Robust reconstruction of aliased data using autoregressive spectral estimates

Autoregressive modeling is used to estimate the spectrum of aliased data. A region of spectral support is determined by identifying the location of peaks in the estimated spatial spectrum of the data. This information is used to pose a Fourier reconstruction problem that inverts for a few dominant wavenumbers that are required to model the data. Synthetic and real data examples are used to illustrate the method. In particular, we show that the proposed method can accurately reconstruct aliased data and data with gaps.     

利用多次波提高地震数据分辨率方法

目前对多次波的有效利用仅围绕多次波成像技术展开,通过成像多次波试图获取更丰富的地下构造信息.不同于该思路,本文另辟蹊径,从利用多次波提高地震数据分辨率角度出发,对多次波的有效利用进行了深入挖掘.首先基于聚焦变换思想在聚焦域内实现多次波的降阶,通过理论推导得出聚焦域内多次波表现为原始数据的多维子波反褶积这一重要结论,从理论上证明了本文方法提高地震数据分辨率的可行性;然后采用引入整形正则化的非稳态回归自适应匹配滤波方法将聚焦域内由多次波构建的高分辨率数据分离出来,实现原始数据的高分辨率转换.与常规反褶积模型不同,该方法基于波动理论推导得出,可以适用于任意复杂情况;每一道输出结果中所有炮记录都参与了运算,从空间上加以约束,在提高纵向分辨率的同时可以改善数据的横向分辨率.最后通过模型试算和实际资料处理对本文方法的有效性、适应性和实用性进行了验证.     

地震资料自适应高分辨率处理方法定量研究

分辨率是地震资料处理的重要问题,常以子波能量展布和震荡长度来定量分析,决定于地震资料的主频和频宽.越来越复杂的勘探对象要求高分辨率算法提供更丰富的波形和相位信息.实践表明自适应滤波方法在提高地震资料分辨率的同时,处理结果表现出更丰富的信息.在对APES方法的自适应滤波原理进行理论探讨和模型分析基础上,提出了加权方式的改进算法（WAPES）.通过统计实验,对改进前后的方法在信噪比和分辨率方面的表现进行了定量分析,同时设计典型模型试验来证明新方法的适用性.最后,改进后的方法应用于实际工区资料的处理,取得了很好的应用效果.

     

微机处理测震分析资料工作程序的改进

简要地论述了为克服微机处理测震数据程序(名为 DBJ)出现的缺点而进行改进的几点设想,改进思路,能产生备份文件及部分进行数据编辑的程序结构及模块,改进程序的特点和使用效果。     

由CDSN数据测定IPz分量谱震级初探

本文尝试用ＣＤｓＮ的ＩＰｚ分量强震记录来测定谱震级。通过对测出的谱震级ｍ＿（Ｔ）与体波震级ｍ＿（Ｂ）、ｍ＿（ｂ）的相关分析，得出其反映震源特性的峰值，出现在周期Ｔ＝１秒左右。此外，谱震级还有随周期而变化的特性。根据谱震级与能量的关系，推导了它的通用形式为ａｍ＿（Ｔ）＝ｌｏｇ（Ｅ／Ｅ０）（式中ａ＝２，ｌｏｇＥ＿０＝５．６）。它的最高震级为９．６级。运用谱震级的通用形式对本文测定的４个谱震级进行检验，结果表明它比传统方法测定的ＩＰｚ分量体波震级ｍ＿（Ｂ）系统偏小０．３１级。因谱震级是扣除了介质滞弹性吸收影响后的产物，故这种偏差是比较合理的。     

复杂构造三维地震观测系统设计的共聚焦分辨率分析

三维地震观测系统共聚焦分辨率特性分析突破传统以点论证为基础的观测系统分辨率分析方法,面向地质目标定量预测三维观测系统地震成像的空间分辨率和振幅精度.基于Fourier有限差分（FFD）大步长波场延拓和Born-Kirchhoff小步长波场插值递推方法,本文介绍了一种复杂介质条件下三维地震观测系统共聚焦分辨率特性快速分析方法.对给定的速度模型,该方法能够分析拟采用的三维地震观测系统设计方案对复杂构造的成像分辨率与AVP属性,从而为进一步的偏移成像与储层分析提供保证.最后本文以SEG/EAGE三维盐丘模型为例设计满覆盖为16次的三维地震观测系统,并实施三维共聚焦分辨率特性分析.     

