First step towards an integrated geophysical-geological model of the W-Alps: A new Vs model from transdimensional ambient-noise tomography

2021 ◽  
Author(s):  
Ahmed Nouibat ◽  
Laurent Stehly ◽  
Anne Paul ◽  
Romain Brossier ◽  
Thomas Bodin ◽  
...  
Keyword(s):  
Group Velocity ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Receiver Functions ◽  
Time Inversion ◽  
Geological Model ◽  
Ambient Noise Tomography ◽  
Low Velocity

<p><span>We have successfully derived a new </span><span>3-D</span><span> high resolution shear wave velocity model of the crust and uppermost mantle of a large part of W-Europe from transdimensional</span><span><strong> </strong></span><span>ambient-noise tomography. This model is intended to contribute to the development of the first </span><span>3-D</span><span> crustal-scale integrated geophysical-geological model of the W-Alps to deepen understanding of orogenesis and its relationship to mantle dynamics. </span></p><p><span>We used an exceptional dataset of 4 years of vertical-component, daily seismic noise records (2015 - 2019) of more than 950 permanent broadband seismic stations located in and around the Greater Alpine region, complemented by 490 temporary stations from the AlpArray sea-land seismic network and 110 stations from Cifalps dense deployments.</span></p><p><span>We firstly performed a </span><span>2-D</span><span> data-driven transdimensional travel time inversion for group velocity maps from 4 to 150 s (Bodin & Sambridge, 2009). The data noise level was treated as a parameter of the inversion problem, and determined within a Hierarchical Bayes method. We used Fast Marching Eikonal solver (Rawlinson & Sambridge, 2005) jointly with the reversible jump algorithm to update raypath geometry during inversion. In the inversion of group velocity maps for shear-wave velocity, we set up a new formulation of the</span><span> approach proposed by Lu et al (2018) by including group velocity uncertainties. Posterior probability distributions on </span><span>Vs</span><span> and interfaces were estimated by exploring a set of 130 millions synthetic </span><span>4-</span><span>layer </span><span>1-D Vs</span><span> models that allow for </span><span>low-velocity zones</span><span><em>.</em></span><span> The obtained probabilistic model was refined using a linearized inversion</span><span><em>. </em></span><span>For the ocean-bottom seismometers of the Ligurian-Provencal basin, we applied a specific processing to clean daily noise signals from instrumental and oceanic noises (Crawford </span><span>&</span><span> Webb, 2000) and adapted the inversion for Vs to include the water column.</span></p><p>Our Vs model evidences strong variations of the crustal structure along strike, particulary in the subduction complex. The European crust includes lower crustal low-velocity zones and a Moho jump of ~8-12 km beneath the W-boundary of the external crystalline massifs. We observe a deep LVZ<em> </em>structure (50 - 80 km) in the prolongation<em> </em>of the European continental subduction beneath the Ivrea body. The striking fit between the receiver functions ccp migrated section across the Cifalps profile and this new Vs model validate its reliability.</p>

scholarly journals Detection of urban hidden faults using group-velocity ambient noise tomography beneath Zhenjiang area, China

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Leiming Zheng ◽  
Xiaoping Fan ◽  
Peng Zhang ◽  
Jingrun Hao ◽  
Hao Qian ◽  
...  
Keyword(s):  
Group Velocity ◽  
Shear Wave ◽  
Shear Wave Velocity ◽  
High Velocity ◽  
Ambient Noise ◽  
Depth Range ◽  
Ambient Noise Tomography ◽  
Low Velocity ◽  
The North ◽  
North Side

AbstractThe Mufushan-Jiaoshan fault (MJF) is a hidden active fault located on the north side of the Ningzhen Mountain Range and developed along the Yangtze River in Zhenjiang area, China. In this paper, the structure of MJF is detected and studied using group-velocity ambient noise tomography. In the study area (18 km × 25 km), 47 short-period seismic stations were deployed with the average station spacing of about 3 km and 24 days (from 27 February to 22 March 2019) of continuous ambient-noise recordings were collected. And 510 group velocity dispersion curves in the period band 0.5–5 s were extracted using the vertical component data. And then the three-dimensional shear-wave velocity structure was inverted using group dispersion data by the direct surface-wave tomographic method. Our results are consistent with the geological background of the study area, showing that in the depth range of 0.6–1.5 km, the north side of MJF presents a relatively high velocity, and the south side presents a distribution pattern of high and low velocity. While in the depth range of 1.5–2.0 km, the shear-wave velocity (Vs) model is relatively simple with relatively low velocity on the north side and relatively high velocity on the south side. And the gradient zone of Vs may be the location of the main fracture surface of MJF. The good correspondence between the Vs model and the fault structure indicates that the ambient noise tomography method can be used as an effective method for detecting hidden faults in urban environments.

