Surface wave tomography of the northern Canadian Cordillera using earthquake Rayleigh wave group velocities

ABSTRACT An understanding of mantle dynamics occurring beneath the Tibetan plateau requires a detailed image of its seismic velocity and anisotropic structure. Surface waves at long periods (>50 s) could provide such critical information. Though Rayleigh-wave phase velocity maps have been constructed in the Tibetan regions using ambient-noise tomography (ANT) and regional earthquake surface-wave tomography, Love-wave phase velocity maps, especially those at longer periods (>50 s), are rare. In this study, two-plane-wave teleseismic surface-wave tomography is applied to develop 2D Rayleigh-wave and Love-wave phase velocity maps at periods between 20 and 143 s across eastern and central Tibet and its surroundings using four temporary broadband seismic experiments. These phase velocity maps share similar patterns and show high consistency with those previously obtained from ANT at overlapping periods (20–50 s), whereas our phase velocity maps carry useful information at longer periods (50–143 s). Prominent slow velocity is imaged at periods of 20–143 s beneath the interior of the Tibetan plateau (i.e., the Songpan–Ganzi terrane, the Qiangtang terrane, and the Lhasa terrane), implying the existence of thick Tibetan crust along with warm and weak Tibetan lithosphere. In contrast, the dispersal of fast velocity anomalies coincides with mechanically strong, cold tectonic blocks, such as the Sichuan basin and the Qaidam basin. These phase velocity maps could be used to construct 3D shear-wave velocity and radial seismic anisotropy models of the crust and upper mantle down to 250 km across the eastern and central Tibetan plateau.

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Crustal structure of Khorasan (E-NE Iran) using the Rayleigh wave tomography

10.5194/egusphere-egu21-1186 ◽

2021 ◽

Author(s):

Maryam Rezaei ◽

Taghi Shirzad

Keyword(s):

Surface Wave ◽

Rayleigh Wave ◽

Global Network ◽

Fault System ◽

International Institute ◽

Surface Wave Tomography ◽

Crust And Upper Mantle ◽

Tectonic Zone ◽

Wave Tomography ◽

Ne Iran

<p>Classical surface wave tomography based on waveform scattering through seismic data has an important role in studying the structure of the Earth&#8216;s crust and upper mantle on regional and global scale. The shallow crustal velocity structure is studied using earthquake waveforms in Khorasan/E-NE Iran. For this purpose, 522 local recorded waveforms with M&#8805;4, which occurred between 53&#176;-63&#176;E and 30&#176;-42&#176;N, were selected. Therefore, all available vertical components of waveforms recorded at the stations in the Iranian Seismological Center (IrSC), the International Institute of Earthquake Engineering and Seismology (IIEES), and the IRIS global network collected in the period between January 2006 to October 2020. Then, some data selection criteria were applied for each waveform, including (i)SNR>4, (ii) the gap time less than 2 s within the expected signal window (1.5-4.5 km/s), (iii) epicentral distance greater than 20 km. The multiple-filter analysis technique was then applied by the computer program in seismology Hermann and Ammon (2013) to measure Rayleigh wave dispersion curves in the period range of 3-50 s. Finally, Rayleigh wave 2D horizontal group velocity maps are calculated by the fast marching surface wave tomography method. Our tomographic results indicate some local low velocity anomalies appeared in the W-NW of the study area where it connected with the East-Alborz tectonic structure. Also, the Doruneh Fault System clearly separates Kopeh-Dagh tectonic zone and Central Iran micro-plateau. However, a high velocity anomaly appears in Kopeh-Dagh tectonic zone at periods larger than 16 s and 30 s.</p>

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Source depopulation potential and surface-wave tomography using a crosscorrelation method in a scattering medium

Geophysics ◽

10.1190/1.3535443 ◽

2011 ◽

Vol 76 (2) ◽

pp. SA51-SA61 ◽

Cited By ~ 6

Author(s):

Pierre Gouédard ◽

Philippe Roux ◽

Michel Campillo ◽

Arie Verdel ◽

Huajian Yao ◽

...

Keyword(s):

Surface Wave ◽

Rayleigh Wave ◽

Group Velocity ◽

Mean Free Path ◽

Dispersion Curves ◽

Velocity Analysis ◽

Surface Wave Tomography ◽

Shallow Subsurface ◽

Active Source ◽

Wave Tomography

We use seismic prospecting data on a 40 × 40 regular grid of sources and receivers deployed on a 1 km × 1 km area to assess the feasibility and advantages of velocity analysis of the shallow subsurface by means of surface-wave tomography with Green’s functions estimated from crosscorrelation. In a first application we measure Rayleigh-wave dispersion curves in a 1D equivalent medium. The assumption that the medium is laterally homogeneous allows using a simple projection scheme and averaging of crosscorrelation functions over the whole network. Because averaging suppresses noise, this method yields better signal-to-noise ratio than traditional active-source approaches, and the improvement can be estimated a priori from acquisition parameters. We find that high-quality dispersion curves can be obtained even when we reduce the number of active sources used as input for the correlations. Such source depopulation can achieve significant reduction in the cost of active source acquisition. In a second application we compare Rayleigh-wave group velocity tomography from raw and reconstructed data. We can demonstrate that the crosscorrelation approach yields group velocity maps that are similar to active source maps. Scattering has an importance here as it may enhance the crosscorrelation performance. We quantify the scattering properties of the medium using mean free path measurements from coherent and incoherent parts of the signal. We conclude that for first-order velocity analysis of the shallow subsurface, the use of crosscorrelation offers a cost-effective alternative to methods that rely exclusively on active sources.