Horizontal to vertical spectral ratio and geological conditions: an analysis of strong motion data from Greece and Taiwan (SMART-1)

Nowadays, several research efforts have been directed towards the evaluation of the horizontal to vertical, (h/v), spectral ratio technique, following the pioneering work of Nakamura originally proposed for microtremor measurements. In the present study, an extension of this technique based on Greek and Taiwanese (SMART-1) strong motion data is attempted. Whenever possible comparisons with results obtained by the standard spectral ratio technique for the same sites are made. Regarding the Greek data it is concluded that (h/v) spectral ratio clearly distinguishes the range of resonant peaks between ‘rock’ and ‘alluvium’ sites. On the other hand, nonlinear effects that take place beneath SMART-1 array most probably obscure the expected consistency between (h/v) and standard spectral ratio technique.     

S-wave spectral analysis of the 1995 Kozani-Grevena (NW Greece) aftershock sequence

S-wave spectral analysis is applied to 174 strong motion accelerationrecords to obtain the source parameters of 27 aftershocks(3.1 M_L 4.3) of the May 13, 1995, M_w 6.6,Kozani-Grevena (NW Greece) earthquake. The data are derived from atemporary network, of three-component digital accelerographs, deployedwithin the strongly affected area some days after the mainshock occurrence.Site effects were evident in the strong motion records at 3 out of the 4stations used, and a correction was applied to account for theoverestimation of seismic moment due to amplification of thelow-frequency part of the spectrum. The data from this analysis arecomplimented with previously obtained source parameters for earthquakesin Greece, in order to study the applicability of the empirical scalingrelations used so far, towards smaller magnitudes. In general, a goodcorrelation was observed in most cases, validating the use of empiricalrelations that are applicable to the Aegean area. Empirical relations aredetermined between seismic moment and seismic slip, as well as, betweenseismic moment and stress drop, applicable to small magnitude earthquakes(M_L < 4.3). Stress drop values were found to be relatively small,ranging from 2 to 41 bars, indicative of inter-plate environments. Thevalues of f_c and of f_max were found in good agreement withrelations based on observations from larger worldwide earthquakes.     

Attenuation characteristics of peak ground acceleration from fault trace of the 1999 Kocaeli (Turkey) earthquake and comparison of spectral acceleration with seismic design code

The 17 August 1999 Kocaeli earthquake in Turkey produced a majorsurface rupture. We traced this surface rupture from Gölcük toDüzce and located it accurately by using GPS. The closest distancefrom the surface rupture to the strong motion observation sites weredetermined. Then the attenuation characteristics of the observed peakground acceleration were compared with the attenuation relation given byFukushima and Tanaka (1992), which is suitable for the near-fault zone inJapan and gives results that closely match data recorded during the 1995Hyogo-ken Nanbu earthquake in Japan. Although this attenuation relationwas developed for Japan, we found that it agreed well with the KOCAELIearthquake. Furthermore, the observed spectral acceleration of 5%damping was compared with the building design code of Turkey and theobserved level was lower than the code.     

