Development of an NEHRP map for the Orleans suburb of Ottawa, Ontario

2008 ◽  
Vol 45 (8) ◽  
pp. 1180-1188 ◽  
Author(s):  
Dariush Motazedian ◽  
James Hunter
Keyword(s):  
Shear Wave ◽  
Ground Surface ◽  
Borehole Data ◽  
Glacial Sediments ◽  
Surface Reflection ◽  
Shear Wave Velocities ◽  
Reflection And Refraction ◽  
Wide Range ◽  
Average Shear ◽  
Geological Units

The average shear-wave velocity to a depth of 30 m (Vs30) has been obtained for 73 sites in the Orleans area in the northeast part of the City of Ottawa. Measurements of Vs30 were made using both ground surface reflection and refraction methods. In addition, borehole data was used to estimate Vs versus depth profiles using average Vs values assigned to distinct geological units. High values of Vs (>1500 m/s) were obtained in areas of thin surficial sediments overlying Paleozoic bedrock, and low Vs values (<180 m/s) were calculated in areas of thick late–post-glacial clay. The Vs30 values have been used to prepare an NEHRP map for the study area. Much of the suburb of Orleans is classified as NEHRP zone E, whereas the perimeter areas and some isolated central areas are classified as zones ranging from zone D to zone A. The presence of thick unconsolidated late–post-glacial sediments deposited in the Champlain Sea is the main contributing factor to the wide range of average shear-wave velocities in the study area.

A Discussion on natural strain and geological structure - Strain and anisotropy in rocks

1976 ◽  
Vol 283 (1312) ◽  
pp. 27-42 ◽  
Keyword(s):  
Magnetic Susceptibility ◽  
Shear Wave ◽  
Finite Strain ◽  
Preferred Orientation ◽  
Seismic Velocities ◽  
Magnetic Susceptibility Anisotropy ◽  
Wave Velocities ◽  
Natural Strain ◽  
Shear Wave Velocities ◽  
Wide Range

The evaluation of finite strain in naturally deformed rocks is restricted by the limited occurrence of good natural strain indicators which are also homogeneous with respect to the matrix. This problem is overcome by establishing the relation between measured finite strain and those physical behaviour characteristics of rocks that are dependent upon the anisotropy resulting from deformation. Accordingly, the strain measured from natural indicators is calibrated against ( degree of preferred orientation, (b) magnetic susceptibility anisotropy, and (r) seismic anisotropy. This _ will permit three approaches to be used independently for the evaluation of strain, provided that a minimal number of actual strains are available. The relation between measured strain and the degree of preferred orientation of layer silicates as revealed by X-ray transmission goniometry is established for a group of fine grained tectonites of dominantly planar fabric which have an average deformation ellipsoid of form 1.6:1 :,0.26. The strains measured from the degree of preferred orientation are in remarkable agreement with those measured from natural strain indicators. The measured deformation ellipsoids for a wide range of strains are also compared to the correlative ellipsoids of magnetic susceptibility anisotropy. The axes of both sets of ellipsoids are coincidental and the shape relationship between deformation and magnetic susceptibility ellipsoids is established by linear regression. Finally, the anisotropy of seismic velocities is determined by measuring the pseudocompressional velocity and two orthogonally polarized pseudo shear wave velocities for each of a minimum of nine non-coplanar directions. The velocity surfaces thus obtained define an elastic or seismic velocity anisotropy ellipsoid, the axes of which are also precisely coincidental with those of the finite deformation ellipsoid. The influence of rock fabric upon seismic velocities is such that for a rock which has undergone a principal finite extension of 135 % and a finite shortening of 65 %, the difference of compressional and shear wave velocities between these two directions is in the ratio 1.26:1 for P waves and 1.33:1 for S waves.

scholarly journals Risks of Solely Relying on VS30 in Ground Motion Response Studies

2018 ◽  
Vol 4 (12) ◽  
pp. 2937
Author(s):  
Amin Ghanbari ◽  
Younes Daghigh ◽  
Forough Hassanvand
Keyword(s):  
Shear Wave ◽  
Ground Motion ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Ground Surface ◽  
Earthquake Excitation ◽  
Site Class ◽  
Velocity Models ◽  
Average Shear ◽  
Classification Tool

The average shear wave velocity of the uppermost 30 m of earth (Vs30) is widely used in seismic geotechnical engineering and soil-structure interaction studies. In this regard, any given subsurface profile is assigned to a specific site class according to its average shear wave velocity. However, in a real-world scenario, entirely different velocity models could be considered in the same class type due to their identical average velocities. The objective of the present study is to underline some of the risks associated with solely using Vs30 as a classification tool. To do so, three imaginary soil profiles that are quite different in nature, but all with the same average Vs were considered and were subjected to the same earthquake excitation. Seismic records acquired at the ground surface demonstrated that the three sites have different ground motion amplifications. Then, the different ground responses were used to excite a five-story structure. Results confirmed that even sites from the same class can indeed exhibit different responses under identical seismic excitations. Our results demonstrated that caution should be practiced when large-contrast velocity models are involved as such profiles are prone to pronounced ground motion amplification. This study, which serves as link between soil dynamics and structural dynamics, warns practitioners about the risks associated with oversimplifying the subsurface profile. Such oversimplifications can potentially undermine the safety of existing or future structures.

