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Sample records for africa seismic experiment

  1. Deep Seismic Reflection Profiling in Africa

    NASA Astrophysics Data System (ADS)

    Attoh, K.; Brown, L. D.

    2006-05-01

    Africa represents one of the true frontiers for systematic deep seismic reflection profiling of the type pioneered by COCORP, LITHOPROBE, BIRPS, DEKORP, and ECORS in the northern hemisphere. However, there have been a number of notable individual surveys that have sampled key components of the African lithosphere, and several systematic regional geophysical initiatives which suggest African is fertile ground for future efforts. Among the latter are the KRISP refraction/wide-angle program to probe the East African Rift system in the 1990's, the Kaapvaal Experiment to image the deep lithosphere with passive techniques and most recently the EAGLE active/passive experiments in the Afar. Examples of true multichannel deep reflection surveys to delineate crustal structure include the transects of the Limpopo Belt, a Neoarchean mobile zone that sutures the Kaapval and Zimbabwe cratons, deep oil prospecting surveys in the Nosop basin of southern Botswana that reveal dramatic basement reflectors off the NW margin of the Kaapvaal craton, and most recently deep vibroseis surveys within the Kaapvaal craton that indicate a crustal stack of tectonic slivers as well as tectonic shingling of the upper mantle. The passive margin of western Africa, with its strategic oil resources, has been a target of several deep studies using marine seismic surveys, including the PROBE initiative of the late 1980's and more recent deep surveys offshore Angola. Reprocessing of lines from oil exploration grids reveal Proterozoic mid-lower crustal features offshore of Ghana. Among the potentially rich targets for future surveys in Africa are the West African and Congo cratons and their suturing Pan-African (Neoproterozoic) mobile belts. This suite of cratonic lithosphere elements is largely largely untouched by modern high resolution seismic methodologies. New initiatives such as LEGENDS ( targeting the East African Orogen) and exploitation of existing oil industry seismic data for deep information

  2. Active seismic experiment

    NASA Technical Reports Server (NTRS)

    Kovach, R. L.; Watkins, J. S.; Talwani, P.

    1972-01-01

    The Apollo 16 active seismic experiment (ASE) was designed to generate and monitor seismic waves for the study of the lunar near-surface structure. Several seismic energy sources are used: an astronaut-activated thumper device, a mortar package that contains rocket-launched grenades, and the impulse produced by the lunar module ascent. Analysis of some seismic signals recorded by the ASE has provided data concerning the near-surface structure at the Descartes landing site. Two compressional seismic velocities have so far been recognized in the seismic data. The deployment of the ASE is described, and the significant results obtained are discussed.

  3. Active Seismic Imaging Experiment

    NASA Astrophysics Data System (ADS)

    Berge, Patricia A.; Dawson, Phillip B.; Evans, John R.

    In September 1985 the U.S. Geological Survey (USGS) and Lawrence Livermore National Laboratory (LLNL) will conduct an active seismic experiment in the Medicine Lake area of northern California. The work is supported by the Geothermal Research Program of USGS and by the Geothermal and Hydropower Technologies Division of the U.S. Department of Energy. We invite interested organizations or individuals to record our explosions from Medicine Lake volcano and surrounding areas not covered by the USGS-LLNL array.

  4. Observational study of rock mass response to mining induced seismic events and controlled blasting experiments at deep level gold mines in South Africa

    NASA Astrophysics Data System (ADS)

    Milev, A.; Durrheim, R. J.; Nakatani, M.; Yabe, Y.; Naoi, M. M.; Ogasawara, H.

    2012-12-01

    The strong ground motion generated by mining induced seismic events was studied to characterize the rock mass response and to estimate the site effect on the surface of the underground excavations. A stand-alone instruments, especially designed for recording strong ground motions, were installed underground at a number of deep level gold mines in South Africa. The instruments were recording data at the surface of the stope hangingwalls. A maximum value of 3 m/s was measured. Therefore data were compared to the data recorded in the solid rock by the mine seismic networks to determine the site response. The site response was defined as the ratio of the peak ground velocity measured at the surface of the excavations to the peak ground velocity inferred from the mine seismic data measured in the solid rocks. The site response measured at all mines studied was found to be 9 ± 3 times larger on average. In addition a number of simulated rockbursts were conducted underground in order to estimate the rock mass response when subjected to strong ground motion. The rockbursts were simulated by means of large blasts detonated in solid rock close to the sidewall of a tunnel. The numerical models used in the design of the simulated rockbursts were calibrated by small blasts taking place at each experimental site. A dense array of shock type accelerometers was installed along the blasting wall to monitor the attenuation of the strong ground motion as a function of the distance from the source. The attenuation of peak particle velocity was found to be proportional to R-1.7. In order to improve the understanding of the rock mass behaviour around deep level mining the rate of tilt was monitor and then compare to the seismic ground motion. A good correspondence between the rate of tilt and seismic ground motion was found. The rate of coseismic and aseismic tilt, as well as seismicity recorded by the mine seismic network, are approximately constant until the daily blasting time

  5. Seismic Hazard Implication of the Seismotectonics of southern Africa

    NASA Astrophysics Data System (ADS)

    Midzi, Vunganai; Mulabisana, Thifelimbilu; Manzunzu, Brassnavy

    2014-05-01

    The work presented in this report / presentation was prepared as part of the requirements for the SIDA/IGCP Project 601 titled "Seismotectonics and Seismic Hazards in Africa" as well as part of the seismic source characterisation of the GEM-Africa Seismic hazard study. An effort was made to compile information necessary to prepare a seismotectonic map of Africa which can then be used in carrying out a seismic hazard assessment of the continent or locations within the continent. Information on major faults, fault plane solutions, geophysical data as well as stress data has so far been collected and included in a database for the southern Africa region. Reports published by several experts contributed much to the collected information. The seismicity data used are part of the earthquake catalogue being prepared for the GEM-Africa project, which includes historical and instrumental records as collected from various sources. An effort has been made to characterise the identified major faults and through further analysis investigate their possible impact on the seismic hazard of southern Africa.

  6. Passive seismic experiment

    NASA Technical Reports Server (NTRS)

    Latham, G. V.; Ewing, M.; Press, F.; Sutton, G.; Dorman, J.; Nakamura, Y.; Toksoz, N.; Lammlein, D.; Duennebier, F.

    1972-01-01

    The establishment of a network of seismic stations on the lunar surface as a result of equipment installed by Apollo 12, 14, and 15 flights is described. Four major discoveries obtained by analyzing seismic data from the network are discussed. The use of the system to detect vibrations of the lunar surface and the use of the data to determine the internal structure, physical state, and tectonic activity of the moon are examined.

  7. Strong ground motion generated by controlled blasting experiments and mining induced seismic events recorded underground at deep level mines in South Africa

    NASA Astrophysics Data System (ADS)

    Milev, A.; Selllers, E.; Skorpen, L.; Scheepers, L.; Murphy, S.; Spottiswoode, S. M.

    2011-12-01

    A number of simulated rockbursts were conducted underground at deep level gold mines in South Africa in order to estimate the rock mass response when subjected to strong ground motion. The rockbursts were simulated by means of large blasts detonated in solid rock close to the sidewall of a tunnel. The simulated rockbursts involved the design of the seismic source, seismic observations in the near and far field, high-speed video filming, a study of rock mass conditions such as fractures, joints, rock strength etc. Knowledge of the site conditions before and after the simulated rockbursts was also gained. The numerical models used in the design of the simulated rockbursts were calibrated by small blasts taking place at each experimental site. A dense array of shock type accelerometers was installed along the blasting wall to monitor the attenuation of the strong ground motion as a function of the distance from the source. The attenuation of peak particle velocities, was found to be proportional to R^-1.7. Special investigations were carried out to evaluate the mechanism and the magnitude of damage, as well as the support behaviour under excessive dynamic loading. The strong ground motion generated by mining induced seismic events was studied, as part of this work, not only to characterize the rock mass response, but also to estimate the site effect on the surface of the underground excavations. A stand-alone instrument especially designed for recording strong ground motions was used to create a large database of peak particle velocities measured on stope hangingwalls. A total number of 58 sites located in stopes where the Carbon Leader Reef, Ventersdorp Contact Reef, Vaal Reef and Basal Reef are mined, were monitored. The peak particle velocities were measured at the surface of the excavations to identify the effect of the free surface and the fractures surrounding the underground mining. Based on these measurements the generally accepted velocity criterion of 3 m

  8. AfricaArray: Building science capacity and improving seismic networks in Africa

    NASA Astrophysics Data System (ADS)

    Nyblade, A.; Dirks, P.; Graham, G.

    2007-05-01

    AfricaArray is a long-term initiative to promote coupled training and research programs in geophysics for building and maintaining a scientific workforce for Africa's natural resource sector. The main goals of AfricaArray are to: 1) maintain and develop further geophysical training programs in Africa, in response to industry, government and university needs, 2) promote geophysical research in Africa, and establish an Africa-to-Africa research support system, 3) obtain geophysical data, through a network of shared observatories, to study scientific targets of economic and societal interest, as well as fundamental geological processes shaping the African continent. AfricaArray is supported by a public-private partnership consisting of many government organizations in the US and Africa, and mining and oil companies. AfricaArray has been built on existing programs and expertise within partner institutions and is being implemented in three phases over ten years. During Phase 1 (1/2005 - 12/2007), the educational program at the University of the Witwatersrand is being expanded and improved to provide B.Sc., M.Sc., and Ph.D. degree training in geophysics for students from across Africa. Seismic stations are being installed or upgraded in participating countries to form a network of shared scientific observatories, and technical personnel are being trained to operate and maintain the seismic equipment. Data from the seismic stations are being used for student thesis research projects, and the seismic network is helping to catalyze scientific community building through educational and research collaborations. During subsequent phases (2007-2014), the in-situ education and research program will grow to provide B.Sc., M.Sc. and Ph.D. training for many more African students, the network of shared scientific observatories will be expanded, temporary networks of seismic stations will be installed, sustainable centers of excellence in geophysics will be established at other

  9. Seismic Empirical Relations for the Tellian Atlas, North Africa, and their Usefulness for Seismic Risk Assessment

    NASA Astrophysics Data System (ADS)

    Beghoul, Noureddine; Chatelain, Jean-Luc; Boughacha, Mohamed-Salah; Benhallou, Hadj; Dadou, Rida; Mezioud-Saïch, Amira

    2010-03-01

    Seismic events that occurred during the past half century in the Tellian Atlas, North Africa, are used to establish fundamental seismic empirical relations, tying earthquake magnitude to source parameters (seismic moment, fault plane area, maximal displacement along the fault, and fault plane length). Those empirical relations applied to the overall seismicity from 1716 to present are used to transform the magnitude (or intensity) versus time distribution into (1) cumulative seismic moment versus time, and (2) cumulative displacements versus time. Both of those parameters as well as the computed seismic moment rate, the strain rate along the Tellian Atlas strike, and various other geological observations are consistent with the existence, in the Tellian Atlas, of three distinct active tectonic blocks. These blocks are seismically decoupled from each other, thus allowing consideration of the seismicity as occurring in three different distinct seismotectonic blocks. The cumulative displacement versus time from 1900 to present for each of these tectonic blocks presents a remarkable pattern of recurrence time intervals and precursors associated with major earthquakes. Indeed, most major earthquakes that occurred in these three blocks might have been predicted in time. The Tellian Atlas historical seismicity from the year 881 to the present more substantially confirms these observations, in particular for the western block of the Tellian Atlas. Theoretical determination of recurrence time intervals for the Tellian Atlas large earthquakes using Molnar and Kostrov formalisms is also consistent with these observations. Substantial observations support the fact that the western and central Tellian Atlas are currently at very high seismic risk, in particular the central part. Indeed, most of the accumulated seismic energy in the central Tellian Atlas crust has yet to be released, despite the occurrence of the recent destructive May 2003 Boumerdes earthquake ( M w = 6.8). The

  10. Seismic Anisotropy and Mantle Flow Beneath Northeastern Africa and Arabia

    NASA Astrophysics Data System (ADS)

    Elsheikh, A.; Gao, S. S.; Liu, K. H.; Abdelsalam, M. G.

