Seleznev V.S.,Geophysical Survey Systems Inc.
Near Surface Geoscience 2012 | Year: 2012
Standing wave field, different from other waves by coherence property in time, is always formed in closed spaces. Standing waves extraction from recorded wave fields on filtering basis by coherence in time and conversion of nonsimultaneous observations in simultaneous standing waves records in studied objects forms the basis of standing wave method. The method performs well in study of self-induced buildings vibrations. Amplitudes and phases maps of standing waves in set of natural frequencies fully characterize object and allow to determine not only seismic stability, but realize physical state diagnostics at a constructional elements level. In microzoning the standing wave method performs well as direct research method of resonant properties of section. As a result of standing wave method use we have set of section natural frequencies and vibration amplification maps. On the basis of maps of standing wave phases a resonance type is simply set. The resonances, formed as multiples between horizontal boundaries, have the same close phase on area, whereas in lenses and block mediums horizontal resonances may appear characterized by banded change of areal phase. Combination of high-accuracy study of resonant properties of areas and buildings provides a new echelon of accuracy in seismic risk assessment. Source
Al-Qadi I.,University of Illinois at Urbana - Champaign |
Xie W.,University of Illinois at Urbana - Champaign |
Roberts R.,Geophysical Survey Systems Inc.
NDT and E International | Year: 2010
This paper discusses the use of ground penetrating radar (GPR) to rapidly, effectively, and continuously assess railroad track substructure conditions, especially ballast. To overcome the limited electromagnetic waves penetration for high-frequency antennae and the low resolution of low-frequency antennae, this study uses a multiple-frequency GPR system to assess railroad substructure conditions. High-frequency antennae were used to detect the scattering pattern, which is related to air void volume in railroad ballast, and low-frequency antennae are used to assess deeper substructure conditions. Considering the scattering energy attenuation is highly frequency and material dependent, a time-frequency method based on tracking the frequency spectrum and energy change over depth can be used to extract ballast fouling conditions. From GPR field collected data, ground-truth observation, and ballast gradation analysis, the multiple-frequency GPR system demonstrates a promising capability to assess railroad track substructure condition. © 2009 Elsevier Ltd. All rights reserved. Source
Gusev A.A.,Institute of Volcanology and Seismology |
Guseva E.M.,Geophysical Survey Systems Inc.
Pure and Applied Geophysics | Year: 2016
We describe a procedure for mass determination of the “source-controlled fmax”—an important though not conventional parameter of earthquake source spectrum, relabeled here as “the third corner frequency,” fc3, and discuss the results of its application. fmax is the upper cutoff frequency of Fourier acceleration spectrum of a record of a local earthquake; both source and path attenuation contribute to fmax. Most researchers believe the role of attenuation (“κ” parameter) to be dominating or exclusive. Still, source effect on fmax is sometimes revealed. If real, it may be important for source physics. To understand better the fmax phenomena, the constituents of fmax must be accurately separated. With this goal, we process seismograms of moderate earthquakes from Kamchatka subduction zone. First, we need reliable estimates of attenuation to recover source spectra. To this goal, an iterative processing procedure is constructed, that adjusts the attenuation model until the recovered source acceleration spectra become, on the average, flat up either to fc3, or up to the high-frequency limit of the frequency range analyzed. The latter case occurs when fc3 is non-existent or unobservable. Below fc3, the double-corner source spectral model is thought to be valid, and the lower bound of acceleration spectral plateau is considered as the second corner frequency of earthquake source spectrum, fc2. The common corner frequency, fc1, is also estimated. Following this approach, more than 500 S-wave spectra of M = 4–6.5 Kamchatka earthquakes with hypocentral distances 80–220 km were analyzed. In about 80 % of the cases, fc3 is clearly manifested; the remaining cases show, at high frequency, flat source acceleration spectra. In addition, in about 2/3 of cases, fc2 is clearly above fc1, showing that double-corner spectra may dominate even at moderate magnitudes. Scaling behavior was examined for each of the corners. The fc1 vs. M0 trend is common and close to similarity (fc1 ∝ M0 −1/3), whereas the trends for two other corners (fc2 ∝ M0 −0.17; fc3 ∝ M0 −0.11) dramatically contradict the concept of similarity. Physical interpretation of such a behavior is discussed. The origin of fc3 is ascribed to existence of the lowermost wavelength/size of fault heterogeneity. Its dependence on M0 may reflect evolution of maturity of a fault in geological time. The approximate scaling fc2 ∝ fc1 0.5 suggests that during propagation of slip pulse over a fault, its width, assumedly related to 1/fc2, grows in a stochastic manner; this reminds the random evolution of propagating boundary in the framework of the known Eden model of random growth. © 2016, Springer International Publishing. Source
Geophysical Survey Systems Inc. | Date: 2015-06-19
The disclosed technology includes a device and method of use for direct printing and ink or other marking, in conjunction with GPR techniques. In a most basic embodiment of the disclosed technology, a relevant date, time, filename, and other parameters are printed or otherwise physically exhibited on the measurement surface, so that RADAR files can be later attributed to a specific data collection site. In a more advanced embodiment of the disclosed technology, actual RADAR target information is printed, or otherwise physically exhibited, on the measurement surface, such as while measuring, or substantially while measuring, the surface and substrate beneath with GPR.
Geophysical Survey Systems Inc. | Date: 2011-06-10
Embodiments of the disclosed technology comprise a ground penetrating radio device and methods of use for obtaining greater resolution. This is achieved by measuring the composition/reflection off a homogeneous material (e.g., metal plate), determining coefficients to correct the measured/reflection in order to make the measurements look like an idealized reference signal, and then using these coefficients in a digital filter to correct measurements/a reflection off a heterogeneous material, such as a road surface. In this manner, the composition of the heterogeneous material is determined with greater accuracy.