Reconstruction of Pressure and Shear Wave Velocity Profiles from Ambient Noise Tomography

2019 ◽  
Author(s):  
A. Konkov ◽  
S. Manakov
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Velocity Profiles ◽  
Ambient Noise Tomography

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>

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.

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>

scholarly journals Using horizontal-to-vertical spectral ratios to construct shear-wave velocity profiles

Solid Earth ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 2015-2030
Author(s):  
Janneke van Ginkel ◽  
Elmer Ruigrok ◽  
Rien Herber
Keyword(s):  
The Netherlands ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Input Parameter ◽  
Velocity Profiles ◽  
Spectral Ratios ◽  
Noise Field ◽  
Resonance Frequencies

Abstract. For seismic hazard assessment and earthquake hypocentre localization, detailed shear-wave velocity profiles are an important input parameter. Here, we present a method to construct a shear-wave velocity profiles for a deep unconsolidated sedimentary layer by using strong teleseismic phases and the ambient noise field. Gas extraction in the Groningen field, in the northern part of the Netherlands, is causing low-magnitude, induced seismic events. This region forms an excellent case study due to the presence of a permanent borehole network and detailed subsurface knowledge. Instead of conventional horizontal-to-vertical spectral ratios (H∕V ratios) from amplitude spectra, we calculate power spectral densities and use those as input for H∕V calculations. The strong teleseisms provide resonance recordings at low frequencies, where the seismic noise field is too weak to be recorded well with the employed geophones and accelerometers. The H∕V ratios of the ambient noise field are compared with several forward modelling approaches to quality check the teleseism-based shear-wave velocity profiles. Using the well-constrained depth of the sedimentary basin, we invert the H∕V ratios for velocity profiles. A close relationship is observed between the H∕V spectral ratios from the ambient noise field, shear-wave resonance frequencies and Rayleigh-wave ellipticity. By processing only five teleseismic events, we are able to derive shear-wave velocities for the deeper sedimentary sequence with a 7 % bias in comparison with the existing detailed velocity model for the Cenozoic sediments overlying the Groningen gas field. Furthermore, a relation between resonance frequency and unconsolidated sediment thickness is derived, to be used in other areas in the Netherlands, where detailed depth maps are not available.

scholarly journals Using Horizontal to Vertical Spectral Ratios to construct shear-wave velocity profiles

2020 ◽  
Author(s):  
Janneke van Ginkel ◽  
Elmer Ruigrok ◽  
Rien Herber
Keyword(s):  
The Netherlands ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Input Parameter ◽  
Velocity Profiles ◽  
Spectral Ratios ◽  
Noise Field ◽  
Resonance Frequencies

Abstract. For hazard assessment and earthquake hypocentre localisation, detailed shear-wave velocity profiles are an important input parameter. Here we present a method to construct a shear-wave velocity profiles for a deep unconsolidated sedimentary layer by using strong teleseismic phases and the ambient noise field. Gas extraction in the Groningen field, in the northern part of the Netherlands, is causing low-magnitude, induced seismic events. This region forms an excellent case study due to the presence of a permanent borehole network and detailed subsurface knowledge. Instead of conventional horizontal-to-vertical spectral ratios (H/V ratios) from amplitude spectra, we calculate power spectral densities and use those as input for H/V calculations. The strong teleseisms provide resonance recordings at low frequencies, where the seismic noise field is too weak to be recorded well with the employed geophones and accelerometers. The H/V ratios of the ambient noise field are compared with several forward modeling approaches to quality check the teleseism-based shear-wave velocity profiles. A close relationship is observed between the H/V spectral ratios from the ambient noise field, shear-wave resonance frequencies and Rayleigh-wave ellipticity. Using the well-constrained depth of the sedimentary basin, we invert the H/V ratios for velocity profiles. By processing only five teleseismic events, we are able to derive shear-wave velocities for the deeper sedimentary sequence with a 7 % bias in comparison with the existing detailed velocity model for the Cenozoic sediments overlying the Groningen gas field. Furthermore, a relation between resonance frequency and unconsolidated sediment thickness is derived, to be used in other areas in the Netherlands, where detailed depth maps are not available.

Seismic imaging of Caosiyao giant porphyry molybdenum deposit using ambient noise tomography

Geophysics ◽  
2021 ◽  
pp. 1-45
Author(s):  
Guoxiong Chen ◽  
Qiuming Cheng ◽  
Yinhe Luo ◽  
Yingjie Yang ◽  
Hongrui Xu ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Mineral Deposit ◽  
Seismic Reflection Profile ◽  
Ambient Noise Tomography ◽  
Potential Field Data ◽  
Velocity Anomalies ◽  
Ore Deposition

As a new emerging seismic method for delineating subsurface structure, the potential of ambient noise tomography is investigated for mineral deposit targeting at exploration scale. This passive seismic technique was used to image the subsurface 3-D shear-wave velocity of the Caosiyao porphyry molybdenum (Mo) deposit in the North China Craton. Intriguingly, the key structures of this giant porphyry mineral system down to the depth of 2 km are characterized by distinct shear-wave velocity anomalies, with ore deposition sites and fluid pathways (faults) characterized by distinct velocity lows, while fluid drivers (granites) generate velocity highs. The 3-D shear-wave velocity anomalies, along with seismic reflection profile and potential field data, allow us to delineate the deep-seated ore-controlling structures including fault systems, granitic plutons and even ore deposition sites under thickly covered sediments in the study area. The results suggest that the occurrence of the Caosiyao ore deposit is closely related to the huge amount of magma fluid intruding along the channel of Datong-Shangyi fault at a depth of gt;2 km. Our study demonstrates that the ambient noise tomography technique has the accuracy and resolution needed for mineral exploration targeting at deposit scale, with a relatively lower environmental impact as well as lower cost than active-source seismology.

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