Geoscience Reference
In-Depth Information
The epicenter of the 1989 Loma Prieta quake was about 10 miles outside of Santa Cruz,
California, and 60 miles from San Francisco. The worst damage was focused in the downtown
area of Santa Cruz, which was built on gravelly wet soils next to the San Lorenzo river, 60
miles away in the Marina District in San Francisco, which is built on loose, poorly compacted
fill from the 1906 San Francisco quake, and in Oakland where the Cypress Freeway was also
built on gravelly soils. At each of these locations, the magnifying effect of gravelly soils com-
bined with liquefaction and older construction methods/materials to result in catastrophic struc-
tural failures and fatalities.
Construction codes, age and type of materials of construction, and soil conditions each
have a lot to do with how well a community will fare during an earthquake. Generally speak-
ing, a 5.0 quake will shake things up a bit, throwing items of shelves and possibly breaking fra-
gile appliances like televisions and computers, but will not cause a lot of structural damage un-
less it strikes old masonry buildings or a third-world location with poor building practices.
When a 5.3 magnitude quake shook us out of bed in 1998, it didn't cause any appreciable dam-
age, but if a quake of that same magnitude had struck downtown Boston, between liquefaction
and the old brownstone buildings that Boston is known for, it would probably have caused ex-
tensive damage and killed a lot of people.
Earthquakes in the magnitude range close to 7.0, such as the 6.7 Northridge quake, the 7.0
Port-au-Prince, Haiti, quake, and the 6.8 Kobe, Japan, quake, will be quite frightening and will
cause significant destruction ranging from the flattening of Port-au-Prince, that killed an estim-
ated 316,000 and left a million people homeless, to the Northridge quake in Southern Califor-
nia that resulted in 33 deaths, injured an estimated 8,700 people, and caused $20 billion in
damages. It is hard to imagine what it would feel like to experience a mega-quake, like the
magnitude 9.5 1960 great Chilean earthquake, which was 316 times as strong as the Haiti
quake, or the 2004 Indian Ocean tsunami earthquake, which had a magnitude of 9.1 to 9.3!
How to Improve the Earthquake Resistance of Your Home
• Tie down your water heater with steel strapping bolted securely to wall studs. Seis-
mic water heater straps are available at most hardware or building supply stores.
Water heaters are quite heavy and will often topple over during an earthquake, break-
ing gas and water lines and causing much damage to your home.
• Do not hang any heavy paintings, or other heavy items, on the wall above your bed.
• If your building is of older construction, inspect the foundation to see if the building
frame is bolted into the foundation. If not, a qualified tradesman should perform a
