Cripple walls are short walls, typically between the foundation and the first floor that provide crawlspace access under the house. They are often weak against the type of lateral movement typical of earthquakes unless they are braced and anchored. The above video demonstrates the process of retrofitting cripple walls, which is easier and more affordable than you might think.
The Los Angeles Times has produced an amazing visual overview of the Hollywood Fault Zone. It illustrates the newest estimations of its boundaries and many of the high profile buildings it endangers. Clients and brokers with buildings in the Hollywood area should definitely give it a watch.