1,721,099 research outputs found
Discussion on "Implications of surface wave data measurement uncertainty on seismic ground response analysis" by Jakka et al
Full text linkThe discussion deals with the effect of shear wave velocity uncertainties on 1D seismic ground response analysis. In particular, the paper refers to uncertainties deriving from the solution of the inverse problem in surface wave methods. We address some issues related to the evaluation of "equivalent" profiles from surface wave data, the inversion strategy and the numerical simulation of seismic site response. The pitfalls in the analyses point out the need for more refined studies to draw general conclusions on the subjec
Geophysical characterization of an unstable rock mass
Full text linkA pre-requisite in rock mass stability analysis is to obtain the internal structure and the mechanical
properties of the investigated rock mass with a reasonable degree of uncertainty. In this respect, geophysical
methods can be profitably used as an imaging and characterization tool. Seismic methods are often more suitable
because the measurements depend on the mechanical properties of the rock mass. The present paper presents
the use of cross-hole seismic tomography in a site (Madonna del Sasso – NW Italy) affected by a rock instability
phenomenon, highlighted by episodes of slow deformation recorded by standard measurement devices.
Geophysical tests have been fundamental in imaging the fracturing state and the relative variation of seismic
velocities between intact an altered rock and in defining the seismic velocity field of the rock mass, a basic
prerequisite for the future planned microseismic monitoring step
Inversion Uncertainty in Surface Wave Analysis
No full textThis study deals with uncertainties associated to solution non-uniqueness in surface wave analysis, with special attention to the influence of maximum available wavelength in experimental data. Typically, it is assumed that the investigation depth is about half the maximum available wavelength in the experimental dispersion curve. In order to assess the validity of this assumption, three different datasets (one synthetic and two real world case histories) have been analyzed with a Monte Carlo approach. Low frequency experimental data have been progressively scalped to assess the consequences on the reliability of the solution. For the selected case histories, a reasonable estimate of average parameters is obtained with a limited amount of experimental information. Nevertheless, the risk of reaching a local minimum in the inversion process is associated to the availability of experimental data. The use of global search method has to be preferred as they can provide an estimate of the reliability of the solutio
Special Issue “Remote Sensing in Applied Geophysics”
Full text linkThe Special Issue "Remote Sensing in Applied Geophysics" is focused on recent and upcoming advances in the combined application of remote sensing and applied geophysics techniques, sharing the advantages of being non-invasive research methods, suitable for surface and near-surface high-resolution investigations of even wide and remote areas. Applied geophysics analyzes the distribution of physical properties in the subsurface for a wide range of geological, engineering and environmental applications at different scales. Geophysical surveys are usually carried out deploying or moving the appropriate instrumentation directly on the ground surface. However, recent technological advances have brought to the development of innovative acquisition systems more typical of the remote sensing community (e.g., airborne surveys and unmanned aerial vehicle systems). At the same time, while applied geophysics mainly focuses on the subsurface, typical remote sensing techniques have the ability to accurately image the Earth's surface with high-resolution investigations carried out by means of terrestrial, airborne, or satellite-based platforms. The integration of surface and subsurface information is often crucial for several purposes, including the georeferencing and processing of geophysical data, the characterization and time-lapse monitoring of surface and near-surface targets, and the reconstruction of highly detailed and comprehensive 3D models of the investigated areas. Contributions to the issue showing the added value of surface reconstruction and/or monitoring in the processing and interpretation of geophysical data, integration and cross-comparison of geophysical and remote sensing techniques were required to the research community. Contributions discussing the results of pioneering geophysical acquisitions by means of innovative remote systems were also addressed as interesting topics. The Special Issue received great attention in the combined community of applied geophysicists and remote sensing researchers. A total of 15 papers are included in the Special Issue, covering a wide range of applications. This is one of the highest number of papers among the Remote Sensing Special Issues, showing great interest in the proposed topic. The relevant number of contributions also highlights the relevance and increasing need for integration between remote sensing and ground-based geophysical exploration or monitoring methods. In particular, one of the main fields of research showing the potential integration of the geophysical and remote sensing techniques is archaeological exploration
The role of surface waves in prediction of ground vibrations from blasting
