Three-dimensional magnetization vector inversion of a seamount

Abstract

A three-dimensional non-uniform magnetic modeling is proposed to obtain information about a magnetization of a seamount, which was divided into many blocks modeled by layered and rectangular prisms, and parameters were assigned to each block describing magnetic three components. Our data were the magnetic total force on the sea. A set of linear observation equations was formulated in terms of three components of magnetization for each block. The solution was obtained by using the conjugate gradients method because of its fast and accurate advantages of calculation. In this inversion, a common set of three components was defined for several blocks to decrease the number of unknown parameters. A computer program has been tested with artificial data and applied to data of Daiichi Kashima Seamount observed during the first phase of the Kaiko project carried out with the R/V Jean Charcot in 1984. In the real application, the crustal structure was divided into three layers (top depth to 5 km depth, 5-6.5 km depth and 6.5-8 km depth). The result of the inversion shows that the top portion and the submerged western half of this seamount are covered with the low magnetization layers, and in the middle layer (5-6.5 km depth) of eastern half side, declinations, inclinations and intensities are almost northward, 15• and 3-5 A/m, respectively. In the third layer (6.5-8 km depth), the reverse magnetizations are revealed in the southeastern and northern sides of Daiichi Kashima Seamount and around Katori Seamount. These reverse magnetizations may reflect part of the magnetic lineations of the Pacific plate.

Estimation of the total magnetization direction of approximately spherical bodies

“…However, in practical applications, this constraint may yield a poor data fit. Finally, Kubota and Uchiyama (2005) discretized the seamount volume as a grid of juxtaposed right rectangular prisms and estimated the Cartesian components of the magnetization vector of each prism.…”

“…where B i is the total magnetic induction vector produced by all magnetic sources (magnetized anomalous susceptibility distribution) at the position (x i , y i , z i ) (Blakely, 1996;Langel and Hinze, 1998). Schematic representation of L = 2 spheres uniformly magnetized at the subsurface.…”

Two-Dimensional Compact Inversion of Magnetic Data in the Presence of Remanent Magnetization

“…Both the magnitude and the magnetic vector are estimated as two unknown parameters. This approach has been proposed with some differences by Kubota and Uchyama [21], Lelivre and Oldenburg [22] and Pratt et al [23]. The method dramatically reduces the risk and error as compared with estimation of the direction of remnant magnetization methods, and is a suitable method for inversion of local and regional magnetic data, but due to increasing model parameters triply, the non-uniqueness of this method will increase.…”

Virtual Pole from Magnetic Anomaly (VPMA): A procedure to estimate the age of a rock from its magnetic anomaly only

“…The determination of magnetic paleopoles from seamount magnetic anomalies constitutes the major data source for the Pacific Apparent Polar Wander Path (APWP); Emilia & Massey (1974); Hilderbrand & Parker (1987); Gee et al (1989); Sager & Koppers (2000); Lee et al (2003); Kubota & Uchiyama (2005). In these cases the bathymetry provides an immediate constrain for the geometry of the magnetic sources, i.e., the submarine volcanic cones.…”