Rich Pedroncelli / AP
Finding very small earthquakes is known to be difficult. The rumble of the ocean, a passing car or even the wind can act as a slight quake of the sensors covering seismically active parts of the US.
This is a problem for scientists looking to examine data on all earthquakes in a land leaving region, which triggers the largest and most destructive.
Now, a team of scientists says it has found a way to pinpoint tiny earthquakes, and it has released a new, more comprehensive list of quakes that have occurred in Southern California over the past decade. The work was published on Thursday in the journal Science
. The team relied on data from a network of about 400 seismic sensors in California, stretching from the border between the US and Mexico to the south of the state. These sensors continuously measure the movement in the earth's crust and look for signs of quakes. In the decade from 2008 to 2017, scientists had already identified 180,000 earthquakes in the region.
"They have a strong seismic network in Southern California," explains Daniel Trugman, seismologist at Los Alamos National Laboratory and author of the study. But while 180,000 looked like a large number of quakes, many, many more undetected, hid in the data.
When Trugman and his associates re-analyzed the data with a powerful array of computer processors, they found ten times more earthquakes – 1.81 million tremors in a decade, or a small earthquake about every three minutes. 19659008] "They do not feel that they happen all the time," says Trugman. But "they happen again and again."
Most quakes found in the study are so small that their strength falls below zero. It is not impossible for man to feel such a delicate trembling in the rock under our feet, but it is unlikely. Trugman equates it with a table in your kitchen. When you stand in the kitchen, when it happens, you will notice that the table touches the floor. But if you're on the road, when it's happening, or even out there, you'll probably miss it.
Trugman and scientists seek to detect the tiny quakes without confusing them for non-quake vibrations (such as a passing truck) The California Institute of Technology and the University of California, San Diego, used computers to pattern a decade's data to search which resembled known earthquakes.
The analysis has been made possible by advances in computer processors over the past decade. Even so, it took tens of thousands of hours for Caltech's suite of graphics processors – basically souped-up versions of the graphics cards in laptops – to search through all the data and detect potential quakes, and hundreds of thousands of hours for other computers to complete the analysis.
The ability to measure more and smaller earthquakes will hopefully help scientists answer some of the most intriguing questions on how, where and why earthquakes occur.
Douglas C. Pizac / AP
In California, many communities rely on trouble cards to pinpoint where earthquakes are most likely to occur in order to make decisions about infrastructure, building codes and contingency plans. More extensive information about quakes in the region could make these maps more complete and help identify so-called blind faults that are not visible on the surface but have the potential to shift underground.
A blind-bludgeon error was responsible for the 1994 Northridge Earthquake in Southern California, which killed more than 50 people, injured thousands, and caused billions in damage. In fact, the network of seismic sensors that made the new study possible was set up after this disaster.
You may also be able to use data from similar sensor networks in other parts of the US – for example, in the Pacific Northwest – to create more comprehensive catalogs of earthquakes in these regions.
The authors of the study hope to use the data to investigate how large earthquakes are triggered and what role small earthquakes play in this process. Understanding this complex relationship could ultimately help seismologists predict earthquakes.
"We will look at many of these questions in more detail," says lead author Zachary Ross, geophysicist at Caltech.
"The holy grail of earthquake seismology has always been a prediction," explains Trugman. For example, in recent years, the US government has introduced a West Coast earthquake warning system using the same sensor networks that scientists are studying. A deeper understanding of the seismic information fed into this early warning system could help to increase accuracy.
"I am cautiously optimistic that we will make progress on earthquake prediction," says Trugman.