Azimuthally anisotropic ambient-noise tomography using the AlpArray seismic network

2020 ◽  
Author(s):  
Emanuel Kästle ◽  
Irene Molinari ◽  
Lapo Boschi ◽  
AlpArray Working Group
Keyword(s):  
Phase Velocity ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Sedimentary Basins ◽  
Shear Velocity ◽  
Velocity Model ◽  
Azimuthal Anisotropy ◽  
Seismic Network ◽  
Fast Axis ◽  
Noise Field

<p>We make use of the AlpArray Seismic Network to study the properties of the ambient-noise field and create a new 3D shear-velocity model of the Alpine crust. The latter will be used to improve our understanding of the tectonic processes that formed the Alps.</p><p>From two years of data, more than 150,000 station-station cross-correlations are extracted and used to evaluate strength and directivity of the noise field and its seasonal variations. Phase-velocity measurements for both Love and Rayleigh waves are obtained and the anisotropic phase-velocity structure is imaged. At mid-crustal levels, the strongest azimuthal anisotropy is found underneath the northern Italian Po plain and in the northern Dinarides, with strengths of 10-20% and a fast axis direction pointing NNE in Italy and NE in the Dinarides. In the western and central Alps we find an approximately NE direction and a strength of 5%; the eastern Alpine fast axis point toward the north with strengths of 2-5%.</p><p>We apply a probabilistic inversion to resolve the 3D shear-velocity structure of the crust. The homogeneous and dense station setup results in a shear-velocity model of unprecedented resolution for the uppermost 60 km of the crust underneath the entire orogen. By using data in the period range between 2 and 100s, we are able to better constrain shallow structures, such as the sedimentary basins, and to link surface-geological features to velocity variations observed at depth.</p>

scholarly journals Three-dimensional shear velocity structure of the Mauleon and Arzacq basins (Western Pyrenees)

2021 ◽  
Author(s):  
Maximilien Lehujeur ◽  
Sébastien Chevrot ◽  
Antonio Villaseñor ◽  
Emmanuel Masini ◽  
Nicolas Saspiturry ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Hanging Wall ◽  
Three Dimensional ◽  
Sedimentary Basins ◽  
Shear Velocity ◽  
Velocity Model ◽  
Tomographic Images ◽  
Reflection Seismic ◽  
Local Earthquake Tomography ◽  
Local Earthquake

We present a 3-D shear wave velocity model of the Mauleon and Arzacq basins from the surface down to 10~km depth. This model is obtained by inverting phase velocity maps for periods from 2 to 9~s measured on coherent surface wavefronts extracted from ambient seismic noise by matched filtering. This new model, which is found in good agreement with local earthquake tomography, reveals the architecture of the Mauleon and Arzacq basins which were poorly imaged by conventional reflection seismic data. Combining these new tomographic images with surface and subsurface geological information allows us to trace major orogenic structures from the basement to the surface. In the basin, the models are successfully imaging first-order folds and thrusts at kilometric scale. The velocity structure within the basement and its geometrical relationship with the base of inverted rift basins supports a progressive northward exhumation of deep crustal and mantle rocks in the hanging wall of north-vergent Pyrenean thrusts. Our tomographic models image in 3-D orogen-perpendicular structures responsible for crustal segmentation as the Saison and Barlanes transfer zones. We propose that these steep structures consist in tear faults that accommodate the deepening of the Mauleon basin basement from west to east. To the west, this basement made of former hyper-extended rift domains (including mantle rocks) is anomalously sampled within the hanging-wall of north-directed orogenic thrusts, explaining its shallow attitude and its best preservation in comparison to the eastern segment of the study area. Eastward, the vertical shift of the basement makes that the former Mauleon basin hyper-extended rift basement remained in a footwall situation in respect of orogenic thrust and was underthrust. The comparison of the tomographic models obtained with surface wave tomography and local earthquake tomography shows that each approach has its own advantages and shortcomings but also that they are very complementary in nature, which would suggest to combine them in joint inversions to further improve passive imaging of the shallow crust and sedimentary basins.

scholarly journals High-resolution 3D shallow crustal structure in Long Beach, California: Application of ambient noise tomography on a dense seismic array

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. Q45-Q56 ◽  
Author(s):  
Fan-Chi Lin ◽  
Dunzhu Li ◽  
Robert W. Clayton ◽  
Dan Hollis
Keyword(s):  
Phase Velocity ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Seismic Array ◽  
Clear Correlation ◽  
Long Beach ◽  
Ambient Noise Tomography ◽  
Station Pair ◽  
Dense Seismic Array

