Magnitude-5.9 Nevada earthquake notification was false alert, USGS says

A notification about a magnitude-5.9 earthquake in western Nevada Thursday morning was a false alert, the USGS said.

The quake alert generated by the ShakeAlert early warning system indicated an earthquake near Dayton, Nevada, about 10 miles northeast of Carson City, Nevada and 30 miles northeast from Lake Tahoe. The alert appeared on the USGS earthquakes map, but was deleted soon after and replaced with a message.

“The ShakeAlert EEW system released an incorrect alert for a magnitude 5.9 earthquake near Reno and Carson City, Nevada,” the USGS said. “The event did not occur, and has been deleted from USGS websites and data feeds. The USGS is working to understand the cause of the false alert.”

The same message was posted to the ShakeAlert early warning system web site.

False alerts can be triggered by several factors, the agency said.

For example, location algorithms sometimes misidentify reflected and refracted seismic waves created by one earthquake, which can turn into events far from the quake’s location. Noise in analog telephone circuits used to bring data from seismic sensors to computers also can be misidentified by automated systems as earthquakes. Software aimed at locating local quakes can sometimes mislocate a large earthquake on the other side of Earth, deep beneath the seismic network, the USGS noted.

“Adding to this complexity, there are multiple seismic monitoring networks that contribute their earthquake locations and magnitudes to the ANSS system,” the agency said on its web site. “These networks use different data and algorithms to locate the earthquakes, and sometimes the spatial separation of the contributed locations is so large that our systems interpret the independent solutions as distinct earthquakes of similar magnitude and location. In this situation, a delete message will be sent for one of the earthquake solutions but an earthquake did occur.”

The agency also notes there’s a trade-off between the speed of a notification and number of false alarms.

“The faster we release earthquake locations and magnitudes, the more likely it is that the information may be erroneous,” the USGS said on its site. “Experience demonstrates that imposing more restrictive quality standards prevents the release of legitimate earthquake information.”

NBCLA has reached out to the USGS for more details.

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