Traveltime measurements from noise correlation: stability and detection of instrumental time-shifts

We test the feasibility of using Green's functions extracted from records of ambient seismic noise to monitor temporal changes in the Earth crust properties by repeated measurements at regional distances. We use about 11 yr of continuous recordings to extract surface waves between three pairs of stations in California. The correlations are computed in a moving 1-month window and we analyse the temporal evolution of measured interstation traveltimes. The comparison of the arrival times in the positive and negative correlation time of Rayleigh and Love waves allows us to separate time-shifts associated with any form of physical change in the medium, those resulting from clock drift or other instrumental errors, and those due to change in the localization of the noise sources. This separation is based on the principle of time symmetry. When possible, we perform our analysis in two different period bands: 5–10 and 10–20 s. The results indicate that significant instrumental time errors (0.5 s) are present in the data. These time-shifts can be measured and tested by closure relation and finally corrected independently of any velocity model. The traveltime series show a periodic oscillation that we interpret as the signature of the seasonal variation of the region of origin of the seismic noise. Between 1999 and 2005, the final arrival time fluctuations have a variance of the order of 0.01 s. This allows us to measure interstation traveltimes with errors smaller than 0.3 per cent of the interstation traveltime and smaller than 1 per cent of the used wave period. This level of accuracy was not sufficient to detect clear physical variation of crustal velocity during the considered 11 yr between the three stations in California. Such changes may be more easily detectable when considering pairs of stations more closely located to each other and in the vicinity of tectonically active faults or volcanoes.     

The Neopleistocene of North European Russia: Stratigraphy,paleogeography, and paleoclimate

The Pleistocene sediments of North European Russia have been studied using different methods to establish their composition and identify the enclosed organic remains. The results obtained elucidate natural climatic environments of the Pleistocene and corresponding sedimentation cycles and development stages. Glaciation centers are identified for different Pleistocene epochs based on lithological criteria. The established secular trends characterizing spatial distribution and composition of different-age glacial horizons facilitate their regional correlation. Climatic conditions and paleogeographic settings of sedimentation during interglacial epochs of the middle-late Pleistocene and Holocene are reconstructed. Variations in development of vegetation, temperature, and humidity are detected for the first time in the Timan-Pechora-Vychegda, Arkhangel’sk and Vologda regions with parallel coordination of obtained data. As is concluded, there was a tendency of climate cooling in North European Russia during the Neopleistocene.     

Tethyan-to-boreal correlation in the Kimmeridgian using high-resolution sequence stratigraphy (Vocontian Basin,Swiss Jura,Boulonnais, Dorset)

Ammonite biostratigraphy plays a central role in the definition of Jurassic stratigraphy. Nevertheless, the strong provincialism of European ammonite species during the Kimmeridgian is a long-standing problem in correlation attempts between the boreal and Tethyan faunal realms. Moreover, the sequence-stratigraphic interpretations for northern and southern Europe given in the Jurassic chronostratigraphic chart of Hardenbol et al. in SEPM Publ. 60 (chart) (1998) are different. The present study aims to resolve this correlation problem in order to better understand the connections between the boreal and the Tethyan realms during the Kimmeridgian. A sedimentological and high-resolution sequence-stratigraphic interpretation is presented for two unpublished sections (Cras d’Hermont and Roche de Mars) in the northern Swiss Jura, where recently discovered ammonites display both boreal and Tethyan influences. Then, these sections are correlated with the same time interval in the central Swiss Jura and Vocontian Basin, which belong to the Tethyan realm. Lastly, a long-distance transect is constructed between the Vocontian Basin, Swiss Jura, northern France, and southern England, the last two areas being part of the sub-boreal realm. The main results of this work are that: (1) third-order depositional sequences, and also higher-frequency sequences, can be correlated from the Tethyan to the boreal realm; (2) the sequence-stratigraphic interpretation given by Hardenbol et al. in SEPM Publ 60 (chart) (1998) for northern Europe seems to be accurate and agrees with the sequence-stratigraphic framework established in the Swiss Jura; (3) the Late Kimmeridgian of the Swiss Jura displays boreal influences; (4) integrated high-resolution sequence-stratigraphic and cyclostratigraphic studies are a valuable approach for bridging the correlation gap between northern and southern Europe.     

The light transmission and seiche depth of Izmir Bay,western Turkey

Izmir Bay is one of the most polluted estuaries in the whole Mediterranean Sea. The inner part of the Bay (Inner Bay) is heavily affected by domestic and industrial discharge. As a result of these loads, strong eutrophication occurs in the Inner Bay, which is temporally anaerobic. The ecologically sensitive approach of the local authorities during the last decade has given rise to a wide variety of monitoring and research studies on this bay. On the other hand, the municipality of Izmir started to operate wastewater treatment facilities since January 2000. The Institute of Marine Sciences and Technology — Izmir (IMST) with its research vessel R/V K Piri Reis has been conducting an intensive monitoring program since 1988 and especially during the recent few years. These investigations provide an opportunity for the evaluation of the performance of the wastewater treatment plant in terms of the change in the optical properties of Izmir Bay water in a positive manner. The turbidity values measured in these monitoring studies indicate that the values have changed drastically after January 2000. Their spatial variation indicates that the values decrease from the Inner Bay towards the Aegean Sea. The turbidity (light transmission) values are measured with an automatic CTD (conductivity, temperature and depth) system during each cruise. The seiche disc depth measurement is carried out only occasionally. The accuracy of the seiche disc depth is dependent on certain daylight conditions and depends on the operator. The seiche disc depth (D _s) is an important parameter to estimate primary production of organic matter (hereafter called production). A relation between light transmission (turbidity) value and seiche disc depth (D _s) is found with very good agreement. The correlations are very high (approximately 0.94) with slight seasonal variation.     

