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1.
This article summarizes work on multiple scattering based on models of media with randomly distributed scatterers. The scatterers are isotropic and statistically uniform. Measuring distance in terms of mean-free pathL s and time in terms of the mean-free timesL s/V, whereV is the velocity of scattered waves, we have more convenient dimensionless distance and time. It can be shown that after the dimensionless time equals 0.65 energy contributed from multiple scattering becomes predominant. Thus the later coda reflects the effect of multiple scattering rather than single scattering. Treating the seismic record, including starting and tail parts, as a whole, the diffusion theory predicts that at a dense distribution of scatterers and a small distance between source and receiver, codas reflect mainly intrinsicQ i. Of course, this conclusion is coincident with the presumption of the diffusion theory,Q s>Q i. However, from a new integral equation of multiple scattering, which deals with the scattered waves and primary waves separately, the conclusion is similar but clearer. This article quotes the new expression for coda energy in two-dimensional space. It shows that if the receiver is close to the source, the coda decay reflects only intrinsicQ i, then as the distance increases, effects of scatteringQ s, are involved in the decay feature. The theoretical plots of coda decay show that it seems in most cases in the earthQ i should not be smaller than one tenth ofQ s.Project Sponsored by the Joint Earthquake Science Foundation of China.  相似文献   

2.
通过对5个湖泊的河川沙塘鳢种群的线粒体DNA细胞色素b基因进行PCR扩增、测序,获得1141 bp的序列全长.序列分析显示,cyt b基因序列中A+T含量(55.8%)略高于G+C含量(44.2%),共检测到806个多态位点,115个样本得到87个单倍型,平均单倍型多样性为0.969±0.012,核苷酸多样性为0.20081±0.00742,遗传多样性表现高度多样性.太湖种群与大纵湖种群间的遗传距离最近,为0.137,巢湖种群和大纵湖种群之间遗传距离最远,为0.424.分子方差分析表明,群体间遗传分化系数Fst为0.531,变异来自群体内及群体间.cyt b基因序列构建的UPGMA系统进化树显示,5个种群分化成不同的分支系谱,种群间存在的基因交流较少.  相似文献   

3.
This paper presents the GIS-based stochastic model and its application to simulate land use change in Shiqian County, Southwestern China. Transition probability of land use change with biophysical factors such as elevation, slope, distance to stream, distance to road and adjacent cells with the same land use are calculated and integrated into this model. Then the model simulated 2001 land use pattern based on 1988 land use pattern and the results are satisfactory. Finally, three different land use scenarios are simulated using this model. This study provides a new tool to predict land use pattern.  相似文献   

4.
解孟雨  孟令媛 《中国地震》2021,37(2):494-507
利用全国统一目录和流动台站目录,研究了四川盆地东南部长宁地区的地震活动特征和b值的空间分布特征.研究结果显示,长宁地区的地震活动在时间上呈现明显的分段特征,地震活动在2015年后明显增强;在空间上,长宁地区的地震活动主要集中在以28.3°N为界限的南、北2个地区,对于这2个区域的b值演化,计算结果显示出不同的分段特征....  相似文献   

5.
A method for generating synthetic strong motion accelerograms for use in engineering design is presented. This method utilizes the model proposed by Trifunac in 197127 in conjunction with the recent empirical scaling functions for characterization of amplitudes and duration of strong shaking in terms of (i) earthquake magnitude, M, and epicentral distance, R, or (ii) Modified Mercalli Intensity (MMI) at the recording station. The method also enables one to consider the desired levels of confidence that the synthetic motion will not be exceeded, direction of ground motion (horizontal or vertical) and the dispersive properties of geologic environment beneath and surrounding the station. The principal features of this approach are that the resulting accelerograms have non-stationary frequency and amplitude characteristics which are in full agreement with known principles of wave propagation through a stratified medium, and that the Fourier amplitudes and the frequency-dependent duration are scaled in accordance with known trends as in recorded accelerograms.  相似文献   

