Uncertainty and sensitivity analysis of a travel-time distribution-based stream water electrical conductivity model

In this paper, we analyse the uncertainty and parameter sensitivity of a conceptual water quality model, based on a travel time distribution (TTD) approach, simulating electrical conductivity (EC) in the Duck River, Northwest Tasmania, Australia for a 2-year period. Dynamic TTDs of stream water were estimated using the StorAge Selection (SAS) approach, which was coupled with two alternate methods to model stream water EC: (1) a solute-balance approach and (2) a water age-based approach. Uncertainty analysis using the Differential Evaluation Adoptive Metropolis (DREAM) algorithm showed that: 1. parameter uncertainty was a small contribution to the overall uncertainty; 2. most uncertainty was related to input data uncertainty and model structure; 3. slightly lower total error was obtained in the water age-based model than the solute-balance model; 4. using time-variant SAS functions reduced the model uncertainty markedly, which likely reflects the effect of dynamic hydrological conditions over the year affecting the relative importance of different flow pathways over time. Model parameter sensitivity analysis using the Variogram Analysis of Response Surfaces (VARS-TOOL) framework found that parameters directly related to the EC concentration were most sensitive. In the solute-balance model, the rainfall concentration C_rain and in the age-based model, the parameter controlling the rate of change of EC with age (λ) were the most sensitive parameter. Model parameters controlling the age mixes of both evapotranspiration and streamflow water fluxes (i.e., the SAS function parameters) were influential for the solute-balance model. Little change in parameter sensitivity over time was found for the age-based concentration relationship; however, the parameter sensitivity was quite dynamic over time for the solute-balance approach. The overarching outcomes provide water quality modellers, engineers and managers greater insight into catchment functioning and its dependence on hydrological conditions.     

基于局部一维模型与走时标定的区域 三维速度模型构建技术研究

构建区域介质三维速度模型并以之获得准确的区域震相走时, 是提高区域地震定位精度的重要手段之一. 为充分利用已有的一维模型、 GT事件、 地质资料等实现三维模型构建, 尝试基于目标区域内已有的部分局部一维模型, 通过克里金空间插值建立初始三维模型, 然后利用GT事件走时数据并参考其它地震地质资料对其不断进行修正, 使得其走时偏差图与GT事件走时偏差图一致, 进而获得能够提高区域地震定位精度的三维模型. 使用不同模型进行的地震定位实验表明, 以此方法建立的三维模型的定位偏差较初始模型减少约20%, 较好地起到了减小区域震相走时残差, 提高区域地震定位精度的作用.     

基于局部一维模型与走时标定的区域三维速度模型构建技术研究

构建区域介质三维速度模型并以之获得准确的区域震相走时,是提高区域地震定位精度的重要手段之一.为充分利用已有的一维模型、GT事件、地质资料等实现三维模型构建,尝试基于目标区域内已有的部分局部一维模型,通过克里金空间插值建立初始三维模型,然后利用GT事件走时数据并参考其它地震地质资料对其不断进行修正,使得其走时偏差图与GT事件走时偏差图一致,进而获得能够提高区域地震定位精度的三维模型.使用不同模型进行的地震定位实验表明,以此方法建立的三维模型的定位偏差较初始模型减少约20％,较好地起到了减小区域震相走时残差,提高区域地震定位精度的作用.     

新型二进制走时表文件的编制与查询

为将新型二进制结构走时表文件实际应用到测震分析软件,利用Matlab软件编写二进制结构综合走时表文件的通用程序,给出查询震相走时的算法,并成功配置到地震分析软件中用于地震定位.使用者只要仿照该通用程序的结构框架,根据需要适当修改程序,就能快速生成适合地震台站定位的走时表文件.     

Partial derivatives of travel-time curves of reflected waves in a layered medium

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Magnitudes and travel-time residuals of the Friuli earthquakes between May and August 1976

Summary The records of the first series of the North-Italian aftershock series from the period May–August 1976 at the stations Prhonice and Kaperské Hory were analyzed from the point of view of the verification of the travel-time tables used for the interpretation of near earthquake seismograms and of the determination of the short-period body wave magnitudes for near shocks. Also the time-energy distribution was investigated for a 90 days period.     

On conditions for the unique inversion of seismic travel-time curves

It is shown that when the travel-time curve of a refracted wave from a surface source is known and at least one of the following conditions is satisfied, i.e. when

1. the travel-time curve of a wave reflected from a horizontal interface lying below the deepest low velocity layer is known, or
2. the travel-time curve of a wave from a deep source situated below the deepest low velocity layer is known, or
3. the measureH(u)=mes {z∶z≥0,v ^?1 (z)≥u} is analytical in some segment [c, d], where \(0< c< d< \infty , c< a_n , H(a_n ) = \bar z_n ,\bar z_n\) is the depth of the lower end of the deepest low velocity layer and in the interval [c, ∞) an analytical functionH(u)) exists which providesH(u)≡H(u)) ifu∈[c, d], then (1) velocityv(z) outside the low velocity layers and (2) the measureH _k (u)=mes {z∶z∈L _k,v ^?1 (z)≥u} for each low velocity layerL _k,k=1, 2, ..., n, are defined unambiguously.

