An earthquake with a preliminary magnitude of 4.2 — initially reported as a 4.5 — struck near San Bernardino Wednesday night shortly before 7:45 p.m. Shaking has been reported to the U.S. Geological Survey’s Did You Feel It? app from Los Angeles and down into Orange County.
No significant damage was immediately reported.
Lucy Jones, a noted seismologist, took to X (formerly known as Twitter) to explain that the location of the epicenter was “pretty deep 15 km) very close to the San Jacinto fault.” Jones went on to saw “that part of the fault is generally locked — it had a M7 in the 19th century.”
M7 references the Mercalli scale, which measured the intensity of shaking.
The U.S. Geological Survey’s earthquake early warning system is triggered depending on intensity of the shaking and can offer seconds of warning. Alerts were delivered Wednesday night. Here’s what the USGS had to say on social media about how they determine when and where to send it: