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The analysis of earthquake recordings from three-component instruments can be challenging due to overlapping events. Time–frequency (TF) polarization methods are efficient tools for this purpose, which can discriminate these events. Previous polarization methods did not consider all three components simultaneously while transferring data to TF domain, which can cause inaccuracies in the reconstruction of wave amplitudes. Therefore, the three-component sparse adaptive S transform (3C-SAST) algorithm is preferred to other TF decompositions since it is mainly developed for polarization analysis purposes, and outperforms other TF methods. In this paper, we developed the 3C-SAST by adding a parameter to adjust the sparseness of the solution and make the resolution flexible. The developed TF decomposition is then used to extend the Morozov & Smithson method to TF domain, and devise a new TF polarization filter whose invertibility and resolution flexibility make it a promising tool for wavefield separation. This filter can eliminate the out-of-plane arrival energies and extract the Rayleigh waves for multicomponent data, which has application in Rayleigh wave tomography and seismological studies. We demonstrated the efficiency of the proposed method for seismic surface waves separation using synthetic signals and three-component teleseismic earthquake recording. [ABSTRACT FROM AUTHOR]

The interrelation between the local site conditions and the severity of destruction during earthquakes has increased the necessity for more investigations on soil characterization in recent years. In residential areas, where active seismic methods are problematic for defining soil properties, passive seismic methods have attracted considerable attention due to their cost-effective and non-invasive features. Therefore, we have utilized 35 single-station ambient seismic noise recordings in the seismically vulnerable city of Babol, Iran, to evaluate the site response (including azimuthal variation and resonance frequency), estimate the seismic vulnerability index (K g), and classify the soil based on the Vs 30 of the region. To address the aim, we extract Rayleigh wave ellipticities from ambient seismic noise using their polarization features and employ them to define the azimuthal variations, resonance frequencies, and K g values of the region. In each station, the ellipticity curve is inverted with the support of supplementary geotechnical information to obtain a shear velocity profile. The inversion results have good consistency with borehole and downhole test information. The study identifies a low resonance frequency of 0.9 Hz with a NE directivity for the majority of the city and a Vs 30 range of 180 m/s to 350 m/s. Moreover, the seismic bedrock of Babol City is represented by a 3D Vs model at a depth of 60 m. Our results reveal that the city is vulnerable to seismic hazards due to the thick and low-velocity deposits responsible for high amplification affecting the study region, which combines with a high seismic vulnerability index, particularly in the southern part. This work has applications for future structural design, urban development, and seismic hazard reduction. • The results represent that single-station ambient noise analysis is a cost-effective and reliable method for soil characterization. • Polarization methods are effective in extracting Rayleigh wave ellipticities from ambient noise recordings. • · The city is characterized by a low resonance frequency with an almost NE orientation and seismic bedrock at a depth of 60 m • · According to Iran's No. 2800 seismic code, the region classified as ground type III • · The soil characterization, high amplification and k g value make the region's southern part vulnerable to seismic shaking [ABSTRACT FROM AUTHOR]

Seismic attribute analysis has been a useful tool for interpretation objectives; therefore, high-resolution images of them are of particular concern. The calculation of these attributes by conventional methods is susceptible to noise, and the conventional filtering supposed to lessen the noise causes the loss of the spectral bandwidth. The challenge of having a high-resolution and robust signal processing tool motivated us to propose a sparse time–frequency decomposition which is stabilised for random noise. The procedure initiates by using sparsity-based, adaptive S-transform to regularise abrupt variations in the frequency content of the non-stationary signals. An adaptive filter is then applied to the previously sparsified time–frequency spectrum. The proposed zero adaptive filter enhances the high-amplitude frequency components while suppressing the lower ones. The performance of the proposed method is compared to the sparse S-transform and the robust window Hilbert transform in the estimation of instantaneous attributes through studying synthetic and real data sets. Seismic attributes estimated by the proposed method are superior to the conventional ones, in terms of robustness and high-resolution imaging. The proposed approach has a detailed application in the interpretation and classification of geological structures. [ABSTRACT FROM AUTHOR]

Obtaining geological information from seismic data motivates researchers to innovate and improve seismic wave processing tools. Polarization‐based methods have received much attention regarding their ability to discriminate between different phases of the seismic wave based on polarity. Combining the intuitive definition of polarity in the frequency domain (monochromatic waves) with the non‐stationary properties provided by time‐domain methods, time‐frequency approaches are attracting widespread interest because they localize the information extracted from the seismic waves in the joint time and frequency domains. Due to the lack of high‐resolution time‐frequency maps, the time‐frequency polarization approach was not able to resolve specific temporal polarity changes in the seismic signal. The main objective of this study was to devise a robust time‐frequency‐based polarization filtering method using high‐resolution polarization attributes obtained directly from the sparse time‐frequency map without using Eigen analysis or analytic signals. The method proposed here utilizes a computationally effective sparsity‐based adaptive S‐transform to obtain a high‐resolution polarization map of an inherently non‐stationary seismogram for the entire frequency content of the signal at different times. The superiority of the proposed method over the S‐transform method was verified using synthetic and real data sets to calculate the polarization attributes in the time‐frequency domain and separate the Rayleigh waves from the seismogram. [ABSTRACT FROM AUTHOR]

The complexity of the NE Iran region in which the 2014 Nargeschal landslide occurred, increased the necessity of detailed survey on the site response properties of this region. New investigations expanded the set of ambient noise measurements acquired in a previous work on the area affected by mass movement. The outcome of electrical resistivity and geotechnical studies were used to provide a comprehensive model of the landslide in addition to the substratum geology. The ambient noise recordings were analysed using the well-established Nakamura's method and a recently devised approach based on the analysis of the Rayleigh wave ellipticity to provide more detailed information on site resonance properties characterized by directional variations. The outputs, which were compared with the results of electrical resistivity tomography and geotechnical investigations, showed the better performance of the latter method in terms of stability and reliability of the results. Indeed, it allowed to detect site resonance characteristics that were unrecognizable by the Nakamura's method. Conclusively, the ambient noise analysis reveals that the directional resonance on different parts are due to the landslide and structural features of the site. The information obtained in this work is relevant for seismic hazard assessment in the study area. • The polarization analysis has more advantages than the Nakamura's method. • The analysis of the Rayleigh wave ellipticity provide more information on site resonance properties. • The outputs are more stable and reliable of the results. • The electrical resistivity and geotechnical studies used for a comprehensive model of the landslide. • The geological and structural features of the site are responsible for the directional resonance. [ABSTRACT FROM AUTHOR]

• Analyzing ambient noise horizontal-to-vertical spectral ratios to study site response • Evaluating site response defined resonance frequencies with amplification direction. • All stations defined by pronounced site response directivity along the same azimuth. • Directional spectral peaks matched with topographic and geologic features direction. • The landslide is responsible for the directional spectral peaks. [ABSTRACT FROM AUTHOR]