Ambient noise tomography has proven to be effective in resolving shallow earth structure. We applied ambient noise tomography on a dense seismic array in Long Beach, California. The array was composed of more than 5200 stations with an average spacing close to 100 m. Three weeks of passive ambient noise were crosscorrelated between each station pair, which resulted in more than 13.5 million crosscorrelations within the area. Clear fundamental-mode Rayleigh waves were observed between 0.5 and 4 Hz, which were most sensitive to structure above 1-km depth. For each station pair, we applied frequency-time analysis to determine the phase traveltime dispersion, and, for each frequency, we applied eikonal tomography to determine the Rayleigh wave phase velocity map. The eikonal tomography accounted for ray bending by tracking the wavefront and allowed uncertainties to be estimated through statistical analysis. The compilation of phase velocity maps was then used to invert for 3D shear velocity structure. The inverted model showed clear correlation with the known geologic features such as the shallow south–north velocity dichotomy and a deeper fast anomaly associated with the Newport-Inglewood fault zone. Our results can potentially be used to complement traditional active source studies.

scholarly journals Shear velocity structure of the Northland Peninsula, New Zealand, inferred from ambient noise correlations

2021 ◽  
Author(s):  
Y Behr ◽  
John Townend ◽  
S Bannister ◽  
Martha Savage
Keyword(s):  
New Zealand ◽  
Love Wave ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Receiver Function ◽  
Shear Velocity ◽  
Moho Depth ◽  
Noise Correlation ◽  
Linear Pattern ◽  
Noise Field

Ambient noise correlation has been successfully applied in several cases to regions with dense seismic networks whose geometries are well suited to tomographic imaging. The utility of ambient noise correlation-based methods of seismic imaging where either network or noise field characteristics are less ideal has yet to be fully demonstrated. In this study, we focus on the Northland Peninsula of New Zealand using data from five seismographs deployed in a linear pattern parallel to the direction from which most of the ambient noise arrives. Shear wave velocity profiles computed from Rayleigh and Love wave dispersion curves using the Neighborhood Algorithm are in good agreement with the results of a previous active source refraction experiment and a teleseismic receiver function and surface wave analysis. In particular, we compute a path-averaged Moho depth of ̃28 km along a ̃250 km profile. The use of both Rayleigh and Love wave measurements enables us to estimate the degree of radial anisotropy in the crust, yielding values of 2-15%. These results demonstrate that ambient noise correlation methods provide useful geophysical constraints on lithospheric structure even for nonoptimal network geometries and noise field characteristics. © 2010 by the American Geophysical Union.

scholarly journals Shear velocity structure of the Northland Peninsula, New Zealand, inferred from ambient noise correlations

2021 ◽  
Author(s):  
Y Behr ◽  
John Townend ◽  
S Bannister ◽  
Martha Savage
Keyword(s):  
New Zealand ◽  
Love Wave ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Receiver Function ◽  
Shear Velocity ◽  
Moho Depth ◽  
Noise Correlation ◽  
Linear Pattern ◽  
Noise Field

Ambient noise correlation has been successfully applied in several cases to regions with dense seismic networks whose geometries are well suited to tomographic imaging. The utility of ambient noise correlation-based methods of seismic imaging where either network or noise field characteristics are less ideal has yet to be fully demonstrated. In this study, we focus on the Northland Peninsula of New Zealand using data from five seismographs deployed in a linear pattern parallel to the direction from which most of the ambient noise arrives. Shear wave velocity profiles computed from Rayleigh and Love wave dispersion curves using the Neighborhood Algorithm are in good agreement with the results of a previous active source refraction experiment and a teleseismic receiver function and surface wave analysis. In particular, we compute a path-averaged Moho depth of ̃28 km along a ̃250 km profile. The use of both Rayleigh and Love wave measurements enables us to estimate the degree of radial anisotropy in the crust, yielding values of 2-15%. These results demonstrate that ambient noise correlation methods provide useful geophysical constraints on lithospheric structure even for nonoptimal network geometries and noise field characteristics. © 2010 by the American Geophysical Union.

scholarly journals A 3-D shear velocity model of the southern North American and Caribbean plates from ambient noise and earthquake tomography

Solid Earth ◽  
2015 ◽  
Vol 6 (1) ◽  
pp. 271-284 ◽  
Author(s):  
B. Gaite ◽  
A. Villaseñor ◽  
A. Iglesias ◽  
M. Herraiz ◽  
I. Jiménez-Munt
Keyword(s):  
North American ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Velocity Model ◽  
Main Role ◽  
Seismic Structure ◽  
The Usa ◽  
Mexico Border ◽  
Group And Phase Velocities

