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 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.

Fluvial Seismology: Case Study of the Contagem River (Brasilia), Brazil

2021 ◽  
Author(s):  
Hans-Balder Havenith ◽  
Yawar Hussain ◽  
Susanne Maciel
Keyword(s):  
Ambient Noise ◽  
Significant Risk ◽  
Federal District ◽  
Dynamic Monitoring ◽  
Data Logger ◽  
Fluvial Systems ◽  
Short Period ◽  
In Situ Investigation ◽  
Rainy Days

<p>Rainfall-induced landslides may pose a significant risk to communities and infrastructures. Such landslides are substantially impacted by the fluvial systems, therefore the continuous monitoring of the seasonal erosive potentials of these rivers are crucial. However, such environmental conditions the direct in-situ investigation is often a challenging task. Therefore, the present study aims at providing a brief overview of the use of ambient seismic noise for the dynamic monitoring of fluvial systems and a discussion about the preliminary results obtained from a Brazilian case study.</p><p>Data were acquired with single short-period (2 Hz) seismometers, REFTEK-130 data-logger and GPS lock, in dry and rainy days installed within a seasonal streams in Ribeirão Contagem watershed of the Federal district of Brazil. The pre-processing of ambient noise records include conversion from REFTEK to mini-seed format and saving data in units of velocity after removing the instrumental response. Then, the frequency content (spectrograms, percentiles), waveform characteristics (envelope) and polarization attributes of changes in ambient noise wave-fields induced by bed-load transport and water flow in dry and flooding days are analyzed.</p><p>A prominent increase in mean probabilistic power spectral density (PPSD) values are observed during rainy days within a frequency range of 10 Hz to 100 Hz. The polarization analysis shows that most of the recorded energy arrived from the river side. It is concluded that seismic attributes have their relation with the river generated ambient noise and can be used for the remote monitoring of such fluvial systems. Future studies dedicated to the dense surficial and geodetic surveying (also with UAV) are recommend for the detailed quantification of these seasonal river dynamics.</p><p><strong>Keywords: </strong>Seismic records; bed-loads; spectrograms; percentile; envelope</p>

Ambient noise tomography for geothermal exploration, a case study of WWs geothermal field

2018 ◽  
Author(s):  
Arzalia Wahida ◽  
Henry Wijaya ◽  
Tedi Yudistira ◽  
Mohammad Rachmat Sule
Keyword(s):  
Ambient Noise ◽  
Geothermal Field ◽  
Ambient Noise Tomography ◽  
Geothermal Exploration

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.

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.

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