Multichannel Analysis Of Surface Waves Research Articles

Multiscale homogenization numerical study on the mechanism of interface debonding detection for steel–concrete composite structures with multichannel surface wave measurements

In order to understand the interface debonding detection mechanism for steel–concrete composite structures (SCCSs) efficiently using multichannel analysis of surface waves (MASW) when the heterogeneity and randomness of the mesoscale structure of concrete are considered, mesoscale homogenization numerical analysis on surface wave propagation in SCCSs is carried out. Firstly, for exploring the theoretical dispersion characteristics of surface waves in SCCSs, dispersion curves of both Lamb wave and Rayleigh wave of three different layering scenarios, including single-layer, two-layer, and three-layer composite models where concrete is treated as homogeneous material, are investigated. Meanwhile, the effect of the steel plate thickness on the dispersion curves is studied. Secondly, to evaluate the effect of mesoscale structure variation of concrete in SCCSs on surface waves, a random aggregate method (RAM) is employed to establish the mesoscale model of concrete composed of randomly distributed aggregates with different shapes. Thirdly, for enhancing numerical simulation efficiency on surface wave propagation, an equivalent homogenization approach and Voigt parallel model are developed to establish the mesoscale homogenization models of SCCSs. Dispersion curves from forwarding analysis on surface wave measurement of the mesoscale models are compared with the corresponding theoretical dispersion curves to reveal surface wave attribution and optimum layering scenarios of SCCSs for MASW method. The influence of mesoscale concrete variation on surface wave fields in SCCSs using equivalent homogenization models is investigated comprehensively and compared with that of the corresponding mesoscale models. Finally, the feasibility of the proposed MASW method for interface debonding length estimation is validated, and wavelength selection criteria of excitation signals considering interface dimension, as well as steel plate thickness, are discussed. The results from the mesoscale homogenization numerical study can provide helpful guidance on the practical application of MASW-based debonding detection for SCCSs where concrete is heterogeneous.

Application of geophysical prospecting methods ERT and MASW in the landslide of Daofu County, China

Natural disasters such as debris flow caused by earthquakes seriously threaten the local infrastructure and economy, as well as the lives of people in the area. As the material source of debris flow, it has significance to accurately and effectively study the underground structure of the landslide to prevent debris flow disasters. A landslide has a complex structural system, and its underground characteristics play an important role in its stability. The early identification of fracture surfaces and unstable bodies, and assessment of potential hazards are essential for prevention and protection. The research object of this paper is a landslide that occurred in Yige Village, Xianshui Town, Daofu County, which is on the Xianshui River Earthquake Zone, an area subject to frequent earthquakes. In western Sichuan, the frequent occurrence of landslides has caused considerable economic losses. Developing methods for efficient and accurate risk assessment is a top priority. The Daofu landslide is a typical example of a landslide directly threatening the road below and forming a debris flow channel. The lithology is composed of Jurassic sedimentary rocks, such as marl and clay, covered by limestone. In this study, we combined traditional methods (drilling and field investigation) with two geophysical techniques, multichannel analysis of surface waves (MASW) and electrical resistivity tomography (ERT) to effectively determine the electrical characteristics, velocity characteristics and spatial structure of the landslide. It is found that the buried depth of the sliding surface of the landslide is about 16–20 m. The sliding body above the sliding surface forms a low velocity and low resistivity Quaternary cover. The rock mass below the sliding surface is Triassic Zhuwo Formation sandstone and slate with high velocity and high resistivity. According to comprehensive analysis, the landslide lacks sufficient stability under rainstorm. Our study shows that the use of MASW and ERT can quickly and effectively characterize the subsurface of landslides to assess landslide risk and prevent debris flow hazards.

Extended Tromograph Surveys for a Full Experimental Characterisation of the San Giorgio Cathedral in Ragusa (Italy).

Geophysical surveys are widely used to reconstruct subsoil seismo-stratigraphic structures with a non-invasive approach. In this study the geophysical surveys were carried out with the aim to characterise the San Giorgio Cathedral in Ragusa (Italy) and the area on which it is built from a dynamic point of view. A 3D subsoil model was realised through the integration of two active (i.e., seismic tomography and multichannel analysis of surface waves) and one passive seismic technique (horizontal to vertical spatial ratio). The instrumentation used for the latter method consists of a tromograph (Tromino®), which is also employed for the characterisation of the building, focusing on the façade and the dome, by means of an ambient vibration test, processed through the standard spectral ratio and frequency domain decomposition methods. Integration of the 3D model, showing the distribution of areas with different physicomechanical characteristics, enables identifying anomalies that are likely attributable to the remains of the ancient Byzantine church of San Nicola. Four lower modes mainly involving the two investigated macroelements are identified. The experimental results outline the advantages of the use of the tromograph both for soil and structural characterisation, especially for massive masonry buildings located in areas with high seismic hazard.

