Ambient noise tomography of the Central Cantabrian Mountains (NW Spain). New insights from the GEOCANTABRICA-COSTA seismic network.

The Cantabrian Mountains (NW Spain) are an Alpine chain that was formed as a result of the collision between Iberia and Europe in the Cenozoic. In their central sector, the uplift of the orogen led to the exhumation of a block of Variscan -Paleozoic- basement, the reactivation of Variscan structures and the formation of new E-W oriented fractures. Moreover, the formation of the Cantabrian Mountains involved the development of a crustal root with a thickness of 45-55 km that decreases up to 30-35 km towards the west. The thickening occurs preferentially in the crust that had previously been extended during the two main rifting episodes that affected this area in the Mesozoic. At the surface, the limit between the normal and the thickened crust roughly coincides with the trace of the Ventaniella fault, a subvertical crustal structure that runs for more than 400 km both inland and offshore. In order to obtain new insights from this complex region, it was installed a network (GEOCANT&#193;BRICA-COSTA, doi:10.7914/SN/YR_2019) of 13 broadband stations covering an area of 160x80 km (~40 km spacing) for 8 months. The phase cross-correlation (PCC) processing technique was used to cross-correlate daily records of the 78 station pairs. After stacking the cross-correlograms, the empirical Green&#8217;s functions and the dispersion curves were obtained. Finally, a Rayleigh wave group velocity tomography was performed, retrieving the seismic signature of the Variscan crust and allowing us to extend to the north our previous seismic ambient noise tomography and complete the tomographic model of the central Cantabrian Mountains. To reveal the structure beneath the seismic stations, we also performed ambient noise auto-correlations, successfully retrieving body-wave reflections from the crust-mantle boundary that provide new information about the limits of the crustal root. The study area presents a lingering, low-magnitude intraplate seismic activity that increases from east to west and extends into the continental shelf. The Ventaniella fault also acts as a seismic barrier to the propagation of earthquakes towards the east while provides nucleation sites along its trace. Thus, another objective of this study was to detect and relocate the local seismicity of the Cantabrian Mountains and the Cantabrian margin activity in particular. Our preliminary catalogue of events, obtained from the automatic analysis of the real-time seismic data with SeiscompP3, comprises 54 local earthquakes. Seven of them have their epicentres in the Cantabrian margin and, as expected, all were located to the west of the Ventaniella fault.

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

Geophysical Journal International ◽

10.1093/gji/ggz308 ◽

2019 ◽

Vol 219 (1) ◽

pp. 479-495 ◽

Cited By ~ 2

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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Assessment of the continuity of the orogenic root beneath the Cantabrian-Pyrenean orogen

10.5194/egusphere-egu2020-13772 ◽

2020 ◽

Author(s):

Gabriela Fernández-Viejo ◽

Patricia Cadenas ◽

Jorge Acevedo ◽

Sergio Llana-Funez

Keyword(s):

Ambient Noise ◽

Accretionary Wedge ◽

Bay Of Biscay ◽

Cantabrian Mountains ◽

The West ◽

Cantabrian Range ◽

Northern Iberian Peninsula ◽

Cantabrian Region ◽

Mountain Systems ◽

Rugged Topography

Crustal roots are a consequence of the contraction of continental masses during orogenesis identified in collisional chains worldwide. Frequently mirroring the summits of mountain systems, they portray the fundamental topic of isostasy. The northern Iberian Peninsula presents a rugged topography resulting of the collision with the European plate and the partial closure of the Bay of Biscay during the Cenozoic. Three differentiated systems formed along, from east to west: &#160;a continental collisional chain, the Pyrenees, occupying the isthmus between Iberia and Europe; facing the Bay of Biscay, a deep Mesozoic basin inverted during contraction, the Basque-Cantabrian region, and in the west a crustal pop-up of Palaeozoic basement, the Cantabrian Mountains. The last two extend underwater in the form of a shortened platform, and an accretionary wedge fossilized by post orogenic sediments. The identification of a crustal root beneath the Pyrenees in the 80&#180;s and the observation of a similar morphology beneath the Cantabrian range in the 90&#180;s gave place to the interpretation of the thickening as a continuous feature of the Iberian crust.&#160; However, a reappraisal of vintage refraction profiles and new data from autocorrelations of ambient noise recordings, challenge the alleged continuity. The Pyrenean-Cantabrian orogeny is a three-plate interaction. Beyond the three types of convergent boundaries we may need to introduce the hyperextended-continent destructive boundary, where this is a well-studied example but not the only one.&#160;

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Geophysical surveys of the East Kirkton Limestone, Viséan, West Lothian, Scotland

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s0263593300006003 ◽

1993 ◽

Vol 84 (3-4) ◽

pp. 197-202 ◽

Cited By ~ 2

Author(s):

Jonathan J. Doody ◽

Rona A. R. McGill ◽

David Darby ◽

David K. Smythe

Keyword(s):

