Banda Arc Geophysics

Data Sources


The gravity data for the Indonesian island, or island groups, of Timor, Tanimbar and Kai were originally included in the author's Ph.D. thesis. These data have been re-levelled, relocated, heights resampled (except for Eastern Timor) and the subsequent gravity data reduced using the latest global, ellipsoidal standard (see Data Processing for details).

Other gravity data for marine and on-shore areas are taken from the Sandwell and Smith gravity dataset (version 18.1, December 2008).

Marine topographic data are taken from the Sandwell and Smith Global Topography dataset (version 13.1, September 2010).

On-shore topographic data are the Shuttle Radar Topography Mission (SRTM) at 90 metre resolution but edited and made available by the Consultative Group for International Agriculture Research (CGIAR) .

Gravity data for Timor, Tanimbar and Kai


All on-shore gravity data were originally listed in:

Kaye, S.J., The Structure of Eastern Indonesia: an approach via gravity and other geophysical methods. Ph.D Thesis, University of London, 1989. (16.5meg)

Other PDF files, of information originally in the full thesis, are:

A geological map of Timor (7meg - this is a badly scanned image, so don't download unless you are desperate for a 1980s vintage map), Gravity model one, Gravity model two and Gravity model profiles.

Please note this thesis is an historical document especially with regard to the stratigraphy of Timor. However, it does contain important information concerning the work conducted to retrieve old gravity surveys on Timor and the 1980's surveys of the Tanimbar and Kai island groups. Also note that the gravity data listed in the back of the original hardcopy thesis should not now be used.

Download the 2011 Complete Bouguer Anomaly data

The following files contain the latest (2011) data where stations have been relocated relative to SRTM data and satellite imagery and have complete Bouguer anomalies (fully terrain corrected and referenced to the ITRF(WGS84) ellipsoid). Please see the Data Processing page for a description of the steps taken.

Western Timor GRDC survey

Eastern Timor surveys

Tanimbar 1987 survey

Tanimbar 1989 survey

Tanimbar ITB survey

Kai 1987 survey

Kai 1989 survey


Timor Island On-Shore Gravity Data

The data for the island of Timor were originally surveyed by the following organisations over a period of four decades:

Eastern Timor

Companhia Ultramarin de Petroleos (Shell) in 1948

Timor Oil in the late 1959-1962

Flinders University, Australia in 1974

Imperial College, London in 1976

Missao Geografica de Timor in 1978

Western Timor

Geological Research and Development Centre, Bandung 1977‑79.

This image shows the gravity station distribution.

Note: the gravity data for Eastern Timor (Timor-Leste) used in this study were originally published in the author's Ph.D. thesis. This study has substantially improved the data gathered in the 1940s and 1960s but has not improved the later surveys, however they have been altered (please see the Data Processing page). Also note that the Bouguer anomaly surface covering western Timor is based on the digitisation of the contours of the published Bouguer anomaly map of Simamora, W.H., and Untung, M.,1983. Preliminary Bouguer Anomaly, West Timor. Geological Research and Development Centre, Bandung.

A full description of the original data processing can be found in the thesis mentioned above. The following data have been re-calculated in 2011 after the re-leveling of the 1940-1960s surveys in southern Timor and the repositioning of all stations to match modern mapping systems. The new work produces a set of gravity surfaces that are superior to those in the original thesis.

Survey names and references for eastern Timor

Survey T62T = Timor Oil company in 1962
Survey SUA* = Timor Oil company, Suau area survey in 1959
Survey VIQ* = Timor Oil company, Viqueque area survey in 1959
Reference: Audley-Charles, M.G. 1959 Report on the gravity surveys carried out in Portuguese Timor from June to November 1959. Timor Oil. (unpublished)
Survey MINM = Various Mines Administration surveys in 1960s
Survey PORT = Portuguese Government survey 1978
Reference: Botelho, F.T. 1978. A Gravimetria No Timor Portuguese. Missao Geografica de Timor
Survey IMPR = Imperial College survey 1974
Reference: Milsom, J. & Richardson, A. 1976. Implications of the occurrence of large scale gravity gradients in northern Timor. Geol. Mijn., v. 55, p. 175-178.
Survey FLIN = Flinders Univ. 1973
Reference: Chamalaun, F.H., et al, 1976. The Bouguer gravity field and crustal structure of eastern Timor. Tectonophysics, 30:241 259.
Survey SHLS = Shell Oil in 1948
Reference: De Snoo, G. 1948. Area report of the gravity survey in Portuguese Timor. Report no.23031, Shell International Petroleum, The Hague. (unpublished)


Tanimbar and Kai Islands On-Shore Gravity Data

The Tanimbar islands data are from surveys conducted in 1987 and 1989 by the University of London and the Geological Research and Development Centre, Bandung, Indonesia.

This image shows the Tanimbar gravity station distribution.

Tanimbar Islands On-Shore Gravity Data

1987 Tanimbar gravity survey.

1989 Tanimbar gravity survey,

Kai Islands On-Shore Gravity Data

1987, University of London and Geological Research and Development Centre, Bandung, Indonesia.1989, University of London and PT Corelab, Jakarta.

This image shows the Kai Islands gravity station distribution.

1987 Kai gravity survey.

1989 Kai gravity survey.

Marine and On-Shore Gravity Data (except for Timor, Tanimbar and Kai)

Gravity data from Satellite Altimetry, 1 minute grid, version 18.1, December 2008. David T. Sandwell and Walter H. F. Smith.

Reference: Sandwell, D. T., and W. H. F. Smith, Global marine gravity from retracked Geosat and ERS-1 altimetry: Ridge Segmentation versus spreading rate, J. Geophys. Res., 114, B01411, doi:10.1029/2008JB006008, 2009

Geoid Data

Geoid data was calculated from the Earth Gravitational Model EGM2008 published by the National Geospacial-Intelligence Agency (NGA).

Topographic/Elevation Data

Marine data from Global Topography version 13.1, September 2010. Bathymetry derived from satellite gravity and ship sounding data (predicted bathymetry).

Reference:  Smith, W. H. F., and D. T. Sandwell, Global seafloor topography from satellite altimetry and ship depth soundings, Science, v. 277, p. 1957-1962, 26 Sept., 1997.


On-shore data from 90 metre land elevations from the NASA Shuttle Radar Topography Mission (SRTM) processed by CIAT.

Reference: Jarvis A., H.I. Reuter, A. Nelson, E. Guevara, 2006, Hole-filled seamless SRTM data V3, International Centre for Tropical Agriculture (CIAT), available from

Earthquake Data

USGS 1973-to-present world-wide earthquake data catalogue at

USGS/NEIC 1977-to-present world-wide earthquake focal mechanism data catalogue at

Steve Kaye. Protected under UK and international law. May be used free of charge. Selling without prior written consent prohibited. Obtain permission before redistributing. In all cases this notice must remain intact.