Revealing the shallow soil structure of the Yigong Lake in the Tibetan Plateau using a portable distributed acoustic sensing interrogator

The harsh and extreme environmental and near surface conditions of the Tibetan Plateau have limited the conventional electrical-based seismic instruments from obtaining high-quality seismic data through long-term and continuous observations, setting challenges for environmental seismology study and natural hazard monitoring in this area. Distributed acoustic sensing (DAS) is an emerging technique based on optical fiber communication and sensing. It provides a possible solution for subsurface imaging in extreme conditions at high spatiotemporal resolution by converting fiber-optic cables into dense seismic strainmeters. We deploy two survey lines with armored optical fiber cables in the Yigong Lake area, Southeastern Tibetan Plateau, to record ambient noise for a week. The DAS interrogator is specifically designed in a portable size with very low power consumption (25 W/h). Hence, we can use a 12V-DC battery for power supply to adjust the power limitation during the field recording. Ambient noise interferometry and multichannel analysis of surface waves are used to get 2D shear wave velocity profiles along the fiber paths. The results highlight the great potential of DAS for dynamic monitoring of the geological evolution of lakes and rivers in areas of extreme environments as in the Tibetan Plateau.

Geological and geotechnical characterisation of soft Holocene marine sediments: A case study from the north Irish Sea

The seabed of the Western Irish Sea Mud Belt (north Irish Sea) comprises a thick sequence of fine-grained Holocene marine sediments that overlay complex glacial deposits. The Holocene sequence preserves a record of environmental change in the area. Part of this area is earmarked for a number of offshore wind farm developments. The area poses a number of geotechnical challenges to such developments, including soft marine silts and clays as well as shallow gas. This paper characterises the soil conditions in the area in the context of offshore renewable energy development using various geophysical techniques, geotechnical data and shallow (3 m) sediment samples obtained across multiple research surveys between 2009 and 2020. The purpose is to assess the use of such techniques, including multichannel sparker seismic and underwater multichannel analysis of surface waves (UMASW), in characterising these kinds of sediments. It is also intended to build on previous research and provide a reference dataset and case study for further work in developing offshore wind in the area. UMASW and in-situ cone penetration testing with pore pressure measurement (CPTu) results showed good agreement in characterising these Holocene sediments, with multichannel sparker delineating shallow gas from surrounding sediments. Core profiles show distinct lithological variation in the upper 3 m, which can be related to CPTu parameters, but is not resolvable by UMASW profiles. Paleoenvironmental reconstruction for this upper 3 m suggests changes in depositional setting over the past ca. 7000 years, which could influence sedimentary structure. These parameters have implications for cable installation design.

Seismic Site Response Analysis of MMMUT Gorakhpur of Uttar Pradesh, India

An endeavour has been made to assess the spatial fluctuation of the profundity of endured and designing bedrock in Gorakhpur Uttar Pradesh, North India utilizing Multichannel Analysis of Surface Wave (MASW) study. One-layered MASW study has been done at Madan Mohan Malaviya University of Technology, Gorakhpur campus and Shear-wave Velocity V S 30 are estimated. MASW overview at 3 location and a Standard Penetration Test SPT-N from the profound geotechnical boreholes data used for comparison of site classification. The deduction of this work might be utilized as contributions for seismic tremor risk the board by lessening the seriousness of earthquake shaking through plan of tremor Earthquake risk resilient structure strong designs. The data that collected from the MASW experimental setup is feed using the software ParkSEIS (v.3.0), we obtain Shear Wave Velocity (VS30 ). The obtained V S 30 is used to plot Response Spectra for MMMUT Gorakhpur. The Time History data used in this thesis is Nepal Earthquake 2015 data which is collected from Indian Metrological Department (IMD) Delhi, India. SPT-N value data is collected from Awas Vikas Parishad for the New Administration Building build at MMMUT campus Gorakhpur. The Time History data of Nepal Earthquake 2015 is analysed using DEEPSOIL v7 Software and a systematic layer wise study of MMMUT Campus soil is carried out, results such as Ground Motion Parameters, Response Spectra, Spectral acceleration vs Frequency plot, Tripartite Spectrum and Response spectra corresponding to 5% damping are obtained.