    2011-12-01

    The Afar Depression in NE Africa hosts the Earth's only RRR triple junction exposed on land, and is an ideal place to study processes involved in the transition from continental rifting to seafloor spreading. In order to image the crust and upper mantle structure under Afar with an unprecedented spatial resolution, eighteen broadband seismic stations were deployed between Dec. 2009 and May 2011 along an approximately 250 km long profile across the Tendaho Graben in central Afar as part of the Afar Lithosphere Imaging Experiment (ALIE). Here we present results from teleseismic shear-wave (XKS) splitting analysis using data from ALIE and all the available broadband seismic data archived at the IRIS Data Center. Several previous studies of shear wave splitting in the region suggested that the observed anisotropy could be attributed to preexisting Precambrian fabrics, while others argue that vertical magmatic dikes or rift parallel mantle flow are responsible for the observed anisotropy. All of those studies utilized limited quality and quantity of XKS measurements which resulted in the inconsistency of conclusions. This work presents about 200 XKS splitting measurements obtained using data from ALIE and over 400 measurements from other stations in Afar, the Main Ethiopian Rift (MER), Ethiopian Plateau, and the Arabian plate. A robust process to reliably assess and objectively rank XKS splitting parameters was used to produce the results. Manual screening was applied to the results of the automatic calculations to ensure that no high quality events were ignored and no low quality results were selected. This study found that the ~450 measurements in the Ethiopian Plateau and in the MER have insignificant azimuthal variations with MER dominated by a rift parallel fast direction suggestive of a single layer of anisotropy. In contrast, measurements in the Afar Depression show a systematic azimuthal dependence of splitting parameters with a 90-degree periodicity, which

  11. New Seismic Images of Crustal Structure Beneath Southern Africa

    NASA Astrophysics Data System (ADS)

    Delph, J. R.; Fouch, M. J.

    2012-12-01

    The deep and complex history of southern Africa makes it a geological nexus for understanding how crust forms, evolves, and survives plate tectonic processes over billions of years. The goal of this study is to provide new constraints on crustal thickness and composition across the Kaapvaal and Zimbabwe Cratons and surrounding mobile belts across a range of geologic terranes ranging in age from the Archean to the Paleozoic. We use data gathered from the 1997-1999 Southern Africa Seismic Experiment (SASE), a broadband seismometer deployment with ~75 km station spacing. We generated P-wave receiver functions for 79 stations using the iterative deconvolution method of Ligorria and Ammon (1999) with a Gaussian pulse width of 2.5, which corresponds to a dominant period of ~2 sec in the receiver functions. We utilized the Funclab receiver function analysis software of Eagar and Fouch (2012) to trace edit receiver functions, and subsequently perform H-κ stacking and Common Conversion Point (CCP) imaging. The use of CCP stacking differentiates our study from previous studies using these data (e.g. Nguuri et al., 2001, Nair et al., 2006), as it provides us with a continuous three-dimensional image of crustal variations throughout southern Africa. We find that crustal thickness in mobile belt regions is thick compared to the cratons, with the exception of the area affected by the Bushveld Complex. The Kaapvaal and eastern Zimbabwe Cratons have a well-defined average Moho depth of ~34 km and Vp/Vs of ~1.73, indicative of intermediate average crustal composition. These results are consistent with a relatively unmodified continental crust due to limited deformation history of these regions since formation. Conversely, the Archean Okwa-Magondi belt, western Zimbabwe Craton, Proterozoic Kheiss thrust belt and Namaqua-Natal, and Paleozoic Cape-Fold belts have Moho depths with a wide range of values from ~36 km to ~47 km, and Vp/Vs values ranging from 1.74 to 1.85 which seem to

  12. Complex Seismic Anisotropy in the Earth's Inner Core Beneath Africa

    NASA Astrophysics Data System (ADS)

    Yu, W.; Wen, L.

    2005-12-01

    Seismic anisotropic velocity structure plays an important role in understanding the geodynamics and mineral physics in the Earth's inner core. Previous seismic studies using the PKiKP-PKIKP phase pairs have suggested no evidence for the presence of anisotropy in velocity in the top 80 km of the inner core. However, the sampling coverage of the PKiKP-PKIKP phase pairs in previous studies was limited, especially along the polar paths. Here we expand our PKiKP-PKIKP dataset by collecting the PKiKP-PKIKP waveforms sampling the inner core globally and along various sampling directions. Our data are selected from the Global Seismographic Network and many regional seismic networks: GEOSCOPE, GEOFON, the Canadian National Seismic Network (CNCN), the Oceanographic Hemisphere Project (OHP), Kazakhstan, and Kyrgyzstan. Our seismic observations show that there is indeed no difference in PKiKP-PKIKP differential travel time residual between the polar and equatorial paths in most regions of the inner core, suggesting no anisotropy in velocity in the top 80 km of the inner core in most regions. Our expanded collection of the PKiKP-PKIKP phases, however, reveals a clear polar-equatorial difference in differential travel time residual in a localized region in the western hemisphere beneath Africa. The PKiKP-PKIKP data sampling along the polar paths in this area of the inner core also exhibit strong lateral variations, requiring the thickness of isotropic layer varying from 10 km or less beneath Uganda and western Africa to 50 km beneath Cameron and Congo. We will show the seismic data grouped according to their sampling regions in the inner core and anisotropic velocity models in each of these regions by waveform modeling the PKiKP-PKIKP data, the PKP data observed at the caustics distance range (141°-145°), and the PKPbc-PKIKP data recorded at larger distances.

  13. Seismic experiment reveals rifting of craton in Tanzania

    NASA Astrophysics Data System (ADS)

    Nyblade, Andrew A.; Langston, Charles A.; Last, Robert J.; Birt, Christopher; Owens, Thomas J.

    A research project in Tanzania, East Africa, is being conducted to examine seismic velocities within the crust and upper mantle in an area where cratonic lithosphere is experiencing extensional tectonism. The results will be used to evaluate models of cratonic structure. Waveforms from several hundred teleseismic earthquakes and over 10,000 regional and local earthquakes recorded in 1994 and 1995 by the Tanzania Broadband Seismic Experiment are not only yielding new insights into deep continental structure, but are also helping to determine the tectonic stability of cratons by identifying the locus of rifting within northeastern Tanzania.

  14. Status of Seismotectonic and seismic hazard studies in South Africa

    NASA Astrophysics Data System (ADS)

    Midzi, V.

    2012-04-01

    Though South Africa is considered to lie in a stable continental region, earthquakes are recorded and located daily. Large events have been recorded that resulted in severe damage to infrastructure in nearby towns, farms, underground mines and even death in some circumstances. Therefore, it is necessary that we consider the effects of these events in the design of our infrastructure. This mitigation is done by carrying out reliable seismic hazard and risk studies of our regions using state of the art methodologies. In South Africa, several regional seismic hazard studies have been carried out and published. Continental wide studies that include the South African region were also published by various scientists from the continent (e.g. GSHAP). However, to ensure that we conform to international best practice in such studies, more studies need and are being done to improve data, knowledge and methodologies used in the assessments. We continue to collect and improve collection methods of historical and instrumental seismicity data. Available geological information is being used to identify and characterize active or capable faults.

  15. Neo-deterministic seismic hazard assessment in North Africa

    NASA Astrophysics Data System (ADS)

    Mourabit, T.; Abou Elenean, K. M.; Ayadi, A.; Benouar, D.; Ben Suleman, A.; Bezzeghoud, M.; Cheddadi, A.; Chourak, M.; ElGabry, M. N.; Harbi, A.; Hfaiedh, M.; Hussein, H. M.; Kacem, J.; Ksentini, A.; Jabour, N.; Magrin, A.; Maouche, S.; Meghraoui, M.; Ousadou, F.; Panza, G. F.; Peresan, A.; Romdhane, N.; Vaccari, F.; Zuccolo, E.

    2014-04-01

    North Africa is one of the most earthquake-prone areas of the Mediterranean. Many devastating earthquakes, some of them tsunami-triggering, inflicted heavy loss of life and considerable economic damage to the region. In order to mitigate the destructive impact of the earthquakes, the regional seismic hazard in North Africa is assessed using the neo-deterministic, multi-scenario methodology (NDSHA) based on the computation of synthetic seismograms, using the modal summation technique, at a regular grid of 0.2 × 0.2°. This is the first study aimed at producing NDSHA maps of North Africa including five countries: Morocco, Algeria, Tunisia, Libya, and Egypt. The key input data for the NDSHA algorithm are earthquake sources, seismotectonic zonation, and structural models. In the preparation of the input data, it has been really important to go beyond the national borders and to adopt a coherent strategy all over the area. Thanks to the collaborative efforts of the teams involved, it has been possible to properly merge the earthquake catalogues available for each country to define with homogeneous criteria the seismogenic zones, the characteristic focal mechanism associated with each of them, and the structural models used to model wave propagation from the sources to the sites. As a result, reliable seismic hazard maps are produced in terms of maximum displacement ( D max), maximum velocity ( V max), and design ground acceleration.

  16. Complex seismic anisotropy in the Earth's inner core beneath Africa

    NASA Astrophysics Data System (ADS)

    Yu, W.; Wen, L.

    2006-05-01

    Seismic anisotropy in the top of the inner core is important to the understanding of the growth and dynamics of the Earth's inner core. The anisotropic structures beneath Africa in the top 80 km of the inner core were not well constrained, due to limited sampling coverage. Here, we analyze a large data-set of the PKiKP-PKIKP phases sampling the top 80 km of the inner core beneath Africa along various sampling directions. The differential travel times of the PKiKP-PKIKP phases sampling Africa reveal polar-equatorial differences. The differential travel times along polar paths are about 0-1.4 s larger than those along equatorial paths, suggesting the presence of anisotropy in velocity in the top 80 km of the inner core beneath Africa. The PKiKP-PKIKP phases along polar paths exhibit a complex lateral gradient from the East to the Middle Africa and a correlation of large (small) differential travel time with small (large) amplitude ratio. Largest differential travel times and smallest amplitude ratios are observed beneath the East Africa (Kenya, Tanzania, Mozambique), while small differential travel times and large amplitude ratios are observed beneath the Middle Africa (Democratic Republic of Congo, Congo, Gabon, Angola). The polar PKiKP-PKIKP waveforms are grouped based on the geographic sampling regions. We perform waveform modeling and iteratively search for the anisotropic velocity and attenuation models that explain the polar PKiKP-PKIKP waveforms in various groups. Most complexities observed in the PKiKP-PKIKP waveforms can be explained by the presence of uniform anisotropy, but with onset of the anisotropy occurring at various depths. The region beneath the East Africa can be explained by a uniform anisotropy model with a magnitude of about 1.7% and an average Q value of 250 present at the inner core boundary (ICB), while the region beneath the Middle Africa can be explained by a model with an isotropic layer in the top and a uniform anisotropy with a

  17. Seismic hazard assessment of Sub-Saharan Africa using geodetic strain rate models

    NASA Astrophysics Data System (ADS)

    Poggi, Valerio; Pagani, Marco; Weatherill, Graeme; Garcia, Julio; Durrheim, Raymond J.; Mavonga Tuluka, Georges

    2016-04-01

    The East African Rift System (EARS) is the major active tectonic feature of the Sub-Saharan Africa (SSA) region. Although the seismicity level of such a divergent plate boundary can be described as moderate, several earthquakes have been reported in historical times causing a non-negligible level of damage, albeit mostly due to the high vulnerability of the local buildings and structures. Formulation and enforcement of national seismic codes is therefore an essential future risk mitigation strategy. Nonetheless, a reliable risk assessment cannot be done without the calibration of an updated seismic hazard model for the region. Unfortunately, the major issue in assessing seismic hazard in Sub-Saharan Africa is the lack of basic information needed to construct source and ground motion models. The historical earthquake record is largely incomplete, while instrumental catalogue is complete down to sufficient magnitude only for a relatively short time span. In addition, mapping of seimogenically active faults is still an on-going program. Recent studies have identified major seismogenic lineaments, but there is substantial lack of kinematic information for intermediate-to-small scale tectonic features, information that is essential for the proper calibration of earthquake recurrence models. To compensate this lack of information, we experiment the use of a strain rate model recently developed by Stamps et al. (2015) in the framework of a earthquake hazard and risk project along the EARS supported by USAID and jointly carried out by GEM and AfricaArray. We use the inferred geodetic strain rates to derive estimates of total scalar moment release, subsequently used to constrain earthquake recurrence relationships for both area (as distributed seismicity) and fault source models. The rates obtained indirectly from strain rates and more classically derived from the available seismic catalogues are then compared and combined into a unique mixed earthquake recurrence model

  18. The Apollo passive seismic experiment

    NASA Technical Reports Server (NTRS)

    Latham, G. V.; Dorman, H. J.; Horvath, P.; Ibrahim, A. K.; Koyama, J.; Nakamura, Y.

    1979-01-01

    The completed data set obtained from the 4-station Apollo seismic network includes signals from approximately 11,800 events of various types. Four data sets for use by other investigators, through the NSSDC, are in preparation. Some refinement of the lunar model based on seismic data can be expected, but its gross features remain as presented two years ago. The existence of a small, molten core remains dependent upon the analysis of signals from a single, far-side impact. Analysis of secondary arrivals from other sources may eventually resolve this issue, as well as continued refinement of the magnetic field measurements. Evidence of considerable lateral heterogeneity within the moon continues to build. The mystery of the much meteoroid flux estimate derived from lunar seismic measurements, as compared with earth-based estimates, remains; although, significant correlations between terrestrial and lunar observations are beginning to emerge.

