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The Compressional to Shear-Wave Velocity Ratio for Surface Soils and Shallow Sediments

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Hilmi S. Salem at SDRI
Hilmi S. Salem
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FOR CITATION: SALEM, Hilmi S., 2000. The Compressional to Shear-Wave Velocity Ratio for Surface Soils and Shallow Sediments. European Journal of Environmental and Engineering Geophysics. 2000 (December), Vol. 5, Issue: 1, Pages: 3-14 (12p). https://www.researchgate.net/publication/324536603_The_Compressional_to_Shear-Wave_Velocity_Ratio_for_Surface_Soils_and_Shallow_Sediments ABSTRACT: The compressional to shear-wave velocity ratio, or velocity ratio (Vp/Vs), is an effective parameter in describing various physical parameters and lithological attributes of porous media, as well as the nature and kind of saturant filling the pores. In this study, Vp/Vs was obtained for surface soils and glacially originated shallow sediments (northern Germany), using in-situ seismic refraction measurements. For the whole column of the soils and sediments investigated, Vp/Vs lies in a general range of 1.28-3.19, with an average value of 2.42. The Vp/Vs shows considerable variations for the direct waves propagating through the surface soils saturated with air, and for the waves refracted from the underlying sediments that are partially or totally saturated with water. The Vp/Vs value of 2 is remarkable in discriminating between the partially and totally saturated sediments. The heterogeneity of the soils and sediments, vertically and laterally, and the variations in porosity, mineralogical composition, grain size, degree of saturation and kind of saturant (air or water) are primary factors responsible for the Vp/Vs varions. Direct relationships between Vp/Vs, on the one hand, and the compressional wave velocity and the shear wave velocity, on the other, and an inverse relationship between Vp/Vs and porosity, were obtained with coefficients of correlation ranging from 0.87 to 0.92. KEYWORDS: Compressional to Shear Wave Velocity (Vp/Vs); Seismic Refraction Measurements; Surface Soils and Shallow Sediments; Porosity; Lithology; Air and Water Saturations.
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FOR CITATION:
SALEM, Hilmi S., 2000. The Compressional to Shear-
Wave Velocity Ratio for Surface Soils and Shallow
Sediments. European Journal of Environmental and
Engineering Geophysics. 2000 (December), Vol. 5,
Issue: 1, Pages: 3-14 (12p).
... For shallow sediments, soil quality is related to the stiffness, or strength, of the sedimentary material. Soil strength refers to a complex condition that may include the effect of clay content, grain size, compaction, and the degree of saturation (Salem, 2000). In this study, the term soil will be used throughout for describing the shallow sedimentary material made of sands, gravels, silts and clays, that provides the material used in ancient earthen constructions; strength will be used instead of stiffness to describe material quality so that it can refer to both soils and rocks. ...
... In an effort to quantify the velocity information relative to soil quality, we calculated porosity and Poisson's ratio, parameters that relate to the engineering state of soils (see e.g. Salem, 2000;Gercek, 2007). Porosity (Φ) is calculated from an empirical relation to P-wave velocity (Vp), Φ = −0.175 ...
... Poisson's ratio (σ) is calculated from an empirical relation to porosity, σ = 0.81734-0.01208 * Φ (Salem, 2000;Eq. 3), derived for shallow unsaturated/partially saturated soils and underlying sediments with porosities in the 25-65% range and Poisson's ratios in the 0.0-0.5 range. ...
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... Poisson's ratio for geologic materials ranges from 0 to 0.5. Poisson's ratio increases as fluid saturation increases (Bachrach et al., 2000;Dvorkin and Nur, 1996;Nur and Simmons, 1969;Salem, 2000). Furthermore, Poisson's ratio is an indicator for determining the difference between gas and fluid saturated materials (Gregory, 1976;Pasquet et al., 2016) and has been shown to be useful to track pressure changes (Prasad, 2002), map the water table depth (Bachrach et al., 2000;Pasquet et al., 2015a;Salem, 2000;Uyanık, 2011), and differentiate gas and fluid in hydrothermal systems (Pasquet et al., 2016). ...
... Poisson's ratio increases as fluid saturation increases (Bachrach et al., 2000;Dvorkin and Nur, 1996;Nur and Simmons, 1969;Salem, 2000). Furthermore, Poisson's ratio is an indicator for determining the difference between gas and fluid saturated materials (Gregory, 1976;Pasquet et al., 2016) and has been shown to be useful to track pressure changes (Prasad, 2002), map the water table depth (Bachrach et al., 2000;Pasquet et al., 2015a;Salem, 2000;Uyanık, 2011), and differentiate gas and fluid in hydrothermal systems (Pasquet et al., 2016). To image the water table with Poisson's ratio, the conceptual model of the geology must be simplified (i.e. ...
