Identification of short polarity events by transforming marine magnetic profiles to the pole

Abstract

A method is presented that permits marine magnetic anomaly profiles from all parts of the world to be stacked for the purpose of enhancing coherent small anomalies due to short geomagnetic polarity events. In general, the shape of a profile depends not only on the sequence of normally and reversely magnetized magnetic prisms that constitute the source, but also on the following five angles: the declination and inclination of the regional field; the declination and inclination of the magnetization; and the azimuth of the magnetic stripes. Our method transforms a measured anomaly to a second anomaly which would have been produced by an identical source with vertical magnetization and vertical regional field. The method uses Fourier transform and linear systems theory and employs filters with a flat spectral response, so that no information is lost at short wavelengths. No assumptions are made about the true depth or shape of the source: this may be any two‐dimensional body or bodies in which the direction of magnetization is constant and the intensity varies arbitrarily. A preliminary application of the method to marine profiles from the East Pacific rise has yielded encouraging results.

Updated interpretation of magnetic anomalies and seafloor spreading stages in the south China Sea: Implications for the Tertiary tectonics of Southeast Asia

“…Both effects are observed on profiles in the Indian Ocean, where the spreading rate varies between 15 and 60 mm/yr, which suggests that Patriat's time scale is more reliable than previous ones for interpreting profiles from ridges spreading at rates of less than 60 mm/yr. In calculating synthetic profiles, we also have taken into account the fact that the change from one anomaly to the next along a magnetic profile generally results from a progressive, rather than sharp, contrast of magnetization between normal and reverse-polarity blocks [e.g., $chouten, 1971;Blakely and Cox, 1972;Tisseau and Patriat, 1981]. We used the method of artificial rates developed by Tisseau and Patriat [1981], in which an artificial spreading rate slower than that corresponding to the model is chosen, and the horizontal scale adjusted to restore the predicted length of the modeled magnetic profile.…”

An Inversion Method for Estimation of Top and Bottom Undulations of Magnetic Layer and Its Application to Aeromagnetic Profiles.

“…Figure 7 shows a magnetic basement model derived from the inversion of profile W2. This figure shows that normal and reversed magnetization blocks are generally bounded not by vertical but by sloping boundaries as shown by BLAKELY and Cox (1972), while undulations of magnetic basement coincide well with features of the block model shown in Fig. 6(a).…”

“…This method is time consuming in constructing block models. Other methods to derive magnetic polarity reversal sequence from anomalies were developed by SCxoUTEN and McCAMY (1972) and BLAKELY and Cox (1972). The former method applies a linear filter method to the Fourier transform of a magnetic anomaly profile to obtain a distribution function of magnetic moment.…”

“…For the analysis of two-dimensional magnetic anomalies, BLAKELY and Cox (1972) presented a method to transform marine magnetic profiles to those at the pole by using the Fourier transform and linear system theory. At nearly the same time, SCHOUTEN (1971) and SCHOUTEN and MCCAMY (1972) derived a linear filtering formula to make operations such as upward and downward continuations and inversions from magnetic anomalies to magnetization of a plane layer or vice versa.…”

A Magnetic Study of the Oceanic Crust in the Vicinity of Sites 482, 483, and 485, Leg 65

“…In order to determine the distribution of crustal magnetization away from the axis of the ridge, these profiles were first transformed to the pole by the method described in Blakely and Cox (1972) and then inverted using the techniques of Parker and Huestis (1974). We assumed a two-dimensional magnetic source, uniform directions for the magnetization and field, no vertical variation in magnetization within the crust, and constant thickness of 500 meters for the magnetized layer.…”