Previous Question 2:

I know California, especially the San Francisco Bay Area & Los Angeles, is famous for their seismic or earthquake activities. How do I know my house is safe from the shakes?

Answer (continue):

If the floor joists bear on a wood plank on top of the concrete stem wall (Fig. B), take a close look to see if any steel anchor bolts presented to hold the wood plank to the stemwall. See Fig. F below. If these anchor bolts are spacing at 4' or less apart, your house passes the basic test; otherwise, a major weakness of your house has been discovered.

Instead of bearing on a concrete stemwall, it is also possible that the floor joists are supported by a cripple wall (Fig. C). When anchor bolts are seen, check if their spacings are, again, 4' or less. If so, then your house do not have the weakness mentioned in CEBC A3.   Next check if the materials attached to the other side of the cripple wall, if the material is plywood (PLY) or oriented strand board (OSB), then you know your house meets the "minimum" bracing requirments. Otherwise, simply install whatever missing.  Illustrations can be found in the How you can strengthen your home for the next big earthquake in the Los Angeles area.

Once you find out the type of foundation your house is sitting on, California Earthquake Authority (CEA) provides some information regarding strengthening. Their website link is: 

In this website, two standard plan sets, Plan Set A and Standard Plan Set 1, are offered to California homeowners in the cities/ counties that has adopted these plan sets and your foundation meets the plan-set requirements. Plan Set A and Standard Plan Set 1 are for the houses in Northern and Southern California, respectively. These plan sets can be used in the incentive program called Earthquake Brace + Bolt (EBB) offered by California Residential Mitigation Program (CRMP) to help homeowners lessen the potential damages during an earthquake by providing $3,000 max. grants to be used toward a code-compliant seismic retrofit for wood-frame residential houses that qualify. CRMP is a joint powers authority created by the California Earthquake Authority and the Governor's Office of Emergency Services.  

Due to the limitations of this website, the information published here is for the basic and general reference of readers only and not intended to be thorough and complete. A publication called "Find out why inadequate earthquake 'retrofits' leave many older homes vulnerable to quakes, and whether your home may still need strengthening" printed by Golden Gate Chapter of the American Society of Home Inspectors in 2012 provides further in-depth discussion regarding common weaknesses of residential houses & reinforcement. (Download link below).

Links to Download Publication: