The ‘earthquake’ felt by some Angelenos on Friday was actually a sonic boom

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© Getty Images / iStockphoto

F-18 Super Hornet Sonic Boom

Some Angelenos reported feeling an earthquake in the Los Angeles area Friday morning at about 9:20 a.m.

But according to the USGS, which tracks recent earthquakes, there has been no geological activity in the Los Angeles area.

so what happened?

According to the USGS Earthquake map, there was a sonic boom event about two kilometers, or 1.2 miles, south of San Dimas.

According to NASA, a sonic boom is a “thunder-like” noise that anyone on Earth can hear when an aircraft is moving faster than the speed of sound.

Because sound is just waves of air or other particles colliding with each other, if something moves faster than the speed of sound, it pushes those particles against each other with enough force to form a shock wave of compressed air particles.

This shock wave can shake things like windows and homes, often like an earthquake.

People were asking about the “earthquake” in Los Angeles around 9:20 this morning. Many people reported feeling it, but the seismograms clearly show that the ground wasn’t moving, only the air. So it was a sonic boom. https://t.co/OmoIoikKdv

— Dr. Lucy Jones (@DrLucyJones) July 9, 2021

Most sonic eruptions are not recorded on seismic instruments, the USGS said, because the wave does not usually translate into seismic energy that those instruments pick up from the ground.

But if multiple reports come in anyway, from people in a wide area who claim to have felt an earthquake, the agency can be “fairly sure” that the cause was something in the atmosphere.

© Provided by NBC Los Angeles This map for the Los Angeles area shows reports from people who said they felt a low-magnitude earthquake on July 9, 2021. The USGS announced that no earthquake occurred, and the event likely was a partial sonic due to the wide distribution for reports.

In this case, “earthquake” was reported from San Dimas, Los Angeles, Long Beach and even Santa Clarita.

NBC4 is looking for the source of the sonic boom, and will update here if and when we find out.

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