An estimated 95,000 people who signed up for an earthquake warning system received a ShakeAlert message, most getting it on their cellphones seconds before the ground shook, California Office of Emergency Management and USGS officials said.

That number represents the wireless providers that have reported their users’ alert figures so far Tuesday, officials said. The figure was likely to increase significantly as other providers weigh in, said USGS ShakeAlert outreach coordinator Robert de Groot.

“People had several seconds of alert time before shaking began at some locations,” he said.

In San Francisco, roughly 80 miles north, some cellphone users had 18 seconds between the alert and shaking, according to Cal OES.

Warning time depends on distance, with those closest to a temblor getting little or no warning and those living farthest receiving alerts that can outrun an earthquake’s wave by as many as two minutes.

Because the quake surpassed a threshold of magnitude 5.0, alerts went out through the federally managed Wireless Emergency Alerts system.

The ShakeAlert system is fully operational in California, Oregon and Washington and can reach more than 50 million people, De Groot said.

Californians as far away as Sacramento and Fresno reported feeling Tuesday’s temblor.

Cal OES officials were coordinating with Bay Area first responders to assess injuries and damage, the office said. The San Jose Fire Department said it received no emergency calls for help or service related to the shaker.

“Following SJFD’s #Earthquake Policy, firefighters are checking on personnel, surveying their immediate response area & inspecting stations and apparatus to ensure they’re ready to respond to any emergencies,” the department tweeted.

The Valley Transportation Authority serving Santa Clara County, where the earthquake was located, said car and track inspections caused a brief, 5-minute delay in train service. No injuries or damage was reported, and service was back on schedule, it said.

Bay Area Rapid Transit, serving San Francisco, the East Bay, and other communities, implemented its own 5-minute lag to facilitate inspections but warned that “major delays” were also possible.

Jones said Tuesday’s temblor likely took place along the Calaveras fault, which was home to the last major quake in the region, Oct. 30, 2007’s Alum Rock earthquake, which measured 5.4 and caused a 3 mile surface rupture.

The Calaveras fault is part of a system of clashing plates ruled by the state’s most feared geological feature, the San Andreas Fault, which runs parallel to the coast along most of California and is estimated to be capable of producing an 8.2 magnitude shaker.

Jones said, however, that the Calaveras fault is best known for producing moderate quakes like Tuesday’s.

“The Calaveras fault is one that tends to have smaller earthquakes,” the Caltech visiting associate professor said. “It’s something that pops off with 5s more often than the other faults. It’s not accumulating much slip [energy], but it does have the capacity for larger.”