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Detailed gravity and magnetic measurements made in Khor Arba'at and the adjoining coastal plain region provide a better definition of the near surface geological features. The Nakasib Shear Zone (NSZ), which represents a reworked suture between two island arcs, is characterized by a gravity low and exhibits a lack of magnetic anomaly. The edges of NSZ, however, display magnetic anomaly associations where the shear zone rocks present a substantial magnetic susceptibility contrast with the surrounding rocks, such as ophiolites. The post-tectonic intrusion of the Arba'at granite has a well defined gravity low which suggests a westward extension of the granite body into the shear zone rocks. The main Arba'at intrusion is estimated to be about 6 km thick. The coastal plain basin containing Mid-Tertiary and younger sediments appear to be laterally segmented by the subsurface relief of the Proterozoic basement. Gravity data suggest a local thickening of sediments in the southern part of the area. Evidence for a regional subsurface fault offsetting the Cenozoic sediments beneath the Recent sediments of the coastal plain is lacking

Regional gravity surveys were done in the state of Kuwait during 1986-1988. The new gravity maps show a good correlation with geomorphological features as well as with deeper geological structures. The free-air anomaly map clearly reflects the topography of the Jal Az Zor and Ahmadi ridges, and Wadi Al-Batin. The Bouguer anomaly map is dominated by two prominent gravity highs correlatable with subsurface structural arches. The north-trending gravity high in eastern Kuwait represents the effect of a major structure, the Kuwait arch, along which many important oil fields are located. A smaller northwest-trending high mapped in western Kuwait indicates the presence of a second subsurface arch, which in this paper is named the Dibdibba arch. The two gravity highs are separate by a wedge-shaped gravity low presumably caused by thicker sediments of the Dibdibba basin. Magnetic measurements along selected profiles show the two arches to be associated with 100-200-nT (nannoTesla) anomalies apparently reflecting the positive subsurface relief of the crystalline basement. Along the length of the Kuwait arch, magnetic data also indicate lateral susceptibility variations possibly related to lithological variations within the basement.

Summary. A new Bouguer anomaly map of India and its generalized interpretation is presented in this paper. Bouguer anomalies in India show good correlation with the geology and tectonics. Isostatic anomalies in India are primarily geologic anomalies caused by intracrustal inhomogeneities. For example, the negative isostatic anomalies in southern India arise from large thicknesses of granitic bodies in the upper crust and the positive anomaly over the Himalaya may be attributed to a possible thickening of the basalt layer in the lower crust. The gravity data suggest that an overall isostatic equilibrium generally prevails in India and the Himalayan region. Crustal thickness estimates from DSS data in India are comparable to the values obtained from gravity data based on the Ahy's concept of isostatic compensation.