ANALISIS MIKROTREMOR UNTUK MIKROZONASI INDEKS KERENTANAN SEISMIK DI KAWASAN JALUR SESAR SUNGAI OYO YOGYAKARTA MICROTREMOR ANALYSIS FOR SEISMIC VULNERABILITY INDEX MICROZONATION AROUND OYO RIVER FAULT YOGYAKARTA

Abstract

Abstrak

Penelitian ini bertujuan untuk mengetahui nilai dan mikrozonasi indeks kerentanan seismik (K_g) di kawasan jalur Sesar Sungai Oyo. Data penelitian diperoleh melalui pengukuran sinyal mikrotremor di 25 titik lokasi dengan spasi 2 km. Data mikrotremor dianalisis menggunakan metode Horizontal to Vertical Spectral Ratio (HVSR) untuk mendapatkan frekuensi predominan dan faktor amplifikasi di setiap titik penelitian. Hasil dari analisis mikrotremor digunakan untuk menentukan nilai indeks kerentanan seismik (K_g), sehingga diketahui bahwa nilai indeks kerentanan seismik (K_g) berkisar 0,1x10^-6sampai 18,1x10^-6 s²/cm. Mikrozonasi indeks kerentanan seismik dengan nilai tinggi berada pada formasi Wonosari yang menyebar di Kecamatan Panggang bagian Barat Laut, Kecamatan Playen bagian Barat Daya, dan Kecamatan Dlingo bagian Selatan. Sedangkan mikrozonasi indeks kerentanan seismik dengan nilai rendah berada pada formasi Nglanggran dan formasi Sambipitu yang menyebar di Kecamatan Playen bagian Barat, Kecamatan Imogiri bagian Timur dan Kecamatan Dlingo bagian Barat.

Kata kunci:     Indeks kerentanan seismik, mikrotremor, Horizontal to Vertical Spectral Ratio

Abstract

The aims of this research was to determine the value and microzonation of seismic vulnerability index (K_g) around Oyo River fault. Data were obtained by microtremor measurement at 25 location with 2 km spacing. The microtremor data were analyzed using Horizontal to Vertical Spectral Ratio (HVSR) method to obtain the predominant frequency and amplification factor at each measurement point to determine the value of seismic vulnerability index (K_g). The results showed that the seismic vulnerability index (K_g) was around 0,1x10^-6 to 18,1x10^-6 s²/cm. Based on microzonation results, the highest seismic vulnerability index was on Wonosari formation that spread across the Northwestern part of Panggang sub district, the Southwestern part of Playen sub district, and the Southern part of Dlingo sub district. Meanwhile, the low seismic vulnerability index was on Nglanggran formation and Sambipitu formation that spread across the Western part of Playen sub district, the Eastern part of Imogiri sub district, and some locations in the Western part of Dlingo sub district.

Keywords:     seismic vulnerability index, microtremor, Horizontal to Vertical Spectral Ratio