  19. Middle East, North Africa and Western Eurasia Seismic Research Database

    SciTech Connect

    O'Boyle, J L; Ruppert, S D; Hauk, T F; Dodge, D A; Ganzberger, M D; Ryall, F

    2003-07-14

    The National Nuclear Security Administration (NNSA) Ground-Based Nuclear Explosion Monitoring Research and Engineering (GNEM R&E) Program at Lawrence Livermore National Laboratory (LLNL) has made significant progress populating a comprehensive Seismic Research Database (SRDB) used for deriving seismic calibration parameters for the Middle East, North Africa and Western Eurasia (ME/NA/WE) regions. In addition to an overview of select individual information products, we present an overview of our visualization, integration, validation, and organizational processes. Development of these processes and the LLNL SRDB was necessitated by both the very large amount of data and information involved (over 15 terabytes) and the varied data and research result formats utilized. The LLNL SRDB allows for the collection of raw and contextual seismic data used in research, provides an interface for researchers to access data, provides a framework to store research results and integrate datasets, and supports assembly, integration and dissemination of datasets to the NNSA Knowledge Base (KB). The LLNL SRDB is a flexible and extensible framework consisting of a relational database (RDB), Geographical Information System (GIS), and associated product/data visualization and data management tools. This framework is designed to accommodate large volumes of data in diverse formats from many sources (both in-house-derived research and integrated contractor products), in addition to maintaining detailed quality control and metadata. In order to efficiently organize information within the LLNL SRDB, it was necessary to automate procedures needed to create and update database tables, but a large effort is still required by technicians and scientists to load special datasets, review results of automated processing and resolve quality issues. The LLNL SRDB currently has 3 million reconciled event origins and arrivals from several global, regional and local seismic bulletins and 30 million

  20. Meteoroid flux from passive seismic experiment data

    NASA Technical Reports Server (NTRS)

    Duennebier, F.; Dorman, J.; Lammlein, D.; Latham, G.; Nakamura, Y.

    1975-01-01

    The meteoroid flux hitting the moon is recomputed using new information on the decrease of seismic signal amplitude with range. The new data are principally 17 large meteoroid impacts whose locations have been computed from recordings at all four of the operating Passive Seismic Experiment stations. These data suggest a rapid decrease in amplitudes beyond about 2200 km (chord range) which was not suspected earlier. The new estimate predicts the abundance of meteoroids with masses between 500 and 50,000 g. The result is considerably lower than estimates from earth-based observations, and close to our previous estimate from long-period lunar seismic data.

  1. Experiments on Seismic Metamaterials: Molding Surface Waves

    NASA Astrophysics Data System (ADS)

    Brûlé, S.; Javelaud, E. H.; Enoch, S.; Guenneau, S.

    2014-04-01

    Materials engineered at the micro- and nanometer scales have had a tremendous and lasting impact in photonics and phononics. At much larger scales, natural soils civil engineered at decimeter to meter scales may interact with seismic waves when the global properties of the medium are modified, or alternatively thanks to a seismic metamaterial constituted of a mesh of vertical empty inclusions bored in the initial soil. Here, we show the experimental results of a seismic test carried out using seismic waves generated by a monochromatic vibrocompaction probe. Measurements of the particles' velocities show a modification of the seismic energy distribution in the presence of the metamaterial in agreement with numerical simulations using an approximate plate model. For complex natural materials such as soils, this large-scale experiment was needed to show the practical feasibility of seismic metamaterials and to stress their importance for applications in civil engineering. We anticipate this experiment to be a starting point for smart devices for anthropic and natural vibrations.

  2. Experiments on seismic metamaterials: molding surface waves.

    PubMed

    Brûlé, S; Javelaud, E H; Enoch, S; Guenneau, S

    2014-04-01

    Materials engineered at the micro- and nanometer scales have had a tremendous and lasting impact in photonics and phononics. At much larger scales, natural soils civil engineered at decimeter to meter scales may interact with seismic waves when the global properties of the medium are modified, or alternatively thanks to a seismic metamaterial constituted of a mesh of vertical empty inclusions bored in the initial soil. Here, we show the experimental results of a seismic test carried out using seismic waves generated by a monochromatic vibrocompaction probe. Measurements of the particles' velocities show a modification of the seismic energy distribution in the presence of the metamaterial in agreement with numerical simulations using an approximate plate model. For complex natural materials such as soils, this large-scale experiment was needed to show the practical feasibility of seismic metamaterials and to stress their importance for applications in civil engineering. We anticipate this experiment to be a starting point for smart devices for anthropic and natural vibrations. PMID:24745420

  3. Apollo 14 active seismic experiment.

    PubMed

    Watkins, J S; Kovach, R L

    1972-03-17

    Explosion seismic refraction data indicate that the lunar near-surface rocks at the Apollo 14 site consist of a regolith 8.5 meters thick and characterized by a compressional wave velocity of 104 meters per second. The regolith is underlain by a layer with a compressional wave velocity of 299 meters per second. The thickness of this layer, which we interpret to be the Fra Mauro Formation, is between 16 and 76 meters. The layer immediately beneath this has a velocity greater than 370 meters per second. We found no evidence of permafrost. PMID:17794200

  4. Apollo 14 active seismic experiment.

    NASA Technical Reports Server (NTRS)

    Watkins, J. S.; Kovach, R. L.

    1972-01-01

    Explosion seismic refraction data indicate that the lunar near-surface rocks at the Apollo 14 site consist of a regolith 8.5 meters thick and characterized by a compressional wave velocity of 104 meters per second. The regolith is underlain by a layer with a compressional wave velocity of 299 meters per second. The thickness of this layer, which we interpret to be the Fra Mauro Formation, is between 16 and 76 meters. The layer immediately beneath this has a velocity greater than 370 meters per second. We found no evidence of permafrost.

  5. Permafrost Active Layer Seismic Interferometry Experiment (PALSIE).

    SciTech Connect

    Abbott, Robert; Knox, Hunter Anne; James, Stephanie; Lee, Rebekah; Cole, Chris

    2016-01-01

    We present findings from a novel field experiment conducted at Poker Flat Research Range in Fairbanks, Alaska that was designed to monitor changes in active layer thickness in real time. Results are derived primarily from seismic data streaming from seven Nanometric Trillium Posthole seismometers directly buried in the upper section of the permafrost. The data were evaluated using two analysis methods: Horizontal to Vertical Spectral Ratio (HVSR) and ambient noise seismic interferometry. Results from the HVSR conclusively illustrated the method's effectiveness at determining the active layer's thickness with a single station. Investigations with the multi-station method (ambient noise seismic interferometry) are continuing at the University of Florida and have not yet conclusively determined active layer thickness changes. Further work continues with the Bureau of Land Management (BLM) to determine if the ground based measurements can constrain satellite imagery, which provide measurements on a much larger spatial scale.

  6. Lunar seismic profiling experiment natural activity study

    NASA Technical Reports Server (NTRS)

    Duennebier, F. K.

    1976-01-01

    The Lunar Seismic Experiment Natural Activity Study has provided a unique opportunity to study the high frequency (4-20 Hz) portion to the seismic spectrum on the moon. The data obtained from the LSPE was studied to evaluate the origin and importance of the process that generates thermal moonquakes and the characteristics of the seismic scattering zone at the lunar surface. The detection of thermal moonquakes by the LSPE array made it possible to locate the sources of many events and determine that they are definitely not generated by astronaut activities but are the result of a natural process on the moon. The propagation of seismic waves in the near-surface layers was studied in a qualitative manner. In the absence of an adequate theoretical model for the propagation of seismic waves in the moon, it is not possible to assign a depth for the scattering layer. The LSPE data does define several parameters which must be satisfied by any model developed in the future.

  7. The SEIS Experiment: A Mars Seismic Package

    NASA Technical Reports Server (NTRS)

    Schibler, P.; Lognonne, P.; Giardini, D.; Banerdt, B.; Karczewski, J. F.; Mimoun, D.; Zweifel, P.; Pike, T.; Ammann, J.; Anglade, A.

    2003-01-01

    This experiment will integrate a VBB (Very Broad Band) two axis seismometer, a three axis Short Period seismometer and a series of environmental sensors for pressure, infra-sounds and temperature. IPGP (France) has the overall responsibility of the experiment and is responsible for the VBB and environmental sensors. ETHZ (Switzerland) is responsible for the electronics of the experiment and JPL (USA) for the SP (Short Period) sensors. SEIS instrument was first proposed and accepted for NetLander mission (and will also be in charge of data acquisition for SPICE experiment). This seismic package should also be proposed for future missions.

  8. Upper Mantle Seismic Structure Beneath Southern Africa: Constraints on the Buoyancy Supporting the African Superswell

    NASA Astrophysics Data System (ADS)

    Brandt, Martin B. C.; Grand, Stephen P.; Nyblade, Andrew A.; Dirks, Paul H. G. M.

    2012-04-01

    We present new one-dimensional SH-wave velocity models of the upper mantle beneath the Kalahari craton in southern Africa obtained from waveform inversion of regional seismograms from an Mw = 5.9 earthquake located near Lake Tanganyika recorded on broadband seismic stations deployed during the 1997-1999 Southern African Seismic Experiment. The velocity in the lithosphere beneath the Kalahari craton is similar to that of other shields, and there is little evidence for a significant low velocity zone beneath the lithosphere. The lower part of the lithosphere, from 110 to 220 km depth, is slightly slower than beneath other shields, possibly due to higher temperatures or a decrease in Mg number (Mg#). If the slower velocities are caused by a thermal anomaly, then slightly less than half of the unusually high elevation of the Kalahari craton can be explained by shallow buoyancy from a hot lithosphere. However, a decrease in the Mg# of the lower lithosphere would increase the density and counteract the buoyancy effect of the higher temperatures. We obtain a thickness of 250 ± 30 km for the mantle transition zone, which is similar to the global average, but the velocity gradient between the 410 and 660 km discontinuities is less steep than in global models, such as PREM and IASP91. We also obtain velocity jumps of between 0.16 ± 0.1 and 0.21 ± 0.1 km/s across the 410 km discontinuity. Our results suggest that there may be a thermal or chemical anomaly in the mantle transition zone, or alternatively that the shear wave velocity structure of the transition zone in global reference models needs to be refined. Overall, our seismic models provide little support for an upper mantle source of buoyancy for the unusually high elevation of the Kalahari craton, and hence the southern African portion of the African Superswell.

  9. Upper Mantle Seismic Velocity Structure Beneath Eastern Africa and the Origin of Cenozoic Extensional Tectonism (Invited)

    NASA Astrophysics Data System (ADS)

    Nyblade, A.; Julia, J.; Adams, A. N.; Mulibo, G. D.; Tugume, F. A.

    2009-12-01

    The seismic structure of the upper mantle beneath eastern Africa will be reviewed using results from body wave tomography, surface wave tomography, and images of the 410 and 660 km discontinuities. Most of the data used for obtaining these results come from temporary deployments of broadband seismic stations in Ethiopia, Kenya, Uganda and Tanzania over the past decade. The ensemble of seismic results point to a deep-seated low velocity zone beneath the East African rift system that extends from the uppermost mantle, through the upper mantle, and into the mantle transition zone. The low velocity anomaly may also extend through the mantle transition zone and link with the low velocity zone in the lower mantle under southern Africa, commonly referred to as the African Superplume. This is in contrast to southern Africa, were there is little evidence for a pronounced low velocity anomaly in the upper mantle. The existence of a seismic low velocity zone beneath eastern African that extends to depths of more than 500 km supports the possibility that there is a geodynamic connection between the African Superplume and the origin of Cenozoic extensional tectonism in eastern Africa.

  10. Expeditionary medicine in Africa: the French experience.

    PubMed

    Kaiser, Eric; Kenane, Maj Nadia; Montcriol, Ambroise; Palmier, Bruno

    2007-07-01

    The French army is often engaged in stability and support operations in Africa, and its military health service has gained much experience. The goal of this article is to present our military medical management strategies during the two main phases of military action. These situations most often begin with an initial combat phase, with combat casualty care. This consists of first aid, i.e., treatment of bleeding points, followed by battlefield forward medical care, damage control surgery, and resuscitation in forward surgical units. The quieter second phase of peacekeeping operations is dominated by the management of tropical diseases and their prevention, essential for the preservation of the military strength. PMID:17691682

  11. Seismic-while-drilling data processing with seismic interferometry in the Daqing Oilfield experiment

    NASA Astrophysics Data System (ADS)

    Liu, Hongtao 1Huang, Weichuan 24Li, Yuquan

    2014-03-01

    Seismic interferometry was used to process the data collected with seismic-while-drilling (SWD) experiments at the Daqing Oilfield. The experiments simultaneously recorded the data at the drilling stem and on the ground. After conducting the frequency and the energy property analysis, the data was processed using the correlation and deconvolution method. Seismic data was then obtained from excitation of the drill bit. The result maps show that the deconvolution method can suppress the source effects and enhance the resolution of the profile, and that the vertical stacks enhance the seismic response of the subsurface. The interferometry process after band-filtering can obtain maps with very high resolution. Seismic interferometry by deconvolution shows great advantages based on the results of this experimental data. The method can also be applied to the SWD data and the ambient seismic data to obtain better processing results.

