Shallow crustal structures of the Tehran basin in Iran resolved by ambient noise tomography
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In this study, we present an application of the ambient noise tomography (ANT) to study the near-surface geological structures of the metropolitan Tehran/Iran region. Short-period fundamental mode Rayleigh wave Green's functions were estimated using cross-correlations of the vertical component of the ambient noise from 2009 October to 2011 May using a variety of seismic sensors, for example, accelerometers and seismometers, deployed in the Tehran area. Standard common low frequency processing procedures were applied to the cross-correlations, and shorter time-windows comprising 10-min segments were used in the processing step to enhance the time resolution of the signal in the frequency range of interest (1–10 s). Stacking was also conducted using the rms of the estimated empirical Green's functions. Our results demonstrate that ambient seismic noise tomography is a viable technique at periods of 1–10 s in length, even when different sensor types are present. Analysis of the empirical Green's functions indicates that the dominant sources of ambient seismic noise originated from the same origin, and no significant seasonal or spatial variations in the ambient noise sources were observed. Multiple-filter analysis was used to extract the group velocities from the estimated empirical Green's functions, which were then inverted to image the spatially varying dispersion at periods of lengths between 1 and 7 s using tomographic inversion of the traveltimes estimated for each frequency. The resulting group velocity maps show high correlations with known geological and tectonic features of the study region. In general, most of the Tehran basin, with certain exceptions, could be clearly resolved with low group velocities, whereas the mountain ranges were found to be correlated with high group velocities. In the Tehran basin, for 2 and 3 s periods, the low-velocity zone deepens towards the south–southwest, which reflects thicker sediments in the southern part of the basin than in the north. This feature has also been observed in other geological studies. The Vs models also show that bedrock depth varies between 400 and 1400 m from north to south within the Tehran basin. At longer periods main faults are associated with abrupt transitions between regions of high- to low-velocity anomalies. In general, our results indicate that ANT can be a flexible and effective approach for studying near-surface heterogeneity using short-period surface wave data.Keywords:
Ambient noise level
Seismic Noise
Seismometer
Seismic Tomography
Passive seismic
Rayleigh Wave
Seismic interferometry
Ambient noise-based seismology is fast expanding and has been widely applied to global and regional Earth′s interior imaging,near-surface investigation,and oil and gas exploration and production.The review article briefly introduced the origins of ambient noises and traced the root and development history of ambient noise-based seismology.Based on numerous work of modeling and observation,we reviewed the effects of source distribution and station separation on Green′s function retrieved for full fields and single mode surface-wave.The theoretical connection and difference between two-station correlation and spatial auto-correlation are also discussed.We then described the methods of ambient noise-based imaging,including ambient noise-based tomography,ambient noise-based eikonal tomography,and seismic interferometry or virtual source method.Finally we summarized its various but emphasizing on near-surface applications and gave an outlook for its future development.
Ambient noise level
Seismic interferometry
Seismic Noise
Mode (computer interface)
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Summary An extensive active and passive seismic survey was carried out in the Thinia Valley (Kefalonia Island, Greece) in May 2022 to investigate the complex geo-structural setting of the area. Surface waves retrieved from the active seismic surveys provided velocity models along the investigated lines. To potentially increase the investigation depth, a passive 2D array of seismic stations continuously acquired ambient seismic noise in the area between the active lines for three days. The passive recordings were preliminary treated for the retrieval of surface waves through a Frequency Domain Beam Forming Method. Few useful events were detected due to the short duration of the acquisition and the lack of strong anthropic noise sources in the area. To increase the coverage, ambient noise interferometry was carried out on the passive data, with successful results. Ambient noise tomography demonstrated to be a valid complementary tool for the retrieval of a subsurface velocity model, when the passive data lack information on the noise source azimuth.
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Ambient noise level
Seismic Noise
Seismic interferometry
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Seismic interferometry can be used to extract useful information about Earth's subsurface from the ambient noise wave field. It is an important new tool for exploring seismically quiescent areas. The method involves extraction of empirical Green's function from the background ambient vibrations of the Earth, followed by computation of group or phase velocity and tomographic imaging. Here we provide a review of seismic interferometry and ambient noise tomography (ANT) and present an example of the method in south India.
Ambient noise level
Seismic interferometry
Seismic Noise
Seismic Tomography
Ambient vibration
Passive seismic
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Summary Ambient-noise seismic interferometry (SI) could retrieve the Green’s function between receivers. Ambient-noise SI for retrieval of surface waves has shown that longer recordings help retrieve better surface waves due to improved illumination. This is also accepted to be the case for retrieval of reflections, but is not necessarily true. Retrieval of reflections depends on availability of body waves in the noise, but body-waves sources, for example seismicity, are bound to specific areas. This means that longer recordings might not improve the illumination of the receivers. We apply SI by cross-correlation to two ambient-noise datasets recorded in 2009 and in 2011 at the same place in Mizil area, Romania. This area is rich in local and regional seismicity. We use the 2009 dataset and the combined dataset from the 2009 and the 2011 surveys. We analyze the illumination of the 2009 and the combined dataset and show that the latter is richer and more diverse in body-wave slownesses. We retrieve common-source gathers and process them to obtain stacked sections of the subsurface. Comparing the two passive sections with a section from active data, we show that the retrieved reflections from the combined dataset correspond better with reflections from the active section.
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Passive seismic
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Cross-correlation of ambient noise is an effective approach to extract seismic responses between two stations using seismic interferometry. Since we frequently calculate the cross-correlation of the ambient noise assuming homogeneous distribution of ambient noise sources, heterogeneous distribution of the ambient noise sources would interfere in constructing seismic responses in the calculation of the cross-correlation. In this study, we identified the ambient noise sources recorded in a dense seismic array and utilized the information for better subsurface imaging. The seismic array was composed of 50 stations installed in a 480 m ×350 m area in the Itoshima Peninsula, Japan. By analyzing direction of incoming ambient noise, we found that most of ambient noise was generated by traffic from the nearby street. The traffic noise generated surface waves in lower frequencies (< ~10 Hz) and Pwaves in higher frequencies (> ~20 Hz). We also identified high frequency surface (or air) waves generated by a point source at ~60 Hz. This localized noise could be derived from the renovation work because the location of the source was estimated around the renovation site. We then estimated low- and high-frequency surface wave velocities between each station pair. Although we estimated the surface wave velocities in the limited azimuth between the stations due to the localized noise distribution, we estimated reliable surface wave velocities by considering the noise heterogeneity. High resolution maps of the surface wave velocities were tomographically constructed from the surface wave velocities between the station pairs. Thus, identifying the sources of the ambient noise acquired with dense seismic arrays is effective to improve the ability of ambient noise data to image subsurface structures. It also contributes to the design of seismic arrays in further ambient noise surveys.
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Passive Seismic Interferometry (PSI) is considered as a revolutionary method characterized by a rapid development especially during the last decade. The method was initially based on the theory that the cross-correlation (CC) of random wave fields of ambient seismic noise recorded on two locations (stations) on the Earth’s surface yields an approximation of the Green’s function (GF) of the medium between the two locations. The retrieved empirical GF represents an approximation of the seismic response as if one of the two stations was acting as an impulsive source of surface waves (e.g. Claerbout, 1968; Lobkis and Weaver, 2001; Campillo and Paul, 2003; Shapiro and Campillo, 2004; Wapenaar, 2004; Cutris et al., 2006). Since the retrieved GF carries the signature of the velocity structure between the stations, the inter-station travel-times for surface- waves on multiple paths within a seismic network can be used in a tomographic inversion to image the seismic velocity perturbations, by performing the commonly called Ambient Noise Tomography (ANT).