Identification of re-liquefaction potential based SPT and MASW data in Mpanau, Sigi after the earthquake 2018

In September 2018, there was an earthquake followed by liquefaction which caused damage to thousands of houses and infrastructure in Central Sulawesi Province, Indonesia. Liquefaction in Central Sulawesi has the potential to recur, so identifying potential liquefaction in areas that have occurred is essential. The objective of this research is to compare the results of determining liquefaction potential based on geotechnical and geophysical data. Based on the peak ground acceleration earthquake value, it shows that the liquefaction potential obtained in Mpanau is resemblant. The simulation will be conducted using Settle3 software based on methods, then the values of Cyclic Resistance Ratio (CRR) and Cyclic Stress Ratio (CSR) will be compared based on existing Multi-Channel Analysis of Surface Waves (MASW) data. MASW needs to be considered in the way of potential identification because it is advantageous. This Research uses MASW data where liquefaction flow and damage do not occur in Mpanau area even though the potential is quite significant. The result of this research shows that at distinct points of the SPT, MASW and the 7.5 Mw earthquake resulted in potential liquefaction still present in several soil layers, especially in the Gumbasa canal. It is necessary to repair and countermeasure to prevent liquefaction from disrupting the irrigation system's performance.

Subsurface identification in the Surabaya and Waru segment areas using the Multichannel Analysis of Surface Waves (MASW) method

Surabaya, especially the western part of Surabaya, has a diverse geological structure. As part of the Kendeng Zone, Surabaya has sedimentary rock formations that form anticlines and alluvium formations. In addition, the Kendeng Fault passes through Surabaya (Surabaya Segment and Waru Segment). This study aims to identify the structure of the soil to a depth of 30 meters using the Multichannel Analysis of Surface Waves (MASW) method which will be further processed into 2D slices with a North-South orientation. This research uses 11 field observation data from the Meteorology, Climatology, and Geophysics Agency in 2020 and 2023. The results of the 2D slices show that the range of Vs30 values is in the range of 92.8 m/s - 213.6 m/s and the Vs values for each depth layer are in the range of 88 m/s - 245 m/s. Based on SNI 1726:2019, both ranges indicate the classification of soft soil (SE) to medium soil (SD). The 2D section also shows a clear anticline on the section and the alleged Kendeng Fault.

Integrated Geophysical Imaging and Remote Sensing for Enhancing Geological Interpretation of Landslides with Uncertainty Estimation—A Case Study from Cisiec, Poland

Landslides, as one of the main problems in mountainous areas, are a challenging issue for modern geophysics. The triggers that cause these phenomena are diverse (including geological, geomorphological, and hydrological conditions, climatic factors, and earthquakes) and can occur in conjunction with each other. Human activity is also relevant, undoubtedly contributing to the intensification of landslide phenomena. One of these is the production of artificial snow on ski slopes. This paper presents a multimethod approach for imaging the landslide structure in Cisiec, in southwestern Poland, where such a situation occurs. In the presented work, the integration of remote sensing with multi-method geophysical imaging was used to visualize landslide zones, and to estimate ground motion. To verify the uncertainty of the obtained data, the combination of electrical resistivity tomography (ERT), multi-channel analysis of surface waves (MASW), and seismic refraction method (SRT) was supported by synthetic modeling. Using geophysical data with accurate GPS-based topography and a terrestrial laser scanning-based digital terrain model (DTM), it was possible to model the spatial variability and surface area of the landslide more precisely, as well as to estimate the velocity field in the nearest surface more accurately. The final result shows displacement up to 1 m on the ground surface visible on the DTM models, while the geophysical methods confirm the change in internal structure. The proposed methodology is fast, cost-effective, and can be used to image the structure of landslides, where the shallowest parts are usually complex and thus difficult to observe seismically.

