1989 Loma Prieta Earthquake

Running Header: 1989 LOMA PRIETA EARTHQUAKE 1


Loma Prieta Earthquake took place in 1989 inSanta Cruz County of California State. The specific time and datewere, October 17 at 5:04 PM Pacific time. The earthquake lasted for15 seconds. According to US Geological Survey, the quake had amagnitude of 6.9 (Stover, 2003).It resulted in the death of 67 peopleand 3,757 sustained injuries. The quake was felt over a wide areacovering about 400,000 square miles. The earthquake was felt incentral California and western Nevada. Aftershocks activity decreasedtremendously with time, although some areas around an epicentercontinued to experience these aftershocks.

Significant aftershocks were felt as late as18thOctober 1990, in Watsonville area which had the largest magnitude of5.4 (Stover, 2003). These aftershocks were much less than expectedfrom an earthquake with such high magnitude. The aftershocks in thefirst day were 51 with a 3.0 magnitude 16 aftershocks on the secondday and by the third week 87 aftershocks had occurred with a 3.0magnitude (Harris, 2008).

The earthquake happened within a 30 mile lengthof the San Andreas Fault line. This part of the San Andrea’s faultline was called the Santa Cruz mountain segment. It was 16kilometers, North East of Santa Cruz and 7 kilometers south of LomaPrieta Mountains of California. The quake’s epicenter was 11. Theepicenter was 47 miles underneath and the specific spot was aroundChina ridge located at Nisene Marks State Park. The surrounding arealand on the seaward had a slip of 5.5 feet in the northwestdirection. Santa Cruz County was the hardest hit area had had thehighest number of casualties (Harris, 2008).

The earthquake had a lot of consequences. Thehuman loss was six in Santa Cruz County and 671 people sustainedfatal injuries. Santa Cruz had the highest number of casualties andhad the highest number of property damages (California, 2009). Anestimated 180, 000 people were directly affected by the quake withimmense loss of property and homes. Many homes were condemned to theimpact of the earthquake and many automobiles were written off. Thesaved homes were inhabitable because they were weak and couldcollapse unless adequate repairs were made. Many people were suddenlyrendered homeless turning to government shelters and friends’ homesfor shelter.

Major property losses occurred in San Franciscoand Oakland areas which were around 100 kilometers North of SanAndrea fault line. San Francisco Marina district built on an areawith no underlying bedrock also experienced immense damage(California, 2009). Due to the liquefaction of the underlying ground,the structures around the area collapsed and were swallowed in. Theliquefaction was caused by sand boils with lateral spreading andslumping which was witnessed for 110 kilometers from the epicenter.Gas and petroleum pipelines were damaged with many bursting andcausing large fires. Airports, highways, bridges, ports and leveeswere also destroyed. A 1.25 mile Cypress Street Viaduct south of SanFrancisco–Oakland Bridge collapsed, causing 42 casualties anddamage to vehicles as the road crashed on them (California, 2009).

The people had to blame for the severity ofdamages seen because some buildings had no reinforced concretemasonry and some buildings were built on ground lacking strongbedrock like the Marina district of San Francisco. The government andfederal/state geological team were to blame too for delayed warningsystems of the impending earthquake. Many people could have beenevicted from the key areas prior to the earthquake resulting in feweror no human casualties.

Some other streets that collapsed includedNimitz Freeway (Interstate 880) in Oakland Highway 101, EmbarcaderoFreeway and Interstate 280 in San Francisco were damaged. A portionof Bay Bridge also collapsed, killing one person. Las Gatos, SantaCruz and Watsonville lay near the epicenter and received unimaginabledamage to the infrastructures and homes. The other majorly hit areawas Watsonville located some mile from the epicenter with a magnitudeof 5.4. Most of her downtown (30%) and 1 in every 8 homes weredestroyed. The San Francisco Bay area assumed major losses in termsof stadiums where major baseball games were underway as well aslosses in homes and infrastructure (Harris, 2008). Electric trainsand cable cars experienced total power loss but there were nocasualties received. The airports and road transport were allgrounded due to the immense destruction of roads and airports.

Thefinancial effects of the quake were unimaginable. According to thereport by California Office of Emergency Services 1990, the estimatedfinancial impact was approximately $5 billion (California, 2009). TheOffice estimates were as follows: damaged private homes- 13,329 774fully destroyed homes 1,615 damaged businesses and 310 completelydamaged businesses. The Santa Cruz inhabitants were forced to pass ameasure E sales tax to help rehabilitate and repair the city(California, 2000). By 1997 the total sales tax was estimated at $21million.

The tax proceeds were used in thereconstruction of streets and downtown infrastructures, parkingstructures, police stations and to finance liability claims. FEMA andOES also contributed in this emergency fund to help the city regainher footing. The San Francisco, Santa Cruz, Oakland and othercommunities affected by the quake enacted strict rules andregulations in the construction of buildings requiring anunreinforced masonry buildings and houses to be reinforced andretrofitted(McDonnell, 2006 ).

Initial rescue missions were carried out by thevarious emergency departments in the cities and from the federalgovernment (McDonnell, 2006). Rescue missions involved mainly savingof human lives through major evictions via air using rescuehelicopters. Fire departments together with the police departmentswere involved in such evictions as well as rescuing trapped people asa result of building collapses. Many people were rescued. Very littlecould be done to salvage the properties.

Repair and recovery process continued withclosure, construction and subsequent reopening of the damagedinfrastructures. Major transportation corridors underwent rebuildingand were opened for public use after determination of their safety.Some notable changes are as follows. Central freeway, US highway 101was reconstructed and reopened fully 15 years later. Southern freeway(interstate 280) was reopened in 1997 after reconstruction. Cypressstreet viaduct was rebuilt and reopened in 1997. SanFrancisco-Oakland Bridge was rebuilt and opened in 2002 (Theguardian, 2013). Trans Bay ferries and Amtrak railway stations wererebuilt and opened 5 years later. Many buildings were rebuilt usingthe policies passed to guide construction of buildings. All buildingshad to have concrete masonry reinforcement fitted with earthquakeresilient foundations. Construction was discouraged along fault linesand susceptible areas. Downtown Oakland, San Francisco, Santa Cruzwas rebuilt over the years with many completions achieved 15 yearslater (Bolt, 2006).

Since 1989, California region has experiencedminor tremors till the August 24, 2014 California earthquake whichmeasured a magnitude of 6.0 on the Richter scale. The quake hit thenorthern California region at 3.20 AM pacific time, 4 miles NorthWest of American Canyon town in Napa County (Culzac, 2015). Therewere no casualties, but there were 87 injured people compounded bypower outages and property loss.


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“The Loma Prieta (Santa Cruz Mountains),California, Earthquake of 17 October1989”. California Division ofMines and Geology, 2009. (Special publication 104)