Fall 2018: Natural Hazards and Disasters
Natural Hazards and Disasters
Class 5: Disasters triggered by EarthquakesCONTENTSMagnitude and LocationsLarge to extreme earthquakes during the last 2000 years (see for example Table x in Plag et al., 2015) illustrate the destruction they can inflict directly and indirectly through tsunamis. The resulting disasters are amplified in areas with poor building infrastructure. As a consequence, the earthquakes with the largest magnitude do not necessarily cause most fatalities or greatest damage. Earthquakes cause disasters mainly due to failing buildings and infrastructure. “Earthquakes don't kill people, buildings do!” The largest disasters caused by earthquakes are in areas where the built environment is not able to withstand the ground shaking. Failing buildings, resulting fires, or other casacading effects in the built environment lead to the largest disasters. For off-shore earthquakes, a resulting tsunami can cause a very large impact. In general, poor countries exposed to the same level of hazards as more developed countries experience a disproportinate number of disasters. Poverty, often paired with corruption, can turn hazards into disasters, and the means to increase preparedness and resilience are not sufficiently available in areas with high degrees of poverty. The largest disasters caused by earthquakes took place in regions with poor building infrastructure. While the largest earthquakes occur at continental plate boundaries, the largest disasters triggered by earthquakes mostly occur within plates. CasesCase 1: Deadliest earthquake on record: 23 January 1556 in Shaanxi, Mw=7.9-8.0, I-XI, Depth unknown. Deaths 820,000-830,000 The 1556 Shaanxi earthquake or Huaxian earthquake was a catastrophic earthquake and is also the deadliest earthquake on record, killing approximately 830,000 people. An area 840 km wide was destroyed, and in some counties as much as 60% of the population was killed. Most of the population in the area at the time lived in yaodongs, artificial caves in loess cliffs, many of which collapsed with catastrophic loss of life. The epicenter was in the Wei River Valley in Shaanxi Province, near the cities of Huaxian, Weinan and Huayin. In Huaxian, every single building and home was demolished, killing more than half the residents of the city, with a death toll estimated in the hundreds of thousands. The situation in Weinan and Huayin was similar. In certain areas, crevices 20 m deep opened. Landslides contributed to the death toll. Case 2: Apr. 18, 1906 San Francisco, Mw=7.9, I=XI, Depth 8 km, Deaths 700 - 3,000 San Francisco earthquake of 1906, major earthquake with a magnitude of 7.9 that occurred on April 18, 1906, at 5:12 am off the northern California coast. The San Andreas Fault slipped along a segment about 270 miles (430 km) long, extending from San Juan Bautista in San Benito county to Humboldt county and from there perhaps out under the sea to an unknown distance. The shaking was felt from Los Angeles in the south to Coos Bay, Oregon, in the north. Damage was severe in San Francisco and in other towns situated near the fault, including San Jose, Salinas, and Santa Rosa. (britannica.com). Case 3: Sep. 19, 1985 Mexico City, Mw=8.0, I=IX, Depth 20 km, Deaths 10,000 (up to 45,000). The central city, constructed on the dry bed of the drained Lake Texcoco, endured the heaviest shaking because loose lacustrine sediments amplified the shock waves. The ground motion in this area measured five times that in the outlying districts, which had different soil foundations. Buildings of 5 to 15 stories were most affected, as their interaction with the shock waves created a harmonic resonance, exacerbating the degree of swaying. More than 400 buildings collapsed, and thousands more were damaged. (britannica.com). Case 4: Jan. 17, 1995, Kobe, Japan, Mw=6.9, I=XI Depth 17.6 km, Deaths 5,502-6,400, Damage $200 billion Damage was extremely widespread and severe. Structures irreparably damaged by the quake included nearly 400,000 buildings,[3][12] numerous elevated road and rail bridges, and 120 of the 150 quays in the port of Kobe. The quake triggered around 300 fires,[3] which raged over large portions of the city. Disruptions of water, electricity and gas supplies were extremely common. Case 5: Oct. 8, 2005, Azad Kashmir, Mw=7.6, I=VIII, Depth 26 km Deaths 86,000 to 87,000, Damage $5.2 billion The official death toll was 79,000 for Pakistani-administered Kashmir and the NWFP, although other sources put it at 86,000, with the number injured estimated at more than 69,000. At least 1,350 people