No full textSurface waves play a fundamental role in the propagation of vibrations caused by blasting. Indeed, active and passive surface wave tests, which are widely used techniques in engineering and geophysical exploration to infer model parameters for soils and rocks, can be profitably applied for the prediction of ground motion from blasting supplying relevant information on subsurface mechanical properties and source parameters (patterns of propagation and dominant wavelengths). In this respect, monitoring systems for ground vibrations can be conceived in order to use the collected data also for ground characterization purposes. Moreover, the interpretation of surface wave data can lead to an estimate of shear modulus and damping ratio (quality factor) as a function of depth. This information can be used to build a numerical model to simulate wave propagation and predict ground vibrations evaluating the performances of vibration mitigation systems. For preliminary assessments of ground vibrations induced by blasting, the information from surface wave tests can be used to improve the predictive capability of attenuation relationships. In particular in the present work reference is made to a recently proposed relationship based on energy spreading in the form of Rayleigh wave propagation. Data from a case history will be presented to exemplify the relevant aspects in the proposed methodolog
Ultrasonic equipment aimed to detect grouting homogeneity in geothermal heat exchangers
Full text linkThe purpose of this study is to assess homogeneity and
integrity of cementing grout in vertical borehole heat
exchangers used for geothermal heat pumps using an
ultrasonic non-destructive test. The used testing
equipment, TUC (Ultrasonic Test to certificate
grouting Continuity), is based on an ultrasonic system
able to generate and record wave propagation from the
inside of heat exchangers to the surrounding
(cementation and soil, possibly). Differences in signal
characteristics of the recorded waves along the pipe
can indirectly provide useful information to evaluate
the successful realization of the well cementation in
terms of vertical homogeneity and continuity. Both
laboratory and field tests have been evaluated and are
hereafter presented to verify tests effectiveness and
discuss eventual limitation of the proposed approach
Effective Vs and Vp characterization from Surface Waves streamer data along river embankments
Full text linkRiver embankments are linearly extended earth structures built for river flood protection. Their continuity and
uniformity are fundamental prerequisites to ensure and maintain their protection efficiency. Weakness points
usually develop in localized areaswhere geotechnical variability is present in the embankment body or in the underlying
subsoil. Given their significant length, and the localized nature of weakness points, the characterization
of river embankments cannot rely on local geotechnical investigations but requires the application of efficient
and economically affordable methods, able to investigate relevant lengths in a profitable way. This is even
more essentialwhen the investigations are conducted near, or in foresee of, significant flood events,when timing
of the surveys is essential. In this paper the application of a procedure (W/D procedure) for the seismic characterization
of river embankments, specifically designed for surface waves streamer data, is presented. The W/D
procedure allows the combined definition of 2D shear (Vs) and compressional (Vp) wave velocity models and
can be developed in order to be automated as a fast imaging tool. Its application to the characterization of a
test site (Bormida river embankment, Piedmont Region, Italy) is presented. It is also shown that the obtained results
are comparable to standard seismic processing approaches with the advantage of reduced survey time and
increased efficiency, giving preliminary results directly in the field
Detecting Slow Deformation Signals Preceding Dynamic Failure: A New Strategy For The Mitigation Of Natural Hazards (SAFER)
Full text linkTime-weighted average shear wave velocity profiles from surface wave tests through a wavelength-depth transformation
No full textWe investigate the possibility of obtaining time-weighted average shear wave velocity profiles through a wavelength-depth transformation of experimental dispersion curves from surface wave tests, without a formal solution of the inverse problem. We evaluate this approach on a wide flat-file database (Polito Surface Wave Database, PSWD) of experimental dispersion curves and related shear wave velocity profiles, both from dispersion curve inversion and invasive tests. The results show that the proposed wavelength-depth transformation can be valuable for seismic site evaluations offering an estimation of time-weighted average shear wave velocity profiles very similar to a state-of-the-art inversion of the experimental dispersion curves and with similar uncertainty with respect to invasive tests. This transformation has the advantage of avoiding time-consuming inversion processes, with related uncertainty sources, and any assumption on layer parameterization and a-priori information. Moreover, in conjunction with an experimental evaluation of the fundamental frequency of the site, from independent surveys, the wavelength-depth transformation can be used to get a direct and fast estimate of the position of the engineering bedrock
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