     

Q and its effect on the observation of upper mantle travel-time branches

There is broad agreement among various seismological studies that the upper mantle has two regions where high positive velocity gradients or transition zones exist. The presence of these zones implies that two major triplications should exist in the travel-time curve for distances less than 30°. Approximately 200 earthquakes from the New Guinea, New Britain, and Solomon Island regions recorded at the Warramunga Array were analyzed using adaptive processing methods in an attempt to identify the positions of the later arrival branches. From measurements made along the first 20 sec of the arrivals, a retrogade travel-time branch associated with the “650-km” discontinuity was clearly identified as extending from 21° to 26°, and some evidence was found near 16° for the lower portion of the triplication associated with the “400-km” discontinuity. A careful search revealed however that the upper portions of the replicated travel-time branches were missing. There were no observed values ofdt/dΔ in the 12–13 sec/deg range for Δ greater than 20°. In this study it was found that if anelastic effects (Q) were not taken into consideration or ifQ were kept constant, the models derived from observed travel-time data all predicted large amplitude arrivals where non existed. The difficulty with the first triplication was resolved by the introduction of a lowQ region at depths of 85–315 km. This region may be associated with “the low-velocity region” but it is not necessary to decrease the P velocity to explain the observations.The difficulty with the second triplication was resolved by the introduction of a layer at a depth of 575–657 km which has no velocity gradient and a value ofQ significantly less than that for the material just below the “650-km” discontinuity. This layer may well represent the return path for an upper mantle convection cell.     

地震初至波走时的计算方法综述

本文选取了2010—2018年发生于安徽区域的M_S2.0以上地震102次,使用单纯形定位法、Hyposat和Locsat定位程序分别配置华南模型与AH2015模型对其进行重定位。统计定位残差和定位深度,对比分析两种模型在安徽区域地震定位中的应用效果,同时对流动台反演深度进行精细分析。结果表明,使用AH2015模型在安徽区域的地震定位中残差更小,定位深度更符合真实深度,比华南模型更适用于安徽区域的地震定位研究。     

Seismoelectric and electroseismic responses to a point source in a marine stratified model

We investigate the seismoelectric/electroseismic wavefields excited by a point source in an air/seawater/three-layered porous medium configuration containing a hydrocarbon layer. The results show that if an explosive source for excitation is used, receivers at seafloor can record the coseismic electromagnetic fields accompanying the P, S, fluid acoustic waves and the interface responses converted from the acoustic waves at seafloor interface and from the seismic waves at the interfaces beneath the seafloor. Employing a vertical electric dipole source shows that, with the exception of the interface responses converted from electromagnetic waves at seafloor, the interface responses converted from transmitted electromagnetic waves at the interfaces beneath the seafloor can also be identified. Given that the strength of the explosive source is within excitation capability of industry air guns, the generated interface responses from the hydrocarbon layer can be detected by current electromagnetic sensors considering the low ambient noise at the seafloor. Our results demonstrate the feasibility of the seismoelectric method applied to marine hydrocarbon exploration. Electroseismic modelling results suggest that it is not practical to employ this method to prospect marine hydrocarbon layer due to the weak interface response signal, unless a much larger current is injected into seafloor.     

Systematic variations of mean travel-time residuals in space and time

Summary Mean travel-time residuals of P waves for the period 1964–1970 at stations in North America and Europe are well separated into large domains of positive and negative values. The spatial distribution of residuals in North America is in good agreement with the structure of the upper mantle obtained from Rayleigh wave dispersion and is in accord with magnitude anomalies and heat flow data. A systematic variation of residuals in time is found to be sensitive to major changes in the nature of the earthquake source distribution, as for example aftershocks, as well as to changes in methods of detection of first arrivals. Residuals at neighboring stations are correlated up to distances of the order of 2°. Half year mean residuals at stations within 2° distance from the epicenters of strong earthquakes have a sudden jump 1.5 years before the occurrence of an earthquake. A formal algorithm based on this pattern permits prediction of the times of all 16 earthquakes with magnitudeM7.5 occurring during the interval 1966–1972. Although the average duration of the alarm periods is about half the total time interval of the catalog, so that the algorithm has no practical importance, these results are statistically significant on a 99% level of confidence.     