Improving the spatial resolution of ground motion variability using earthquake and seismic noise data: the example of Bishkek (Kyrgyzstan)

Site response analysis plays an important role in seismic hazard and risk assessment, and in defining the optimal engineering design for civil structures. However, due to increasing urbanization, target areas are often too vast to be covered by standard approaches, resulting in large uncertainties in the spatial variability of the expected ground motion. Here, we propose a method to improve the spatial resolution of ground motion variability in terms of Standard Spectral Ratios (SSRs), using earthquakes recorded at a few selected sites for a relatively short amount of time, and seismic noise data collected over a denser grid, taking advantage of clustering and correlation analysis. The method is applied to Bishkek, Kyrgyzstan. Using the K-means clustering algorithm, three clusters of site response types have been identified, based on their similarity of SSRs. The cluster’s site responses were adopted for sites where only single station noise measurements were carried out, based on the results of correlation analysis. The spatial variability of the site response correlates well with the main geological features in the area. In particular, variability is noted from south to north, consistent with both the changes in the thickness of the sedimentary cover over the basin and in the Quaternary material outcropping at the surface. This method has therefore the potential to improve the estimation of site effects at the local scale in the future.     

Application of spectral analysis to determine hydraulic diffusivity of a sandy aquifer (Pingtung County,Taiwan)

The study demonstrates spectral relationships in the time–frequency domain for one‐dimensional groundwater flow in aquifers bounded by fluctuating boundaries. By nature, the solutions of spectral equations are non‐linear complex functions. To determine hydraulic diffusivity in the governing equations, it is required that the data are collected from the spectra of water levels at the fluctuating boundaries and observation wells. Hydraulic diffusivity thus can be obtained by an iterative inverse approach. This paper presents an application in Pingtung County of Taiwan to determine the hydraulic diffusivity of a sandy aquifer under confined conditions. Spectral density function of water level obtained from tidal boundaries and observation wells are used to approximate hydraulic diffusivity, which yields an averaged value of 1·26 × 10⁶ m²/h. Copyright © 2004 John Wiley & Sons, Ltd.     

Evidence of nonlinear site response in HVSR from SMART1 (Taiwan) data

Deamplification of strong motion and the increase of the effective period of soil deposits are typical nonlinear effects; we seek them in SMART1-array data by applying the horizontal-to-vertical spectral ratio (HVSR) technique. The recordings, from four soil and one rock stations, represent 23 earthquakes (M_L 4.9–7.0); PGA varies between 20–260 cm/s². For each station, mean HVSR curves are calculated for two PGA ranges: <75 cm/s² and >100 cm/s² (weak and strong motion). At the soil stations, the “weak” (linear) and “strong” (nonlinear) responses are significantly different. Below 1–1.8 Hz, the nonlinear response exceeds the linear one. Above 2 Hz, the nonlinear response drops below the linear one and above 4–6 Hz below unity (deamplification). From 10 to 16 Hz, the two responses converge. One soil site shows significant negative correlation between resonance frequency and ground acceleration. Such behaviour agrees with other empirical studies and theoretical predictions. Our results imply that the HVSR technique is sensitive to ground-motion intensity and can be used to detect and study nonlinear site response.     

2-D spectral element simulations of destructive ground shaking in Catania (Italy)

This study wants to estimate the strong ground motion in the municipal area of Catania (Italy) for a catastrophic earthquake scenario. It is part of a larger research program funded by the National Research Council – National Group for the Defence Against Earthquakes (CNR-GNDT), The Catania Project, devoted to evaluating the seismic risk of a highly urbanised area, such as that of Catania, located in a seismically active region. The reference earthquake simulates the catastrophic event (M 7.2) of 1693. The ground shaking is computed solving the 2-D full-wave equation by the Chebyshev spectral element method (SPEM). Particular emphasis is given to the construction of realistic structural models, also including the finest local detail, obtained from the geophysical, geological and geotechnical data available. Simulations are performed for several sources, to account for both a change in source position and orientation, and the finite extension of the fault along its dip. Synthetic seismograms and peak ground acceleration (PGA) envelopes, calculated at the surface for four transects across the Catania area, constitute the main result of this study which can be used for practical purposes. Simulations show that ground motion is strongly influenced by both source characteristics and crustal structure. We have found that PGA values range between 0.1 g and 0.5 g, although particular site conditions strongly affect these values locally. For example, the frequencies of maximum interest in civil engineering (1.5–4 Hz) are enhanced selectively by a thick portion of surface sediments (i.e., 30–100 m for an average shear wave velocity of 500–600 m/s). An unexpected feature is the appreciable increase of PGA at large epicentral distances, which contradicts classical attenuation relations. All the results are examined through an analysis of the propagating wavefield.     

