数据驱动型多次波衰减方法的研究

In the practical seismic profile multiple reflections tend to impede the task of even the experienced interpreter in deducing information from the reflection data. Surface multiples are usually much stronger, more broadband, and more of a problem than internal multiples because the reflection coefficient at the water surface is much larger than the reflection coefficients found in the subsurface. For this reason most attempts to remove multiples from marine data focus on surface multiples, as will I. A surface-related multiple attenuation method can be formulated as an iterative procedure. In this essay a fully data-driven approach which is called MPI —multiple prediction through inversion (Wang, 2003) is applied to a real marine seismic data example. This is a pretty promising scheme for predicting a relative accurate multiple model by updating the multiple model iteratively, as we usually do in a linearized inverse problem. The prominent characteristic of MPI method lie in that it eliminate the need for an explicit surface operator which means it can model the multiple wavefield without any knowledge of surface and subsurface structures even a source signature. Another key feature of this scheme is that it can predict multiples not only in time but also in phase and in amplitude domain. According to the real data experiments it is shown that this scheme for multiple prediction can be made very efficient if a good initial estimate of the multiple-free data set can be provided in the first iteration. In the other core step which is multiple subtraction we use an expanded multi-channel matching filter to fulfil this aim. Compared to a normal multichannel matching filter where an original seismic trace is matched by a group of multiple-model traces, in EMCM filter a seismic trace is matched by not only a group of the ordinary multiple-model traces but also their adjoints generated mathematically. The adjoints of a multiple-model trace include its first derivative, its Hilbert transform and the derivative of the Hilbert transform. The third chapter of the thesis is the application for the real data using the previous methods we put forward from which we can obviously find the effectivity and prospect of the value in use. For this specific case I have done three group experiments to test the effectiveness of MPI method, compare different subtraction results with fixed filter length but different window length, invest the influence of the initial subtraction result for MPI method. In terms of the real data application, we do fine that the initial demultiple estimate take on a great deal of influence for the MPI method. Then two approaches are introduced to refine the intial demultiple estimate which are first arrival and masking filter respectively. In the last part some conclusions are drawn in terms of the previous results I have got.

中国大陆地区远震体波接收函数与岩石圈厚度的研究

Movements of separation and convergence between the continental plates, as well as the interaction beween the lithosphere and asthenosphere is the dominant factor in plate evolution. Moreover, those phenomena, the formation, enrichment and storage of energy and mineral strorage, as well as intraplate earthquakes are all relate to plate movement and evolution. Therefore, the study of continental lithosphere, is not only helpful to analysing the dynamic model between lithosphere and asthenoshere as well as different plates, but also important to the nation's economy and the people's livelihood. And the lithospheric thickness or Lithosphere-Asthenosphere Boundary (LAB) is one of the most important parameters in study of continental lithospheric formation and evolution. Chinese continent composed by many small plates, possesses diverse type of lithospheric structure. But our knowledge ahout Chinese continental lithosphere, especially the regional research, is almost based on the low-resolution results of surface wave dispersion analysis and seismic wave tomography. Howere, recently a technique employing S-to-P converted body waves (the S receiver function technique) has been developed that can be used to identify the LAB with a higher resolution. This thesis has collected waveform data of 232 broadband seismic stations that are located in China and neighboring regions. Using teleseismic S-wave and P-wave receiver functions have studied the Chinese continental lithospheric structure. The results of this study indicate that, the thickness of Chinese continental lithosphere become thinner from west to east, and obvious difference exists between different blocks. Four types of lithosphere have been detected: (1) Convergence thicking lithosphere in Tibetan Plateau; (2) Stable lithosphere in Tarim basin and upper Yangtze craton; (4) Active lithosphere in Orogenic belts; (4) Break-up thinning lithosphere in east China craton