Seismic mapping of shallow bedrock shelves in the hanging wall of the Wasatch fault

The Wasatch fault (WF) has been the subject of intensive study. Adjacent to a large and growing urban corridor, it poses a distinct seismic hazard for ∼2.5 million residents who live on its hanging wall, and has numerous Quaternary scarps and produced a M5.7 quake in March of 2020. Thus, the shallow architecture of the fault is important for understanding its earthquake hazards.Prior work has revealed shallow bedrock shelves in the hanging wall near the fault. To detect and image these shelves, we have employed the HVSR method (horizontal-to-vertical spectral ratio) at three locations along and across the WF. This method is powerful in that data can be collected rapidly in an urban setting. However, this method requires knowledge of the Vs of sediment overlying bedrock in order to estimate bedrock depth. We employed the MASW (multichannel-analysis of surface waves) method to obtain the characteristic Vs of sediment overlying bedrock.At Corner Canyon in Draper, Utah, Lake Bonneville sands and gravels overlie intrusive rocks of the Little Cottonwood Stock. Fault offsets inferred from HVSR correlate to mapped scarps. At Traverse Ridge, an HVSR profile co-located to a prior seismic reflection profile also detected shallow bedrock beneath alluvial fan sediment, including a graben system. However, at this site the geology is more complex. Fan sediment is underlain by altered volcanic rocks with subjacent quartzite. The HVSR method detected and characterized these boundaries.A majority of data were collected across the WF in the vicinity of Rock Canyon, Utah in order to create a 3D surface of the bedrock shelf. This area is heavily developed, but with numerous mapped scarps. A 3D model of the bedrock shelf indicates that it is broad, >1 km from the main trace of the WF. This width was not previously known. The HVSR results conform to mapped fault offsets, but also reveal a large, buried (and previously unknown) graben.One main finding of this study is that HVSR is a useful tool for mapping the shallow architecture of bedrock shelves in the hanging wall of normal faults, as long as a reasonable estimate of the Vs of sediment overlying bedrock can be made. Mapping can be accomplished rapidly in uneven topography or in urban settings as the instrumental footprint is very small. A second main finding is that large normal faults may commonly have concealed bedrock shelves. These shelves may affect engineering inputs like Vs30. However, they may also have other unanticipated effects on the nature of ground shaking, perhaps due to the trapping of energy or reverberation between the ground surface, bedrock shelf, and bedrock in the foot wall.

Common‐midpoint cross‐correlation stacking tomography: A 3D approach for frequency‐dependent mapping of Rayleigh waves, group and phase velocity throughout an active seismic network

AbstractShear‐wave velocity constitutes an important characterization parameter in terms of engineering properties. Several techniques of surface wave analysis have been widely adopted for building near‐surface 1D, or even 2D, S‐wave velocity models, but comparable 3D approaches, such as the surface wave tomography (SWT) method, are usually limited to global or regional seismological studies. Moreover, a reliable 3D subsurface imaging in a complex and noisy near‐surface environment becomes difficult when using the fully automated processing techniques that are commonly suggested for the SWT method. Here, a new strategy that is well adapted to geotechnical investigations is proposed to accomplish automatically the frequency‐dependent mapping of Rayleigh waves, both for group and phase velocity, throughout an active seismic network. The specific methodology can be implemented in both 2D and 3D active seismic data acquisition schemes involving both uniform and non‐uniform layouts of receivers. It combines the advantages of a newly created common‐midpoint (CMP) cross‐correlation (CC) analysis technique, with the precision of the travel‐time tomography method that is usually used in regional seismological studies. The main analysis is based on partitioning the different wave propagation directions, weighting the CC frequency–velocity analysis around one‐wavelength and stacking the CMP dispersion images. The tomographic inversion is applied to frequency‐dependent virtual travel‐times, produced from the azimuth‐dependent results of the specific analysis, in order to generate, as output, the local dispersion curves. The output of the proposed processing method can be interpreted with any preferred inversion algorithm for group and phase velocity, either individually or jointly. Simple synthetic tests together with a 3D seismic experiment in well‐known conditions, using standard refraction and multichannel analysis of surface waves (MASW) equipment, confirmed the effectiveness of the proposed methodology in detecting both lateral and vertical S‐wave velocity variations. A ‘construction site’ case study finally highlighted the potential of the new tool in a very difficult and noisy environment.