Identifying recharge under subtle ephemeral features in a flat-lying semi-arid region using a combined geophysical approach
Article
Full-text available
  • Sep 2020
  • HESS
Identifying and quantifying recharge processes linked to ephemeral surface water features is challenging due to their episodic nature. We use a combination of well-established near-surface geophysical methods to provide evidence of a surface and groundwater connection under a small ephemeral recharge feature in a flat, semi-arid region near Adelaide, Australia. We use a seismic survey to obtain P-wave velocity through travel-time tomography and S-wave velocity through the multichannel analysis of surface waves. The ratios between P-wave and S-wave velocities are used to calculate Poisson's ratio, which allow us to infer the position of the water table. Separate geophysical surveys were used to obtain electrical conductivity measurements from time-domain electromagnetics and water contents from downhole nuclear magnetic resonance. The geophysical observations provide evidence to support a groundwater mound underneath a subtle ephemeral surface water feature. Our results suggest that recharge is localized and that small-scale ephemeral features may play an important role in groundwater recharge. Furthermore, we show that a combined geophysical approach can provide a perspective that helps shape the hydrogeological conceptualization of a semi-arid region.
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... Poisson's ratio for geologic materials ranges from 0 to 0.5. Poisson's ratio increases as fluid saturation increases (Bachrach et al., 2000;Dvorkin and Nur, 1996;Nur and Simmons, 1969;Salem, 2000). Furthermore, Poisson's ratio is an indicator for determining the difference between gas and fluid saturated materials (Gregory, 1976;Pasquet et al., 2016) and has been shown to be useful to track pressure changes 205 (Prasad, 2002), map the water table depth (Bachrach et al., 2000;Pasquet et al., 2015b;Salem, 2000;Uyanık, 2011), and differentiate gas and fluid in hydrothermal systems (Pasquet et al., 2016). ...
... Poisson's ratio increases as fluid saturation increases (Bachrach et al., 2000;Dvorkin and Nur, 1996;Nur and Simmons, 1969;Salem, 2000). Furthermore, Poisson's ratio is an indicator for determining the difference between gas and fluid saturated materials (Gregory, 1976;Pasquet et al., 2016) and has been shown to be useful to track pressure changes 205 (Prasad, 2002), map the water table depth (Bachrach et al., 2000;Pasquet et al., 2015b;Salem, 2000;Uyanık, 2011), and differentiate gas and fluid in hydrothermal systems (Pasquet et al., 2016). To image the water table with Poisson's ratio, the conceptual model of the geology must be simplified (i.e. ...
Identifying recharge under subtle ephemeral features in flat-lying semi-arid region using a combined geophysical approach
Preprint
Full-text available
  • Jan 2020
Abstract. Identifying and quantifying recharge processes linked to ephemeral surface water features is challenging due to their episodic nature. We use a unique combination of well-established near-surface geophysical methods to provide evidence of a surface and groundwater connection under a small ephemeral recharge feature in a flat, semi-arid region near Adelaide, Australia. We use a seismic survey to obtain P-wave velocity through travel-time tomography and S-wave velocity through the multichannel analysis of surface waves. The ratios between P-wave and S-wave velocities allow us to infer the position of the water table. A separate survey was used to obtain electrical conductivity measurements from time-domain electromagnetics and water contents were acquired by downhole nuclear magnetic resonance. The combined geophysical observations provide evidence to support a groundwater mound underneath a subtle ephemeral feature. Our results suggest that recharge is localized and that small-scale ephemeral features play an important role in groundwater recharge. Furthermore, we show that a combined geophysical approach can provide a unique perspective that helps shape the hydrogeological conceptualization of a semi-arid region.
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... The estimated V P =V S and ν-values for all profiles are consistent with those found earlier for similar shallow sediments using seismic refraction data (e.g., Lankston, 1990;Salem, 2000a,b;Uyanik, 2010;Essien et al., 2014). In profiles VFX5, PAN46, and PSE49-all acquired over alluvium sediments where the water table is very shallow (1 m)-we estimated for the second layer much higher V P =V S values than those usually found for partially saturated or dry shallow sediments (Lankston, 1990;Salem, 2000a). However, such high values (up to 9) for V P =V S have been reported earlier for water-saturated, unconsolidated, or clayey sediments (e.g., Salem, 2000a). ...
... In profiles VFX5, PAN46, and PSE49-all acquired over alluvium sediments where the water table is very shallow (1 m)-we estimated for the second layer much higher V P =V S values than those usually found for partially saturated or dry shallow sediments (Lankston, 1990;Salem, 2000a). However, such high values (up to 9) for V P =V S have been reported earlier for water-saturated, unconsolidated, or clayey sediments (e.g., Salem, 2000a). Figure 7 show a plot of V P versus V S for all the refraction profiles acquired in this study, and also for the old P-wave profiles from which V S was derived following the methodology explained in the previous section. ...
