Geological Sciences

Earthquakes

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Web Links for Earthquake Information California Geological Survey Southern California Earthquake Center U. S. Geological Survey Richard Marquez Earthquake Center - CSULA Did you feel it? Report what an earthquake felt like and the USGS will convert the data they receive into an Earthquake Intensity Map.	Lower Van Norman Dam and Reservoir were constructed in 1918 by the Los Angeles Department of Water and Power. The water level was lowered by 10 feet in the 1960's because of earthquake safety concerns. During the 1971 San Fernando earthquake, the north side of the dam liquefied. The dam came exceedingly close to complete failure. The dam was only 4 feet above water level after the earthquake. This photo shows the dangerous condition of the dam on February 9, 1971.

The 1971 San Fernando earthquake was a magnitude 6.6 event that caused extensive surface rupture along the fault zone. The fault intersected Foothill Boulevard at this location and turned the parking lane into the vertical position. Notice the landslides on the hills in the background.	The 1971 surface rupture passed through an orange grove and can be seen behind the two people in this photo. Look closely and you can see the sag in the fence behind the person on the left. This sag was caused by compression bringing two of the fence posts closer together.

San Fernando Valley lies largely over poorly consolidated sediment and soil. Areas of weakest subsurface materials suffered badly in the 1971 earthquake.	The newly constructed Oliveview Hospital was destroyed in the 1971 earthquake. The soil beneath this stairway structure liquefied and the structure toppled over . The 6:00 a.m. timing of the earthquake minimized fatalities at this site.

The 1989 Loma Prieta Earthquake was a 7.1 magnitude event. The epicenter was near Santa Cruz, California. This photo shows the damage to the older and more poorly reinforced buildings in downtown Santa Cruz. Notice the piles of bricks that fell from these buildings.	The Nimitz Freeway in Oakland was destroyed when the southbound lanes fell onto the northbound lanes. Soil liquefaction of bay fill is the probable cause. Timing of the earthquake again saved many lives. The temblor occurred as the World Series between the Oakland Athletics and the San Francisco Giants was beginning.

The section of freeway crossing the stream channel collapsed as the soft, wet sediment liquefied.	Supports for the freeway bridge punched through the road surface as the bridge collapsed during the Loma Prieta earthquake.

Soil liquefaction occurs when compressional forces of an earthquake force the water in the sediment to move and try to escape to the surface. Sand will sometime pour out on the surface where soil liquefaction occurs. These features are called sand boils.	Landslides are another form of geological damage that often occurs during earthquakes. Landslides occur in areas of rocks that are either inherently weak or are weakened by joints, faults, or bedding planes. This landslide closed the freeway until the slide material could be removed. The roadcut was regraded at a slightly safer angle.

The 6.7 magnitude Northridge earthquake produced severe shaking and heavy damage in 1994. The first floor of the Northridge Meadows Apartments collapsed killing the occupants. Emergency vehicles driving past immediately after the temblor did not recognize that the building on the left was severely damaged.	California State University Northridge suffered the worst damage to any American university as a result of a natural disaster. Again the timing of the event at 4:00 a.m. saved many lives. This campus parking structure would have taken many lives if the earthquake had been a few hours later.

Look closely at this destroyed Kaiser clinic. The second floor has collapsed. Notice the support column rises vertically from the ground but is folded back on itself at the second floor level.	This is Bullocks department store in the Northridge Fashion Mall. Damage was far worse than anything that was anticipated perhaps due to the exceedingly high horizontal acceleration that occurred during this earthquake.

Many apartment buildings have a so-called "soft first floor". The parking structure beneath these buildings creates a weakness that can result in collapse during an intense earthquake.	This infrared photo shows a landslide that occurred along Pacific Coast Highway during the Northridge earthquake. One home was destroyed.

Freeways close to the mountains in the northern San Fernando Valley suffered in both the 1971 and 1994 earthquakes. Complete sections of this freeway fell to the ground below leaving some people stranded on the wobbling remains for the bridges.	This portion of the Santa Monica Freeway is constructed over an old channel of the Los Angeles River. Soil liquefaction in the river channel sediments may be the cause of this failure.

Does Earth Science look interesting to you? Perhaps you would like to major in Geology or Natural Science. Maybe a General Education course in geology would appeal to you. Here are two links that you should explore. Be an Earth Scientist Geology General Education Courses Return to Photo Gallery index page.
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