PEMODELAN TIGA DIMENSI AREA MANIFESTASI PANASBUMISANGUBANYU BERDASARKAN DATA MIKROTREMOR

Abstract

Tujuan dari penelitian ini adalah untuk menggambarkan model tiga dimensi sebaran nilai kecepatan gelombang P (VP) dan kecepatan gelombang S (VS) serta rasio VP/VS berdasarkan metode Horizontal to Vertical Spectrum Ratio (HVSR) dan kaitannya dengan kemunculan mata air panas di Desa Sangubanyu. Manifestasi panas bumi Sangubanyu terletak di Kecamatan Bawang, Kabupaten Batang, dan Kecamatan Plantungan, Kabupaten Kendal, Provinsi Jawa Tengah. Metode HVSR digunakan dalam pengolahan data mikrotremor yang menghasilkan nilai frekuensi dominan dan faktor amplifikasi kemudian dilakukan inversi pada kurva H/V melalui software Dinver untuk mendapatkan nilai kecepatan gelombang P dan kecepatan gelombang S. Hasil pengolahan data mikrotremor dengan menggunakan metode HVSR diperoleh sebaran nilai frekuensi dominan di area penelitian antara 0,62-0,73 Hz dan nilai faktor amplifikasi 1,09-1,39, hasil inversi pada kurva H/V diperoleh sebaran nilai VPantara 131,76 m/s hingga 2.181,19 m/s, nilai VSantara 76,61 hingga 1.129,42 m/s, dan rasio VP/VS 1,64 – 3,35. Berdasarkan hasil analisis dan interpretasi kecepatan gelombang, kondisi bawah permukaan area manifestasi Sangubanyu tersusun oleh soil atau lapisan tanah penutup dengan nilai VP antara 0 – 350 m/s, ketebalan lapisan 3 – 30 m, weathered layered dengan nilai VP antara 350 – 500 m/s, ketebalan lapisan antara 5 – 80 m, sand and gravel (saturated) dengan nilai VP antara 500 – 1.000 m/s, ketebalan lapisan berkisar 20 – 100 m, dan lapisan paling bawah yaitu sand (saturated) dengn nilai VP antara 1.000 – 2.200 m/s dengan ketebalan antara 75 – 150 m, terdapat sesar normal dengan arah relatif baratlaut – tenggara, blok selatan relatif turun dari blok utara, sesar yang berkembang memicu munculnya mata air panas di area penelitian. Energi panas bumi yang tersedia dapat dimanfaatkan secara langsung sebagai tempat pemandian air panas dan pengeringan produk pertanian. Kata kunci: Manifestasi panas bumi, mikrotremor, HVSR, VP/VS, sangubanyu The aims of this study is to describe the 3D model of the distribution of P wave velocity (VP) and S wave velocity (VS) value and VP/VS ratio based on microtremor Horizontal to Vertical Spectrum Ratio (HVSR) method and its relationship with the appearance of hot spring at Sangubanyu Village. Geothermal manifestations in the Sangubanyu area are located in Bawang sub-district, Batang regency, and Plantungan sub-district, Kendal regency, Central Java province. HVSR method is used to process microtremor data which produces the dominant frequency value and amplification factor then do inversion using Dinver on the H/V curve to get the value of the P wave velocity and S wave velocity. The results of the microtremor HVSR processing obtained the distribution of the dominant frequency values in the study area between 0.62 to 0.73Hz and amplification factor values 1.09 to 1.39, the inversion results on the H/V curve obtained the distribution of VP values between 131.76 m/s to 2,181.19 m/s, VS values between 76.61 to 1,129.42 m/s, VP/VS ratio 1.64 – 3.35. Based on the analysis and interpretation of the wave velocity, the subsurface conditions of the Sangubanyu manifestation area are composed of soil with a VP value between 0 - 350 m/s, thickness of 3 - 30 m, weathered layered with a VP value between 350 - 500 m/s, thickness is between 5 - 80 m, sand and gravel (saturated) with a VP value between 500-1,000 m/s, thickness of the layer ranges from 20 - 100 m, and the lowest layer is sand (saturated) with a VP value between 1,000 - 2,200 m/s with thickness between 75 - 150 m, there were normal faults with relative direction is northwest – southeast, southern blocks relatively downthrown of the northern blocks, that cause the appearrance of hot springs.The available geothermal energy can be used directly as a place for bathing and drying agricultural products. Keywords: Geothermal manifestation, microtremor, HVSR, VP/VS, sangubanyu