Shear-Wave Velocity Model of the Bohemian Massif Crust from Ambient Noise Tomography

2020 ◽  
Author(s):  
Jiří Kvapil ◽  
Jaroslava Plomerová ◽  
Vladislav Babuška ◽  
Hana Kampfová Exnerová ◽  
Luděk Vecsey ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Seismic Noise ◽  
Ambient Noise ◽  
Velocity Model ◽  
Receiver Functions ◽  
P Wave ◽  
Ambient Noise Tomography ◽  
Moldanubian Unit

<p><span><span>The current knowledge of the structure of the Bohemian Massif (BM) crust is mostly based on interpretation of refraction and reflection seismic experiments performed along 2D profiles. The recent development of ambient noise tomography, in combination with dense networks of permanent seismic stations and arrays of passive seismic experiments, provides unique opportunity to build the high-resolution 3D velocity model of the BM crust from long sequences of ambient seismic noise data.</span></span></p><p><span><span>The new 3D shear-wave velocity model is built from surface-wave group-velocity dispersion measurements derived from ambient seismic noise cross-correlations by conventional two-step inversion approach. First, the 2D fast marching travel time tomography is applied to regularise velocity dispersions. Second, the stochastic inversion is applied to compute 1D shear-wave velocity profiles beneath each location of the processing grid.</span></span></p><p><span><span>We processed continuous waveform data from 404 seismic stations (permanent and temporary stations of passive experiments BOHEMA I-IV, PASSEQ, EGER RIFT, ALPARRAY-EASI and ALPARRAY-AASN) in a broader region of the BM (in an area of 46-54</span></span><sup><span><span>0 </span></span></sup><span><span>N 7-21</span></span><sup><span><span>0 </span></span></sup><span><span>E). The overlapping period of each possible station-pair and cross-correlation quality review resulted in more than 21,000 dispersion curves, which further served as an input for surface-wave inversion </span></span><span><span>at h</span></span><span><span>igh-density grid with the cell size of 22 km. </span></span></p><p><span><span>We present the new high-resolution 3D shear-wave velocity model of the BM crust and uppermost mantle with preliminary tectonic interpretations. We compare this model with a compiled P-wave velocity model from the 2D seismic refraction and wide-angle reflection experiments and with the crustal thickness (Moho depth) extracted from P-wave receiver functions (see Kampfová Exnerová et al., EGU2020_SM4.3). 1D velocity profiles resulting from the stochastic inversions exhibit regional variations, which are characteristic for individual units of the BM. Velocities within the upper crust of the BM are ~0.2 km/s higher than those in its surroundings. The highest crustal velocities occur in its southern part (Moldanubian unit). The velocity model confirms, in accord with results from receiver functions and other seismic studies, a relatively thin crust in the Saxothuringian unit, whilst thickness of the Moldanubian crust is at least 36 km in its central and southern parts. The most distinct interface with a velocity inversion at the depth of about 20 to 25 km occurs in the Moldanubian unit. The velocity decrease in the lower crust reflects probably its transversely isotropic structure.</span></span></p>

Diversity in the Indian lithosphere revealed from ambient noise and earthquake tomography

2020 ◽  
Author(s):  
Gokul Kumar Saha ◽  
Shyam S. Rai
Keyword(s):  
Group Velocity ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Lithospheric Mantle ◽  
Ambient Noise ◽  
Deccan Volcanic Province ◽  
Volcanic Province ◽  
Dispersion Data ◽  
Indian Lithosphere