DAS24-3B数据采集系统控制系统软件的研制与开发

Under the auspices of the 'knowledge-Innovation Program' of CAS, Institute of Geology and Geophysics has established the Broadband Seismic Laboratory. A new kind of 24-bit high-resolution seismograph DAS24-3B has been designed and manufactured in an effort of developing China's own technology of seismic array. Since these instruments will primarily be used in field operation, there is a need to optimize the system software of data acquisition system (DAS) to enhance its stability, compatibility and maintenance. The design ideas of the system software of DAS24-3B are partly learned from the advanced DAS 72A-08. In this system there are two exclusive communication programs DNAPI-COM1 and DNAPI-LPT1, which are suitable for all standard industrial computers with ECP parallel port and serial port. By these exclusive parallel and serial communication interface the system software is split into three parts, acquisition program, user's control program and graphical display program, which can function well in separate units and can run correctly in whole. The three parts of DAS24-3B's system software possess different functions and advantages. The function of acquisition program is to control the process of seismic data acquisition. DAS24-3B system reduced its power and harddisk read-write disturbance by using the extended memory attached to its CPU, which functions as enlarging the data buffer of system and lessening the times of harddisk read-write operations. Since GPS receiver of DAS is strongly sensitive to the around environment and has the possibility of signal loss the acquisition program has been designed with the ability to automatically trail the GPS locked time. The function of user's controlling program is to configure the system's work environment, to inform the user's commands to DAS, to trail the status of DAS in real-time. The function of graphical display program is to illustrate data in figures, to convert data file into some common formatted file, to split data file in parts and combine data files into one. Both user's control program and graphical display program are API (Application Programming Interface) in window 95/98 system. Both possess the features of clearness and friendship by use of all kind of window controls, which are composed by menu, toolbar, statusbar, dialogue box, message box, edit box, scrollbar, time control, button and so on. Two programs of systemic exception handles are provided to treat the trouble in field. The DAS24-3B DAS has been designed to be easier to use-better ability, more stable and simpler. It has been tested in field and base station and has been proved more suitable for field operation of seismic array than other native instruments.

接收函数方法与中国及邻区上地幔间断面的研究

The receiver function method applied in researching the discontinuities in upper mantle was systematically studied in this paper. Using the theoretical receiver functions, the characteristics of P410S and P660S phases were analyzed, and the influencing factors for detection of these phases were discussed. The stability of receiver function was studied, and a new computational method of receiver function, RFSSMS (Receiver Function of Stack and Smooth of Multi seismic-records at a Single station), was put forward. We built initial reference velocity model for the media beneath each of 18 seismic stations respectively; then estimated the buried depths of 410-km and 660-km discontinuities(simply marked as '410' and '660') under the stations by using the arrive time differences of P410S and P660S with P. We developed a new receiver function inversion method -PGARFI (Peeling-Genetic Algorithm of Receiver Function Inversion), to obtain the whole crust and upper mantle velocity structure and the depths of discontinuities beneath a station. The major works and results could be summarized as follows: (1) By analysis of the theoretical receiver functions with different velocity models and different ray parameters, we obtain the knowledge: The amplitudes of P410S and P660S phases are decreasing with the increasing of epicentral distance A , and the arrival time differences of these phases with P are shorter as A is longer. The multiple refracted and/or reflected waves yielded on Moho and the discontinuities in the crust interfere the identification of P410S. If existing LVZ under the lithosphere, some multiple waves caused by LVZ will interfere the identification of P410S. The multiple waves produced by discontinuity lied near 120km depth will mix with P410s phase in some range of epicentral distance; and the multiple waves concerned with the discontinuity lied near 210km depth will interfere the identification of P660S. The epicentral distance for P4i0s identification is limited, the upper limit is 80° . The identification of P660S is not restricted by the epicenter distance obviously. The identification of P410S and P6gos in the theoretical receiver functions is interfered weakly from the seismic wave attenuation caused by the media absorption if the Q value in a reasonable range. (2) The stability of receiver function was studied by using synthetic seismograms with different kind of noise. The results show that on the condition of high signal-noise-ratio of seismic records, the high frequency background noise and the low frequency microseism noise do not influence the calculating result of receiver function. But the media "scattering noise" influence the stability of receiver function. When the scattering effect reach some level, the identification of P4iOs and P66os is difficult in single receiver function which is yielded from only one seismic record. We provided a new method to calculate receiver function, that is, with a group of earthquake records, stacking the R and Z components respectively in the frequency domain, and weighted smooth the stacked Z component, then compute the complex spectrum ratio of R to Z. This method can improve the stability of receiver function and protrude the P4i0s and P66os in the receiver function curves. (3) 263 receiver functions were provided from 1364 three component broadband seismograms recorded at 18 stations in China and adjacent areas for the tele-earthquakes. The observed arrival time differences of P410S and P660S with P were obtained in these receiver functions. The initial velocity model for every station was built according to the prior research results. The buried depths of '410' and '660' under a station were acquired by the way of adjusting the depths of these two discontinuities in the initial velocity model until the theoretical arrival time differences of P410S and P660S with P well conformed to the observed. The results show an obvious lateral heterogeneity of buried depths of ' 410' and (660' . The depth of '410' is shallower beneath BJI, XAN, LZH and ENH, but deeper under QIZ and CHTO, and the average is 403km . The average depth of '660' is 663km, deeper under MDJ and MAJO, but shallower under QIZ and HYB. (4) For inversing the whole crust and upper mantle velocity structure, a new inversion method -PGARFI (Peeling-Genetic Algorithm of Receiver Function Inversion) has- been developed here. The media beneath a station is divided into segments, then the velocity structure is inversed from receiver function from surface to deep successively. Using PGARFI, the multi reflection / refraction phases of shallower discontinuities are isolated from the first order refraction transform phase of deep discontinuity. The genetic algorithm with floating-point coding was used hi the inversion of every segment, and arithmetical crossover and non-uniform mutation technologies were employed in the genetic optimization. 10 independent inversions are completed for every segment, and 50 most excellent velocity models are selected according to the priority of fitness from all models produced in the inversion process. The final velocity structure of every segment is obtained from the weighted average of these 50 models. Before inversion, a wide range of velocity variation with depth and depth range of the main discontinuities are given according to priori knowledge. PGARFI was verified with numerical test and applied in the inversion of the velocity structure beneath HIA station down to 700km depth.

