A bit of a shaky morning in LA. Hope everyone is safe. Did you feel the M4.2 #earthquake about 1 mile north of Pacoima just after 4:29 am PT? The #ShakeAlert system issued a message and passed it along to our delivery partners. More info: earthquake.usgs.gov/earthquakes/ev…
If you felt it please fill out a Did You Feel It report at: earthquake.usgs.gov/earthquakes/ev…
Thanks for all of your great reports on what you felt and whether or not you got an alert. The first #ShakeAlert message was issued by USGS 3.6 seconds after sensors detected the event and the last one was issued at 12.8 s. See: earthquake.usgs.gov/earthquakes/ev…
What happened between 3.6 and 12.8 s? #ShakeAlert is like one of those super fast cameras developed by Harold Edgerton that took pictures of balloons popping. mitmuseum.mit.edu/exhibition/fla… @MITMuseum
During the about 9 seconds between when the first and last #ShakeAlert Message was issued multiple updates (snapshots) were taken by ShakeAlert and made available to delivery partners.
Each #ShakeAlert Message has its own estimated magnitude and shaking profile. It turns out that one of the snapshots estimated the earthquake at M4.5+. Again this is all happening really fast!
At M4.5 #ShakeAlert App partners can start delivering alerts to people who could feel weak shaking (MMI 3+). If you were outside the MMI 3 area you likely didn't get an alert and if you were very close to the epicenter you might have felt shaking before the alert arrived.
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