• Hayward fault earthquake damage 1868

    Hayward 1868

  • Looking down Sacramento Street towards the bay after the San Francisco earthquake of 1906

    Sacramento Street, San Francisco 1906

  • How much will the ground shake? A comparison with the Loma Preita earthquake
  • Northridge earthquake damaged house 1994

    Northridge 1994

  • Seismic strengthening diagram showing earthquake retrofitting of substructure, including foundation bolting and cripple wall bracing

    You can prevent quake damage

Seismic Upgrades for Wood Frame Houses

Many people living in the Bay Area have a fatalistic view regarding earthquakes. If it happens there’s nothing I can do, so why worry about it? While it is certainly true that another great quake is inevitable in the Bay Area, identifying and correcting certain well-known structural deficiencies can avoid a tremendous amount of damage to existing wood frame houses.

Experience from the October 17, 1989 Loma Prieta earthquake has confirmed what previous engineering studies have stressed: Almost all serious damage to wood frame houses has been a result of either 1) insufficient connections between frame and foundation and/or 2) insufficient lateral bracing (shear-strength) in the load bearing, supporting walls.

Without adequate frame-to-foundation connections, a house can be displaced completely from its foundation in a strong quake. Insufficient lateral bracing typically results in either a partial or complete collapse of the perimeter cripple walls, which form the basement and crawl space areas. Either form of damage can amount to a total loss scenario for the homeowner.

The good news is that properly reinforced houses in the hardest-hit areas of Santa Cruz and Watsonville performed very well during the Loma Prieta quake, suffering little or no damage. The overall pattern of residential performance not only mirrored the experience of previous California earthquakes, but also corroborated what various engineering reports have predicted for years.

There is no question that the Bay Area is due for another quake far worse than the Loma Prieta earthquake. The impact on homeowners could range from minimal to disastrous depending on whether appropriate reinforcing measures are taken.

Source: USGS
Photos courtesy of The Bancroft Library, USGS and FEMA.

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