中强地震震源的破裂过程

With the large developments of the seismic sources theory, computing technologies and survey instruments, we can model and rebuild the rupture process of earthquakes more realistically. On which earthquake sources' properties and tectonic activities law are realized more clearly. The researches in this domain have been done in this paper as follows. Based on the generalized ray method, expressions for displacement on the surface of a half-space due to an arbitrary oriented shear and tensile dislocation are also obtained. Kinematically, fault-normal motion is equivalent to tensile faulting. There is some evidence that such motion occurs in many earthquakes. The expressions for static displacements on the surface of a layered half-space due to static point moment tensor source are given in terms of the generalized reflection and transmission coefficient matrix method. The validity and precision of the new method is illustrated by comparing the consistency of our results with the analytical solution given by Okada's code employing same point source and homogenous half-space model. The computed vertical ground displacement using the moment tensor solution of the Lanchang_Gengma earthquake displays considerable difference with that of a double couple component .The effect of a soft layer at the top of the homogenous half-space on a shallow normal-faulting earthquake is also analyzed. Our results show that more seismic information would be obtained utilizing seismic moment tensor source and layered half-space model. The rupture process of 1999 Chi-Chi, Taiwan, earthquake investigated by using co-seismic surface displacement GPS observations and far field P-wave records. In according to the tectonic analysis and distributions of aftershock, we introduce a three-segment bending fault planes into our model. Both elastic half-space models and layered-earth models to invert the distribution of co-seismic slip along the Chi-Chi earthquake rupture. The results indicate that the shear slip model can not fit horizontal and vertical co-seismic displacements together, unless we add the fault-normal motion (tensile component) in inversions. And then, the Chi Chi earthquake rupture process was obtained by inversion using the seismograms and GPS observations. Fault normal motions determined by inversion, concentrate on the shallow northern bending fault from Fengyuan to Shuangji where the surface earthquake ruptures reveal more complexity and the developed flexural slip folding structures than the other portions of the rupture zone For understanding the perturbation of surface displacements caused by near-surface complex structures, We have taken a numeric test to synthesize and inverse the surface displacements for a pop-up structure that is composed of a main thrust and a back thrust. Our result indicates that the pop-up structure, the typical shallow complex rupture that occurred in the northern bending fault zone form Fengyuan to Shuangji, can be modeled better by a thrust fault added negative tensile component than by a simple thrust fault. We interpret the negative tensile distributions, that concentrate on the shallow northern bending fault from Fengyuan to Shuangji, as a the synthetic effect including the complexities of property and geometry of rupture. The earthquake rupture process also reveal the more spatial and temporal complexities form Fenyuan to SHuangji. According to the three-components teleseismic records, the S-wave velocity structure beneath the 59 teleseismic stations of Taiwan obtained by using the transform function method and the SA techniques. The integrated results, the 3D crustal structure of Taiwan reveal that the thickest part of crustal local in the western Central Range. This conclusion is consistent with the result form the Bouguer gravity anomaly. The orogenic evolution of Taiwan is young period, and the developing foot of Central Range dose not in static balancing. The crustal of Taiwan stays in the course of dynamic equilibrium. The rupture process of 2003)2,24,Jiashi, Xinjiang earthquake was estimated by the finite fault model using far field broadband P wave records of CDSN and IRIS. The results indicate that the earthquake focal is north dip trust fault including some left-lateral strike slip. The focal mechanism of this earthquake is different form that of earthquakes occurred in 1997 and 1998, but similar to that of 1996, Artux, Xinjiang earthquake. We interpreted that the earthquake caused trust fault due to the Tarim basin pushing northward and orogeny of Tianshan mountain. In the end, give a brief of future research subject: Building the Real Time Distribute System for rupture process of Large Earthquakes Based on Internet.