  12. Preliminary maps of crustal thickness and regional seismic phases for the Middle East and North Africa

    SciTech Connect

    Sweeney, J.J.

    1995-09-06

    As part of the development of regional seismic discrimination methods for the Middle East and North Africa (MENA) the author is building a database of information related to seismic propagation and crustal structure as well as associated geologic-tectonic and geophysical data. He hopes to use these data to construct and test models of regional seismic propagation and evaluate various detection/discrimination scenarios. To date, the database has been developed by building on a list of references for MENA provided by the Institute for the Study of the Continents (INSTOC) at Cornell University. To this list the author has added an equal number of references resulting from his own literature search which has emphasized papers dealing with seismicity and regional and teleseismic phase data. This paper represents an initial attempt to consolidate some of the information from the database into a form useful to researchers modeling regional seismic waveforms. The information compiled in this report is supplemental to the INSTOC database and has not been compiled anywhere else. What follows is a series of maps which illustrate the spatial variation of seismic phase velocities and crustal thickness. The text identifies the sources of information used in the map preparation. Data for the compilation of these maps has come from an initial search of the database as it presently exists and is not intended to be exhaustive. The author hopes that this initial exercise will help to identify areas and types of data that are deficient and help to focus future data gathering activities.

  13. Seismic anisotropy and mantle fabrics beneath eastern Africa and Arabia

    NASA Astrophysics Data System (ADS)

    Elsheikh, A. A.; Gao, S. S.; Liu, K. H.

    2013-12-01

    In spite of numerous studies, the mechanisms for the rifting, uplifting, and volcanism on the African plate remain enigmatic. The most popular hypotheses proposed to explain these tectonic phenomena involve edge-driven small-scale mantle convection and the thermal or dynamic effects of one or more mantle plumes. In particular, several recent models suggested that the rise of the African plateaus and western Arabia was due to the dynamic upwelling of an active mantle plume located beneath southern Africa, despite of the fact that most studies revealed that the mantle transition zone beneath southern Africa has a normal temperature. In this study we use continental scale shear-wave splitting measurements to provide additional constraints on the various models of rifting and uplifting of the African plate. The splitting of P-to-S converted phases at the core-mantle boundary on the receiver side (XKS including PKS, SKKS, and SKS) is one of the most effective approaches to image mantle flow, and to constrain convective mantle flow patterns. Most of the previous shear-wave splitting (SWS) studies in eastern Africa and Arabia assumed a single anisotropic layer as the source of the observed shear-wave splitting. Some studies attributed the observed anisotropy to Precambrian lithospheric fabric developed during compressional orogenic events, while others emphasized the role of mantle flow. Almost all of these studies focused on restricted geographic regions or used a limited number of stations, which led to results applicable to localized areas rather than a continent-wide scale. In addition, the results were presented as station-averages, which prevent the identification of complex anisotropy. This presentation reports preliminary results from an ongoing study using all the broadband XKS data available at the IRIS Data Management Center. The data set was recorded by more than 200 stations in east Africa and Arabia. We are in the process to produce a uniform SWS database

  14. An integrated study of reservoir-induced seismicity and Landsat imagery at Lake Kariba, Africa

    SciTech Connect

    Pavlin, G.B.; Langston, C.A.

    1983-04-01

    Seismological techniques combined with Landsat imagery were used to study the seismic activity near Lake Kariba in southern Africa. The activity began after construction of a reservoir. Under investigation since the 1930s, reservoir-induced seismicity (RIS) has been limited to reservoirs with a volume larger than 1.2 billion cu m. Attempts have been made to identify the fault plane orientation best correlated with RIS to understand the triggering mechanisms. Concatenated Landsat imagery from band 6 provided lineaments and constrained the fault parameter solutions. An occurrence of P and SH waveforms recorded during a 1963 6.0 Richter scale event served for identifying the faulting orientation, the seismic moments, source depth, and an estimation of the spatially integrated slip function at the source. The source depths were less than 10 km, and it is suggested that a Precambrian basement, separated by normal faults, was adjusting dynamically to the reservoir loads.

  15. Crust and Upper Mantle of North Africa Using Libyan Seismic Data

    NASA Astrophysics Data System (ADS)

    Pasyanos, M. E.; Eshwehdi, A.

    2005-12-01

    We investigate the crust and upper mantle structure of North Africa using Libyan seismic data. Libya sits at the transition between the relatively aseismic continental crust of the African plate and the seismically active oceanic crust under the Mediterranean Sea which is subducting under the Eurasian Plate along the Calabrian, Hellenic, and Cyprean Arcs. The country also encompasses the Sirte Basin to the north and the smaller Murzuk and Kufra basins in the south. Broadband data from several seismic stations in Libya provide an opportunity for studying the velocity structure of the region. We have made some preliminary dispersion measurements from these stations and have found notable improvements in the group velocity tomography model by incorporating the additional measurements. We will be adding to this analysis by making dispersion measurements from regional events and receiver functions for teleseismic events. Recently, we have been employing methods to jointly invert both surface wave dispersion data and teleseismic receiver functions. The technique holds great promise in accurately estimating seismic structure, including important tectonic parameters such as basin thickness, crustal thickness, upper mantle velocity, as well as more detail about the upper mantle (lithospheric thickness and presence of anisotropy). We propose to apply this method to data from several Libyan stations where we can and, in the absence of receiver functions, invert the dispersion data only. The technique holds the promise of improving our understanding of the crust and upper mantle in Libya and how it fits into the larger tectonic picture of North Africa.

  16. Seismic Anisotropy beneath the African Plate using Shear Wave Splitting Measurements from AfricaArray Stations

    NASA Astrophysics Data System (ADS)

    Nunley, M. E.; Weeraratne, D.; Nyblade, A.

    2011-12-01

    The African continental plate is made up of a series of cratons and fold belts with activation ages ranging from present to Archean. Recent studies have shown that this tectonic assemblage occurred over a long history of accretion and rifting cycles that likely left behind the complex crust and lithospheric fabric that we see today. Here we study seismic anisotropy beneath the African continent using a large array of permanent AfricaArray and Global Seismic Network seismic stations located throughout Africa. We supply shear wave splitting techniques to teleseismic earthquake events using the eigenvalue method where the second eigenvalue is minimized to determine anisotropy. Stations located in the Ethiopian rift zone yield a NE-SW fast direction with the largest delay times of 1.5s. One station (KOWA) located in the west African craton displays a NW-SE fast direction. Stations located near Cameroon, at the coastal edge of the central African shear zone, produce NW-SE fast directions oriented perpendicular to the shear zone axis. . A group of stations located on Archean crust in central Africa skirt the Congo craton and display consistent NNE fast directions and delay times of 1.0s. Two stations, LSZ and TEZI are located in the Damara suture belt between the Congo and Kaapvaal cratons display a NE-SW fast direction parallel to the suture axis. In the Kaapvaal craton region the average anisotropic direction is NNE with a 1.0s delay time. New stations available south of the Kaapvaal craton reveal a NE fast direction with delay times that vary from 0.5 to 1.3 s. Several splitting measurements are made for the southern station HVD which display backazimuth dependence producing NW-SE fast directions for ray paths coming from the east and are consistent with observations at GRM located east of HVD. These results show that seismic anisotropy across the continent is not uniform and shows significant variation between tectonic regions. While mantle flow and lithospheric

  17. Shallow lunar structure determined from the passive seismic experiment

    NASA Technical Reports Server (NTRS)

    Nakamura, Y.; Dorman, J.; Duennebier, F.; Lammlein, D.; Latham, G.

    1975-01-01

    Data relevant to the shallow structure of the moon obtained at the Apollo seismic stations are compared with previously published results of the active seismic experiments. It is concluded that the lunar surface is covered by a layer of low seismic velocity which appears to be equivalent to the lunar regolith defined previously by geological observations. This layer is underlain by a zone of distinctly higher seismic velocity at all of the Apollo landing sites. The regolith thicknesses at the Apollo 11, 12, and 15 sites are estimated from the shear-wave resonance to be 4.4, 3.7, and 4.4 m, respectively. These thicknesses and those determined at the other Apollo sites by the active seismic experiments appear to be correlated with the age determinations and the abundances of extralunar components at the sites.

  18. Seismic Migration Imaging of the Lithosphere beneath the Afar Rift System, East Africa

    NASA Astrophysics Data System (ADS)

    Lee, T. T. Y.; Chen, C. W.; Rychert, C.; Harmon, N.

    2015-12-01

    The Afar Rift system in east Africa is an ideal natural laboratory for investigating the incipient continental rifting, an essential component of plate tectonics. The Afar Rift is situated at the triple junction of three rifts, namely the southern Red Sea Rift, Gulf of Aden Rift and Main Ethiopian Rift (MER). The ongoing continental rifting at Afar transitions to seafloor spreading toward the southern Red Sea. The tectonic evolution of Afar is thought to be influenced by a mantle plume, but how the plume affects and interacts with the Afar lithosphere remains elusive. In this study, we use array seismic data to produce high-resolution migration images of the Afar lithosphere from scattered teleseismic wavefields to shed light on the lithospheric structure and associated tectonic processes. Our preliminary results indicate the presence of lithospheric seismic discontinuities with depth variation across the Afar region. Beneath the MER axis, we detect a pronounced discontinuity at 55 km depth, characterized by downward fast-to-slow velocity contrast, which appears to abruptly deepen to 75 km depth to the northern flank of MER. This discontinuity may be interpreted as the lithosphere-asthenosphere boundary. Beneath the Ethiopian Plateau, on the other hand, a dipping structure with velocity increase is identified at 70-90 km depth. Further synthesis of observations from seismic tomography, receiver functions, and seismic anisotropy in the Afar region will offer better understanding of tectonic significance of the lithospheric discontinuities.

  19. Mammoth Mountain, California broadband seismic experiment

    NASA Astrophysics Data System (ADS)

    Dawson, P. B.; Pitt, A. M.; Wilkinson, S. K.; Chouet, B. A.; Hill, D. P.; Mangan, M.; Prejean, S. G.; Read, C.; Shelly, D. R.

    2013-12-01

    Mammoth Mountain is a young cumulo-volcano located on the southwest rim of Long Valley caldera, California. Current volcanic processes beneath Mammoth Mountain are manifested in a wide range of seismic signals, including swarms of shallow volcano-tectonic earthquakes, upper and mid-crustal long-period earthquakes, swarms of brittle-failure earthquakes in the lower crust, and shallow (3-km depth) very-long-period earthquakes. Diffuse emissions of C02 began after a magmatic dike injection beneath the volcano in 1989, and continue to present time. These indications of volcanic unrest drive an extensive monitoring effort of the volcano by the USGS Volcano Hazards Program. As part of this effort, eleven broadband seismometers were deployed on Mammoth Mountain in November 2011. This temporary deployment is expected to run through the fall of 2013. These stations supplement the local short-period and broadband seismic stations of the Northern California Seismic Network (NCSN) and provide a combined network of eighteen broadband stations operating within 4 km of the summit of Mammoth Mountain. Data from the temporary stations are not available in real-time, requiring the merging of the data from the temporary and permanent networks, timing of phases, and relocation of seismic events to be accomplished outside of the standard NCSN processing scheme. The timing of phases is accomplished through an interactive Java-based phase-picking routine, and the relocation of seismicity is achieved using the probabilistic non-linear software package NonLinLoc, distributed under the GNU General Public License by Alomax Scientific. Several swarms of shallow volcano-tectonic earthquakes, spasmodic bursts of high-frequency earthquakes, a few long-period events located within or below the edifice of Mammoth Mountain and numerous mid-crustal long-period events have been recorded by the network. To date, about 900 of the ~2400 events occurring beneath Mammoth Mountain since November 2011 have

  20. 2013 East Bay Seismic Experiment (EBSE): implosion data, Hayward, Calif

    USGS Publications Warehouse

    Catchings, Rufus D.; Strayer, Luther M.; Goldman, Mark R.; Criley, Coyn J.; Garcia, Susan; Sickler, Robert R.; Catchings, Marisol K.; Chan, Joanne; Gordon, Leslie C.; Haefner, Scott; Blair, James Luke; Gandhok, Gini; Johnson, Michaela R.

