{"id":1248,"date":"2026-05-10T17:01:47","date_gmt":"2026-05-10T17:01:47","guid":{"rendered":"https:\/\/sandiegorelocationnews.com\/index.php\/2026\/05\/10\/swarm-of-more-than-150-earthquakes-slams-southern-california-city-what-to-know\/"},"modified":"2026-05-10T17:01:47","modified_gmt":"2026-05-10T17:01:47","slug":"swarm-of-more-than-150-earthquakes-slams-southern-california-city-what-to-know","status":"publish","type":"post","link":"https:\/\/sandiegorelocationnews.com\/index.php\/2026\/05\/10\/swarm-of-more-than-150-earthquakes-slams-southern-california-city-what-to-know\/","title":{"rendered":"Swarm of more than 150 earthquakes slams Southern California city. What to know"},"content":{"rendered":"
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A swarm of more than 150 earthquakes reaching up to magnitude 4.5 rattled Brawley in Southern California near the Salton Sea, the U.S. Geological Survey reports.<\/p>\n

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The other quakes in the Saturday evening swarm ranged from magnitude 1.3 to 4.4, according to the USGS.<\/p>\n

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The swarm began with a quake at 4:14 p.m 2 miles southwest of Brawley in Imperial County, the USGS reported. More followed overnight with the most recent, a magnitude 2.0 quake, striking at 8:51 a.m. Sunday.<\/p>\n

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The 10-mile deep 4.5 quake hit at 8:39 p.m. Saturday, according to the USGS.<\/p>\n

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More than 165 people from as far away as Santa Monica and Glendale reported feeling the tremors to the agency. A Shake Alert was sent on the earthquake.<\/p>\n

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Brawley is about 200 miles southeast of Los Angeles.<\/p>\n

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\u201cThe Imperial Valley has seen dozens if not hundreds of these sort of swarms over the century we have recorded,\u201d said seismologist Lucy Jones on Blueskey. \u201cA swarm is a group of quakes (dozens to thousands) where there are many quakes close in size and no obvious mainshock.\u201d<\/p>\n

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\u201cIt has been a shaky night in Imperial County, CA,\u201d said the USGS Shake Alert account on X.<\/p>\n

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What to know about earthquakes<\/h2>\n

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Magnitude measures the energy released at the source of the earthquake, the U.S. Geological Survey says. It replaces the old Richter scale.<\/p>\n

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Earthquakes between magnitudes 2.5 and 5.4 are often felt but rarely cause much damage, according to Michigan Tech. Quakes below magnitude 2.5 are seldom felt by most people.<\/p>\n

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Earthquakes\u2019 sudden, rapid shaking can cause fires, tsunamis, landslides or avalanches. They can happen anywhere, but they\u2019re most common in Alaska, California, Hawaii, Oregon, Puerto Rico and Washington, according to the U.S. Department of Homeland Security.<\/p>\n

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What is an earthquake swarm?<\/h2>\n

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An earthquake swarm is a series of small quakes that \u201cmay occur in a region for months without a major earthquake,\u201d according to Britannica.<\/p>\n

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Such swarms are commonly associated with volcanic activity, but can occur elsewhere.<\/p>\n

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How are earthquake swarms different from aftershocks?<\/h2>\n

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Aftershocks are a series of smaller quakes that typically follow a larger tremor, the U.S. Geological Survey said.<\/p>\n

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The magnitude of the smaller shocks, which normally start about an order of magnitude below the main earthquake, tends to fall off over a period of time, from weeks to even decades.<\/p>\n

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\u201cHowever, not all earthquake sequences follow this pattern,\u201d the U.S. Geological Survey said.<\/p>\n

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In a swarm, there\u2019s often no identifiable main shock or the largest quake may take place in the middle of the swarm, the agency said.<\/p>\n

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Also, many of the quakes may be around the same magnitude, geologists said.<\/p>\n

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\u201cSometimes sequences don\u2019t decay over time, but rather remain steady or even increase in their activity rates over periods of days, weeks, or even months,\u201d the U.S. Geological Survey said.<\/p>\n

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There\u2019s no precise technical division between aftershocks and swarms, though.<\/p>\n

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\u201cIn reality, the distinction is not sharp,\u201d the agency said.<\/p>\n

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What causes earthquake swarms?<\/h2>\n

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Researchers are still trying to figure out what causes earthquake swarms, the U.S. Geological Survey said, but they have a few ideas.<\/p>\n

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\u201cBased on past research, we understand that swarms probably indicate that an extra \u2018ingredient\u2019 is involved where the earthquakes are happening \u2014 an ingredient that isn\u2019t as prevalent in mainshock-aftershock sequences,\u201d geologists with the federal agency said.<\/p>\n

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That special factor could be a fault that is slipping slowly, popping off \u201csmall, sticky patches\u201d \u2014 or magma pushing up through the Earth\u2019s crust, the U.S. Geological Survey said.<\/p>\n

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Most often, quake swarms are caused by fluids \u2014 typically water \u2014 interacting with fault lines, the federal agency said.<\/p>\n

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A fault slipping in an earthquake becomes permeable and when it\u2019s saturated by water, can result in further slipping and more tremors, geologists said.<\/p>\n

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\u201cWe still have much to learn about earthquake swarms and their underlying physical processes,\u201d the USGS said.<\/p>\n

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How to stay safe during an earthquake<\/h2>\n

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If an earthquake strikes, it\u2019s best to protect yourself right away, the Department of Homeland Security said. Here are tips from experts:<\/p>\n

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  • If you\u2019re in a car: Pull over and stop. Set your parking brake.<\/li>\n
  • If you\u2019re in bed: Turn face-down and cover your head with a pillow.<\/li>\n
  • If you\u2019re outdoors: Stay away from buildings. Don\u2019t go inside.<\/li>\n
  • If you\u2019re inside: Stay and don\u2019t run outdoors. Stay away from doorways.<\/li>\n<\/ul>\n

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    The best way to protect yourself during an earthquake is to drop, cover and hold on, officials say.<\/p>\n

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    \u201cWherever you are, drop down to your hands and knees and hold onto something sturdy,\u201d officials say. \u201cIf you\u2019re using a wheelchair or walker with a seat, make sure your wheels are locked and remain seated until the shaking stops.\u201d<\/p>\n

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    Be sure to cover your head and neck with your arms, and crawl under a sturdy table if possible. If no shelter is available, crawl to an interior wall away from windows.<\/p>\n

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    Once under a table, officials say you should hold on with one hand and be ready to move with it.<\/p>\n

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    \u201cThere can be serious hazards after an earthquake, such as damage to the building, leaking gas and water lines, or downed power lines,\u201d officials say. \u201cExpect aftershocks to follow the main shock of an earthquake. Be ready to Drop, Cover, and Hold On if you feel an aftershock.\u201d<\/p>\n

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