GRAVITY COURSE INSTITUT TEKNOLOGI BANDUNG
INTRODUCTION Gravitasi : metoda geofisika tarik-menarik massa “ Hukum Newton ” Pemetaan struktur bawah permukaan rapat massa (r => gr/cm3)
Model: The Delson Fault, St Lawrence Lowlands P T H r=2.49 r=2.71 r=2.96 r=2.49 r=2.96
Gravitasi : Land gravity (survey) Airborne gravity Marine gravity Borehole gravity Goal : Dalam (deep) Eksplorasi hidrokarbon Geothermal Kerak, mantel Gunung api Monitoring (EOR, gunung api, geothermal) Dangkal (shallow/near surface) Gua bawah tanah Longsor
Sedimen Jenis batuan rapat massa (g/cm3) Clay 1.63-2.60 Gravel 1.70-2.40 Sand 1.70-2.30 Silt 1.80-2.20 Soil 1.20-2.40 Sandstone 1.61-2.76 Shale 1.77-3.20 Limestone 1.93-2.90 Dolomite 2.28-2.90
Batuan Beku Jenis batuan Rapat massa (g/cm3) Rhyolite 2.35-2.70 Trachyte 2.42-2.80 Andesite 2.40-2.80 Granite 2.50-2.81 Basalt 2.70-3.30
Metamorf Jenis batuan rapat massa (g/cm3) Quartzite 2.50-2.70 Marble 2.60-2.90 Gneiss 2.59-3.00 Amphibolite 2.90-3.04
Material lain Rapat massa (g/cm3) Petroleum 0.60-0.90 Sea water 1.01-1.05 Asphalt 1.10-1.20 Soft coal 1.20-1.50 Graphite 1.90-2.30 Bauxite 2.30-2.55 Gold 15.6-19.4
Theoretical Background Hukum Newton: m2 m1 Percepatan gravitasi: r 1 mgal = 10-3 cm s-2 = 10-5 m s-2 1 g.u = 10-6 cm s-2 = 0.1 mgal
Pemisahan residual dan regional
Bola
Silinder
Kotak h1 h2 t
EXERCISE PROSEDUR SURVEY: TOPOGRAFI GRID TITIK PENGAMATAN KOREKSI ANOMALI BOUGUER KONTUR PEMISAHAN REGIONAL – RESIDUAL PEMODELAN PENAFSIRAN
X Y gBA X Y gBA 1 1 5.292 1 2 5.3 1 3 5.3 1 4 5.3 1 5 5.29 2 1 5.31 2 2 5.32 2 3 5.325 2 4 5.32 2 5 5.318 3 1 5.326 3 2 5.33 3 3 5.34 3 4 5.33 3 5 5.32 4 1 5.324 4 2 5.32 4 3 5.315 4 4 5.315 4 5 5.31 5 1 5.312 5 2 5.305 5 3 5.295 5 4 5.3 5 5 5.3
1 2 3 4 5 1 2 3 4 5