Pilot Studies of Seismic Hazard and Risk in North Sulawesi Province, Indonesia

Abstract

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.

Recent faulting along Gorontalo fault based on seismicity data analysis and lineament mapping

“…The fault accommodates the different velocity between the east and west block of Minahasa Peninsula which is estimated to be around 11 mm/year based on geodetic modelling [6]. However, there were no major earthquakes recorded along Gorontalo Fault [7] in historical record as well as during a temporary seismic network campaign in 1990 [6].…”

Penerapan Teorema Probabilitas Total dalam Analisis Resiko Gempa

“…Hasil analisis resiko gempa dengan menggunakan bantuan program Ez-Frisk dengan memasukkan faktor logic tree dapat dilihat pada Gambar 14. [18][19][20][21][22]. Perioda ulang yang ditinjau adalah 500 tahun.…”