Near surface radial anisotropy in the Rigan area/SE Iran

This study presents a three‐dimensional (3D) model of the crustal and uppermost mantle shear wave velocity and radial anisotropy beneath the Iran Plateau constructed by Rayleigh and Love waves from ambient noise. We correlate three years of continuous seismic ambient noise data recorded in 98 stations to obtain cross correlation functions. Then, we measure Rayleigh (8–60 s) and Love (8–50 s) wave dispersion curves from these cross‐correlation functions to generate two‐dimensional dispersion maps using a fast marching surface tomography method. Finally, we build a quasi‐3D shear wave velocity and radial anisotropy model by jointly inverting Rayleigh and Love local phase velocity dispersion curves using a Bayesian Markov chain Monte Carlo inversion method. Observed radial anisotropy beneath Central Iran is weaker than adjacent areas. Negative radial anisotropy is observed in the shallow structures across our study region, which is most likely attributed to vertically aligned cracks in the upper crust. Strong positive radial anisotropy in the middle to the lower crust beneath the Zagros is imaged, which is associated with ductile shear zones in the crust. Radial anisotropy changes from positive values in the crust to negative values in the upper mantle beneath the Zagros, which may be evidence for the decoupling of the crust from the upper mantle beneath the Zagros.

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“…Shirzad et al. (2017) investigated near surface radial anisotropy in the Rigan area using ambient noise and earthquake data.…”

Section: Introductionmentioning

confidence: 99%

Crustal Radial Anisotropy of the Iran Plateau Inferred From Ambient Noise Tomography

et al. 2021

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“…It is locally focused near the Bolivian Orocline, with less shortening of the overriding plate to the north and south of the CAP. There has been a concerted effort to understand the response of the midcrust and lower crust to large crustal thicknesses resulting from tectonic shortening (e.g., Beaumont et al, , ; Chen et al, ; Cheng et al, ; Guo et al, ; Guo et al, ; Huang et al, ; Ling et al, ; Luo et al, ; Moschetti et al, ; Ojo et al, ; Pawlak et al, ; Royden et al, ; Shapiro et al, ; Shirzad et al, ; Shirzad & Shomali, ; Xie et al, ). In the Andes, numerous studies have suggested north–south crustal flow away from the regions with highest estimated shortening, near the Bolivian Orocline, to regions with less shortening (Eichelberger et al, ; Gerbault et al, ; Hindle et al, ; Husson & Sempere, ; Kley & Monaldi, ; McQuarrie et al, ; Oncken et al, ; Ouimet & Cook, ; Schepers et al, ; Yang et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…Anisotropy is seismically observable when the alignment of structures or mineral axes is pervasive and has a broadly organized orientation (e.g., Moschetti et al, ). We measure radial anisotropy in the crust through the determination of shear velocities from Rayleigh (sensitive to V sv ) and Love (sensitive to V sh ) waves (e.g., Bensen et al, ; Chen et al, ; Cheng et al, ; Guo et al, , ; Huang et al, ; Ling et al, ; Luo et al, ; Moschetti et al, ; Ojo et al, ; Pawlak et al, ; Shapiro et al, ; Shirzad et al, ; Shirzad & Shomali, ; Xie et al, ). By inverting both phases, we constrain radial anisotropy at depths with overlapping sensitivity.…”

Section: Introductionmentioning

confidence: 99%

Midcrustal Deformation in the Central Andes Constrained by Radial Anisotropy

et al. 2018

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The Central Andes are characterized by one of the largest orogenic plateaus worldwide. As a result, they are home to some of the thickest continental crust observed today (up to ~75‐km thick). Understanding the response of the crust to such overthickening provides insights into the ductile behavior of the midcrust and lower crust. One of the best tools for examining crustal‐scale features is ambient noise tomography, which takes advantage of the ambient noise wavefield to sample crustal depths in great detail. We extract Love and Rayleigh wave phase velocities from ambient noise data to invert for Vsh, Vsv, and radial anisotropy throughout the Central Andes. We capture detailed crustal structure, including pronounced along‐strike isotropic velocity heterogeneity and substantial (up to 10%) radial anisotropy that varies with depth. This crustal anisotropy may have several origins, but throughout the majority of the Central Andes, particularly beneath the Altiplano, we interpret radial anisotropy as the result of mineral alignment due to ductile crustal deformation. Only in the strongly volcanic Altiplano‐Puna Volcanic Complex is radial anisotropy likely caused by magmatic intrusions.

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“…During the convergence, the transitional crust of the Bay of Biscay was underthrusted southwards beneath the Iberian continental crust (e.g. Boillot et al, 1979;Fernández-Viejo et al, 2012;2017). The bulk of the deformation was mainly accommodated by East-West oriented reverse faults and thrusts, but there are numerous examples of the reworking and retightening of favourably oriented earlier Variscan thrusts and folds, with a different degree of development across the study area (e.g.…”

Section: Tectonic Historymentioning

confidence: 99%

Radial anisotropy and S-wave velocity depict the internal to external zones transition within the Variscan orogen (NW Iberia)

Acevedo

Fernández‐Viejo

Llana‐Fúnez

et al. 2021

Preprint

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Abstract. The cross-correlation of ambient noise records registered by seismic networks has proven to be a valuable tool to obtain new insights into the crustal structure at different scales. Based on 2- to 14-s-period Rayleigh and Love dispersion data extracted from the seismic ambient noise recorded by 20 three-component broadband stations belonging to two different temporary experiments, we present the first i) upper crustal (1–14 km) high-resolution shear wave velocity and ii) radial anisotropy variation models of the continental crust in NW Iberia. The area of study represents one of the best exposed cross-sections along the Variscan orogen of western Europe, showing the transition between the external eastern zones towards the internal areas in the west. Both the 2-D maps and an E-W transect reveal a close correspondence with the main geological domains of the Variscan orogen. The foreland-fold and thrust-belt of the orogen, the Cantabrian Zone, is revealed by a zone of relatively low shear wave velocities (2.3–3.0 km/s), while the internal zones generally display higher homogeneous velocities (> 3.1 km/s). The boundary between both zones is clearly delineated in the models, depicting the arcuate shape of the orogen grain. The velocity patterns also reveal variations of the bulk properties of the rocks that can be linked to major Variscan structures, such as the basal detachment of the Cantabrian Zone or the stack of nappes involving pre-Variscan basement; or sedimentary features such as the presence of thick syn-orogenic siliciclastic wedges. Overall, the radial anisotropy magnitude varies between −5 and 15 % and increases with depth. The depth pattern suggests that the alignment of cracks is the main source of anisotropy at < 8 km depths, although the intrinsic anisotropy seems to be significant in the West-Asturian Leonese Zone, the low-grade slate belt adjacent to the Cantabrian Zone. At depths > 8 km, widespread high and positive radial anisotropies are observed, caused by the presence of subhorizontal alignments of grains and minerals in relation to the internal deformation of rocks either during the Variscan orogeny or prior to it.

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Near surface radial anisotropy in the Rigan area/SE Iran

Cited by 20 publications

References 30 publications

Crustal Radial Anisotropy of the Iran Plateau Inferred From Ambient Noise Tomography

Crustal Radial Anisotropy of the Iran Plateau Inferred From Ambient Noise Tomography

Midcrustal Deformation in the Central Andes Constrained by Radial Anisotropy

Radial anisotropy and S-wave velocity depict the internal to external zones transition within the Variscan orogen (NW Iberia)

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