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.

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

2020 ◽  
Author(s):  
Jorge Acevedo ◽  
Gabriela Fernández-Viejo ◽  
Sergio Llana-Fúnez ◽  
Carlos López-Fernández ◽  
Luis Pando ◽  
...  
Keyword(s):  
Ambient Noise ◽  
Body Wave ◽  
Processing Technique ◽  
Ambient Noise Tomography ◽  
Cantabrian Mountains ◽  
Nw Spain ◽  
The West ◽  
The North ◽  
New Information ◽  
Nucleation Sites

<p><span><span>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. </span></span></p><p><span><span>In order to obtain new insights from this complex region, it was installed a network (GEOCANTÁBRICA-COST</span></span><span><span>A, doi:</span></span><span><span><span>10.7914/SN/YR_2019</span></span></span><span><span>) of 13 broadban</span></span><span><span>d stations covering an area of 160x80 km (</span></span><span><span>~40 km spacing) for 8 months.</span></span> <span><span>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’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. </span></span></p><p><span><span>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 </span></span><span><span><em>SeiscompP3</em></span></span><span><span>, 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.</span></span></p>

Stability of ambient noise H/V spectra obtained from OBS near the Japan Trench

2020 ◽  
Author(s):  
Atikul Haque Farazi ◽  
Emmanuel Soliman M. Garcia ◽  
Yoshihiro Ito
Keyword(s):  
Ambient Noise ◽  
Temporal Stability ◽  
Spectral Ratio ◽  
Japan Trench ◽  
Future Application ◽  
Ocean Bottom ◽  
S Wave ◽  
Slow Earthquakes ◽  
Short Period ◽  
Ocean Bottom Seismometers

<p>Ocean bottom seismometers (OBS) are widely in use since recent past to monitor seismicity of slow earthquakes as well as that of ordinary earthquakes. Seismic velocity structures, especially of S-wave are essential to estimate hypocenters of them with accuracy. Here we focus on spatial and temporal stability of ambient noise horizontal to vertical spectral ratio (H/V) spectra calculated from ocean bottom seismometers, as the first step toward future application of ambient noise H/V to estimate S-wave velocity structure. We aim to use the Nakamura’s method (1989) for ambient noise H/V spectra using a 3-component OBS array in the Japan Trench, to image deep structure above the plate interface near the trench. To achieve the imaging, it is necessary to examine spatial and temporal stability of the derived H/V spectra from these seismometers. First, we split each 24-hours record into 1-hour windows after removing the instrumental response, Then, Fourier amplitude spectra of each component is taken and smoothed using Konno and Ohmachi (1998) method, with applying downsampling, mean and trend removal, and tapering to each window. Finally, a 1-hour H/V spectral ratio is calculated with taking quadratic mean of two horizontal components. However, a total of 21 OBS, 3 broadband and 18 short-period, stations have been used in this study. A daily variation and stability of the H/V spectra are examined along with comparing them spatially from one station to another. Stability of the H/V spectra from OBS is promising for carrying out our future endevour of deeper observation using the ambient noise H/V method.</p>

scholarly journals South Ilan Plain High-Resolution 3-D S-Wave Velocity from Ambient Noise Tomography

2016 ◽  
Vol 27 (3) ◽  
pp. 375 ◽  
Author(s):  
Kai-Xun Chen ◽  
Po-Fei Chen ◽  
Li-Wei Chen ◽  
Huajian Yao ◽  
Hongjian Fang ◽  
...  
Keyword(s):  
High Resolution ◽  
Wave Velocity ◽  
Ambient Noise ◽  
S Wave ◽  
Ambient Noise Tomography

Application of 3D ambient noise tomography for an efficient S-wave velocity structure investigation

2019 ◽  
Author(s):  
Chisato Konishi ◽  
Koichi Hayashi ◽  
Ying Liu ◽  
Haruhiko Suzuki ◽  
Tadashi Sato
Keyword(s):  
Wave Velocity ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Structure Investigation ◽  
S Wave ◽  
Ambient Noise Tomography

Shallow Structure of the Longmen Shan Fault Zone from a High-Density, Short-Period Seismic Array

