ANALYSIS OF LANDSLIDE RISKS BASED ON PEAK GROUND ACCELERATION (PGA) VALUES IN PURWOSARI VILLAGE GIRIMULYO KULON PROGO

Abstract

Abstrak Telah dilakukan penelitian tentang risiko tanah longsor berdasarkan nilai peak ground acceleration (PGA) menggunakan data mikrotremor di Desa Purwosari. Penelitian ini bertujuan untuk mengetahui nilai frekuensi predominandan PGA. Selain itu juga untuk mengetahui potensi tanah longsor berdasarkan nilai PGA dan kemiringan lereng di Desa Purwosari. Data mikrotremor diambil di 35 titik pengukuran dengan jarak antar titik 1 km. Data mikrotremor dianalisis menggunakan metode HVSR (Horizontal to Vertical Spectral Ratio) untuk memperoleh nilai frekuensi predominan. Data hasil pengolahan mikrotremor digunakan untuk menghitung nilai PGA menggunakan metode Kanai. Nilai PGA dan kemiringan lereng digunakan untuk membuat peta zonasi rawan tanah longsor di Desa Purwosari. Hasil penelitian menunjukkan bahwa nilai frekuensi predominan di Desa Purwosari berada pada kisaran 0,61 – 18,57 Hz dan nilai PGA berada pada kisaran 32 – 185 cm/s^2. Potensi tanah longsor di Desa Purwosari berdasarkan nilai PGA dan kemiringan lereng terbagi menjadi 3 zona yaitu zona risiko rendah, zona risiko sedang, dan zona risiko tinggi. Berdasarkan kejadian tanah longsor di Desa Purwosari dari tahun 2017 sampai tahun 2018, zona risiko tinggi mempunyai kejadian tanah longsor paling banyak, yaitu 25 kejadian. Kata kunci : Peak Ground Acceleration, mikrotremor, lereng. Abstract Research on landslide risks based on peak ground acceleration (PGA) had been carried out using microtremor data in Purwosari Village. This research aimed to determine the predominant frequency value and PGA. In addition, it also aimed to determine the potential for landslides based on PGA values and slope in Purwosari Village. The microtremor data were taken at 35 measurement points with distance between points of 1 km. Microtremor data were analyzed using HVSR (Horizontal to Vertical Spectral Ratio) method to obtain predominant frequency values. Data from the microtremor analysis is used to calculate the PGA value using Kanai method. The PGA value and slope were used to make landslide-prone zoning maps in Purwosari Village. The results showed that the predominant frequency value in Purwosari Village was in the range of 0.61 – 18.57 Hz and the PGA value was in the range of 32 – 185 cm/s^2. Landslide potential in Purwosari Village based on PGA values and slope were divided into 3 zones, which were low risk zone, medium risk zone, and high risk zone. Based on landslide incident in Purwosari Village from 2017 to 2018, High risk zones have the most landslide incidents with 25 incidents. Keywords : Peak Ground Acceleration, microtremor, slope.