利用宏观烈度资料估计历史地震震源参数的研究概述

历史地震宏观烈度资料指史料中对地震破坏程度的记录,是研究历史地震最基本也是最重要的数据来源.由于有仪器记录地震波形的时间相对短暂,对历史地震震源参数的估算成为地震危险性分析的重要组成部分,前人尝试使用不同方法解决这一问题.本文以使用的工具和计算手段为依据,分类介绍了基于烈度资料估计震源参数的主要方法,对这些方法的优势、不足和应用范围做了概述,并展望了利用烈度资料估计震源参数研究的发展方向.     

地震海啸传播过程数值模拟研究

运用数值模拟的方法,对常水深4 000 m,8.0级纯倾滑直立断层触发的地震海啸,在大洋中传播的前2 000 s各时刻的形态以及峰值进行研究.结果表明,地震海啸产生后的前1 000 s左右的时间内,存在数值震荡,幅值先快速衰减,再逐渐增大,此后,幅值随着时间的推移缓慢衰减.     

A three-dimensional numerical model of advection and diffusion of urban source pollutants

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黏弹性介质VSP记录模拟及在估算Q值研究中应用

采用标准线性固体模型,本文建立了黏弹性介质完全匹配层吸收边界的高阶速度-应力交错网格有限差分算法,并对黏弹性介质中的地震波传播进行了数值模拟.基于黏弹性波动方程正演模拟提供的零偏VSP全波场数据,本文进行了质心频移法计算Q值的反演分析.结果表明,反射波、转换波及短程多次波对频谱的影响较大,对Q值反演造成一定误差.本文的结论为实际零偏VSP资料估算地层Q值提供了有益的指导.     

Vertical groundwater flux estimation from borehole temperature profiles by a numerical model,RFLUX

We developed a numerical model, RFLUX, which uses the heat tracer method for vertical groundwater flux estimation, and applied it to the Leizhou Peninsula, South China, to provide information to inform local groundwater resource utilization and management. The temperature–depth (TD) profiles of 24 boreholes, along with the observed ground surface temperature (GST) and surface air temperature (SAT) series in recent decades, were collected in this area. Underground TD data demonstrated the capacity to identify groundwater flow patterns, and local GST and SAT data demonstrated a strong correlation with each other over monthly, seasonal, and annual scales. In the RFLUX model, the average GST and SAT series were applied as an upper boundary condition, and a nonlinear initial condition was set using an analytical solution from the literature. The model results of selected TD profiles demonstrated that the annual vertical groundwater flux was about 0.15 m a^?1, which tended to be overestimated if a linear initial condition was used. This model can be easily applied with minor modifications, considering its clear purpose and simplicity.     

多震源地震正演数值模拟技术

常规地震采集技术因受相邻时间激发炮之间时间间隔的制约而存在采集周期过长,采集成本过高的问题,而多震源同步激发地震采集技术可以克服这方面的缺陷,但存在着波场过于复杂的问题,地震正演模拟技术可以帮助我们提高对这种复杂波场的认识水平,为此采用2D弹性波方程交错网格高阶有限差分格式,开发了多震源同步激发波场正演数值模拟技术,能够模拟任意多个同步激发震源的弹性波波场,震源函数可以是雷克子波,也可以是可控震源扫描信号,且同步激发震源之间可以有随机时差.模型试算结果分析表明,该技术既是一项高精度的多震源正演模拟技术,也是一项高效率的地震正演数值模拟技术.     

A numerical method for estimation of impulse response and its application to laboratory data

Following Burg's algorithm, we develop a new mathematical method of estimating the impulse response of a linear system. Since no data-invariant time window is used in this method, the estimated impulse response gives us reliable information on both the amplitude and the phase spectra of the system.The method is applied to laboratory data to investigate the dynamical response of rock specimens. The experimental results show that the waveform distortion with travel distance may well be described by a standard viscoelastic solid model. However, they also show that there is an additional factor of attenuation which is independent of the frequency and therefore not accompanied by any velocity dispersion.     