2019 ◽  
Vol 110 (1) ◽  
pp. 38-48 ◽  
Author(s):  
Yuting Zhang ◽  
Hongyi Li ◽  
Yafen Huang ◽  
Min Liu ◽  
Yong Guan ◽  
...  
Keyword(s):  
Surface Wave ◽  
Wenchuan Earthquake ◽  
Fault Zone ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Wave Dispersion ◽  
Ambient Noise Tomography ◽  
Surface Rupture ◽  
Short Period ◽  
Longmen Shan Fault

ABSTRACT The Longmen Shan fault zone that was shocked by the 12 May 2008 M 8.0 Wenchuan earthquake acts as the boundary between the western edge of the Sichuan basin and the steep eastern margin of the Songpan-Ganze block. In this study, continuous seismic data recorded by 176 temporary short-period seismic stations between 22 October and 20 November 2017 are used to study the shallow crustal structure of the Longmen Shan fault zone by applying ambient-noise tomography and horizontal-to-vertical spectral ratio (HVSR) analysis. From ambient-noise analysis, fundamental-mode Rayleigh-wave dispersion curves between 0.25 and 1 Hz are extracted. Then, the direct surface-wave tomographic method is used to invert surface-wave dispersion data for the 3D shallow shear-wave velocity structure. Our results show that low shear-wave velocities are mainly distributed around the surface rupture trace of the Wenchuan earthquake at least down to 2 km. From the HVSR method, the sites are sorted into two types according to the pattern of HVSR curves with single peak or double peak. By converting frequency to depth, the results show that the sediments are thicker near the surface rupture. The low-velocity zone based on ambient-noise tomography agrees well with the distribution of sedimentary cover estimated from HVSR, which are generally consistent with geological information. Our results provide high-resolution shallow crustal velocity structure for future detailed studies of the Longmen Shan fault.

Ambient Noise Tomography with Short-Period Stations: Case Study in the Borborema Province

2021 ◽  
Author(s):  
Cícero Costa da Silva ◽  
Esteban Poveda ◽  
Renato Ramos da Silva Dantas ◽  
Jordi Julià
Keyword(s):  
Ambient Noise ◽  
Ambient Noise Tomography ◽  
Borborema Province ◽  
Short Period

scholarly journals Delineation of Upper Crustal Structure Beneath the Island of Lombok, Indonesia, Using Ambient Seismic Noise Tomography

2021 ◽  
Vol 9 ◽  
Author(s):  
Achmad F. N. Sarjan ◽  
Zulfakriza Zulfakriza ◽  
Andri D. Nugraha ◽  
Shindy Rosalia ◽  
Shengji Wei ◽  
...  
Keyword(s):  
Group Velocity ◽  
Ambient Noise ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Inversion Method ◽  
Good Resolution ◽  
Ambient Noise Tomography ◽  
Fast Marching ◽  
Waveform Data ◽  
Short Period

We have successfully conducted the first ambient noise tomography on the island of Lombok, Indonesia using local waveform data observed at 20 temporary stations. Ambient noise tomography was used to delineate the seismic velocity structure in the upper crust. The waveform data were recorded from August 3rd to September 9th, 2018, using short-period and broadband sensors. There are 185 Rayleigh waves retrieved from cross-correlating the vertical components of the seismograms. We used frequency-time analysis (FTAN) to acquire the interstation group velocity from the dispersion curves. Group velocity was obtained for the period range of 1 s to 6 s. The group velocity maps were generated using the subspace inversion method and Fast Marching Method (FMM) to trace ray-paths of the surface waves through a heterogeneous medium. To extract the shear wave velocity (Vs) from the Rayleigh wave group velocity maps, we utilize the Neighborhood Algorithm (NA) method. The 2-D tomographic maps provide good resolution in the center and eastern parts of Lombok. The tomograms show prominent features with a low shear velocity that appears up to 4 km depth beneath Rinjani Volcano, Northern Lombok, and Eastern Lombok. We suggest these low velocity anomalies are associated with Quaternary volcanic products, including the Holocene pyroclastic deposits of Samalas Volcano (the ancient Rinjani Volcano) which erupted in 1257. The northeast of Rinjani Volcano is characterized by higher Vs, and we suggest this may be due to the presence of igneous intrusive rock at depth.

Sign in / Sign up

Export Citation Format

Share Document