Reverse time migration of CMP-gathers an effective tool for the determination of interval velocities

One of the most important steps in the conventional processing of reflection seismic data is common midpoint (CMP) stacking. However, this step has considerable deficiencies. For instance the reflection or diffraction time curves used for normal moveout corrections must be hyperbolae. Furthermore, undesirable frequency changes by stretching are produced on account of the dependence of the normal moveout corrections on reflection times. Still other drawbacks of conventional CMP stacking could be listed.One possibility to avoid these disadvantages is to replace conventional CMP stacking by a process of migration to be discussed in this paper. For this purpose the Sherwood-Loewenthal model of the exploding reflector has to be extended to an exploding point model with symmetry to the lineP _EX M whereP _EX is the exploding point, alias common reflection point, andM the common midpoint of receiver and source pairs.Kirchhoff summation is that kind of migration which is practically identical with conventional CMP stacking with the exception that Kirchhoff summation provides more than one resulting trace.In this paper reverse time migration (RTM) was adopted as a tool to replace conventional CMP stacking. This method has the merit that it uses the full wave equation and that a direct depth migration is obtained, the velocityv can be any function of the local coordinatesx, y, z. Since the quality of the reverse time migration is highly dependent on the correct choice of interval velocities such interval velocities can be determined stepwise from layer to layer, and there is no need to compute interval velocities from normal moveout velocities by sophisticated mathematics or time consuming modelling. It will be shown that curve velocity interfaces do not impair the correct determination of interval velocities and that more precise velocity values are obtained by avoiding or restricting muting due to non-hyperbolic normal moveout curves.Finally it is discussed how in the case of complicated structures the reverse time migration of CMP gathers can be modified in such a manner that the combination of all reverse time migrated CMP gathers yields a correct depth migrated section. This presupposes, however, a preliminary data processing and interpretation.     

Vertical concentration profile of nonuniform sediment

A new formula for the concentration profile of nonuniform sediment is derived using the diffusion differential equation with equilibrium bed concentration.The interaction coefficient for nonuniform sediment particles as a function of both relative diameter and geometric standard deviation of nonuniform sediment is taken into account in the settling velocity.The diffusion coefficient is obtained from the logarithmic velocity profile.This new formula possesses several advantages as follows:(1)avoids theoretical defect of the Rouse formula,which states that the sediment concentration is infinite at the bottom and zero at the water surface.(2)suitable for an arbitrary fraction of nonuniform sediment,and(3)easy to apply with a simple form.The formula yields less difference among concentration profiles for various particles than that for uniform sediment and reveals the lawfor fractional concentration distribution of nonuniform sediment.The calculated concentration agrees well with the measured data from the Yangtze River.     

京西盆岭构造区积累库仑破裂应力变化对强震的影响

Since 231 B. C.,a total of 15 M6.0 - 7.5 earthquakes have been recorded in the west Beijing basin-range tectonic region( 38.3°- 41.5° E,112°- 116.2° N),a region mainly under the action of tensional normal faulting. In this paper,we calculate the Coulomb stress change of each earthquake and the cumulative Coulomb stress change,and on this basis we analyze the stress triggering of strong earthquakes. The research shows that there are 10 of 14 earthquakes that occurred in the trigger zones,in which the Coulomb stress change is positive,and the trigger rate is 71%. The positive areas of cumulative Coulomb stress change caused by these 15 earthquakes are: middle of northern Liulengshan fault,Northern Huaizhuo basin fault,Xinbaoan-Shacheng fault,Sangganhe fault and Southern Yuxian basin fault. This necessarily increases the seismic risk of these faults and can be used as a reference for future seismic risk analysis in this area.     

Climate changes in the Lhasa River basin,Tibetan Plateau: irrigation-induced cooling along with a warming trend

Characterizing the response of temperature variables to agricultural irrigation is expected to be an important challenge for understanding the full impact of water management on regional climate change. In this paper, the trend analysis and abrupt change test were applied to detect the global warming effect. Then, the quantitative irrigation-induced cooling effects on temperature variables between April and August from 1970 to 2010 in the Lhasa River basin were estimated using historical time series of gridded meteorological records and a map of the area equipped for irrigation. Trends in the maximum temperature (Tmax) were statistically positive, and a significant increasing trend for the minimum temperature (Tmin) was detected at the 0.01 and 0.05 confidence levels. No abrupt changing point of warming was detected in the time series for Tmax. The abrupt changes in Tmin in the irrigation concentration period took place in 1995, 5 years later than the corresponding change in April. Affected by global warming, the increase in temperature was the largest in July and August, when the irrigation-induced cooling effect was also the most significant. The irrigation-induced cooling effect for Tmax and Tmin in April–August (except for June) ranged from − 0.017 to − 0.009 °C/decade and from − 0.011 to − 0.001 °C/decade, respectively, and the cooling effect for diurnal temperature range (DTR) ranged from − 0.011 to 0 °C/decade. The cooling effect on temperature reached above 0.01 °C in July and August, but for the growing seasons, the effect was weak, only 0.001 °C. The Tmax and Tmin trends during the whole growing seasons decreased by both 0.002 °C/decade, respectively, with a 10% increase in irrigation land proportion. Even in July and August, the trends were expected to decrease by about 0.005 °C/decade with a 10% increase in irrigation land proportion. The irrigation-induced cooling effect could partially slow global warming.     

