
 The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

Ground Motion Characteristics Estimated from Spectral Ratio between Horizontal and Verticcl Components of Mietremors.

http://www.vliz.be/imisdocs/publications/242609.pdf

Seawater intrusion processes, investigation and management: Recent advances and future challenges

Interpretation theory in applied geophysics: Grant, F S ... Interpretation theory in applied geophysics Unknown Binding – January 1, 1965 5.0 out of 5 stars 1 rating. See all formats and editions Hide other formats and editions. The Amazon Book Review Book recommendations, author interviews, editors' picks, and more. Read it now. Enter your mobile number or email address below and we'll send you a ...

Interpretation Theory in Applied Geophysics Grant (McGraw-Hill, 140s.)

The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma).

https://science.sciencemag.org/content/sci/260/5114/1617.full.pdf

Seismicity Remotely Triggered by the Magnitude 7.3 Landers, California, Earthquake

We present a comprehensive review of methods to measure soil water content with ground penetrating radar (GPR) We distinguish four methodologies: soil water content determined from reflected wave velocity, soil water content determined from ground wave velocity, soil water content determined from transmitted wave velocity between boreholes, and soil water content determined from the surface reflection coefficient For each of these four methodologies, we discuss the basic principles, illustrate the quality of the data with field examples, discuss the possibilities and limitations, and identify areas where future research is required We hope that this review will further stimulate the community to consider ground penetrating radar as one of the possible tools to measure soil water content

Measuring Soil Water Content with Ground Penetrating Radar: A Review

A simple hypothesis is proposed to explain the occurrence of localized zones of tectonic deformation and seismicity within intraplate regions subjected to relatively uniform far-field tectonic stresses. In most intraplate regions (especially continental shield areas and old oceanic basins), temperatures in the lower crust and upper mantle are quite low so that the upper mantle is cold and strong. In these regions, significant lithospheric deformation does not occur because the cumulative strength of the lithosphere far exceeds the magnitude of plate-driving forces. If lower crust and upper mantle temperatures are relatively high, however, plate-driving forces are largely supported by the upper crust because the lower crust and upper mantle are relatively weak. In this case, the regions can deform relatively rapidly because the cumulative strength of the lithosphere is comparable in magnitude to that of the forces acting on the lithosphere. In this paper, we apply this hypothesis to the New Madrid seismic zone and the surrounding central and eastern United States. Within the seismic zone, the heat flow appears to be slightly elevated (about 60 mW/m2) relative to the background regional value of 45 mW/m2. Calculated crustal geotherms and laboratory-derived ductile flow laws suggest that the lower crust and upper mantle are sufficiently weak within the seismic zone that intraplate stresses are largely transmitted through the upper crust and deformation can occur at relatively rapid rates for this intraplate area. In marked contrast, in the surrounding area where the heat flow is relatively low, cumulative lithospheric strength appears to far exceed the plate-driving force, and the tectonic stress is carried in both the crust and upper mantle. Thus the marked contrast in seismicity between the seismic zone and the surrounding area appears largely because of heat flow and whether or not the lower crust and upper mantle support an appreciable fraction of the plate-driving forces.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97TC01467

Lithospheric strength and intraplate seismicity in the New Madrid seismic zone

Ultra-wideband (UWB) radar plays an important role in search and rescue at disaster relief sites. Identifying vital signs and locating buried survivors are two important research contents in this field. In general, it is hard to identify a human's vital signs (breathing and heartbeat) in complex environments due to the low signal-to-noise ratio of the vital sign in radar signals. In this paper, advanced signal-processing approaches are used to identify and to extract human vital signs in complex environments. First, we apply Curvelet transform to remove the source-receiver direct coupling wave and background clutters. Next, singular value decomposition is used to de-noise in the life signals. Finally, the results are presented based on FFT and Hilbert-Huang transform to separate and to extract human vital sign frequencies, as well as the micro-Doppler shift characteristics. The proposed processing approach is first tested by a set of synthetic data generated by FDTD simulation for UWB radar detection of two trapped victims under debris at an earthquake site of collapsed buildings. Then, it is validated by laboratory experiments data. The results demonstrate that the combination of UWB radar as the hardware and advanced signal-processing algorithms as the software has potential for efficient vital sign detection and location in search and rescue for trapped victims in complex environment.

Advanced Signal Processing for Vital Sign Extraction With Applications in UWB Radar Detection of Trapped Victims in Complex Environments

Finite-difference, time-domain (FDTD) calculations are typically performed with partial differential equations that are first order in time. Equation sets appropriate for FDTD calculations in a moving inhomogeneous medium (with an emphasis on the atmosphere) are derived and discussed in this paper. Two candidate equation sets, both derived from linearized equations of fluid dynamics, are proposed. The first, which contains three coupled equations for the sound pressure, vector acoustic velocity, and acoustic density, is obtained without any approximations. The second, which contains two coupled equations for the sound pressure and vector acoustic velocity, is derived by ignoring terms proportional to the divergence of the medium velocity and the gradient of the ambient pressure. It is shown that the second set has the same or a wider range of applicability than equations for the sound pressure that have been previously used for analytical and numerical studies of sound propagation in a moving atmosphere. Practical FDTD implementation of the second set of equations is discussed. Results show good agreement with theoretical predictions of the sound pressure due to a point monochromatic source in a uniform, high Mach number flow and with Fast Field Program calculations of sound propagation in a stratified moving atmosphere.

Equations for finite-difference, time-domain simulation of sound propagation in moving inhomogeneous media and numerical implementation

The inverse problem of electrical resistivity surveys (ERSs) is difficult because of its nonlinear and ill-posed nature. For this task, traditional linear inversion methods still face challenges such as suboptimal approximation and initial model selection. Inspired by the remarkable nonlinear mapping ability of deep learning approaches, in this article, we propose to build the mapping from apparent resistivity data (input) to resistivity model (output) directly by convolutional neural networks (CNNs). However, the vertically varying characteristic of patterns in the apparent resistivity data may cause ambiguity when using CNNs with the weight sharing and effective receptive field properties. To address the potential issue, we supply an additional tier feature map to CNNs to help those aware of the relationship between input and output. Based on the prevalent U-Net architecture, we design our network (ERSInvNet) that can be trained end-to-end and can reach a very fast inference speed during testing. We further introduce a depth weighting function and a smooth constraint into loss function to improve inversion accuracy for the deep region and suppress false anomalies. Six groups of experiments are considered to demonstrate the feasibility and efficiency of the proposed methods. According to the comprehensive qualitative analysis and quantitative comparison, ERSInvNet with tier feature map, smooth constraints, and depth weighting function together achieve the best performance.

Deep Learning Inversion of Electrical Resistivity Data

https://pangea.stanford.edu/departments/geophysics/dropbox/SWP/publications/GPRFreqShift.pdf

Lanbo Liu

Papers

Lithospheric strength and intraplate seismicity in the New Madrid seismic zone

Advanced Signal Processing for Vital Sign Extraction With Applications in UWB Radar Detection of Trapped Victims in Complex Environments

Equations for finite-difference, time-domain simulation of sound propagation in moving inhomogeneous media and numerical implementation

Deep Learning Inversion of Electrical Resistivity Data

Radar attenuation tomography using the centroid frequency downshift method