Twenty years after the Northridge earthquake, experts say a huge temblor across Southern California today could cripple cellphone and Wi-Fi Internet service.

Seismic safety officials increasingly have been studying how telecommunications would be affected after a quake even bigger than Northridge and expressed concerns it would make communications difficult for days or longer.

Like water and gas lines, most Southern California Internet lines run across the San Andreas Fault, and officials fear the Big One could cut off service.

PHOTOS: The 1994 Northridge earthquake

In the case of a huge earthquake, fiber-optic telecommunication lines could be severed by the violent dislocation of the fault. Cellphone towers in areas that experience heavy shaking could collapse or be damaged, experts say.

Even if the towers are not damaged, a surge in phone usage after a major quake is sure to bring interruptions.

The relatively modest magnitude 5.5 Chino Hills quake in 2008 caused major problems with cellphone and land-line communications. Some cellphone companies reported up to an 800% increase in calls, far more than they had expected in a true disaster. Even phones in some police agencies near the epicenter were knocked off-line.

Full coverage: Northridge quake: 20 years later

The same thing happened after the 2011 Washington, D.C.-area quake. Several companies said many customers struggled to make phone calls but could still send and receive text messages.

When Los Angeles Mayor Eric Garcetti announced an extensive new earthquake safety effort Tuesday, he said one focus would be strengthening the telecommunication network to better withstand a quake.

"We created a society that requires the Internet to function," said U.S. Geological Survey seismologist Lucy Jones, who is heading L.A.'s new effort. "The Internet is adding this whole new level of ... complexity to our society."

Seismic experts say it's important to put the communications risk in context. They said damage to unstable buildings — which would bring loss of life — and the possible cutoff of the water supply are much more serious concerns.

Graphic: You live in earthquake country; get ready before the next one hits

But they also argue that the seismic risks to telecommunications need more study because so many basic functions are now controlled by computers.

"It used to be that grocery stores in Southern California had big warehouses in the Inland Empire where food was stockpiled," Jones told quake experts in a December speech in San Francisco. She said the development of the Internet helped create a more efficiency-minded "just-in-time economy" where far less food is stored on the L.A. side of the San Andreas Fault.

Though the 6.7 Northridge earthquake killed about 60 people and caused billions of dollars in damage, experts warn that the region is overdue for a much larger temblor. A 7.8 or larger earthquake along the southern end of the San Andreas Fault that has long been predicted would be exponentially more powerful and destructive over a much larger area.