Abstract. We use group velocities from earthquake tomography together with group and phase velocities from ambient noise tomography (ANT) of Rayleigh waves to invert for the 3-D shear-wave velocity structure (5–70 km) of the Caribbean (CAR) and southern North American (NAM) plates. The lithospheric model proposed offers a complete image of the crust and uppermost-mantle with imprints of the tectonic evolution. One of the most striking features inferred is the main role of the Ouachita–Marathon–Sonora orogeny front on the crustal seismic structure of the NAM plate. A new imaged feature is the low crustal velocities along the USA-Mexico border. The model also shows a break of the east–west mantle velocity dichotomy of the NAM and CAR plates beneath the Isthmus of the Tehuantepec and the Yucatan Block. High upper-mantle velocities along the Mesoamerican Subduction Zone coincide with inactive volcanic areas while the lowest velocities correspond to active volcanic arcs and thin lithospheric mantle regions.

scholarly journals A 3-D shear velocity model of the southern North America and the Caribbean plates from ambient noise and earthquake tomography

2014 ◽  
Vol 6 (2) ◽  
pp. 2971-3002 ◽  
Author(s):  
B. Gaite ◽  
A. Villaseñor ◽  
A. Iglesias ◽  
M. Herraiz ◽  
I. Jiménez-Munt
Keyword(s):  
Ambient Noise ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Velocity Model ◽  
Main Role ◽  
Seismic Structure ◽  
Mexico Border ◽  
The Caribbean ◽  
Group And Phase Velocities ◽  
Mantle Velocity

Abstract. We use group velocities from earthquake tomography together with group and phase velocities from ambient noise tomography (ANT) of Rayleigh-waves to invert for the 3-D shear-wave velocity structure (5–70 km) of the Caribbean (CAR) and southern North American (NAM) plates. The lithospheric model proposed offers a complete image of the crust and uppermost-mantle with imprints of the tectonic evolution. One of the most striking features inferred is the main role of the Ouachita-Marathon-Sonora orogeny front on the crustal seismic structure of NAM plate. A new imaged feature is the low crustal velocities along USA-Mexico border. The model also shows a break of the E-W mantle velocity dichotomy of the NAM and CAR plates beneath the Isthmus of Tehuantepec and Yucatan Block. High upper-mantle velocities along the Mesoamerican Subduction Zone coincide with inactive volcanic areas while the lowest velocities correspond to active volcanic arcs and thin lithospheric mantle regions.

scholarly journals Imaging New Zealand's Crustal Structure Using Ambient Seismic Noise Recordings from Permanent and Temporary Instruments

2021 ◽  
Author(s):  
◽  
Yannik Behr
Keyword(s):  
Seismic Noise ◽  
Cross Correlation ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Ambient Seismic Noise ◽  
Uppermost Mantle ◽  
Noise Sources ◽  
Noise Field ◽  
Rayleigh And Love Waves ◽  
Noise Cross Correlation

<p>We use ambient seismic noise to image the crust and uppermost mantle, and to determine the spatiotemporal characteristics of the noise field itself, and examine the way in which those characteristics may influence imaging results. Surface wave information extracted from ambient seismic noise using cross-correlation methods significantly enhances our knowledge of the crustal and uppermost mantle shear-velocity structure of New Zealand. We assemble a large dataset of three-component broadband continuous seismic data from temporary and permanent seismic stations, increasing the achievable resolution of surface wave velocity maps in comparison to a previous study. Three-component data enables us to examine both Rayleigh and Love waves using noise cross-correlation functions. Employing a Monte Carlo inversion method, we invert Rayleigh and Love wave phase and group velocity dispersion curves separately for spatially averaged isotropic shear velocity models beneath the Northland Peninsula. The results yield first-order radial anisotropy estimates of 2% in the upper crust and up to 15% in the lower crust, and estimates of Moho depth and uppermost mantle velocity compatible with previous studies. We also construct a high-resolution, pseudo-3D image of the shear-velocity distribution in the crust and uppermost mantle beneath the central North Island using Rayleigh and Love waves. We document, for the first time, the lateral extent of low shear-velocity zones in the upper and mid-crust beneath the highly active Taupo Volcanic Zone, which have been reported previously based on spatially confined 1D shear-velocity profiles. Attributing these low shear-velocities to the presence of partial melt, we use an empirical relation to estimate an average percentage of partial melt of < 4:2% in the upper and middle crust. Analysis of the ambient seismic noise field in the North Island using plane wave beamforming and slant stacking indicates that higher mode Rayleigh waves can be detected, in addition to the fundamental mode. The azimuthal distributions of seismic noise sources inferred from beamforming are compatible with high near-coastal ocean wave heights in the period band of the secondary microseism (~7 s). Averaged over 130 days, the distribution of seismic noise sources is azimuthally homogeneous, indicating that the seismic noise field is well-suited to noise cross-correlation studies. This is underpinned by the good agreement of our results with those from previous studies. The effective homogeneity of the seismic noise field and the large dataset of noise cross-correlation functions we here compiled, provide the cornerstone for future studies of ambient seismic noise and crustal shear velocity structure in New Zealand.</p>

scholarly journals Upper-plate structure in Ecuador coincident with the subduction of the Carnegie Ridge and the southern extent of large mega-thrust earthquakes

