3D forward and inverse modeling of total-field magnetic anomalies caused by a uniformly magnetized layer defined by a linear combination of 2D Gaussian functions

Geophysics ◽  
2008 ◽  
Vol 73 (1) ◽  
pp. L11-L18 ◽  
Author(s):  
Juan García-Abdeslem
Keyword(s):  
Linear Combination ◽  
Magnetic Anomaly ◽  
Synthetic Data ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Nonlinear Inversion ◽  
Total Field ◽  
Gaussian Functions ◽  
Estimated Parameters ◽  
Forward And Inverse Modeling

I develop a method for 3D forward modeling and nonlinear inversion of the total-field magnetic anomaly caused by a uniformly magnetized layer with its top and bottom surfaces represented by a linear combination of 2D Gaussian functions. The solution of the forward problem is found through both analytic and numerical methods of integration to calculate the theoretical magnetic anomaly. The magnetic anomalies computed by the present numerical method compare well with the ones calculated by using an analytic solution. To test the robustness of the algorithm, the inversion is performed with noisy synthetic data. The estimated parameters in the case of a synthetic model were found to deviate only modestly from the true parameters in the presence of noise. The algorithm is used to interpret a dipolar magnetic anomaly of high amplitude attributable to a laccolith of intermediate composition in northern Mexico.

scholarly journals Acquisition procedures, processing methodologies and preliminary results of magnetic and ROV data collected during the TOMO-ETNA experiment

2016 ◽  
Vol 59 (4) ◽  
Author(s):  
Danilo Cavallaro ◽  
Luca Cocchi ◽  
Mauro Coltelli ◽  
Filippo Muccini ◽  
Cosmo Carmisciano ◽  
...  
Keyword(s):  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Structural Features ◽  
Magnetic Survey ◽  
Remotely Operated Vehicle ◽  
Ne Sicily ◽  
Mt Etna ◽  
Source Study ◽  
Anomaly Map

<p>The TOMO-ETNA experiment was devised for the investigation of the continental and oceanic crust beneath Mt. Etna volcano and northeastern Sicily up to the Aeolian Islands, through an active source study. In this experiment, a large amount of geophysical data was collected both inland and in the Ionian and Tyrrhenian Seas for identifying the major geological and structural features offshore Mt. Etna and NE Sicily. One of the oceanographic cruises organized within the TOMO-ETNA experiment was carried out on the hydrographic vessel “Galatea” by Italian Navy. During the cruise a detailed magnetic survey and a set of ROV (remotely operated vehicle) dives were performed offshore Mt. Etna. The magnetic survey allowed the compilation of a preliminary magnetic map revealing a clear direct relationship between volcanic structures and high frequency magnetic anomalies. Significant positive magnetic anomalies were identified offshore the Timpa area and along the easternmost portion of the Riposto Ridge <span>and</span> correlated to a primitive volcanic edifice and to shallow volcanic bodies, respectively. On the whole, the magnetic anomaly map highlights a clear SW-NE decreasing trend, where high amplitude positive magnetic anomaly pattern of the SW sector passes, northeastwardly, to a main negative one. ROV dives permitted to directly explore the shallowest sectors of the Riposto Ridge and to collect several videos and seafloor samples, allowing us to identify some locally developed volcanic manifestations.</p>

Magnetic interpretation using a least-squares, depth-shape curves method

Geophysics ◽  
2005 ◽  
Vol 70 (3) ◽  
pp. L23-L30 ◽  
Author(s):  
El-Sayed M. Abdelrahman ◽  
Khalid S. Essa
Keyword(s):  
Least Squares ◽  
Magnetic Anomaly ◽  
Least Squares Method ◽  
Random Noise ◽  
Synthetic Data ◽  
Theoretical Data ◽  
Magnetic Anomalies ◽  
Shape Factors ◽  
Characteristic Points ◽  
Horizontal Cylinders

We have developed a least-squares approach to depth determination from residual magnetic anomalies caused by simple geologic structures. By normalizing the residual magnetic anomaly using three characteristic points and their corresponding distances on the anomaly profile, the problem of determining depth from residual magnetic anomalies has been transformed into finding a solution to a nonlinear equation of the form z = f(z). Formulas have been derived for spheres, horizontal cylinders, thin dikes, and contacts. The method is applied to synthetic data with and without random noise. We have also developed a method using depth-shape curves to simultaneously define the shape and depth of a buried structure from a residual magnetic anomaly profile. The method is based on determining the depth from the normalized residual anomaly for each shape factor using the least-squares method mentioned above. The computed depths are plotted against the shape factors on a graph. The solution for the shape and depth of the buried structure is read at the common intersection of the depth-shape curves. The depth-shape curves method was successfully tested on theoretical data with and without random noise and applied to a known field example from Ontario.

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