Ambient noise Rayleigh wave tomography across the Madagascar island

SUMMARY The unusual complex lithospheric structure of Madagascar is a product of a number of important geological events, including: the Pan-African Orogeny, episodes of Late Cenozoic intraplate volcanism and several phases of deformation and metamorphism. Despite this rich history, its detailed crustal structure remains largely underexplored. Here, we take advantage of the recently obtained data set of the RHUM-RUM (Réunion Hotspot and Upper Mantle–Réunions Unterer Mantel) seismological experiment, in addition to previously available data sets to generate the first Rayleigh wave group velocity maps across the entire island at periods between 5 and 30 s using the ambient noise tomography technique. Prior to preliminary data preparation, data from Ocean Bottom Seismometers are cleaned of compliance and tilt noise. Cross-correlating noise records yielded over 1900 Rayleigh wave cross-correlation functions from which group velocities were measured to perform surface wave tomography. Dispersion curves extracted from group velocity tomographic maps are inverted to compute a 3-D shear velocity model of the region. Our velocity maps have shown relative improvement in imaging the three sedimentary basins in the western third of the island compared to those of previous studies. The Morondava basin southwest of the island is the broadest and contains the thickest sedimentary rocks while the Antsirinana basin at the northern tip is narrowest and thinnest. The lithosphere beneath the island is characterized by a heterogeneous crust which appears thickest at the centre but thins away towards the margins. A combined effect of uneven erosion of the crust and rifting accommodates our observations along the east coast. Average 1-D shear velocity models in six different tectonic units, support the causes of low velocity zones observed in the west coast of the island and reveal an intermediate-to-felsic Precambrian upper and middle crust consistent with findings of previous seismic studies. Our findings, especially at short periods provide new constraints on shallow crustal structure of the main island region.

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Short-Period Surface-Wave Tomography in the Continental United States—A Resource for Research

Seismological Research Letters ◽

10.1785/0220200462 ◽

2021 ◽

Author(s):

Robert B. Herrmann ◽

Charles J. Ammon ◽

Harley M. Benz ◽

Asiye Aziz-Zanjani ◽

Joshua Boschelli

Keyword(s):

United States ◽

Group Velocity ◽

Group Velocity Dispersion ◽

Upper Crust ◽

Data Set ◽

Regional Patterns ◽

Moment Tensors ◽

Velocity Models ◽

Short Period ◽

Wave Tomography

Abstract The variation of phase and group velocity dispersion of Love and Rayleigh waves was determined for the continental United States and adjacent Canada. By processing ambient noise from the broadband channels of the Transportable Array (TA) of USArray and several Program for the Array Seismic Studies of the Continental Lithosphere experiments and using some earthquake recordings, the effort was focused on determining dispersion down to periods as short as 2 s. The relatively short distances between TA stations permitted the use of a 25 km×25 km grid for the four independent tomographic inversions (Love and Rayleigh and phase and group velocity). One reason for trying to obtain short-period dispersion was to have a data set capable of constraining upper crust velocity models for use in determining regional moment tensors. The benefit of focusing on short-period dispersion is apparent in the tomography maps—shallow geologic structures such as the Mid-Continent Rift, and the Michigan, Illinois, Anadarko, Arkoma, and Appalachian basins are imaged. In our processing, we noted that the phase velocities were more robustly determined than the group velocities. We also noted that the inability to obtain dispersion at short periods shows distinct regional patterns that may be related to the local upper crust structure.

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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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Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography

Geophysical Journal International ◽

10.1093/gji/ggt309 ◽

2013 ◽

Vol 195 (2) ◽

pp. 1300-1313 ◽

Cited By ~ 9

Author(s):

Nicholas Harmon ◽

Mariela Salas De La Cruz ◽

Catherine Ann Rychert ◽

Geoffrey Abers ◽

Karen Fischer

Keyword(s):

Costa Rica ◽

Rayleigh Wave ◽

Ambient Noise ◽

Velocity Structure ◽

Shear Velocity ◽

Wave Tomography ◽

Rayleigh Wave Tomography

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3D crustal structure of the Ligurian Sea revealed by ambient noise tomography using ocean bottom seismometer data

10.5194/se-2021-55 ◽

2021 ◽

Author(s):

Felix Noah Wolf ◽

Dietrich Lange ◽

Anke Dannowski ◽

Martin Thorwart ◽

Wayne Crawford ◽

...

