Are California Buildings Earthquake-Resistant?

The perception is that homes in California are safe for frequent small and moderate earthquakes. However, the reality is more nuanced, especially when considering the possibility of larger seismic events. While many new constructions are reasonably safe, they certainly do not guarantee safety in the event of a major earthquake such as a 9.1 on the southern Cascadia or a 7.9 on the Ventura-Pitas Point fault.

The Cost of Safety

The engineering required to withstand the most powerful quakes comes with a significant cost. It is not feasible to build structures earthquake-proof, as the term implies absolute safety under any circumstances. For example, a 9.1 earthquake in the southern Cascadia region would cause widespread destruction, regardless of any safety measures in place.

Current Building Standards

However, many newer constructions in California meet reasonable safety standards. New homes are often built to withstand quakes of magnitude 4 or 5 on the Richter scale, though whether they are safe for an 8-magnitude quake is uncertain. This highlights that while advancements in construction technology have improved safety, they do not eliminate all risks.

The Debate on Safety

Questions about the safety of buildings in earthquake-prone regions often reduce to a subjective comparison. For instance, asking whether a tree is 'tall' is relative to the height of other trees or objects. Similarly, the safety of a building depends on its performance compared to the potential hazards it might face. To accurately assess the safety of buildings in California, it is crucial to compare their construction codes and retrofit regulations with those in areas with a proven track record of stringent safety standards, such as Japan.

Historic and Modern Building Challenges

Many apartment buildings constructed in the 1950s and 1960s present significant safety concerns. I myself experienced the Whittier Narrows earthquake during my first year in such a building. While buildings can be made incredibly strong, the cost often outweighs the benefit, especially for such rare and powerful events. The building codes in California, like elsewhere, are designed to account for expected hazards, such as the largest earthquake ever recorded in a particular area. These codes are based on the largest destructive event, not the average or frequency of earthquakes.

Specific Examples and Concerns

The Northridge earthquake demonstrated that open-faced carports with apartments above them were particularly vulnerable in such events. Older homes might not need to meet current code requirements unless they undergo significant modifications or substantial changes that necessitate retrofitting to meet modern standards.

Conclusion

No engineer would call buildings 'earthquake-proof' or even 'earthquake safe.' Instead, they would classify them as resistant to lateral stresses from earthquakes and other natural events like hurricane-force winds. While these measures enhance safety, they are subject to economic and practical limitations. Therefore, while many new structures in California are designed to handle moderate earthquakes, they do not offer foolproof protection in severe events.