Hot Spring ◽

Magnetic Data ◽

The West ◽

Near Surface ◽

The North ◽

New Information ◽

Geophysical Surveys ◽

Volcanic Formation ◽

Electrical Sounding ◽

Surface Occurrence

ABSTRACTMagnetic and resistivity geophysical surveys conducted across the only known exposure of the East Kirkton Limestone have produced new information upon its extent. This is important to determine because of its unique faunal assemblage and possible hot spring deposition, suggesting a potential for precious metal mineralisation. Magnetic anomalies are attributed to basalts within the Bathgate Hills Volcanic Formation. Modelling of the magnetic data demonstrates a general dip to the west of about 25°, and the presence of significant local faulting. Modelling of vertical electrical sounding data shows the East Kirkton sequence (the limestone and associated beds) to be a low resistivity layer within the more highly resistive volcanic sequence. The East Kirkton sequence is seen to deepen to the west, and also to the north probably by faulting. Therefore the present exposure is the only near surface occurrence of the East Kirkton Limestone locally, but within the area of the survey no lateral limits to the formation are observed.

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Transversely isotropic lower crust of Variscan central Europe imaged by ambient noise tomography of the Bohemian Massif

Solid Earth ◽

10.5194/se-12-1051-2021 ◽

2021 ◽

Vol 12 (5) ◽

pp. 1051-1074

Author(s):

Jiří Kvapil ◽

Jaroslava Plomerová ◽

Hana Kampfová Exnerová ◽

Vladislav Babuška ◽

György Hetényi ◽

...

Keyword(s):

Bohemian Massif ◽

Lower Crust ◽

Ambient Noise ◽

Regional Scale ◽

Crustal Thickening ◽

Scale Model ◽

Significant Feature ◽

Ambient Noise Tomography ◽

North East ◽

The North

Abstract. The recent development of ambient noise tomography, in combination with the increasing number of permanent seismic stations and dense networks of temporary stations operated during passive seismic experiments, provides a unique opportunity to build the first high-resolution 3-D shear wave velocity (vS) model of the entire crust of the Bohemian Massif (BM). This paper provides a regional-scale model of velocity distribution in the BM crust. The velocity model with a cell size of 22 km is built using a conventional two-step inversion approach from Rayleigh wave group velocity dispersion curves measured at more than 400 stations. The shear velocities within the upper crust of the BM are ∼0.2 km s−1 higher than those in its surroundings. The highest crustal velocities appear in its southern part, the Moldanubian unit. The Cadomian part of the region has a thinner crust, whereas the crust assembled, or tectonically transformed in the Variscan period, is thicker. The sharp Moho discontinuity preserves traces of its dynamic development expressed in remnants of Variscan subductions imprinted in bands of crustal thickening. A significant feature of the presented model is the velocity-drop interface (VDI) modelled in the lower part of the crust. We explain this feature by the anisotropic fabric of the lower crust, which is characterised as vertical transverse isotropy with the low velocity being the symmetry axis. The VDI is often interrupted around the boundaries of the crustal units, usually above locally increased velocities in the lowermost crust. Due to the north-west–south-east shortening of the crust and the late-Variscan strike-slip movements along the north-east–south-west oriented sutures preserved in the BM lithosphere, the anisotropic fabric of the lower crust was partly or fully erased along the boundaries of original microplates. These weakened zones accompanied by a velocity increase above the Moho (which indicate an emplacement of mantle rocks into the lower crust) can represent channels through which portions of subducted and later molten rocks have percolated upwards providing magma to subsequently form granitoid plutons.

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Controls on the development and termination of failed continental rifts: Insights from the crustal structure and rifting style of the North Sea via ambient noise tomography

10.31223/osf.io/m9kbe ◽

2019 ◽

Author(s):

Emily Crowder ◽

Nick Rawlinson ◽

David Cornwell ◽

Carmelo Sammarco ◽

Erica Galetti ◽

...

Keyword(s):

North Sea ◽

Crustal Structure ◽

Ambient Noise ◽

Ambient Noise Tomography ◽

The North ◽

Continental Rifts ◽

The North Sea

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Seismic interferometry ambient noise tomography—a study in the north-central part of Iran

Arabian Journal of Geosciences ◽

10.1007/s12517-021-06655-w ◽

2021 ◽

Vol 14 (5) ◽

Author(s):

Mohsen Beygi Nya ◽

Habib Rahimi ◽

Hooshmand Zandi

Keyword(s):

Ambient Noise ◽

Seismic Interferometry ◽

Ambient Noise Tomography ◽

North Central ◽

The North

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

Scientific Reports ◽

10.1038/s41598-020-80249-6 ◽

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.

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

10.5194/egusphere-egu21-20 ◽

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

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.In order to acquire new passive data from this region, a portable seismic network consisting of 13 three-component broadband stations was deployed (GEOCANT&#193;BRICA-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&#8217;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 &#8211; 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.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.

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