    2015-01-01

    In August 2013, the California State University, East Bay (CSUEB) in Hayward, California imploded a 13-story building (Warren Hall) that was deemed unsafe because of its immediate proximity to the active trace of the Hayward Fault. The U.S. Geological Survey (USGS) and the CSUEB collaborated on a program to record the seismic waves generated by the collapse of the building. We refer to this collaboration as the East Bay Seismic Experiment (EBSE). The principal objective of recording the seismic energy was to observe ground shaking as it radiated from the source, but the data also may be useful for other purposes. For example, the seismic data may be useful in evaluating the implosion process as it relates to structural engineering purposes. This report provides the metadata needed to utilize the seismic data.

  1. Education in Colonial Africa: The German Experience

    ERIC Educational Resources Information Center

    vanderPloeg, Arie J.

    1977-01-01

    Examines the introduction and growth of state-supported schools in two German colonies in Africa, Kamerun and Deutsch Ostafrika, describes African reaction to and utilization of them, assesses, from the colonial perspective, why such schools were introduced and what they were intended to accomplish, and examines the reasons for their differential…

  2. The Mars SEIS Experiment: A Mars Seismic Package

    NASA Technical Reports Server (NTRS)

    Mimoun, D.; Lognonne, P.; Banerdt, W. B.; Schibler, P.; Giardini, D.; Pont, G.

    2005-01-01

    The Mars SEIS experiment. The SEIS experiment was first proposed by IPGP (and accepted) for the NetLander mission. It integrates two VBB (Very Broad Band) seismometers, a three axis Short Period seismometer and a series of environmental sensors for pressure, infra-sounds and temperature. IPGP (France) has the overall responsibility of the experiment and is responsible for the seismic and environmental sensors. ETHZ (Switzerland) is responsible for the electronics of the experiment and JPL (USA) for the SP (Short Period) sensors. As NetLander mission has been cancelled (while fortunately the development still goes on), this seismic package can be proposed for future Mars missions.

  3. Results from the Apollo passive seismic experiment

    NASA Technical Reports Server (NTRS)

    Latham, G.; Nakamura, Y.; Dorman, J.; Duennebier, F.; Ewing, M.; Lammlein, D.

    1977-01-01

    Recent results from the Apollo Seismic Network suggest that primitive differentiation occurred in the outer shell of the moon to a depth of approximately 300 km and the central region of the moon is presently molten to a radius of between 200 and 300 km. If early melting to a depth of 300 to 400 km was a consequence of accretional energy, very short accretion times are required. It was shown that the best model for the zone of original differentiation is a crust 40 to 80 km thick, ranging in composition from anorthositic gabbro to gabbro, and overlying an ultramafic cumulate about 250 km thick. The best candidate for the molten core appears to be iron or iron sulphide. A new class of seismic signals recently were identified that may correspond to shallow moonquakes. These are rare, but much more energetic than the more numerous, deep moonquakes.

  4. Results from the Apollo passive seismic experiment

    NASA Technical Reports Server (NTRS)

    Lathum, G.; Nakamura, Y.; Dorman, J.; Duennebier, F.; Ewing, M.; Lammlein, D.

    1974-01-01

    Recent results from the Apollo seismic network suggest that primitive differentiation occurred in the outer shell of the moon to a depth of approximately 300 km; and the central region of the moon is presently molten to a radius of between 200 and 300 km. If early melting to a depth of 300 to 400 km was a consequence of accretional energy, very short accretion times are required. The best model for the zone of original differentiation appears to be a crust 40 to 80 km thick, ranging in composition from anorthositic gabbro to gabbro; overlying an ultramafic cumulate (olivine-pyroxene) about 250 km thick. The best candidate for the molten core appears to be iron or iron sulphide. A new class of seismic signals has recently been identified that may correspond to shallow moonquakes. These are rare, but much more energetic than the more numerous, deep moonquakes.

  5. Participation in the Apollo passive seismic experiment

    NASA Technical Reports Server (NTRS)

    Press, F.; Toksoez, M. N.; Dainty, A.

    1972-01-01

    Computer programs which were written to read digital tapes containing lunar seismic data were studied. Interpreting very early parts of the lunar seismogram as seismic body-wave phases enabled the determination of the structure of the outer part of the moon in the Fra Mauro region. The crust in the Fra Mauro region is 60 to 65 km-thick, overlaying a high velocity mantle. The crust is further divided into an upper part, 25 km thick, apparently made of material similar to the surficial basalts, and a lower part of seemingly different composition, possibly an anorthositic gabbro. The generation of the exceedingly long reverberating wave-train observed in lunar seismogram was also studied. This is believed to be due to an intense scattering layer with very high quality coefficient overlying a more homogeneous elastic medium. Titles and abstracts of related published papers are included.

  6. Explosives for Lunar Seismic Profiling Experiment (LSPE)

    NASA Technical Reports Server (NTRS)

    1973-01-01

    Explosive charges of various sizes were investigated for use in lunar seismic studies. Program logistics, and the specifications for procurement of bulk explosives are described. The differential analysis, thermal properties, and detonation velocity measurements on HNS/Teflon 7C 90/10 are reported along with the field tests of the hardware. It is concluded that nearly all large explosive charges crack after fabrication, from aging or thermal shock. The cracks do not affect the safety, or reliability of the explosives.

  7. The Lusi seismic experiment: An initial study to understand the effect of seismic activity to Lusi

    NASA Astrophysics Data System (ADS)

    Karyono, Mazzini, Adriano; Lupi, Matteo; Syafri, Ildrem; Masturyono, Rudiyanto, Ariska; Pranata, Bayu; Muzli, Widodo, Handi Sulistyo; Sudrajat, Ajat; Sugiharto, Anton

    2015-04-01

    The spectacular Lumpur Sidoarjo (Lusi) eruption started in northeast Java on the 29 of May 2006 following a M6.3 earthquake striking the island [1,2]. Initially, several gas and mud eruption sites appeared along the reactivated strike-slip Watukosek fault system [3] and within weeks several villages were submerged by boiling mud. The most prominent eruption site was named Lusi. The Lusi seismic experiment is a project aims to begin a detailed study of seismicity around the Lusi area. In this initial phase we deploy 30 seismometers strategically distributed in the area around Lusi and along the Watukosek fault zone that stretches between Lusi and the Arjuno Welirang (AW) complex. The purpose of the initial monitoring is to conduct a preliminary seismic campaign aiming to identify the occurrence and the location of local seismic events in east Java particularly beneath Lusi.This network will locate small event that may not be captured by the existing BMKG network. It will be crucial to design the second phase of the seismic experiment that will consist of a local earthquake tomography of the Lusi-AW region and spatial and temporal variations of vp/vs ratios. The goal of this study is to understand how the seismicity occurring along the Sunda subduction zone affects to the behavior of the Lusi eruption. Our study will also provide a large dataset for a qualitative analysis of earthquake triggering studies, earthquake-volcano and earthquake-earthquake interactions. In this study, we will extract Green's functions from ambient seismic noise data in order to image the shallow subsurface structure beneath LUSI area. The waveform cross-correlation technique will be apply to all of recordings of ambient seismic noise at 30 seismographic stations around the LUSI area. We use the dispersive behaviour of the retrieved Rayleigh waves to infer velocity structures in the shallow subsurface.

  8. The Lusi seismic experiment: An initial study to understand the effect of seismic activity to Lusi

    SciTech Connect

    Karyono; Mazzini, Adriano; Sugiharto, Anton; Lupi, Matteo; Syafri, Ildrem; Masturyono,; Rudiyanto, Ariska; Pranata, Bayu; Muzli,; Widodo, Handi Sulistyo; Sudrajat, Ajat

    2015-04-24

    The spectacular Lumpur Sidoarjo (Lusi) eruption started in northeast Java on the 29 of May 2006 following a M6.3 earthquake striking the island [1,2]. Initially, several gas and mud eruption sites appeared along the reactivated strike-slip Watukosek fault system [3] and within weeks several villages were submerged by boiling mud. The most prominent eruption site was named Lusi. The Lusi seismic experiment is a project aims to begin a detailed study of seismicity around the Lusi area. In this initial phase we deploy 30 seismometers strategically distributed in the area around Lusi and along the Watukosek fault zone that stretches between Lusi and the Arjuno Welirang (AW) complex. The purpose of the initial monitoring is to conduct a preliminary seismic campaign aiming to identify the occurrence and the location of local seismic events in east Java particularly beneath Lusi.This network will locate small event that may not be captured by the existing BMKG network. It will be crucial to design the second phase of the seismic experiment that will consist of a local earthquake tomography of the Lusi-AW region and spatial and temporal variations of vp/vs ratios. The goal of this study is to understand how the seismicity occurring along the Sunda subduction zone affects to the behavior of the Lusi eruption. Our study will also provide a large dataset for a qualitative analysis of earthquake triggering studies, earthquake-volcano and earthquake-earthquake interactions. In this study, we will extract Green’s functions from ambient seismic noise data in order to image the shallow subsurface structure beneath LUSI area. The waveform cross-correlation technique will be apply to all of recordings of ambient seismic noise at 30 seismographic stations around the LUSI area. We use the dispersive behaviour of the retrieved Rayleigh waves to infer velocity structures in the shallow subsurface.

  9. Transformative Learning Experiences of International Graduate Students from Africa

    ERIC Educational Resources Information Center

    Kumi-Yeboah, Alex

    2014-01-01

    This article examines factors that influence transformative learning experiences of international graduate students from Africa. In general, 84.8% of the participants experienced transformative learning while 15.2% reported no transformative experiences. For those who experienced transformative learning, 26.1% of the transformative experiences…

  10. Third Party Borehole Seismic Experiments During the Ocean Drilling Program

    NASA Astrophysics Data System (ADS)

    Swift, S. A.; Stephen, R. A.; Hoskins, H.; Bolmer, T.

    2003-12-01

    Third party borehole seismic experiments on the Ocean Drilling Program began with an oblique seismic experiment on Leg 102 at Site 418 in the Western Atlantic. Upper ocean crust here is characterized by a normal seismic layer 2 vertical velocity gradient, lateral velocity variations, azimuthal anisotropy, and azimuth dependent scattering. A normal incidence VSP was run on Leg 118 in the gabbro sequence at Hole 735B on the Southwest Indian Ridge. The vertical seismic velocity inferred from arrival times is similar to that observed horizontally by refraction in ocean layer 3, but attenuation is anomalously high, which prompted the hypothesis that the gabbro cored may not actually represent the bulk of Layer 3 material. The VSP data acquired at Hole 504B in the eastern equatorial Pacific on Legs 111 and 148 helped to constrain the P and S velocity structure at the site and showed that upper layer 3 at this site, at a depth of over 2 km into the crust, consisted of the lower portion of the sheeted dikes rather than gabbro. Both offset and normal incidence VSPs were run on Leg 164 to study the seismic velocity structure of gas hydrates on the Blake Ridge. A new innovation on ODP was the deployment of broadband seismometers in boreholes. Whereas the conventional VSPs and offset VSPs mentioned above operate in the frequency range from 1 to 100Hz, broadband seismometers are used in earthquake seismology and operate in the range from 0.001 to 10Hz. The first broadband seismometer test was carried out from the drill ship on Leg 128 in the Japan Sea. Subsequently 4 permanent broadband borehole seismic observatories were installed in the Western Pacific and Japan Trench on Legs 186, 191 and 195. The ODP era also saw the development of systems for re-entering boreholes from conventional research vessels after the drill ship left the site. Borehole seismic experiments and installations that used this wireline re-entry technology were carried out in DSDP Holes 534 (Blake

  11. Small Arrays for Seismic Intruder Detections: A Simulation Based Experiment

    NASA Astrophysics Data System (ADS)

    Pitarka, A.

    2014-12-01

    Seismic sensors such as geophones and fiber optic have been increasingly recognized as promising technologies for intelligence surveillance, including intruder detection and perimeter defense systems. Geophone arrays have the capability to provide cost effective intruder detection in protecting assets with large perimeters. A seismic intruder detection system uses one or multiple arrays of geophones design to record seismic signals from footsteps and ground vehicles. Using a series of real-time signal processing algorithms the system detects, classify and monitors the intruder's movement. We have carried out numerical experiments to demonstrate the capability of a seismic array to detect moving targets that generate seismic signals. The seismic source is modeled as a vertical force acting on the ground that generates continuous impulsive seismic signals with different predominant frequencies. Frequency-wave number analysis of the synthetic array data was used to demonstrate the array's capability at accurately determining intruder's movement direction. The performance of the array was also analyzed in detecting two or more objects moving at the same time. One of the drawbacks of using a single array system is its inefficiency at detecting seismic signals deflected by large underground objects. We will show simulation results of the effect of an underground concrete block at shielding the seismic signal coming from an intruder. Based on simulations we found that multiple small arrays can greatly improve the system's detection capability in the presence of underground structures. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

  12. Bighorns Arch Seismic Experiment (BASE): Amplitude Response to Different Seismic Charge Configurations

    SciTech Connect

    Harder, S. H., Killer, K. C., Worthington, L. L., Snelson, C. M.

