PEMETAAN KERENTANAN DAERAH POTENSI LIKUIFAKSI, AKIBAT GEMPABUMI TEKTONIK STUDI KASUS DAERAH DESA PANJANGREJO DAN SEKITARNYA, KECAMATAN PUNDONG, KABUPATEN BANTUL, DAERAH ISTIMEWA YOGYAKARTA

Abstract

Earthquake, is an event that generally occurs in the places where the active
tectonic plates passed. One of the impact caused by earthquake is liquefaction.
Liquefaction is a phenomenon where the soil loss it’s strenght due to the tremor.
Liquefaction occurs in loose sandy soil (not solid) and highly contained by water. The
studies location is located in Panjangrejo village and surrounding, Sub-district Pundong,
Bantul Regency, Special Region of Yogyakarta. The studies is located in South Java
Region, which included in earthquake prone area. In a research location included in the
Young Mount Merapi Volcaniv Deposit Formation (Qmi) which contained by loose
material result by volcanic deposits and Nglanggran Formation (Tmn) which composed
by volcanic breccia. The depth of groundwater on the studies area is relatively shallow.
The purpose of this research is to determine zoning area with potential liquefaction.
This studies using lithology mapping method and groundwater surface mapping by
measuring 41 points of recidence’s well. Another method used is mechanical soil sample
test, undisturbed type in 4 points and calculation method of analytic hierarchy process for
determining the liquefaction prone zone. The result based on mapping method is
geological map, geomorfology map, and groundwater surface map.
Based on the result of data processing and the result of soil test and direct shear
test on undisturbed type of soil sample test, result obtained in the area Klisat (water
content 25.07%, porosity 49.57%, cohession 0.06 kg/cm
2
), Panjang Area (water content
20.82%, porosity 47.67%, cohession 0.04 kg/cm
2
), Nglorong Area (water content
32.35%, porosity 52.54%, cohession 0.13 kg/cm
2
) and Ngentak Area (water content
26.40%, porosity 50.24%, cohession 0.11 kg/cm
2
). The result of measurements of
groundwater surface and soil mechanics test result are used as paremeter factor for
calculation using analytic hierarchy process method for making clasification from those
area based on their class value. From the calculation results, obtained three classes of
potential liquefaction susceptibility zonation, first is a zone of high liquefaction potential,
zone of medium / moderate liquefaction potential, and low – very low liquefaction
potential.