ANALYSIS OF MASS MOVEMENT AREA FROM MICROTREMOR MEASUREMENT IN NGROTO HAMLET PURWOSARI VILLAGE GIRIMULYO SUBDISTRICT KULONPROGO REGENCY

Abstract

Abstrak Penelitian ini bertujuan untuk mengetahui karakteristik sinyal dan parameter mikrotremor yang berkorelasi dengan gerakan tanah. Penelitian ini menggunakan 33 data mikrotremor dengan jarak antar titik sejauh 85 m. Sinyal mikrotremor dianalisis menggunakan metode HVSR sehingga diperoleh data berupa frekuensi predominan dan faktor amplifikasi dalam bentuk kurva H/V. Data tersebut menjadi input pada metode ellipticity curve untuk mendapatkan nilai kecepatan gelombang geser (Vs). Berdasarkan hasil penelitian diperoleh nilai frekuensi predominan (fo) berkisar antara 1,9−9,9 Hz, nilai faktor amplifikasi (Ao) berkisar antara 2,8−9,6, dan nilai indeks kerentanan seismik berkisar antara 1−18 s2/m. Mikrozonasi frekuensi predominan, faktor amplifikasi, dan indeks kerentanan seismik menunjukkan pola bidang rekahan dengan peningkatan nilai faktor amplifikasi di sekitar jalur rekahan. Pola bidang rekahan menunjukkan nilai Ao = 9,36 dengan ketebalan sedimen 8,8 meter. Kata kunci: gerakan tanah, tanah longsor, indeks kerentanan seismik, ellipticity curve. Abstract It aimed to find out the characteristics of the signal and the microtremor parameter that correlates to mass movement.This research used 33 microtremor data with distance between points of 85 m. Microtremor signal was analyzed using HVSR method to get predominant frequency and amplification factors in the form of H/V curve. The data was being the input of the ellipticity curve method to get the value of shear wave velocity (Vs). Based on the research results obtained, predominant frequency (fo) ranged between 1.9 – 9.9 Hz, value of amplification factor (Ao) ranged between 2.8 – 9.6, and seismic vulnerability index value ranged from 1 − 18 s2/m. Microzonation of the predominant frequency, amplification factors, and seismic vulnerability index shows a pattern of fracture plane with increasing value of amplification factor around the path of the fracture. The pattern on the plane shows value of Ao = 9.36 with sediment thickness of 8.8 meters. Keywords: landslide, ground motions, seismic vulnerability index, ellipticity curve.