6.
对长江中下游5个湖泊的黄颡鱼种群的线粒体DNA细胞色素b基因进行了PCR扩增、测序,获得了955 bp的序列.分析显示,cyt b序列中A+T含量略高于G+C含量,共检测到54个变异位点,60个样本得到37个单倍型,平均单倍型多样性为0.945±0.018,核苷酸多样性为0.00419±0.00043,遗传多样性表现中等.太湖种群与滆湖种群间的遗传距离最远为0.00651,鄱阳湖种群和巢湖种群之间遗传距离最近为0.00375.分子方差分析(AMOVA)表明,群体间遗传分化系数Fst为0.0684,几乎所有变异都来自群体内,群体间遗传分化极小.cyt b序列构建UPGMA系统进化树显示,5个种群没有分化成不同的分枝谱系,种群间存在广泛的基因交流.  相似文献   

7.
Coda site amplification factors are used to eliminate the site effect from records of three circum-PacificT phases recorded by the Hawaiian Volcano Observatory (HVO) network on the island of Hawaii. ObservedT-phase amplitudes across the island generally decrease with increasing distance from the conversion point where acoustic waves in the SOFAR channel become seismic waves propagating through the crust. However, the decay of the observedT-phase signal across the island is not regular in regions of dense station coverage, in particular, the Kilauea caldera region. We divide the maximum observedT-phase amplitudes at a given station by the coda site amplification factor obtained for the same station and frequency band (3.0Hz); the distribution of these amplitudes reveals a smooth pattern over the entire island. The distance over which the site effect-correctedT-phase amplitude decreases by one-half, combined with the apparent velocity of propagation ofT phases across the island, allows for an approximate determination of near-surfaceQ over much of the island of Hawaii. We found a region of lowQ in the Kilauea summit area (Q≈30) and east rift zone (Q≈60) with considerably higherQ in the Kaoiki and northern portions of the island (Q≈150 to 200). The lowQ values obtained in the Kilauea summit region and east rift zone are significantly lower than estimates of codaQ in the same region, suggestingT phases may be sampling the earth's near-surface properties.  相似文献   

8.
溯河洄游长江刀鲚(Coilia nasus)摄食虾类的调查   总被引：4，自引：0，他引：4  
姜涛  刘洪波  李孟孟  杨健 《湖泊科学》2018,30(2):458-463
刀鲚(Coilia nasus)是长江的名贵经济鱼类.虽然传统上认为其溯河生殖洄游全过程不会摄食,但该问题一直尚未完全弄清.作为有效解明这一问题的第一步,本研究在前期长江流域干流和湖泊刀鲚资源调查的基础上,先利用耳石微化学技术筛选出长江河口区、江苏江段、安徽江段和鄱阳湖水域溯河洄游型的刀鲚个体,再对其胃、肠容物的大型游泳动物(鱼、虾类)进行调查分析.结果发现,在河口区、江苏和安徽江段所有刀鲚个体胃充塞度为0级,均未发现摄食有游泳动物;而鄱阳湖水域刀鲚个体的胃充塞度达4~5级,均发现有摄食淡水虾类的日本沼虾(Macrobrachium nipponense)和秀丽白虾(Exopalaemon modestus)的情况.其中29%和71%的刀鲚胃中分别含有1只和2只虾.所有刀鲚个体肠内均未发现有内容物.鉴于鄱阳湖已被确定为溯河洄游型刀鲚的产卵场之一,结果表明长江刀鲚在经河口,通过长江江苏和安徽江段干流到达鄱阳湖产卵场的过程中应该不会摄食大型游泳动物;而进入鄱阳湖产卵场后会开始摄食日本沼虾和秀丽白虾.这种两阶段的现象可能反映出了刀鲚的一种在洄游通道上节约能量,以利长距离溯河;而在产卵场补充能量,以利于性腺最终成熟的生存策略.  相似文献   

