Geophysics
Afsaneh Nasrabadi; Fateme Azimi; MohammadReza Sepahvand
Abstract
Crustal velocity structure and Moho discontinuity depth have investigated beneath 7 the broadband seismic stations, AFRZ, TKDS, TPRV, TNSJ, ANAR, KRSH of the Iranian Seismological Center (ISC) and YZKH of Iranian National Seismic Network (INSN) located in the center of Iran by joint inversion of receiver ...
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Crustal velocity structure and Moho discontinuity depth have investigated beneath 7 the broadband seismic stations, AFRZ, TKDS, TPRV, TNSJ, ANAR, KRSH of the Iranian Seismological Center (ISC) and YZKH of Iranian National Seismic Network (INSN) located in the center of Iran by joint inversion of receiver functions and Rayleigh waves group velocity dispersion. Three years (2012 to 2014) teleseismic waveforms (with epicentral distance 25o-90o) for computation receiver functions by iterative approach in time domain have been processed. The Rayleigh waves group velocity dispersion curves were incorporated into our joint inversion scheme from an independent surface wave tomography study. Receiver function is response of local structure of ground (located beneath the three–component broadband seismic station) to teleseismic P-wave, that is sensitive to seismic discontinuities. Since there is very little absolute-velocity information contained in the receiver function, its inversion for shear-wave velocity structure is non-unique (velocity-depth trade-off). On the other hand, dispersion curves are sensitive to the average velocity structure of the upper layers rather than to seismic discontinuities. So the non-uniqueness problem can be solved by combining receiver function inversion with surface-wave dispersion. Results from joint inversion in center of Iran indicates that Moho discontinuity depth depth beneath AFRZ, TKDS and TPRV stations is 40 Km, beneath TKDS 42 Km, beneath ANAR is 38 Km and beneath KRSH and YZKH stations are 44 Km. It was shown that the joint inversion method can cause ±2 kilometers of error. The average Moho depth is about 42±2 kilometers beneath center of Iran.
Geophysics
Abbas Gholamzadeh; Nasim Haydarpoor
Abstract
The main purpose of this paper is studying sedimentary layer in the Qeshm Island. We use aftershocks of 27 Nov. 2005 Qeshm Island (Mb=6.0), to perfume 2D tomography of Rayleigh waves. We have analyzed surface wave data for 856 aftershocks, consist 9821 waveforms. The dispersion curves are calculated ...
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The main purpose of this paper is studying sedimentary layer in the Qeshm Island. We use aftershocks of 27 Nov. 2005 Qeshm Island (Mb=6.0), to perfume 2D tomography of Rayleigh waves. We have analyzed surface wave data for 856 aftershocks, consist 9821 waveforms. The dispersion curves are calculated in the period range between 0.1 seconds and 10 seconds, which correspond to the shallow structures of uppermost crust including sedimentary layer. Surface wave tomography has also been performed to estimate the two-dimensional group velocity maps of Rayleigh waves in the region. The isolated surface wave fundamental modes by Herman and group velocities dispersion curves obtained by it, using Yanovskaya-Ditmar linear inversion method for estimation of 2D tomography maps. Based on the ray coverage, the area divided into cells with dimension 1 Km ×1 Km. in every cell and for distinct periods the velocities were calculated. The minimum dimension of distinct heterogeneities estimated as about 3 km. Low-velocity anomalies in tomography maps can be related to the accumulation of salt plugs and some soft sediment in the area. In periods up to 4 sec, which related to shallower depths, a distinct lineation observed that may relate to a fault. It seems that this fault has cut off the sediments. Into the deeper sediment, this fault disappeared which means the sediments were softer and unbreakable.
Z Mohammadipour; F Yaminifard; M Tatar
Abstract
Nearly one-third of the shortening in Iran plateau due to Arabia-Eurasia convergence is accommodated in the Zagros fold and thrust belt, which is seismically one of the most active regions among the continental collision zones in the world. Deploying a temporary seismic network in the north of Bandar ...
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Nearly one-third of the shortening in Iran plateau due to Arabia-Eurasia convergence is accommodated in the Zagros fold and thrust belt, which is seismically one of the most active regions among the continental collision zones in the world. Deploying a temporary seismic network in the north of Bandar Abbas in Hormozgan Province, which consisted of 32 three-component seismograph stations operating for a duration of about 3.5 months, provided appropriate data for studying the upper crustal structure of the easternmost Zagros by usingLocal Earthquake Tomography. Three dimensional velocity model obtained from the conversion of P-wave arrival times indicates southwestward overthrusting of the lower crust of northern parts, supporting active underthrusting of the Arabian plate beneath Central Iran in the easternmost Zagros. A very low velocity zone is also observed in the eastern part of the study area that could be associated with the Zendan-Minab-Palami fault system.
