Seismic Hazards In the Region of Japan and Indonesia - Essay Example

? A Comparative Investigation of Seismic Hazards (In the Region of Japan and Indonesia) Seismic hazards are the intrinsic natural occurrences of earthquakes and the resulting ground motion and other effects (Wang). ‘Seismic Hazard Analysis’ is the science of deriving a relationship between hazards and their frequency of occurrence. The purpose of such an analysis is to provide parameters for estimating seismic risk. The objective of this assignment is to undertake a comparative study of the seismic hazards and approaches to mitigation in two regions of our choice. For this study, we shall investigate the seismic hazards of the regions of Japan and Indonesia. Both the countries being islands and possessing a history of frequent and violent earthquakes thus lay a lot of emphasis on such studies. We shall also look into the measures adopted by the two countries to diminish the effects of the hazards of an earthquake. Seismic Hazards and Seismic Risk ‘Seismic Hazards’ and ‘Seismic Risks’ are often confused with one another. Seismic hazards may also be defined as any physical phenomena (for example, ground shaking) that are associated with an earthquake and that may produce adverse effects on human activities. It is restricted to the study of likely earthquake ground motions at any point on the earth. Seismic risk constitutes the results of a seismic hazard analysis, including both the consequence and the probability. Seismic risk is used to describe earthquake effects that include ground shaking, surface faulting, landslide, and economic loss and casualties (Algermissen 1). The following statement may help to distinguish between a hazard and a risk: A building located in a region of high seismic hazard is at lower risk if it is built on the basis of sound seismic engineering principles; whereas, a building located in a low seismic hazard zone is said to possess a high risk if not built in accordance to the seismic engineering principles applicable to that zone. Probabilistic Seismic Hazard Analysis (PSHA) PSHA quantifies the probability, rather the rate, of exceeding the level of various ground motions at a site given all possible earthquakes (Field). Cornell was the first seismologist to develop this numerical approach to PSHA in 1968. PSHA involves three steps: 1. Specification of the seismic-hazard source model. 2. Specification of the ground motion model. 3. The probabilistic calculation. Hazard curves developed through PSHA show the likelihood of exceeding the various ground motion values at a specific site; on a typical hazard curve 10% probability of exceedance in 50 years is considered as one point. Actually, there is no alternative for a hazard curve to compare hazards at different locations. These curves are crucial in helping us to understand different types of ground motions. Not only this, the hazard curve helps to determine the expected losses. Losses can occur from both frequent smaller events or from less frequent large events. An annual rate of exceedance versus peak ground acceleration (PGA) is defined as a hazard curve plot. An example is shown below: Seismic Hazard Analysis of Japan A group of island arcs related to various subduction zones constitute Japan. These islands stretch from the Kurile Islands in the northeast to the Ryukyu chain in the south. Japan uses its own seismic scale, in units of Shindo, to measure the strength of earthquakes. The JMA scale differs from other seismic scales in the way that it describes the degree of shaking at a given point on the Earth's surface. The magnitude of JMA scale is measured between 0 and 7. The JMA reports of earthquake level are based on the peak ground acceleration (PGA). A relationship of Shindo Number along with PGA and the effects on people, Ground and Slopes and Outdoor Situations (JMA) is represented in the Table below: Shindo Number Peak Ground Acceleration (PGA) People Grounds & Slopes Outdoor Situations 0 Less than 0.008 m/s? Imperceptible to people. 1 0.008–0.025 m/s? Felt by only some people indoors. 2 0.025–0.08 m/s? Felt by most people indoors. Some people awake. 3 0.08–0.25 m/s? Felt by most people indoors. Some people are frightened. Electric wires swing slightly. 4 0.25–0.80 m/s? Many people are frightened. Some people try to escape from danger. Electric wires swing considerably. People walking on a street notice the tremor. 