9.
This paper provides a generic equation for the evaluation of the maximum earthquake magnitude mmax for a given seismogenic zone or entire region. The equation is capable of generating solutions in different forms, depending on the assumptions of the statistical distribution model and/or the available information regarding past seismicity. It includes the cases (i) when earthquake magnitudes are distributed according to the doubly-truncated Gutenberg-Richter relation, (ii) when the empirical magnitude distribution deviates moderately from the Gutenberg-Richter relation, and (iii) when no specific type of magnitude distribution is assumed. Both synthetic, Monte-Carlo simulated seismic event catalogues, and actual data from Southern California, are used to demonstrate the procedures given for the evaluation of mmax.The three estimates of mmax for Southern California, obtained by the three procedures mentioned above, are respectively: 8.32 ± 0.43, 8.31 ± 0.42 and 8.34 ± 0.45. All three estimates are nearly identical, although higher than the value 7.99 obtained by Field et al. (1999). In general, since the third procedure is non-parametric and does not require specification of the functional form of the magnitude distribution, its estimate of the maximum earthquake magnitude mmax is considered more reliable than the other two which are based on the Gutenberg-Richter relation.  相似文献   

10.
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11.
Attenuation of seismic waves is very essential for the study of earthquake source parameters and also for ground-motion simulations, and this is important for the seismic hazard estimation of a region. The digital data acquired by 16 short-period seismic stations of the Delhi Telemetric Network for 55 earthquakes of magnitude 1.5 to 4.2, which occurred within an epicentral distance of 100 km in an area around Delhi, have been used to estimate the coda attenuation Qc. Using the Single Backscattering Model, the seismograms have been analyzed at 10 central frequencies. The frequency dependence average attenuation relationship Qc = 142f 1.04 has been attained. Four Lapse-Time windows from 20 to 50 seconds duration with a difference of 10 seconds have been analyzed to study the lapse time dependence of Qc. The Qc values show that frequency dependence (exponent n) remains similar at all the lapse time window lengths. While the change in Q0 values is significant, change in Q0 with larger lapsetime reflects the rate of homogeneity at the depth. The variation of Qc indicates a definitive trend from west to east in accordance with the geology of the region.  相似文献   

12.
An interpretative method based on a nonlinearly mathematical optimization concept has been developed in this paper, in order to interpret self-potential anomalies (SP) due to horizontal cylinder, vertical cylinder, sphere and sheet-like structures. This interpretative method comprises three main steps. The first step is to formulate mathematically a nonlinearly constrained minimization problem (NCMP) to describe the geophysical problem related to the studied structure. The second one is to suggest an interior penalty function in order to convert the nonlinearly constrained minimization problem (NCMP) into a nonlinearly unconstrained minimization one (NUMP). The third step is to solve the converted nonlinearly unconstrained minimization problem (NUMP) by the well-known Hooke and Jeeves direct search algorithm in order to estimate the geophysical parameters of the studied structure, i.e., depth, polarization angle, electric dipole moment (magnitude of polarization) and geometric shape factor. The Hooke and Jeeves direct search algorithm is purposely chosen for being robust and its application to SP data allows a rapid convergence towards the optimal estimate of parameters. This interpretative method was first tested on theoretical synthetic models with different random noise, where a very close agreement was obtained between assumed and evaluated parameters.The validity of the proposed interpretative method is also tested on practical field examples taken from Turkey, India and Germany, where available SP data existed and was previously analyzed by different interpretative methods. The agreement between the results obtained by the developed method and those obtained by other published methods is good.Acknowledgment Authors would like to thank Dr. I. Othman Director General of the Atomic Energy Commission of Syria for his interest and continuous encouragement to achieve this work. Special thanks to the reviewers for their constructive suggestions aimed at enhancing the quality of this paper.  相似文献   

13.
A formula to determine the local magnitude (ML) following Richters original definition was empirically derived for the Korean Peninsula. A total of 1,644 digital seismograms from 142 Korean earthquakes that occurred from 1997 to 2000 were corrected for instrument response and convolved with the nominal Wood-Anderson torsion seismograph response to be appropriate for the original definition of ML. Then, the zero-to-peak amplitude was measured in millimeters on the synthetic Wood-Anderson seismogram. Multiple regression analysis was conducted to determine distance and station correction terms for the measured peak amplitudes. The best-fit solution for ML yielded the following formula for the Korean Peninsula:where A() and S denote the peak amplitude on the synthetic Wood-Anderson seismogram at distance and the station correction term, respectively. Note that the second term, distance correction, was adjusted with Richters ML, taking into consideration attenuation differences between the Korean Peninsula and southern California, where Richter originally introduced ML. On average, the magnitudes determined in this study are nearly the same as those determined by the Korea Institute of Geoscience and Mineral Resources (KIGAM), but are larger than those of the Korea Meteorological Administration (KMA) by as much as 0.36.  相似文献   

