An open-source program for calculating the depth to the bottom of magnetization.

The depth to the bottom of magnetization (DBM) or Curie surface, calculated with magnetic data using spatial frequency domain techniques, is a classic alternative to understand the thermal structure of the crust. Traditionally, the calculation is done using the centroid method, based on spectral analysis. This technique has been successfully applied in many investigations all around the globe despite its limitations, such as the need for large windows, uncorrelated sources, and difficult interpretation of the geological meaning. One of the challenges of the method is choosing a window size large enough to contain the wavelengths of the magnetic bottom without contaminating the spectrum with magnetic environments around it.

Geophysical data processing requires using computer programs due to the desirable large number of samples and mathematical routines. Because the purchase and maintenance of commercial programs require considerable investments from research institutions, the use of open-source code that does not entail large investments is largely encouraged. The objective of this work is to present a user-friendly and public domain open-source code for DBM estimates.

We have developed a Python program based on the analytical solution of exponential equations obtained from Fourier transformation of magnetic data to calculate the DBM for square windows. We have used a few public domain libraries. The program provides a function to automatically select square windows from a database, perform its spectral analysis for depth estimation and return an image of the Curie surface or an XYZ database. We applied the program to estimate the depth to the bottom of magnetization for the Parecis basin in the Amazonian Craton. It has been assumed that Curie depth is close to Mohorovic discontinuity as shown by several authors, an average crustal thickness of 40 km in the region, based on receiver function data, and windows of 250 km has been used.

The results of our program were satisfactory compared to those obtained by a well-established Matlab algorithm. The DBM values vary between 27 and 60 km. The shallower depths occur in the east and west portions of the basin. The deep values are in the center of the basin. These solutions deeper than 50 km might indicate overestimated solutions, requiring more tests using different window sizes.