Some significant earthquakes and learnings (1980-1999)
Some significant earthquakes and learnings (1980-1999)
Uploaded At: 01 May 2024Some significant earthquakes and learnings (1980-1999)
The 1985 Chilean earthquake (MW=8.0), a subduction zone interplate event, hit the central part of Chile with human fatalities of 177. Geotechnical damage was associated with settlement, liquefaction, and failure of several small irrigation dams. The Cerro Negro and Veta del Agua tailings dams built with the upstream method underwent liquefaction-induced flow failures. Part of the stored tailings of Cerro Negro flowed downstream for about 8 km[1], generating a significant environmental impact. One of the main lessons learned is associated with the phenomenon of topographic amplification, which was observed in the Canal Beagle, in Vina del Mar, where extensive damage occurred in structures sited on ridges[2].
The offshore Michoacan earthquake of 1985 (MW=8.0) is also called the Mexico City earthquake because of the widespread death and injuries caused in Mexico’s capital. Nearly 10,000 people were killed. Although at a distance of 320 km, thick, soft clay deposits amplified the ground shaking especially at the period range of 1 to 2 seconds, which caused collapse of hundreds of 10 to 20-story buildings and damaged thousands more[3]. The earthquake motivated seismic site response studies that led to increasing the amplification factor for soft clay sites.
The timing of the 1989 Loma Prieta, California earthquake (MW=6.9), which struck during the U.S. Baseball World Series, was fortuitous because traffic was light when the Cypress Street Viaduct collapsed, and a section of the east span of the San Francisco–Oakland Bay Bridge fell onto its lower deck[4]. Yet, 63 people perished. The amplification of earthquake shaking at the section of the Cypress Structure overlying soft clay contributed significantly to its collapse (Figure 1). Much of the damage from the Loma Prieta earthquake was localized at soft clay sites. These observations motivated several studies that led to improved intensity-dependent short and long period site amplification factors in the 1997 International Building Code. Soil liquefaction also played a major role in the observed patterns of damage in the San Francisco Bay Area[4]. This event also demonstrated the benefits of ground improvement to mitigate the liquefaction hazard, which in turn motivated research, development, and employment of liquefaction mitigation measures in U.S. engineering practice. Several major slope failures occurred, and an earth dam deformed significantly, but the reservoir elevation was low due to the drought that preceded the earthquake. Lastly, the 1989 Loma Prieta earthquake provided several case histories that documented the seismic performance of municipal solid-waste landfills, an engineered system that had not been studied extensively.
Figure 1. Collapsed section of the Cypress Street Viaduct due to amplified ground shaking at a soft clay site during the 1989 Loma Prieta earthquake[4].
Figure 2. Liquefaction-induced fire at Balboa Blvd. during the 1994 Northridge Earthquake (LA Times)[5].
The 1994 Northridge, California earthquake (MW=6.7) produced extensive damage in the Los Angeles area. Several important bridge structures and buildings collapsed, which led to 57 deaths[5]. It was fortuitous that it occurred early in the morning on a holiday when traffic was light. Intense forward-directivity near-fault pulse ground motions exceeded anticipated design motions and contributed to the collapse of several structures. This event motivated an increase in the building code-specified design shaking levels for structures sited near major active faults. Near-fault pulse motions are now routinely included in the suite of design motions employed in dynamic analyses in California. Site effects focused damage in localized areas in the LA area. Nonlinear effective stress analyses were shown to be required to capture these effects. Liquefaction produced significant damage in areas of lateral spreads and ground settlement. The lateral spread at Balboa Boulevard ruptured natural gas pipelines and water transmission lines leading to a deadly fire and a temporary loss of water supply (Figure 2). A tailings dam failed due to liquefaction. Damaging ground settlement due to seismic compression of partially saturated compacted earth fills caused considerable economic losses, which led to the development of improved standards for their construction.
