GRID SEARCH MODELING OF RECEIVER FUNCTIONS - IMPLICATIONS FOR CRUSTALSTRUCTURE IN THE MIDDLE-EAST AND NORTH-AFRICA

A grid search is used to estimate average crustal thickness and shear wave velocity structure beneath 12 three-component broadband seismic s tations in the Middle East, North Africa, and nearby regions. The crus tal thickness in these regions is found to vary from a minimum of 8.0 +/- 1.5 km in East Africa (Afar) region to possibly a maximum of 64 +/ - 4.8 km in the lesser Caucasus. Stations located within the stable Af rican platform indicate a crustal thickness of about 40 km. Teleseismi c three-component waveform data produced by 165 earthquakes are used t o create receiver function stacks for each station.. Using a grid sear ch, we have solved for the optimal and most simple shear velocity mode ls beneath all 12 stations. Unlike other techniques (linearized least squares or forward modeling), the grid search methodology guarantees t hat we solve for the global minimum within our defined model parameter space. Using the grid search, we also qualitatively estimate the leas t number of layers required to model the observed receiver functions' major seismic phases (e.g., PSMoho). A jackknife error estimation meth od is used to test the stability of our receiver function inversions f or all 12 stations in the region that had recorded a sufficient number of high-quality broadband teleseismic waveforms. Five of the 12 estim ates of crustal thicknesses are consistent with what is known of crust al structure from prior geophysical work. Furthermore, the remaining s even estimates of crustal structure are in regions for which previousl y there were few or no data about crustal thickness.