ANALISIS GSS (GROUND SHEAR STRAIN) DENGAN METODE HVSR MENGGUNAKAN DATA MIKROSEISMIK PADA JALUR SESAROPAK ANALYSIS OF GSS (GROUND SHEAR STRAIN) USING HVSR METHOD FROM MICROSEISMIC DATA ON OPAK FAULTLINES
Abstract
Abstrak
Telah dilakukan penelitian tentang GSS (Ground Shear Strain) dengan metode HVSR (Horizontal to Vertical Spectral Ratio) menggunakan data mikroseismik pada jalur Sesar Opak. Penelitian bertujuan untuk mengetahui nilai GSS sepanjang jalur Sesar Opak dan memprediksi fenomena berdasarkan nilai GSS di sepanjang jalur Sesar Opak. Data mikrotremor diambil di 39 titik pengamatan sebagai data primer dengan jarak antar titik 2 km dan penambahan data sekunder sebanyak 46 titik yang berasal dari peneliti sebelumnya dan BMKG. Data mikrotremor dianalisis menggunakan metode HVSR untuk memperoleh nilai faktor amplifikasi dan nilai frekuensi predominan. Data hasil pengolahan mikrotremor digunakan untuk menghitung nilai indeks kerentanan seismik dan nilai percepatan tanah maksimum (PGA). Nilai percepatan tanah maksimum ditentukan dengan metode Kanai, dengan parameter data gempabumi 27 Mei 2006. Nilai indeks kerentan seismik dan nilai percepatan tanah maksimum digunakan untuk menentukan nilai GSS. Hasil penelitian ini menunjukkan bahwa nilai GSS di sepanjang jalur Sesar Opak berkisar 3,9 ×10-5 sampai dengan 5,3 × 10-3. Daerah yang memiliki GSS tertinggi berada di daerah Sanden dan terendah di daerah Piyungan. Fenomena yang mungkin terjadi yaitu getaran, keretakan tanah dan penurunan tanah.
Kata kunci: Ground Shear Strain, Horizontal to Vertical Spectral Ratio, mikrotremor
Abstract
The research about GSS (Ground Shear Strain) using Horizontal to Vertical Spectral Ratio (HVSR) method from microseismic data on Opak fault lines had been finished. The research aimed to determine GSS value along Opak fault lines and to predict phenomena based on GSS value along Opak fault lines. The microtremor data was taken on 39 observation points with 2 km spacing as primary data and 46 points added as secondary data from previous research and BMKG. Microtremor data was analysed using HVSR method to get amplification factor and predominant frequency. The data from microtremor signal were used to determine the seismic vulnerability index and peak ground acceleration (PGA). Peak ground acceleration value was determined using Kanai method, with parameter data taken from 27 Mei 2006 earthquake source. Seismic vulnerability index value and peak ground acceleration value were used to determine GSS value. The result of this research showed that GSS value along Opak fault lines was about 3,9 x 10-5 to 5,3 x 10-3. Area that has highest GSS was in Sanden area and the lowest one was in Piyungan area. The phenomena that can happen were vibration, cracked ground and land subsidence.
Keywords : Ground Shear Strain, Horizontal to Vertical Spectral Ratio, microtremor
Telah dilakukan penelitian tentang GSS (Ground Shear Strain) dengan metode HVSR (Horizontal to Vertical Spectral Ratio) menggunakan data mikroseismik pada jalur Sesar Opak. Penelitian bertujuan untuk mengetahui nilai GSS sepanjang jalur Sesar Opak dan memprediksi fenomena berdasarkan nilai GSS di sepanjang jalur Sesar Opak. Data mikrotremor diambil di 39 titik pengamatan sebagai data primer dengan jarak antar titik 2 km dan penambahan data sekunder sebanyak 46 titik yang berasal dari peneliti sebelumnya dan BMKG. Data mikrotremor dianalisis menggunakan metode HVSR untuk memperoleh nilai faktor amplifikasi dan nilai frekuensi predominan. Data hasil pengolahan mikrotremor digunakan untuk menghitung nilai indeks kerentanan seismik dan nilai percepatan tanah maksimum (PGA). Nilai percepatan tanah maksimum ditentukan dengan metode Kanai, dengan parameter data gempabumi 27 Mei 2006. Nilai indeks kerentan seismik dan nilai percepatan tanah maksimum digunakan untuk menentukan nilai GSS. Hasil penelitian ini menunjukkan bahwa nilai GSS di sepanjang jalur Sesar Opak berkisar 3,9 ×10-5 sampai dengan 5,3 × 10-3. Daerah yang memiliki GSS tertinggi berada di daerah Sanden dan terendah di daerah Piyungan. Fenomena yang mungkin terjadi yaitu getaran, keretakan tanah dan penurunan tanah.
Kata kunci: Ground Shear Strain, Horizontal to Vertical Spectral Ratio, mikrotremor
Abstract
The research about GSS (Ground Shear Strain) using Horizontal to Vertical Spectral Ratio (HVSR) method from microseismic data on Opak fault lines had been finished. The research aimed to determine GSS value along Opak fault lines and to predict phenomena based on GSS value along Opak fault lines. The microtremor data was taken on 39 observation points with 2 km spacing as primary data and 46 points added as secondary data from previous research and BMKG. Microtremor data was analysed using HVSR method to get amplification factor and predominant frequency. The data from microtremor signal were used to determine the seismic vulnerability index and peak ground acceleration (PGA). Peak ground acceleration value was determined using Kanai method, with parameter data taken from 27 Mei 2006 earthquake source. Seismic vulnerability index value and peak ground acceleration value were used to determine GSS value. The result of this research showed that GSS value along Opak fault lines was about 3,9 x 10-5 to 5,3 x 10-3. Area that has highest GSS was in Sanden area and the lowest one was in Piyungan area. The phenomena that can happen were vibration, cracked ground and land subsidence.
Keywords : Ground Shear Strain, Horizontal to Vertical Spectral Ratio, microtremor
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