Near‐Surface Characterization of the Lisbon and Lower Tagus Valley Area, Portugal, for Seismic Hazard Assessment: VS30 and Soil Classification Maps
Article
  • Sep 2018
The Lower Tagus Valley (LTV) region includes the metropolitan area of Lisbon and has the highest population density in Portugal, with about 3.5 million inhabitants. The LTV has been struck by several historical earthquakes that caused significant economic and human losses, and therefore, earthquake damage mitigation is of great importance. The present research was directed toward preparation of the first detailed VS30 and soil classification maps for the LTV region using in situ shear-wave velocity (VS) measurements. These maps were built using P- and S-wave seismic velocities in the shallowest surface, obtained mostly from seismic refraction and a few crosshole datasets, together with lithostratigraphic studies and analyses of boreholes drilled for water supply and geotechnical investigations. Borehole data were used to confirm layer thicknesses and lithologies, and to overcome the limitations of traditional refraction interpretation. Our results (VS30 and soil classification maps) show that lithological changes within each formation prevent simple generalization of geophysical data/interpretations based solely on geological mapping. Contrary to previously available VS30 maps based on proxies or gross geological generalizations, different classes are obtained inside the Holocene alluvial sediments and theMiocene units, for instance. Certain areas with Miocene outcropping, such as the district capital of Santarém, unexpectedly fall into a moderate risk class, albeit showing hard-rock outcrops. Though there is scope for further improvements in the future, the maps presented results from the first rigorous near-surface characterization campaign undertaken in the region. Velocity information assembled in this work can be further used to correct earthquake records from a number of seismological stations and to update velocity models used in ground-motion simulations. Furthermore, seismic refraction interpretation was compared among different acquisition geometries for seismic noise measurements at three geologically distinct sites to evaluate the use of these techniques for future S-wave data acquisition.
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... The determined values of VP/VS ratios are compatible with those found in the literature for similar shallow sediments (e.g. Salem, 2000;Lankston, 1989). ...
... Profiles VFX5, PAN46 and PSE49 e.g. (Table 1), acquired over alluvium sediments with a very shallow (1 m) water table, present, for the second layer, very high VP/VS ratios (up to 9), similar to those found for totally saturated shallow unconsolidated or clayish sediments (Salem, 2000;Lankston, 1989). For other profiles, the interfaces depth discrepancy can be attributed to the different properties that P-waves and S-waves respond to. ...
Site effect studies in the lower tagus region
Article
Full-text available
  • Jan 2014
The Lower Tagus Valley region of central Portugal mainland is located about 350 Km from the Eurasian-African plate boundary. It is characterized by low slip-rates (<0.4 mm/year) and a moderate seismicity, occasionally shaken by some important historical earthquakes causing significant damages and economical losses. The most well know damaging earthquakes occurred in 1344, 1531, 1755, 1909 and 1969. The seismic hazard evaluation and mitigation is therefore of great importance to this densely populated area. This paper focuses on the evaluation of P-wave and S-wave seismic velocities of the near surface using seismic refraction data interpretation and in-situ lithostratigraphic studies to obtain the first detailed VS30 and soil classification maps based on shear wave velocity. Hundreds of available boreholes drilled for engineering (with SPT data) and water supply were used to confirm layer thicknesses and lithologies at depth. The soil classification is based upon the European Code 8 for civil engineering which was carried out for land use planning and design of critical facilities. © 2014, LNEG – Laboratório Nacional de Geologia e Energia IP.
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... The ratio of P-and S-wave velocities, Vp/Vs, is a key parameter that provides information about the physical properties, lithological changes, mineral compositions, clay contents, grain sizes, fracture densities, porosity, fluid saturations and types of soil and rocks (Tatham 1982;Salem 2000;Uyanık 2011), and recently, it has been widely used for the characterization of soil and rocks (Keçeli 2012). According to Telford et al. (1976), Poisson's ratio is calculated based on the Vp/Vs ratio, and these two parameters are linearly related. ...
Subsurface characterization by active and passive source geophysical methods after the 06 February 2023 earthquakes in Turkey
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  • NAT HAZARDS
Two large earthquakes (Mw = 7.7 and Mw = 7.6) that occurred in Turkey on February 6, 2023, affected a very extent region and caused a lot of loss of life and property. This paper presents preliminary results from geophysical measurements (Seismic Refraction Tomography-SRT, Multi-Channel Surface Wave Analysis-MASW and Microtremor-MT) on eight profiles in four provinces (Kahramanmaraş, Hatay, Malatya, Gaziantep) to understand the relationship between subsurface properties and the destruction that occurs immediately after earthquakes. By analyzing the geophysical data, the dynamic-elastic properties of ground and the soil classification according to Vs30 were determined. It is generally understood that the near-surface (< ~ 10–15 m) units in the measurement areas are very loose, and the deeper ones (≥ ~ 15–20 m) have a very porous/fractured structure. Soil classes were defined as ZD (Malatya-1, Hatay-1 and Kahramanmaraş-1) and ZC (Malatya-2, Hatay-2, Gaziantep-1,2 and Kahramanmaraş-2). In addition, by evaluating the information of strong ground motion station closest to the measurement profiles, it is observed that the PGA values versus epicenter distances are higher at stations in the zone parallel to the direction of both faults than those in the perpendicular zones. This leads directivity effect in the propagation of earthquake waves. The results indicate that one of the basic reasons for the damages is that the earthquake-ground-structure relationship has not been fully and accurately reflected in building designs. Therefore, future researches involving more geophysical data and PGA values will provide more information about the structural, physical and geotechnical properties of subsurface and definitive results.
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