Kuliah Geofisika Terapan Metoda Gayaberat (Gravity)

MK Eksplorasi Geofisika Metoda Gayaberat (Gravity Method) Dr. A. Syaeful BahriPeralatan: Gravimeter

In general Gravity Anomaly:g = gobserved gtheory

Free Air theory:gFree Air = g(,h) = g() 0.307 h

Free air anomaly:gfaa = gobserved - gFree Air 3Formula Gayaberat (delta g)

Dimana:

Dasar TeoriKoreksi Pasang Surut

Tujuan: menghilangkan pengaruh gaya tarik matahari dan bulan terhadap bumi. Untuk melakukan koreksi ini digunakan Longman formula.

Tide Correction (TC)

Data Pasang surut Semarang (Sarkowi, 2007)Dasar Teori

Dasar Teori

Terrain Correction

Bouguer Correction

Free-air correction (FAC)Terjadi karena perbedaan elevasi antara titik pengamatanPerbedaan elevasi terjadi karena perubahan topografi permukaan bumi pembacaan gravitymeter berbedaPerlu dilakukan koreksi elevasiKoreksi elevasi mengasumsikan massa yang terdapat pada titik observasi (elevasi tinggi titik B) berupa slab dengan densitas dan ketebalan sama

Spinning Earth -> centrifugal force, equatorial bulge centrifugal force => less g at equator, no effect at poles equatorial bulge (~elliptical)more mass near equator => g increasesr larger at equator => g decreasesDependence of g on latitude ()g() = 978032(1+0.0052789.sin2 0.00000235sin4) mgal

Elevation change r -> r + h => g decreases (free air effect) ee air correction:g(r+h) = g(r) + (dg/dr) hdg/dr = -2g/r = -0.307 mgal/m

14Terrain has an effect

h in feet!15Dasar TeoriDrift CorrectionKoreksi ApunganTujuan: menghilangkan perubahan kondisi alat

Driftstation = x ( Tstation TA1 ) A12A3A4A

18Gravimeter

Fully digital reading systemAutomatic Leveling system High accuracy (0.5Gal)Automatic Lock Spring systemHigh Repeatability

Digital reading system High Accuracy (1 5 Gal)High Repeatability

Graviton Lacoste & Romberg G with Alliod Sistem Dasar Teori

Fully digital reading System Automatic LevelingHigh Accuracy (1Gal)Automatic Lock Spring system

Scintrex AutoGrav CG-5