scholarly journals The Variscan structure of the western Cantabrian Mountains (NW Spain) from ambient noise interferometry

2021 ◽  
Author(s):  
Jorge Acevedo ◽  
Gabriela Fernández-Viejo ◽  
Sergio Llana-Fúnez ◽  
Luis Pando ◽  
Diego Pérez-Millán ◽  
...  
Keyword(s):  
Group Velocity ◽  
Wave Velocity ◽  
Ambient Noise ◽  
Dispersion Curves ◽  
Low Grade ◽  
Variscan Belt ◽  
S Wave ◽  
Cantabrian Mountains ◽  
The West ◽  
Lower Velocity

<p>The Variscan belt was formed as a consequence of the collision of two major continents, Laurasia and Gondwana, in the late Paleozoic. Nowadays, it constitutes the basement of the Iberian peninsula (Iberian Massif) and a large part of western and central Europe. In the NW of Spain, the convergence between Iberia and Europe in the Cenozoic originated the uplift of the Cantabrian mountains (CM). In its central sector, the erosion of the Mesozoic sedimentary cover during orogenesis led to the exhumation of the underlying Variscan basement in their western sector. The section of the Variscan belt that is currently exposed in the CM illustrates the transition from the internal zones of an orogen, in the west, to the external ones, to the east.</p><p>In order to acquire new passive data from this region, a portable seismic network consisting of 13 three-component broadband stations was deployed (GEOCANTÁBRICA-COSTA, doi:10.7914/SN/YR_2019). The recorded ambient noise seismic signal was cross-correlated using the phase cross-correlation (PCC) processing technique and the resulting daily cross-correlograms were stacked to obtain the empirical Green’s function of the medium between each station pair. Since the vertical and the rotated horizontal components were processed, Rayleigh- and Love-wave group velocity dispersion curves were extracted. From these measurements, group velocity tomographic maps at periods between 2 – 14 s were calculated. Based on this set of tomographic maps, a final 3D S-wave velocity model (2 - 12 km) was derived from the joint inversion of the pseudo-dispersion curves created by extracting the Rayleigh and Love velocity values for each point of a dense grid.</p><p>Both the surface-wave and the S-wave velocity maps highlight essential elements of the surface geology of the area. The velocity pattern shows the boundary between two main geological domains: The Cantabrian Zone (CZ), to the east, which constitutes the foreland fold and thrust belt of the Variscan orogen; and the West Asturian-Leonese Zone (WALZ), to the west, the slate belt representing the low grade part of the internal zones. An E-W cross-section of the study area shows a high velocity unit to the west thrusting the lower velocity rocks of the CZ at the transition between the WALZ and the CZ.</p>

scholarly journals Radial anisotropy and S-wave velocity depict the internal to external zones transition within the Variscan orogen (NW Iberia) 

2021 ◽  
Author(s):  
Jorge Acevedo ◽  
Gabriela Fernández-Viejo ◽  
Sergio Llana-Fúnez ◽  
Carlos López-Fernández ◽  
Javier Olona ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Ambient Noise ◽  
Variscan Orogeny ◽  
Low Grade ◽  
The West ◽  
Cantabrian Zone ◽  
Variscan Orogen ◽  
Nw Iberia ◽  
Radial Anisotropy

Abstract. The cross-correlation of ambient noise records registered by seismic networks has proven to be a valuable tool to obtain new insights into the crustal structure at different scales. Based on 2- to 14-s-period Rayleigh and Love dispersion data extracted from the seismic ambient noise recorded by 20 three-component broadband stations belonging to two different temporary experiments, we present the first i) upper crustal (1–14 km) high-resolution shear wave velocity and ii) radial anisotropy variation models of the continental crust in NW Iberia. The area of study represents one of the best exposed cross-sections along the Variscan orogen of western Europe, showing the transition between the external eastern zones towards the internal areas in the west. Both the 2-D maps and an E-W transect reveal a close correspondence with the main geological domains of the Variscan orogen. The foreland-fold and thrust-belt of the orogen, the Cantabrian Zone, is revealed by a zone of relatively low shear wave velocities (2.3–3.0 km/s), while the internal zones generally display higher homogeneous velocities (> 3.1 km/s). The boundary between both zones is clearly delineated in the models, depicting the arcuate shape of the orogen grain. The velocity patterns also reveal variations of the bulk properties of the rocks that can be linked to major Variscan structures, such as the basal detachment of the Cantabrian Zone or the stack of nappes involving pre-Variscan basement; or sedimentary features such as the presence of thick syn-orogenic siliciclastic wedges. Overall, the radial anisotropy magnitude varies between −5 and 15 % and increases with depth. The depth pattern suggests that the alignment of cracks is the main source of anisotropy at < 8 km depths, although the intrinsic anisotropy seems to be significant in the West-Asturian Leonese Zone, the low-grade slate belt adjacent to the Cantabrian Zone. At depths > 8 km, widespread high and positive radial anisotropies are observed, caused by the presence of subhorizontal alignments of grains and minerals in relation to the internal deformation of rocks either during the Variscan orogeny or prior to it.

