receiver function

Crust velocity structure beneath two broadband seismic stations of Iran National Seismic Network (INSN), DAMV and THKV located in Central Alborz has been investigated by joint inversion of receiver function and Rayleigh wave phase and group velocity dispersion curves. The result suggests that Moho depth beneath the THKV and DAMV stations are 50-51 km and 52-54 km, respectively. Beneath the THKV station, there is a thin layer of very low-velocity materials at the surface and a sedimentary layer having a thickness of 10-12 km above a crystalline crust with a thickness of 34 km. Beneath the DAMV station, there is a thin sedimentary layer of low velocity with a thickness of 3-4 km, and also, a velocity change from 3.2 to 3.6 km/s at the depth of 14-16 km, indicating a discontinuity, which might be attributed to the border between the upper and lower crusts. The average Moho depth on the southern edge of Central Alborz is 52±2 km.

Crustal velocity structure in the Western Alborz have been investigated using joint inversion of receiver functions and Rayleigh wave group velocity dispersion curves. To determine the receiver functions, time domain iterative deconvolution and teleseismic events, which are recorded at five broadband seismic stations of the Iranian Seismological Center (IRSC), were used. The fundamental mode Rayleigh wave group velocity dispersion curves were provided by the study on the structure of crust and upper mantle of the Iranian Plateau. The results show that the average thickness of the crust in the southern margin of the Caspian Sea beneath of the CSN1 and RST1 stations is 38 km. Toward south, the depth of Moho increases up to 52, 54 and 50 km beneath the QALM, QCNT and QSDN stations. The low thickness of the crust in the southern shore of the Caspian Sea indicates that the Caspian crust is thin. Moreover, the moderate thickness of the crust in western Alborz, which is not in balance with its elevation, indicates the lack of root in Alborz.

Seismic velocity changes and shear wave anisotropy analysis can provide insights into deep structures. In multi-layered structures, cosine moveout pattern of radial component is observed for converted Ps phase. The method to calculate anisotropy parameters in layered structures has been developed by Ruempker et al. (2014). Some seismic stations do not have enough coverage in some azimuths, and we can split parameters (φ, δt) by fitting the best curve on Ps arrivals using the grid-search method. In this study, using synthetic data, the effect of the azimuth coverage is investigated and the sensibility of the results is also examined.

Summary: Crustal velocity structure beneath four broadband seismic stations located in northeast of Iran, including Shahrood (SHRO) and Maraveh Tappeh (MRVT) stations set up by Iran National Seismic Network (INSN) and Sabzevar (SZBV) and Jarkhoshk (JRKH) stations set up by Iranian Seismology Center (IRSC), have been investigated by joint inversion of P receiver function and Rayleigh wave phase and group velocity dispersion curves. A three-year teleseismic data (2012 -2014) with epicentral distance of 25o-90o and magnitude more than 5.5 have been used to determine the receiver functions by iterative deconvolution in time domain proposed by Ligorria and Ammon (1999). Iterative deconvolution in time domain to determine the receiver functions are more stable with noisy data in comparison to frequency domain. The fundamental mode of Rayleigh wave group and phase velocity dispersion curves have been provided by the study on the structure of crust and upper mantle of the Iranian Plateau for the period interval of 10-100 seconds made by Rahimi (2010). A combined inversion of body wave receiver functions and Rayleigh wave velocities increases the uniqueness of the solution over the separate inversions, and also, facilitates explicit parameterization of the layer thickness in the model space. Moho discontinuity depth is one of the most important parameters for investigation of crustal structure. The results of this study indicate an average crustal thickness varying from 38 km beneath Maraveh Tappeh (MRVT) station in north of the study region up to 44 km beneath Shahrood (SHRO) station in west of the region. Moreover, the results of this study suggest that the average crust thickness beneath Sabzevar (SZBV) and Jarkhoshk (JRKH) stations located in center and east of the study region is 40 km. In general, northeastern Iran region has a thin crust compared to the crusts in the other areas investigated in this research work. It has also been shown that the joint inversion method can cause ±2 kilometers of error.
Introduction: 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. The seismicity within Iran suggests that much of the deformation is concentrated in the Zagros, Alborz and Koppeh Dagh mountains, and in east of Iran, surrounding Central Iran and the Lut desert. The aim of this research is to study the crustal structure and Moho discontinuity of northeastern Iran region, Binalood mountains and Koppeh Dagh by the analysis of receiver function and surface waves dispersion.

