The separation and parameter determination of PS converted phases in deep sounding by converted waves of earthquakes

The practice of deep sounding by converted waves of Earthquakes shows that the time duration of the PS converted phases is usually longer than the arrival time delay between the converted phases coming from the adjacent boundaries. So, the mutual interference of the converted phases from adjacent boundaries may form a complicated interference series of the waves. It is difficult to recognize and determine exactly the parameters of the converted waves in the interfering records. In this paper the method of omni-azimuthal polarization analysis and the method of separation of interfering waves are described. The theoretical examples show that the procedure given in the paper is rather effective to separate the interfering waves and to determine their parameters, and so, is important to improve the resolving power and the reliability of the method of deep sounding by converted waves of earthquakes. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 39–45, 1993. The research reported here is a part of proposal sponsored by State Seismological Bureau and China Joint Seismological Science Foundation.     

Identification of a one-dimensional model for a soil-layer–bedrock system during an earthquake

The propriety of adopting a multi-degree-of-freedom lumped mass–spring–dampers system driven by white noise support excitation as a one-dimensional model for a soil-layer–bedrock system during an earthquake is investigated by means of statistical system identification of the model with noisy measurement of the earthquake ground velocity. The present discussion also suggests that this model may not be applicable to all observed earthquake records, since the model itself depends on the statistical nature of the earthquake motion. For appropriate earthquake records, the system identification procedure may be accomplished; then dynamical properties of the soil-layer and the power spectral density for white noise excitation acting upon the bedrock can be estimated as shown in a numerical example.     

Multi-method pIRIR dating of sedimentary sequences at the southern edge of the Gurbantunggut Desert,NW China and its palaeoenvironmental implications

The Gurbantunggut Desert is the second-largest desert in China, located in the westerly-dominated region of north-western China. Previous understanding of palaeoclimate of this desert was mostly based on lake and loess records from the Junggar Basin and Tian Shan Mountains, whilst direct dating of sedimentary records from the desert was very limited. This study applies high-resolution post-infrared infrared stimulated luminescence (pIRIR) dating to three sedimentary profiles at the southern edge of the Gurbantunggut Desert, which contain aeolian sand and water-lain sediments, recording palaeoenvironmental changes at the desert margin since the Last Glacial Maximum (LGM). Different pIRIR dating procedures were applied for samples with different ages. For Holocene-aged samples, a single-aliquot regenerative-dose (SAR) pIRIR procedure based on a three-stepped pIRIR measurement at 110 °C, 140 °C and 170 °C was used, and a standard growth curve (SGC) procedure yields an equivalent dose (D_e) similar to that of the full-SAR procedure; thus, is applicable for accelerating D_e measurement. For samples much older than the Holocene, a multi-aliquot regenerative-dose (MAR) pIRIR procedure based on a three-stepped pIRIR measurement at 150 °C, 200 °C and 250 °C was found to be the optimal dating procedure, because a SAR procedure would yield underestimated ages due to uncorrected initial sensitivity change. pIRIR dating results of the investigated profiles reveal a substantial sand accumulation during the LGM, an intensification of aeolian deposition at ∼12 ka and a wetter depositional environment at ∼10–8 ka. A rapid fluvial deposition is dated at ∼20–19 ka, corresponding to the deglaciation period. The sedimentary records from the desert margin show some correlation with lake and loess records in the same region and suggest a complex response of the desert environment to different climatic factors.     

Estimation of phosphorus loads with sparse data for agricultural watersheds in the Czech Republic

Abstract

Agricultural watersheds in the Czech Republic are one of the primary sources of non-point-source phosphorus (P) loads in receiving waters. Since such non-point sources are generally located in headwater catchments, streamflow and P concentration data are sparse. We show how very short daily streamflow and P concentration records can be combined with nearby longer existing daily streamflow records to result in reliable estimates of daily and annual P concentrations and loads. Maintenance of variance streamflow record extension methods (MOVE) can be employed to extend short streamflow records. Constituent load regressions are used to predict daily P constituent loads from streamflow and other time varying characteristics. Annual P loads are then estimated for individual watersheds. Resulting annual P load estimates ranged from 0.21 to 95.4 kg year^-1 with a mean value of 11.77 kg year^-1. Similarly annual P yield estimates ranged from 0.01 to 0.3 kg ha^-1 year^-1 with an average yield of 0.07 kg ha^-1 year^-1. We document how short records of daily streamflow and P concentrations can be combined with a national network of daily streamflow records in the Czech Republic to arrive at meaningful and reliable estimates of annual P loads for small agricultural watersheds.