Environmental Impact Assessment of the Subsurface in a Former W-Sn Mine: Integration of Geophysical Methodologies

Associated with the exploitation of metallic minerals in Europe during the 20th century, several mining areas were abandoned without adequate environmental intervention. Furthermore, these areas lack studies to characterize the impact of pollution on the hydrogeological system. The area surrounding the tungsten mine of Regoufe, in northern Portugal, is one such area exploited during the Second World War. The accumulation of sulfide-rich tailings may have caused an acid mine drainage (AMD), where the leaching processes caused by seepage water led to soil contamination, evidenced by its acid character and anomalous concentrations of some Potentially Toxic Elements (PTE) reported in previous studies. The present research proposes an innovative approach that seeks the integration of different geophysical techniques to characterize the impact of mining activity on the subsurface. Electrical resistivity (ER) and electromagnetic (EM) were used to measure subsurface electrical properties. In addition, seismic refraction and Multichannel Analysis of Surface Waves (MASW) were performed to characterize the geometry, depth, and geomechanical behavior of the soil and rock bodies. The integration of these techniques allowed the interpretation of hydrogeological sections and a 3D resistivity volume to gain insight into the distribution of potentially contaminating fluids and tailings material present in the mining valley.

Application of a global–local full‐waveform inversion of Rayleigh wave to estimate the near‐surface shear wave velocity model

AbstractWe present a global–local full‐waveform inversion (FWI) of surface waves to estimate a high‐resolution shear wave velocity model of the near‐surface at the site of Grenoble (France). The seismic data we use have been acquired in the framework of the InterPACIFIC project. A first attempt is made by employing the multichannel analysis of surface waves (MASW) to invert the fundamental modes of Rayleigh waves. This inversion is solved through a global optimization driven by the neighbourhood algorithm. However, the limiting 1D assumption, together with the severely ill‐posedness of the MASW inversion motivate us to exploit all the information content of the recorded Rayleigh waves (i.e., travel‐times and amplitudes) by implementing a global–local FWI approach. We first perform a global FWI in which a genetic algorithm (GA) is used to minimize the L2 norm difference between observed and simulated seismic waveforms up to 30 Hz. This inversion employs a two‐grid scheme in which the subsurface is described by a fine grid input to the forward modelling, whereas the unknowns are defined on a coarse grid. A bilinear interpolation brings the coarse‐grid model into the fine grid. To accelerate the convergence, two strategies are considered; offset marching and frequency marching. Then, the long‐wavelength velocity profile provided by the GA inversion is used as the starting point for a local FWI for further refinement of the predicted model. In this case, we employ a frequency‐marching strategy up to a maximum frequency of 60 Hz. Both the global and local approaches use a finite difference code for the forward computation. Despite the limited a priori information infused into the inversion framework, the presented global–local FWI scheme provides reliable results as demonstrated by the good match between recorded and predicted seismograms and by the agreement of the estimated velocity with both nearby borehole data and stratigraphic information on the study site. Our global–local strategy also achieves better data fitting and improved matching with the available borehole data with respect to the velocity profile estimated when the local FWI is started from the MASW predictions.

Dispersive staggered grid finite difference modelling of Rayleigh waves

Non-destructive surface wave-based ground exploration techniques such as multichannel analysis of surface wave (MASW) require a rigorous numerical model to predict the soil properties accurately. The staggered grid finite difference (SGFD) method is widely used to simulate elastic wave propagation due to its stability and ease of implementation. However, in the presence of low-velocity layers, the SGFD method requires computationally expensive high spatial grid resolution to accurately model the surface waves. On the other hand, velocity dependent grid approaches become unstable for the highly irregular soil profile. In order to overcome these challenges, a vertically non-uniform dispersive staggered grid scheme is proposed that significantly reduces the computing time without sacrificing accuracy. The proposed non-uniform discretization strategy is based on the Rayleigh wave dispersion relation, where the penetration depth of each frequency is assumed to be roughly one and half of the wavelength. Based on the above assumption, an exponential relationship between grid size and grid number is developed. The proposed method calculates continuously increasing grid length while ensuring grid points at the exact layer interface. Five different soil profiles: a homogenous elastic half-space, an irregularly dispersive crustal level profile, a low velocity layer at a deeper depth model, a real-world model, and a lateral heterogeneous model are used to demonstrate the efficacy of the proposed approach. For all the cases, the results of the proposed dispersive grid match those of the uniform grid with a correlation coefficient value (R) > 0.99. Compared to the uniform and velocity dependent grid approaches, the proposed dispersive grid scheme requires ½ to 1/4th of elements and CPU time. Furthermore, unlike the velocity dependent grid scheme, the proposed method does not become unstable for a highly irregular profile. Results indicate that the proposed method is superior to the traditional uniform and velocity dependent grid approaches for modelling elastic waves in layered media.