Methodology and Approaches: Receivers functions are time series obtained from three-component seismometers, and are created by deconvolving the vertical component from the radial and transverse components of the seismogram to isolate the receiver site effects from the other information contained in a teleseismic P and S wave. The depth-velocity trade-off in receiver function causes nonuniqueness in the inverse problem. However, by incorporating information of absolute shear wave from dispersion estimates and joint inversion of these two datasets, this shortcoming can be compromised. To determine the receiver functions, we have used iterative deconvolution in time domain, proposed by Ligorria and Ammon (1999) that is more stable with noisy data in comparison to frequency domain. We have processed teleseismic events with epicentral distance of 25o-90o and magnitudes more than 5.5 that are recorded at a three-year time interval of 2012 to 2014. We have set the parameter a of the Gaussian filter to 1.00, which gives an effective high frequency limit of about 0.5 in the P wave. In order to eliminate the source, path and instrument effects, deconvolution of the vertical component from the horizontal components of the seismograms has been used. All receiver functions have been grouped by azimuth (<10◦) and distance (<15◦), and in order to improve the signal-to-noise ratio, the individual receiver functions within each group have been stacked. The fundamental mode of the Rayleigh wave group and phase velocities dispersion curves have been provided from the study carried out by Rahimi et al., (2014) on the structure of crust and upper mantle of the Iranian Plateau for the period interval of 10-100 seconds. Joint inversion of two independent data sets has been performed by considering appropriate weighting parameter obtained from Herrmann and Ammon program (2003). Minimizing standard error between real and predicted data is the criteria for getting the desired final and close to the earth real model. The inversion package requires that the real velocity structure is represented by a set of flat-lying, homogeneous, isotropic velocity layers. The starting model comprises of the layers having 1-km thick as the top 6 km of the model space, 2-km thick between the depths of 6 and 66 km, and 4 km thick between the depths of 66 and 78 km. The starting velocity for each layer in the model has been Vp=8.0 km/s, which equates to upper mantle velocity.

Results and Conclusions: The results of this study suggest that the average crust thickness beneath Shahrood (SHRO) station, located in west of the study region is 44 km and the average crust thickness beneath Sabzevar (SZBV) and Jarkhoshk (JRKH) stations located in center and east of the study region is 40 km. Furthermore, the crust thickness beneath Maraveh Tappeh (MRVT) station located in north of Koppeh Dagh region in is 38 km. In general, northeastern Iran region has a thin crust compared to the crust in other areas of northeast of Iran.

We analyzed the teleseismic data gathered by a broad-band (CHBR) and four short-period (CDK, CNT, KHB, KSM) seismometers, located in western coastal Makran, north of Chabahar, Iran. The data were gathered by the roughly north-south direction quasi-linear profile and used to calculate P (for all stations) and S (only for CHBR) receiver functions utilizing iterative deconvolution technique of Ligorria and Ammon (1999). Because of backazimuth gaps in south and western directions, we used PKiKP and Pdiff phases to calculate receiver functions in a similar processing approach. Calculated P receiver functions are migrated to depth to clarify the geometry of velocity boundaries at the base of sediments and Moho. The result shows that there is a dipping interface lying at a depth of 27 km (beneath CHBR) to 31 km (beneath CDK), which imply a 2.5o dipping Moho boundary beneath the study region. To avoid the trade-off between velocity model and reported depth, we jointly modeled the stacked receiver function, and group velocity dispersion curve for CHBR and the output model was considered for any time to depth migration of receiver functions.
We analyzed the effects of P and S anisotropy on teleseismic converted waves to map the presence, the strike, and the depth of anisotropic structures. High-resolution PRFs are considered for such analysis. The following criteria are considered to select the high-quality receiver function (Schulte-Pelkum and Mahan, 2014): the signal-to-noise ratio of the three components of the seismograms is at least 1.5; the convolution of the PRF with the vertical component of the seismogram reproduces at least 60% of the horizontal component (defined as variance reduction by Ligorria and Ammon, 1999); the PRF shows a positive polarity direct P arrival; the receiver function amplitude does not exceed 1; any arrivals’ pulse length does not exceed 3.5 s. The latter two criteria are employed because very high amplitudes and long oscillatory pulses are typical characteristics of an unstable deconvolution (Schulte-Pelkum and Mahan, 2014). The calculated PRFs were then binned in 5° azimuthal groups with 5° overlap. In CHBR station, we recognized signs of the top (at 1 km depth) and bottom (at 9 km depth) of an anisotropic layer with almost north-south anisotropic symmetry axis. In addition, we recognized a flat interface beneath CHBR station at 27 km depth that is not in consistency with the result of migration to a depth of RFs showing a 2.5o dip Moho at the same place. For this reason, we utilize forward modelling to calculate synthetic PRFs to explain periodic amplitude variation of P to S converted phases with back-azimuths in each station that could be a signature for anisotropic velocity features. The forward modeling indicates that the horizontal interface makes a similar pattern on simulated PRfs as a low angle dipping interface with dip less than 10o.
Migration of S receiver functions reveals a deep velocity discontinuity at depth around 80 to 100 km that might be considered as a shallow lithosphere-asthenosphere boundary beneath the study region.

