Shear wave velocity and attenuation structure of Ischia island using broad band seismic noise records

Summary The seismic response of the Santiago City, the capital of Chile with more than 5.5 million inhabitants, is controlled by the properties of the shallower quaternary deposits and the impedance contrast with the underlying Abanico formation, among other factors. In this study, we process continuous records of ambient seismic noise to perform an ambient seismic noise tomography with the aim of defining the shallower structure of the Abanico formation underneath the densely populated metropolitan area of Santiago, Chile. The seismic signals were recorded by a network consisting of 29 broadband seismological stations and 12 accelerograph stations, located in a 35 × 35 km2 quadrant. We used the average coherency of the vertical components to calculate dispersion curves from 0.1 to 5 Hz and Bootstrap resampling to estimate the variance of the travel times. The reliable frequency band of the dispersion curves was defined by an empirical method based on sign normalization of the coherency real part. The ambient noise tomography was solved on a domain discretized into 256 2 × 2 km2 cells. Using a regularized weighted least squares inversion, we inverted the observed travel-times between stations, assuming straight ray paths, in order to obtain 2D phase velocity maps from 0.2 Hz to 1.1 Hz, linearly spaced every 0.05 Hz, in 157 of the 256 square cells of the domain. In each square cell with information, dispersion curves were assembled and used to invert shear wave velocity profiles, which were interpolated using the ordinary Kriging method to obtain a 3D shear wave velocity model valid from 0.6 to 5 km depth. The 3D velocity model shows that the Abanico formation is stiffer in the south of the study area with larger velocity anomalies towards the shallower part of the model. The value of the shear wave velocity narrows with depth, reaching an average value of 3.5 km/s from 3 to 5 km depth.

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Shear wave velocity versus quality factor: results from seismic noise recordings

Geophysical Journal International ◽

10.1093/gji/ggx161 ◽

2017 ◽

Author(s):

Tobias Boxberger ◽

Marco Pilz ◽

Stefano Parolai

Keyword(s):

Quality Factor ◽

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Seismic Noise ◽

Velocity Versus

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Shear-wave velocity and attenuation structure beneath Antarctica determined from surface waves

Geophysical Journal International ◽

10.1111/j.1365-246x.1994.tb03982.x ◽

1994 ◽

Vol 118 (3) ◽

pp. 515-528 ◽

Cited By ~ 1

Author(s):

D. D. Singh

Keyword(s):

Surface Waves ◽

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Attenuation Structure

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Crustal shear-wave velocity structure of northeastern Tibet revealed by ambient seismic noise and receiver functions

Gondwana Research ◽

10.1016/j.gr.2015.08.009 ◽

2017 ◽

Vol 41 ◽

pp. 400-410 ◽

Cited By ~ 10

Author(s):

Zhenbo Wu ◽

Tao Xu ◽

José Badal ◽

Huajian Yao ◽

Chenglong Wu ◽

...

Keyword(s):

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Seismic Noise ◽

Velocity Structure ◽

Receiver Functions ◽

Ambient Seismic Noise ◽

Northeastern Tibet ◽

Shear Wave Velocity Structure

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

10.5194/egusphere-egu2020-7916 ◽

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

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.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.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 46-540 N 7-210 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 at high-density grid with the cell size of 22 km. 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 Kampfov&#225; Exnerov&#225; 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.

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Crustal structure of the Basque-Cantabrian Zone (N Spain) from seismic noise and receiver functions

10.5194/egusphere-egu2020-9603 ◽

2020 ◽

Author(s):

Andrés Olivar-Castaño ◽

Marco Pilz ◽

David Pedreira ◽

Javier A. Pulgar ◽

Alba Díaz-González ◽

...

Keyword(s):

Shear Wave ◽

Wave Velocity ◽

Crustal Structure ◽

Shear Wave Velocity ◽

Seismic Noise ◽

Receiver Functions ◽

Linear Inversion ◽

African Plate ◽

Cantabrian Zone ◽

Non Linear

The Basque-Cantabrian Zone was one of the most subsident areas between the European plate and the Iberian sub-plate during the Mesozoic rifting process that gave birth to the Bay of Biscay. Since the latest Cretaceous and during the Cenozoic, a change to a contractional setting driven by the northward drift of the African Plate made this hyperextended rift basin to be inverted and incorporated into the Pyrenean-Cantabrian mountain belt. The resulting crustal structure shows a high complexity, as evidenced by the many existing geophysical observations pointing to the presence of intracrustal high-velocity bodies, deep transfer structures, and sharply-varying Moho depths across the area.In this work, we use data provided by the dense SISCAN and MISTERIOS seismic networks, deployed in the region between 2014 and 2018, to obtain a detailed 3D shear-wave velocity model. We use the continuous recordings to compute seismic noise cross-correlation functions, from which we extract surface wave dispersion measurements. We use these measurements to obtain a set of phase velocity maps, and then perform a non-linear inversion at regularly spaced locations for the 1D shear-wave velocity structure. In the non-linear inversion, the forward modeling accounts for the presence of higher modes of surface waves, which have been shown to be more sensitive to velocity decreases with depth than the fundamental model. In order to better constrain the deeper layers of the model, we complement the seismic noise observations with an analysis of teleseismic receiver functions, which allows us to better constrain the depths of the major crustal discontinuities. Our results agree with previous geophysical studies, but significantly improve the availability of high-resolution information in the Basque-Cantabrian Zone.

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Imaging of a Magma System Beneath the Merapi Volcano Complex, Indonesia, using Ambient Seismic Noise Tomography

Geophysical Journal International ◽

10.1093/gji/ggab104 ◽

2021 ◽

Author(s):

T Yudistira ◽

J-P Metaxian ◽

M Putriastuti ◽

S Widiyantoro ◽

N Rawlinson ◽

...

Keyword(s):

Rayleigh Wave ◽

Group Velocity ◽

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Seismic Noise ◽

Ambient Seismic Noise ◽

Wave Group ◽

Velocity Anomaly ◽

Cross Correlations

Summary Mt. Merapi, which lies just north of the city of Yogyakarta in Java, Indonesia, is one of the most active and dangerous volcanoes in the world. Thanks to its subduction zone setting, Mt Merapi is a stratovolcano, and rises to an elevation of 2968 m above sea level. It stands at the intersection of two volcanic lineaments, Ungaran–Telomoyo–Merbabu–Merapi (UTMM) and Lawu–Merapi–Sumbing–Sindoro–Slamet, which are oriented north-south and west-east, respectively. Although it has been the subject of many geophysical studies, Mt Merapi's underlying magmatic plumbing system is still not well understood. Here, we present the results of an ambient seismic noise tomography study, which comprise of a series of Rayleigh wave group velocity maps and a 3-D shear wave velocity model of the Merapi-Merbabu complex. A total of 10 months of continuous data (October 2013–July 2014) recorded by a network of 46 broadband seismometers were used. We computed and stacked daily cross-correlations from every pair of simultaneously recording stations to obtain the corresponding inter-station empirical Green's functions. Surface wave dispersion information was extracted from the cross-correlations using the multiple filtering technique, which provided us with an estimate of Rayleigh wave group velocity as a function of period. The group velocity maps for periods 3–12 s were then inverted to obtain shear wave velocity structure using the neighbourhood algorithm. From these results, we observe a dominant high velocity anomaly underlying Mt. Merapi and Mt. Merbabu with a strike of 152° N, which we suggest is evidence of old lava dating from the UTMM double-chain volcanic arc which formed Merbabu and Old Merapi. We also identify a low velocity anomaly on the southwest flank of Merapi which we interpret to be an active magmatic intrusion.

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