Introduction
On October 17, 1989, a 10-15 second earthquake measuring 7.0 on the Richter scale hit the San Francisco Bay area. (Federal Construction Council 4) The epicentre was located 70 miles south of San Francisco in the Santa Cruz Mountains, near Loma Prieta peak from which the earthquake gets its name. (Karl 12)
This was the largest earthquake in the San Francisco Bay area since 1906 and although it did not tear the ground surface it caused 63 deaths and close to $6 billion in property damage including 1,018 homes destroyed, 23,408 homes damaged, 366 businesses destroyed and 3,530 businesses damaged. (Karl 12) Infrastructure, including a section of the San Francisco – Oakland Bay Bridge, was also damaged.
The area of San Francisco that suffered the most damage was the Marina district where four buildings were destroyed by fire and several others collapsed, many of which were apartment buildings common in the area. (Karl 12) To understand why this was the case a brief history of the Marina district is required.
The Marina District
The Marina district was built following the devastating 1906 San Francisco earthquake and in preparation for the 1915 Panama-Pacific International Exposition hosted by the city by filling in a shallow inlet of San Francisco Bay using a mixture of sand, dirt, discarded rubble from the 1906 earthquake, and other materials containing a high percentage of groundwater. (Tobriner 264)
After the Exposition apartment buildings were built on the filled land where the sand and the gravel are the major components of the ground. In this respect, the district is particular for its primordially dangerous background for building apartments. The thing is that all soft massive materials are more destructive for even small vibrations. Thus, the Marina district was concerned initially with relatively close to the area’s beaches and dunes which contributed to the fill of the region. In general, the structural estimation of the ground components in the district showed that the major material in it is the sand. In turn, it is a prerequisite for the cataclysms in nature, such as earthquakes and the effect of liquefaction which was particular to the Marina district in the disaster of 1989 (Arulanandan et al 967).
Impact of Soil Conditions on Ground Movements
Soil conditions of the Marina district were the main reason for the disastrous outcomes of the Loma Prieta earthquake. The point is that, as was stated above, the softness of the ground does not give a guarantee for buildings’ safety. In other words, the role of the fill was significant for counting on the dangerous outcomes of the earthquake along with the numbers of possible lost people, etc. Though, it is necessary to state and analyze the peculiarities of the soil as for its components in San Francisco and the Marina district, in particular.
The soil conditions of the San Francisco area are terrifying by its initially deep fill structured with sand and clay. It is dangerous owing to “sandy fills that were not densified before construction of buildings and other facilities on them” (Mitchell et al 3). Nevertheless, the grounds for the liquefaction in this small region of San Francisco were predetermined by huge deposits of soft and rather destructive materials on which the region stands: “In the Marina district, where loose, sandy hydraulic-fill soils are underlain by deep clay depo0sits, this amplification is believed to have contributed to the generation of lateral ground deformations” (Asociacion Espanola de Ingenieria Sismica 6577).
Thus, the unstable performance of soil conditions straightforwardly points out the destruction in the region. However, according to the report by some major researchers in the discussed area who surveyed the reasonable factors for apartment building ruination, within three sites of the district, the huge destruction falls into solely one which is closer to the sea and placed next to the Santa Cruz Mountains (Arulanandan et al 968). This supposition is too logical due to the soil deformations which were observed after the earthquake.
Varying from bay mud to rock site, soil conditions in the district provide quite astonishing contrast according to the geo-seismic colouring of the region and its placement within allegedly “between the devil and the deep sea” (Grossi and Kunreuther 72). In this situation, the scientists and geologists, particularly, could not even presuppose and predict the further evaluation of seismic activity in the relevantly young mountain region. What is more, the logical assumption about the unstable character of the fill in the district did not give scientists enough grounds for making specifically shaped constructions of buildings with the use of modern achievements in the sphere of mechanics, architecture, and the Theory of Strength of Materials. Hence, the design of the buildings should be correlated accordingly. However, since the year 1906 engineers tried their best to assume the most convenient construction for buildings and their blocking as well.
Typical Construction Practices for Apartment Buildings in the Area
The construction of most apartment buildings in the Marina district did not include the possibility of quakes in the region. Such an assumption can be made owing to the inhabiting tendency since the early twentieth century. At that time the cultural and precise architectural heritage of mankind along with the achievements of the science at the time did not show the awareness of the engineers in how the structure should be strengthened to prevent it from a probable earthquake. In this respect the main approach in most cases fell into wood-frame constructions: “Most of the failures came from structural weakness in the first floor, typically called a “soft” first story, which collapsed when the soft soils these were built on liquefied during the quake” (Comerio 70). Thereupon, the so-called “soft” story appeared as a result of building parking garages under the three-story apartments. The consequence of suchlike a building can be shaped by the “card house” destruction. Inadequate construction of soft-story can be result, as shown below:
One more wrong constructive approach of engineers due to the huge family stock in the area was considered with the masonry buildings (Johnson 75). It is so due to the inapplicable use of stone materials in this very region because the debris of cracked houses represents even more hazards for the population and the municipal heritage of the Marina district. The aftershocks of multiple numbers of engineers were reflected on the numerous debris of what was constructed for years.
The situation displayed the architects and the wrong way of building houses, and its particular construction in the Marina district emphasized that the work of the thousand smartest people over the project of apartment buildings was in vain. This was registered, but the idea of the soft story still evaluates the construction of houses not only in San Francisco but throughout the United States. The Lesson of Loma Prieta made scientists evaluate the main reason for the collapse of apartment buildings in the inappropriate setting and structuring of the three- and four-story houses in the district. Furthermore, such carelessness of engineers can be stated on grounds of the seismically active region. Though, all precaution measures were ignored due to the relatively long period of seismic silence in the region.