Iran is one of the seismically active areas of the world because it is located in the Alpine-Himalayan orogenic belt, at a 1000-km-wide zone of the compression between the colliding Eurasian and Arabian continents. Studying the crust velocity structure and Moho discontinuity in Iranian plateau is conducive to an understanding of its evolution and the tectonic history of its seismotectonic zones. Nowadays, it is indispensable to acquire sufficient and accurate data from the crust and upper mantle velocity structure or its specification.
To specify the receiver functions with an iterative approach, we made use of a two-year teleseismic data (with epicentral distance 25o-90o) recorded by six seismic stations located in the southeast Zagros (BNDS, NIAN and GENO), Makran (CHBR) and eastern Iran (SZD1 and ZHSF) . In order to delete high frequencies, Gaussian parameter 1.0 was used. So as to augment the signal to noise ratio, RFs were clustered in 10˚ azimuthal and less than 15˚ epicentral distance ranges. Finally, the RFs were stacked.
Receiver functions (RFs) show Earth’s local structure response to P-wave vertical arrival approximately beneath a three-component seismometer; these functions are sensitive to shear-wave velocity impedance. Depth-velocity trade-off in RFs information poses inversion non-uniqueness issues, but a combined inversion of receiver functions and surface wave dispersion increases the uniqueness of the solution over separate inversions, further facilitating the explicit parameterization of layer thickness in the model space, providing more exact constraints as to the crustal structure. Surface wave velocity dispersion depends more on S wave velocity than on P wave velocity, and its dependence on density is slight. In previous studies, it has been shown that it improves the inversions of receiver functions for crustal structures (Julia et al. 2000). Surface wave velocity dispersion provides information as to the absolute seismic shear velocity, yet is relatively insensitive to sharp velocity changes. The group velocities were incorporated into our joint inversion scheme from an independent surface wave tomography study by Rham (2009). Group velocities from regional events, recorded at permanent and broadband stations, were measured for fundamental mode Rayleigh waves within 10–100s period range. The region was parameterized using a uniform, 1×1°, grid of constant slowness cells. The dispersion curve is the result of separate tomographic imaging for each period. Fundamental mode Rayleigh wave group velocities are taken from the corresponding tomographic cell containing the stations. The joint inversion of the two independent data sets was performed considering a proper combination of weighting parameters done by Herrmann and Ammon’s program (2003). Minimizing the standard error between the real and predicted data is the criterion for the desired final model which is close to Earth’s real model.
Models resulting from joint inversion in the south-east Zagros (Hormozgan province) suggest that Moho discontinuity depths beneath BNDS, GENO and NIAN stations are about 54, 54 and 48 kilometers, respectively, while the average depth of Moho discontinuity in the region is about 52±2 kilometers. In the Makran’s seismotectonic state, the resulted models pertaining to single station in the region (CHBR, near the city of Chabahar) show that the average depth of Moho discontinuity in this region is about 28 kilometers and thickness of the sediments is about 10 km, consistent with the shallow subduction of a high-velocity oceanic crust of Arabian plate beneath the southern side of Makran. In the Flysch zone (eastern Iran), the models of the two stations (SZD1, ZHSF) show that the average depth of Moho is about 40±2 kilometers.