Seismic interferometry
Seismic Noise
Ambient noise level
Passive seismic
Seismic Tomography
Cross-correlation
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To study the applicability of the passive seismic interferometry technique to near-surface geological studies, seismic noise recordings from a small scale 2-D array of seismic stations were performed in the test site of Nauen (Germany). Rayleigh wave Green's functions were estimated for different frequencies. A tomographic inversion of the traveltimes estimated for each frequency from the Green's functions is then performed, allowing the laterally varying 3-D surface wave velocity structure below the array to be retrieved at engineering–geotechnical scales. Furthermore, a 2-D S-wave velocity cross-section is obtained by combining 1-D velocity structures derived from the inversion of the dispersion curves extracted at several points along a profile where other geophysical analyses were performed. It is shown that the cross-section from passive seismic interferometry provides a clear image of the local structural heterogeneities that are in excellent agreement with georadar and geoelectrical results. Such findings indicate that the interferometry analysis of seismic noise is potentially of great interest for deriving the shallow 3-D velocity structure in urban areas.
Seismic interferometry
Seismic Tomography
Seismic Noise
Passive seismic
Rayleigh Wave
Vertical seismic profile
Microseism
Seismic array
Dispersive body waves
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Summary Near-surface imaging is crucial for a broad range of studies, with seismic monitoring becoming an increasingly important tool due to recent developments in Distributed Acoustic Sensing (DAS) and ambient noise interferometry (ANI). Using a dataset acquired on the Rutford Ice Stream, West Antarctic, we develop ANI approach for DAS datasets which retrieves the Rayleigh wave response from the ambient seismic wavefield. We find that a conventional ANI approach, which uses a single DAS channel as a virtual source and the entire continuous dataset is stacked, produces unstable, poor quality interferograms. This is due to coherent instrument noise and an absence of continuous ambient seismic noise. To overcome these issues, we develop an approach based on selective-stacking and hybrid seismic receivers, which significantly improves the quality of the Rayleigh waves retrieved using DAS. Our findings highlight the impacts that coherent DAS instrument noise and the transient nature of seismic noise above 1Hz has on ambient seismic noise studies.
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Seismic Noise
Rayleigh Wave
Seismic interferometry
Passive seismic
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Passive seismic interferometry is a new promising methodology for seismic exploration. Interferometry allows information about the subsurface structure to be extracted from ambient seismic noise. In this study, we apply the cross-correlation technique to approximately 25 hr of recordings of ambient seismic noise at the Ketzin experimental CO2 storage site, Germany. Common source gathers were generated from the ambient noise for all available receivers along two seismic lines by cross-correlation of noise records. This methodology isolates the interstation Green's functions that can be directly compared to active source gathers. We show that the retrieved response includes surface waves, refracted waves and reflected waves. We use the dispersive behaviour of the retrieved surface waves to infer geological properties in the shallow subsurface and perform passive seismic imaging of the subsurface structure by processing the retrieved reflected waves.
Seismic interferometry
Seismic Noise
Ambient noise level
Passive seismic
Vertical seismic profile
Cross-correlation
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Seismic Interferometry (SI) is the process of generating seismic traces from the crosscorrelation of existing traces. One application of SI is the retrieval of surface-wave arrivals between two passive stations at the Earth’s surface from the crosscorrelation of ambient noise. Another application is the retrieval of body-wave reflections from the crosscorrelation of ambient noise recorded at the Earth's surface. Retrieved reflections would afford the construction of subsurface velocity models and subsurface reflection images with higher resolution than provided by surface-wave tomography. So far the extraction of body-wave reflections has proven to be more challenging. Several factors contribute to this difficulty: e.g., the difference in geometrical spreading between body and surface waves and the reliance on a random distribution of noise sources in the subsurface, as opposed to the ubiquitous and well-studied surface noise.
Seismic interferometry
Ambient noise level
Reflection
Seismic Noise
Passive seismic
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