Communities in California’s Mojave Desert tallied damage and made emergency repairs to cracked roads and broken pipes Friday as aftershocks from the largest earthquake in 20 years to hit the region kept rumbling.
The small town of Ridgecrest, close to the epicenter, assessed damage after several fires and multiple injuries that were blamed on the magnitude 6.4 quake. A shelter drew 28 people overnight, but not all of them slept inside amid the shaking.
“Some people slept outside in tents because they were so nervous,” said Marium Mohiuddin of the American Red Cross.
The quake was felt widely, including in the Los Angeles region 150 miles (240 km) away. The largest aftershock thus far, magnitude 5.4, was also felt in Los Angeles before dawn Friday.
But damage appeared limited to the desert region, where it opened three cracks across a short stretch of state route 178 near the tiny town of Trona, said California Department of Transportation District Nine spokeswoman Christine Knadler.
Bridges in the area were also being checked.
Thursday’s quake was the most powerful California-centered earthquake to strike the region since 1994, when the 6.7 magnitude Northridge quake hit the populated San Fernando Valley. That event caused 57 deaths and billions in dollars of damages from collapsed buildings and destroyed freeways.
Southern California residents should expect more earthquakes in coming years, experts warned.
“This is the first magnitude 6 quake in 20 years. It’s the longest interval we’ve ever had,” seismologist Lucy Jones told the Guardian. “We know that the last 20 years was abnormal … we should expect more earthquakes than we’ve been having recently.”
She added: “Chances are, we’re going to have more earthquakes in the next five years than we’ve had in the last five years.”
Los Angeles on Friday revealed plans to lower slightly the threshold for public alerts from its earthquake early warning app. The technology gave scientists at the California Institute of Technology’s seismology lab 48 seconds of warning but did not trigger a public notification.
“Our goal is to alert people who might experience potentially damaging shaking, not just feel the shaking,” said Robert de Groot, a spokesman for the US Geological Survey’s ShakeAlert system, which is being developed for California, Oregon and Washington.
The West Coast ShakeAlert system has provided non-public earthquake notifications on a daily basis to many test users, including emergency agencies, industries, transportation systems and schools.
Late last year, the city of Los Angeles released a mobile app intended to provide ShakeAlert warnings for users within Los Angeles county.
The trigger threshold for the app required a magnitude 5 or greater and an estimate of level 4 on the separate Modified Mercali Intensity scale, the level at which there is potentially damaging shaking.
Although Thursday’s quake was well above magnitude 5, the expected shaking for the Los Angeles area was level 3, de Groot said.
A revision of the magnitude threshold down to 4.5 was already underway, but the shaking intensity level would remain at 4. The rationale is to avoid numerous ShakeAlerts for small earthquakes that do not affect people.
“If people get saturated with these messages, it’s going to make people not care as much,” he said.
Construction of a network of seismic-monitoring stations for the west coast is just over half complete, with most coverage in southern California, San Francisco Bay Area and the Seattle-Tacoma area. Eventually, the system will send out alerts over the same system used for Amber Alerts to define areas that are expected to be affected by a quake, de Groot said.
California is partnering with the federal government to build the statewide earthquake warning system, with the goal of turning it on by June 2021. The state has already spent at least $25m building it, including installing hundreds of seismic stations throughout the state.
This year, Governor Gavin Newsom said the state needed $16.3m to finish the project, which included money for stations to monitor seismic activity, plus nearly $7m for “outreach and education”. The state legislature approved the funding last month, and Newsom signed it into law.