Abstract: The north coast of Jepara is a region where the development of Muria nuclear power plant takes place which is chosen by the central government through National Nuclear Energy Agency of Indonesia. This nuclear power plant is located in Muria peninsula which will be affected because of tectonics and volcanic activities in such area, mainly in Muria mountain. This study uses gravimetric method to determine the subsurface structure in Muria mountain area. The gravity data is obtained from https://topex.ucsd.edu/cgi-bin/get_data.cgi is dispersed in Muria mountain. The value of anomaly which is obtained is reduced with several corrections and the value of Complete Bouguer Anomaly is achieved. The separation of regional and residual anomaly uses Second Vertical Derivative. The modeling of subsurface used forward modelling method. From this modelling, the rock density widening is in the value of 2.4 g/cm³ for basalt lava or andesite, 2.43 g/cm³ for lava tuff and sand tuff, 2.5 g/cm³ for sandstone tuff and conglomerate tuff with clay stone inserted, and 2.7 g/cm³ for sand limestone and clay limestone. The result of this modelling is shown that there is fault around Muria mountain and is identified as Tempur and Rahwatu fault.

Abstrak: Pesisir utara Jepara dijadikan sebagai lokasi pengembangan PLTN Muria yang dipilih oleh pemerintah pusat melalui Badan Nuklir Nasional (Batan). Lokasi PLTN yang berada di Semenanjung Muria akan terkena dampak karena adanya aktivitas tektonik dan vulkanik di daerah tersebut, terutama di Gunung Muria. Penelitian ini menggunakan metode gravitasi untuk mengetahui struktur bawah permukaan di sekitar Gunung Muria. Data gravitasi yang diperoleh melalui https://topex.ucsd.edu/cgi-bin/get_data.cgi tersebar sebanyak 566 titik di Semenanjung Muria. Nilai anomali yang didapatkan direduksi dengan beberapa koreksi dan didapatkan nilai Anomali Bouguer Lengkap (CBA). Pemisahan anomali regional dan residual menggunakan Secong Vertical Derivative. Pemodelan bawah permukaan menggunakan metode pemodelan kedepan (Forward Modelling). Pada pemodelan ini didapatkan sebaran densitas batuan sebesar 2,4 g/cm³ (lava basalt atau andesit), 2,43 g/cm³ (tufaan, lahar dan tufaan pasiran), 2,5 g/cm³ (batu pasir tufaan dan konglomerat tufaan yang bersisipan batu lempung), dan 2,7 g/cm³ (batu gamping pasiran dan batu gamping lempungan). Hasil pemodelan menunjukkan adanya patahan di sekitar Gunung Muria dan diidentifikasikan sebagai patahan Tempur dan Rahtawu.