Dinocyst biostratigraphy of the Lower Cretaceous in North Siberia

The described scheme of the Lower Cretaceous (Berriasian-Barremian) stratigraphic subdivisions is elaborated based on palynological study of sections in the Khatanga depression, Ust-Yenisei region, Pur-Taz interfluve, and around the Ob River latitudinal segment, the North Siberia. Stratigraphic distribution of microphytoplankton studied in detail is used to distinguish 10 biostratigraphic units in the rank of dinocysts zones. Stratigraphic position of the zones is determined with confidence using data on the Lower Cretaceous reference sections in the Khatanga depression, which were principal ones by constructing the Boreal standard zonation. In majority, boundaries of the dinocysts beds are of a high correlation potential and can be regarded as reliable stratigraphic markers, as they are recognizable not only in Siberia, but also in northern Europe and America.     

Inferred ground motions on Guadeloupe during the 2004 Les Saintes earthquake

Accurate estimates of the ground motions that occurred during damaging earthquakes are a vital part of many aspects of earthquake engineering, such as the study of the size and cause of the uncertainties within earthquake risk assessments. This article compares a number of methods to estimate the ground shaking that occurred on Guadeloupe (French Antilles) during the 21st November 2004 (M _w 6.3) Les Saintes earthquake, with the aim of providing more accurate shaking estimates for the investigation of the sources of uncertainties within loss evaluations, based on damage data from this event. The various techniques make differing use of the available ground-motion recordings of this earthquake and by consequence the estimates obtained by the different approaches are associated with differing uncertainties. Ground motions on the French Antilles are affected by strong local site effects, which have been extensively investigated in previous studies. In this article, use is made of these studies in order to improve the shaking estimates. It is shown that the simple methods neglecting the spatial correlation of earthquake shaking lead to uncertainties similar to those predicted by empirical ground-motion models and that these are uniform across the whole of Guadeloupe. In contrast, methods (such as the ShakeMap approach) that take account of the spatial correlation in motions demonstrate that shaking within roughly 10 km of a recording station (covering a significant portion of the investigated area) can be defined with reasonable accuracy but that motions at more distant points are not well constrained.     

Suspended sediment load transport in the Mississippi River basin at St. Louis: temporal scaling and nonlinear determinism

This study investigates the dynamic behavior of suspended sediment load transport at different temporal scales in the Mississippi River basin. Data corresponding to five successively doubled temporal scales (i.e. daily, two‐day, four‐day, eight‐day and 16‐day) from the St. Louis gaging station in Missouri are analyzed. The investigation is focused on identifying possible low‐dimensional deterministic behavior in the suspended sediment load transport dynamics, with an aim towards reduction in model complexity. The correlation dimension method is used to identify low‐dimensional determinism. The suspended sediment load dynamics are represented through phase‐space reconstruction, and the variability is estimated using the (proximity of) reconstructed vectors in the phase space. The results indicate the presence of low‐dimensional determinism in the suspended sediment load series at each of the five temporal scales, with the variables dominantly governing the dynamics in the order of three or four. These results not only suggest the appropriateness of relatively simpler models but also hint at possible scale invariance in the suspended sediment load transport dynamics. Copyright © 2006 John Wiley & Sons, Ltd.     

Nonlinear determinism in river flow: prediction as a possible indicator

Whether or not river flow exhibits nonlinear determinism remains an unresolved question. While studies on the use of nonlinear deterministic methods for modeling and prediction of river flow series are on the rise and the outcomes are encouraging, suspicions and criticisms of such studies continue to exist as well. An important reason for this situation is that the correlation dimension method, used as a nonlinear determinism identification tool in most of those studies, may possess certain limitations when applied to real river flow series, which are always finite and often short and also contaminated with noise (e.g. measurement error). In view of this, the present study addresses the issue of nonlinear determinism in river flow series using prediction as a possible indicator. This is done by (1) reviewing studies that have employed nonlinear deterministic methods (coupling phase‐space reconstruction and local approximation techniques) for river flow predictions and (2) identifying nonlinear determinism (or linear stochasticity) based on the level of prediction accuracy in general, and on the prediction accuracy against the phase‐space reconstruction parameters in particular (termed as the ‘inverse approach’). The results not only provide possible indications to the presence of nonlinear determinism in the river flow series studied, but also support, both qualitatively and quantitatively, the low correlation dimensions reported for such. Therefore, nonlinear deterministic methods are a viable complement to linear stochastic ones for studying river flow dynamics, if sufficient caution is exercised in their applications and in interpreting the outcomes. Copyright © 2006 John Wiley & Sons, Ltd.     

地图数字化数据坐标变换的相关性分析

将用于求定地图数字化坐标转换参数的已知点的地面坐标和数字化坐标都当作观测值，用随有参数的条件平差求定转换参数，对采用4个已知点、9个已知点分别进行相似与仿射变换进行了分析，计算了格网点之间的相关系数，进一步分析了格网点间相关系数的分布规律，对转换后的坐标相关性进行了讨论。     

浅析解析测图仪相对定向的不定性

通过长期的生产实践提出了相对定向不定性的问题,从相对定向的数学关系着手,列出解求相对定向元素的方程组,分析了产生相对定向不定性的原因,提出了相对定向的结果必须是模拟显示结果与数字显示结果的统一.