A swarm of earthquakes struck the Disneyland area this morning, including one which left a southern California visitor wondering if he was still on a theme park ride. While relatively light, the 2.7 magnitude earthquake which struck at 12:41 am this morning, was felt by more than 300 people that reported it to the USGS using their “Did you feel it?” online survey tool. The quake hit at a depth of 2.7 miles and was followed by 9 aftershocks, most of which struck within 4 miles of the Disneyland complex.
— Quinn (@RedFlagsLadies) May 31, 2021
An earthquake swarm, according to the USGS, is a sequence of mostly small earthquakes with no identifiable mainshock. Swarms are usually short-lived, but they can continue for days, weeks, or sometimes even months. They often recur at the same locations. Most swarms are associated with geothermal activity. Swarms are usually not tied to aftershocks. Aftershocks are a sequence of earthquakes that happen after a larger mainshock on a fault. Aftershocks occur near the fault zone where the mainshock rupture occurred and are part of the “readjustment process” after the main slip on the fault. Aftershocks become less frequent with time, although they can continue for days, weeks, months, or even years for a very large mainshock.
A total of 18 earthquakes rocked the greater Los Angeles region over the last 24, including a 3.0 that hit shortly after 7 am today off the coast of Malibu Beach. A 2.1 struck Malibu Beach just moments before the 3.0 earthquake. Using the “Did you feel it?” tool, residents of Malibu, Simi Valley, Glendale, Inglewood, Lawndale, Long Beach, and Los Angeles reported feeling weak shaking from that off-shore quake.
Today’s Disneyland quake swarm is among many earthquakes rocking America and beyond this Memorial Day Weekend. Earlier today, moderate earthquakes rocked the Mid Atlantic ridge. Just through Sunday night, more than 130 earthquakes rocked the Continental United States. Overnight, a strong 6.1 earthquake rocked south central Alaska. And seismic activity continues on Hawaii’s Big Island due to volcanic unrest there.