Citation Beránková, T., Vogel, R. M., Fiala, D. & Rosendorf, P. (2010) Estimation of phosphorus loads with sparse data for agricultural watersheds in the Czech Republic. Hydrol. Sci. J. 55(8), 1417–1426.     

3D description and inversion of reflection moveout of PS‐waves in anisotropic media

Common‐midpoint moveout of converted waves is generally asymmetric with respect to zero offset and cannot be described by the traveltime series t²(x²) conventionally used for pure modes. Here, we present concise parametric expressions for both common‐midpoint (CMP) and common‐conversion‐point (CCP) gathers of PS‐waves for arbitrary anisotropic, horizontally layered media above a plane dipping reflector. This analytic representation can be used to model 3D (multi‐azimuth) CMP gathers without time‐consuming two‐point ray tracing and to compute attributes of PS moveout such as the slope of the traveltime surface at zero offset and the coordinates of the moveout minimum. In addition to providing an efficient tool for forward modelling, our formalism helps to carry out joint inversion of P and PS data for transverse isotropy with a vertical symmetry axis (VTI media). If the medium above the reflector is laterally homogeneous, P‐wave reflection moveout cannot constrain the depth scale of the model needed for depth migration. Extending our previous results for a single VTI layer, we show that the interval vertical velocities of the P‐ and S‐waves (V_P0 and V_S0) and the Thomsen parameters ε and δ can be found from surface data alone by combining P‐wave moveout with the traveltimes of the converted PS(PSV)‐wave. If the data are acquired only on the dip line (i.e. in 2D), stable parameter estimation requires including the moveout of P‐ and PS‐waves from both a horizontal and a dipping interface. At the first stage of the velocity‐analysis procedure, we build an initial anisotropic model by applying a layer‐stripping algorithm to CMP moveout of P‐ and PS‐waves. To overcome the distorting influence of conversion‐point dispersal on CMP gathers, the interval VTI parameters are refined by collecting the PS data into CCP gathers and repeating the inversion. For 3D surveys with a sufficiently wide range of source–receiver azimuths, it is possible to estimate all four relevant parameters (V_P0, V_S0, ε and δ) using reflections from a single mildly dipping interface. In this case, the P‐wave NMO ellipse determined by 3D (azimuthal) velocity analysis is combined with azimuthally dependent traveltimes of the PS‐wave. On the whole, the joint inversion of P and PS data yields a VTI model suitable for depth migration of P‐waves, as well as processing (e.g. transformation to zero offset) of converted waves.     

Velocity imaging by tau–p transformation of refracted seismic traveltimes

We present a new method for producing a ‘brute’ velocity image rapidly and automatically from traveltimes picked from densely sampled refraction data. The procedure involves imaging by data transformation from the time–offset domain into the tau–p (intercept–slope) domain, and does not include conventional modelling steps. Differences in apparent velocity and tau along reciprocal paths in the up- and downdip directions allow the estimation of the true velocity and geometrical position of the ray turning points. The tau–velocity–turningpoint (τ–ν–x) map distributes phases automatically on the basis of geometry and velocity to give a two-dimensional representation of subsurface structure. This map may be converted simply to depth and two-way-time images. Such images have potential for direct geological interpretation, for use as a starting model for seismic inversion, for superimposition on to conventional reflection images, or for input into prestack depth migration and other processing routines.     

Sign-change correction for prestack migration of P-S converted wave reflections1

The polarization direction or 'sign’ of reflected converted P–S waves depends upon the angle of incidence of the incident P-wave. Sign reversal due to reversal of the angle of incidence is often encountered and is an impediment to P–S wave processing and imaging, because when P–S events or P-S migrated images with mixed signs are stacked, destructive interference occurs. We have created and demonstrated a means of correcting for this reversal. To do this, a P-wave angle of incidence is calculated for every point in the image space. This is done by calculating a P–S reflected waveform for every point, by extrapolating the reflected S-wavefield backwards from the receiver line, and then cross-correlating this waveform with the S-wave reflections observed at the receiver line. A multiplier, (sgn α) is assigned to each point in the image space, where α is the angle of incidence of the P-wave. The multiplier was applied to a set of prestack reverse time migration images derived from a cross-borehole physical elastic model data set. The improvement in the stacked image when the sign correction is applied is spectacular. The P-S image quality is comparable to, or better than, stacked migrated P-P images. The method appears to be applicable to all reflection modes and to all recording geometries.     