Summary In this study, crustal velocity structure beneath two broadband seismic stations of Iran National Seismic Network (INSN), Ashtian-Arak (ASAO) and Naein (NASN) located in northwest of the Central Iran seimotectonic zone near the Ashtian and Nain cities have been investigated by joint inversion of P receiver function and of Rayleigh wave phase and group velocity dispersion curves. To determine the receiver functions, we have used iterative deconvolution in time domain proposed by Ligorria and Ammon (1999). which is more stable with noisy data in comparison to frequency domain. The fundamental mode Rayleigh wave group and phase velocities dispersion curves have been provided by the study of Rahimi et al. (2014) on the structure of crust and upper mantle of the Iranian Plateau for the period interval of 10-100 sec. The result of this study suggests that Moho discontinuity depth beneath Ashtian-Arak station (ASAO is 50 ± 2 km and beneath Naein station (NASN), it is 56 ± 2 km. Relative high crustal thickness beneath NASN station in comparison 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). It can also attributed to the existence of thick Magma masses in Urumieh– Dokhtar magmatic assemblage and increase of the density and relative thickness of the area based on the isostasy theory. The average Moho depth in northwest edge of Central Iran is 53 ±2 km.
Introduction Iran is situated in one of the world seismic regions and the possibility of occurring destructive earthquakes in most regions of the country has given a great significance to recognition of Iranian seismic nature from a seismotectonic standpoint. The seismicity within Iran suggests that much of the deformation is concentrated in the Zagros, Alborz and Kopeh Dagh mountains, and also, in east Iran, surrounding Central Iran and the Lut desert, which are virtually aseismic and behave as relatively rigid . The aim of this research is the study of the crustal structure and Moho discontinuity of the northwest of the Central Iran from analysis of receiver function and surface waves dispersion.
Methodology and Approaches Receiver functions are the response of the local earth structure to the near-vertical arrival of p waves under a threecomponent seismogram and are susceptible to shear wave velocity contrasts. The depth-velocity trade-off in receiver function causes non-uniqueness in the inverse problem. However, by incorporating information of absolute shear wave from dispersion estimates and joint inversion of these two datasets, this shortcoming can be compromised. In this study, crustal velocity structure beneath two broadband seismic stations of INSN, i.e. ASAO and NASN located in northwest of the Central Iran seimotectonic zone near the Ashtian and Nain cities have been investigated by joint inversion of P receiver function and of Rayleigh wave phase and group velocity dispersion curves. To determine the receiver functions, we use iterative deconvolution in time domain proposed by Ligorria and Ammon (1999) which is more stable with noisy data in comparison with frequency domain and teleseismic events with source-receiver great circle paths larger than 30° and smaller than 90° with magnitudes more than 5.0 that are recorded at time period of 2009 to 2013. The 210 desired RFs have been recorded at two permanent stations. To remove high frequencies, Gaussian parameter 1.0 has been used. In order to eliminate the source, path and instrument effects, deconvolution of the vertical component from the horizontal components of the seismograms is used. For increasing signal to noise ratio, RFs have been clustered in 20˚ azimuthal and less than 15˚ epicentral distance ranges. Finally, the RFs are stacked. The fundamental mode Rayleigh wave group and phase velocities dispersion curves have been provided by the study of Rahimi et al. (2014) on the structure of crust and upper mantle of the Iranian Plateau for the period interval of 10-100 sec. In this way, more accurate information about the crustal structure can be obtained. Joint inversion of two independent data sets has been performed by considering combination of appropriate weighting parameter 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.
Results and Conclusions The result of this study suggests that Moho discontinuity depth beneath ASAO is 50 ± 2 km and beneath NASN is 56 ± 2 km. Relative high crustal thickness beneath NASN station in comparison 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). It can also attributed to existence of thick Magma masses in Urumieh–Dokhtar magmatic assemblage and increase the density and relative thickness of the area based on the isostasy theory. The average Moho depth in northwest edge of Central Iran is 53 ± 2 km.

