Least squares collocation method in Moho depth determination in Iran using gravity gradient data

In this study, an approach using gravity observations utilizing the Least Squares Collocation (LSC) method is developed with the aim of mapping the depth spatial variability of the Mohorovičić discontinuity. This approach is based on a spherical two-layer isostatic model where the exterior gravity field only varies because of the shifting topographic masses and the related isostatic adjustment since it is believed that the Earth's core has a uniform density distribution. Assuming mass conservation between the Moho column of height δ R with respect to R m representing the mean Moho and following a Helmert condensation approach, the relationship between the surface layer density to the potential δ T can be obtained and δ R can be estimated via LSC from observed values of any functional derived from δ T . With such approach, the depth of Moho in the Iranian Plateau is estimated from T r r data generated by GOCO06S model reduced by topography, bathymetry and sediments effects by considering GEBCO2021 and CRUST1.0 models. The needed a-priori assumptions on R m and the density contrast Δ ρ are tuned so to obtain the best fit with seismic Moho depths reported by literature. 73 stations were matched with 3 km of standard deviation, which is coherent with the expected accuracy of the benchmark values. The remaining greater discrepancies showed to be clustered in defined areas like the Zagros chain and the reliefs along the Caspian coastline and the East borders.

A recovered Moho model by integrated inversion of gravity and seismic depths in Iran

This research aims to define the depth of Moho in Iran by collocation method using gravimetric data with seismic information. The definition of the Moho in the Iranian region is of considerable importance due to the geological complexity of the area also characterized by tectonic and orogenic events of particular uniqueness. We applied the collocation method to Moho recovery using the gravity data generated by GOCO03S model reduced by topography/bathymetry, sediment and consolidated crust effects from CRUST1.0. These data have been complemented with seismic Moho depth estimates. A compilation of 213-points seismic depth has been collected over Iran and used in the integrated gravimetric-seismic inversion. Among them, 140 seismic points have been selected completely random and included as data in the integrated collocation approach for Moho depth estimation. The 73 remaining seismic points have been used as checking points for validating the estimated Moho. In the first run, gravity data only have been considered to collocation Moho recovery. When comparing this gravimetric solution with the 73 seismic checking points, a standard deviation of 6.2 km was found. In case of considering the regional seismic depths into the collocation approach, the standard deviation of the residuals between our results and seismic checking Moho depths improved to 4.9 km. It must be stated that, even in the integrated inversion, a significant discrepancy between the seismic and the integrated gravimetric-seismic Moho is present in the South Caspian Basin. Low quality of CRUST1.0 could explain this inconsistency in this area.

Seismic signature of the Alpine indentation, evidence from the Eastern Alps

The type of collision between the European and the Adriatic plates in the easternmost Alps is one of the most interesting questions regarding the Alpine evolution. Tectonic processes such as compression, escape and uplift are interconnected and shape this area. We can understand these ongoing processes better, if we look for signs of the deformation within the Earth's deep crust of the region. By collecting records from permanent and temporary seismic networks, we assemble a receiver function dataset, and analyze it with the aim of giving new insights on the structure of the lower crust and of the shallow portion of the upper mantle, which are inaccessible to direct observation. Imaging is accomplished by performing common conversion depth stacks along three profiles that crosscut the Eastern Alpine orogen, and allow isolating features consistently persistent in the area. The study shows a moderately flat Moho underlying a seismically anisotropic middle-lower crust from the Southern Alps to the Austroalpine nappes. The spatial progression of anisotropic axes reflects the orientation of the relative motion and of the stress field detected at the surface. These observations suggest that distributed deformation is due to the effect of the Alpine indentation. In the shallow upper mantle right below the Moho interface, a further anisotropic layer is recognized, extended from the Bohemian Massif to the Northern Calcareous Alps.