scholarly journals 3-D Ambient Noise Tomography of Llaima Volcano, Chile

2021 ◽  
Author(s):  
Claudia Kristina Rossavik
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ambient Noise ◽  
Geochemical Data ◽  
Ambient Noise Tomography ◽  
Structural Framework ◽  
South Central ◽  
Velocity Anomalies ◽  
Llaima Volcano

Llaima is a glaciated, basaltic-andesitic stratocone in the South-Central Andean Volcanic Zone. It is one of the largest and most active volcanoes in Chile. However, uncertainty remains regarding the depths and geometry of where magma is stored and the routes which it takes towards the Earth's surface. To provide a structural framework for the interpretation of petrological and geochemical data, I apply ambient noise tomography (ANT) to produce a 3-D shear wave velocity (vs) model of Llaima's magmatic plumbing. The results of this project show slow shear wave velocity anomalies within the upper 8 km of the crust which are interpreted as the locations of upper and lower magma reservoirs. Among the structures that are revealed by fast shear wave velocity anomalies is a geometry that is interpreted as a dike within a cluster of volcano tectonic (VT) activity. This VT cluster has been suggested to have followed the 2010 M8.8 Maule megathrust earthquake off the coast of Chile (Mora-Stock et al., 2014; Franco, 2019). I use information that has been derived from previous studies such as the coordinates of scoria cones along Llaima's flanks, gravitational anomalies, and local seismicity (which includes the depths and locations of volcano tectonic and long period seismicity) to place the resulting model within a framework that provides insight on the current state of this magmatic system.

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.

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>

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