Multichannel Analysis of Surface Waves (MASW) to Estimate the Shear Wave Velocity for Engineering Characterization of Soils at Hawassa Town, Southern Ethiopia

Site characterization is a prerequisite for the successful and economic design of engineering structures and earthworks by providing geological information for any proposed project. Until now, no detail study has been carried out on the site characterization and classification using shear wave velocity (Vs) up to the top 30 m depth in Hawassa town. For this study, multichannel analysis of surface waves (MASW) was used to determine the variation of Vs for a proper civil engineering design in the town. In addition, vertical electrical sounding (VES) and standard penetration test (SPT) were employed to characterize the near-surface materials. The Vs30 map was prepared for Hawassa town using the estimated Vs30 values which ranges from 248.9 m/s to 371.3 m/s while the SPT-N values were ranges from 5bpf to 50bpf. The correlation of Vs and SPT-N values has been done by considering both corrected and uncorrected SPT-N values. The VES result showed that groundwater is found at a shallow depth. The correlation of Vs and SPT-N value was validated using regression model. The 1D Vs profile and 2D cross-section showed low Vs at a shallow depth. The near-surface soils of the town are classified based on the Vs30 as site class C (stiff soil and soft rock) and D class (stiff soils) according to the NEHRP (Natural Earthquake hazards Reduction Program) and as subsoil classes B and C according to the Eurocode 8. The geotechnical tests also showed that the soils in the study area are silty sand, sand and silty sand with some gravel. The low Vs values observed at a shallow depth should be given much attention during foundation design for the stability of civil engineering structures.

Analysis on the dispersion characteristics of surface waves in a layered slope

For landslide detection and monitoring, surface wave methods (such as multichannel analysis of surface waves and array microtremor measurements), can be exploited to infer the subsurface shear-wave velocity (VS), which is a key physical parameter for calculating the soil vulnerability index and slope stability. To facilitate implementation, the seismic sources and geophones of survey lines traversing the slope of a landslide are commonly deployed along the direction of gravity. Considering that single (vertical)-geophones are extensively utilized in a variety of practical applications, it is meaningful to analyze the dispersion characteristics of the gravity-oriented component in a layered slope. Based on the stiffness matrix method and a coordinate rotation, we derive an explicit relationship for the gravity-oriented component in a layered slope. We further analyze the dispersion characteristics of the gravity-oriented component in three typical layered slopes by using a new developed tool comprising a seismic wavefield simulation and a modified frequency–Bessel transform. The results show that the dispersion spectra of the gravity-oriented component may be contaminated by Love waves, which can cause the Rayleigh wave dispersion curves to be misidentified. As the slope angle and the included angle between the survey line and dip direction increase, Love waves interfere more with the dispersion spectra of the gravity-oriented component. Numerical experiments indicate that if the slope angle is <17° or the angle between the survey line and dip direction is kept below a certain reasonable threshold, the dispersion spectra of the gravity-oriented component are determined mainly by Rayleigh waves. Moreover, we propose an azimuth filter method to suppress the interference of Love waves for passive surface wave dispersion measurements. The presented method offers useful guidance and emphasizes the great potential of surface wave methods in landslide detection and monitoring applications.

Comparative analysis of Geotechnical and Geophysical Investigations for average shear wave velocity in Metro Manila

Philippines is one of the most seismically active countries in Southeast Asia and records at least 20 earthquakes per day according to the PHIVOLCS. Vs30 is defined as the shear wave velocity of the upper 30-meter subsurface profile which is an important seismic parameter to determine the dynamic behavior of soils or rocks. This research aims to determine the Vs30 of three sites in Metro Manila using two methods Geotechnical Investigation(GI) and Geophysical Investigation(GPI) by Multichannel Analysis of Surface Waves (MASW) method and compare their results. The data used for GI are SPT N-values for soils and Rock Quality Designation. Conversely, a seismic survey using the MASW method was conducted along the three sites and Vs30 was determined based on the processed seismic data from Geogiga software. The results of the methods were compared in terms of the ratio between the Vs30 difference from geotechnical investigation and geophysical investigation with the calculated range based on the NEHRP classification table. The calculated ratios showed 43.68% for MNHS, 6.44% for BES, while 48.16% for VFMHS. Comparison of methods showed that ratio between Vs30-difference from GI and GPI with the calculated range based on the NEHRP was found to be acceptable (≤1.0) for all sites. Moreover, the seismic soil classification based on the NEHRP was found to be consistent for both methods.

