Are we ready to face another earthquake

Transcription

1 Are we ready to face another earthquake by Ramancharla Pradeep Kumar in The Master Builder, Mar-Apr 2005 Report No: IIIT/TR/2006/6 Centre for Earthquake Engineering International Institute of Information Technology Hyderabad , INDIA January 2006

2 (1991) (1997) Earthquake Engineering Research International Institute of Information Technology, Gachibowli, Hyderabad , AP Are we ready to face another earthquake? by Pradeep Kumar Ramancharla Asst Prof. & Head, EERC Introduction: Earthquake, now everyone is familiar with this word. We have clearly witnessed during the recent Sumatra, Indonesia earthquake (M 9.0) the amount of damage an earthquake can cause to the society. Had this earthquake occurred on land, it would have easily damaged few hundreds of kilometers and the damage estimates would have been unimaginable. Earthquakes are not new to our country. We have had the long history of earthquake occurrences. Some of the major earthquakes of the world occurred in our country and neighborhood areas. During past 15 years also we have witnessed 6 moderate earthquakes: Bihar-Nepal border (M6.4) in 1988, Uttarkashi, Uttaranchal (M6.6) in 1991, Latur, Maharastra (M6.3) in 1993, Jabalpur, Madhya Pradesh (M6.0) in 1997, Chamoli, Uttaranchal (M6.8) in 1999 and Bhuj, Gujarat (M6.9) in ). These earthquakes caused around 40,000 casualties (see Table 1) and innumerable property loss. These events occurred with a time gap of 2 ~ 3 years. Are we ready to face another event? Table 1: Casualties during past earthquakes Number of deaths Bihar (1988) Uttarkashi Killari 8000 (1993) Jabalpur Chamoli (1999) Bhuj (2001) Where? (when?) Even with the current level of understanding, it is very difficult to predict the occurrence time and exact location of next earthquake. The only way to ensure the safety is to get prepared. Severity of the problem: According to latest seismic zonation map given in IS: 1893: ), more than 60% of India is prone to earthquakes. Metropolitan cities like Delhi, Calcutta, Mumbai, Chennai, Ahmedabad etc., lie in zone III or above. Not only are these cities but many other cities in India are prone to moderate to severe earthquakes 3). Will the structures constructed in these areas withstand next event? If we look at the trend from past 15 years, urbanization is rapidly increasing and due to increase in land cost, many multistoried structures are being constructed. We must ensure that

3 Table 2 Casualties during Kobe Earthquake Time Ž S of death úžž No. of Casualties S@ŽÒ@ ŠÄŽ@ˆ by Medical ã ÝŒv Examiners Õ by Ordinary ˆ ã ÝŒv Doctors Total Ž SŽÒ ÝŒv Number 1/ 17 `6:00 2,221 2,221 ( 91.9 %) ( 58.2 %) 2,940 ( 80.5 %) `9: ,237 ( 92.6 %) ( 62.9 %) 3,014 ( 82.6 %) `12: ,284 ( 94.5 %) ( 67.9 %) 3,122 ( 85.5 %) `23: ,296 ( 95.0 %) 212 1,050 ( 85.0 %) 3,346 ( 91.6 %) unidentify Žž s Ú 110 2,406 ( 99.6 %) 84 1,134 ( 91.8 %) 3,540 ( 97.0 %) 1/ ,411 ( 99.8 %) 62 1,196 ( 96.8 %) 3,607 ( 98.8 %) 1/ 19 2,411 ( 99.8 %) 13 1,209 ( 97.9 %) 3,620 ( 99.2 %) 1/ ,413 ( 99.9 %) 8 1,217 ( 98.5 %) 3,630 ( 99.4 %) 1/ ,414 ( 99.9 %) 6 1,223 ( 99.0 %) 3,637 ( 99.6 %) 1/ ,415 ( %) 1 1,224 ( 99.1 %) 3,639 ( 99.7 %) 1/ 24 2,415 ( %) 1 1,225 ( 99.2 %) 3,640 ( 99.7 %) 1/ ,416 ( %) 1 1,226 ( 99.3 %) 3,642 ( 99.8 %) 1/ 26 2,416 ( %) 2 1,228 ( 99.4 %) 3,644 ( 99.8 %) 1/ 27 2,416 ( %) 1 1,229 ( 99.5 %) 3,645 ( 99.8 %) 1/ 28 2,416 ( %) 1 1,230 ( 99.6 %) 3,646 ( 99.9 %) 2/ 4 2,416 ( %) 1 1,231 ( 99.7 %) 3,647 ( 99.9 %) No ú record t È µ 2,416 ( %) 4 1,235 ( %) 3,651 ( %) Total Œv Number 2,416 1,235 3,651 from: Kobe Earthquake report (1995) earthquake forces are considered while designing these structures. Otherwise the damage will be catastrophic. Based on the technology advancement and knowledge gained after earthquake occurrences, the seismic code is usually revised. Last revision of IS 1893 was done in 2002 after a long gap of about 18 years. Some new clauses were included and some old provisions were updated. Assuming that concerned authorities will take enough steps for code compliance and the structures that are being constructed are earthquake resistant. In this light, what will happen to the safety of pre-code revision structures? These structures carry major percentage of vulnerable structure stock. Even if we have a very good disaster response system, it is impossible to reduce earthquake damage without considering the safety of pre-code revision structures. Table 2 shows the number of casualties and estimated time of death (by Hyogo prefecture medical examiners) due to Kobe earthquake occurred on 17 Jan 1995 in Kobe city. From this table, we can understand that many people were killed during initial few hours only. Even we can say that these casualties occurred during initial few minutes and the reporting time is recorded as and when the dead bodies are found. Casualties during initial few minutes are mainly due to the collapse of structures or the dynamic behavior of the furniture. As the occurrence time of the Kobe earthquake is in the morning, 5:46 am, 97% of people were killed in their own houses. After every earthquake there will be emergency activities, recovery activities and reconstructions activities (see Figure 1,). Various problems that are generated after an earthquake are; 1) Disruption of the community, 2) refuge camps, 3) temporary shelters, 4) psychological problems of people in the affected areas, 5) demolition and disposal of collapsed structures and their environmental effects, 6) ill function of social and lifeline systems due to heavy demand, 7) local economy and business interruption, 8) problems during recovery and reconstruction, and many more. The magnitude of all these problems will not be so severe, if the number of damaged structures is less. In order to reduce this, we need to concentrate on effective countermeasures. After every earthquake in India, there is a lot of discussion among

