This paper presents the development of spectral hazard maps for Sumatra and Java islands, Indonesia and microzonation study for Jakarta city. The purpose of this study is to propose a revision of the seismic hazard map in Indonesian Seismic Code SNI 03-1726-2002. Some improvements in seismic hazard analysis were implemented in the analysis by considering the recent seismic activities around Java and Sumatra. The seismic hazard analysis was carried out using 3-dimension (3-D) seismic source models (fault source model) using the latest research works regarding the tectonic setting of Sumatra and Java. Two hazard levels were analysed for representing 10% and 2% probability of exceedance (PE) in 50 years ground motions for Sumatra and Java. Peak ground acceleration contour maps for those two hazard levels and two additional macrozonation maps for 10% PE in 50 years were produced during this research. These two additional maps represent short period (0.2 s) and long-period (1.0 s) spectra values at the bedrock. Microzonation study is performed in order to obtain ground motion parameters such as acceleration, amplification factor and response spectra at the surface of Jakarta. The analyses were carried out using nonlinear approach. The results were used to develop contour of acceleration at the surface of Jakarta. Finally, the design response spectra for structural design purposes are proposed in this study.
Reconnaissance surveys of building and infrastructure damage related to geotechnical engineering aspects were conducted four to six weeks after the 26 December 2004 earthquake and five weeks after the 28 March 2005 earthquake. These surveys identified many instances of building collapse and infrastructure damage that were probably caused by strong ground shaking and/or liquefaction-induced foundation or embankment failures. The survey results suggest the need for earthquake engineering research that identifies likely future earthquakes and their ground motion characteristics. Because of the observed variation in the level of damage, a seismic microzonation study should be performed to identify the spatial variability of strong ground shaking for the purpose of reconstruction and future planning of cities in Nangroe Aceh Darrusalam Province and Nias Island.
Earthquake ground motions in North Sulawesi on soft soil that have a 90 percent probability of not being exceeded in 50 years are estimated to be 0.63 g (63 percent of the acceleration of gravity) at Palu, 0.31 g at Gorontalo, and 0.27 g at Manado. Estimated ground motions for rock conditions for the same probability level and exposure time are 56 percent of those for soft soil. The hazard estimates are obtained from seismic sources that model the earthquake potential to a depth of 100 km beneath northern and central Sulawesi and include the Palu fault zone of western Sulawesi, the North Sulawesi subduction zone, and the southern most segment of the Sangihe subduction zone beneath the Molucca Sea. An attenuation relation based on Japanese strong-motion data and considered appropriate for subduction environments of the western Pacific was used in determination of ground motions. Field investigations following the 18 April 1990 North Sulawesi earthquake (Ms 7.3) established the Modified Mercalli intensity (MMI) distribution throughout Kodya Gorontalo (the mayorial province of Gorontalo). The total number of masonry houses (permanent and semipermanent dwellings) within the MMI V isoseismal was approximated from housing counts obtained from a sampling of 19 villages. From the post-earthquake damage investigation and from comparisons to masonry construction in the United States, a vulnerability curve was constructed for masonry housing in Gorontalo. Assuming an average value for a house of $1,053, total economic loss to masonry housing from the 18 April 1990 earthquake is estimated to be $1,198,578, a loss equivalent to the destruction of 9.6 percent of the masonry dwelling stock of Gorontalo. Simulation of the earthquake history for the past 31 years within 300 km of Gorontalo indicates an average annual loss to masonry housing of $358,609, or $30 on a per house basis. Catastrophe potential (a worst-case loss) for masonry housing in Gorontalo that has a 90 percent probability of not being exceeded in 250 years is estimated to be $3,083,525, a loss equivalent to the destruction of 25 percent of the masonry dwelling stock of Gorontalo.
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