Crustal velocity structure of a seismically active region such as the Alborz located in North of Iran has a great influence on the precise location of earthquakes, attributing the seismicity to the active faults, and improving the reliability of the seismic hazard assessment. In spite of several researches carried out on the Central Alborz crustal structure, very little is known about the structure and thickness of the crust beneath the Western Alborz which is significant due to occurrence of the 1990 Manjil-Tarom earthquake with Ms = 7.3. In this study, we intend to examine the thickness and structure of the crust beneath three stations of Zanjan, Roudbar and Ghazvin located in Western Alborz by joint inversion of the receiver functions and Rayleigh wave group velocity dispersion measurements. A combined inversion of Rayleigh wave group velocities and body wave receiver functions increases the uniqueness of the solution over separate inversions and also facilitates explicit parameterization of layer thickness in the model space. The time-domain iterative deconvolution procedure, which has higher stability with noisy data compared to frequency-domain methods, is employed to deconvolve the vertical component of the teleseismic P waveforms from the corresponding horizontal components and obtain radial and transverse receiver functions for two broadband stations of ZNJK and RUD, and one short-period station of GZV. The waveforms were corrected from the instrument response before proceeding with the receiver function deconvolution. High frequencies were filtered using a Gaussian filter, at 2.5, 1.6, and 1.0, giving an effective high-frequency limit of about 1.2, 0.8 and 0.5 Hz, respectively. As the structure may vary with azimuth and with epicentral distance, all the observations were grouped by azimuth (< 10°) and distance (Δ < 10°). To increase the signal-to-noise ratio of the deconvolved traces, the individual receiver functions were aligned according to the P-wave arrival and point-to-point stacked waveforms. The stacked receiver function was then allocated an average slowness and the back-azimuth of every event was included in the stack. Rayleigh wave group velocity dispersion came from tomographic images in a time period between 10 s and 70 s produced by a study of regional fundamental modes of Rayleigh waves propagating across Iran and surrounding regions. Fundamental-mode Rayleigh wave group velocities to each stations were taken from the corresponding tomographic cell containing the station. The results show that the crust beneath the Roudbar station has a thickness of 36 ±3 km. A shallow low velocity sedimentary layer, of about 4 km thickness, and a velocity discontinuity at a depth of ~12 km is observed in the crustal model of this station. Beneath the Zanjan Station, the Moho depth varies from 38 to 42 km. The same sedimentary layer as beneath the Roudbar station and an interface at about 15 km depth are observed. Toward east, beneath the Ghazvin station, the thickness of the crust increases up to 52 km which is close to that proposed for the crust of the Central Alborz. Our seismological results show that the Western Alborz has a moderate crustal root but of insufficient thickness to compensate the elevation of the range.

Crustal structure of the Iranian plateau which is located between two convergent Arabian and Eurasian plates is studied. Teleseismic earthquakes recorded by broad band stations of Iranian National Seismic Network (INSN) are used to compute the receiver functions for each station. Rayleigh wave phase velocity dispersion curves were estimated employing two-station methods for all possible station pair of the above mentioned seismic network. A combined inversion of Rayleigh wave phase velocities and body wave receiver functions increases the uniqueness of the solution over separate inversions and also facilitates explicit parameterization of layer thickness in the model space. Our result indicates the crustal thickness differs from a minimum of 40 ±2 km in southeast of Iran, (ZHSF) to a maximum of 56 ±2km beneath the Sanandaj-Sirjan zone (SNGE). We observe a crustal thickness of 47 ±2km beneath the central Zagros (GHIR) to 52 ±2km below the eastern most of Zagros (BNDS), then to 47 ±2km beneath the northwestern part of the Zagros (SHGR). Crust of the Central Iran (KRBR) has a thickness of 48 ±2 km while the average Moho depth in southern parts of the Central Alborz (DAMV and THKV stations) is 54±2km. Our analysis shows a thinning of the crust to 43 ±2 km beneath the northwest of Iran (MAKO) and western part of the Caspian basin (GRMI).