Keyword(s):

Group Velocity ◽

Ambient Noise ◽

Cross Correlation ◽

Time Windows ◽

Ocean Bottom ◽

Ocean Bottom Seismometer ◽

S Wave ◽

Noise Sources ◽

Ligurian Sea ◽

Velocity Models

Abstract. The Liguro-Provençal basin was formed as a back-arc basin of the retreating Calabrian-Apennines subduction zone during the Oligocene and Miocene. The resulting rotation of the Corsica-Sardinia block is associated with rifting, shaping the Ligurian Sea. It is still debated whether oceanic or atypical oceanic crust was formed or if the crust is continental and experienced extreme thinning during the opening of the basin. We invert velocity models using an amphibious network of seismic stations, including 22 broadband Ocean Bottom Seismometers (OBS) to investigate the lithospheric structure of the Ligurian sea. The instruments were installed in the Ligurian Sea for eight months between June 2017 and February 2018 as part of the AlpArray seismic network. Because of additional noise sources in the ocean, OBS data are rarely used for ambient noise studies. However, we attentively pre-process the data, including corrections for instrument tilt and seafloor compliance. We took extra care to exclude higher modes of the ambient-noise Rayleigh waves. We calculate daily cross-correlation functions for the LOBSTER array and surrounding land stations. Additionally, we correlate short time windows that include teleseismic earthquakes that allow us to derive surface wave group velocities for longer periods than using ambient noise only. Group velocity maps are obtained by inverting Green’s functions derived from the cross-correlation of ambient noise and teleseismic events, respectively. We then used the resulting 3D group velocity information to calculate 1D depth inversions for S-wave velocities. The shear-wave velocity results show a deepening of the Moho from 12 km at the southwestern basin centre to 20–25 km at the Ligurian coast in the northeast and over 30 km at the Provençal coast. We find no hint on mantle serpentinisation and no evidence for an Alpine slab, at least down to depths of 25 km. However, we see a separation of the southwestern and northeastern Ligurian Basin that coincides with the promoted prolongation of the Alpine front.

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Ambient noise cross-correlation observations of fundamental and higher-mode Rayleigh wave propagation governed by basement resonance

10.26686/wgtn.13818893.v1 ◽

2021 ◽

Author(s):

Martha Savage ◽

FC Lin ◽

John Townend

Keyword(s):

Rayleigh Wave ◽

Correlation Functions ◽

Rayleigh Waves ◽

Ambient Noise ◽

Cross Correlation ◽

Amplitude Ratio ◽

Sedimentary Basins ◽

Longitudinal Motion ◽

Resonance Frequencies ◽

Noise Cross Correlation

Measurement of basement seismic resonance frequencies can elucidate shallow velocity structure, an important factor in earthquake hazard estimation. Ambient noise cross correlation, which is well-suited to studying shallow earth structure, is commonly used to analyze fundamental-mode Rayleigh waves and, increasingly, Love waves. Here we show via multicomponent ambient noise cross correlation that the basement resonance frequency in the Canterbury region of New Zealand can be straightforwardly determined based on the horizontal to vertical amplitude ratio (H/V ratio) of the first higher-mode Rayleigh waves. At periods of 1-3 s, the first higher-mode is evident on the radial-radial cross-correlation functions but almost absent in the vertical-vertical cross-correlation functions, implying longitudinal motion and a high H/V ratio. A one-dimensional regional velocity model incorporating a ~ 1.5 km-thick sedimentary layer fits both the observed H/V ratio and Rayleigh wave group velocity. Similar analysis may enable resonance characteristics of other sedimentary basins to be determined. © 2013. American Geophysical Union. All Rights Reserved.

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Imaging the Nechako Basin, British Columbia, using ambient seismic noise1This article is one of a series of papers published in this Special Issue on the theme of New insights in Cordilleran Intermontane geoscience: reducing exploration risk in the mountain pine beetle-affected area, British Columbia.

Canadian Journal of Earth Sciences ◽

10.1139/e11-007 ◽

2011 ◽

Vol 48 (6) ◽

pp. 1038-1049 ◽

Cited By ~ 3

Author(s):

O.A. Idowu ◽

A.W. Frederiksen ◽

J.F. Cassidy

Keyword(s):