<p>We present evidence of significant diversity in the Indian cratonic lithosphere mantle based on the analysis of 3-D shear wave velocity maps. These images are obtained through the inversion of 21600 fundamental mode Rayleigh wave group velocity dispersion data retrieved from ambient noise and from earthquake waveforms. The velocity model is constructed using two step approach-firstly generating group velocity maps at 1<sup>°</sup> square grid at time periods from 10s to 100s; and subsequently inversion of dispersion data at each grid node to a depth of 200 km in terms of velocity-depth model. Analysis of velocity images suggest a bipolar characteristics of lithospheric mantle. We observe a two layer-lithospheric mantle correlated with the Eastern Peninsular India comprising of Archean cratons like east Dharwar, Bastar, Singhbhum, Chotanagpur, Bundelkhand and Proterozoic Vindhyan Basin. The intra lithospheric mantle boundary is at a depth of ~90 km where Vs increases from 4.5 km/s to over 4.7 km/s. The positive velocity gradient continues to a depth of 140-180 km beyond which it reverses the trend and mapped as layer with lower velocity Vs of 4.3-4.4 km/s, as which could be possibly defined as the lithosphere-asthenosphere boundary. Geologically, the region correlates with the kimberlite fields with the xenoliths showing presence of eclogite in them. The other group of Precambrian terrains like 3.36 Ga western Dharwar, eastern Deccan Volcanics, southern Granulite terrane and the Marwar block in western India are characterized by an almost uniform mantle with shear wave velocity of 4.4-4.5 km/s, also supported by other seismological studies. We do not observe any low-velocity layer underlying these terrains. Presence of such a uniform lower than expected mantle velocity could be due to its fertilization through an early geodynamic process. The velocity imprint of Deccan volcanism is best preserved in term of the thinned lithosphere (100-120 km) restricted to the westernmost part of Deccan Volcanic Province (DVP). This suggests that the plume-Indian lithosphere interaction was primarily confined to the western most Deccan volcanic province and possibly extending into the Indian ocean.</p>

3-D crustal structure of the Iran plateau using phase velocity ambient noise tomography

2019 ◽  
Vol 220 (3) ◽  
pp. 1555-1568 ◽  
Author(s):  
R Movaghari ◽  
G Javan Doloei
Keyword(s):  
Phase Velocity ◽  
Shear Wave ◽  
Wave Velocity ◽  
Crustal Structure ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Velocity Model ◽  
Central Iran ◽  
Ambient Noise Tomography ◽  
Iran Plateau

SUMMARY More accurate crustal structure models will help us to better understand the tectonic convergence between Arabian and Eurasian plates in the Iran plateau. In this study, the crustal and uppermost mantle velocity structure of the Iran plateau is investigated using ambient noise tomography. Three years of continuous data are correlated to retrieve Rayleigh wave empirical Green's functions, and phase velocity dispersion curves are extracted using the spectral method. High-resolution Rayleigh wave phase velocity maps are presented at periods of 8–60 s. The tomographic maps show a clear consistency with geological structures such as sedimentary basins and seismotectonic zones, especially at short periods. A quasi-3-D shear wave velocity model is determined from the surface down to 100 km beneath the Iran plateau. A transect of the shear wave velocity model has been considered along with a profile extending across the southern Zagros, the Sanandaj-Sirjan Zone (SSZ), the Urumieh-Dokhtar Magmatic Arc (UDMA) and Central Iran and Kopeh-Dagh (KD). Obvious crustal thinning and thickening are observable along the transect of the shear wave velocity model beneath Central Iran and the SSZ, respectively. The observed shear wave velocities beneath the Iran plateau, specifically Central Iran, support the slab break-off idea in which low density asthenospheric materials drive towards the upper layers, replacing materials in the subcrustal lithosphere.

Shallow Shear-Wave Velocity Structure in Oklahoma Based on the Joint Inversion of Ambient Noise Dispersion and Teleseismic P-Wave Receiver Functions

2020 ◽  
Author(s):  
Jiayan Tan ◽  
Charles A. Langston ◽  
Sidao Ni
Keyword(s):  
Surface Wave ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Sedimentary Basins ◽  
Velocity Model ◽  
Receiver Functions ◽  
P Wave ◽  
Velocity Models

ABSTRACT Ambient noise cross-correlations, used to obtain fundamental-mode Rayleigh-wave group velocity estimates, and teleseismic P-wave receiver functions are jointly modeled to obtain a 3D shear-wave velocity model for the crust and upper mantle of Oklahoma. Broadband data from 82 stations of EarthScope Transportable Array, the U.S. National Seismic Network, and the Oklahoma Geological Survey are used. The period range for surface-wave ambient noise Green’s functions is from 4.5 to 30.5 s constraining shear-wave velocity to a depth of 50 km. We also compute high-frequency receiver functions at these stations from 214 teleseismic earthquakes to constrain individual 1D velocity models inferred from the surface-wave tomography. Receiver functions reveal Ps conversions from the Moho, intracrustal interfaces, and shallow sedimentary basins. Shallow low-velocity zones in the model correlate with the large sedimentary basins of Oklahoma. The velocity model significantly improves the agreement of synthetic and observed seismograms from the 6 November 2011 Mw 5.7 Prague, Oklahoma earthquake suggesting that it can be used to improve earthquake location and moment tensor inversion of local and regional earthquakes.

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