Common-reflection-point time migration     

Tiago A. Coimbra  Jorge H. Faccipieri  Dany S. Rueda  Martin Tygel 《Studia Geophysica et Geodaetica》2016,60(3):500-530

Since the early days of seismic processing, time migration has proven to be a valuable tool for a number of imaging purposes. Main motivations for its widespread use include robustness with respect to velocity errors, as well as fast turnaround and low computation costs. In areas of complex geology, in which it has well-known limitations, time migration can still be of value by providing first images and also attributes, which can be of much help in further, more comprehensive depth migration. Time migration is a very close process to common-midpoint (CMP) stacking and, more recently, to zero-offset commonreflection- surface (CRS) stacking. In fact, Kirchhoff time migration operators can be readily formulated in terms of CRS parameters. In the nineties, several studies have shown advantages in the use of common-reflection-point (CRP) traveltimes to replace conventional CMP traveltimes for a number of stacking and migration purposes. In this paper, we follow that trend and introduce a Kirchhoff-type prestack time migration and velocity analysis algorithm, referred to as CRP time migration. The algorithm is based on a CRP operator together with optimal apertures, both computed with the help of CRS parameters. A field-data example indicates the potential of the proposed technique.  相似文献   

Methods for estimating the velocities of the Brazil Current in the pre-salt reservoir area off southeast Brazil (23∘ S–26∘ S)     

Tiago Carrilho Biló  Ilson Carlos Almeida da Silveira  Wellington Ceccopieri Belo  Belmiro Mendes de Castro  Alberto Ricardo Piola 《Ocean Dynamics》2014,64(10):1431-1446

The Brazil Current (BC) is likely the least observed and investigated subtropical western boundary current in the world. This study proposes a simple and systematic methodology to estimate quasi-synoptic cross-sectional speeds of the BC within the Santos Basin (23^° S–26^° S) based on the dynamic method using several combinations of data: Conductivity, temperature, and depth (CTD), temperature profiles, CTD and vessel-mounted Acoustic Doppler Current Profiler (VMADCP), and temperature profiles and VMADCP. All of the geostrophic estimates agree well with lowered Acoustic Doppler Current Profiler (LADCP) velocity observations and yield volume transports of -5.56 ±1.31 and 2.50 ±1.01 Sv for the BC and the Intermediate Western Boundary Current (IWBC), respectively. The LADCP data revealed that the BC flows southwestward and is ～100 km wide, 500 m deep, and has a volume transport of approximately -5.75 ±1.53 Sv and a maximum speed of 0.59 m s^?1. Underneath the BC, the IWBC flows northeastward and has a vertical extent of approximately 1,300 m, a width of ～60 km, a maximum velocity of ～0.22 m s?¹, and a volume transport of 4.11 ± 2.01 Sv. Our analysis indicates that in the absence of the observed velocities, the isopycnal (σ ₀) of 26.82 kg m^?3 (～500 dbar) is an adequate level of no motion for use in geostrophic calculations. Additionally, a simple linear relationship between the temperature and the specific volume anomaly can be used for a reliable first estimate of the BC-IWBC system in temperature-only transects.  相似文献   

Classification of washover dynamics in barrier islands   总被引：1，自引：0，他引：1  

Ana Matias   scar Ferreira  Ana Vila-Concejo  Tiago Garcia  Joo Alveirinho Dias 《Geomorphology》2008,97(3-4):655-674

This study systematically classifies washover dynamics with reference to coastal changes along the Ria Formosa barrier islands (Southern Portugal). Identification of washovers using a sequence of 11 sets of aerial photographs dated between 1947 and 2001 allowed a classification to be developed based on: (1) overwash evolution (increasing, decreasing, or constant overwash processes); (2) the mechanisms promoting washover formation (exceptional to infrequent oceanographic conditions, washout processes, structural erosion, inlet dynamics, and human interventions); and (3) the mechanisms promoting washover cessation (berm development, structural erosion, dune development, inlet dynamics, and human interventions). A total of 369 different washovers were observed along the Ria Formosa barriers during the study period, with 209 washovers being formed in various types of dune morphology and 303 being obliterated. The number of washovers was relatively stable from 1947 to 1972, and increased dramatically between 1972 and 1976 probably as a result of the development of immature inlet margins and downdrift starvation. From 1976 to 2001, washover occurrences declined and their spatial dimensions decreased, leading to a decrease in overwash activity over this time. Overall, the dominant formation mechanisms of washovers in the Ria Formosa were inlet dynamics (accounting for 57% of washovers formed) and structural erosion (20%), with human intervention mechanisms accounting for 12%. The cessation of washovers was dominated by dune development (33% of the washovers obliterated) followed by inlet dynamics (24%) and structural erosion (19%), while human intervention mechanisms accounted for 13%. The classification should be of use for the coastal management of barrier systems including the definition of overwash-prone areas and the determination of the relative importance of the mechanisms contributing to washover formation and cessation.  相似文献   

Seismic vulnerability assessment of a mixed masonry–RC building aggregate by linear and nonlinear analyses     

Tiago Ferrito  Jelena Milosevic  Rita Bento 《Bulletin of Earthquake Engineering》2016,14(8):2299-2327