14.
A method for determining medium quality factor is developed on the basis of analyzing the attenuation dispersion of the arrived first period P wave. In order to enhance signal to noise ratio, improve the resolution in measurement and reduce systematic error we applied the data resampling technique. The group velocity delay of P wave was derived by using an improved multi-filtering method. Based on a linear viscoelastic relaxation model we deduced the medium quality factor Q m, and associated error with 95% confidence level. Applying the method to the seismic record of the Xiuyan M=5.4 earthquake sequences we obtained the following result: (1) High Q m started to appear from Nov. 9, 1999. The events giving the deduced high Q m value clustered in a region with their epicenter distances being between 32 and 46 km to the Yingkou station. This Q m versus distance observation obviously deviates from the normal trend of Q m linearly increasing with distance. (2) The average Q m before the 29 Dec. 1999 M=5.4 earthquake is 460, while the average Q m between the M=5.4 event and the 12 Jan. 2000 M=5.1 earthquake is 391, and the average Q m after the M=5.1 event is 204. Foundation item: State Key Project of Science and Technology during the Tenth Five-year Plan (2004BA601B01-03-01).  相似文献   

15.
Teleseismic long-period P waves from the June 20, 1978, Thessaloniki (N. Greece) earthquake (M s=6.4) were modeled in an attempt to extract information about asperities or barriers on the fault plane. The analysis is based on the inversion method of complex P waves developed by Kikuchi and Kanamori (1982). A far-field source time function with a rise time of 2 sec and a process time of 5 sec is inferred, corresponding to a source dimension of about 10 km when a rupture velocity of 2 km/sec is assumed.The source depth of this shock, estimated by matching synthetic seismograms to observations, is found to be 8 km. The sum of the seismic moments of the individual subevents amounts to 3.3×1025 dyn-cm.  相似文献   

16.
QC-estimates of Kachchh Basin in western India have been obtained in a high frequency range from 1.5 to 24.0 Hz using the aftershock data of Bhuj earthquake of January 26, 2001 recorded within an epicentral distance of 80 km. The decay of coda waves of 30 sec window from 186 seismograms has been analysed in four lapse time windows, adopting the single backscattering model. The study shows that Qc is a function of frequency and increases as frequency increases. The frequency dependent Qc relations obtained for four lapse-time windows are: Qc=82 f1.17 (20–50 sec), Qc=106 f1.11 (30–60 sec), Qc=126f1.03 (40–70 sec) and Qc=122f1.02 (50–80 sec). These empirical relations represent the average attenuation properties of a zone covering the surface area of about 11,000, 20,000, 28,000 and 38,000 square km and a depth extent of about 60, 80, 95, 110 km, respectively. With increasing window length, the degree of frequency dependence, n, decreases marginally from 1.17 to 1.02, whereas Q0 increases significantly from 82 to 122. At lower frequencies up to 6 Hz, Qc−1 of Kachchh Basin is in agreement with other regions of the world, whereas at higher frequencies from 12 to 24 Hz it is found to be low.  相似文献   

17.
Absorption of seismic energy in the earth reduces amplitudes and changes phases of the propagating seismic waves. Amplitudes are usually recovered according to an estimated exponential decay curve, while phase distortions are generally disregarded. Therefore, accurate processing of seismic data requires a careful investigation of the relationship between absorption and phases. In this paper a procedure is suggested to achieve this goal, and some related topics are worked out. A method is outlined for computing synthetic seismograms and vertical seismic profiles with phase distortion due to absorption. The algorithm works in the frequency domain, and it provides for absorption according to the usual model of exponential decay of amplitude with distance. The absorption coefficient is a linear function of frequency and is related to the quality factor Q of the rocks. Complex seismic velocities are introduced and minimum-phase delay due to absorption is assumed for all cases considered. Methods for estimating Q profiles from seismic well surveys and seismic data are described. Comparison between field and synthetic data shows the effectiveness and benefits of the procedure. Some applications of the method to phase distortion recovery and wavelet processing are presented.  相似文献   