The 1995 Kobe, Japan earthquake (MW=6.9) produced severe damage with human fatalities more than 6,000 in a highly developed urban infrastructure, with harbor facilities, highway/railway systems, buildings, etc (Figure 3). Geotechnical engineering played a key role in most aspects of the damage because the City of Kobe was developed along a narrow coastal area between hills and reclaimed lands. Buildings and highway/railway viaducts on competent soils located inland were damaged by earthquake inertia while similar structures near the coast in reclaimed soils were damaged not so much in their superstructures but damaged heavily in their foundations due to liquefaction-related settlements and lateral spreading[6]. Harbor facilities, such as piers, caisson walls, and crane/bridge foundations, were deformed because of significant soil settlements and lateral spreading in reclaimed islands built with decomposed granite fill which heavily liquefied[7]. Dynamic soil response during the liquefaction was successfully monitored in the Port Island-vertical array situated in a thick reclaimed fill that liquefied intensively. De-amplification of horizontal accelerations due to liquefaction at the ground surface was first demonstrated to occur in situ in a good contrast to vertical acceleration which showed ordinary amplification toward the surface[8]. The lateral spreading behind displaced caisson walls in liquefied ground was thoroughly investigated in its mechanism and its effect on pile/pier foundations[9,10]. Various soil improvements as liquefaction mitigation measures were demonstrated to have clearly reduced soil settlement during the earthquake[11].
Figure 3. Damage in the 1995 Kobe earthquake (Photos: Akai et al. 1995 GEER Report)
Other earthquakes with marked geotechnical impacts occurred in Japan were the 1983 Nihonkai-chubu (MW=7.7), 1993 Hokkaido Nansei-oki (MW=7.8), and 1993 Kushiro-oki (MW=7.6) earthquakes. The first one triggered severe damage in port facilities constructed by diaphragm walls as well as large settlements of levees[12], while the third one inflicted large displacements of caisson quay port facilities similar to the Kobe earthquake and uplift of many sewage manholes by liquefaction[13] (Figure 4). During the second one, liquefaction-induced settlement of houses occurred in a coarse-gravelly volcanic soils normally considered difficult to liquefy[14].
Figure 4: Damaged levee in the 1983 Nihonkai-chubu earthquake (left); K. Ishihara next to an uplifted manhole after the 1993 Kushiro-oki earthquake (right)
The 1999 Kocaeli, Turkey earthquake (MW=7.4) caused devastation in towns and cities along a 100-km-long strip, with more than 20,000 human fatalities. The seismogenic fault, part of the North Anatolian Fault, emerged on the ground surface with strike-slip as well as normal dislocations reaching 4 m. Numerous facilities such as buildings, bridges, harbor quay walls, electrical transmission pylons were displaced by surface fault rupture. Despite some failures, several structures performed remarkably well[15,16], apparently due to their stiff, strong box-type foundations and the soft underlying soil. These findings are the basis for design recommendations and new building code provisions for proper design against surface fault rupture[17,18]. In the City of Adapazari, numerous 4-6 story buildings underwent ground-related settlement, tilting, and overturning[19,20,21] (Figure 5). In most cases, the buildings remained structurally intact. The main cause was liquefaction-triggered bearing-capacity failure of the raft foundations, aggravated by asymmetric accumulation of deformation in the soil immediately below the foundations of contiguous buildings[22]. Large-scale ground movements in the coastal region of the Izmit Bay caused the “sinking” of whole building blocks in the town of Degirmedere due to lateral spreading. In the southern shore of Lake Sapanca, lateral spreading displaced a large hotel building and damaged the houses of a nearby community[15]. Istanbul, located 35 - 50 km from the seismogenic fault, did not suffer much with the exception of the region of Avcilar, in which there were numerous fatalities in collapsed multi-story buildings, apparently due to soil amplification of the ground motion (i.e., peak ground accelerations increased from less than 0.10g in Istanbul to about 0.25g in Avcilar).
Figure 5: Tilted building at silty soil site that liquefied during the 1999 Kocaeli earthquake[15].
The 1999 Chi-Chi, Taiwan earthquake (MW=7.6) killed about 2,300 people and produced a variety of damage due to fault displacement, slope failure, and liquefaction[23]. Extraordinarily large fault displacements exceeding several meters appeared on the ground surface along the rupture fault which produced significant damage in buildings, roads, bridges and dams crossing the fault (Figure 6). Many slope failures were triggered in steep slopes in mountainous areas, followed by subsequent long-lasting rain-induced slope instability and debris flows[24]. Wide-spread liquefaction damage occurred in lowland alluvial and reclaimed areas where the soils were mostly clayey silty sand with significant fines, similar to the soils of Adapazari which liquefied during the 1999 Kocaeli earthquake. Port facilities suffered similar damage as 1995 Kobe earthquake in caisson quay-walls and reclaimed lands[25].
