Preparing a software pack for gravity data processing

Gravity method in geophysics examines underground mass distributions using mass and location parameters with Newton's Law of Universal Gravitation. The gravity data is collected using gravimeters and require a group of correction and reduction processes to achieve a discussable data set. Bouguer anomalies, which are calculated after all the correction and reduction processes, are summations of all the masses' and geological layers' effects around the area where the data belongs. Effects of these different units can be separated from the Bouguer anomaly data with various separating methods such as filtering, analytical continuation and boundary analysis. Separated Bouguer data then could be used with various modelling techniques to achieve mass or density distribution models. Literature scan revealed that even though there are various submitted softwares capable of processing gravity data, there is not a software available, specifically developed for processing steps through a user-friendly interface. In this study, the aim is to develop a MATLAB® based software that is easy-to-use and capable of applying all the gravity data processing steps without the need of any external softwares. Along with carrying out gravity data calculations, the software also will be able to calculate small-scaled processes such as calculating Bouguer anomalies from raw gravity data collected on field, perform simple coordinate trasformations from decimal degrees to UTM meters and cropping the gravity data. The software is planned to be useful in academical researches, have enough capacity to be used in private sector and operate simple enough to be used by undergraduate geophysics students. Developed gravity data processing software pack, that is named as "GravPack" accepts data files separated into columns in ASCII DAT format. Input data should consist of at least three columns of data, two of which being the coordinates in decimal degrees or UTM meters and the third one being raw of Bouguer gravity data. The software uses UTM meters for calculations, therefore if the coordinates are input in decimal degrees format, the "Units in degrees" checkbox on Data Tab should be checked and conversion datum should be selected to perform the conversion. If input data file include elevation and terrain correction data along with raw gravity data, then the conversion into Bouguer data is possible. User can possibly re-define Bouguer calculation parameters if required. There is also an option to merge points with similar coordinates in order to decrease further processing steps. Gridding Tab is the first tab that can display the data graphically. The Tab consists of a cropping panel to select and crop a portion of the area, resampling panel where used defines sampling rate for the grid and display buttons that display the data on the axes below the window. Gridded data then can be used in depth estimations in Spectral Analysis Tab. Spectral analysis process calcualtes radially averaged power spectrum of the data and separates linear alignments on the spectrum to calculate different mass depths from the data. The cutting wave numbers defined in spectral analysis step then can be used in Filtering Tab to separate each masses effects from the anomaly, using low pass, band pass or high pass filters. Analytical Continuation Tab is the part of the GravPack software where the user can calculate upwards and downwards analytical continuations of the gravity the data. Derivative Analysis Tab which is the next tab after Analytical Continuation Tab can be used to analyze the boundaries that could be found in gravity data in order to visually point out possible mass boundaries. Analysis include first and second degree derivatives, Finite Differences Method and six different image processing methods for boundary detection. Modelling Tab is the last data processing tab of the GravPack where user can define 4 different layers, each having separate mean depth, density difference and data grids. Defined layers then used in modelling calculations with Vertical Prisms Method in order to achieve approximate layer geometry around defined mean depths. Iterations are carried out with Newton's least squares method and can be stopped either after reaching a certain amount of RMS error, or reaching a maximum iteration number, both of which are defined by the user. User also has an option to visually follow the modelling process using a Live Watch window which display calculation results and calculated data during modelling processes if activated beforehand. User is given option to display, save and delete the data from the data pool of the Gravpack on the Manage Data tab. Data can be saved in DAT, TXT, MAT and GRD formats, either in three-columns form or matrix form. GRD format output can only be saved in matrix form and specifically prepared to import the data directly into Goldensoft Surfer ©. During and after the preparation of the software, the Bouguer gravity data from Konya-Çumra area is used to cross-check the accuracy of the calculation processes. There appears to be an anomaly area around Konya – Çumra region with relatively higher Bouguer values. The anomaly is located on a suture zone left from closing of Thetis ocean between Mid-Jurassic to Lower Cretaceous periods and is now covered with a thick layer of young sediments. The gravity data from the area is used with GravPack in order to interpret a posibble reason for the high Bouguer anomalies. The data loaded into software and since it is already in UTM coordinates and Bouguer data, no conversion operation were needed. The data then displayed on Gridding Tab and gridded with one kilometer sampling interval. For the next step the gridded data's power spectrum is calculated in Spectral Analysis Tab for depth estimation. The spectrum is divided into 4 parts, each showing linear alignments with different slopes and thus different slopes. Cutting wave numbers from the spectral analysis ten used in Filtering Tab to separate each layers effects from the Bouguer anomaly. Before going to Modelling Tab straight, Analytical Continuation Tab and Derivative Analysis Tab are checked using the gridded data and verified working properly. Lastly on the modelling tab, only the first layers filtered Bouguer data is used in calculations along with the main depth calculated from spectral analysis and mean density difference between continental crust and oceanic crust. Iterations are continued until the RMS values are lower than 1 and then modelling process stopped automatically. After getting the final results, the data are saved using Manage Data tab. After verifying the accuracy of the prepared software, the results are discussed and concluded. Konya – Çumra region has several rock formations from different time periods as a result of the location's geological past. In the Konya Basin, there is a relatively high Bouguer anomaly despite the area having a flat topography and sediment cover. The anomaly is studied using spectral analysis for depth estimation and modelled using the prepared program that calculates a rough underground model using vertical prisms method. The modelling process carried assuming a single layer with constant mean depth and density contrast. Further on the model is used for an extra mass estimation that is buried under the sedimentary layers. The area being an ancient suture zone, containing surfaced ophiolites marking positive Bouguer anomalies in places indicate that the possibility of an obducted oceanic crust block emplaced beneath Çumra area is considerable.