Reason for the Collapse of Apartment Buildings
Above stated prerequisites for the collapse should be evaluated as those which were outlined in terms of the natural characterization of the district as well as the engineer drawbacks. One should bear in mind that the harm because of the earthquake could have been lessened if the engineers had followed the world practice in repairing or reconstructing the existing houses. Unfortunately, the risk was inevitable due to several major points. Some among them are the dangerous and rather risky area between two elements of nature (mountains and the ocean); soft fill covered deep in the ground; and technical and scientific misconduct in applicable structuring of the buildings. On the other hand, the researchers highlight the following lessons learned from the Loma Prieta earthquake, namely:
- Notwithstanding pitching and swaying high-rise structures did not sustain significant damage;
- Earthquake-resistant designs should be performed immediately in the area in their experimental character;
- Deep, soft soils are dangerous, but with the implementation of new technologies it is available to produce safer landfills;
- Unreinforced masonry buildings are potential killers (Johnson 75).
Along with the ignorant attitudinal framework of architectural designers, the firmness of the basal complex and floor area of the apartment buildings was not enough to resist the vibrations. Moreover, there were no implications even to inform the population and the engineers in primordial wrong projects for the buildings being built: “The main reason for failure was the lack of adequate bracing, such as plywood shear walls” (Chen and Lui 11). Thus, the constructive ideas about the material choice were not determined from the very beginning. However, the formation of the typically soft story in each building is just the result of the car industry spread in the United States during the twentieth century. So there is an cultural alleged drawback for the district. The garage was necessary to be included in the whole structure of the building. This is why it reasoned the breakdown in the Marina district. Moreover, engineers did not take into consideration that with the such-designed ground floor buildings should be strengthened by more massive and vibration-resistant bolsters. This would prevent the floors from cracking.
What is more, the sustainability of materials seems not to be correlated by the strength of materials in its theoretical approach. The evidence after the earthquake showed that the buildings were highly damaged more due to the lack of resistant materials in the whole structure of each building in the area. Of course, one may suppose that it is because of the soil conditions which cannot be changed due to the scope and amounts of sand in it. However, the technical approach can be implemented to protect the lives of people from the disastrous and rather risky challenges of nature in the area of San Francisco.
Conclusion
To sum up, it is significant to outline the lessons which were learned from the Loma Prieta earthquake in terms of scientific thought of the particular time. In this respect, the discussion maintained in the paper showed the analytical data of aftereffects which were caused by the quake and reasons for such negative occurrences in the Marina district. One should bear in mind that the seismically active region cannot be stopped in its growing risk for people’s lives. However, the scientific and technical approaches are available to be implemented in San Francisco’s buildings, so that to repair existing and to build new ones. Thus, the stabilization methods should include the experience of other countries where suchlike hazards frequently occur, meaning Japan, in particular.
The corrective action plan should also contemplate the provision of a new technique and technologically guaranteed landfill for prevention from deeper soft layers of ground. It may supposedly decrease the levels of liquefaction in the Marina district. Contemporary science suggests many-faceted technologies for the decrease of buildings ruination after the earthquake. Swaying and pitching pylons may serve to be measured for the safety of apartment buildings and people living in them. Hence, there are several lessons to be taught, and modern engineers should relate their rational suggestions to the experience of Loma Prieta.
Works Cited
Arulanandan, Kandiah, Muraleetharan, Kanthasamy K. and Yogachandran, Chelvarajah. ‘Seismic Response of Soil Deposits in San Francisco Marina District’. Journal of Geotechnical and Geoenvironmental Engineering. 123 (10), 1997, pp. 965-974.
Asociacion Espanola de Ingenieria Sismica, International Association for Earthquake Engineering. Earthquake engineering: 10th World conference: Papers. Vol. 11. London: Taylor & Francis, 1994.
Chen, Wai-Fah and Lui, E. M. Handbook of structural engineering. Ed. 2. Boca Raton, FL: CRC Press, 2005.
Comerio, Mary C. Disaster hits home: new policy for urban housing recovery. Berkley, CA: University of California Press, 1998.
Earthquake Hazard Information.Photos of Earthquake Damage, Modes of Building Failure – Part 1, 2003.
Federal Construction Council. Consulting Committee on Civil and Structural Engineering. Retrofitting buildings for seismic safety: summary of a symposium: Issue 109 of Technical report (Federal Construction Council).
Washington, DC: National Academies, 1991.
Grossi, Patricia and Kunreuther, Howard. Catastrophe modelling: a new approach to managing risk. Vol. 25. Berlin: 2005.
Johnson, Joseph T. The ‘Lessons of Loma Prieta: How we’ll build better for the Big One’. Popular Science. 236 (3). 1990, 74-81.
Karl, Herman A. Beyond the Golden Gate: oceanography, geology, biology, and environmental issues in the Gulf of the Farallones. Oxford: DIANE Publishing, 2000.
Mitchell, James K., Masood, Tahir, Kayen, Robert E. and Seed, Raymond B. Soil Conditions and Earthquake Hazard Mitigation in the Marina District of San Francisco. Earthquake Engineering Research Center. Berkley, CA: University of California. 1990.
Tobriner, Stephen. Bracing for disaster: earthquake-resistant architecture and engineering in San Francisco, 1838-1933. Berkeley, CA: Heyday Books, 2006.