Source characterisation by mixing long-running tsunami wave numerical simulations and historical observations within a metamodel-aided ABC setting

Uncertainty related to the source parameters of earthquake can largely impact the tsunami-induced wave characteristics, especially in the case of near-field tsunami source. The combination of numerical simulations and historical eyewitness accounts can be used to better constrain those uncertainties. In the present study, we propose a Bayesian procedure to infer (i.e. learn) the probability distribution of the source parameters of the earthquake. The strategy is based on the combination of: (1) kriging-based metamodelling techniques to overcome the high computation time cost of the numerical simulator; and (2) Approximate Bayesian Computation (ABC) procedure to perform the Bayesian inference. The procedure is applied to the Ligurian (North West of Italy) 1887 tsunami case, for which tsunami-induced sea surface elevations at the coast have been reported at four locations, namely Marseille, Imperia, Diano-Marina and Genoa. The kriging metamodels are trained using only 300 long-running numerical simulations that were performed using the FUNWAVE-TVD code. Contrary to recent inversion exercises that can benefit from current modern observation networks (like tide gauges, sea bottom pressure gauges, GPS-mounted buoys), the case of historical tsunami like Liguria is complicated by the imprecision and scarcity of the observations: this is accounted for by conducting the combined ABC-kriging procedure a large number of times (i.e. 1000); each time a new set of observations being randomly generated to account for this observational error. The combined analysis of the inference results and of the observation uncertainty reveals that: (1) the coseismic slip is the most important source parameter with a very peaky density distribution around low values ranging from 0.3 to 0.6 m; (2) The fault width has a peaky density distribution around low values ranging from 10 to 12 km; (3) The rake and azimuth distribution only slightly deviate from the uniform prior, hence indicating a low influence of those parameters; (4) The bi-modal distribution of the dip is also evidenced.     

海啸传播模型与数值模拟研究进展

海啸在浅水大陆架的传播问题由于其非线性作用和浅水效应而变得十分复杂,然而目前成熟的海啸传播理论及数值模拟结果在这方面与实际并不一致.本文比较分析了可用来模拟大陆架海啸传播的浅水波模型和数值方法,并提出对我国东海陆架边缘可能发生的近海海啸需要开展数值试验研究.     

声波方程频率域高精度正演的17点格式及数值实现

频率域正演计算是频率域全波形反演的基础.传统的最优9点格式只具有二阶精度,不能满足高精度地震成像的需要.本文考虑两个四阶精度的格式,即经典的四阶9点格式和优化的17点格式.17点格式可将最小波长内所需网格点数减小到2.56.通过在简单模型和Overthrust模型上的数值实验,比较分析了三种格式的正演效果;简单模型数值实验显示了17点格式克服频散误差的能力优于四阶9点格式和最优9点格式;复杂模型数值实验则进一步承认了算法的可行性.     

A note on differences in tsunami source parameters for submarine slides and earthquakes

The nature of tsunami sources is reviewed, including source duration, displacement amplitudes, and areas and volumes of selected past earthquakes, slumps and slides that have or may have generated a tsunami. This review shows that the velocity of spreading of submarine slides and slumps (1–100 m/s) can be comparable to the long wavelength tsunami velocity (30–140 m/s for water depth 100<h<2000 m). In contrast, typical velocities of spreading dislocations during most earthquakes are one order of magnitude larger (2–3 km/s). Other significant differences between earthquake and slide and slump sources are that the balance of the total uplifted material in the case of slides is essentially zero, while for earthquakes it can be considerable, and that the vertical displacements for slides and slumps, per unit area of their horizontal projection, can be orders of magnitude larger than during earthquakes. This can result in high concentrations of the total change in the potential energy of fluid, above the source, over much smaller areas than during earthquakes.     

A new technique of physical dissipation and its application to a mesoscale numerical weather prediction model

In terms of statistical physics, a fluid such as the atmosphere is a many-body system which has a vast amount of degree of freedom and thus obeys the second law of thermodynamics. In this paper, a noticeable improvement of the prognostic outputs is made by reconstructing the terms of the horizontal diffusion of MM5 according to the principles of the second law of thermodynamics; besides, the computational noise is effectively and significantly suppressed since the physical dissipative technique for reconstructing suggested in this paper is based on the physical law rather than on the computational method such as the artificial viscosity.     

Source model and the macroseismic effect of the 1991 Racha earthquake

Coherency of the source model of the 1991 Racha earthquake in the Greater Caucasus with different data types is analyzed. Authors, when interpreting macroseismic data, accept complex nature of macroseismic effects generation but, nevertheless, consider that its spatial distribution follows certain regularities. First time in the practice, method of evaluation of the mecroseismic material completeness is proposed based on the intensity attenuation along with distance. It is demonstrated the character of macroseismic intensity attenuation can be used for verification of the source model elements constructed based on other seismological data. Dependence of the macroseismic effect distribution on azimuth in near field of the 1991 Racha earthquake is recognized.     