    2010-09-02

    Contrary to popular belief, charge weight is not the most important engineering parameter determining the seismic amplitudes generated by a shot. The scientific literature has long claimed that the relationship, A ~R2L1/2, where A is the seismic amplitude generated by a shot, R is the radius of the seismic charge and L is the length of that charge, holds. Assuming the coupling to the formation and the pressure generated by the explosive are constants, this relationship implies that the one should be able to increase the charge radius while decreasing the charge length and obtain more seismic amplitude with less charge weight. This has significant implications for the economics of lithospheric seismic shots, because shallower holes and small charge sizes decrease cost. During the Bighorns Array Seismic Experiment (BASE) conducted in the summer of 2010, 24 shots with charge sizes ranging from 110 to 900 kg and drill hole diameters of 300 and 450 mm were detonated and recorded by an array of up to 2000 single-channel Texan seismographs. Maximum source-receiver offset of 300 km. Five of these shots were located within a one-acre square in an effort to eliminate coupling effects due to differing geological formations. We present a quantitative comparison of the data from these five shots to experimentally test the equation above.

  13. Small-scale variations in seismic anisotropy near Kimberley, South Africa

    NASA Astrophysics Data System (ADS)

    Fouch, Matthew J.; Silver, Paul G.; Bell, David R.; Lee, Jean N.

    2004-05-01

    We have exploited a new data set of broad-band seismic waveforms recorded near the region of Kimberley, South Africa to place new constraints on seismic anisotropy in an area of extensive mantle modification within an Archaean cratonic setting. The Kimberley region is significant in that it represents Archaean cratonic mantle that has been studied extensively via petrologic, geochemical and seismic means, and provides a unique opportunity to meld the results of a broad range of data sets to examine processes of crust and mantle deformation. Shear wave splitting observations using SKS phases recorded by a dense broad-band seismic array in the Kimberley region exhibit consistent fast polarization directions of ~NE-SW and splitting times that range from 0.15 s in the SE to nearly 0.75 s in the NW regions of the array. Multi-channel cross-correlation of relative arrival times of teleseismic SKS phases across the array reveals clear azimuthal variations and a relative arrival-time range comparable to the shear wave splitting delay-time range. A like analysis of teleseismic PKPdf phases does not exhibit significant differences in relative arrival times across the array. The combined relative arrival time and splitting analyses indicate that a significant change in the strength of anisotropic structure is required across the region. Our results are most consistent with a model in which variations in seismic anisotropy near the Kimberley region are constrained to the lithosphere with an average anisotropic strength of ~1.8 per cent, extend to depths no greater than 150 km and are primarily controlled by a significant change in the strength of anisotropy within the lateral bounds of the seismic array. This inferred structural boundary is near the location of the ca 2.9 Gyr old Colesberg magnetic lineament, a prominent aeromagnetic feature interpreted as the primary suture zone joining the eastern Meso-Archaean and western Neo-Archaean blocks of the Kaapvaal craton. The

  14. An active seismic experiment proposal onboard the NASA 2009 MSL

    NASA Astrophysics Data System (ADS)

    Lognonné, P.; Experiment Team

    NASA will launch in 2009 a 900 kg class rover to Mars. This rover will land with a new descent system, called the ``sky-crane''. After releasing the rover on the ground, the sky-crane will have a final flight until a hard landing about 2 km away from the rover. The science objectives of the 2009 MSL mission, among others, are to characterize the geology of the landing region at all appropriate spatial scales, to interpret the processes that have formed and modified rocks and regolith and to determine present state, distribution, and cycling of water. We propose to perform with the sky-crane an active seismic experiment for subsurface characterization. This experiment will be conducted after the rover deployment. The proposed idea is to deploy a seismic receiver line by ejecting about 10 seismic nodes from the sky-crane and then to record then the reflected signals from the impact of the sky-crane. Preliminary modeling and tests indicate that a penetration depth of several hundred meters will be reached. The experiment will be used to determine a 2D geological profile of the landing site subsurface, to determine the depth and shape of the dry regolith/icy regolith discontinuity and to identify possible layering structures in the subsurface. In addition, information on the structure of the regolith (mean size of building blocs) and on the presence of liquid water will be obtained by an analysis of the seismic coda and attenuation. The seismic high frequency noise will also be monitored, especially during windy periods, and will be used to get additional information on the subsurface. The proposed experiment is based on a consortium between academics laboratories and seismic industry and will be a first example of a resource oriented experiment on another planet than Earth. The complete mass of the experiment will be 2.5 kg. Seismic nodes will have their own acquisition/power and telemetry system and will be based on high sensitive geophones developed for seismic

  15. The LUSI Seismic Experiment: Deployment of a Seismic Network around LUSI, East Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Karyono, Karyono; Mazzini, Adriano; Lupi, Matteo; Syafri, Ildrem; Haryanto, Iyan; Masturyono, Masturyono; Hadi, Soffian; Rohadi, Suprianto; Suardi, Iman; Rudiyanto, Ariska; Pranata, Bayu

    2015-04-01

    The spectacular Lusi eruption started in northeast Java, Indonesia the 29 of May 2006 following a M6.3 earthquake striking the island. Initially, several gas and mud eruption sites appeared along the reactivated strike-slip Watukosek fault system and within weeks several villages were submerged by boiling mud. The most prominent eruption site was named Lusi. Lusi is located few kilometres to the NE of the Arjuno-Welirang volcanic complex. Lusi sits upon the Watukosek fault system. From this volcanic complex originates the Watukosek fault system that was reactivated by the M6.3 earthquake in 2006 and is still periodically reactivated by the frequent seismicity. To date Lusi is still active and erupting gas, water, mud and clasts. Gas and water data show that the Lusi plumbing system is connected with the neighbouring Arjuno-Welirang volcanic complex. This makes the Lusi eruption a "sedimentary hosted geothermal system". To verify and characterise the occurrence of seismic activity and how this perturbs the connected Watukosek fault, the Arjuno-Welirang volcanic system and the ongoing Lusi eruption, we deployed 30 seismic stations (short-period and broadband) in this region of the East Java basin. The seismic stations are more densely distributed around LUSI and the Watukosek fault zone that stretches between Lusi and the Arjuno Welirang (AW) complex. Fewer stations are positioned around the volcanic arc. Our study sheds light on the seismic activity along the Watukosek fault system and describes the waveforms associated to the geysering activity of Lusi. The initial network aims to locate small event that may not be captured by the Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) seismic network and it will be crucial to design the second phase of the seismic experiment that will consist of a local earthquake tomography of the Lusi-Arjuno Welirang region and temporal variations of vp/vs ratios. Such variations will then be ideally related to

  16. Seismic Analysis of Magmatism in the Galapagos Archipelago and East Africa

    NASA Astrophysics Data System (ADS)

    Tepp, Gabrielle

    Magmatism and deformation are consequences of fundamental processes shaping Earth's ˜150 km-thick continental and <125 km-thick oceanic plates. Earthquake seismology encompasses many methods to detect compositional and thermal boundaries from Earth's surface to the dynamic mantle driving plate tectonics. This work uses three different seismic methods to probe magma migration and storage and tectonism in two intraplate hotspot provinces: the Galapagos and East Africa. First, seismic body-wave tomography is used to image magma within oceanic crust of the largest Galapagos volcano, Sierra Negra. A laterally large, low-velocity region with many smaller, high-magnitude velocity anomalies is imaged at 8--15.5 km depths. No sharp seismic velocity increase is imaged within the resolvable depths, indicating that the thickened crust is at least 16 km deep. The second study involves a spectral analysis of earthquakes induced by the intrusion of thin sheets of magma rising beneath the Afar rift, East Africa. Earthquakes have varying spectral content, some with unusually large amplitude low-frequency content and enhanced surface waves. The analysis showed no clear boundaries between spectral types, suggesting that they are all primarily the result of brittle failure. Deep dike segments (tops > 3 km) induce only high-frequency volcano-tectonic earthquakes, while shallower dike segments induce the full range of spectral types. This suggests that low-frequency content is a result of shallow hypocenters, with path and site effects, surface ruptures, and dike fluid interactions all possible secondary causes. In the final study, shear-wave splitting analysis of teleseismic body-wave phases is conducted to evaluate strain and crack fabrics at the base of the continental plate as a consequence of magmatism, mantle flow, and plate stretching in the Western rift, East Africa. On average, fast directions are northeast, consistent with geodynamic models of mantle flow from the African

  17. Deep seismic refraction experiment in northeast Brazil: New constraints for Borborema province evolution

    NASA Astrophysics Data System (ADS)

    Lima, Marcus Vinicius A. G. de; Berrocal, Jesus; Soares, José E. P.; Fuck, Reinhardt A.

    2015-03-01

    The Borborema Province of northeastern Brazil is a major Proterozoic crustal province that, until now, has never been explored using deep crustal seismic methods. Here are reported the first results obtained from a high-quality seismic refraction/wide-angle reflection profile that has defined the internal seismic velocity structure and thickness of the crust in this region. Almost 400 recording stations were deployed in the Deep Seismic Refraction (DSR) experiment through an NW-SE ca. 900 km linear array and 19 shots were exploded at every 50 km along the line. Data from the 10 southeastern most shots of the seismic profile were processed in this work. The main features and geological structures crossed by the studied portion of the profile belong to the so-called Central Sub-province of the Borborema tectonic province. The crustal model obtained is compatible with a typical structure of extended crust. The model was essentially divided into three layers: upper crust, lower crust, and a half-space represented by the shallower portion of the mantle. The Moho is an irregular interface with depth ranging between 31.7 and 34.5 km, and beneath the Central Sub-province it varies from 31.5 to 33 km depth, where its limits are related to major crustal discontinuities. The distribution of velocities within the crust is heterogeneous, varying vertically from 5.7 to 6.3 km/s in the upper crust and from 6.45 to 6.9 km/s in the lower crust. From the average crustal velocity distribution it is evident that the Central Sub-province has seismic characteristics different from neighboring domains. The crust is relatively thin and crustal thickness variations in the profile are subtle due to stretching that occurred in the Cretaceous, during the fragmentation of Pangaea, opening of the South Atlantic Ocean and separation of South America from Africa.

  18. Advancing drug availability-experiences from Africa.

    PubMed

    Powell, Richard A; Kaye, Richard Mugula; Ddungu, Henry; Mwangi-Powell, Faith

    2010-07-01

    International health and drug regulatory authorities acknowledge that analgesics (especially opioids) are insufficiently available for pain management in many countries. In Africa, reported morphine consumption is far below the global mean, with multiple factors hampering opioid supply. Since 2006, the African Palliative Care Association has hosted three regional drug availability workshops across the continent to address this issue. Using an interactive format, the workshops have identified country-specific barriers to opioid and other essential medication accessibility before supporting participants to develop action plans to address recognized impediments. Despite multiple challenges, a number of successes have arisen from the implementation of the plans. However, key issues remain, including the introduction of supportive policy environments, effective educational initiatives, and measures to address supply-chain obstacles impeding drug availability. PMID:20619205

  19. Seismic experiments, nuclear dismantlement go hand in hand in Kazakhstan

    NASA Astrophysics Data System (ADS)

    Leith, William; Kluchko, Luke J.

    Unique seismic experiments involving large chemical explosions at different depths have been conducted in Kazakhstan, thanks to nuclear dismantlement activity there. Collaborative efforts of several bodies have provided this creative, cost-efficient extension of the dismantling work, improving technical monitoring and verification of the Comprehensive Test Ban Treaty (CTBT).For the past several years, the Defense Special Weapons Agency (DSWA) has been closing the nuclear test tunnels and bore-holes at the former Soviet nuclear test site nearSemipalatinsk, eastern Kazakhstan, as part of the Nunn-Lugar Cooperative Threat Reduction (CTR) Program. The existence of this program and the infrastructure that was in place to implement it made it possible to conduct the seismic experiments. As a result, benchmark data have been collected on the variations in seismic signals from explosions at different burial depths.

  20. Apollo 14 and 16 Active Seismic Experiments, and Apollo 17 Lunar Seismic Profiling

    NASA Technical Reports Server (NTRS)

    1976-01-01

    Seismic refraction experiments were conducted on the moon by Apollo astronauts during missions 14, 16, and 17. Seismic velocities of 104, 108, 92, 114 and 100 m/sec were inferred for the lunar regolith at the Apollo 12, 14, 15, 16, and 17 landing sites, respectively. These data indicate that fragmentation and comminution caused by meteoroid impacts has produced a layer of remarkably uniform seismic properties moonwide. Brecciation and high porosity are the probable causes of the very low velocities observed in the lunar regolith. Apollo 17 seismic data revealed that the seismic velocity increases very rapidly with depth to 4.7 km/sec at a depth of 1.4 km. Such a large velocity change is suggestive of compositional and textural changes and is compatible with a model of fractured basaltic flows overlying anorthositic breccias. 'Thermal' moonquakes were also detected at the Apollo 17 site, becoming increasingly frequent after sunrise and reaching a maximum at sunset. The source of these quakes could possibly be landsliding.

