Gravity and Magnetics of the Central Indian Ridge: Preliminary Findings for the Vicinity of 18o S to 7o S

Abstract

We devised a semi-automated approach for computing synthetic magneticanomalies at the intersections of survey lines and spreading ridges. In the CentralIndian Ridge vicinity, the ridge axis and offsetting transform faults are stronglyvisible in the latest vertical gravity gradient field derived from satellite altimetry.By first digitizing these plate boundaries in Google Earth, their intersections withship tracks were then determined rapidly using the x2sys_cross programdistributed with the popular Generic Mapping Tools (GMT) software. Thisprogram outputs the location of intersections as well as the heading of ship tracksand of the ridge as well. These outputs include ridge latitude and ridge strikewhich are the necessary parameters for computing synthetic magnetic anomaliesvia the method of Schouten (1971). By this approach, synthetic anomalies arecalculated at each survey line&#8212 ridge intersection in a fast, iterative manner. Bycomputing synthetic anomalies at the exact location of each ship track&#8212 ridgeintersection, we were able to model variations in magnetic asymmetry along theridge axis. In order to improve correspondence between ship and synthetic data,we projected each shipboard profile to be perpendicular to the ridge axis. This stepalso brought the ship data into the reference frame of the synthetic profiles (i.e.,distance-from-axis). Interpretation of the data is visible in the latest vertical gravity gradient field derived from satellite altimetry.By first digitizing these plate boundaries in Google Earth, their intersections withship tracks were then determined rapidly using the x2sys_cross programdistributed with the popular Generic Mapping Tools (GMT) software. Thisprogram outputs the location of intersections as well as the heading of ship tracksand of the ridge as well. These outputs include ridge latitude and ridge strikewhich are the necessary parameters for computing synthetic magnetic anomaliesvia the method of Schouten (1971). By this approach, synthetic anomalies arecalculated at each survey line&#8212 ridge intersection in a fast, iterative manner. Bycomputing synthetic anomalies at the exact location of each ship track&#8212 ridgeintersection, we were able to model variations in magnetic asymmetry along theridge axis. In order to improve correspondence between ship and synthetic data,we projected each shipboard profile to be perpendicular to the ridge axis. This stepalso brought the ship data into the reference frame of the synthetic profiles (i.e.,distance-from-axis). Interpretation of the data is