Why cellphones didn’t work during the quake

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The walls started shaking, the earth was quaking and all you wanted to do was call your relatives and reassure them that no, a brick did not fall on your head during the quake. But of course, in the hour or so following the 5.4 temblor that rocked Southern California, it wasn’t easy to make a call. Perhaps you got a busy signal, or it went straight to voice mail or it started to ring and then just dropped the call.

What gives? Why are cellphones most useless when you need them the most?

Mobile carriers project how many people will be using their phones during a crisis and try to ensure that their networks can handle that call volume, Verizon Wireless spokesman Ken Muche said. Today’s call volume was 40% higher than what Verizon had projected for a crisis. During last year’s wildfires, call volume was 600% higher, he said. Because of high call volume, Verizon had to start blocking some calls so that others could get through.

“No network has an infinite amount of capacity,” he said.

Every time you place a call, the call reaches out to the nearest cell tower and tries to connect, according to Sprint Nextel spokeswoman Kathleen Dunleavy. If it doesn’t find an open space on that site, it reaches out to the next one and pings around to different towers. In times when lots of people are using their phones, towers are all at capacity.

It doesn’t help that people keep trying and trying to make a call after their first attempt fails. So rather than handling 3 million calls, for instance, the towers have to handle 3 million people each trying five times to make a call, Dunleavy said.

There are things carriers can do in an extended emergency ...

... or if they know something like a quake is coming (by listening to toads, perhaps?). Carriers can bring in cell towers on wheels to expand the volume they can handle, Dunleavy said, and they do for events such as the Super Bowl and political conventions to ensure that everyone who wants to make a call can do so.

Since we haven’t quite gotten to the point where we can predict earthquakes, Chinese toads notwithstanding, what’s a cellphone user to do? For once, the iPhone isn’t an answer: not even the new iPhone’s 3G network was immune to the quake, an AT&T spokesman said. (Verizon’s Muche did say some handsets are better at holding onto calls than others so might drop fewer calls during peak periods.)

The good news is that text messaging and e-mail should work just fine in high call-volume situations, because both use less bandwidth than voice calls. So while you might not be able to call your relatives and tell them that you’re fine, you can still text them (whether they know what a text message is is anyone’s guess).

Another solution: “Push to talk” services provided by companies such as Verizon and Sprint. Operating from point to point rather than through towers, they weren’t affected by the quake or the high call volume that followed. But they work only for talking to someone a few miles away, which, in the spread-out city that is Los Angeles, probably won’t get you very far in a crisis.

Have any stories about how your cellphone worked (or didn’t) during the quake? Feel free to vent in the comments below. Oh, and now would be a good time to remind you that we moderate comments, so keep it clean.

-- Alana Semuels

Semuels, a Times staff writer, covers marketing and the L.A. tech scene.