Magnetic Gradiometer Survey at Bukit Bunuh, Perak: Preliminary Study on Unrevealed Meteorite Impact Crater

Magnetic gradiometer survey was used in this study to analyze the subsurface structure correspond to the crater. Gradiometry is one of the components in geophysical magnetic method and it can measure the local disturbances in the earth's magnetic field caused by the presence of magnetic materials. Therefore, the quantification of variations and concentration of magnetic grains in rocks can be defined. The study site of this area was in Bukit Bunuh, in the northern state of Perak. Archeological research shows the evidence of shock metamorphisms (suevite breccia) and crater morphology (Bukit Bunuh rings). The fission track dating on the suevite breccias give a date of 1.74 million years ago. There are eight survey lines with a maximum of 100 meter station spacing has been conducted through 0.9 meter magnetic sensor spacing. The data were interpreted both qualitatively and quantitatively. The qualitative interpretation is based on anomalies signature on the contour maps, and the quantitative interpretation is based on data modeling. Along with the interpretation, some specific sample was acquired from the study site for laboratory testing verification. Magnetic gradient contour map calculated and extrapolated from raw data shows some significant anomaly pattern correspond to the crater structure and the locality of magnetic anomalous body. The depth estimation of anomalous body has been done by using half-width and maximum slope method and followed by forward modeling scheme. Few borehole data and other geophysical method such as gravity and resistivity surveys have been carried out for monitoring and verification purpose. Thus, by comparing all of the result, the preface of the crater structure was confirmed.