Twin earthquakes rattle Northern California, trigger ShakeAlert warnings

The ground jolted twice across Northern California on Wednesday afternoon (early morning in the Gulf) as back-to-back earthquakes struck near the remote community of Covelo, briefly sending warning alerts to residents and putting emergency systems to the test.

The US Geological Survey recorded the quakes at about 3:21 p.m. local time Wednesday, or 2:43 a.m. Thursday in the Gulf.

The stronger earthquake was centered about 19 miles (31 kilometers) northwest of Covelo, near the Trinity-Mendocino county line, at a shallow depth of roughly 3 miles (5 kilometers).

ShakeAlert, the US earthquake early-warning system, pushed alerts to mobile devices in parts of Northern California, giving people potentially crucial seconds to protect themselves before stronger shaking arrived.

Because the quake occurred relatively close to the surface, shaking was felt across parts of the region, ranging from light to moderate.

For some residents, the first warning came not from the shaking itself but from their phones.

There were no immediate reports of injuries or significant damage.

Twin jolts

But the twin jolts added to a string of recent earthquakes in the region, including a magnitude 4.4 quake in July and a magnitude 5.6 earthquake in June, keeping residents alert in an area accustomed to living with seismic risk.

The latest earthquakes struck in a relatively remote part of Northern California, limiting the potential for widespread damage. Still, shallow earthquakes can produce noticeably stronger shaking near the epicenter than deeper events of similar magnitude.

Emergency officials continue to remind residents that earthquakes can strike without warning and that the safest immediate response is simple: Drop. Cover. Hold On.

When the ground starts moving, those few seconds of warning from a phone can make a critical difference.