地震前兆观测数据处理系统

作者用Visual foxpro开发的《地震前兆观测数据处理系统(台站版)》是专门为地震台站的需要而设计的，系统用登录表单的方式来选择形变、流体学科的4种观测手段，通过不同的菜单，不但能完成前兆观测资料的日常处理，又能完成资料入库、资料解释、资料预处理等工作，从而帮助台站观测人员及时分析处理本区的观测资料，做好地震短临预报工作。     

An indication of the soil topmost layer response in Quito (Ecuador) using noise H/V spectral ratio

H/V noise spectral ratio (HVSR), standard spectral ratio (SSR), and receiver functions (RF) techniques have been used in the Quito (Ecuador) urban area to estimate the frequency dependence of soil response. Two amplified frequencies obtained by the HVSR method appear on about 60 sites. Taking into account the most amplified frequency rather than considering only the first amplified frequency, generally associated with the fundamental frequency, we find that iso-frequency curves tightly fit the surface geology. The second amplified frequency is interpreted as the fundamental frequency of the soft thin topmost layer, which in some cases amplifies the surface ground motion more than the rest of the soil column. This hypothesis is further supported by the results provided from the SSR and RF studies at a station located on top of a solid waste landfill, and by a study of known thickness of a waste landfill, using the HVSR method.     

Spatial and temporal changes in the structure of groundwater nitrate concentration time series (1935–1999) as demonstrated by autoregressive modelling

Autoregressive modelling is used to investigate the internal structure of long-term (1935–1999) records of nitrate concentration for five karst springs in the Mendip Hills. There is a significant short term (1–2 months) positive autocorrelation at three of the five springs due to the availability of sufficient nitrate within the soil store to maintain concentrations in winter recharge for several months. The absence of short term (1–2 months) positive autocorrelation in the other two springs is due to the marked contrast in land use between the limestone and swallet parts of the catchment, rapid concentrated recharge from the latter causing short term switching in the dominant water source at the spring and thus fluctuating nitrate concentrations. Significant negative autocorrelation is evident at lags varying from 4 to 7 months through to 14–22 months for individual springs, with positive autocorrelation at 19–20 months at one site. This variable timing is explained by moderation of the exhaustion effect in the soil by groundwater storage, which gives longer residence times in large catchments and those with a dominance of diffuse flow. The lags derived from autoregressive modelling may therefore provide an indication of average groundwater residence times. Significant differences in the structure of the autocorrelation function for successive 10-year periods are evident at Cheddar Spring, and are explained by the effect the ploughing up of grasslands during the Second World War and increased fertiliser usage on available nitrogen in the soil store. This effect is moderated by the influence of summer temperatures on rates of mineralization, and of both summer and winter rainfall on the timing and magnitude of nitrate leaching. The pattern of nitrate leaching also appears to have been perturbed by the 1976 drought.     

Seismic fragility and reliability of structures isolated by friction pendulum devices: seismic reliability‐based design (SRBD)

