Kobe Earthquake Essays - Seismology, Great Hanshin Earthquake

Kobe Earthquake An earthquake is defined as a shaking or trembling of the earth that is volcanic or tectonic in origin. In the case of the Great Hyogo (Hanshin) earthquake of Kobe, Japan it is tectonic in origin. This devastating earthquake which occurred on the 17th of January at 5:46 a.m measured at a whopping 7 (7.2) on the Richter scale. This was the largest recorded earthquake to ever hit Japan. According to the Japan Meteorological its epicentre was in 34.6? north and 135.0? east in the northern tip of Awaji Island with a focal depth of 14 km. According to the results of the recorded in 24 observation centre, the fracture which triggered the earthquake was happened inside the Nojima Fault. Also investigation in the sea bed by the Ocean observatory Centre shows that the cracks occurred in Nojima Fault. This fault forms a part of a group of faults known as the "Rokko Fault', which extends from Awaji Island through Kobe City to the foot of Mount Rokko. The movement of the fault can be explained by the Tectonic characteristic of west Japan. The main reason for the big earthquakes in west part of Japan are the tectonic activities of the Eurasian, the Pacific, the North America and the Philippine plates. The collision between these plates in the central part of Honshu (Japan main island) is the main source of strain accumulation in the crust of western part of Japan. Casualty figures quickly mounted by the hour and when it was all said and done 5,472 people had lost their lives and 415,000 people were left injured. By the fourth day after the earthquake about 310,000 residents spent the night at 1,077 refugee centres. More than 350 fires broke out wiping out around 100 hectares of densely populated area. Fire fighting was virtually ineffective due to an inadequate water supply and access to fires. Lifeline facilities were severely damaged over a large area and following the earthquake, 900,000 households were left without electricity, 850,000 households were without gas, and water supply cuts affected about 2.5 million people. Nippon Telegraph and Telephone (NTT) Corp.'s 160,000 lines out of 800,000 lines were out of order. The damage to major infrastructure, especially to the elevated expressway and shinkansen (bullet train) tracks, shocked engineers, planners and the general public. According to news reports its tracks were damaged at 42 locations. The first Shinkansen train was to run 30 minutes after the time of the earthquake. Had the disaster occurred few hours later, with an average capacity of about 1,600 passengers/train, casualty rate could have been much higher. Sections of elevated Hanshin expressway toppled virtually cutting off major transport lines to the affected areas. A contiguous section supported by eighteen single columns had fallen sideways in Higashi Nada-ku. Modern buildings -- and structures retrofitted with up-to-date engineering techniques -- fared well in the Great Hyogo quake. Much of the damage occurred in traditionally built older homes and in areas near the coast where liquefaction of the soil caused instability in structures. A large number of reinforced concrete structu res were completely devastated. The economic damage estimates vary from around 100 - 150 billion dollars US. The most extensively and severely damaged structures were smaller commercial buildings (often with residences upstairs) constructed with limited engineering design and traditional homes. The smaller commercial and mixed occupancy buildings are typically framed with wood or light steel and have walls of stucco over wood slats. Many of these buildings have a large shop window in the front and lack interior walls, factors which weaken the first floor. Traditional homes, typically those built before the 1970s, have heavy tile roofs with tiles set in a thick clay and mud mortar, few partitions, and are not waterproofed which causes widespread dry rot and water damage. Little nailing is used; wood joinery is more common. Many casualties were found in damaged and collapsed traditional homes. The heavy tile roofs stressed the walls, which cracked, crumbled and often collapsed, triggering fires from broken gas pipes. The Kobe earthquake exposed more modern and engineered buildings to stronger forces than any previous earthquake. The preliminary report indicates more studies are needed to evaluate seismic codes, design practice and construction