用宽频带远震体波波形研究中国及邻近地区地壳构造及地质意义初探

The theory and approach of the broadband teleseismic body waveform inversion are expatiated in this paper, and the defining the crust structure's methods are developed. Based on the teleseismic P-wave data, the theoretic image of the P-wave radical component is calculated via the convolution of the teleseismic P-wave vertical component and the transform function, and thereby a P-wavefrom inversion method is built. The applied results show the approach effective, stable and its resolution high. The exact and reliable teleseismic P waveforms recorded by CDSN and IRIS and its geodynamics are utilized to obtain China and its vicinage lithospheric transfer functions, this region ithospheric structure is inverted through the inversion of reliable transfer functions, the new knowledge about the deep structure of China and its vicinage is obtained, and the reliable seismological evidence is provided to reveal the geodynamic evolution processes and set up the continental collisional theory. The major studies are as follows: Two important methods to study crustal and upper mantle structure -- body wave travel-time inversion and waveform modeling are reviewed systematically. Based on ray theory, travel-time inversion is characterized by simplicity, crustal and upper mantle velocity model can be obtained by using 1-D travel-time inversion preliminary, which introduces the reference model for studying focal location, focal mechanism, and fine structure of crustal and upper mantle. The large-scale lateral inhomogeneity of crustal and upper mantle can be obtained by three-dimensional t ravel-time seismic tomography. Based on elastic dynamics, through the fitting between theoretical seismogram and observed seismogram, waveform modeling can interpret the detail waveform and further uncover one-dimensional fine structure and lateral variation of crustal and upper mantle, especially the media characteristics of singular zones of ray. Whatever travel-time inversion and waveform modeling is supposed under certain approximate conditions, with respective advantages and disadvantages, and provide convincing structure information for elucidating physical and chemical features and geodynamic processes of crustal and upper mantle. Because the direct wave, surface wave, and refraction wave have lower resolution in investigating seismic velocity transitional zone, which is inadequate to study seismic discontinuities. On the contrary, both the converse and reflected wave, which sample the discontinuities directly, must be carefully picked up from seismogram to constrain the velocity transitional zones. Not only can the converse wave and reflected wave study the crustal structure, but also investigate the upper mantle discontinuities. There are a number of global and regional seismic discontinuities in the crustal and upper mantle, which plays a significant role in understanding physical and chemical properties and geodynamic processes of crustal and upper mantle. The broadband teleseismic P waveform inversion is studied particularly. The teleseismic P waveforms contain a lot of information related to source time function, near-source structure, propagation effect through the mantle, receiver structure, and instrument response, receiver function is isolated form teleseismic P waveform through the vector rotation of horizontal components into ray direction and the deconvolution of vertical component from the radial and tangential components of ground motion, the resulting time series is dominated by local receiver structure effect, and is hardly irrelevant to source and deep mantle effects. Receiver function is horizontal response, which eliminate multiple P wave reflection and retain direct wave and P-S converted waves, and is sensitive to the vertical variation of S wave velocity. Velocity structure beneath a seismic station has different response to radial and vertical component of an accident teleseismic P wave. To avoid the limits caused by a simplified assumption on the vertical response, the receiver function method is mended. In the frequency domain, the transfer function is showed by the ratio of radical response and vertical response of the media to P wave. In the time domain, the radial synthetic waveform can be obtained by the convolution of the transfer function with the vertical wave. In order to overcome the numerical instability, generalized reflection and transmission coefficient matrix method is applied to calculate the synthetic waveform so that all multi-reflection and phase conversion response can be included. A new inversion method, VFSA-LM method, is used in this study, which successfully combines very fast simulated annealing method (VFSA) with damped least square inversion method (LM). Synthetic waveform inversion test confirms its effectiveness and efficiency. Broadband teleseismic P waveform inversion is applied in lithospheric velocity study of China and its vicinage. According to the data of high quality CDSN and IRIS, we obtained an outline map showing the distribution of Asian continental crustal thickness. Based on these results gained, the features of distribution of the crustal thickness and outline of crustal structure under the Asian continent have been analyzed and studied. Finally, this paper advances the principal characteristics of the Asian continental crust. There exist four vast areas of relatively minor variations in the crustal thickness, namely, northern, eastern southern and central areas of Asian crust. As a byproduct, the earthquake location is discussed, Which is a basic issue in seismology. Because of the strong trade-off between the assumed initial time and focal depth and the nonlinear of the inversion problems, this issue is not settled at all. Aimed at the problem, a new earthquake location method named SAMS method is presented, In which, the objective function is the absolute value of the remnants of travel times together with the arrival times and use the Fast Simulated Annealing method is used to inverse. Applied in the Chi-Chi event relocation of Taiwan occurred on Sep 21, 2000, the results show that the SAMS method not only can reduce the effects of the trade-off between the initial time and focal depth, but can get better stability and resolving power. At the end of the paper, the inverse Q filtering method for compensating attenuation and frequency dispersion used in the seismic section of depth domain is discussed. According to the forward and inverse results of synthesized seismic records, our Q filtrating operator of the depth domain is consistent with the seismic laws in the absorbing media, which not only considers the effect of the media absorbing of the waves, but also fits the deformation laws, namely the frequency dispersion of the body wave. Two post stacked profiles about 60KM, a neritic area of China processed, the result shows that after the forward Q filtering of the depth domain, the wide of the wavelet of the middle and deep layers is compressed, the resolution and signal noise ratio are enhanced, and the primary sharp and energy distribution of the profile are retained.

