MIKROZONASI PERCEPATAN GETARAN TANAH MAKSIMUM MENGGUNAKAN METODE KANAI (1966) DAN INTENSITAS GEMPABUMI DI KAWASAN JALUR SESAR OPAK MICROZONATION OF PEAK GROUND ACCELERATION USING KANAI (1966) METHOD AND EARTHQUAKE INTENSITY IN OPAK FAULT LINES AREA

Abstract

Abstrak

Penelitian ini bertujuan untuk mengetahui nilai dan mikrozonasi percepatan getaran tanah maksimum (PGA) dan intensitas gempabumi dalam skala Modified Mercalli Intensity (MMI), dan mengetahui mikrozonasi tingkat resiko kerusakan gempa berdasarkan peta kerusakan gempabumi Yogyakarta 27 Mei 2006. Data penelitian ini diambil menggunakan seismometer tipe TDV-23S dan TDL-303S. Data mikrotremor diambil dari 39 titik data primer dengan interval setiap titik 2 km dan 48 titik data sekunder. Data mikrotremor dianalisis menggunakan metode Horizontal to Vertical Spectral Ratio (HVSR) untuk mendapatkan nilai frekuensi predominan dan faktor amplifikasi di setiap titik pengamatan. Nilai frekuensi predominan digunakan untuk mencari nilai periode predominan yang selanjutnya digunakan untuk mencari nilai percepatan getaran tanah maksimum menggunakan metode Kanai (1966). Intensitas gempabumi dicari menggunakan persamaan Wald (1999) dengan input nilai percepatan getaran tanah maksimum. Hasil penelitian menyatakan bahwa nilai percepatan getaran tanah maksimum berkisar antara 39,24 – 485,37 cm/s² dengan intensitas gempabumi berada pada skala V, VI, VII, dan VIII MMI. Mikrozonasi percepatan getaran tanah maksimum dengan nilai tertinggi (titik 2) berada di Kecamatan Imogiri, sedangkan nilai PGA terendah (titik 31) berada di Kecamatan Prambanan. Berdasarkan hasil mikrozonasi tingkat resiko kerusakan gempa, terdapat 3 desa yang termasuk dalam tingkat resiko tinggi kerusakan gempa yaitu Desa Wukirsari dan Desa Karangtengah yang berada di Kecamatan Imogiri, serta Desa Srimulyo yang berada di Kecamatan Piyungan. Untuk tingkat resiko sedang dan rendah menyebar di berbagai desa di kawasan jalur Sesar Opak.

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

Abstract

The aims of this research were to determine the value of peak ground acceleration (PGA) and earthquake intensity in Modified Mercalli Intensity (MMI) scale, and to determine microzonation of the risk level of earthquake damage of Yogyakarta 27 May 2006 earthquake.This research data were taken using TDV-23s and TDL-303S seismometer. The primary data were taken from 39 points with 2 km interval and 48 secondary data points. Microtremor data were analyzed using Horizontal to Vertical Spectral Ratio (HVSR) method to get predominant frequency and amplification factor at each point of observation. The predominant frequency was used to calculate the value of predominant period, then it was used to calculate the value of peak ground acceleration using Kanai method (1966). The earthquake intensity was obtained using Wald method (1999) with peak ground acceleration value as the input.The result showed that the value of peak ground acceleration ranged from 39.24 to 485.37 cm/s² with earthquake intensity was on scale of V, VI, VII, and VIII MMI. The highest value of peak ground acceleration (point 2) was located in Imogiri sub district, while the lowest PGA value (point 31) was located in Prambanan sub district. Based on the results of microzonation of earthquake damage risk level, 3 villages had the high-risk earthquake damage, they were Wukirsari Village and Karangtengah Village which are located in Imogiri sub district, and Srimulyo Village in Piyungan sub district. For the medium and low risk level of earthquake damages spread at various villages in Opak Fault lines area.

Keywords: Microtremor, Horizontal to Vertical Spectral Ratio, PGA, Earthquake Intensity, Opak Fault