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Crust and upper mantle structures of the Makran subduction zone in south-east Iran by seismic ambient noise tomography

Solid Earth Discussions ◽

10.5194/sed-6-1-2014 ◽

2014 ◽

Vol 6 (1) ◽

pp. 1-34 ◽

Cited By ~ 4

Author(s):

M. Abdetedal ◽

Z. H. Shomali ◽

M. R. Gheitanchi

Keyword(s):

Surface Wave ◽

Rayleigh Wave ◽

Group Velocity ◽

Ambient Noise ◽

Surface Wave Tomography ◽

Seismic Ambient Noise ◽

Velocity Anomaly ◽

Empirical Green’S Functions ◽

Wave Tomography ◽

Cross Correlations

Abstract. We applied seismic ambient noise surface wave tomography to estimate Rayleigh wave empirical Green's functions from cross-correlations to study crust and uppermost mantle structure beneath the Makran region in south-east Iran. We analysed 12 months of continuous data from January 2009 through January 2010 recorded at broadband seismic stations. We obtained group velocity of the fundamental mode Rayleigh-wave dispersion curves from empirical Green's functions between 10 and 50 s periods by multiple-filter analysis and inverted for Rayleigh wave group velocity maps. The final results demonstrate significant agreement with known geological and tectonic features. Our tomography maps display low-velocity anomaly with south-western north-eastern trend, comparable with volcanic arc settings of the Makran region, which may be attributable to the geometry of Arabian Plate subducting overriding lithosphere of the Lut block. At short periods (<20 s) there is a pattern of low to high velocity anomaly in northern Makran beneath the Sistan Suture Zone. These results are evidence that surface wave tomography based on cross correlations of long time-series of ambient noise yields higher resolution group speed maps in those area with low level of seismicity or those region with few documented large or moderate earthquake, compare to surface wave tomography based on traditional earthquake-based measurements.

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Eurasian surface wave tomography: Group velocities

Journal of Geophysical Research Atmospheres ◽

10.1029/97jb02622 ◽

1998 ◽

Vol 103 (B3) ◽

pp. 4839-4878 ◽

Cited By ~ 269

Author(s):

Michael H. Ritzwoller ◽

Anatoli L. Levshin

Keyword(s):

Surface Wave ◽

Surface Wave Tomography ◽

Wave Tomography ◽

Group Velocities

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Observation and inversion of surface wave group velocities across central India

Bulletin of the Seismological Society of America ◽

10.1785/bssa0710051489 ◽

1981 ◽

Vol 71 (5) ◽

pp. 1489-1501

Author(s):

S. N. Bhattacharya

Keyword(s):

Surface Wave ◽

Rayleigh Wave ◽

Fundamental Mode ◽

Central India ◽

Inversion Method ◽

Bengal Basin ◽

Wave Group ◽

Crust And Upper Mantle ◽

Group Velocities ◽

Sedimentary Layer

abstract Surface wave group velocities across central India are measured from computer plots of frequency-time analysis using multiple-filter technique. Periods range from 5 to 56 sec for fundamental mode Rayleigh wave, 5 to 16 sec for first higher mode Rayleigh wave, and 5 to 49 sec for fundamental mode Love wave. The wave paths from Koyna earthquakes to Bokaro cross purely through the Peninsular Plateau. The group velocities for these paths are found to be similar to those of surface waves recorded at Poona from earthquake which lie to the northeast of Bokaro in sub-Himalayan regions. From this, it is concluded that the shield structure of the peninsula extends to the sub-Himalayan regions to northeast of the Peninsular Plateu with a negligible part of sedimentary layer. Group velocities of fundamental mode Rayleigh and Love waves are also obtained for the paths from Koyna earthquakes to Shillong and are found to be similar to the above-mentioned group velocities except at very low periods where group velocities are affected by the small part of each path through thick sedimentary layer of Bengal Basin. Northern limit of this basin sedimentary layer has been identified. Mean and standard deviation of observed group velocity at each period are obtained for each of Rayleigh fundamental, Rayleigh first higher, and Love fundamental modes. The group velocities closely agree with those obtained earlier for the path between New Delhi and Kodaikanal and are also found to be similar to those observed in some shield regions. Monte Carlo inversion method is applied and crust and upper mantle structure of the Indian Shield across central India is obtained. Crustal structure obtained shows a marked resemblance to the results obtained earlier through body wave study.

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