利用宽频带台阵资料研究华北地区地壳及上地幔间断面结构

Intense tectonic renovation has occurred in the eastern continent of china since Mesozoic, as evidenced by the high heat flow, widespread magma extrusion and volcanic activities, and development of large sedimentary basins. To explain the cause and mechanism for the tectonic process in this period, some researchers have put forward various models, such as mantle plume, subduction of the Pacific slab, Yangtze Block-North China Block collision, etc. Their seismological evidence, however, is still scarce..During the period from 2000 to 2003, large temporary seismic arrays were established in North China by the Institute of the Geology and Geophysics, Chinese Academy of Sciences. Total 129 portable seismic stations were linearly emplaced across the western and eastern boundaries of the Bohai Bay Basin, and accumulated a large amount of high-quality data. Moreover, abundant data were also collected at the capital digital seismic network established in the ninth five-year period of national economic and social development. These provide an unprecedented opportunity for us to study the deep structure and associated geodynamic mechanism of lithospheric processes in North China using seismological techniques.Seismology is a kind of observation-based science. The development of seismic observations greatly promotes the improvement of seismologic theory and methodology. At the beginning of this thesis, I review the history of seismic observation progress, and present some routine processing techniques used in the array seismology. I also introduce two popular seismic imaging methods (receiver function method and seismic tomography).Receiver function method has been widely used to study the crustal and upper mantle structures, and many relevant research results have been published. In this thesis I elaborate the theory of this method, including the basic concept of receiver functions and the methodology for data pre-processing, stacking and migration. I also address some problems often encountered in practical applications of receiver function imaging.By using the teleseismic data collected at the temporary seismic arrays in North China, in particular, the traveltime information of P-to-S conversion and multiple reverberations of the Moho discontinuity, I obtain the distributions of the crustal thickness and the poisson ratio at the northwest boundary area of the Bohai Bay Basin and discuss the geological implications of the results.Through detailed intestigations on the crustal structural feature around the middle part of the Tanlu fault, considerable disparity in poisson ratios is found in the western and eastern sides of the Tanlu fault. Moreover, an obvious Moho offset is coincidently observed at the same surface location. A reasonable density model for the Tanlu fault area is also derived by simulating the observed gravity variations. Both receiver function study and gravity anomaly modeling suggest that the crustal difference between the western and eastern sides of the Tanlu fault is mainly resulted from their different compositions.With common conversion point imaging of receiver functions, I estimate the depths of the upper and lower boundaries of the mantle transition zone, i.e., the 410 and 660 km discontinuities, beneath most part of the North China continent The thickness of the transition zone (TTZ) in the study area is calculated by subtracting the depth of .410 km discontinuity from that of the 660km discontinuity. The resultant TTZ is 10-15 km larger in the east than in the west of the study area. Phase transitions at the 410 km and the 660 km discontinuities are known to have different Clapeyron slopes. Therefore, the TTZ is sensitive to the temperature changes in the transition zone. Previous studies have shown that the TTZ would be smaller in the mantle plume areas and become larger when the remnants of subducted slabs are present The hypothesis of mantle plume cannot give a reasonable interpretation to the observed TTZ beneath North China, Instead, the receiver function imaging results favor a dynamic model that correlates the thermal structure of the mantle transition zone and associated upper mantle dynamics of North China to the Pacific plate subduction process.