Features of different types of seismic events in China’s Capital Region

Seismic records produced by different seismic sources vary. In this study, we compared the waveform records and time-frequency characteristics of tectonic earthquakes, artificial explosions, and mine collapses in China’s Capital Region. The results show that tectonic earthquakes are characterized by stronger S-wave energy than P-wave energy, obvious high-frequency components, and wide frequency bands of P and S waves. Artificial explosions are characterized by greater P-wave amplitude than S-wave amplitude and near-station surface wave development. Mine collapses are characterized by lower overall frequency, more obvious surface waves, and longer duration. We extracted quantitative discriminants based on the analysis of different event records, with 31 feature values in 7 categories (P/S maximum amplitude ratio, high/low frequency energy ratio, P/S spectral ratio, corner frequency, duration, the second-order moment of spectrum, and energy strongest point). A comparison of the ability of these feature values to recognize distinct events showed that the 6–17 Hz P/S spectral ratio was able to completely distinguish artificial explosions from the other two types of events. The S-wave corner frequency performed relatively well in identifying all three types of events, with an accuracy of over 90%. Additionally, a support vector machine was used to comprehensively distinguish multiple features, with an accuracy for all three types of events reaching up to 100%.     

大别造山带地壳S波速度结构

在大别造山带深地震测深剖面H维P波地壳速度结构的基础上,从地震记录的水平分量得到S波地壳速度结构,并用P波和S波的资料共同约束地壳的组成.剖面上大多数炮点的记录均显示了清晰的Sg和SmS震相.在埠塔寺炮和金拱炮的记录上还较清晰地显示出莫霍界面的反射转换震相PmS,表明在相应的范围内莫霍界面是一级间断面.在Pn和SmS震相都比较强的记录截面图上缺少相应的Sn震相,表示在上地幄顶部泊松比随深度急剧增大,在这一深度上物质可能存在局部熔融状态.剖面的地壳泊松比模型表明,上地壳在深度10km以内泊松比为025左右,仅北淮阳弧后复理石带较低,为0.23；扬子板块和华北板块的下地壳泊松比为0.26-0.27；在大别选山带,上地壳下部泊松比为0.22-0.24,而下地壳泊松比为0.27-0.30,其中超高压变质带最高.P、S波速度和泪松比表明超高压变质带下地壳主要由基性麻粒岩组成.大别造山带中、下地壳组成的横向不均匀性反映了在三叠纪造山作用期间扬子板块向华北板块俯冲,以及存在与地慢物质相联系的岩浆侵入体.     

大别造山带地壳S波速度结构

在大别造山带深地震测深剖面H维P波地壳速度结构的基础上,从地震记录的水平分量得到S波地壳速度结构,并用P波和S波的资料共同约束地壳的组成.剖面上大多数炮点的记录均显示了清晰的Sg和SmS震相.在埠塔寺炮和金拱炮的记录上还较清晰地显示出莫霍界面的反射转换震相PmS,表明在相应的范围内莫霍界面是一级间断面.在Pn和SmS震相都比较强的记录截面图上缺少相应的Sn震相,表示在上地幄顶部泊松比随深度急剧增大,在这一深度上物质可能存在局部熔融状态.剖面的地壳泊松比模型表明,上地壳在深度10km以内泊松比为025左右,仅北淮阳弧后复理石带较低,为0.23;扬子板块和华北板块的下地壳泊松比为0.26-0.27;在大别选山带,上地壳下部泊松比为0.22-0.24,而下地壳泊松比为0.27-0.30,其中超高压变质带最高.P、S波速度和泪松比表明超高压变质带下地壳主要由基性麻粒岩组成.大别造山带中、下地壳组成的横向不均匀性反映了在三叠纪造山作用期间扬子板块向华北板块俯冲,以及存在与地慢物质相联系的岩浆侵入体.     

用长周期面波波形拟合及P波初动方向估计中等地震的震源机制

提出利用周期范围４５-１００ｓ间的面波波形拟合与Ｐ波初动符号相结合,估计中小地震震源机制的方法．给出两个倾滑为主和三个走滑为主的震例．其中最小的是１９９６年１２月１６日北京顺义ＭＬ４．５级地震.比较了１９９６年２月５日云南丽江Ｍｓ６．０级余震的机制解与美国哈佛大学ＣＭＴ结果的相似程度,各震例记录图与理论图的相似程度,以及初动分布与主压力轴Ｐ和主动力轴Ｔ分布区的一致程度．从比较结果看,得到的震源机制解有参考价值,开发的软件有可用性．     

