ShakeAlert, the west coast's still young but operating earthquake warning system, scared some Bay Area folks Thursday evening who thought they would soon be hit by a substantial earthquake.
ShakeAlert is still a work in progress and what it did last night was done one without passion, instantaneously and using the best evidence available.
At 9:35 p.m. PT, and much quicker than in the blink of an eye, the west coast ShakeAlert system notified hundreds of thousands northern Californians to expect an immediate earthquake.
To provide the quickest warning, ShakeAlert makes its decision to alert in nano second, decided by a sophisticated computer program, called an algorithm.
But, because there are still not enough sensors in the area near Truckee where the quake hit, ShakeAlert thought that the moderate 4.7 magnitude quake was actually a more serious 6.0.
"Earthquake warning is not a perfect system. We estimate the magnitude and in this case we overestimated the magnitude by just a little bit," said Berkeley Seismological Laboratory Director Richard Allen.
The alerts are near instantaneously passed on to critical infrastructure operators such as BART and Caltrans.
At the same time they're sent to consumer applications such as MyShake, Android Emergency Alerts and Wireless Emergency Alerts warning of a 6.0 quake.
"Because the bigger the earthquake, the broader the region of shaking and, hence, the broader region of people that would be alerted in this case," said Robert deGroot, Ph.D. of these U.S. Geological Survey ShakeAlert expert. "As we add more stations, as we have denser station coverage, it just means that there are more stations, more data available more quickly."
So far, California has installed 780 of its goal of 1,115 sites. As more earthquake sensors are built out into the system, accuracy will increase because the system learns from every earthquake it senses and improves its predictions.
"Even if people did not feel and shaking but they still got the alert, we still hope that they took that protective action," said deGroot. "So when we get an alert, we shouldn't be scared. We should know that we're ready and we take that action: drop, cover and hold on," said Allen.
And, your phone, if you download the MyShake app, can be a part of the sensor network.
"Using the MyShake application, we're actually detecting the earthquakes with the phones themselves," said Allen.
Best practice: download multiple different apps on your phone to have a backup and adjust each app to your particular type and brand of phone for better accuracy.