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Effect of seawater on incident plane P and SV waves at ocean bottom and engineering characteristics of offshore ground motion records off the coast of southern California, USA

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Earthquake Engineering and Engineering Vibration 2014年第2期13卷 181-194页

作者： Diao Hongqi Hu Jinjun Xie Lili Key Laboratory of Earthquake Engineering and Engineering Vibration Institute of Engineering MechanicsChina Earthquake Administration College of Earth Science University of Chinese Academy of Sciences School of Civil Engineering and Architecture Harbin Institute of Technology

The effect of seawater on vertical ground motions is studied via a theoretical method and then actual offshore ground motion records are analyzed using a statistical method. A theoretical analysis of the effect of seawater on incident plane P and SV waves at ocean bottom indicate that on one hand, the affected frequency range of vertical ground motions is prominent due to P wave resonance in the water layer if the impedance ratio between the seawater and the underlying medium is large, but it is greatly suppressed if the impedance ratio is small; on the other hand, for the ocean bottom interface model selected herein, vertical ground motions consisting of mostly P waves are more easily affected by seawater than those dominated by SV waves. The statistical analysis of engineering parameters of offshore ground motion records indicate that:(1) Under the infl uence of softer surface soil at the seafl oor, both horizontal and vertical spectral accelerations of offshore motions are exaggerated at long period components, which leads to the peak spectral values moving to a longer period.(2) The spectral ratios(V/H) of offshore ground motions are much smaller than onshore ground motions near the P wave resonant frequencies in the water layer; and as the period becomes larger, the effect of seawater becomes smaller, which leads to a similar V/H at intermediate periods(near 2 s). These results are consistent with the conclusions of Boore and Smith(1999), but the V/H of offshore motion may be smaller than the onshore ground motions at longer periods(more than 5 s).

关键词： offshore ground motion seawater P and SV waves vertical ground motions spectral ratio

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The effect of spall on Lg waves

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Acta Seismologica Sinica(English Edition) 2005年第3期18卷 331-337,379页

作者：何永锋陈晓非张海明 School of Earth & Space Sciences Peking University Beijing 100871 ChinaNorth-west Institute of Nuclear Technology Xi'an 710024 China School of Earth & Space Sciences Peking University Beijing 100871 China

The generation mechanism of Lg wave from underground nuclear explosion is still not clear at present. The gen-eral viewpoint is that the S wave generated by the near-source scattering of explosion-generated Rg appears to be the primary contributor to the low-frequency Lg (0.2~2.0 Hz) from nuclear explosions. The viewpoint is supported by the analysis of regional data from several Yucca Flats, NTS explosions by Patton and Taylor (1995), who fur-ther indicated that the prominent low-frequency spectral null in Lg is due to Rg from a compensated linear vector dipole (CLVD) source. In the paper, the data from Kazakstan Test Sites are investigated by a spectral ratio method. We have found that the spectral ratio of Lg waves is characterized by a spectral scalloping and a pronounced null, and the spectral null does not shift with spall dwell times, showing a strong dependence on shot depth and a very good agreement with those expected from Rg due to a CLVD source.

关键词： spectral ratio spall Lg wave CLVD source null

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Interval attenuation estimation from prestack seismic data:A case study from the Arabian Peninsula

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Applied Geophysics 2020年第4期17卷 475-488页

作者： Abdullah Alshangiti Hua-Wei Zhou University of Houston Department of Earth and Atmospheric SciencesHoustonTexasThe United States

Accurately estimated interval attenuation(1/Q)values have several applications,such as in quantitative interpretation and seismic resolution *** Q values can be estimated by measuring the spectral ratio between seismic reflections from a target and a reference reflector,the results are influenced by factors such as overburden ***,we quantitatively analyze the overburden influence on interval Q estimations using the spectral ratio method,time-space domain prestack Q inversion(PSQI),andτ-p domain *** compare these three methods using a synthetic dataset and a field dataset acquired onshore the Arabian *** seismic gathers are generated from a three-layer model with a low-Q inclusion in the first layer to mimic overburden *** fi eld data are preconditioned image gathers from a producing oil fi *** synthetic data test shows that the small low-Q body produces a considerable error in estimated Q *** smallest error(i.e.,13.3%)is in theτ-p domain PSQI ***,τ-p domain PSQI could obtain more accurate Q values when there are overburden infl uences because of the simultaneous inversion scheme and the application in theτ-p *** fi eld data application also illustrates that theτ-p domain PSQI produces reasonable interval Q *** measured Q values are also comparable with the Q values estimated from hydrocarbon saturated carbonate reservoirs.

关键词： Attenuation quality factor Q overburden inhomogeneity spectral ratio prestack Q inversion

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Q Inversion and Comparison of Influential Factors among Three Methods: CFS, SR, and AA

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Communications in Computational Physics 2020年第6期28卷 356-371页

作者： Yinting Wu J.T.Wu School of Geological and Surveying&Mapping Engineering Chang’an UniversityXi’an 710064P.R.China School of CML Engineering&Architecture Ningbo Institute of TechnologyZhejiang UniversityNingbo 315100P.R.China

The goals of this study were to examine factors influencing Q inversion and to provide references for practical *** different methods for inverting Q values with VSP data were explored,including centroid frequency shift(CFS),spectral ratio(SR),and amplitude attenuation(AA).Comparison between the CFS and the other two methods was conducted on frequency band widths and low attenuation,wavefield components,interface interference,and thin *** from several sets of VSP modeling data indicated that the CFS method is more stable and accurate for dealing with thin and high Q *** band width,especially the presence of high frequencies,influences the inversion effect of all three *** wider the band,the better the results.Q inversion from downgoing wavefield was very similar to that of the upgoing *** CFS method had fewer outliers or skip values from the full wavefield than the other two ***,the applications to Q inversion for the set of field VSP data demonstrated that the Q curves from the CFS method coincided with the geological interpretations better than the Q curves of the other ***,inverse Q filtering shifted the frequency component from 25 Hz to 35 *** results demonstrated that the Q curve is more sensitive to geological horizons than velocity.

关键词： Q inversion centroid frequency shift amplitude attenuation spectral ratio zero-offset VSP data

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Site amplification in the Lijiang Valley,Yunnan Province

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Acta Seismologica Sinica(English Edition) 1999年第2期12卷 193-198页

作者：李白基秦嘉政罗娣华叶建庆陈敏恭蔡绍平刘学军 The Western Yunnan Earthquake Prediction Study Area China Seismological Bureau Kunming China

The site amplifications for three stations, Libin (LIBI), Baisha (BASH) and Yulong (YULG) situated respectivelyin the southern, middle and northern parts of Lijiang Valley, are obtained by analyzing the S-wave soil/bedrockand microtremor horizontal/vertical spectral ratios. The data are digital recordings for the aftershocks of the Lijiang Ms=7.0 earthquake on February 3, 1996. In the frequency range of 1-4 Hi, the S-wave soil/bedrock spectralratio of E-W component for LIBI is the largest and amounts to 4.5. The microtremor soil N-S/vertical (V) spectralratio is approximate to l, E-W/V is about 4.5 and the same with above soil/bedrock spectral ratio. It is shown thatthe vertical and N-S components of microtremor have not been amplified by the soil and the Nakamura's method isapplicable. With this method, the microtremor spectral ratios for BASH and YULG are further evaluated. Theyhave similar characteristics with that of LIBI. In above frequency range, both N-S/V ratios are approximate to 1,while the E-W/V ratio is about 6 for BASH, 4.5 for YULG. Ljiang Valley is characterized by the trans-valleydirectional site response.

关键词： site amplification spectral ratio microtremor Lijiang

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