用长周期面波波形拟合及P波初动方向估计中等地震的震源机制

提出利用周期范围４５—１００ｓ间的面波波形拟合与Ｐ波初动符号相结合,估计中小地震震源机制的方法．给出两个倾滑为主和三个走滑为主的震例．其中最小的是１９９６年１２月１６日北京顺义ＭＬ４．５级地震.比较了１９９６年２月５日云南丽江Ｍｓ６．０级余震的机制解与美国哈佛大学ＣＭＴ结果的相似程度,各震例记录图与理论图的相似程度,以及初动分布与主压力轴Ｐ和主动力轴Ｔ分布区的一致程度．从比较结果看,得到的震源机制解有参考价值,开发的软件有可用性．     

Test of high sampling density OSL dating of aeolian samples from the south margin of the Tengger Desert using the global standardised growth curve (gSGC) method

Chronostratigraphic records in the drylands of north China provide basic archives to reveal the dynamic connections between climate changes and the behaviour of aeolian systems. However, the interpretation of aeolian chronostratigraphy is not straightforward and may be associated with significant uncertainty due to a number of external and localised forces. Taking into account this complexity of aeolian systems, excluding preservation and sampling bias from palaeoclimatic signals requires that the interpretation of chronostratigraphic records be based on as many dates from as many sites as possible. Optically stimulated luminescence (OSL) dating provides a direct way to date aeolian sediments. However, the determination of equivalent dose (D_e) using the commonly applied single-aliquot regenerative dose (SAR) protocol is relatively time-consuming for samples with burial doses exceeding 50 or 100 Gy.In this study, the global standardised growth curve (gSGC) method is applied to multi-grain aliquots of coarse quartz from various sites covering a wide region of the south margin of the Tengger Desert in north China to rapidly determine D_e for a large number of aliquots and samples. The large between-aliquot variability in the shape of the dose response curve (DRC) is significantly reduced using a least-squares normalisation procedure. The results of a leave-one-out cross-validation (LOOCV) protocol demonstrates that D_e values determined using the gSGC and SAR methods are very consistent with each other up to at least 200 Gy and 400 Gy, for the 90–150 μm and 63–90 μm fractions, respectively. It suggests that the gSGC protocol can be used as an efficient procedure for D_e determination of a large number of aeolian samples from multiple sites. This in turn provides a better constraint for the interpretation of Late Quaternary aeolian chronostratigraphic records in drylands of north China.     

Borehole study of compressional and shear attenuation of basalt flows penetrated by the Brugdan and William wells on the Faroes shelf

We investigated the seismic attenuation of compressional (P‐) and converted shear (S‐) waves through stacked basalt flows using short‐offset vertical seismic profile (VSP) recordings from the Brugdan (6104/21–1) and William (6005/13–1A) wells in the Faroe‐Shetland Trough. The seismic quality factors (Q) were evaluated with the classical spectral ratio method and a root‐mean‐square time‐domain amplitude technique. We found the latter method showed more robust results when analysing signals within the basalt sequence. For the Brugdan well we calculated effective Q estimates of 22–26 and 13–17 for P‐ and S‐waves, respectively, and 25–33 for P‐waves in the William well. An effective Q_S/Q_P ratio of 0.50–0.77 was found from a depth interval in the basalt flow sequence where we expect fully saturated rocks. P‐wave quality factor estimates are consistent with results from other VSP experiments in the North Atlantic Margin, while the S‐wave quality factor is one of the first estimates from a stacked basalt formation using VSP data. Synthetic modelling demonstrates that seismic attenuation for P‐ and S‐waves in the stacked basalt flow sequence is mainly caused by one‐dimensional scattering, while intrinsic absorption is small.     

Basin-scale analysis of rainfall and runoff in Peru (1969–2004): Pacific,Titicaca and Amazonas drainages

Abstract

We present a procedure for estimating Q95 low flows in both gauged and ungauged catchments where Q95 is the flow that is exceeded 95% of the time. For each step of the estimation procedure, a number of alternative methods was tested on the Austrian data set by leave-one-out cross-validation, and the method that performed best was used in the final procedure. To maximise the accuracy of the estimates, we combined relevant sources of information including long streamflow records, short streamflow records, and catchment characteristics, according to data availability. Rather than deriving a single low flow estimate for each catchment, we estimated lower and upper confidence limits to allow local information to be incorporated in a practical application of the procedure. The components of the procedure consist of temporal (climate) adjustments for short records; grouping catchments into eight seasonality-based regions; regional regressions of low flows with catchment characteristics; spatial adjustments for exploiting local streamflow data; and uncertainty assessment. The results are maps of lower and upper confidence limits of low flow discharges for 21 000 sub-catchments in Austria.     

