FILTERING OF GRAVITY BOUGUER FIELD .OF THE TUZ GOLDREGION AND INVESTIGATION OF THE BASEMENT DEPTH     In order to invt.lstigate the depth of the basement of Tuz Golil, first, a numerical filtering is applied over its Bouguer anomaly map. F:or this purpose two Low - pass filters are bunt by using two dimensional Fourier transformation. In the design principls of the filters, one must define the cut - off frequencies of the filters accurately as they are the important feature of the filters. In the procedure of the filters designed here, at first, several profiles were ta:ken on the Bouguer anomaly map for computing Bouguer profiles and then, by eixamining FourlPr spectrum of these profiles a iwave - numbers 1which separate the signal from noise were selected as a cut - off wave - numbers. Thus, after having been defined the cut - off wave number, the coefficient of the filters in the space domain iwere found by means of Fourier integral •w.hich has a property of circular symmetry. In order to check the validity of these coefficients for our purpose, the characteristics of the filters were also checked. by transforming the filtering functions into the domain of wave - number. The operation of the filti~rlng was completed by means of two dimensional convolutfon using the numeritical values of Bouguer and rule of Nyquist. As a result Of this filtering, the effects of shallOIW disturbing bodies (Which they have high wave - number) ' are filtered downward step by step retainning only lOIW changes of large mas.ses. Using filtered map III, sedimanter strafification of the basin of Tuz Golu is quantified up to the basement. By making use of methods of Tal'Wani and Morgan • Faessler, the depth of the sediments in the azea is 4 Km. North of Sultanham was calculated as 8 ·Km. in the direction from Northeast to Southwest.