CHARACTERISATION OF THE ELASTIC PROPERTIES OF SOILS IN SOME PARTS OF LAGOS WETLANDS FOR ENGINEERING PURPOSES

The results obtained from the evaluation of elastic properties of some part of Lagos Wetlands were presented for the determination of the competent soil for engineering structures. The study area falls within the reclaimed part of the Lagos wetlands signifying the presence of unstable geological materials. The study area is characterized with alluvium sediments which comprises of materials of low shear strength. Five (5) seismic profile lines were established via the ground rolling technique of Multi-Channel Analysis of Surface Waves (MASW). The data acquisition was carried out with twenty-four (24) channels 4.5Hz vertical geophones connected to the ABEM Mark 6 Terraloc Seismograph. The acquired MASW data were processed using SeisImager to obtain the two-dimensional (2-D) shear wave velocity (Vs) profiles which gives the contrast in the distribution of the velocity along each profile. In addition, dynamic parameters such as rigidity modulus, poisson ratio were estimated for further classification of the geo-earth materials in the study area. In the study area, the shear wave velocity (Vs) values obtained ranged between 94 – 1320 m/s representing different sediments such as saturated loose sand (163 – 204 m/s), loose silty sand (165- 225 m/s), medium – dense sand (220 – 350 m/s), medium dense sand (400 – 700 m/s) and dense-coarse sand (900 - 1380 m/s). However, based on these classification, it is found that saturated loose sand and loose silty sand are not competent for founding layer of engineering structures. Therefore, deep foundation inform of piling system is recommended for engineering structure that will devoid unexpected collapse and partial and differential settlement. The study has revealed that the area is generally comprise of problematic soil(s) that are inimical to construction of engineering structures

Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world

Constrained Parameterization of the Multichannel Analysis of Surface Waves Approach with Application at Yuma Proving Ground, Arizona

Field data from Yuma Proving Ground, Arizona was used to test the feasibility of merging common multichannel analysis of surface waves (MASW) processing routines with mode- consistent shear-wave refraction traveltime tomography and synthetic modeling to optimize and constrain inversion results. Shear-wave first-arrival refraction tomography was used to enhance layer-model resolution and refine the MASW layer model with independent body-wave information. Shear-wave tomograms suggested a high-velocity layer, not found in initial `smooth' MASW velocity sections that were used as initial models for tomographic inversion. Increasing the stratification of the MASW layer model, to generally match tomogram structure, resulted in a higher-resolution MASW model constrained through joint analysis. This mutual analysis of shear-wave velocity (Vs) provided multiplicity to the structural interpretation of the site. Constrained-parameterization MASW results, compressional-wave tomography (Vp:Vs ratio), and density well logs populated a 2D model for numerical modeling, which was manually updated over several iterations to converge upon the site's first-arrival and dispersion characteristics. Further evaluation of the synthetic seismograms gave insight into the relationship between acquisition geometry (offset selection) and the associated dispersion-image character. Furthermore, modeling gave a secondary measurement on depth to half-space, velocity structure, and relative Vp:Vs ratios, which formulated a final MASW profile. The gradual change of the earth model, given an evolving hierarchy of constraint, is seen as the main finding of this thesis. The calculated movement towards a higher-resolution inversion based on joint geophysical measurements, analysis, and interpretation, engenders a constrained-parameterization solution with highest confidence

Robust Earthquake Site Classification Assessment at Ontario Bridge Sites.

Canadian seismic design guidelines classify subsurface ground conditions based on the average shear-wave velocity (VS) of the upper 30 meters (VS30). We seek to optimize a robust earthquake site classification procedure for Ontario bridge sites, assessed primarily from blind comparison of non-invasive VS depth profiling techniques. Non-invasive seismic testing is performed at 10 bridge sites in southern Ontario co-located with invasive penetration and/or borehole VS measurements. Non-invasive surface wave dispersion and site amplification functions are jointly inverted to retrieve VS profiles at each site. A general correlation between corrected VS and cone tip resistance (qc1) is developed for all soils encountered in Windsor, Ontario. We determine an overall average relative difference in VS between methodologies of 17% for soil layers at all bridge sites. Earthquake site classification based on VS is consistent at all sites regardless of methodology. Non-invasive techniques offer an efficient but lower-resolution VS profiling alternative to invasive earthquake site classification techniques with the advantages of measuring site period and VS of the impenetrable substratum

Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world.The authors would like to acknowledge the project INTERGEO (CGL2013-47412-C2-1-P) GEO3BCNCSIC for the data access. Data are public access through SeisDARE (DeFelipe et al., 2021), dataset Martí et al. (2015). The Ministry of Education and Culture of the Republic of Indonesia is thanked for the main author’s Ph.D. scholarship (D3.2/KD.02.01/2019). JA is funded by MICINN (IJC2018-026335-I). I.P. is funded by the Spanish Government and the Universidad de Salamanca (Beatriz Galindo grant BEGAL 18/00090). IDF is funded by a FEDER-Junta de Castilla y León Postdoctoral contract (SA0084P20). We thank the GIPP-GFZ, (Germany) and Lisbon University (Portugal) for the instrumentation provided. Generalitat de Catalunya (AGAUR) grant 2017SGR1022 (GREG); EU (H2020) 871121 (EPOSSP); and EIT-RawMaterias 17024 (SIT4ME). WPeer reviewe

Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

Acknowledgement. The authors would like to acknowledge the project INTERGEO (CGL2013-47412-C2-1-P) GEO3BCNCSIC for the data access. Data are public access through SeisDARE (DeFelipe et al., 2021), dataset Martí et al.(2015). The Ministry of Education and Culture of the Republic of Indonesia is thanked for the main author's Ph.D. scholarship (D3.2/KD.02.01/2019). JA is funded by MICINN (IJC2018-026335-I). I.P. is funded by the Spanish Government and the Universidad de Salamanca (Beatriz Galindo grant BEGAL 18/00090). IDF is funded by a FEDER-Junta de Castilla y León Postdoctoral contract (SA0084P20). We thank the GIPP-GFZ, (Germany) and Lisbon University (Portugal) for the instrumentation provided. Generalitat de Catalunya (AGAUR) grant 2017SGR1022 (GREG); EU (H2020) 871121 (EPOSSP); and EIT-RawMaterias 17024 (SIT4ME). We sincerely thank Seismic Unix CWP (Center for the Wave Phenomena, Colorado School of Mines (Cohen and Stockwell, 2019)). We also thank all the people involved directly or indirectly in this work.The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world

Acquisition of active multichannel analysis of surface waves (MASW) data in karst terrain

This study was designed to verify the effects and data reproducibility when the length of receiver array, receiver spacing, source offset and array orientation parameters are changed for data acquired using multichannel analysis of surface waves (MASW), at intended target depth of 30ft (9m), and to compare the results with electrical resistivity tomography (ERT) data obtained for the same study site. The MASW data acquired for 34 sites, along four profiles for each site using variable source offsets of 10ft (3m) and 30ft (9.1m), and variable receiver spacings of 2.5ft (0.76m) and 5.0ft (0.76m), concurrently. Out of the 272 profiles studied, 136 profiles were oriented east-west, and 136 profiles were oriented north-south. The MASW data was used in conjunction with ERT data to ensure the accuracy of the ERT data. The comparative analysis indicated the profile configuration measurements have significant influence on the quality of the data and that the best inversion analysis is obtained when the dispersion curves are created using the north-south oriented arrays. The MASW survey study concluded that the most consistent and beneficial karst terrain dispersion images were those obtained from the predicted optimal acquisition, using receiver spacing (dx) = 2.5ft, source offset (X1) =10ft and depth of investigation of about 30ft --Abstract, page iii

Geophysical assessment of soil and rock in the New Madrid seismic zone

The research presented here consists of two case studies: the first from a study site in Illinois and the second from a site in Arkansas. In both instances, geophysical investigations were conducted to characterize the subsurface. At the Illinois site, borehole control, downhole seismic (DHS), seismic refraction tomography (SRT) and multichannel analysis of surface waves (MASW) data were acquired for the purpose of seismic site characterization. Shear wave and compressional wave velocities were used to estimate depth to bedrock and to generate 1-D plots depicting variations in Poisson\u27s Ratio, elastic moduli and density. The average shear wave velocity in the upper 100 ft was calculated and the national earthquake hazards reduction program (NEHRP) class D was assigned to the site based on MASW and DHS data results. At the Arkansas site, borehole control, electrical resistivity tomography (ERT), seismic refraction tomography (SRT), and multichannel analysis of surface waves (MASW) data were acquired with the objective of verifying and mapping a postulated fault. A comparative evaluation of the overall usefulness of the ERT, SRT and MASW techniques was also performed. The comparison showed that ERT and SRT tools generated remarkably similar images of the fault. The MASW tool generated a slightly different image of the fault. The research demonstrates that integrated use of seismic (seismic refraction tomography, multichannel analysis of surface waves and downhole seismic) and electrical (electrical resistivity tomography) methods is an effective approach in terms of assessing soil and rock in the New Madrid Seismic Zone --Abstract, page iii

Imaging and mitigating karst features

Over the last three years, a comprehensive subsurface investigation that combines both conventional and geophysical techniques has been conducted near Springfield in southwest Missouri, United States. This study, which forms part of the comprehensive subsurface investigation, aimed to (1) image and characterize the subsurface, (2) map variations in engineering properties of soil/rock, (3) map variable depth to top of rock, (4) explore the utility of the geophysical techniques, (5) determine the factors contributing to karst processes, and (6) propose karst mitigation. Electrical resistivity tomography (ERT) and multichannel analysis of surface waves (MASW) were employed for the acquisition of subsurface geophysical data. Borehole controls were used to verify and constrain the geophysical interpretation. In some instances, the ERT and MASW techniques produced complementary, high quality, and reliable data consistent with borehole control. Bedrock was pervasively fractured and extensively weathered with pronounced uneven surface. The topography of the surface was observed to depict the topography of the karst bedrock in many of the investigative areas. Moisture content was the major parameter influencing resistivity of the subsurface. A pervasive and systematic network of discontinuities characterizing the bedrock could serve as conduits for percolating acidic waters, ultimately resulting in distinct karst features. Anthropogenic activities were observed as a major contributor to the karst processes. Minimizing the amounts and rate of percolating acidic waters can significantly reduce karst processes and mitigate related features --Abstract, page iii