  1. Creating Cultural Competence: An Outreach Immersion Experience in Southern Africa

    ERIC Educational Resources Information Center

    West-Olatunji, Cirecie; Goodman, Rachael D.; Mehta, Sejal; Templeton, Laura

    2011-01-01

    With disasters on the rise, counselors need to increase their cultural awareness, knowledge, and skills to work with affected communities. This study reports outcomes of a four-week immersion experience in southern Africa with six counselor-trainees. Data sources for this qualitative study were: daily journals and demographic forms. Outcomes…

  2. Seismicity in Central North Africa at low magnitudes: A first look at the TAM event detected data base

    SciTech Connect

    Harben, P.E.,

    1997-01-01

    Teleseismic observations of seismicity in the central North Africa region show that the region is aseismic. This is true for earthquakes with a body wave magnitude greater than about 4 or so. For earthquakes with body wave magnitudes substantially below about 4, the teleseismic observations of seismicity in the central Sahara are incomplete since smaller earthquakes would probably not be detected and located by the current teleseismic monitoring networks. Only one known open seismic station has been operating in the central Sahara. This is the Tamanrasset (TAM) seismic station in southern Algeria. A simple analysis of data records from this station can be used to determine if the central Sahara is also relatively aseismic at magnitudes substantially below 4. That is the primary purpose of this study.

  3. Results from the apollo-12 passive seismic experiment

    USGS Publications Warehouse

    Latham, G.

    1971-01-01

    The objective of the passive seismic experiment is to measure vibrations of the lunar surface produced by all natural and artificial sources of seismic energy and to use these data to deduce the internal structure and composition of the moon, the nature of forces which may cause deformation of the moon and moonquakes, and the numbers and masses of meteoroids striking the lunar surface. The ALSEP* seismometers can magnify lunar surface vibrations 10 million times. No instrument can operate on earth with this sensitivity, because weather and man produce too much seismic noise. To obtain answers to the above questions, seismic data must be combined with data from laboratory measurements of the physical and chemical properties of surface rocks, and many other geophyiscal and geochemical measurements. Thus far, we have had the opportunity to record data from two lunar seismic stations which were installed by the astronauts during Apollo misions  and 12. The combined recording time from the stations is presently over 12 months, but there was no overlap to permit recording of the same event at two stations. 

  4. Possible Biases in Characteristic Earthquake and Seismic Hazard Studies: Illustrations for the Wasatch, New Madrid, North Africa, and Eastern Canadian Seismic Zones

    NASA Astrophysics Data System (ADS)

    Swafford, L.; Stein, S.; Newman, A.; Friedrich, A.

    2005-12-01

    Attempts to study earthquake recurrence in space and time are limited in simple but frustrating ways by the short history of instrumental seismology compared to the long and variable recurrence time of large earthquakes. If major seismicity is spread uniformly with a seismic zone but the recurrence interval is long compared to the earthquake record, apparent differences in seismic hazard within the seismic zone inferred from the earthquake history are likely to simply reflect the short earthquake record. Simple numerical simulations suggest that this may be the case for the concentrated areas of high predicted hazard with seismic zones in North Africa, along the St. Lawrence valley, and the eastern coast of Canada. If so, with more time and a longer earthquake record, large earthquakes would likely occur over the entire seismic zone and show that the real hazard is uniform. Similarly, large earthquakes are likely to appear "characteristic", more frequent than would be inferred from the rates of smaller ones, for two reasons. First, a short history is likely to overestimate the rate of large earthquakes because fractions of earthquakes cannot be observed. Second, because the rates of small earthquakes are typically determined from the seismological record whereas the rates of large earthquakes are inferred from paleoseismology, biases in estimating paleomagnitudes can produce apparent characteristic earthquakes, as appears to have occurred for New Madrid. A further complexity is illustrated by results for the Wasatch seismic zone, where some studies find characteristic earthquake behavior whereas others do not. The discrepancy arises primarily because some studies consider the entire Wasatch front area whereas others focus on the Wasatch fault, on which only some of the smaller earthquakes but all of the large paleoearthquakes occur. Similar situations may arise in other seismic zones containing a major fault and a number of smaller ones.

  5. Seismotectonic of Southern Apennines from recent passive seismic experiments

    NASA Astrophysics Data System (ADS)

    Frepoli, A.; Maggi, C.; Cimini, G. B.; Marchetti, A.; Chiappini, M.

    2011-03-01

    We used data of local earthquakes collected during two recent passive seismic experiments carried out in southern Italy in order to study the seismotectonic setting of the Lucanian Apennine and the surrounding areas. Based on continuous recordings of the temporary stations we extracted over 15,600 waveforms, which were hand-picked along with those recorded by the permanent stations of the Italian national seismic network obtaining a dense, high-quality dataset of P- and S-arrival times. We examined the seismicity occurring in the period 2001-2008 by relocating 566 out of 1047 recorded events with magnitudes ML ≥ 1.5 and computing 162 fault-plane solutions. Earthquakes were relocated using a minimum one-dimensional velocity model previously obtained for the region and a Vp/ Vs ratio of 1.83. Background seismicity is concentrated within the upper crust (between 5 and 20 km of depth) and it is mostly clustered along the Lucanian Apennine chain axis. A significant feature extracted from this study relates to the two E-W trending clusters located in the Potentino and in the Abriola-Pietrapertosa sector (central Lucania region). Hypocentral depths in both clusters are slightly deeper than those observed beneath the Lucanian Apennine. We suggest that these two seismic features are representative of the transition from the inner portion of the chain to the external margin characterized by dextral strike-slip kinematics. In the easternmost part of the study area, below the Bradano foredeep and the Apulia foreland, seismicity is generally deeper and more scattered. The sparse seismicity localized in the Sibari Plain, in the offshore area along the northeastern Calabrian coast and in the Taranto Gulf is also investigated thanks to the new recordings. This seismicity shows hypocenters between 12 and 20 km of depth below the Sibari Plain and is deeper (foci between 10 and 35 km of depth) in the offshore area of the Taranto Gulf. 102 well-constrained fault-plane solutions

  6. A Community Seismic Experiment in the ENAM Primary Site

    NASA Astrophysics Data System (ADS)

    Van Avendonk, H. J.

    2012-12-01

    Eastern North America (ENAM) was chosen as a GeoPRISMS Rift Initiation and Evolution primary site because it represents a mature continental margin with onshore and offshore rift basins in which the record of extension and continental break-up is preserved. The degree to which syn-rift magmatism and preexisting lithospheric weaknesses controlled the evolution of the margin can be further investigated if we image its 3-D structure at small and large length scales with active-source and earthquake seismic imaging. In the Summer of 2012 we submitted a proposal to the US National Science Foundation for an ambitious plan for data acquisition on a 400 km wide section of the mid-Atlantic East Coast margin around Cape Hatteras, from unextended continental lithosphere onshore to mature oceanic lithosphere offshore. This area includes an important along-strike transition in the morphology of the margin from the Carolina Trough to the Baltimore Canyon Trough, and two major fracture zones that are associated with significant offsets at the modern Mid-Atlantic Ridge. The study area also covers several features representing the post-rift modification of the margin by slope instability and fluid flow. As the Earthscope Transportable Array reaches the East Coast of the US in 2013 and 2014, we will have an unprecedented opportunity to image the detailed structure of the rifted margin. To make effective use of the research infrastructure, including the seismic vessel R/V Marcus Langseth, the Earthscope seismic instrumentation, and US OBS Instrument Pool, we propose to collect a suite of seismic data at the mid-Atlantic margin in the context of a community-driven experiment with completely open data access. This multi-faceted seismic experiment offers an immense opportunity for education of young scientists. We propose an integrated education effort during and after acquisition. The science and field parties for data acquisition will largely consist of young scientists, who will be

  7. A deployment of broadband seismic stations in two deep gold mines, South Africa

    USGS Publications Warehouse

    McGarr, Arthur F.; Boettcher, Margaret S.; Fletcher, Jon Peter B.; Johnston, Malcolm J.; Durrheim, R.; Spottiswoode, S.; Milev, A.

    2009-01-01

    In-mine seismic networks throughout the TauTona and Mponeng gold mines provide precise locations and seismic source parameters of earthquakes. They also support small-scale experimental projects, including NELSAM (Natural Earthquake Laboratory in South African Mines), which is intended to record, at close hand, seismic rupture of a geologic fault that traverses the project region near the deepest part of TauTona. To resolve some questions regarding the in-mine and NELSAM networks, we deployed four portable broadband seismic stations at deep sites within TauTona and Mponeng for one week during September 2007 and recorded ground acceleration. Moderately large earthquakes within our temporary network were recorded with sufficiently high signal-to-noise that we were able to integrate the acceleration to ground velocity and displacement, from which moment tensors could be determined. We resolved the questions concerning the NELSAM and in-mine networks by using these moment tensors to calculate synthetic seismograms at various network recording sites for comparison with the ground motion recorded at the same locations. We also used the peak velocity of the S wave pulse, corrected for attenuation with distance, to estimate the maximum slip within the rupture zone of an earthquake. We then combined the maximum slip and seismic moment with results from laboratory friction experiments to estimate maximum slip rates within the same high-slip patches of the rupture zone. For the four largest earthquakes recorded within our network, all with magnitudes near 2, these inferred maximum slips range from 4 to 27 mm and the corresponding maximum slip rates range from 1 to 6 m/s. These results, in conjunction with information from previous ground motion studies, indicate that underground support should be capable of withstanding peak ground velocities of at least 5 m/s.

  8. The SEIS experiment : a Mars seismic package

    NASA Astrophysics Data System (ADS)

    Schibler, P.; Lognonne, P.; Giardini, D.; Banerdt, B.; Karczewski, J. F.; Mimoun, D.; Zweifel, P.; Pike, W. T.; Seis Team

    2003-04-01

    The determination of the deep internal structure of Mars, especially the state and size of the core, the structure of the mantle and shape of discontinuities will be the goal of a the SEIS experiment, which integrates a Very Broad Band 2 axis seismometer, a 3 axis short period seismometer and a serie of environmental sensors for pressure, infrasounds and temperature. We describe the scientific objective of the experiment. We then focuse on the technical description of the package of sensors, which will allow: - to measure signals in an ultra-broad band, from the tidal frequencies (0.05 mHz) up to the short period frequencies (50 Hz) - to perform environmental decorrelations of the temperature and pressure variation on Mars, allowing the sensor to operate in a thermal environment with daily variations of about 40°K - to search for infrasounds which might be associated to dust devils and atmospheric discharge. The overall mass of the SEIS experiment is 2.3 kg, including all sensors, data control processors and installation devices. Acquisition will be performed by a series of 24 bits A/D converters, while the thermal and drift control will be performed by a feedback generated by a 24 bits D/A converter. Two VBB axis will be delivered by industry at mid 2003 and functional breadboard of sphere (15 cm diameter) containing 2 VBB axis, environmental sensors and electronics will be delivered at the end of 2003. IPGP has the overall responsibility of the experiment and is responsible for the VBB sensor and environmental sensors. ETHZ is responsible for the electronics of the experiment and JPL for the Short Period sensors. The SEIS is one of the core instruments of the Netlander mission, which objective is to deploy in 2009 a network of 4 stations on Mars for one Martian year of operation. This design of "multiparameter station" can be used for other Martian missions (e.g. Mars SmartLander) and a simplified and lighter instrument could also be proposed on other planet

  9. Ambient seismic noise levels: A survey of the permanent and temporary seismographic networks in Morocco, North Africa

    NASA Astrophysics Data System (ADS)

    El Fellah, Y.; Khairy Abd Ed-Aal, A.; El Moudnib, L.; Mimoun, H.; Villasenor, A.; Gallart, J.; Thomas, C.; Elouai, D.; Mimoun, C.; Himmi, M.