Predictions of shear-wave velocities in southern California using surface geology

1998 ◽  
Vol 88 (3) ◽  
pp. 677-685 ◽  
Author(s):  
Stephen Park ◽  
Scott Elrick
Keyword(s):  
Information System ◽  
Geographic Information System ◽  
Shear Wave ◽  
Velocity Profiles ◽  
Velocity Data ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Average Shear ◽  
Surface Geology ◽  
Better Than

Abstract A new model of the average shear-wave velocity in the uppermost 30 m has been generated by extrapolation of discrete velocity profiles using surface geology at several scales. Statistical methods have been applied to create a map that is no more complicated than is supported by the velocity data; several geologic units with similar responses are grouped together. The resulting map is simpler than previous ones and yet fits the observed velocity profiles better than earlier, more complicated maps. Analysis within a geographic information system will permit updates and modification of the map as new velocity data are added.

scholarly journals Vs30Estimate for Southwest China

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Yan Yu ◽  
Walter J. Silva ◽  
Bob Darragh ◽  
Xiaojun Li
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Southwest China ◽  
Strong Motion ◽  
Site Classification ◽  
Borehole Data ◽  
Data Set ◽  
Average Shear ◽  
Shear Wave Velocity Profile

Several methods were used to estimateVs30from site profiles with borehole depths of about 20 m for the strong-motion stations located in Southwest China. The methods implemented include extrapolation (constant and gradient), Geomatrix Site Classification correlation with shear-wave velocity, and remote sensing (terrain and topography). The gradient extrapolation is the preferred choice of this study for sites with shear-wave velocity profile data. However, it is noted that the coefficients derived from the California data set are not applicable to sites in Southwest China. Due to the scarcity of borehole profiles data with depth of more than 30 m in Southwest China, 73 Kiknet profiles were used to generate new coefficients for gradient extrapolation. Fortunately, these coefficients provide a reasonable estimate ofVs30for sites in Southwest China. This study showedVs30could be estimated by the time-average shear-wave velocity (average slowness) of only 10 meters of depth. Furthermore, a medianVs30estimate based upon Geomatrix Classification is derived from the results of the gradient extrapolation using a regional calibration of the Geomatrix Classification withVs30. The results of this study can be applied to assignVs30to the sites without borehole data in Southwest China.

scholarly journals Vs30 Mapping and Soil Classification in The Southern Part of Kulon Progo Using Rayleigh Wave Ellipticity Inversion

2019 ◽  
Vol 1 (2) ◽  
Author(s):  
Bambang Sunardi
Keyword(s):  
Seismic Hazard ◽  
Rayleigh Wave ◽  
Shear Wave ◽  
Soil Type ◽  
Interpolation Method ◽  
Measurement Data ◽  
Ground Surface ◽  
Soft Rock ◽  
Soil Classification ◽  
Shear Wave Velocities

Shear wave velocity from the ground surface to a depth of 30 meters (Vs30) is a parameter to determine dynamic characteristics of the soil, which can be used to assess the level of seismic hazard. Thus, Vs30 mapping has an important role in seismic hazard mitigation efforts. Vs30 can be determined by Multichannel Analysis of Surface Waves (MASW) and Spatial Autocorrelation (SPAC) methods. A simpler alternative can be done by using Rayleigh wave ellipticity. The main objective of this research is to map Vs30 in the southern part of Kulon Progo using Rayleigh wave ellipticity inversion. In this study, Rayleigh wave ellipticity inversion was performed on 42 microtremor single measurement data, scattered in the southern part of Kulon Progo. The inversion results are used to estimate the value of Vs30 and classify the soil type at the measurement points, referring to SNI 1726:2012. A Vs30 distribution map and soil type classification are obtained by applying the geostatistical interpolation method. The mapping result showed that most of the southern part of Kulon Progo has a relatively low Vs30 value. These values are in the range of 180-342 m/s, which categorized as stiff soil (SD). In this region, some parts located in the hilly and transition zones have relatively high shear wave velocities in the range of 357-578 m/s and included in the category of very dense soil/ soft rock (SC) types

scholarly journals Multichannel analysis of the surface waves of earth materials in some parts of Lagos State, Nigeria

2016 ◽  
Vol 63 (2) ◽  
pp. 81-90
Author(s):  
R.B. Adegbola ◽  
K.F. Oyedele ◽  
L. Adeoti ◽  
A.B. Adeloye
Keyword(s):  
Surface Waves ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Velocity Data ◽  
Low Velocity ◽  
Borehole Data ◽  
Shear Wave Velocities ◽  
Multichannel Analysis ◽  
Rigidity Modulus

Abstract We present a method that utilizes multichannel analysis of surface waves (MASW), which was used to measure shear wave velocities, with a view to establishing the probable causes of road failure, subsidence and weakening of structures in some local government areas in Lagos, Nigeria. MASW data were acquired using a 24-channel seismograph. The acquired data were processed and transformed into a two-dimensional (2-D) structure reflective of the depth and surface wave velocity distribution within a depth of 0–15 m beneath the surface using SURFSEIS software. The shear wave velocity data were compared with other geophysical/ borehole data that were acquired along the same profile. The comparison and correlation illustrate the accuracy and consistency of MASW-derived shear wave velocity profiles. Rigidity modulus and N-value were also generated. The study showed that the low velocity/ very low velocity data are reflective of organic clay/ peat materials and thus likely responsible for the failure, subsidence and weakening of structures within the study areas.

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