عنوان مقاله [English]
Iran is situated in one of the world's seismic regions and the possibility of destructive earthquakes in most regions of the country has given great significance to recognition of Iranian seismic nature from a seismic and seismotectonic standpoint. Study of the crust and upper mantle velocity structure in the Iranian plateau provides better understanding of its evolution and tectonic history of seismotectonic zones. Crustal velocity structure is used as initial information for various geological and geophysical studies, and therefore it is a basic and important issue in seismology. Receiver functions show Earth local structure response to P-wave vertical arrival approximately beneath of a three-component seismometer and are sensitive to shear-wave velocity impedance. Depth-velocity trade-off in RFs information is causing of inversion non-uniqueness problem, but one can overcome to this limitation by incorporating information from absolute velocity from dispersion estimations and joint inversion of this two data sets. By this, more exact constraints are provided about crustal structure. In this study, crustal velocity structure and Moho discontinuity depth beneath of four broadband stations of Kerman seismological network have been investigated from joint inversion of P-wave receiver functions (RFs) and Rayleigh wave group velocity dispersion. The teleseismic waveformes in time interval more than two years was used to compute RFs from the time domain iterative deconvolution procedure Ligorria and Ammon (1999) which has higher stability with noisy data compared to frequency-domain methods. The 165 desired RFs were computed from these waveforms that have magnitude bigger than 5.5 and have recorded at four permanent stations in epicentral distance 25˚-90˚. To delete high frequencies, Gaussian parameter 1.0 used. For increasing signal to noise ratio, RFs clustered in 10˚ azimuthal and less than 15˚ epicentral distance ranges. Finally, the RFs were stacked. This work performed under software SAC. Due to changes in group and phase velocity of surface waves with depth for different periods and dispersion in these waves and sensitivity of the waves dispersion curve to shear wave velocity, inversion of dispersion curve is an efficient method for determining the average shear wave velocity in a vast region of the depth between two seismic stations. Group velocity dispersion curves were incorporated into our joint-inversion scheme from an independent regional fundamental-mode Rayleigh waves tomography images for within the 20–80s period range in Iran by Rahimi et al. (2014). Joint inversion of two independent data sets was performed with considering combination weighting parameter appropriate performed from Herrmann and Ammon program (2003). Minimizing standard error between real and predicted data is the criteria for getting to desired final and close to earth real model.
The results from this study show that Moho discontinuity boundary is beneath of CHMN station at 52±2 km depth, beneath of KHGB station at 50±2 km depth, beneath of NGRK station at 54±2 km depth and beneath of TVBK station at 52±2 km depth. We used forward modeling test for error estimation and resulting models accuracy.
Relative high crustal thickness in this region compared to other regions of central Iran can be attributed to abut the region to the Sanandaj–Sirjan zone (SSZ) and Urumieh–Dokhtar magmatic assemblage (UDMA) that underthrusting of the Arabian plate beneath Central Iran along the main Zagros thrust fault is caused of thickening. It can also attributed to exist of thick Magma masses in Urumieh–Dokhtar magmatic assemblage and increase the density and relative thickness of the area based on the Isostasy theory.