the earth’s surface, but these can only record a limited amount of oscillatory movement in a given time span. Seismometers can saturate during larger earthquakes of 7.0 or greater, the high frequencies are “clipped” and the calculations for high magnitudes cannot be quickly computed.
Now, hundreds of GPS sensors on the Earth’s surface controlled by EarthScope will supplement the seismic ones. These GPS sensors often monitor exceedingly small ground motions and demonstrate gradual tectonic plate activity. But in big shocks they record considerable displacements, or one fragment of the earth’s surface shifts away from another. For instance, in the 1906 San Francisco earthquake, land on one side of the San Andreas fault moved 8 meters relative to the other side. 5 feet after the other side had been reached. For instance, in the southern San Andreas earthquake in 1857, the ground rose and fell by 10 feet.
The first calculation of the early-warning system will still be based on the measurements of ground velocity and acceleration using the sensors. As a quake goes on GPS equipment will determine how much the ground has shifted. According to De Groot, GPS enables the determination of the quake’s size at a faster rate. This implies that the system could warn of an earthquake of magnitude 7 or higher a few seconds before it used to.
