PEMETAAN PERCEPATAN GETARAN TANAH MAKSIMUM DAN INTENSITAS GEMPABUMI DI KAWASAN JALUR SESAR SUNGAI OYO YOGYAKARTA (MICROZONATION OF PEAK GROUND ACCELERATION AND EARTHQUAKE INTENSITY IN OYO RIVER FAULT LINES AREA, YOGYAKARTA)

Abstract

Abstrak

Penelitian ini bertujuan untuk mengetahui nilai dan mikrozonasi dari percepatan getaran tanah maksimum (PGA) dan intensitas gempabumidi kawasan jalur sesar Sungai Oyoakibat gempabumi Yogyakarta 27 Mei 2006. Pengambilan data mikrotremor dilakukan di 25 titik pengamatan yang terletak di Kabupaten Bantul dan Kabupaten Gunungkidul. Data mikrotremor diolah menggunakan metode Horizontal to Vertical Spectral Ratio (HVSR) untuk mendapatkan kurva H/V yang menghasilkan nilai frekuensi predominan (f₀) di setiap titik pengamatan sebagai parameter untuk menghitungPGA menggunakan metode Kanai (1966)danintensitas gempabumi menggunakan metode Wald (1999). Hasil penelitian menyatakan bahwa nilai PGAberkisar antara 84,74 – 363,1 cm/s² dengan intensitas gempabumi berada pada skala VI, VII, dan VIII MMI.Mikrozonasi PGA dengan nilai relatif lebih tinggi berada di formasi Nglanggran (Kecamatan Imogiri bagian timur dan Kecamatan Dlingo bagian barat)dan formasi Sambipitu (Kecamatan Playen bagian barat).Sementara itu, mikrozonasi PGA dengan nilai relatif lebih rendah berada di formasi Wonosari (Kecamatan Panggang bagian Utara dan Kecamatan Playen bagian Barat daya, serta Kecamatan Imogiri bagian Tenggara dan Kecamatan Dlingo bagian Selatan).

Kata kunci:    PGA, Intensitas gempabumi, Mikrotremor, Horizontal to Vertical Spectral Ratio, Sesar Sungai Oyo

Abstract

The aims of this research were to determine and microzonate the peak ground acceleration (PGA) and earthquake intensity in Oyo River Fault Line Area which was caused by May 27th, 2006 Yogyakarta earthquake. The research data were acquired from microtremor signal measurement in 25 observation pointslocated in Bantul Regency and Gunungkidul Regency. Microtremor data were analyzed using Horizontal to Vertical Ratio (HVSR) method to determine predominant frequency for every observation point as parameter to determinePGA using Kanai method (1966) and earthquake intensity using Wald method (1999).The result showed that the value of peak ground acceleration was between 84,74 – 363,1 cm/s²with earthquake intensity of VI, VII and VIII MMI. Higher value of PGA was located in  Nglanggran formation (easternpart of Imogiri sub district and westernpart of Dlingo sub district) and Sambipitu formation (western part of Playen sub district). In addition, microzonation of PGA with lower value located in Wonosari formation (northern part of Panggang sub district and southwestern part of Playen sub district, also southeastern part of Imogiri sub district and southern part of Dlingo subdistrict).

Keywords:     PGA, Earthquake Intensity, Microtremor, Horizontal to Vertical Spectral Ratio, Oyo river fault