Multiresolution tectonic features over the Earth inferred from a wavelet transformed geoid

Geoid signals give information about the underlying density structure and can be used to locate the source depth of the mass anomalies. Wavelet analysis allows a multiresolution analysis of the signal and permits one to zoom into a specific area bounded by a particular length scale. The ability of wavelets to resolve the geoid signal into individual wavelength components without losing the spatial information makes this method superior to the more common spherical harmonic method. The wavelet analysis allows one to zoom into a specific area and look at the regional geology. We have used a wavelet transform of the geoid to study the regional geology of Japan and the Philippine Plate, South America, Europe, North America, East Africa and the Middle East, India and the Himalayas, China and Southeast Asia, and Australia. By filtering the Earth's geoid anomalies with 2-D Gaussian wavelets at various horizontal length scales, one can detect the subduction zones along South America, the Aleutians, and the western Pacific; the Himalayas; the Zagros Mountains; the Mid-Atlantic ridge; and the island chains of the mid-Pacific. We have processed geoid data with a horizontal resolution down to approximately 200 km. Using an adjustable wavelet, one can detect structures that can only be picked up visually with much higher resolution spherical harmonic gravity data. We have also looked at the wavelength at which the maximum signal occurs over a range of scales. This method, known as E-max and k-max, is especially effective for detecting plate tectonic boundaries and ancient suture zones along with areas of strong non-isostatic gravitational potential due to high differential stress. These areas are likely to be at high risk of earthquakes. These methods will be especially useful to future studies of the geoid potentials of other planets, such as Mars and Venus, since they will allow careful studies of the regional geology variations with geoid data of the resolution available from satellites.