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Roger Weller, geology instructor
by Victoria Martinez
Shake and Quake of 1989
Natural hazards are traumatic events that come when you least expect it. One of those hazards was the San Francisco earthquake of 1989. Before going into detail about the quake, one must understand how earthquakes occur. The earth’s crust is covered with a series of plates that move slowly under the earth’s surface. In California there are two of these plates, which contain the San Adreas fault. These two plates are what cause earthquakes to occur along the California coast.
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Well, what is an earthquake? An earthquake occurs when the plates are being deformed by pressure within the earth. The ground bends, to a certain point before it breaks and snaps to a new position. Due to the moving and breaking, vibrations occur, which are the earthquakes. There are two types of vibrations: compression waves and transverse waves. Compression waves are ones that arrive at a distant point first because they travel faster while transverse waves arrive later and are referred to as “S” waves which are the aftershocks.
These earthquakes are measured on the Richter scale, which measures the magnitude of an earthquake. Magnitude of 2 is the smallest earthquake felt by humans. Any earthquake measured on the Richter scale of 5 or higher is potentially going to cause damage. The San Francisco earthquake was a magnitude of 7.1 and caused plenty of damage.
It was a nice fall evening on October 17, 1989. The third game of
the World Series was scheduled for that evening, when at 5:04 P.M., the ground
began to shake in Loma Prieta. It lasted 15 seconds, which is an extremely long
time for an earthquake and it caused plenty of damage. It was so incredibly
strong that it collapsed a section of the Bay Bridge that links San Francisco
and Oakland together.
The quake caused the power to go out. Numerous fires occurred due to the breakage of gas lines throughout the Marina in San Francisco, which is 60 miles north of Loma Prieta. San Francisco’s Marina District was in the worst condition as far as earthquake aftermath is concerned. It was built on uncompacted, sandy ground, which was the ruins from the 1906 quake, in an area with a shallow water table. These conditions caused shaking to be amplified and some areas of ground to "liquefy." The fires were hard to fight because the water lines broke as well which made it difficult to retrieve excessive amounts of water, but the fire department was about to draw water from the nearby lagoon. Interstate 880 rocked so viciously that sections of the freeway slammed into one another, which cracked off pieces. Damage not only stretched across the Bay area but the Monterey Bay as well, which is almost 3 hours away. The earthquake triggered a 4 foot tsunami wave and a huge undersea landslide. The sea level at Santa Cruz dropped 3 feet as water rushed out of the harbor.
(Pictures courtesy of Lt. CJ Byron)
Earthquakes, like all other natural disasters come at unexpected times, but since the quake of ’89, California is constantly monitored of activity among the plates along the fault. Of course these quakes can’t be prevented but improvements in construction and technology have allowed builders to construct buildings and bridges that can withstand an earthquake. If one lives near an earthquake bound area, it is safe to have knowledge on what to do when one occurs. If one occurs while in the home, it is important to not stand by anything heavy that can fall over like a bookshelf. Instead it’s the safest to stand inside a door entrance. The reasoning behind that is the beams above the door are one of the strongest beams because they need to help support the ceiling. Be sure to have an emergency kit handy with a wind up radio, flashlights, candles, and other necessities because you never know if they quake will take out the power and water like the San Francisco quake. It’s better to be safe than sorry.
Miller, Mary K. "Remembering Loma Prieta." Exploritorium: Faultline.
Exploritorium, Web. 23 Nov 2009.
Page, Robert A., Peter H. Stauffer, and James W. Hendley II. "Progress Toward a
Safer Future Since the 1989 Loma Prieta Earthquake." 06 May 2005. USGS, Web. 23
Nov 2009. http://pubs.usgs.gov/fs/1999/fs151-99/
Schulz, Sandra S., and Robert E. Wallace. "The San Andreas Fault." 24 Jun 1997. USGS General Interest Publications , Web. 23 Nov 2009. http://pubs.usgs.gov/gip/earthq3/safaultgip.html