IDENTIFIKASI DAERAH RAWAN LONGSOR DENGAN METODE MIKROTREMOR DI KECAMATAN BAGELEN KABUPATEN PURWOREJO

Abstract

Abstrak Penelitian ini bertujuan untuk mengidentifikasi karakteristik frekuensi predominan (𝑓0), faktor amplifikasi (𝐴), ketebalan lapisan sedimen (𝐻) dan indeks kerentanan seismik (𝐾𝑔) di daerah rawan longsor di Kecamatan Bagelen, Kabupaten Purworejo menggunakan metode mikrotremor. Penelitian dilakukan pada 32 titik penelitian dengan spasi 1 Km. Data berupa sinyal mikrotremor yang kemudian diolah dengan metode HVSR untuk memperoleh kurva H/V dan metode ellipticity curve untuk memperoleh ground profiles. Hasil penelitian menunjukkan bahwa nilai 𝑓0 berkisar antara 0,77 – 17,43 Hz, nilai 𝐴 berkisar antara 1,01 – 15,50, nilai 𝐻 berkisar antara 3,09 – 100 m dan nilai 𝐾𝑔 berkisar antara 6,27×10-5 – 1,59×10-3 s2/m. Daerah longsor Kecamatan Bagelen berada pada daerah yang didominasi batuan keras breksi-andesit, batuan lempung dan batuan pasir. Daerah dengan kemiringan curam serta berada pada topografi tinggi menyebabkan proses pelapukan terjadi lebih cepat dan mempermudah material lapuk untuk terlongsorkan. Kata kunci: tanah longsor, mikrotremor, Kecamatan Bagelen Abstract The research aimed to identify the characteristics of predominant frequency (𝑓0), amplification factor (𝐴), sediment layer thickness (𝐻), and seismic vulnerability index (𝐾𝑔) of landslide area in Bagelen District, Purworejo Regency using microtremor method. The research was done at 32 research points with 1 Km spacing. Data in the form of microtremor signals were then processed by HVSR method to obtain the H/V curve and then ellipticity curve method to obtain the ground profiles. The results of the research showed that the value of 𝑓0 in Bagelen district ranged from 0.77 to 17.43 Hz, the value of 𝐴 ranged from 1.01 to 15.50, the value of 𝐻 ranged from 3.09 to 100 m and the value of 𝐾𝑔 ranged from 6.27×10-5 to 1.59×10-3 s2/m. The landslide area of Bagelen district were in areas dominated by breccia-andesite hard rock, clay rock and sandstone. Areas with a steep slope and on a high topography caused the weathering process occurred more quickly and then the weathered material were easier to cause a landslide. Keywords: landslide, microtremor, Bagelen District