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Waveform modelling
Published in Rajib Biswas, Recent Developments in Using Seismic Waves as a Probe for Subsurface Investigations, 2023
Tomography is a technique to extract information on earth's internal structure and numerous techniques are available in the literature, namely, body wave travel time tomography, surface wave tomography, attenuation tomography and ambient noise tomography (Wang and Rao, 2020). Waveform-modelling technique can also be used to extract information on earth's subsurface physical properties such as, seismic velocity structure, attenuation, amplification, also known as seismic waveform tomography. Many seismic tomography methods use the arrival time or amplitude of the waveform as the input data. These methods are generically referred to as travel time or amplitude tomography. In these methods, the input data consists of travel times, amplitudes, or some other secondary attributes of the recorded data, whereas, in waveform tomography the complete waveform data is used giving a better resolution compared to the travel time or amplitude tomography methods. The underlying numerical method for waveform tomography is based on the full-wave equation, as opposed to a ray approximation or a Born approximation for the others. Thus, waveform tomography becomes more accurate than the travel time or amplitude tomography, but it makes the inverse problem more difficult to solve. It uses every wiggle of seismograms to determine the structure of earth's interior, which is constrained by the laws of seismic wave propagation. Therefore, it can image earth's interior even in complex environment that cannot be approximated using simple models.
Surface Displacement in an Elastic Half Space Due to an Earthquake Source on an Inclined Fault Plane
Published in Arabinda Roy, Rasajit Kumar Bera, Linear and Non-Linear Deformations of Elastic Solids, 2019
Arabinda Roy, Rasajit Kumar Bera
Computation of a synthetic seismogram associated with an assumed seismic source is possibly the first step towards computation of a hazard map of the earthquake affected region. Essentially the steps involved include a suitable model of the earth which we will take as an elastic half space and a source which is assumed to trigger the earthquake. Traditionally Lamb’s source or a point source (Pekeris and Lifson, 1957) is used. Other models that are used are pressure on a circular area (Mitra, 1964, Roy, 1975, Tupholme, 1970). Moving source model (Gakenheimer and Miklowitz, 1969, Gakenheimer, 1971) has also been used. Roy (1974) used a point source moving along an inclined direction. Most studies on finite sources over a circular area are usually parallel to the free surface. However, sites of earthquakes are situated on a geologic fault, in general an inclined one. Recently De and Roy (2012) considered such model.
Neo-Deterministic Scenario-Earthquake Accelerograms and Spectra: A NDSHA Approach to Seismic Analysis
Published in Junbo Jia, Jeom Kee Paik, Engineering Dynamics and Vibrations, 2018
Paolo Rugarli, Claudio Amadio, Antonella Peresan, Marco Fasan, Franco Vaccari, Andrea Magrin, Fabio Romanelli, Giuliano F. Panza
The properties of the sources and structural models of the Earth are needed in order to perform NDSHA. As a rule, NDSHA allows for the use of all the available information about the spatial distributions of the sources, their magnitudes and focal mechanisms, as well as about the properties of the inelastic media crossed by earthquake waves. The procedure can be divided into three steps:identification of possible seismic sources;characterization of the mechanical properties of the medium in which the seismic waves propagate;computation of the seismograms at sites of interest.