等价各向异性介质一阶拟声波 方程正演模拟及其效率分析

为克服各向异性弹性波动方程正演模拟的局限,本文研究了各向异性介质拟声波方程的交错网格有限差分数值解法.首先,从VTI介质胡克定律和qP-qSV波频散关系两种思路出发,通过声假设近似,给出了两种不同形式的VTI介质一阶拟声波方程,并通过引入波场的伪速度分量,推导了一种新的VTI介质一阶应力-速度方程,并通过旋转坐标系将其推广到TTI介质中;其次,构造了一阶拟声波方程的交错网格高阶有限差分格式,并推导了相应的PML边界条件;最后,对本文方法中固有的qSV人为干扰波的产生机制和压制方法进行了简单讨论.数值结果表明:3种一阶拟声波方程在运动学和动力学上是等价的,相对于各向异性弹性波正演模拟,其节省了内存,提高了计算效率;各向异性因素会影响反射波旅行时和振幅等波场特征,在后续的处理、反演和解释中不可忽略;VTI介质HESS模型的逆时偏移结果也验证了本文方法的合理性.      

A numerical approach for modeling near-fault ground motion and its application in the 1994 Northridge earthquake

An approach for simulating near-fault ground motion was presented by combining the finite fault model with a numerical algorithm, named investigated lump method presented in this paper for wave propagation. The investigated lumps are constructed from the auxiliary quadrilateral grids. The dynamic equilibrium equations of a typical investigated lump have been derived and obtained by integrating the stresses along the contour of the investigated lump. The stresses are calculated using the constitutive relations and the interpolation techniques. The investigated lump method is then implemented using the equilibrium equations of investigated lumps and the calculations of stresses alternately in time domain. The stability criterion of the algorithm has been given. Comparisons with the discrete wave-number method solutions for predicting the ground motions at the Pacoima Dam during the San Fernando earthquake show the validity of the method presented in this paper for simulating near-field ground motions. A finite fault source model has been implemented in the algorithm here. The source parameters given by Wald et al. (1996) [18] are applied to synthesize the ground motions at three stations during the 1994 Northridge earthquake. The simulating results qualitatively match to the corresponding ground motion records. The studies demonstrated that the approach presented in this paper is an effective tool for the numerical simulation of near-fault ground motion.     

Numerical identification of tsunami boulders and estimation of local tsunami size at Ibaruma reef of Ishigaki Island,Japan

Tsunami boulders deposited along the coast constitute important geological evidence for paleotsunami activity. However, boulders can also be deposited by large storm waves. Although several sedimentological and theoretical methods have been proposed to differentiate tsunami and storm wave affected boulders, no appropriate numerical method exists for their differentiation. Therefore, we developed a new numerical scheme to differentiate tsunami and storm wave boulders for coastal boulders on Ishigaki Island, Japan. In this area, tsunami and storm waves have emplaced numerous boulders on the reef and the coast. By conducting numerical calculations of storm waves in this region, we estimated the size of a storm wave that can explain the maximum clast size distribution of boulders on the reef. Consequently, we showed that a wave with a combination of 8 m in initial wave height and 10 s period can satisfy the above conditions when we assume mean sea level. In contrast to the boulders on the reef, all boulders deposited along the shore are heavier than the calculated possible maximum clast size distribution by the storm wave. Therefore, we confirmed these boulders as being of tsunami origin. Results of previous studies showed that they were most likely deposited or reworked by the 1771 Meiwa tsunami. Then, using the tsunami boulders, we numerically estimated the wave period and amplitude of the 1771 Meiwa tsunami, which should have had a 4–5 min period and 5.6–5.9, 6.3–7.0 m amplitude, respectively. Using the proposed scheme, it is possible to differentiate tsunami and storm wave boulders and estimate the size of past storm waves and tsunami waves, although it is noteworthy that there are exceptions for which the scheme cannot be applied.     

