Investigation of Ancient River at Lembah Bujang, Kedah, Malaysia S. Ramzul Ihsan Student, Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail: [email protected] Dr. M.M. Nordiana Senior Lecturer Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail: [email protected] Dr. Rosli Saad Senior Lecturer Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:[email protected] Dr. Mokhtar Saidin Professor Centre for Global Archeological Research Malaysia, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:[email protected] Umi Maslinda Student, Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail: [email protected] Hazrul Hisham Student, Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail: [email protected] Nabila Sulaiman Student, Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail: [email protected] ABSTRACT The use of geophysical methods in archeological survey is a technology often used nowdays because this method is not too difficult and easy to administer. The objective of the study was to detect the possible ancient river in Sungai Batu, Lembah Bujang Kedah using magnetic method. The magnetic method was performed using G-856 proton magnometer and the spacing between stations was 20m spacing gridding. The magnetic data was processed by ulitizing Microsoft Excels and Surfer8 software which was displayed in a form of countaring and revealed low residual zones shown possible ancient river. The results of low magnetic values(-280nT to - 400nT) indicated the existed of ancient river within study area. These findings indicated that magnetic method suitable use in a search of archeological features. KEYWORDS:Archaeology, Sungai Batu, Lembah Bujang, Magnetic, ancient river, G-856 - 4385 - Vol. 20 [2015], Bund. 11 4386 INTRODUCTION The study area was situated near to Gunung Jerai and Sungai Merbok. The mid-south of Kedah was recorded as marine area in 1st and 2nd century. Since the sea level was rise, the area change to be a landed area in years 1400 (Wheatley, 1961). Sungai Batu has been used since the 5th century BC, continued, from time to time, until the 17th century BC, during the 2200 years. This confirms the Sungai Batu Complex is the oldest civilization in the region. The soil types of the area are sandy clay covered with fine sand. The sediment was transported from the river and being settled around this area. The sea level rises, the settled area turn to be landed area (Jane, 1990). The geomorphology of the study area was flat landed fill with palm and rubber tree. There are few small rivers and swamp at the eastern of the area. Archaeologists found some of ancient structure and old jetty. Magnetic methods are widely used in exploration, engineering, borehole, and global geophysics and the subjects of this monograph are the physical and mathematical principles of these methods regardless of the area of application. Geotechnical studies are usually used for subsurface, engineering and environmental works. Geophysical studies provide supported data in order to save cost and time. Geophysical methods can be used to determine depth of bedrock, nature of overburden materials and near surface structures such as sinkholes, cavities, voids, faults and boulders. Selection of the appropriate geophysical method is based on project objectives and site conditions. Magnetic geophysical surveys measure small, localized variations in the Earth’s magnetic field. The magnetic properties of naturally occurring materials such as magnetic ore bodies and basic igneous rocks allows them to be identified and mapped by magnetic surveys. Strong local magnetic fields or anomalies are also produced by buried steel objects. Magnometer surveys find underground storage tanks, drums, piles, and reinforced concrete foundations by detecting the magnetic anomalies they produce. THEORY OF MAGNETIC SURVEY The purpose of the magnetic survey is used to record spatial variation in the Earth’s magnetic field. In archeology, magnetic surveys are used to detect and map archeological artifacts and features The magnetic surveying consists of measuring the magnitude of the earth’s magnetic field at each point on a grid established over a site. Variations in the magnetic properties of the subsurface material can produce an observable variation (anomaly) in the measured magnetic field. At any site successful application of the method depends on the magnetic properties of the local subsurface, the extent and nature of human activity. The gravitational force exerted between two point masses of mass m1 and m2 separated by a distance r is given by Newton's law of gravitation, which is written as where G is the gravitational constant. This law, in words, simply states that the gravitational force exerted between two bodies decreases as one over the square of the distance separating the bodies. Since mass, distance, and the gravitational constant are always positive values, the gravitational force is always an attractive force : Vol. 20 [2015], Bund. 11 4387 PREVIOUS STUDY Magnetic surveys have been used in the study at Gem Valley, Adoho basalt aquifers in several areas, particularly in the snake river plain and columbia plateau, with varying degrees of success. magnetic data from gem valley in southeastern Idaho illustrate some of the potentials and limitations of magnetic surveys in the study of volcanic rocks (Mabey and Oriel, 1970). gem valley is an intermontane basin about 56 km (35 miles) long and as much as 13 km ‘(8 miles) wide. the enclosing ranges are paleozoic sedimentary rocks. much of the valley floor consists of cenozoic basalt flows f,rom vents in the southeastern part of the valley and from an extensive volcanic field northeast of the valley. the ‘basalt flows inundated a surface of unknown relief on the older cenozoic sediments. post-basalt sediments overlap the basalt in several areas but sin most of the valley the basalt is overlain by a thi,n cover of windblown soil. water is pumped from basalt in several parts of the valley and information on the extent, thickness, and structure of the ,& salt is important to ground-water investigations in the valley. tlhe first magnetic observations in the valley consisted of measurements with a magnetometer moun,ted on a l-m tripod. the magnetic field in areas where the basalt was within a few feet of the surface varied several ‘hundred gammias over distances of a few meters. these abrupt variations reflect the magnetization of the upper few meters of the basalt and were of little value in determining the thickness or gross structure of the flows, so the survey was abandoned. the method could have been used to locate the edge of the ibasalt where it was at shallow depths. At the Antelope Valley California, the magnetic method used in studying the structure of the basin. an example of this application of magnetic measurements is an aeromagnetic profile in eastern antelope valley.The basement in this part of antelope valley is igneous rock of approximately quartz monzonite com,position. a cenozoic basin several thousand feet deep has been defined by drilling and gravity measurements on the south side of rosamond lake (Mabey, 1960). The aeromagnetic and gravity profiles across the basin, and the configuration inferred from the gravity data and one deep drill hole (not along the profile) that did not penetrate the basement rock. on the southern half of the profile are three local magnetic anomalies produced by lithologic variations in the basement rock. the character of these anomalies, which is better revealed on a contour map, is typical of anomalies over quartz monzonite in this part of the mojave desert. a skilled interpreter would infer from these anomalies that the rock producing the anomalies ,is similar to the quartz monzonite exposed a few miles to the east. depths determined for sources of anomalies a and b were used to supplement the gravity data as control for the base of basin fill along the southern part of the profile. this interpretation involved assumptions on the geometry of the disturb a ing mass, which were not critical, and the assumption that the top of the disturbing mass extended to the top of the basement. however, because the determination of depths from these magnetic anom,alies does not involve assumptions of physical properties or the removal of a regional gradient as do the gravity data, the magnetic depths for this part of the profile are more reliable than the depths determined from the gravity data. the magnetic data provide only two depths and do not provide a continuous indication of the depth to basement along the profile. near the north end of the profile is a double-peaked magnetic high. the extent of the gradients on this high indicate an elevation of the top of the magnetic mass consistent with the elevation of the basement surface inferred from the gravity. the contrast in character between this anomaly and the anomalies at the south end of the profile suggests a difference in magnetic properties of the rock producing the anomalies, although all the anomalies probably are produced by intrusive rocks. the magnetic low near the center of the profile is over the deepest part of the basin, but the lowest value is produced by the steeply dipping interface, probably a fault on the south side of the basin. the location of the fault and also a crude approximation of the vertical displacement could be inferred from the magnetic anomaly. over the deepest part of the basin no Vol. 20 [2015], Bund. 11 4388 local magnetic anomalies suitable for precise depth analysis were recorded; therefore, the thickness of the basin fill in this area could not be determined from the magnetic data.