Influence of the seismic shear proportioning factor on steel MRFs seismic performances

A numerical method is proposed to study the scattering of seismic shear waves induced by the presence of underground cavities in homogeneous soils. The method is based on the superposition of two solutions: the solution of the free-wave propagation problem in a uniform half-space, easily determined analytically, and the solution of the wave scattering problem due to the cave presence, evaluated numerically by means of an ad hoc code implemented by using the ANSYS Parametric Design Language. In the two-dimensional setting, this technique is applied to the case of a single cave, placed at a certain depth from the ground level. The frequency spectrum of the seismic shear oscillation on the ground surface is determined for different dimensions and depths of the cave and compared with the spectrum registered without caves. The influence of the cave dimensions and depth on the spectrum amplification is analyzed and discussed.

Download Full-text

Measuring Shear Wave Splitting Using the Silver and Chan Method

10.26686/wgtn.17003470.v1 ◽

2021 ◽

Author(s):

◽

Ernestynne Walsh

Keyword(s):

Shear Wave ◽

Statistical Tests ◽

Tectonic Stress ◽

Shear Wave Splitting ◽

Parameter Estimates ◽

Transverse Waves ◽

Seismic Shear ◽

Wave Splitting ◽

Orthogonal Components ◽

Automated Grading

<p>Seismic shear waves emitted by earthquakes can be modelled as plane (transverse) waves. When entering an anisotropic medium they can be split into two orthogonal components moving at different speeds. This splitting occurs along an axis, the fast direction, that is determined by the ambient tectonic stress. Shear wave splitting is thus a commonly used tool for examining tectonic stress in the Earth’s interior. A common technique used to measure shear wave splitting is the Silver and Chan (1991) method. However, there is little literature assessing the robustness of this method, particularly for its use with local earthquakes, and the quality of results can vary. We present here a comprehensive analysis of the Silver and Chan method comprising theoretical derivations and statistical tests of the assumptions behind this method. We then produce an automated grading system calibrated against an expert manual grader using multiple linear regression. We find that there are errors in the derivation of certain equations in the Silver and Chan method and that it produces biased estimates of the errors. Further, the assumptions used to generate the errors do not hold. However, for high quality results (earthquake events where the signal is strong and the earthquake geometry is optimal), the standard errors are representative of the spread in the parameter estimates. Also, we find that our automated grading method produces grades that match the manual grades, and is able to identify mistakes in the manual grades by detecting substantial inconsistencies with the automated grades.</p>

Download Full-text

Practical aspects of in situ measurements of material damping with the seismic cone penetration test

Canadian Geotechnical Journal ◽

10.1139/t93-018 ◽

1993 ◽

Vol 30 (2) ◽

pp. 211-219 ◽

Cited By ~ 6

Author(s):

W. P. Stewart ◽

R. G. Campanella

Keyword(s):

Shear Wave ◽

Cone Penetration Test ◽

Material Damping ◽

Penetration Test ◽

Cone Penetration ◽

Seismic Shear ◽

Laboratory Results ◽

Calculation Methodology ◽

Seismic Cone Penetration Test

The downhole seismic cone penetration test (SCPT) procedure has been extended to allow the measurement of material damping at small strains at minimum expense while one is measuring shear wave velocity. The nature of damping, the required equipment characteristics, and the recommended procedure and calculation methodology are presented in a practical way. SCPT results from four different sites give results that are in general agreement with laboratory measurements of damping for sands and clays and with values recommended by other authors. It appears, however, that previously reported measurements of damping by borehole methods are higher, by a factor of two or more, when compared with SCPT and laboratory results. Key words : in situ, damping, seismic, shear wave, cone penetrometers, procedures.

Download Full-text