Earthquake Disasters and Earthquake Engineering in Japan

Major earthquakes occur somewhere every year with accompanying devastations. For example, the center of the city of Managua was destroyed completely in December 1972 with the loss of more than 15,000 lives. Government buildings also did not escape destruction which brought about a paralysis in Governmental functioning for a short time. In April of the same year, in Iran an earthquake of magnitude 6.9 attacked the town of Ghir causing the loss of 5,000 lives. Large earthquakes accompanied by large losses of life occur frequently in Iran. Another type of earthquake destruction was caused in Peru in 1970 resulting in the loss of more than 50,000 lives under a huge mud slide that accompanied the big earthquake. In 1971, the San Fernando Earthquake, in the U.S.A. caused very heavy damage to the modern reinforced concrete buildings and highway overpasses calling serious attention to the devastation which might be brought about in modern large cities if a destructive earthquake should occur. The figure for lives lost by the San Fernando earthquake was small, assisted by the extremely lucky time of the occurrence of the earthquake at 6 A.M., when daily activity had not yet started. In 1968 an earthquake occurred in the city of Manila, the Philippines, crashing down completely an apartment house burying 260 people under the debris together with the destruction of many large reinforced concrete buildings. In the same year another big earthquake occurred in the northern part of Japan causing very heavy damage to the reinforced concrete buildings, all of which had been designed to resist earthquake force according to the Japanese regulations for antiseismic design. Repeated destruction of reinforced concrete buildings by earthquakes in recent years has caused a questioning of construction engineering. Such heavy destruction as experienced by reinforced concrete buildings in this earthquake (buildings which were designed and constructed under the antiseismic regulations) raised serious discussions among Japanese earthquake engineers which call for urgent studies. In Table 1 is shown a list of earthquakes that have resulted in heavy destruction since 1960. It may be surprising to find that about 20 earthquakes are included in the table showing that an average of three earthquakes of a destructive nature occurs somewhere on earth every two years. According to UNESCO statistics, between 1926 and 1950 over 350,000 people were killed by earthquakes, and the damage to buildings and public works totaled nearly $ 10,000 million. In proportion to the spread of urban civilization throughout the world, the toll taken by these destructive earthquakes has been steadily increasing and will increase more rapidly in the future. The only way to ensure against these substantial economic losses is to design and build, and to strengthen existing buildings, in such a way that the structure will resist the seismic forces to be expected in each area.