Pemodelan Kondisi Geologi Bawah Permukaan Di Kawasan Karst Pacitan Bagian Barat Menggunakan Metode Gaya Berat

Daerah Kabupaten Pacitan bagian barat memiliki bentang alam dominan berupa karst. Penelitian ditujukan untuk mengetahui kondisi bawah permukaan kawasan karst meliputi ketebalan batuan sedimen dan struktur di daerah penelitian. Salah satu metode geofisika yang dapat digunakan adalah metode gaya berat. Metode gaya berat memanfaatkan variasi medan gravitasi untuk mendapatkan gambaran ketebalan litologi, batas kontak formasi dan keberadaan struktur geologi mayor daerah penelitian. Dilakukan pengukuran pada 3 lintasan yaitu Utara-Selatan, Timur-Barat I dan Timur-barat II dengan total 75 titik pengukuran. Data hasil pengukuran selanjutnya dikoreksi sehingga menghasilkan nilai Complete Bouguer Anomaly (CBA). Pemodelan dilakukan dengan menggunakan metoda inversi Singular Value Decomposition (SVD) dan Occam inversion untuk model densitas 2D. Hasil pemodelan menunjukan pada lintasan Utara-Selatan dan ujung barat lintasan Barat-Timur I, diidentifikasi bahwa lapisan batugamping Formasi Wonosari dari arah selatan menuju arah utara semakin menipis. Terdapat struktur geologi pada Lintasan Barat-Timur I didapatkan di X = 506 dan pada X = 510, dan pada Lintasan Barat-Timur II didapatkan di X = 504 dan X = 507. Pada lintasan Utara-Selatan di koordinat Y = 9096 – 9098 dan pada lintasan Barat-Timur II di koordinat X = 497 – 501 ada kenaikan densitas yang disebabkan adanya struktur. Dilihat dari sebaran nilai densitas dan ketebalan pada model densitas 2D, area selatan lokasi penelitian adalah area perkembangan karst paling baik. Hal ini dikarenakan letaknya di dekat garis pantai. Dimana garis pantai menjadi tempat yang baik untuk perkembangan batugamping karbonat yaitu dari hasil sedimentasi tumbuhan dan hewan pada perairan dangkal. ===================================================================================================== The western part of Pacitan Regency has a dominant landscape in the form of karst. The aim of this study is to determine the subsurface conditions of the karst area including the thickness of sedimentary rocks and structures in the study area. One of the geophysical methods that can be used is the gravity method. The gravity method utilizes variations in the gravitational field to get an overview of lithological thickness, formation contact boundaries and the presence of major geological structures in the study area. Measurements were made on 3 routes, namely North-South, East-West I and East-west II with a total of 75 measurement points. The measurement data are then corrected to produce a Complete Bouguer Anomaly (CBA) value. The modeling is done by using Singular Value Decomposition (SVD) inversion and Occam inversion method for 2D density model. The modeling results show that on the North-South trajectory and the western end of the West-East I trajectory, it is identified that the limestone layers of the Wonosari Formation from the south to the north are getting thinner. There is a geological structure on the West-East Track I found at X = 506 and at X = 510, and on the West-East Track II it is found at X = 504 and X = 507. On the North-South track at coordinates Y = 9096 – 9098 and on the West-East II route at coordinates X = 497 – 501 there is an increase in density due to the structure. Judging from the distribution of density and thickness values in the 2D density model, the southern area of the research location is the best karst development area. This is because it is located near the coastline. Where the coastline is a good place for the development of carbonate limestone, namely from the sedimentation of plants and animals in shallow waters