Enhancing noise sources in stationary-phase zones for accurate phase-velocity estimation of high-frequency surface waves

Passive surface-wave methods are appealing tools for their ability to noninvasively obtain shear-wave velocity with high accuracy and low costs. A linear array of stations is widely adopted in urban areas for its convenient deployments and efficient utilization of ambient noise energy from stationary-phase zones (SPZs), which contributes the most to surface-wave retrieval. However, noise sources in nonstationary-phase zones may threaten the reliability of velocity estimation when they possess strong energy. To obtain reliable phase-velocity estimation of high-frequency surface waves (&gt;1 Hz), we enhance the contribution of noise sources in SPZs by using the multichannel-coherency-weighted stack (MCWS) method for the stacking of noise crosscorrelation functions and dispersion spectra. We model a nonuniform source distribution with strong offline sources. The seismic interferometry (SI) and passive multichannel analysis of surface waves (PMASW) methods overestimate velocities at lower frequencies (&lt;5 Hz), whereas phase velocities of short wavelengths are relatively accurate. The true velocities of short wavelengths are then set as the velocity scanning range for MCWS, and the waves whose apparent velocities lie within the scanning range would be emphasized by MCWS. Noise sources in SPZs are enhanced because the apparent velocities of waves from other noise sources are higher and not in the scanning range. After using MCWS, the phase-velocity estimations of SI and PMASW are consistent with the theoretical dispersion curve. A field data example at a crossroads demonstrates that uneven source distributions might cause serious artifacts and the feasibility of our method is again confirmed. In addition, the enhancement of noise sources in SPZs is verified through noise source distribution imaging by a matched field processing technique.

Near-Surface Geophysical Characterization of Lithologies in Corfu and Lefkada Towns (Ionian Islands, Greece)

Lefkada and Corfu old towns are located in the western part of Greece, in the Ionian Sea. Their proximity to the Hellenic subduction zone (HSZ) is the reason for their intense seismicity. The main goal of this study was the estimation of the geotechnical characteristics of the subsurface, with the contribution of applied geophysical techniques. Therefore, seismic refraction tomography (SRT) and multichannel analysis of surface waves (MASW) were applied. A total of thirty-three (33) seismic and geoelectrical profiles were performed in both towns in order to evaluate the geotechnical characteristics of the subsurface formations. Additionally, subsurface resistivity distributions were investigated with the application of electrical resistivity tomography (ERT). Some important elastic moduli were calculated through the combination of estimated seismic wave velocities and laboratory density measurements. The horizontal distribution of seismic velocities and mechanical properties (σ, E, K, G) of Corfu town was illustrated in maps, for the depth of 5 m. The geophysical interpretation also revealed that Lefkada’s subsurface consists of only one compact geological formation, with little or no variation of its geophysical-geotechnical characteristics. Beyond that, the ground type classifications for the two towns were determined according to the European Committee for Standardization Eurocode 8, based on VS30 values.

Seismic Site Classification Using the Multichannel Analysis of Surface Waves Method

The soil has a variety of qualities that affect its ability to support the weight of a structure. One of these features is soil stiffness, which can be determined using the surface wave method to prevent soil collapse. Multichannel Analysis of Surface Waves (MASW) is one of the non-invasive methodologies used in this study to investigate subsurface structures in North Sumatra, Indonesia. This method utilizes the dispersion properties of Rayleigh waves, producing a dispersion curve to get the shear wave velocity (Vs) through inversion. The shear wave velocity can be used to examine the soil stiffness qualities. The dispersion curve explains the relationship between shear wave velocity and depth, which can subsequently be used as a site class parameter. This survey uses three lines with one shot for each line which uses thirty geophones. The seismic source used is a gun with the type M16.38 Cal. Each line consists of 30 geophones with a distance of 5 m. The entire track is 160 m long and lasts for 2048 seconds with a sampling rate of 0.00025 seconds. The average shear wave velocity measured at three measurements was 372.5 m/s on line P1, 347.1 m/s on line P2A, and 311.0 m/s on line P2B, respectively. Overall, the soil classification on the P1 line is class C, and the P2A and P2B lines are class D, which is suitable for development planning areas.