British Columbia ◽

Surface Wave ◽

Group Velocity ◽

Large Scale ◽

Green's Functions ◽

Green’S Functions ◽

Noise Analysis ◽

Sedimentary Basins ◽

Seismic Exploration ◽

Velocity Models

The Nechako Basin in British Columbia, Canada is suspected to have hydrocarbon potential. However, it has been a difficult basin to explore because of the presence of Tertiary volcanic outcrop. The volcanic outcrop makes the use of conventional seismic exploration methods difficult owing to a strong velocity inversion at its base. An alternative is the passive source method known as ambient noise surface wave tomography. The method, which examines the high-frequency surface wave field that is obtained from noise analysis, is sensitive to large-scale crustal structure and has been successfully applied to measuring the depths of sedimentary basins. Station-to-station Green’s functions within the basin were estimated by cross-correlating the vertical components of the seismic noise data recorded by 12 POLARIS (Portable Observatories for Lithosphere Analysis and Research Investigating Seismicity) and CNSN (Canadian National Seismgraph Network) seismic stations between September 2006 and November 2007. The resulting Green’s functions were dominated by Rayleigh waves. The dispersion characteristics of the Rayleigh waveforms were measured within the microseismic band. Inversion of the dispersion curves produced 1-D and 2-D thickness models and 2-D group velocity models for the Nechako Basin and its surrounding region. The velocity models indicate two low group velocity structures within the basin that might represent sedimentary packages, and some pockets of high-velocity zones that show the presence of volcanic rocks within and on the basin. The thickness models indicated the presence of about six different velocity layers, in which the average thickness of the basin and the crust are ∼4.8 and 30–34 km, respectively.

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Group velocity maps using subspace and Trans-dimensional inversions: ambient noise tomography in the Western part of Java, Indonesia

Geophysical Journal International ◽

10.1093/gji/ggz498 ◽

2019 ◽

Cited By ~ 1

Author(s):

Shindy Rosalia ◽

Phil Cummins ◽

Sri Widiyantoro ◽

Tedi Yudistira ◽

Andri Dian Nugraha ◽

...

Keyword(s):

Rayleigh Wave ◽

Group Velocity ◽

Ambient Noise ◽

Regularization Parameter ◽

Least Square ◽

Disaster Mitigation ◽

Wave Group ◽

Ambient Noise Tomography ◽

Waveform Data ◽

Subspace Optimization

Summary In this paper, we compare two different methods for group velocity inversion: iterative, least-squares subspace optimization, and probabilistic sampling based on the Trans-dimensional Bayesian method with tree-based wavelet parameterization. The wavelet parameterization used a hierarchical prior for wavelet coefficients which could adapt to the data. We applied these inversion methods for ambient noise tomography of the western part of Java, Indonesia. This area is an area prone to multiple geological hazards due to its proximity to the subduction of the Australia Plate beneath Eurasia. It is therefore important to have a better understanding of upper crustal structure to support seismic hazard and disaster mitigation efforts in this area. We utilized a new waveform dataset collected from 85 temporary seismometers deployed during 2016–2018. Cross-correlation of the waveform data was applied to retrieve empirical Rayleigh wave Green's functions between station pairs, and the spatial distribution of group velocity was obtained by inverting dispersion curves. Our results show that, although computationally expensive, the Trans-dimensional Bayesian approach offered important advantages over optimization, including more effective explorative of the model space and more robust characterization of the spatial pattern of Rayleigh wave group velocity. Meanwhile, the iterative, least-square subspace optimization suffered from the subjectivity of choice for reference velocity model and regularization parameter values. Our Rayleigh wave group velocity results show that for short (1–10 s) periods group velocity correlates well with surface geology, and for longer periods (13–25 s) it correlates with centers of volcanic activity.

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Crustal structures beneath the Eastern and Southern Alps from ambient noise tomography

10.5194/se-2019-177 ◽

2020 ◽

Author(s):

Ehsan Qorbani ◽

Dimitri Zigone ◽

Mark R. Handy ◽

Götz Bokelmann ◽

Keyword(s):

High Resolution ◽

Crustal Structure ◽

Ambient Noise ◽

Eastern Alps ◽

Southern Alps ◽

Ambient Noise Tomography ◽

Tauern Window ◽

Velocity Models ◽

Cross Correlations ◽

Velocity Anomalies

Abstract. We study the crustal structure under the Eastern and Southern Alps using ambient noise tomography. We use cross-correlations of ambient seismic noise between pairs of 71 permanent stations and 19 stations of the EASI profile to derive new high-resolution 3-D shear-velocity models for the crust. Continuous records from 2014 and 2015 are cross-correlated to estimate Green's functions of Rayleigh and Love waves propagating between the station pairs. Group velocities extracted from the cross-correlations are inverted to obtain isotropic 3-D Rayleigh and Love-wave shear-wave velocity models. Our high resolution models image several velocity anomalies and contrasts and reveal details of the crustal structure. Velocity variations at short periods correlate very closely with the lithologies of tectonic units at the surface and projected to depth. Low-velocity zones, associated with the Po and Molasse sedimentary basins, are imaged well to the south and north of the Alps, respectively. We find large high-velocity zones associated with the crystalline basement that forms the core of the Tauern Window. Small-scale velocity anomalies are also aligned with geological units such as the Ötztal and the Gurktal nappes of the Austroalpine nappes. Clear velocity contrasts in the Tauern Window along vertical cross-sections of the velocity model show the depth extent of the tectonic units and their bounding faults. A mid-crustal velocity contrast is interpreted as a manifestation of intracrustal decoupling in the Eastern Alps and decoupling between the Southern and Eastern Alps.

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