Using regional regression within index flood procedures and an empirical Bayesian estimator

Studies have illustrated the performance of at-site and regional flood quantile estimators. For realistic generalized extreme value (GEV) distributions and short records, a simple index-flood quantile estimator performs better than two-parameter (2P) GEV quantile estimators with probability weighted moment (PWM) estimation using a regional shape parameter and at-site mean and L-coefficient of variation (L-CV), and full three-parameter at-site GEV/PWM quantile estimators. However, as regional heterogeneity or record lengths increase, the 2P-estimator quickly dominates. This paper generalizes the index flood procedure by employing regression with physiographic information to refine a normalized T-year flood estimator. A linear empirical Bayes estimator uses the normalized quantile regression estimator to define a prior distribution which is employed with the normalized 2P-quantile estimator. Monte Carlo simulations indicate that this empirical Bayes estimator does essentially as well as or better than the simpler normalized quantile regression estimator at sites with short records, and performs as well as or better than the 2P-estimator at sites with longer records or smaller L-CV.     

Estimation of shear moduli and damping factors of earth dam materials

Abdel-Ghaffar and Scott developed a procedure for extracting the shear moduli and damping factors of soils based upon strong motion records from earth dams. It is a very efficient procedure for earth dams that exhibited predominantly first mode response along the upstream-downstream direction. In their approach, they employed digital band-pass filters on the crest and abutment acceleration records, and constructed the hysteresis loops of soils by treating these filtered records as the input-output to a non-linear SDOF structure. In the process an important superposition assumption was implicitly introduced. This study looked into the implications of this linear superposition assumption on presumed nonlinear systems. Specifically, numerical simulations were conducted in finding out whether or not such a procedure is capable of extracting a known input dynamic behaviour of soils. It was found that the hysteresis loops were generally distorted, and to minimize errors only those loops of larger strain amplitudes should be used. Simple guidelines were suggested accordingly. Applications to real records from two dams were carried out following the proposed guidelines. Results of such applications were explored.     

对地震转换波的数字滤波处理

本文讨论运用低通滤波、偏振滤波、频率加强滤波、相关滤波及迭加处理等数字滤波方法,对地震转换波测深资料进行数字处理的方法及效果.数字滤波处理结果在一定程度上提高了记录的信噪比,为准确地进行相位对比和震相识别提供了可靠基础.      

Hydrological trend analysis with innovative and over-whitening procedures

Different statistical methodologies can be employed to identify possible trend components in any hydro-meteorological time series. A pre-whitening (P-W) procedure has been suggested to reduce the serial correlation effect on Mann-Kendall (M-K) trend analysis. In this paper, instead of P-W, an over-whitening (O-W) procedure is suggested, which generates serially independent series with the same trend slope value. Analytically necessary formulations for O-W are presented with a non-parametric but simple innovative trend assessment procedure, which are supported by extensive simulation studies. The applications of the methodology are presented for eight factual time series records from tropical, temperate and arid regions including temperature, rainfall, streamflow, relative humidity and CO₂ concentrations for different short and long durations. Relative humidity and CO₂ records are monthly time series and, hence, there are trend and periodicity components. It is noticed in all cases that the natural trends remain as they were after the O-W procedure, thus providing an opportunity to determine reliably the trends embedded even in the serially dependent series. The O-W procedure is applicable even in the cases of periodicity in the original records.     

转换波方位各向异性裂缝检测技术研究及应用

HTI裂缝各向异性介质中,转换波随方位角的变化比较复杂,目前还没有解析公式可以表达其变化特征,只能通过物理实验或数值模拟来分析其应用的可能性.数值模拟结果表明,转换波在裂缝各向异性介质中传播时,其R分量和T分量的振幅属性都具有明显的方位各向异性特征,R分量振幅方位各向异性拟合椭圆的长轴方向指示裂缝方位,这与纵波方位各向异性特征相似;根据P波AVAZ方位各向异性分析原理,对转换波R分量振幅方位各向异性曲线进行方位椭圆拟合,寻找椭圆的长轴方向,即裂缝主方位,再由P波AVAZ技术中振幅响应与炮检方向和裂缝走向之间的夹角关系式得到裂缝的发育密度,从而构建转换波方位各向异性AVAZ裂缝检测技术.该技术已用于川西新场气田某区块的裂缝储层预测,取得了较好的应用效果.