Analysis of the Site Effects in the North East Region of India Using the Recorded Strong Ground Motions from Moderate Earthquakes
Published in Journal of Earthquake Engineering, 2022
Manisha Sandhu, Babita Sharma, Himanshu Mittal, Prasantha Chingtham
An earthquake seismogram/accelerogram is the combination of source, path, and site effects. The main objective in estimating site effects is to remove the influence of source and path effects from the recordings, which can be achieved using the HVSR method, a non-reference site technique. This method using microtremors was introduced by Nogoshi and Igarashi (1971) and later on, popularized by Nakamura (1989), and found that this method is capable of providing better estimates of the fundamental frequency . Nakamura’s (1989) technique relies on the fact that horizontal components contain the site effect, while the vertical component does not. Lermo and Chavez-Garcia (1993) extended this approach using strong-motion earthquake records and stated that the technique is quite reliable for estimating the frequency and amplitude of the first resonant mode, though the higher modes don’t appear in this case. When compared the results of the HVSR method with the SSR method, a good agreement is found in , while the level of amplification differs (Bonilla et al. 1997; Coutel and Mora 1998). Field and Jacob (1995) found the uncertainty level to be the same for both of the techniques. The main assumption in this method is that the vertical component of ground motion contains more information on the source of ground motion than that of the horizontal component and the vertical component is free of any kind of site effects (Field and Jacob 1995; Mittal et al. 2016a; Sandhu, Kumar, and Teotia 2017). In this method, it is assumed that the site effects are caused by a single sedimentary layer over half-space. The transfer function corresponding to the ground amplification in the frequency domain is given by:
Seismic attractor can assist in finding of geothermal area?
Published in International Journal of Parallel, Emergent and Distributed Systems, 2018
Tatyana A. Smaglichenko, Alexander V. Smaglichenko, Ivan Zelinka, Boris Chigarev
The Earth is dynamic system, whose processes can not be under human’s control. In spite of a large number of earthquakes especially in seismic active areas there is no the statistical regularity, which could accurately predicts the behavior of the system. On the other hand, the visible information about seismic events is a key to understand the system. By analyzing seismograms, selecting signals, applying numerical techniques one can determine characteristics of seismic waves propagating through geological medium.
Road subsurface distress recognition method using multiattribute feature fusion with ground penetrating radar
Published in International Journal of Pavement Engineering, 2022
Guanghua Yue, Yuchuan Du, Chenglong Liu, Shili Guo, Yishun Li, Qian Gao
When road surface distress caused by subsurface distress appears, if only the road surface distress is treated and the subsurface is ignored, the road surface distress can reappear in a short time, which easily leads to frequent maintenance of the road. Therefore, it is necessary to conduct nondestructive testing techniques to detect subsurface distress and evaluate severity levels to take targeted maintenance treatment measures. At present, for the detection of subsurface distresses, many experts and scholars have made attempts with different technical methods, such as Rayleigh waves, seismic imaging, falling weight deflectometers, ultrasonic techniques, infrared thermography and ground penetrating radar (GPR). Rayleigh waves are a type of surface wave that travels near the surface of solids, and their advantage is that they can propagate over longer distances (Aggelis et al. 2009), which are used for the detection of cavities under pavement. Seismic imaging is the set of methods that obtain images of the Earth using observed seismograms as inputs, and it is a tool used to characterize subsurface geology (Guo et al. 2016). Falling weight deflectometer testing has been used to evaluate the structural condition of pavements to predict the layer moduli using a backcalculation process (Bachar et al. 1999). Ultrasonic techniques have been used as a nondestructive technique in the case of crack characterization. The transit time of longitudinal waves diffracted by the tip of the crack can be used to estimate the crack depth (Khazanovich et al. 2005). Infrared thermography is a nondestructive testing and remote sensing technique that offers the identification of subsurface flaws with reasonable accuracy (Vyas et al. 2019). GPR is a geophysical method that uses high-frequency electromagnetic waves to detect and locate underground targets and media anomalies (Saarenketo and Scullion. 2000). Ground-coupled and air-coupled GPR systems are the two common systems, and they are either used as hand-held devices or mounted on vehicles. To overcome some cases, such as mine detection, GPR sensor systems that are operated on unmanned airborne systems have been developed (Christopher and Su. 2018). Compared with other road nondestructive testing means, GPR has become the most effective long-distance road testing method due to its advantages of continuity, high speed, high accuracy, and low cost. It is widely used to detect underground cavities in urban roads (Kang et al. 2020), cracks, and loose damage to the base in the structural layer of roads (Dai and Hoegh 2017; Krysiński and Sudyka 2013).