Figure 6: Fault rupture-induced failure of Shih-Kang Dam with vertical offset 9.1 m in 1999 Chi-Chi, Taiwan EQ[17]
References
[1] Castro G. and Troncoso J. 1989. Seismic Behavior of Three Tailings Dams During the March 3, 1985 Earthquake. 5th Chilean Conference on Seismology and Earthquake Engineering.
[2] Çelebi, M. 1987. Topographical and geological amplifications determined from strong-motion and after-shock records of the 3 March 1985 Chile earthquake. Bulletin of the Seismological Society of America. 77 (4): 1147–1167.
[3] Seed, H.B., Romo, M.P., Sun, J.I., Jaime, A., and Lysmer, J. 1988 The Mexico Earthquake of September 19, 1985 – Relationship between soil conditions and earthquake ground motions. Earthquake Spectra. https://doi.org/10.1193%2F1.1585498.
[4] Seed, R., Dickenson, S., Riemer, M., Bray, J., Sitar, N., Mitchell, J., Idriss, I., Kropp, A., Harder, L., and Pow-er, M. 1990. Preliminary report on the principal geotechnical aspects of the October 17, 1989 Loma Pri-eta Earthquake. Earthquake Engineering Research Center, Report No. UCB/EERC-90/05, Univ. of Cal-ifornia, Berkeley, April, 137 pp.
[5] Stewart, J., Bray, J., Seed, R., and Sitar, N., Eds. 1994. Preliminary Report on the Principal Geotechnical Aspects of the January 17, 1994 Northridge Earthquake. Earthquake Engineering Research Center, Report No. UCB/EERC-94/08, Univ. of California, Berkeley, June, 238 pp.
[6] Matsui, T. and Oda, K. (1996): Foundation damage of structures, Special Issue on Geotechnical Aspects of the January 17 1995 Hyogo-ken Nambu Earthquake, Soils and Foundations, 189-200.
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[14] Kokusho,T., Tanaka,Y., Kawai, T., Kudo, K., Suzuki, K., Tohda, S. and Abe, S. 1995. Case study of rock debris avalanche gravel liquefied during 1993 Hokkaido-Nansei-Oki Earthquake, Soils and Founda-tions, Japanese Geotechnical Society, Vol.35, No.3, 83-95
[15] Youd TL, Bardet J-P, Bray JD 2000. Kocaeli, Turkey, Earthquake of August 17, 1999 Reconnaissance Report. Earthquake Spectra Suppl. A to 16:456
[16] Anastasopoulos I, Gazetas G. 2007. Foundation-structure systems over a rupturing normal fault: Part I. Observations after the Kocaeli 1999 earthquake, Bulletin of Earthquake Engineering DOI 10.1007/s10518-007-9029-2.
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[19] Bray, J. and Sancio, R. 2009. Performance of buildings in Adapazari during the 1999 Kocaeli, Turkey earthquake. Earthquake Geotechnical Case Histories for Performance Based Design, Kokusho, T, Ed., TC4 Committee, ISSMFE, CRC Press/Balkema, The Netherlands, pp. 325-340 & Data on CD-ROM.
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[22] Gazetas, G., Anastasopoulos I., & Gerolymos, N. 2005. Overturning of Buildings in Adapazari, during the 1999 Kocaeli earthquake”, Proceedings, 2nd International Conference on Urban Earthquake Engineer-ing, Tokyo Institute of Technology, K. Tokimatsu, Ed., 193-198.
[23] Ueng, T. S., Lin M. L. & Chen, M. H. 2001. Some Geotechnical Aspects of 1999 Chi-Chi, Taiwan Earth-quake. 4th International Conf. on Recent Advances in Geotech. Eng. & Soil Dynamics. SPL.-10.1.
[24] Lin, M. L, Wang K.L. & Chen T.C. 2009. Chiufenerhshan landslide in Taiwan during 1999 Chi-Chi earthquake. . Geotechnical Case History Volume, Balkema, 259-272.
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