There is no proven method for predicting earthquakes. Geologists are striving to create an early warning system, but there is still a lot to learn about what happens shortly before an earthquake strikes. Part of the issue is that earthquakes do not always act consistently—some indications appear at varying times (days, weeks, or seconds before the catastrophe), while others may not appear at all. Continue reading to learn about earthquake warning signs and how to be prepared in the event of an earthquake.
According to a new study, three-dimensional fault models are often more accurate than two-dimensional line models at sending ground shaking alerts to the correct places as part of an earthquake early warning system.
According to Jessica Murray and colleagues at the US Geological Survey, the benefits of 3D fault models vary depending on the fault style (a strike slip versus a reversal fault, for example), whether the event is a subduction or crustal earthquake, and the degree of shaking that triggers the alarm.
They propose that 3D models would outperform 2D models at an alert threshold of MMI 4.5, implying that the warning would be triggered for shaking above the “mild” intensity category, where most persons indoors would feel some shaking. In addition, 3D models significantly enhanced alert accuracy for all subduction zone earthquakes at MMI 4.5 and MMI 2.5 (mild motion felt by only a few individuals) thresholds in their study.
ShakeAlert® is an earthquake early warning (EEW) system that identifies severe earthquakes quickly, allowing alerts to reach a large number of people before shaking occurs. The findings of the study could be valuable for earthquake early warning systems such as the United States’ West Coast’s ShakeAlert.
Jessica Murray
The findings of the study could be valuable for earthquake early warning systems such as the United States’ West Coast’s ShakeAlert, according to the researchers in the Bulletin of the Seismological Society of America. For the time being, ShakeAlert’s algorithms employ seismic data to identify an earthquake source as a point or line. However, academics are already working on ways to include 3D source information into ShakeAlert, which is derived from fault displacement data collected by Global Navigation Satellite Systems (GNSS).
ShakeAlert® is an earthquake early warning (EEW) system that identifies severe earthquakes quickly, allowing alerts to reach a large number of people before shaking occurs. ShakeAlert is not a prediction of an earthquake; rather, a ShakeAlert Message indicates that an earthquake has occurred and shaking is impending.
“It was expected that such information would improve alerting since it would provide a better categorization of major earthquake sources than a point source,” Murray added. “This assumption has not been investigated in terms of how a more realistic source characterization might transfer to ground motion estimations, so that is one of the things we set out to examine.”
In their study, the researchers used synthetic data derived from hypothetical 3D and line sources. While 3D source models were more accurate than line sources in general for notifying the relevant regions, the benefit afforded by 3D models was particularly obvious for subduction interface earthquakes. Within the more detailed collection of observations, the researchers discovered several intriguing results. At the MMI 2.5 alert level, for example, the results of a strike-slip or reverse crustal earthquake are comparable whether 3D or point source representations are utilized, as long as the location, magnitude, and depth to the top of the seismic rupture are known.
According to the researchers, adding a 3D representation would not provide much of an advantage over a point source representation in this case, though GNSS data could be useful in places with poor seismic station coverage or seismic data outages, such as the 2019 California Ridgecrest earthquake sequence.
Murray and colleagues also found that when using a line source representation and calculating the earthquake’s magnitude from the projected length, an inaccurate length can considerably reduce alert region accuracy.
“Estimated ground motion depends on both earthquake magnitude and a user’s distance to the source, so it’s not surprising that modifying both of those elements at the same time would have a big influence on the alert outcomes,” Murray explained.
When magnitude estimations from ShakeAlert’s line source models do not match earthquake catalog magnitude, she believes it may be due to “real differences in stress drop, which would, in turn, alter shaking.” “It is very vital to investigate this problem further utilizing data from real-world situations, which is one of our ongoing projects.”
