In response to the last May 27, 2006 of Bantul Earthquake with the magnitude of 5.9 Richter Scale, more
than 5000 people died and about hundred thousands of houses in Bantul, Sleman and Gunung Kidul
Regencies were damaged or collapced. To support the recovery and reconstruction of those damaged
areas it is urgent to provide a microzonation map which can estimate the zonation of earthquake
vulnerability at various level of risk.
Interpretation on the aerial photographs and satelite images, reviews on previous geological study at
Yogyakarta Basin and the surrounding areas, and site investigations by drilling, well logging,
geophysical surveys (georadar, magneto tuleric and resistivity surveys) as well as micro tremor survey
have been conducting to establish the microzonation map, especially at the area surrounding Opak – Oya
rivers.
Some preliminary results of this investigation confirm that distribution of faults, as well as the
characteristics and thickness of overburden sediments above the bedrock dictate the severity of
construction damages. Accordingly, the relative distance of any particular zone to the fault zone (i.e.
exposed and burried faults), the types and thickness of loose sediments above the bedrock of andesitic
breccia, and the wave amplification patterns of each type of the sediments are selected as the main
variables to be analysed for the establishment of the earthquake microzonation map. In addition, some
soil mechanic analyses will also be conducted to support the enhancement of Building Code in the
earthquake vulnerable area.
By D. Karnawati1 , S. Pramumijoyo1, S. Hussein1, A.Ratdomopurbo2, K. Watanabe3 and R.
Anderson4
1 Geological Engineering Department, Gadjah Mada University, Yogyakarta, Indonesia
2 BPPTK, Vocanic Survey of Indonesia
3 Earth Resouces Engineering Department, Kyushu University, Japan.
4 California Seismic Safety Commission, USA
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