Judy Woodruff:

After two serious earthquakes rocked Southern California, questions are raised anew about the extent to which residents and governments are prepared for an even bigger quake.

Seismologists and public officials have warned repeatedly for years about the big one, shorthand for a major earthquake along a different crack in the earth, the San Andreas Fault. Scientists say last week's quakes and the aftershocks since don't make ruptures along the San Andreas any more or less likely.

But this is a good time to revisit the larger concerns and what people need to know.

Jacob Margolis has laid this out extensively in a podcast called "The Big One: Your Survival Guide." He is a science reporter with KPCC. That's Southern California public radio.

Jacob Margolis, thank you very much for being with us.

So when we talk with the big one, am I right that we're not talking about if, we're talking about when?