18.
Excavations in the former Roman provincial capital of Pannonia Superior, Carnuntum, 40 km east of Vienna revealed damaged masonry structures from many parts of the ancient settlements. A compilation of structurally damaged buildings has formerly been given by Kandler (Acta Archaeol Acad Sci Hung, 41:313–336, 1989), who related damage to an earthquake in the middle of the fourth century a.d. This paper reviews and supplements these data, and discusses the significance of the style of damage. It is concluded that seismic damage is the only likely interpretation for the damaging mechanism. Although archaeological age dating for the individual collapsed buildings only constrains the timing of their destruction to a few decades around 350 a.d., we assume a single damaging event. In spite of the restrictions on damage assessment by the nature of the archaeological data, it is possible to give a reasonable appraisal of macroseismic intensity. The tentative seismological interpretation of damage leads to an intensity estimate of about nine of the European macroseismic scale (EMS-1998). Comparison with macroseismic data of modern earthquakes in the region, which show a rapid decrease of intensity with distance form the epicentre, indicate a near-by seismic source unless exceptionally high epicentral intensities are assumed for the fourth century event. The most likely source is an active sinistral strike-slip fault (Lassee Fault) passing about 8 km NW of the archaeological site. The fault belongs to Vienna Basin fault system with about 2 mm sinistral movement per year. The system is characterized by fault segmentation and distinct seismicity along the different segments. Moderate seismicity during the last centuries at the southern segments (e.g., Schwadorf 1927, I 0=8) strongly contrasts from the Lassee fault segment with Carnuntum as the only known severe earthquake. The earthquake of Carnuntum provides evidence for the overall seismic style of deformation along this segment, which previously has not been regarded seismically active. Also, the fourth century earthquake is the strongest event known from the Vienna Basin fault so far.  相似文献   

19.
四川盆地南部的长宁页岩气开发区附近地震频发,近年来已发生近10次ML＞4.0的中型地震和万余次ML1.0～3.0的小微地震,灾害风险持续增高.由于国家地震台网的固定台站较为分散,难以捕捉到1级以下微震事件的精确信息,通过近场微震监测数据来分析页岩气开发区的地震风险演化趋势,已经成为势在必行的科学问题.本文基于专门布设的...  相似文献   

20.
万洪秀  覃志豪  徐永明 《湖泊科学》2018,30(5):1429-1437
以博斯腾湖流域为研究区,基于2001-2016年时间序列的MODIS NDVI数据分析了研究区植被的时空变化趋势,并结合流域气象站点的气温、降水、日照时数和相对湿度数据分析了植被生长季累积NDVI和16天NDVI与气候因子之间的响应特征.结果表明:(1)流域植被覆盖变化呈改善趋势,生长季累积NDVI年变化率为0.014 a-1,16天NDVI变化率均为正值,植被改善趋势显著区域主要分布在高山草原湿地和农业灌溉区边缘的新增农田.(2)植被生长季累积NDVI主要受降水和相对湿度影响,植被总体生产力与水分条件关系最密切,生长季逐16天NDVI与同期气温和日照时数在植被生长初期和末期关系显著,而与降水没有显著的相关性,说明植被短期瞬时长势对热量条件更为敏感.(3)在植被生长不同阶段对气候变化具有不同的滞后效应,其中植被生长初期和末期对气温有0.5~1个月的滞后,生长盛期对降水有0.5~3个月的滞后、日照时数有1.5~2.5个月的滞后、相对湿度有0.5~2.5个月的滞后,揭示了植被不同生长阶段水热条件对其生长韵律的控制差异.  相似文献   

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