were killed and 6,266 injured in Jammu and Kashmir state in India, and the tremors were felt at a distance of up to 620 miles (1,000 km), as far away as Delhi and Punjab in northern India. Four fatalities and 14 injured survivors were reported in Afghanistan. The property loss caused by the quake left an estimated four million area residents homeless. The severity of the damage and the high number of fatalities were exacerbated by poor construction in the affected areas. (britannica.com) Case 6: Jan. 12, 2010, Haiti, Mw=7.0, I=VIII, Depth 13 km Deaths 80,000 to 315,000 The earthquake was generated by contractional deformation along the Léogâne fault, a small hidden thrust fault discovered underneath the city of Léogâne. The Léogâne fault, which cannot be observed at the surface, descends northward at an oblique angle away from the Enriquillo–Plantain Garden (EPG) strike-slip fault system, and many geologists contend that the earthquake resulted from the slippage of rock upward across its plane of fracture. Case 7: Apr. 6, 2009, L’Aquila M 6.1, I=VIII, Depth 9.5 km Deaths 309, Damage $16 billion The L'Aquila earthquake occurred in the region of Abruzzo, in central Italy. The epicentre near L'Aquila, the capital of Abruzzo, which together with surrounding villages suffered most damage. There were several thousand foreshocks and aftershocks since December 2008, more than thirty of which had magnitude greater than 3.5. 309 people are known to have died, making this the deadliest earthquake to hit Italy since the 1980 Irpinia earthquake. Extreme EventsFor extreme events, the questions of how big, how bad, how often are difficult to answer because these events are rare and statistics are not readily available. Knowledge of rare events is limited. The knowledge of the “why” and “how” is often better developed than knowledge on the “when”. The probability is difficult to assess, which makes risk assessment challenging. What can be summarized is that earthquakes do not kill people, but buildings (corruption, irresponsibility, ignorance …). In general, geohazards cannot be reduced, but vulnerability of the built environment can be greatly reduced. Reducing predictive uncertainties in geohazard research and enhancing modeling capabilities also can contribute to make risk assessments a better basis for the planning of the built environment. Dealing with multiple and/or sequential events can be a challenge. To address this, developing a trans-disciplinary link and research is important. Links between science and policy-makers, media and insurances are also crucial for risk management and disaster reduction. Enhancing science education and improving awareness on extreme hazards and disaster risk further can increase preparedness and reduce the disaster risk. Managing Disaster RiskThe design of critical coastal infrastructure is often based on unjustifiably long recurrence intervals for these extreme events. A scenario-based assessment of the tsunami hazard can provide more insight and guidance for the planning of coastal infrastructure. Direct impacts of tsunamis are restricted to coastal zones, while indirect and cascading effects can reach regional and global scales. Mitigation of tsunami impacts is more a local problem, which require local governments to assess the threat, increase awareness and develop resilience plans. Large tsunamis like the one triggered by the May 22, 1960 Chile Earthquake, the March 27, 1964 Alaskan Good Friday earthquake, the December 26, 2004 Sumatra-Andaman earthquake or the March 11, 2011 Tohoku earthquake generated waves, which killed people thousands of kilometers away from the epicenter. The catastrophic effects of such tsunamis prompted governments to develop both local resilience plans and to progress in the establishment of tsunami warning centers across the globe. TsunamisTsunamis are waves in the ocean or large lakes that can be immensely destructive when they reach the shores and can destroy vast coastal regions. Earthquakes, landslides, and rockfalls can cause tsunamis in the ocean or in lakes. The extent of destruction a tsunami causes depends, among other factors, on the local population and infrastructure in the coastal region impacted by a tsunami. Class Reading ListIntergovernmental Oceanographic Commission. 2014. Tsunami, The Great Waves, Revised Edition. Paris, UNESCO, 16 pp., illus. IOC Brochure 2012-4. (English.), revised 2014. Language versions at: http://unesdoc.unesco.org/ulis/cgi-bin/ulis.pl?lin=1&catno=148609. pdf. Bernard, E. N., n.d. The Tsunami Story. NOAA, http://www.tsunami.noaa.gov/tsunami_story.html. |
