Prospective Cohort Study


 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.

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.)

Lunar sourcebook. A user's guide to the moon

Ground penetrating radar (GPR) is a tool for indirectly looking at underground objects (such as graves), gravel and sand layers, and other underground structures. The information or data received by GPR is like an x-ray or map of the underground. In fact, GPR uses electromagnetic (EM) waves, as xray machines do, but GPR uses radio waves, which have a longer wavelength (see Figure A1). The wavelength, or the length of one wave, is the fundamental difference between the forms of electromagnetic energy. For example, the wavelength of x-rays range from about 10 billionths of a meter to about 10 trillionths of a meter, whereas radio waves can be a few meters long.

Ground Penetrating Radar

Study of bird attitude effect and corrections on frequency-domain helicopter em system

The Moon-based ground-penetrating radar (GPR) onboard the Chang’E-4 (CE-4) Yutu-2 rover has deployed on the Moon’s far side, providing an unprecedented opportunity to study the shallow surface geological process and the history of the volcanic eruption of the Moon. The high-frequency radar observed a buried lens structure <inline-formula> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula>27 m below the lunar surface, interpreted as paleoregolith by previous studies. In this study, we conducted a quantitative analysis of the dielectric properties of the buried lens structure observed during the CE-4 mission. Our results reveal that the relative permittivity and loss tangent of the structure is <inline-formula> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula>10.5 and <inline-formula> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula>0.037, respectively. Comparing our estimated dielectric properties with those of Apollo samples and radar-observed lava flows shows that the buried lens is neither regolith nor ejecta material but possibly basalt flow. In addition, we speculate that the buried basalt flow may represent the latest volcanic eruption on the Moon, possibly from the Eratosthenian-aged volcano that occurred approximately 2.5–2.2 billion years ago. Finally, we update the interpretation of the regolith stratigraphic structure observed by the Yutu-2 high-frequency radar at the CE-4 landing site.

Moon-Based Ground-Penetrating Radar Observation of the Latest Volcanic Activity at the Chang’E-4 Landing Site

Due to unexpected environmental variations and poor consistencies in land data acquisition, complex near-surface seismograms are usually polluted unreasonably with a low signal-to-noise ratio (SNR). These complicated circumstances bring more challenges in identifying accurate first arrivals for the following wave-equation traveltime (WT) inversion. Recently, the autoencoder (AE) is a typical unsupervised learning network, whose basic principle is to compress the input seismic data for their intrinsic features in the latent space with an encoder and, thereafter, to decipher these features for seismic profiles as the output with a decoder. This process is fully automatic with high stability and is not very sensitive to data quality. In this article, we propose an elastic WT inversion algorithm based on the AE method (AEWT) to invert the $P$ -velocity model. Compared with the standard WT, the AEWT method automatically extracts the intrinsic features of the refractions with AE as reference data for the misfit functionals. Feature images in the latent space show similar but intensified sensitivity to the traveltimes with respect to velocity perturbations. We present one synthetic and two field data tests for comparing the proposed AEWT and the standard WT tomograms to investigate the locations of a buried fault and the depth of a buried sinkhole. All these experiments demonstrate that the proposed elastic AEWT method can reduce errors caused by low SNR and obtain a more reliable and stable $P$ -velocity tomogram.

Jing Li

Papers

Study of bird attitude effect and corrections on frequency-domain helicopter em system

Moon-Based Ground-Penetrating Radar Observation of the Latest Volcanic Activity at the Chang’E-4 Landing Site

Autoencoded Elastic Wave-Equation Traveltime Inversion: Toward Reliable Near-Surface Tomogram