Pemodelan bidang batas lempeng subduksi dan struktur regional bawah permukaan :: Kajian anomali gravitasi regional Jawa Tengah

INDRIANA, Rina Dwi, Dr. Kirbani Sri Brotopuspito

2006 | Tesis | S2 Fisika

Telah dilakukan penelitian anomali medan gravitasi regional di d a d Jawa Tengah Daerah penelitian meliputi pantai Utara Jawa Tengah sampai palung Jawa di Samudera Indonesia. Tujuan dari penelitian untuk memperkirakan model basement dari palung Jawa sampai pantai Utara Jawa. Data anomali Bouguer lengkap yang digunakan merupakan data digital, yang merupakan hasil digitasi peta kontur anomali Bouguer lengkap (GRDC).Data digital anomali Bouguer lengkap disajikan dalam bentuk matriis XYZ dengan grid 64 x 64. Data digital topografi dengan grid yang sama ditumpang tindihkan dengan data digital anomali Bouguer sehingga diperoleh data digital XYZH. Proses pengangkatan ke bidang datar mempergunakan metode sumber ekuivalen tit& massa sehingga diperoleh peta anomali Bouguer pada bidang horisontal. Anomali regional gravitasi diperoleh pada ketinggian 25 km dengan mempergunakan metode kontinuasi ke atas. Proses estimasi kedalaman mempergunakan power spectrum 1 dimensi. Pemodelan bawah permukaan mempergunakan metode Talwani. Interpretasi kuantitatif anomali regional menunjukkan adanya anomali negatif yang besar di Samudera Indonesia (-900 mgal). Anomali positif (100 mgal) terdapat di bagian Timur Laut Jawa Tengah dan anomali positif yang bear terdapat di sepanjang pesisu Selatan Jawa Tengah (600 - 800 mgal). Anomali positif terbesar texdapat di Barat Daya Jawa Tengah sebesar 1000 mgal. Pemodelan 2 dimensi dan 3 dimensi menghasilkan model lipatan di Timur Laut Jawa Tengah dengan arah Timur Barat dengan kedalaman basement rata-rata 9 -15 km, Basement di Selatan Jawa Tengah lebih tinggi dari Utam Jawa Tengah. Model struktur regional pertemuan 2 lempeng tektonik Indo Australia dan Eurasia berada pada kedalaman yang bervariasi antara 10 -15 km dari reference spheroid dengan posisi di bawah zona akresi dan cekungan busur depan. Besar sudut subduksi bervariasi antara 27' 59'.

Regional Gravitation field research which covers from North coast of Central Java to Java trench has been carried out. The major purpose of this research was to interpret the regional anomaly of gravity field. The Central Java Bouguer anomaly map which is produced by Indonesian Geological Research and development was digitized and decimated to a 64 x 64 grid digital data. Anomaly gravity and topography digital data are arranged for further process. Upward continuation is applied to data, which had been located at an irregular surface of topography to a horizontal plane surface. The result of up ward continuation is a regional gravitation anomaly, which is located at regular surface on 25 km above spheroid reference. The power spectrum methode is used for basement depth estimation. The Talwani method is used as the last process. The results of quantitative anomaly are regional positive anomaly along southern coast of central Java (600 - 800 mgal), the highest anomaly (1000 mgal) was on South - West of Central Java, and the lowest anomaly Bouguer was on the Indonesian Ocean (-900 mgal). A positive anomaly (100 mg) on North-East of central Java was interpreted as a folding zone. A Negative anomaly was interpreted as subduction zone. The depth of subduction plate was varies from 10 to I5 km under spheroid reference. The subduction dip of descending plate was around 27' - 59'. The Subduction boundaries of Indo Australia and Eurasia plates were beneath accretionary zone and forearc basin.

Kata Kunci : Anomali Gravitasi, Pemetaan, Model Basement