Geohazard: Effects of the Kobe Earthquake - Coursework Example

Geohazard (Geology Report) In 1995 the Kobe earthquake happened in japan with a magnitude of Mw of 6.9. Compared to other earthquakes it is comparable to the Loma Prieta 1989 and 1994 Northridge earthquakes that had magnitudes of 6.9 and 6.7 respectively. The average depth of rapture of the Kobe earthquake was less than that of California and it reached the surface and came within almost 4km beneath Kobe. Most structures in Kobe were built on soft soil thus was subject to being affected by the earthquake more. Kobe was directly above the fault rapture zone. The earthquake and the subsequent fires in Kobe caused 6,300 deaths, 30,000 injuries, 150,000 buildings destroyed and 300,000 people rendered homeless. The country made a loss of 200 billion dollars. The Kombi earthquake caused extensive damage to bridges and buried lifelines.The lifelines were concentrated near Osaka Bay in an area of soft soils and fill that amplified the earthquake motions. The transportation systems were disrupted by failure of some utility poles and collapse of story buildings that blocked most of the streets. There was a lot of damage on most important systems such as the gas and water systems, and power and communication systems (Anshe 1998). Effects of the earthquake One of the major damages that happened was on the power system. Kansai Electric power company services were serving the people of Kobe. The area which is 1.47 million metered has services of 500kV, 275kV, 154kV, and 77kV transmission and sub transmission lines. The dead tank circuit breaker bushings were damaged. There was a massive failure of equipment anchorage that contributed to bushing damage. The earthquake indicated that if a site is subject to liquefaction the flexible bus should be used with liberal slack. The subsidence of the sites must have contributed to the failure of the bushings connected to vertical conductor drops since there is usually very little slack that is provided to such connections. The disruption of power was highly associated with the damage caused on the distribution system. Spun thin concrete poles were highly damaged by the ground vibrations, subsidence in liquefied soils and by damage when hit by collapsed houses (Dickenson 1995). The communication system in Kobe was also highly destroyed. Operations from the central office got disrupted when the regular power was lost and the emergency power was disrupted due to emergency power system damage. There was loss of service to 285000 lines. Extensive damage was also experienced in the outside plant. The damage caused by the earthquake cost the communication system 3 billion dollars. The water and wastewater system experienced damages that were not even expected. Since the earthquake took place in a highly populated area, the outcomes were fatal. Water outages went on in Kobe city for 60 days after the earthquake. This long duration of water outages was caused more by the destruction of buried water pipes. The buried water pipes were highly damaged due to the strong ground shaking and modest ground settlements over widespread built areas. Before the day of the earthquake some replacement of all asbestos cement pipes with ductile iron pipes had been done. However, the earthquake still caused damage on the ductile iron. The city tried to use buried cisterns for supply of water for fire flows but this too was not effective. There were a lot of fire ignitions, fire spread and a lot of burned structures and deaths due to fire. This was despite that the wind conditions were calm. Fire boats that were operating from Osaka bay were also not effective in fighting the fire which was one kilometer away. There was heavy damage to the wastewater collection pipes. There was sewage spill from the damaged system. The gas system was severely affected by the earthquake due to lack of coordination thus causing the fire hazards that were experienced. In the medium pressure system 96 failures to the steel pipe, 14 at welded joints, 22 atfledgejoint and 60 at mechanical joints. The railway system was also damaged. The damage was inclusive of derailment of the trains running in the area. There was failure on a large number of viaduct columns. A lot of bridge damage was caused by loading from the embankment behind the abutments. There was failure on a large number of concrete pole catenary supports. The track damage was caused by ground displacements and a lot of damage occurred to buildings in the station. The Kobe earthquake damaged the highways as well. 60% of all the bridges had some damage. Many people lost their lives because the fire fighters could not be able to access areas of damage. The fire would have been put off but the firefighters could not find their way through the blocked highways and broken bridges. The airport was also highly affected by the earthquake. The administration building was damaged, and there was loss of elevators temporarily. The following is a picture of some of the effects of the Kobe earthquake. Geology issues associated with the earthquake The earthquake occurred some short distance from the plate margin and therefore it can be considered as an intraplate event. The coseimic crustal rapture associated with this earthquake got initiated on the Nojima fault that is located on AwanjiIsland. This rapture then extended to the ground surface on a 9 km segment of the Awaji Island. There were maximum surface displacements of 1.7 m right-lateral, horizontal and 1.0 m vertical that were observed. Aftershocks during the first two days suggest there was a rupture surface that extended between 35 km and 50km. the seismicity pattern with mapped surface faults suggest that the rapture zone extended about 46km from about 19km southwest of the epicenter to around 27km northwest of the epicenter. The shallowest seismicity occurred beneath the Awaji Island and downtown of Kobe city (Huzita 1983). There were three suggested sub events and were inferred to have a moment magnitude of 6.8, 6.3, and 6.4. The third sub event is suggested to be located beneath Kobe city near the region of shallow seismicity. Rapture for the first sub event was bilateral, and it proceeded unilaterally with the other two subsequent events in a northeasterly direction below Kobe city. The rapture duration was 11 seconds with an average depth inferred at 8km. the hypocenter depth was 14.3 km (Huzita 1995). Earthquakes in japan are as a result of subduction of the pacific plate. This is mainly in the coastal regions and northern parts of japan. The Kobe earthquake is said to have occurred along active faults. There were strong motion recordings that were obtained using instruments installed. Some agencies reported maximum value of three orthogonal components the strong motion data that was recorded from the Kobe earthquake provided an exceptional set of near source measurements of strong shaking. The mapped locations of the stations show that there 20 measurements within 20km of the surface projection of the inferred rapture surface. Around 60% of the three component measurements are on soft soil deposits of Holocene age. Peak ground shaking was near 0.5 g and in some sites it exceeded 0.8 g. the