Combined model state and parameter estimation with an ensemble Kalman filter in a North Sea station 1-D numerical model

The combined estimation of model state and parameters is investigated by using an ensemble Kalman filter in a 1-D numerical study of the temperature profile at a North Sea station located at 55°30??North and 0°55??East. This simplified model implementation allows to test many configurations for the sampling of the model error for the model state as well as for the parameters. Temperature profiles from thermistor data are assimilated. The influence of a vertically or non-vertically correlated model error is examined through the computation of correlation coefficients, root mean square errors, and model bias. As the CS station is located in the North Sea region stratified in summer, vertically non-correlated model error terms have a slight positive impact on the assimilative runs. The benefit of the combined estimation of the model state and parameters is examined by comparison of a simulation where the model parameters are not adjusted to simulations with the combined estimation of the model state either with one parameter or with a set of parameters related to the surface heat exchange. The optical attenuation coefficient, the sensible, and latent heat exchange coefficients are considered. The best results are obtained when a set of parameters are simultaneously adjusted.     

利用流固耦合模型模拟地震和海啸全过程

海底地震引起的海啸过程在力学上是一个流固耦合问题。地震引起的海底变形会影响流体的运动,流体运动会影响地震引起的海底变形。海啸的数值模拟,通常采用浅水波控制方程,把地震引起的海底变形作为海啸波动的边界条件或初始条件,不考虑它们之间的相互作用。本文采用势流体的流固耦合有限元方法模拟了地震和海啸的全过程。地震过程的模拟与地震位错模型不同,在位错模型中,断层的位错是事先指定的;而在本文中,首先形成自重作用下的初始应力场,然后通过断层材料的突然软化引起的错动,模拟地震震源的动力学过程。模拟结果显示,在海面除了可以看到大振幅的海啸波外,还可以发现体波震相和面波震相。在600 km的海面震中距上,它们要比海啸波早到48分钟,在此处面波的最大平均振幅可达0.55 m,是相同震中距海底面波最大平均振幅的2倍。因此,海啸预警信息在海面可以比在地表更早地得到。海啸波的传播速度在水深3 km的开阔海面是175.8 m/s,它要比理想长波理论预测的大,其平均振幅为2 m,波长可达32 km. 到达大陆架后其速度、波长都减小,在岸边可以激起10 m高的巨浪,水平方向深入陆地达53 m。震中附近海面和地震断层上的最大垂直加速度分别为5.9 m/s2和16.3 m/s2,后者是前者的2.8倍。由此看来,海水是很好的减震器。海啸波的加速度到达岸边会衰减10倍。与加速度不同,海面震中处的振动速度为3.2 m/s, 是海底震源处的1.4倍。震源处的最大位移小于震中海面的最大位移, 其差就是海啸波源的振幅。值得注意的是,海底地震的最大位错在震后23 s达到,不是发生在断层滑动的开始。      

Modeling the dynamic process of tsunami earthquake by liquid-solid coupling model

Tsunami induced by earthquake is an interaction problem between liquid and solid.Shallow-water wave equation is often used to modeling the tsunami,and the boundary or initial condition of the problem is determined by the displacement or velocity field from the earthquake under sea floor,usually no interaction between them is consid-ered in pure liquid model.In this study,the potential flow theory and the finite element method with the interaction between liquid and solid are employed to model the dynamic processes of the earthquake and tsunami.For model-ing the earthquake,firstly the initial stress field to generate the earthquake is set up,and then the occurrence of the earthquake is simulated by suddenly reducing the elastic material parameters inside the earthquake fault.It is dif-ferent from seismic dislocation theory in which the relative slip on the fault is specified in advance.The modeling results reveal that P,SP and the surface wave can be found at the sea surface besides the tsunami wave.The surface wave arrives at the distance of 600 km from the epicenter earlier than the tsunami 48 minutes,and its maximum amplitude is 0.55 m,which is 2 times as large as that of the sea floor.Tsunami warning information can be taken from the surface wave on the sea surface,which is much earlier than that obtained from the seismograph stations on land.The tsunami speed on the open sea with 3 km depth is 175.8 m/s,which is a little greater than that pre-dicted by long wave theory,(gh)1/2=171.5 m,and its wavelength and amplitude in average are 32 km and 2 m,respectively.After the tsunami propagates to the continental shelf,its speed and wavelength is reduced,but its amplitude become greater,especially,it can elevate up to 10 m and run 55 m forward in vertical and horizontal directions at sea shore,respectively.The maximum vertical accelerations at the epicenter on the sea surface and on the earthquake fault are 5.9 m/s2 and 16.5 m/s2,respectively,the later is 2.8 times the former,and therefore,sea water is a good shock