MIKROZONASI INDEKS KERENTANAN SEISMIK BERDASARKAN ANALISIS MIKROTREMOR DI KECAMATAN ARJOSARI PACITAN JAWA TIMUR MICROZONATION OF SEISMIC VULNERABILITY INDEX BASED ON MICROTREMOR ANALYSIS IN ARJOSARI SUBDISTRICT PACITAN EAST JAVA

Abstract

Abstrak
Penelitian ini bertujuan untuk mengetahui karakteristik mikrotremor, nilai indeks kerentanan seismik, dan mikrozonasi indeks kerentanan seismik di Kecamatan Arjosari. Data mikrotremor dianalisis menggunakan Fast Fourier Transform (FFT) radix-64, penghalusan data dengan Konno-Ohmachi dan Horizontal to Vertical Spectral Ratio (HVSR). Hasil studi ini menunjukkan bahwa karakteristik mikrotremor di Kecamatan Arjosari dengan frekuensi predominan antara 1,76-14,88 Hz, faktor amplifikasi antara 0,224-11,73, nilai ketebalan lapisan sedimen antara 9,94-103 m, nilai kecepatan gelombang geser permukaan tanah sampai kedalaman 30 m antara 353,174-760 m/s, dan nilai kecepatan geser batuan dasar antara 170,544-7124,474 m/s. Nilai indeks kerentanan seismik di Kecamatan Arjosari adalah 1,291 10-7 sampai 1,008 10-5 (s2/cm). Mikrozonasi indeks kerentanan seismik dengan nilai tinggi menyebar di Desa Mangunharjo, Desa Jatimalang, Desa Sedayu dan Desa Borang sedangkan nilai rendah menyebar di Desa Mlati, Desa Temon, Desa Karangrejo, Desa
Kata Kunci : Indeks Kerentanan Seismik, Horizontal to Vertical Spectral Ratio, Mikrotremor, Arjosari.
Abstract
The aims of this study are to know the microtremor characteristic, the seismic vulnerability index, and its mikrozonation in Arjosari Subdistrict. The microtremor data were analyzed using Fast Fourier Transform (FFT) radix-64, then they smoothed by using Konno-Ohmachi Equation, and Horizontal to Vertical Spectral Ratio (HVSR). The result shows that the microtremor characteristic in Arjosari Subdistrict with predominant frequency between 1.76-14.88 Hz, the amplification factor between 0.224-11.73, the sediment thickness between 9.94-103.261 m, the surface shear velocity ( ) between 353.174-760 m/s, and bedrock shear velocity between 170.544-7124.474 m/s. The vulnerability index in Arjosari Subdistrict between 1.291 10-7 to 1.008 10-5 (s2/cm). High seismic vulnerability index microzonation spread in Mangunharjo, Jatimalang, Sedayu and Borang village. The low value spread in Mlati, Temon, Karangrejo, Kedungbendo, Gembong, Gayuhan, Gegeran, Gunungsari, and Pagutan Village.
Key Words : Seismic Vulnerability Index, Horizontal to Vertical Spectral Ratio, Microtremor, Arjosari.