Geological variation in S-wave velocity structures in Northern Taiwan and implications for seismic hazards based on ambient noise analysis

2014 ◽  
Vol 96 ◽  
pp. 353-360
Author(s):  
Ya-Chuan Lai ◽  
Bor-Shouh Huang ◽  
Yu-Chih Huang ◽  
Huajian Yao ◽  
Ruey-Der Hwang ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Ambient Noise ◽  
Noise Analysis ◽  
Seismic Hazards ◽  
S Wave ◽  
Northern Taiwan

Extracting Long-Period Surface Waves and Free Oscillations Using Ambient Noise Recorded by Global Distributed Superconducting Gravimeters

2020 ◽  
Vol 91 (4) ◽  
pp. 2234-2246
Author(s):  
Hang Li ◽  
Jianqiao Xu ◽  
Xiaodong Chen ◽  
Heping Sun ◽  
Miaomiao Zhang ◽  
...  
Keyword(s):  
Surface Waves ◽  
Group Velocity ◽  
Ambient Noise ◽  
Velocity Dispersion ◽  
Group Velocity Dispersion ◽  
Dispersion Curves ◽  
Free Oscillations ◽  
Long Period ◽  
Superconducting Gravimeters ◽  
Noise Data

Abstract Inversion of internal structure of the Earth using surface waves and free oscillations is a hot topic in seismological research nowadays. With the ambient noise data on seismically quiet days sourced from the gravity tidal observations of seven global distributed superconducting gravimeters (SGs) and the seismic observations for validation from three collocated STS-1 seismometers, long-period surface waves and background free oscillations are successfully extracted by the phase autocorrelation (PAC) method, respectively. Group-velocity dispersion curves at the frequency band of 2–7.5 mHz are extracted and compared with the theoretical values calculated with the preliminary reference Earth model. The comparison shows that the best observed values differ about ±2% from the corresponding theoretical results, and the extracted group velocities of the best SG are consistent with the result of the collocated STS-1 seismometer. The results indicate that reliable group-velocity dispersion curves can be measured with the ambient noise data from SGs. Furthermore, the fundamental frequency spherical free oscillations of 2–7 mHz are also clearly extracted using the same ambient noise data. The results in this study show that the SG, besides the seismometer, is proved to be another kind of instrument that can be used to observe long-period surface waves and free oscillations on seismically quiet days with a high degree of precision using the PAC method. It is worth mentioning that the PAC method is first and successfully introduced to analyze SG observations in our study.

scholarly journals Investigating Near Surface S-Wave Velocity Properties Using Ambient Noise in Southwestern Taiwan

2015 ◽  
Vol 26 (2-2) ◽  
pp. 205 ◽  
Author(s):  
Chun-Hsiang Kuo ◽  
Kuo-Liang Wen ◽  
Che-Min Lin ◽  
Strong Wen ◽  
Jyun-Yan Huang
Keyword(s):  
Wave Velocity ◽  
Ambient Noise ◽  
S Wave ◽  
Near Surface ◽  
Southwestern Taiwan

P- and S-wave velocity models from surface wave dispersion curves data transform

2017 ◽  
Author(s):  
Valentina Socco ◽  
Farbod Khosro Anjom ◽  
Cesare Comina ◽  
Daniela Teodor
Keyword(s):  
Surface Wave ◽  
Wave Velocity ◽  
Wave Dispersion ◽  
Dispersion Curves ◽  
S Wave ◽  
Surface Wave Dispersion ◽  
Velocity Models

