A magnitude 3.4 earthquake struck offshore Los Angeles County at 9:40 p.m. PST on February 22, 2026, rattling coastal communities. The quake originated roughly 15 kilometers beneath the ocean floor, and a smaller aftershock followed just eight minutes later. The sudden jolt served as a reminder of the geological forces at work beneath the surface.
Offshore Origin and Depth of the Quake
The earthquake, cataloged as event ci41401864, registered a local magnitude of 3.4 (Ml) according to a seismologist-reviewed summary from the Southern California Seismic Network, operated jointly by Caltech and USGS Pasadena. The origin time was precisely 9:40:35 p.m. PST, with the epicenter located at coordinates 33.623 degrees north latitude and 118.436 degrees west longitude, placing it in open water off the L.A. County coast. The hypocentral depth of 15.19 kilometers means the rupture occurred well below the seafloor, a factor that influences how energy radiates outward and how strongly shaking is felt onshore.
That depth is significant because deeper earthquakes tend to distribute energy over a wider area while producing less intense shaking at any single point, whereas very shallow events can feel sharper and more localized. In a shallow coastal zone, however, even a moderate-depth event can still be felt across densely populated neighborhoods if local geology focuses the waves. The offshore location also raises questions about which fault structures were involved. Researchers at the Southern California Earthquake Data Center maintain focal mechanism and centroid moment tensor catalogs that can help clarify the style of faulting once enough data has been processed. As of the SCSN event summary cited above, a detailed focal mechanism was not shown, leaving open whether the motion was primarily strike-slip, normal, or reverse in character.
Aftershock Followed Within Minutes
Eight minutes after the initial event, a magnitude 1.9 aftershock struck at 9:48:08 p.m. PST, according to Southern California Seismic Network records for event ci41401872. That smaller tremor was centered at 33.638 degrees north and 118.436 degrees west, nearly identical in longitude to the mainshock but slightly farther north. Its depth was 10.80 kilometers, about four kilometers shallower than the initial rupture. The close spatial and temporal relationship between the two events is consistent with a typical mainshock–aftershock sequence, in which stress changes from the first quake can contribute to slip on nearby patches of rock as the crust adjusts.
While a 1.9-magnitude event is far too small for most people to feel, its rapid arrival matters for seismologists tracking whether a sequence is growing or decaying over time. The Southern California Earthquake Data Center’s catalog tools allow researchers and the public to monitor whether additional aftershocks emerge in the hours and days ahead, building a statistical picture of how quickly activity is tapering. A single small aftershock does not, on its own, signal an escalating sequence, but its proximity to the mainshock and to populated coastal areas underscores why scientists pay close attention to even minor follow-up events in an already stressed tectonic setting.
How Shaking Reports Are Collected
Within minutes of a detected earthquake above a certain threshold, the U.S. Geological Survey begins compiling community observations through its “Did You Feel It?” system, which gathers online questionnaires about shaking and minor damage. These citizen reports are a primary way scientists measure how shaking was experienced at the surface, especially in neighborhoods that may be far from seismic instruments or where ground conditions vary sharply over short distances. For an offshore event like this one, DYFI submissions can reveal whether coastal residents actually felt the jolt or whether the ocean and intervening sediment layers dampened the energy before it reached land in a noticeable way.
The program’s technical background guidance explains that DYFI products update frequently in the early hours after an event and may be removed entirely if no citizen reports arrive, a normal part of the quality-control process. Origin information fed into the system comes from regional seismic networks that rapidly locate earthquakes and estimate their magnitudes. As more residents submit responses, the felt-intensity picture for the February 22 quake will sharpen, revealing patterns such as stronger shaking on certain soil types or in multi-story buildings. The USGS then uses the Modified Mercalli descriptions to translate those narratives into standardized intensity values that emergency managers can interpret quickly when deciding whether to inspect infrastructure or activate response protocols.
Ground Motion Modeling and Emergency Tools
Separate from community reports, the USGS produces ShakeMap products that model and measure ground motion and intensity patterns using a combination of seismic station recordings and predictive equations. For a 3.4-magnitude offshore event, the resulting map can help emergency managers quickly assess whether shaking exceeded thresholds that typically cause structural damage, even before field inspections or on-the-ground surveys are possible. ShakeMaps also highlight how shaking varied from one neighborhood to another, reflecting the influence of basin geometry, sediment thickness, and local site conditions that can amplify or dampen seismic waves.
Beyond real-time mapping, the USGS maintains a suite of earthquake scenario tools that allow planners to compare actual events against hypothetical larger ruptures on the same or nearby faults. By examining how a small offshore quake fits into these scenarios, local agencies can gauge whether the latest shaking resembles the outer fringes of a much larger pattern or is more likely an isolated release of stress. Such scenario-based planning supports long-term investments in retrofitting buildings, hardening lifelines, and refining evacuation routes, ensuring that even modest earthquakes are used as opportunities to test assumptions and improve readiness rather than treated as one-off anomalies.
From Data Streams to Operational Decisions
Automated systems like the USGS ShakeCast platform extend ShakeMap data directly into operational decision-making by pushing tailored analyses to infrastructure owners, utilities, and transportation agencies. For a moderate quake like the one recorded on February 22, these tools help answer the most pressing question for operators: which facilities, if any, are likely to have experienced shaking strong enough to warrant immediate inspection. Rather than sending crews everywhere, agencies can prioritize bridges, substations, pipelines, and other assets that ShakeCast algorithms flag as having exceeded user-defined shaking thresholds, conserving resources while still maintaining a safety margin.
In practice, this means that even a relatively small offshore earthquake can trigger a cascade of automated checks in control rooms across the region, from rail systems verifying track integrity to hospitals confirming that critical equipment remains fully functional. When combined with community intensity reports and instrument-based ground motion data, these systems offer a layered view of impact that is far richer than magnitude alone. For residents who felt only a brief jolt, much of this activity remains invisible, but it reflects a broader shift toward data-driven resilience: every event, including the February 22 offshore quake and its aftershock, becomes a real-time test of sensors, models, and communication channels that will be crucial when a much larger earthquake eventually strikes.
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*This article was researched with the help of AI, with human editors creating the final content.