5 lower 0.80–1.40 m/s? Most people try to escape from a danger. Some people find it difficult to move. People notice electric-light poles swing. Unreinforced concrete-block walls collapse. Occasionally, cracks appear in soft ground, small slope failures take place in mountainous terrain. 5 upper 1.40–2.50 m/s? Many people are considerably frightened and find it difficult to move. In many cases, unreinforced concrete-block walls collapse and tombstones overturn. Many automobiles stop because it becomes difficult to drive. Occasionally, cracks appear in soft ground and rock falls and small slope failures take place in mountainous districts. 6 lower 2.50–3.15 m/s? Difficult to keep standing. In some buildings, wall tiles and windowpanes damage and fall. Occasionally, cracks appear in the ground, and landslides take place. 6 upper 3.15–4.00 m/s? Impossible to keep standing and to move without crawling. In many buildings, wall tiles and windowpanes damage and fall. Most unreinforced concrete-block walls collapse. Occasionally, cracks appear in the ground, and landslides take place. 7 Greater than 4 m/s? Thrown by the shaking and impossible to move at will. In most buildings, wall tiles and windowpanes damage and fall. In some cases, reinforced concrete-block walls collapse. The ground is considerably distorted by large cracks and fissures, slope failures and landslides change topographic features. The Seismic Hazard Map of Japan is shown below together with the tectonic plates . After studying the two figures, it becomes clear that Japan is extremely prone to frequent, and very often, strong earthquakes. Japan is divided into northern, central and western regions; the possibility of seismic intensity equal to or larger than 6 Lower, within 30 years from the present is studied meticulously (Earthquake Research Committee). Northern Japan Region Areas with high probability of hazard are noted on the Pacific coast of Hokkaido, the Pacific coast of Miyagi Prefecture, and the Pacific coast of Fukushima Prefecture, Yamagata Basin and the Hachiro-gata region of Akita Prefecture. Also, areas with fairly high probabilities extend across the inland areas and to the Japan Sea side. Sapporo City (Hokkaido) has a fairly high possibility of shaking equal to or larger than seismic intensity 6 Lower, within 30 years from the present; the influence is highest from the characteristic earthquakes of the 98 major active fault zones. This is caused by the Ishikari-teichi-toen fault zone which has a high occurrence probability. Central Japan These areas are largely influenced by earthquakes along the Nankai Trough (Tokai and Tonankai earthquakes), which have been evaluated with a high probability for the entire area of Shizuoka and Aichi Prefectures. Areas with high probability extend over the whole of Kanto Plain, where the Tokyo Metropolis, the prefectures of Kanagawa, Saitama and Chiba, and the southern part of Ibaraki Prefecture are located. In addition, regions with high probability extend in north-south in central portion of Nagano Prefecture. Yokohama City (Kanagawa Prefecture) has a high possibility for seismic intensity equal to or larger than 6 Lower, and earthquakes that have a high degree of influence are similar to the Shinjuku Ward. In addition, earthquakes in the Kannawa/Kozu-Matsuda fault zone, which have a higher occurrence probability among the 98 major active fault zones, have a relatively high influence. Western Japan In this area the influence is large for earthquakes along the Nankai Trough (Tokai, Tonankai and Nankai earthquakes) and the probability is high in nearly all areas of the Kii Peninsula and Shikoku Island. Areas with high probability are also observed along the parts of the coast of the Seto Inland Sea coast of Honshu, the Pacific coast of Oita and Miyazaki prefectures, and parts of the coast of Kumamoto Prefecture. In inland areas, the probability is also high in the vicinity of Lake Biwa. Seismic Hazard Analysis of Indonesia The country of Indonesia lies within the Southern-Sumatra and Java section of Sunda Subduction Zone (Petersen, Harmsen and Rukstales). The Southern Sumatra zone encompasses one of the most seismically-active plate tectonic margins on the earth, and accommodates oblique north-eastward convergence of about 50 mm/yr between the Australia plate and the Sunda plate. Within the Java zone, earthquakes have caused damage from either shaking or tsunamis as the result of thrust-faulting on the plate interface and faulting within the Australia or Sunda