A paper entitled: 2-D FAULTS AND LIQUEFACTION POTENTIAL MAPPING OF SOIL DEPOSIT LAYERS IN YOGYAKARTA, INDONESIA, written by authors: Sri Atmaja P. Rosyidi , Mohd. Raihan Taha , Surya Budi Lesmana was presented in the International Technical Conference 2010 at Seoul, Republic of Korea, 19-21 October 2010 (http://www.itc2010.co.kr/). The paper describes the capability of integrated geophysical surveys for developing the 2-D map of liquefaction potential and faults/discontinuity in “deep” soil deposit layers. Some earthquake scenarios were implemented to determine the change of liquefaction due to ground shaking. This paper shows the contribution of geophysical surveys for the purpose of geohazards analysis. The discussion during session was quite interesting. The questions from the floor related to the need of updated building code, the shallow foundation for liquefaction sites, the capability of geophysical survey for soil dynamics and lesson learned from current earthquakes in Indonesia.
ABSTRACT : The earthquake of Yogyakarta on May 27, 2006 caused widespread destruction to the heavily populated and relatively prosperous region. Ground surface cracks, soil displacement, landslides and liquefactions were the ground failure events mostly observed. This paper presents the capability of integrated geophysical surveys, i.e., georesisitivity and surface wave method, to investigate underground faults and liquefaction potential in 2-D cross section. These surveys were conducted in selected area in Universitas Muhammadiyah Yogyakarta (UMY)‘s campus in Yogyakarta, Indonesia which consists of deep loose sand and sandy soil deposit. Minor to moderate building damage were found close to the fault, local liquefaction and soil boiling. From the 2-D cross section from georesistivity survey, the discontinuity and faults of sandy soil layers and sand deposits in fault locations were clearly found in the subsurface depth varied from 6 to 30 m. Local liquefactions were found in several sites at UMY campus caused by 6.3 MW earthquake closed to the fault lines in which water table was found at relatively shallow. The 2-D liquefaction potential map was generated from shear wave velocity profile and soil data in observed locations based on several earthquake scenarios, from 6.3, 7 and 8 MW. When the earthquake was simulated to be stronger at 7.5 and 8 MW, the 2-D analysis map shows that the liquefaction widely occurs distributed in observed sandy soil and sand deposit layer. Finally, the integrated georesistivity and surface wave method is becoming an effective tool for developing the 2-D faults and liquefaction potential map in the site investigation program, particularly for the purpose of geohazards analysis.
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