Twenty years ago tomorrow, LA was shaken awake by a 6.7 magnitude tremor. Scientists are certain there will be more shaking. We hear what’s been learned since the Northridge Earthquake and what’s being done to prepare for what might — or might not -- happen next. We hear recollections of an event that killed at least 57 people, damaging 40,000 buildings at a cost of $2 billion. What’s been learned since about the risks and likely locations of earthquakes? Are developers taking needed precautions? Is it worth the cost to protect against a disaster that could strike in the next minute — or 100 years from now?