The paper deals with the seismic reliability of elastic structural systems equipped with friction pendulum isolators (friction pendulum system). The behavior of these systems is analyzed by employing a two‐degree‐of‐freedom model accounting for the superstructure flexibility, whereas the friction pendulum system device behavior is described by adopting a widespread model that considers the variation of the friction coefficient with the velocity. With reference to medium soil condition, the uncertainty in the seismic inputs is taken into account by considering a set of artificial records, obtained through Monte Carlo simulations within the power spectral density method, with different frequency contents and characteristics depending on the soil dynamic parameters and scaled to increasing intensity levels. The sliding friction coefficient at large velocity is also considered as random variable modeled through a uniform probability density function. Incremental dynamic analyses are developed in order to evaluate the probabilities exceeding different limit states related to both r.c. superstructure and isolation level defining the seismic fragility curves through an extensive parametric study carried out for different structural system properties. Finally, considering the seismic hazard curves related to a site near L'Aquila (Italy), the seismic reliability of the r.c. superstructure systems is evaluated, and seismic reliability‐based design abacuses are derived with the aim to define the radius in plan of the friction pendulum devices in function of the structural properties and reliability level expected. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of horizontal-to-vertical (H/V) Fourier spectral ratio for analysis of site effect on rock (NEHRP-class B) sites in Taiwan

The frequency-dependent amplification for rock (NEHRP-class B) sites was studied using earthquake ground-motion database collected in Taiwan during implementation of the Taiwan Strong Motion Instrumentation Program. The database used includes several hundred records from earthquakes of M_L 4.0–7.3 occurred between 1993 and 2004. The characteristics of amplification were evaluated using the well-known technique of horizontal-to-vertical Fourier spectral ratio (H/V) of the S-wave phase [Lermo J, Chavez-Garcia FJ. Site effect evaluation using spectral ratios with only one station. Bull Seism Soc Am 1993;83:1574–94]. The study allows us to analyze peculiarities of rock sites amplification in Northern and Eastern Taiwan. It was suggested to divide the NEHRP-class B site amplification into four types based on frequency of maximum amplification and the shape of amplification function. The applicability of the technique was also checked for a few stiff and soft soil sites (NEHRP-classes D and E).     

Variations of local seismic response in Benevento (Southern Italy) using earthquakes and ambient noise recordings

The city of Benevento (Southern Italy) has been repeatedly struck by large historical earthquakes. A heterogeneous geologic structure and widespread soft soil conditions make the estimation of site effects crucial for the seismic hazard assessment of the city. From 2000 until 2004, we installed seismic stations to collect earthquake data over zones with different geological conditions. Despite the high level of urban noise, we recorded more than 150 earthquakes at twelve sites. This data set yields the first, well documented experimental evidence for weak to moderate local amplifications. We investigated site effects primarily by the classical spectral ratio technique (CSR) using a rock station placed on the Benevento hill as reference. All sites in the Calore river valley and in the eastern part of the Benevento hill show a moderate high-frequency (f > 4 Hz) amplification peak. Conversely, sites in the Sabato river valley share weak-to-moderate amplification in a wide frequency band (from 1–2 to 7–10 Hz), without evident frequency peaks. Application of no-reference-site techniques to earthquake and noise data confirms the results of the CSRs in the sites of the Calore river valley and of the eastern part of the Benevento hill, but fails in providing indications for site effects in the Sabato river valley, being the H/V ratios nearly flat. One-dimensional modeling indicates that the ground motion amplification can be essentially explained in terms of a vertically varying geologic structure. High-frequency narrow peaks are caused by the strong impedance contrast existing between near-surface soft deposits and stiff cemented conglomerates. Conversely, broad-band amplifications in the Sabato river valley are likely due to a more complex layering with weak impedance contrasts both in the shallow and deep structure of the valley.     

坑（井）-地电阻率成像技术数据处理方法研究

开发坑（井）一地电阻率成像技术数据处理软件包,对分布式地面一坑道电磁信号接收仪记录的时间序列进行分析处理,最终得到相应的视电阻率和相位参数。实际资料处理结果表明,在远区情况下,需考虑信噪比水平,选择合适的计算方法。当信噪比很低或较高时,可选择根据卡尼亚电阻率定义式直接比值的方法,该方法计算简便、效率高;当信噪比一般时,采用最小二乘或Robust等估算方法,能在一定程度上改善数据处理质量。