The southern San Andreas is capable of and has produced earthquakes exceeding 8. When it does again, and that is a when, not an if, then these things will happen. No rail, road, or pipeline will stay intact when moved 15 ft across. Will the next large earthquake there be a 6, a 7 or an 8? No one knows. Will there be an 8+ someday? Yes.
Most buildings in Southern California will survive the shaking because of the work was done over decades by engineers on building codes (don't be in any 14 story ones, as there is a resonance frequency attuned to it). Fire will erupt in some parts, mostly from broken gas lines. If it is raining, fine. If it is a Santa Ana wind at the end of a long drought, then expect a firestorm. Logistics is the problem. Few people understand just how dependent on daily stocking people in the cities are. Without rail and trucking, Social becomes a patchwork of airports. Even with the airports, distribution will be near impossible because of damage to local roads. Unlike regional disasters like hurricanes, there will be no warning and the escape paths will be shocked almost immediately, trapping almost everyone to fend for themselves. Look at what had moved and realize that was done in about a minute or so, then imagine what would have occurred with infrastructure crossing over it.
The West Coast of the United States is currently due for a massive earthquake, known as the big one. I do not think the West Coast is prepared for it either. Most buildings are not prepared for a giant earthquake and I doubt the people who live there are ready at all.
It is common knowledge that California is fraught with earthquakes. Architects are employed and concerned with building buildings that can withstand the devastation of major earthquake action. But even with all the preparations that could be made, can anyone ever truly be prepared for this kind of disaster? Unless construction is changed to rubber houses, I think it's presumptuous of us to claim we are prepared.
There is no way to be 100% prepared for a major natural disaster like an earthquake. There are, however, important steps that can be taken that can help deal with the aftermath of a large earthquake on the West Coast. California, along with the Federal government, need to do more to invest in developing a response plan to such a disaster. For example, building codes need to be continually revised, major bridges and overpasses should be reinforced, the national guard and emergency response workers should go through more earthquake preparedness drills. In short, there is always more that can be done to prepare the West Coast for another major earthquake.