Investigation of the 600-km discontinuity under France through travel-time and amplitude anomalies

In this paper, we give a model of the 600-km discontinuity under France, which explains large travel-time and amplitude anomalies on teleseisms as recorded in the French network. It features a large descent from the Ardennes to the Pyrénées, of which tectonic implications are discussed.     

火山区基本压力源模型及应用

通过简要介绍火山区不同压力源模型引起的垂直形变与水平形变特征,总结不同模型引起的最大水平位移与最大垂直位移的比值R,得到膨胀模型产生的地表形变多以中心为对称,R小于0.5;腔状模型产生的地表形变多为轴对称,可得到更高的R比值;这些结论为模拟分析火山区压力源参数选用模型时提供依据.最后利用所得结果,分析了长白山天池火山可...     

Performance of the complete travel-time equation of state at simultaneous high pressure and temperature

The complete travel-time equation of state (CT-EOS) is presented by utilizing thermodynamics relations, such as; $$K_T = K_S (1 + \alpha \gamma T)^{ - 1} , \gamma = \frac{{\alpha K_S }}{{\rho C_P }}, \left. {\frac{{\partial C_P }}{{\partial P}}} \right)_T = - \frac{T}{\rho }\left[ {\alpha ^2 + \left. {\frac{{\partial \alpha }}{{\partial T}}} \right)_P } \right], etc.$$ The CT-EOS enables us to analyze ultrasonic experimental data under simultaneous high pressure and high temperature without introducing any assumption, as long as the density, or thermal expansivity, and heat capacity are also available as functions of temperature at zero pressure. The performance of the CT-EOS was examined by using synthesized travel-time data with random noise of 10^?5 and 10^?4 amplitude up to 4 GPa and 1500 K. Those test conditions are to be met with the newly developed GHz interferometry in a gas medium piston cylinder apparatus. The results suggest that the combination of the CT-EOS and accurate experimental data (10^?4 in travel time) can determine thermodynamic and elastic parameters, as well as their derivatives with unprecedented accuracy, yielding second-order pressure derivatives (?² M/?P ²) of the elastic moduli as well as the temperature derivatives of their first-order pressure derivatives ?² M/?P?T). The completeness of the CT-EOS provides an unambiguous criterion to evaluate the compatibility of empirical EOS with experimental data. Furthermore because of this completeness, it offers the possibility of a new and absolute pressure calibration when X-ray (i.e., volume) measurements are made simultaneously with the travel-time measurements.     

Incorporating variable source area hydrology into a curve-number-based watershed model

Many water quality models use some form of the curve number (CN) equation developed by the Soil Conservation Service (SCS; U.S. Depart of Agriculture) to predict storm runoff from watersheds based on an infiltration-excess response to rainfall. However, in humid, well-vegetated areas with shallow soils, such as in the northeastern USA, the predominant runoff generating mechanism is saturation-excess on variable source areas (VSAs). We reconceptualized the SCS–CN equation for VSAs, and incorporated it into the General Watershed Loading Function (GWLF) model. The new version of GWLF, named the Variable Source Loading Function (VSLF) model, simulates the watershed runoff response to rainfall using the standard SCS–CN equation, but spatially distributes the runoff response according to a soil wetness index. We spatially validated VSLF runoff predictions and compared VSLF to GWLF for a subwatershed of the New York City Water Supply System. The spatial distribution of runoff from VSLF is more physically realistic than the estimates from GWLF. This has important consequences for water quality modeling, and for the use of models to evaluate and guide watershed management, because correctly predicting the coincidence of runoff generation and pollutant sources is critical to simulating non-point source (NPS) pollution transported by runoff. Copyright © 2007 John Wiley & Sons, Ltd.     

Balancing the source terms in a SPH model for solving the shallow water equations

A shallow flow generally features complex hydrodynamics induced by complicated domain topography and geometry. A numerical scheme with well-balanced flux and source term gradients is therefore essential before a shallow flow model can be applied to simulate real-world problems. The issue of source term balancing has been exhaustively investigated in grid-based numerical approaches, e.g. discontinuous Galerkin finite element methods and finite volume Godunov-type methods. In recent years, a relatively new computational method, smooth particle hydrodynamics (SPH), has started to gain popularity in solving the shallow water equations (SWEs). However, the well-balanced problem has not been fully investigated and resolved in the context of SPH. This work aims to discuss the well-balanced problem caused by a standard SPH discretization to the SWEs with slope source terms and derive a corrected SPH algorithm that is able to preserve the solution of lake at rest. In order to enhance the shock capturing capability of the resulting SPH model, the Monotone Upwind-centered Scheme for Conservation Laws (MUSCL) is also explored and applied to enable Riemann solver based artificial viscosity. The new SPH model is validated against several idealized benchmark tests and a real-world dam-break case and promising results are obtained.     

