Magnitude of the Earthquake: The larger the earthquake results in larger earthquake amplitudes, longer shaking duration, as well as the most important stronger ground motions. As might be predicted the larger earthquakes would result in shaking over a larger area, as opposed to small earthquakes that would not be felt distances away.
Ground Failure: Southern California has been proven time and again to be suseptible to ground failure, especially when considering the amound of mudslides and fires that constantly ravage the area. This can be attriputed to the amount of rainfall in the area. With southern California, this varies quite a bit, from strong downpours to widespread droughts. As this was in the middle of winter, there had been quite a large amount of rainfall at the time of this particular quake.
Water waves: The most dangerous, yet rarely seen wave is called a trunami. This large sea wave is created by the sudden movement of a large quantity of water. While no tsunami's were a result of this seaside earthquake, waves in the area did increase substantially for a period of time after the quakes and aftershocks.
Distace to the Earthquake Focus: As the distance to the focus of the earthquake increases, the amplitude decreases. Therefore the deeper the quake, the less it will be felt.