plates. New seismic hazard maps for Indonesia (Petersen and others, 2004) developed after tsunami of 2004 suggest significantly higher ground motions than that of current Indonesia building code. Most earthquakes that occur in Indonesia can cause double damage by vigorous shakes and causing tsunamis. It is clear from the hazard map that the southern regions of Java and Sumatra islands are vulnerable to high shakes, whereas Borneo is relatively safer. Comparative Analysis of Japan & Indonesia Preparedness towards a Hazard Although both the countries are island nations and both lie in seismic zones of high risk, both countries have vastly different levels of preparedness towards a hazard. This can be attributed to the overall socio-economic situation that exists in each country. The studies undertaken in Japan for risk and hazard analysis are far more exhaustive than that in Indonesia. After the Great Hanshin Earthquake (Kobe Earthquake) of 1995, which registered 7.2 on the JMA magnitude scale and in large-scale devastation and loss of 6,434 lives, Japan developed the best in the world disaster preparedness system. In 2000, the country revised its building codes, stipulating specific requirements and mandatory inspections. Japan’s early-warning earthquake system is considered as the world's most sophisticated one. In Japan, emergency drills are common in public and private organizations. As far as mitigation of the hazards is concerned, Japan excels in this field as well. Landslides, liquefaction, tsunamis and volcanoes—the possible hazards associated with earthquakes have their monitoring system well in place. Set up in 1952, Japan's tsunami warning system consists of 300 sensors (80 aquatic sensors), monitoring seismic activity 24/7 in this island nation. The network has been largely successfully predict accurately the height, speed, location, and arrival time of any tsunami along the Japanese coast, except in the case of Tsunami of 2011 that wreaked havoc on central Japan. Tsunami safety has always been observed in the coastal city planning in Japan. The tsunami-prone east coast has hundreds of earthquake-proof and tsunami-proof shelters. Majority of cities have tsunami walls and floodgates to keep at bay the ocean waves that travel inland through river systems. The use of GPS systems to accurately pinpoint the fault lines and develop hazard maps is also carried out in the country. The evidence of Japan’s preparedness comes from their recent handling of Tsunami of 2011. Although the property damage was high, their disaster preparedness regime ensured minimum loss of human lives. On the other hand, Indonesia has undertaken very few corrective measures after its worst disaster in 2004. Even the Indonesian Tsunami Early Warning System, installed in 2005, is still in the early stages of development (Kuntjoro, Jamil). On the Mentawai Islands, there is a dearth of suitable infrastructure and funds to support efficient early warning system facilities. Many local governments are also reluctant to invest in disaster management. Coordination is also very hard when the area is remote as is the case in Mentawai. Several disasters since the Tsunami of 2004 have occurred in the country, but the efforts of the local and the national government were still found to be lacking Bibliography 1. Algermissen, S. T. Seismic risk, AccessScience@McGraw-Hill, http://www.accessscience.com 2. Cornell, C.A. Engineering seismic risk analysis. "Bulletin of the Seismological Society of America", 1968: 3. Field, E. H. Probabilistic Seismic Hazard Analysis (PSHA) A Primer, http://www.relm.org/tutorial_materials, 4. Wang, Z. A Clear Definition of Seismic Hazard and Risk: A Basis for Hazard and Risk Assessment, Communication, and Management. American Geophysical Union, 2005. 5. Petersen, M. Harmsen, S. Mueller, C. Haller, K. Dewey, J. Luco, N. Crone, A. Lidke, D. and Rukstales, K. Documentation for the Southeast Asia Seismic Hazard Maps. Virginia: U.S. Geological Survey, 2007. 6. National Seismic Hazard Maps for Japan (2005). Headquarters for Earthquake Research Promotion, 2005. 7. Kuntjor, I. and A. Jamil. S.Triple Trouble in Indonesia: Strengthening Jakarta’s Disaster Preparedness. NTU. 2010. 8. The Fundamental Plans for Survey and Observation. Headquarters for Earthquake Research Promotion, 1997. 9. Ikeda,Y., Imaizumi, T., Togo, M., Hirakawa, K., Miyauchi, T. and Sato, H. Atlas of Quaternary Thrust Faults in Japan. University of Tokyo Press, 2002. Read More