The Role of Polarization Analysis in Reducing Natural Hazard

The complexity of the regions where the landslide occurred requires a detailed survey of the site response properties of these regions. Ambient noise analysis is a common and nondestructive approach that provides more detailed information on site resonance properties characterized by directional variations. Obtaining geological information from seismic data motivates researchers to innovate and improve efficient tools for seismic wave processing. Polarization-based methods have received much attention regarding their capability to discriminate between different phases of the seismic wave based on their polarities. Using polarization filtering to extract Rayleigh wave ellipticity provides more detailed information on site resonance properties characterized by directional variations. The outputs showed better performance of the method in terms of stability and reliability of the results. Indeed, it enabled the detection of site resonance characteristics that were previously undetectable by classic Nakamura method

Directional variations of site response in a landslide area using ambient noise analysis via Nakamura’s and polarization-based method

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 crustal and upper mantle structure beneath NW Iran : an integrated analysis of surface waves and gravity data

Understanding the crustal seismic characteristics of tectonically active regions is crucial for seismic hazard assessment. The study conducted in NW Iran utilized surface wave tomography, radial anisotropy, and density information to analyze the complex crustal structure of the region, which is outstanding because of diverse tectonic features, sedimentary basins, and volcanic formations. By selecting a dataset of 1243 events out of over 3,500 earthquakes with M>4, and employing strict data selection criteria (such as SNR, M, Δ), the researchers calculated Rayleigh and Love wave group velocity dispersion curves using Gaussian multiple filters and phase-matched filtering. The tomographic procedure was initiated by excluding data with residuals > 2σ for enhanced stability. Individual inversions were then carried out for local Rayleigh and Love wave dispersion measurements to obtain 1D VSV and VSH models. Radial anisotropy and VS iso were determined through a discrepancy and averaging of the obtained VSH and VSV, respectively. Gravity modeling was also employed alongside surface wave analysis to understand the region's complex geology, revealing insights into upper-middle-lower crust boundaries, subsurface structures, and Moho depths. The study's velocity maps reveal significant findings related to geological units and tectonic features in various regions based on the provided results. Low velocities in the South Caspian Basin (SCB) and Kura Depression (KD) regions are attributed to substantial sedimentary layers, while low velocities, and depth of VS in NW Iran and Eastern Anatolian Accretionary Complex (EAAC) regions suggest the presence of partially molten materials in the upper and middle crust. The Sanandaj-Sirjan Zone (SSZ) region shows a low velocity anomaly in longer periods and greater depths of VS, surrounded by normal to high velocities, indicating a thick middle crust. Analyzing radial anisotropy and VS iso profiles offers insights into upper-middle-lower crust boundaries, subsurface structures, and Moho depths, highlighting middle crust thickening and lower crust thinning beneath the SSZ. The study confirms the gentle subduction of the SCB oceanic-like lower crust beneath NW Iran in the Talesh (TAL) region, with a rigid middle crust. Additionally, cross-sections reveal igneous laccoliths underplate with a VS iso of 3.7 km/s in the volcanic region. The difference observed by subtracting the velocity models at two adjacent depths, combined with parametric test results, indicates that the Sahand volcanic system is clearly identifiable, while the influence of subtle subduction on the Sabalan volcano at depths up to 30 km remains less distinct. The magma chamber beneath Sahand is situated at depths ranging from 18 to 25 km