4 Integrated Earthquake Disaster Reduction System Three major Hazard countermeasures Implementation and Reinforcement of? Mitigation? Preparedness? Optimum Recovery/? Mitigation? Preparedness? Optimum Recovery/ Disaster-free Period Medicine Social Science Inhabitants Governments Earthquak e Event Science Utilities Mass Media Research of Hazard and Disaster Effects of Mitigation Emergency Engineering Recovery NGO, NPO Reconstruction Disaster Time Effects of Preparedness Effects of Optimum Recovery & Fig 1. Integrated earthquake disaster reduction system (Figure courtesy: Prof. Kimiro Meguro, University of Tokyo, Japan) engineering community and scientific community towards earthquake safety, however, there is not much campaign for retrofitting. Retrofitting is very essential to ensure the safety the already built structures. This is essential because post earthquake disaster response works directly depend on the number of collapsed or seriously damaged structures. Integrated earthquake disaster reduction system: Integrated earthquake disaster reduction system (shown in figure 1) consists of three parts, viz., Mitigation, preparedness and optimum recovery and reconstruction strategies. From the figure, it can be seen that magnitude of disaster is inversely proportional to mitigation level and this is directly related to the strength of built environment. Strength of built environment in a broader sense includes all the construction types including old & new structures, structures constructed considering the codal provisions and the structures constructed ignoring codal provisions. Earthquake will not see whether the structure is built before code revision or not. In this regard, it is important to ensure the safety of all structures. An earthquake resistant structure has following four qualities viz., 1. good configuration, 2. enough strength, 3) adequate stiffness and 4) ductility. The structures which ensured the above four qualities performed well during past earthquakes. However the advanced technology we have in designing earthquake resistant structures, the community is not safe if it is not prepared for natural disasters. A person may be killed or seriously injured because of the dynamic behavior of furniture or other equipment where as the structure as a whole is earthquake resistant. Preparedness is very essential for safety. It is required at two levels viz., at

5 community level and at individual level. At community level all the people should be aware about natural disasters. For raising awareness, government, scientists, engineers, mass media and inhabitants should play to a major role. At individual level every person should know how to act during the time of disaster. He/she should know about safety aspects. Regular drills must be conducted for the people who will be potential volunteers during the time of disaster. Awareness must be generated at all levels. Whenever the disaster strikes there will be chaos. Authorities involved in emergency services must ensure the following viz., nodal agency, proper medical support and good communication system. Without these, an optimum recovery and reconstruction is not possible. After every disaster, enormous amount of money and resources are spent on rescue and recovery operations and some additional money and resources are spent on reconstruction activity. This cycle is repeating after every disaster. The better way to handle the situation is concentrating on mitigation and preparedness. The more we concentrate on these the less will be magnitude of disaster. Conclusion: Earthquakes are not new to our country. Especially during the past 15 years there were 6 moderate events with a time gap of around 2 to 3 years indicating the lacuna in our understanding the phenomena, shortcomings in our construction practices and the quality of construction. In this paper, it is stressed that the amount and resources spent on pre-disaster stages i.e., mitigation and preparedness will result in enormous reduction in emergency, rescue and recovery operations. A coordinated effort from all the people involved in this is a must to achieve a disaster resistant country. References: 1. IS 1893:2002, Indian Standard criteria for earthquake resistant design of structures, Bureau of Indian Standards, New Delhi. 2. Jain, S.K., Indian earthquakes: an overview, The Indian Concrete Journal, Vol. 72, No. 11, November GOI-UNDP disaster risk management programme, Urban earthquake vulnerability reduction project. 4. Kobe net: Kobe earthquake report 1995.