基于地理实体的基础测绘生产组织模式探索

首先分析了目前我国基础地理信息资源建设存在的主要问题,提出了通过构建地理实体数据库实现基础地理信息资源的共享和深入应用的构想。其次,深入分析了目前国内外地理实体数据库的研究及建设现状。在以上基础上,最后以优先满足国家事权为原则,提出了基于地理实体数据采集的我国基础测绘国家、省、市县任务分工和生产组织模式构想。     

Moravian and Silesian nationalities: A new phenomenon in the ethnic map of the Czech Lands?

In the 1991 population census, 1.4 million inhabitants of the Czech Republic applied for Moravian or Silesian nationality, which did not exist before.They expressed their consciousness of territorial appurtenance to the historical provinces of Moravia and Silesia and by this declaration they set it above the appurtenance to the Czech nation. New social cleavage thus developed in ethnically almost homogeneous environment of the Czech Republic, which constitutes a potential threat of the further splitting of the State. Trying to find the causes of such a phenomenon, the author deals with the territorial differentiation of these inhabitants and factors which influenced it. The close interconnection with political demands is stressed. The insensive centralizing measures of the communist regime are considered as the direct impulses of the present development. The phenomenon is understood as a specific manifestation of the posttotalitarian social crisis in Central and Eastern Europe.     

Lithospheric extension and the opening of the Red Sea: sediment-basalt relationships in Yemen*

This paper analyses new field and radiometric age data on the timing of extension, sedimentation and magmatism related to the opening of the Red Sea. The first evidence of widespread extension is found in synsedimentary fissures in the fluviatile to shallow marine Tawilah Formation of Cretaceous to early Tertiary age. The first indication of magmatism is the eruption of alkaline basalts (43.5–21.2 Ma) on to marine and non-marine sandstones of lower to middle Tertiary age. The lack of an angular unconformity at the sediment-basalt contact, over a period of 25 Myr, corroborates a diachronous relationship between the Tawilah sandstones and the Yemen Volcanics. These data also indicate that the onset of volcanism in Yemen was in the Eocene, as is the case in Ethiopia and Saudi Arabia. A passive rifting model is supported by early extension and sedimentation followed by syn- and post-tectonic magmatism.     

航空磁测在黑龙江伊春地区夕卡岩型锌多金属矿的找矿应用

依据1：5万高精度航磁异常和地质特征进行选区,结合1：2万综合物化探查证技术,在小兴安岭伊春地区航磁异常区发现了夕卡岩型锌多金属矿,体现了航空磁测技术在夕卡岩型多金属矿找矿中的适用性.查证结果认为,下寒武统含大理岩地层与侵入岩接触部位航磁异常区是重要的夕卡岩型多金属矿找矿靶区,赋矿部位显示低阻高极化地球物理特征;土壤地球化学特征表现为地层与侵入岩接触部位存在Ag、As、Sb、Mo、W、Bi、Pb、Cu、Zn元素组合异常,异常套合好,Sb异常值高,出现于内带,Zn常见于中带.     

Influences of climate change on California and Nevada regions revealed by a high-resolution dynamical downscaling study

In this study, the influence of climate change to California and Nevada regions was investigated through high-resolution (4-km grid spacing) dynamical downscaling using the WRF (Weather Research & Forecasting) model. The dynamical downscaling was performed to both the GFS (Global forecast model) reanalysis (called GFS-WRF runs) from 2000?C2006 and PCM (Parallel Climate Model) simulations (called PCM-WRF runs) from 1997?C2006 and 2047?C2056. The downscaling results were first validated by comparing current model outputs with the observational analysis PRISM (Parameter-elevation Regressions on Independent Slopes Model) dataset. In general, the dominant features from GFS-WRF runs and PCM-WRF runs were consistent with each other, as well as with PRISM results. The influences of climate change on the California and Nevada regions can be inferred from the model future runs. The averaged temperature showed a positive trend in the future, as in other studies. The temperature increases by around 1?C2°C under the assumption of business as usual over 50?years. This leads to an upward shifting of the freezing level (the contour line of 0°C temperature) and more rain instead of snow in winter (December, January, and February). More hot days (>32.2°C or 90°F) and extreme hot days (>37.8°C or 100°F) are predicted in the Sacramento Valley and the southern parts of California and Nevada during summer (June, July, and August). More precipitation is predicted in northern California but not in southern California. Rainfall frequency slightly increases in the coast regions, but not in the inland area. No obvious trend of the surface wind was indicated. The probability distribution functions (PDF) of daily temperature, wind and precipitation for California and Nevada showed no significant change in shape in either winter or summer. The spatial distributions of precipitation frequency from GFS-WRF and PCM-WRF were highly correlated (r?=?0.83). However, overall positive shifts were seen in the temperature field; increases of 2°C for California and 3°C for Nevada in summer and 2.5°C for California and 1.5°C for Nevada in winter. The PDFs predicted higher precipitation in winter and lower precipitation in the summer for both California and Nevada.