The Bengkulu, Southern Sumatra, Earthquake of 4 June 2000 (Mw = 7.7): Another Warning to Remote Metropolitan Areas

Abstract

It has been recognized that urban areas located rather distantly from earthquake sources may, under some special circumstances, be affected by the earthquake tremors. A well known example is the 1985 Michoacan earthquake, in which a large earthquake ( Ms = 8.1) along the coast of Mexico caused destruction and loss of life in Mexico City, 350 km away from the epicenter. Much of the destruction was due to significant amplification of the earthquake ground motions by thick sedimentary deposits in the down-town area of the city (Seed et al., 1987). This might be a peculiar case, but obviously soft-soil amplification effects are, to some extent, present in many places. The Malay Peninsula and Singapore are located in a low-seismicity region, where the closest known earthquake sources, the Sumatra Fault and the Sumatra subduction zone, are located more than 350 km away. Earthquakes have never posed any real problems in the region. The two greatest earthquakes on the subduction zone, Mw = 8.8 in 1833 and Mw = 8.4 in 1861 (Newcomb and McCann, 1987), occurred during a time when there were practically no high-rise structures. Although they were reportedly felt in Singapore (Pan and Sun, 1996), these earthquakes did not cause any damage. In line with the rapid regional economic development in recent decades, many high-rise buildings and complex infrastructures have been constructed, some of which are on soft soils or reclaimed land. Long-period structures, such as tall buildings, are known to be more susceptible to distant earthquakes than shorter-period structures. Consequently, the number of felt earthquake tremors in the high-rise buildings of Singapore has been increasing in recent years (Pan, 1997). In February 1994, some buildings in the densely populated areas of Singapore responded to an earthquake of Ms = 7.0 that occurred near …