From the beginning of the twentieth century, and due to the rapid increase of reinforced concrete (RC) usage, mixed masonry–RC buildings have emerged. In Lisbon, Portugal, old mixed masonry–RC buildings appeared between 1920 and 1960, representing the transition period between masonry and proper RC. These buildings are often integrated in blocks, and frequently share the side-walls, implying, thus, the need to assess the seismic vulnerability of building aggregates. The present paper approaches the seismic vulnerability assessment of a specific type of old mixed masonry–RC buildings in Lisbon. The study comprises the analysis of a building, both as an isolated structure and inserted in its aggregate, using two approaches: (1) linear dynamic analysis with SAP2000 and (2) nonlinear static analysis by means of 3Muri/Tremuri software. A comparison of both approaches derives a good matching between the obtained results. However, a nonlinear analysis is required to identify, in an adequate manner, the critical areas of the structure requiring strengthening.  相似文献   

Reference data enhancement for geographic information retrieval using linked data   总被引：1，自引：0，他引：1       下载免费PDF全文

Tiago H. V. M. Moura  Clodoveu A. Davis Jr.  Frederico T. Fonseca 《Transactions in GIS》2017,21(4):683-700

Gazetteers are instrumental in recognizing place names in documents such as Web pages, news, and social media messages. However, creating and maintaining gazetteers is still a complex task. Even though some online gazetteers provide rich sets of geographic names in planetary scale (e.g. GeoNames), other sources must be used to recognize references to urban locations, such as street names, neighborhood names or landmarks. We propose integrating Linked Data sources to create a gazetteer that combines a broad coverage of places with urban detail, including content on geographic and semantic relationships involving places, their multiple names and related non‐geographic entities. Our final goal is to expand the possibilities for recognizing, disambiguating and filtering references to places in texts for geographic information retrieval (GIR) and related applications. The resulting ontological gazetteer, named LoG (Linked OntoGazetteer), is accessible through Web services by applications and research initiatives on GIR, text processing, named entity recognition and others. The gazetteer currently contains over 13 million places, 140 million attributes and relationships, and 4.5 million non‐geographic entities. Data sources include GeoNames, Freebase, DBPedia and LinkedGeoData, which is based on OpenStreetMap data. An analysis on how these datasets overlap and complement one another is also presented.  相似文献   

Flood-related leptospirosis outbreaks in Brazil: perspectives for a joint monitoring by health services and disaster monitoring centers     

Luciana de Resende Londe  Rodrigo Silva da Conceição  Tiago Bernardes  Mariane Carvalho de Assis Dias 《Natural Hazards》2016,84(2):1419-1435

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Interpretation of the behaviour of agrowell systems in Sri Lanka using radial flow models     

C. S. DE SILVA  K. R. RUSHTON 《水文科学杂志》2013,58(6):825-835

Abstract

This paper describes a study of the use of large diameter “agrowells” used for irrigation in Sri Lanka. Detailed field information for a single location is presented and a numerical radial flow model was used to interpret the field response. Initially the model was used to represent a pumping test in which the pumping and subsequent recovery were monitored. It was then used to investigate the operation of the well during a dry season. Satisfactory agreement could only be obtained when account was taken of the withdrawal of water from below the water table by trees. From the simulation it was possible to show that skilful farming practice could be used in steadily exploiting the resources for irrigation over the whole of the dry season.  相似文献   

CEMPS: A prototype spatial decision support system to aid in planning emergency evacuations     

MICHAEL PIDD  RICHARD EGLESE  F NISHAKUMARI DE  SILVA 《Transactions in GIS》1996,1(4):321-334

CEMPS is a prototype spatial decision support system which links the topographical support and analysis provided by a geographic information system, ARC/INFO, with the ability to simulate the dynamics of an evacuation process. CEMPS has been designed to enable emergency planners to experiment with different emergency evacuation plans in order to devise a plan which meets their requirements. ARC/INFO is used to parameterize a dynamic simulation with topographical information and to display its results. The prototype runs on a Sun SPARCStation cluster but could be modified to run on other hardware and software.  相似文献   

FINITE ELEMENT MODELLING OF A DEEP SEA CLAY IN LONG-TERM LABORATORY CREEP TESTS     

H. G. BRANDES  M. H. SADD  A. J. SILVA 《国际地质力学数值与分析法杂志》1996,20(12):887-905

A new finite element program is introduced and its predictive capabilities are compared to results from two long-term, drained laboratory creep tests on a deep sea clay. The constitutive behaviour is based on Cam clay critical state plasticity theory with creep and time-dependent hardening. Creep is computed using either Singh–Mitchell's three-dimensional equation or Taylor's secondary compression relationship. The experimental creep data include a triaxial specimen subjected to two deviatoric stress increments and a one-dimensional consolidation specimen subjected to three vertical stress increments. In addition, the pore pressure behaviour following an increase in stress is examined in the triaxial sample. Predictions compare favourably to test data, which provide confidence for applying the chosen constitutive model and numerical formulation to solve seabed-related problems on the continental slope that are of interest to geologists, the oil industry and the navy, among others.  相似文献   

Stretch-free generalized normal moveout correction     

Jorge H. Faccipieri  Tiago A. Coimbra  Rodrigo Bloot 《Geophysical Prospecting》2019,67(1):52-68

The effective application of normal moveout correction processes mainly depends on four factors: the chosen traveltime approximation, the stretching associated with the given traveltime, crossing events and phase changes, the last two being inherent to the seismic data. In this context, we conduct a quantitative analysis on stretching considering a general traveltime expression depending on half-offset and midpoint coordinates. Through this analysis, we propose a mathematically proven procedure to eliminate stretching, which can be applied to any traveltime approximation. The proposed method is applied to synthetic and real data sets, considering different traveltime approximations and achieved complete elimination of stretching.  相似文献