recordings taken suggested a well-defined velocity pulse of 1 second period. They indicate that the peak amplitude of the ground velocity decreased rapidly within the first few kilometers of the projected surface rapture. The duration of shaking extended from 11-15 seconds for a site near the Pleistocene deposits and more than 60 seconds on sites within Holocene soil deposits (Huzita 1983). The ground motions that were recorded at the Kobe ocean meteorological station indicated peak acceleration amplitude of 818 gal. The severity of ground shaking on the artificial fill was recorded at two locations where one had no liquefaction and one had liquefaction. The following is a picture showing the plates of Kobe. Lessons learnt From the Kobe earthquake the citizens and government of japan and the rest of the world had lessons to learn. One of the lessons learnt is the importance of carrying out strategic research to compare the preparedness and response strategies that have been put in place in case of hazards. Through this research then it is easy to tell how prepared a country is to deal with a disaster at all times. The countries that are threatened by occurrence of earthquakes need to have enough money set aside in case of such hazards to help in reconstruction and rebuilding after earthquakes occur. Through this way then the country or city is able to get back to its normal activities easily without a lot of borrowing and making huge losses. People also need to learn from experience and use it to take preventive measures. In Japan this was not the first earthquake experienced but still they were not able to reduce damage during the Kobe earthquake (Kikuchi 1996). There is need for a long term disaster management approach to be set in every country and city so that incase of disasters they will be able to deal with it easily. A major lesson on the importance of having good infrastructure was learnt as well. If the buildings had been constructed using the engineering codes that help buildings withstand earthquakes then the damage caused would have been less. Another major lesson learnt is that ignorance is very costly. Japan had always been proud to be well prepared for earthquakes however, the Kobe earthquake proved them wrong. If the responsible people had not just ignored they were ready then they would have been able to save many lives and buildings. The government received a lot of criticizing for being slow to rescue people and for refusing help from other nations. Therefore the government needs to learn from this and act differently when such a disaster occurs. Reduction of damage Earthquakes are naturally occurring and cannot be prevented. However, the damage that accompanies them can be reduced through various ways. These ways include good communication strategies, good structural design, very well planned emergency preparedness, education for all and using safe building standards. To be able to respond to tragic loss of life and the cost incurred in rebuilding after earthquakes, countries should establish safety and regulatory agencies. The agencies need codes for engineers to use for the sake of regulation of development and construction. The buildings that are constructed according to these codes can survive earthquakes better and ensure the risk associated with earthquakes is reduced. Engineers are able to minimize earthquake damage to the buildings through using flexible, reinforced materials that have the ability to withstand shaking in buildings. There are a lot of improvements that engineers and geologists have come up with to withstand earthquakes. They have made improved earthquake resistant designs for buildings which are compatible with the modern architecture and building materials. They use the computer models in order to predict responses of a building to ground shaking patterns and then use those patterns to compare with real seismic events. In addition they also analyze these computer models of the motions of buildings in the most affected earthquake areas to be able to make predictions the possible damages and suggest the reinforcement that is needed. If these precautions had been taken before the Kobe earthquake took place then the damage that occurred would have been less than the one that was experienced (Werner 1996). The geologists and engineers would have used risk assessment maps like the geologic hazard and seismic hazard zoning maps to be able to understand where the faults are actually located and how to build near them safely. They can use these maps to predict the average ground motions in an area and the predicted motions can be applied during engineering design phases of construction projects. The engineers would have used the risk assessment maps to avoid building on the major faults or at least make sure that buildings constructed in these areas have proper earthquake bracing. In a city like Kobe where the buildings were made of non-reinforced brick, stone, and concrete blocks the seismic risk is great. This is because such buildings cannot resist the strong horizontal forces that are as a result of seismic waves. Therefore engineers could help in curbing such instances through making sure that buildings are constructed under modern construction codes. In addition making sure that people are educated and prepared on earthquakes would help in reducing deaths and injuries that are caused by earthquakes. People can be advised to take preventive measures in their homes and places of work. They can be taught on the importance of having an earthquake survival kit at home and in the office. People need to know the importance of protecting themselves from falling objects when they are indoors and the earthquake occurs. The damages would be reduced by predicting of earthquakes where seismologists predict when an earthquake is likely to occur and its estimated size. When earthquakes are predicted people are prepared to face them and they are able to take precautionary measures (Werner 1996). Conclusion Earthquakes are natural hazards and cannot be stopped. The Kobe earthquake occurred in 1995 in Kobe city which is the second most populated area in Japan. The earthquake caused a lot of damage and loss of life. Many systems were damaged and it cost the government a lot of money to reconstruct them. The geology of the earthquake shows that the earthquake was a major one and a lot of earth shaking was experienced. The seismic shockwaves travelled from Awaji Island along the Nojima fault. From the experience of the earthquake there was a lot to learn. Even though earthquakes cannot be prevented the damage they cause can be reduced by engineers and geologists. Bibliography Anshel, J, 1998. Hyogoken-Nanbu (Kobe) earthquake of January 17, 1995 : lifeline performance. Reston, Va. : American Soc. of Civil Engineers . Dickenson, S, 1995. Kobe Post Earthquake Reconnaissance of Port Facilities. Gathersburg: NIST. Huzita, K, 1983. Geological Survey of Japan. Huzita, K, 1995. Geology of Kobe District. Japan: YCU. Kikuchi, M, 1996. The Mechanism of the Kobe Earthquake of January 1995. Japan: YCU. Werner, D, 1996. Kobe Earthquake; Performance of Structures, Lifelines, and Fire Protection Systems. Gathersburg: NIST. Read More