What Size Earthquake Would Damage Oklahoma City?

Oklahoma is home to Tornado Alley. According to the US Geological Survey, we've experienced a dramatic increase in seismic activity since 2008.  

Many people have felt the tremors but few had been affected by them until last November's record breaking 5.6, when homes, businesses and schools were damaged.

The question is, what size earthquake could Oklahoma City structures handle before sustaining substantial damage?  Kelly Ogle traveled to San Francisco and met with experts to find out.