2019 ◽  
Vol 220 (3) ◽  
pp. 1965-1977 ◽  
Author(s):  
Colton Lynner ◽  
Clinton Koch ◽  
Susan L Beck ◽  
Anne Meltzer ◽  
Lillian Soto-Cordero ◽  
...  
Keyword(s):  
Ambient Noise ◽  
Velocity Structure ◽  
Sedimentary Basins ◽  
Past Century ◽  
Ambient Noise Tomography ◽  
Plate Interface ◽  
Crust And Upper Mantle ◽  
Southern Boundary ◽  
Plate Structure ◽  
Velocity Anomaly

SUMMARY The Ecuadorian convergent margin has experienced many large mega-thrust earthquakes in the past century, beginning with a 1906 event that propagated along as much as 500 km of the plate interface. Many subsections of the 1906 rupture area have subsequently produced Mw ≥ 7.7 events, culminating in the 16 April 2016, Mw 7.8 Pedernales earthquake. Interestingly, no large historic events Mw ≥ 7.7 appear to have propagated southward of ∼1°S, which coincides with the subduction of the Carnegie Ridge. We combine data from temporary seismic stations deployed following the Pedernales earthquake with data recorded by the permanent stations of the Ecuadorian national seismic network to discern the velocity structure of the Ecuadorian forearc and Cordillera using ambient noise tomography. Ambient noise tomography extracts Vsv information from the ambient noise wavefield and provides detailed constraints on velocity structures in the crust and upper mantle. In the upper 10 km of the Ecuadorian forearc, we see evidence of the deepest portions of the sedimentary basins in the region, the Progreso and Manabí basins. At depths below 30 km, we observe a sharp delineation between accreted fast forearc terranes and the thick crust of the Ecuadorian Andes. At depths ∼20 km, we see a strong fast velocity anomaly that coincides with the subducting Carnegie Ridge as well as the southern boundary of large mega-thrust earthquakes. Our observations raise the possibility that upper-plate structure, in addition to the subducting Carnegie Ridge, plays a role in the large event segmentation seen along the Ecuadorian margin.

Near-surface Structure of Downtown Jinan, China: Application of Ambient Noise Tomography with a Dense Seismic Array

2019 ◽  
Vol 24 (4) ◽  
pp. 641-652
Author(s):  
Feng Liang ◽  
Zhihui Wang ◽  
Hailong Li ◽  
Kai Liu ◽  
Tao Wang
Keyword(s):  
Surface Wave ◽  
Human Activities ◽  
High Frequency ◽  
Urban Areas ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Shear Velocity ◽  
Ambient Noise Tomography ◽  
Surface Wave Dispersion ◽  
Near Surface

Urban geophysics ups the ante in the world of applied geophysics, which requires innovative thinking and seemingly off-the-wall approaches, if for no other reason than the settings. Ambient-noise-tomography (ANT) can play a pivotal role in yielding subsurfa2ce information in urban areas, which is capable of dealing with challenges related to these scenarios ( e.g., human activities and low signal-to-noise ratio). In this study, the ANT was conducted to investigate the near-surface shear-velocity structure in the surrounding area of the Baotu Spring Park in downtown Jinan, Shandong Province, China. Quiet clear Rayleigh waves have been obtained by the cross-correlation, which indicates that strong human activities, such as moving vehicles and municipal engineering constructions, can produce approximately isotropic distribution of noise sources for high-frequency signals. The direct surface-wave tomographic method with period-dependent ray-tracing was used to invert all surface-wave dispersion data in the period band 0.2-1.5 s simultaneously for 3D variations of shear-velocity (Vs) structure. Our results show a good correspondence to the geological features with thinner Quaternary sediments, the geological structural characteristic of the limestone surrounded by the igneous which has the highest velocity than that of the limestone in the study area, and several concealed faults of which specific location has been detected at depth. The results demonstrate that it is possible to successfully use ANT with high-frequency signal in an urban environment provided a detailed planning and execution is implemented.

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