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

&lt;p&gt;&lt;span&gt;We have successfully derived a new &lt;/span&gt;&lt;span&gt;3-D&lt;/span&gt;&lt;span&gt; high resolution shear wave velocity model of the crust and uppermost mantle of a large part of W-Europe from transdimensional&lt;/span&gt;&lt;span&gt;&lt;strong&gt; &lt;/strong&gt;&lt;/span&gt;&lt;span&gt;ambient-noise tomography. This model is intended to contribute to the development of the first &lt;/span&gt;&lt;span&gt;3-D&lt;/span&gt;&lt;span&gt; crustal-scale integrated geophysical-geological model of the W-Alps to deepen understanding of orogenesis and its relationship to mantle dynamics. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;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.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;We firstly performed a &lt;/span&gt;&lt;span&gt;2-D&lt;/span&gt;&lt;span&gt; data-driven transdimensional travel time inversion for group velocity maps from 4 to 150 s (Bodin &amp; 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 &amp; 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&lt;/span&gt;&lt;span&gt; approach proposed by Lu et al (2018) by including group velocity uncertainties. Posterior probability distributions on &lt;/span&gt;&lt;span&gt;Vs&lt;/span&gt;&lt;span&gt; and interfaces were estimated by exploring a set of 130 millions synthetic &lt;/span&gt;&lt;span&gt;4-&lt;/span&gt;&lt;span&gt;layer &lt;/span&gt;&lt;span&gt;1-D Vs&lt;/span&gt;&lt;span&gt; models that allow for &lt;/span&gt;&lt;span&gt;low-velocity zones&lt;/span&gt;&lt;span&gt;&lt;em&gt;.&lt;/em&gt;&lt;/span&gt;&lt;span&gt; The obtained probabilistic model was refined using a linearized inversion&lt;/span&gt;&lt;span&gt;&lt;em&gt;. &lt;/em&gt;&lt;/span&gt;&lt;span&gt;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 &lt;/span&gt;&lt;span&gt;&amp;&lt;/span&gt;&lt;span&gt; Webb, 2000) and adapted the inversion for Vs to include the water column.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;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&lt;em&gt; &lt;/em&gt;structure (50 - 80 km) in the prolongation&lt;em&gt; &lt;/em&gt;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.&lt;/p&gt;

Nodal Seismograph Recordings of the 2019 Ridgecrest Earthquake Sequence

2020 ◽  
Vol 91 (6) ◽  
pp. 3622-3633
Author(s):  
Rufus D. Catchings ◽  
Mark R. Goldman ◽  
Jamison H. Steidl ◽  
Joanne H. Chan ◽  
Amir A. Allam ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Large Volume ◽  
Ambient Noise ◽  
Temporal Variations ◽  
Earthquake Sequence ◽  
S Wave ◽  
Data Set ◽  
Fault Structure ◽  
Nodal Data ◽  
Dense Arrays

Abstract The 2019 Ridgecrest, California, earthquake sequence included Mw 6.4 and 7.1 earthquakes that occurred on successive days beginning on 4 July 2019. These two largest earthquakes of the sequence occurred on orthogonal faults that ruptured the Earth’s surface. To better evaluate the 3D subsurface fault structure, (P- and S-wave) velocity, 3D and temporal variations in seismicity, and other important aspects of the earthquake sequence, we recorded aftershocks and ambient noise using up to 461 three-component nodal seismographs for about two months, beginning about one day after the Mw 7.1 mainshock. The ∼30,000Mw≥1 earthquakes that were recorded on the dense arrays provide an unusually large volume of data with which to evaluate the earthquake sequence. This report describes the recording arrays and is intended to provide metadata for researchers interested in evaluating various aspects of the 2019 Ridgecrest earthquake sequence using the nodal data set.

scholarly journals Ambient noise tomography of the southern sector of the Cantabrian Mountains, NW Spain

2019 ◽  
Vol 219 (1) ◽  
pp. 479-495 ◽  
Author(s):  
Jorge Acevedo ◽  
Gabriela Fernández-Viejo ◽  
Sergio Llana-Fúnez ◽  
Carlos López-Fernández ◽  
Javier Olona
Keyword(s):  
Ambient Noise ◽  
Broad Band ◽  
Shear Zones ◽  
Seismic Velocities ◽  
S Wave ◽  
Ambient Noise Tomography ◽  
Cantabrian Mountains ◽  
Nw Spain ◽  
Time Frequency ◽  
Short Period

SUMMARY This study presents the first detailed analysis of ambient noise tomography in an area of the continental upper crust in the Cantabrian Mountains (NW Spain), where a confluence of crustal scale faults occurs at depth. Ambient noise data from two different seismic networks have been analysed. In one side, a 10-short-period station network was set recording continuously for 19 months. A second set of data from 13 broad-band stations was used to extend at depth the models. The phase cross-correlation processing technique was used to compute in total more than 34 000 cross-correlations from 123 station pairs. The empirical Green's functions were obtained by applying the time–frequency, phase-weighted stacking methodology and provided the emergence of Rayleigh waves. After measuring group velocities, Rayleigh-wave group velocity tomographic maps were computed at different periods and then they were inverted in order to calculate S-wave velocities as a function of depth, reaching the first 12 km of the crust. The results show that shallow velocity patterns are dominated by geological features that can be observed at the surface, particularly bedding and/or lithology and fracturing associated with faults. In contrast, velocity patterns below 4 km depth seem to be segmented by large structures, which show a velocity reduction along fault zones. The best example is the visualization in the tomography of the frontal thrust of the Cantabrian Mountains at depth, which places higher velocity Palaeozoic rocks over Cenozoic sediments of the foreland Duero basin. One of the major findings in the tomographic images is the reduction of seismic velocities above the area in the crust where one seismicity cluster is nucleated within the otherwise quiet seismic area of the range. The noise tomography reveals itself as a valuable technique to identify shear zones associated with crustal scale fractures and hence, lower strain areas favourable to seismicity.

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