2015年尼泊尔地震破裂过程的统一模型

模拟2015年尼泊尔地震（主震M_W7.8及最大余震M_W7.3）GPS/InSAR同震位移、远震体波、高频GPS位移波形和强震加速度记录,构建统一震源模型.统一模型分布特征主要由InSAR观测决定,地震矩释放过程则与P波模型相似,静态与高频GPS观测增加了对破裂时空特征的约束强度;各种比对表明,该模型对各基于单一类型反演模型具有很好的兼容性,棋盘测试展现其具有更优空间分辨率,最小可恢复20 km×20 km尺度的空间特征,压缩了非同震信号或误差导致的零散瑕疵,主、余震破裂具有更好的空间对应关系.主震展布范围为140 km×80 km;4 m以上破裂集中在加德满都以北30 km、深度15 km的狭长区域内,最大滑动量为7.4 m;破裂持续总时长为60 s,破裂速度为3.3 km·s^-1,子断层上升时间在10 s内.M_W7.3余震破裂区域位于主震东侧边缘,滑动量围绕震中扩散,扩展范围为30 km×20 km,最大滑动量约为4.4 m,总破裂持续时间为35 s.本次地震中静态和高频的GPS观测亦具备独立约束主震破裂扩展过程的能力.

     

龙门山地区地壳及上地幔结构的应用多重尺度有限频宽走时层析成像(英文)

With an innovative technique of multi-scale, finite-frequency tomography, we present results of P-wave velocity structure of the crust and upper mantle in the Longmenshan region, where the devastating magnitude 7.9 Wenchuan earthquake occurred on 12 May, 2008.     

A worldwide comparison of predicted S-wave delays from a three-dimensional upper mantle model with P-wave station corrections

This paper is a comparison, on a worldwide scale, between P-station corrections deduced from ISC residuals (Dziewonski and Anderson) and synthetic S-station corrections computed using a three-dimensional upper mantle model obtained from mantle wave data (Woodhouse and Dziewonski). The upper mantle S-velocity model is described by a spherical harmonic expansion up to degree 8; the P-station corrections are smoothed using a similar expansion, in order that the two data sets can be compared.Correlations between P-station corrections, δt_P, and synthetic S-station corrections, δt_S relevant to various depths of integration indicate that a station correction contains information about structures down to at least 670 km. For this depth of integration, the correlation coefficient of the two data sets is 0.59; the slope ‘a’ of the relation δt_S = aδt_P + b, obtained for the worldwide distribution of stations, is in good agreement with results of previous regional studies using direct readings of P and S arrival times (a = 3.61 ± 0.13).An analysis of regional variations of the relation δt_S = aδt_P + b is carried out on the basis of two published global tectonic patterns (Okal; Jodan). Results for oceanic regions are not reliable, due to the lack of data. On continental areas, a significant difference appears between mountains (a = 2.7 ± 0.3) and shields (a = 4.5 ± 0.4 for Okal's pattern, a = 5.7 ± 1.5 for Jordan's pattern). The largest a-value for shields rules out an explanation by partial melting, as proposed in previous studies. Thermal heterogeneities lead to low a-values; undulations of the lithosphere-asthenosphere boundary appear to be the most feasible explanation of the high slope beneath shields; they are also able to explain the range of variation of the station corrections; the lowest values of the station corrections correspond to a total vanishing of the low velocity zone beneath the oldest shields. For mountains, the mean values of the station corrections as well as the low a-value can be accounted for by a slight increase of Poisson's ratio together with a significant density increase.     

On the origin of the Italian potassic magmas: a one-dimensional diffusion-controlled model of source metasomatism

A new geochemical model is used here for the first time in the interpretation of intra-plate igneous rocks. This model is able to simulate one major and so far unexplained feature of the Italian potassic magmas: the regional isotopic trends along the chain of volcanoes. Starting from the now widely accepted inference that these trends are a result of large-scale mixing between continental-crustal and mantle materials within the lithosphere and prior to magma generation and volcanism, isotopic requirements of a suitable magma source are illustrated. This mixing has been linked with extreme enrichment in potassium and associated elements by the concept of source metasomatism. Here a one-dimensional diffusion-controlled advective flow model to simulate concentration and isotopic changes during metasomatism is described, as are the conditions under which this model can schematically reproduce the required source features.Modelling suggests that progressive regional changes from northwest to southeast in end-member contributions (i.e. the fluid/rock ratio in a metasomatic model) was controlled by progressive variations in either the fluid velocity or the duration of the fluid flow. Both could have acted concomitantly if the fluid was released by a mantle hotspot and infiltrated crustal material—possibly located in the lithospheric mantle—during anti-clockwise rotation of Italy in the Tertiary. It is suggested that previously metasomatised domains in the lithosphere were susceptible to fusion under tensional stress, so that the alkaline volcanism now traces the path of the ancient plate movement over the asthenosphere hotspot.