    2013-12-01

    Abstract The results, of a conducted study carried out to analyze variations in ambient seismic noise levels at sites of the installed broadband stations in Morocco, North Africa, are obtained. The permanent and the temporary seismic stations installed in Morocco of the Scientific Institute ( IS, Rabat, Morocco), institute de Ciencias de la Tierra Jaume almera (ICTJA, Barcelona, Spain) and Institut für Geophysik (Munster, Germany) were used in this study. In this work, we used 23 broadband seismic stations installed in different structural domains covering all Morocco from south to north. The main purposes of the current study are: 1) to present a catalog of seismic background noise spectra for Morocco obtained from recently installed broadband stations, 2) to assess the effects of experimental temporary seismic vault construction, 3) to determine the time needed for noise at sites to stabilize, 4) to establish characteristics and origin of seismic noise at those sites. We calculated power spectral densities of background noise for each component of each broadband seismometer deployed in the different investigated sites and then compared them with the high-noise model and low-noise Model of Peterson (1993). All segments from day and night local time windows were included in the calculation without parsing out earthquakes. The obtained results of the current study could be used forthcoming to evaluate permanent station quality. Moreover, this study could be considered as a first step to develop new seismic noise models in North Africa not included in Peterson (1993). Keywords Background noise; Power spectral density; Model of Peterson; Scientific Institute; Institute de Ciencias de la Tierra Jaume almera; Institut für Geophysik

  10. Seismic imaging of sandbox experiments - laboratory hardware setup and first reflection seismic sections

    NASA Astrophysics Data System (ADS)

    Krawczyk, C. M.; Buddensiek, M.-L.; Oncken, O.; Kukowski, N.

    2012-10-01

    With the study and technical development introduced here, we combine analogue sandbox simulation techniques with seismic physical modelling of sandbox models. For that purpose, we designed and developed a new mini-seismic facility for laboratory use, comprising a seismic tank, a PC-driven control unit, a positioning system, and piezo-electric transducers used here the first time in an array mode. To assess the possibilities and limits of seismic imaging of small-scale structures in sandbox models, different geometry setups were tested in the first experiments that also tested the proper functioning of the device and studied the seismo-elastic properties of the granular media used. Simple two-layer models of different materials and layer thicknesses as well as a more complex model comprising channels and shear zones were tested using different acquisition geometries and signal properties. We suggest using well sorted and well rounded grains with little surface roughness (glass beads). Source receiver-offsets less than 14 cm for imaging structures as small as 2.0-1.5 mm size have proven feasible. This is the best compromise between wide beam and high energy output, and being applicable with a consistent waveform. Resolution of the interfaces of layers of granular materials depends on the interface preparation rather than on the material itself. Flat grading of interfaces and powder coverage yields the clearest interface reflections. Finally, sandbox seismic sections provide images of very good quality showing constant thickness layers as well as predefined channel structures and fault traces from shear zones. Since these can be regarded in sandbox models as zones of decompaction, they behave as reflectors and can be imaged. The multiple-offset surveying introduced here improves the quality with respect to S/N-ratio and source signature even more; the maximum depth penetration in glass bead layers thereby amounts to 5 cm. Thus, the presented mini-seismic device is

  11. A Preliminary Look at the Crust and Upper Mantle of North Africa Using Libyan Seismic Data

    SciTech Connect

    Pasyanos, M

    2005-08-05

    In recent years, LLNL has been developing methods to jointly invert both surface wave dispersion data and teleseismic receiver functions. The technique holds great promise in accurately estimating seismic structure, including important tectonic parameters such as basin thickness, crustal thickness, upper mantle velocity, etc. We proposed applying this method to some recently available data from several Libyan stations, as we believe the technique has not been applied to any stations in Libya. The technique holds the promise of improving our understanding of the crust and upper mantle in Libya and North Africa. We recently requested seismic data from stations GHAR (Gharyan) and MARJ (Al Marj) in Libya for about 20 events. The events were large events at regional distances suitable for making dispersion measurements. An example of waveforms recorded at the two stations from an earthquake in Italy is shown in Figure 1. The paths traverse the Ionian Sea. Notice the slow short period group velocities of the surface waves across the Mediterranean, particularly to the easternmost station MARJ. However, because of data availability, signal-to-noise ratio, etc. we were unable to make measurements for every one of these events at both stations. Figure 2 shows a map of paths for 20 sec Rayleigh waves in the eastern Mediterranean region. Paths measured at the two Libyan stations are shown in green. Rayleigh wave dispersion measurements at 20 sec period are sensitive to velocities in the upper 20 km or so, and reveal sediment thickness, crustal velocity, and crustal thickness. Tomographic inversions reveal the sharp group velocity contrast between regions with deep sedimentary basins and those without. Figure 3, the result of an inversion made before adding the new dispersion measurements, shows slow group velocities in the Black Sea, Adriatic Sea, and Eastern Mediterranean. In general, these features correspond well with the sediment thickness model from Laske, shown in Figure

  12. Fault Kinematics and Seismic Anisotropy Patterns in the Natron-Magadi Basins, Africa

    NASA Astrophysics Data System (ADS)

    Weinstein, A.

    2015-12-01

    Early-stage continental rift zones provide important insights into the deformation behavior of crust and mantle lithosphere, and its modification by the migration of magma and volatiles. In East Africa, lower crustal earthquakes provide opportunities to probe the deformation behavior of the entire crust. We use a catalogue of 3068 earthquakes of 1 < ML < 4.5 recorded on a 39-station seismic array spanning three 3 rift segments ( Magadi-Natron-Manyara) of the Eastern rift, Africa to determine kinematics of large offset border faults, their along-strike linkage, and their possible interactions with tomographically imaged magma conduits and reservoirs beneath active and dormant volcanoes. Earthquake focal mechanisms are predominantly NS-striking normal faults with steep dips from near surface to 25 km in the Natron and Magadi basins, whereas the strike of normal faults locally rotates to N60E at the northern tip of the Manyara border fault. This rift-oblique structure links the Manyara border fault to Gelai shield volcano via Oldoinyo Lengai volcano, and may be a zone of magma transfer. Crustal anisotropy measurements from lower crustal earthquakes provide information on the orientation of fluid-filled cracks and any strain fabric. We compare our new crustal splitting observations with the rift parallel anisotropy determined by ambient noise tomography, and with mantle anisotropy patterns determined from SKS-splitting. Initial results of SKS-splitting (> 1 s) show both the NS and NE fast directions at different stations, suggesting that aligned melt-filled cracks contribute to the observed patterns, as in more evolved rift sectors, like the Ethiopian and Afar rifts.

  13. Cataloguing Seismic Waveform Properties Recorded With a 3D Network in a Gold Mine in South Africa

    NASA Astrophysics Data System (ADS)

    Julia, J.; Nyblade, A. A.; Gok, R.; Walter, W. R.; Linzer, L.; Durrheim, R. J.; Dirks, P.

    2007-12-01

    The SAVUKA gold mine is located in the northwestern edge of the Witwatersrand basin, a Late Archean (3.07- 2.71~Ga) intracratonic basin in South Africa that hosts the largest known gold-uranium-pyrite ore deposits in the world. Seismic events related to the mine activity span several orders of magnitude through a variety of sources that include mine blasts, pillar collapses, and faulting events. These events are systematically recorded and catalogued through an in-mine, 3D seismic network consisting of 20, three-component, short-period stations with natural frequencies ranging between 4.5 and 28.0~Hz and deployed as deep as ~3.5 km. After 5 months of seismic monitoring of the mine, we have been able to assemble a database of over 6000 events spanning magnitudes in the -2.5 < ML < 4.4 range. The potential of this unique data set for characterizing the detailed seismic properties of the basin and studying source properties of non-double couple events is explored through simple, first-pass analysis on the recorded waveforms. Moreover, the in-mine network is complemented by a small array of 4 broadband stations interspaced ~10~km apart on the surface of the mine, and by a number of AfricaArray stations in South Africa and neighboring countries located at regional distances (50- 1000~km) from the mine. The largest mine-induced events are clearly recorded at distances as far away from the mine as 450~km and provide a unique opportunity for studying the regional propagation of seismic phases as well as the structure of the cratonic crust underlying the basin.

  14. Seismic attribute analysis to enhance detection of thin gold-bearing reefs: South Deep gold mine, Witwatersrand basin, South Africa

    NASA Astrophysics Data System (ADS)

    Manzi, M. S. D.; Hein, K. A. A.; Durrheim, R.; King, N.

    2013-11-01

    The gold-bearing Upper Elsburg Reef clastic wedge (UER) in the South Deep gold mine in the Witwatersrand basin (South Africa) hosts the highly auriferous basal conglomerate known as the Elsburg Conglomerate (EC) reef. The reef is less than 20 m thick and together with quartzite and conglomerate beds in the UER (1-120 m thick) is below the seismic tuning thickness, or the dominant quarter wavelength. They are extremely difficult to identify on migrated seismic sections using traditional amplitude interpretations. In order to enhance the detection of the EC reef and its subcrop position against the overlying Ventersdorp Contact Reef (VCR), complex-trace seismic attributes, or instantaneous attributes and volume attribute analysis were applied on prestack time migrated (PSTM) seismic sections. In particular, the instantaneous phase and paraphase allowed the clear identification of the continuity of the EC reef, and overlapping and interfering wavelets produced by the convergence of VCR and the EC reef. In addition, these attributes increased confidence in the interpretation of the EC, in particular its offsets (faults), and its depth. A high correlation between the seismically determined depth of the EC reef and borehole intersections was observed, with several depth discrepancies below the vertical seismic resolution limit (~ 25 m). This information can now be incorporated into the current mine geological model, thus improving the resource evaluation of the Upper Elsburg Reef in the South Deep gold mine.

  15. Seismic imaging beneath southwest Africa based on finite-frequency body wave tomography

    NASA Astrophysics Data System (ADS)

    Youssof, Mohammad; Yuan, Xiaohui; Tilmann, Frederik; Heit, Benjamin; Weber, Michael; Jokat, Wilfried; Geissler, Wolfram; Laske, Gabi

    2016-04-01

    We present a seismic model of southwest Africa from teleseismic tomographic inversion of the P- and S- wave data recorded by an amphibious temporary seismic network. The area of study is located at the intersection of the Walvis Ridge with the continental margin of northern Namibia, and extends into the Congo craton. Utilizing 3D finite-frequency sensitivity kernels, we invert traveltime residuals of the teleseismic body waves to image seismic structures in the upper mantle. To test the robustness of our tomographic imaging, we employed various resolution assessments that allow us to inspect the extent of smearing effects and to evaluate the optimum regularization weights (i.e., damping and smoothness). These tests include applying different (ir)regular parameterizations, classical checkerboard and anomaly tests and squeezing modeling. Furthermore, we performed different kinds of weighing schemes for the traveltime dataset. These schemes account for balancing between the picks data amount with their corresponding events directions. Our assessment procedure involves also a detailed investigation of the effect of the crustal correction on the final velocity image, which strongly influenced the image resolution for the mantle structures. Our model can resolve horizontal structures of 1° x 1° below the array down to 300-350 km depth. The resulting model is mainly dominated by the difference in the oceanic and continental mantle lithosphere beneath the study area, with second-order features related to their respective internal structures. The fast lithospheric keel of the Congo Craton reaches a depth of ~250 km. The orogenic Damara Belt and continental flood basalt areas are characterized by low velocity perturbations down to a depth of ~150 km, indicating a normal fertile mantle. High velocities in the oceanic lithosphere beneath the Walvis Ridge appear to show signatures of chemical depletion. A pronounced anomaly of fast velocity is imaged underneath continental NW

  16. Free online seismic data from a sand tank experiment

    NASA Astrophysics Data System (ADS)

    Lorenzo, J. M.; Smolkin, D.; White, C.; Chollett, S.; Sun, T.

    2012-12-01

    Theoretical fluid flow models are used regularly to predict and analyze porous media flow but require verification against natural systems. Seismic monitoring in a controlled laboratory setting at a nominal scale of 1:1000 in the acoustic frequency range can help improve fluid flow models as well as elasto-granular models for uncompacted, saturated-unsaturated soils. A mid-scale sand tank allows for many highly repeatable, yet flexible, experimental configurations with different material compositions and pump rates while still capturing phenomena such as patchy saturation, flow fingering, or layering. The tank (~6 x 9 x 0.44 m) contains a heterogeneous sand pack (1.52-1.7 phi). In a set of eight experiments the water table is raised inside the sand body at increments of ~0.05 m. Seismic events (vertical component) are recorded by a pseudo-walkaway 64-channel accelerometer array (20 Hz-20 kHz), at 78 kS/s, in 100- scan stacks so as to optimize signal-to-noise. Three screened well sites monitor water depth (+/- 3 mm) inside the sand body. Data sets comprise SEG-Y formatted files (seismic) and are publicly downloadable from the internet (http://github.com/cageo/Lorenzo-2012), in order to allow comparisons of different seismic and fluid flow analyses. The capillary fringe does not appear to completely saturate, as expected, because the interpreted compressional-wave velocity values remain so low (< 210 m/s). Even the highest water levels there is no large seismic impedance contrast across the top of the water table to generate a clear reflector. Preliminary results indicate an immediate need for several additional experiments whose data sets will be added to the online database. Future benchmark data sets will grow with a control data set to show conditions in the sand body before water levels rise, and a surface 3D data set. In later experiments, buried sensors will help reduce seismic attenuation effects and in-situ saturation sensors will provide calibration values.

  17. Seismic architecture and morphology of Neogenic sediment waves and drifts, offshore West Africa

    NASA Astrophysics Data System (ADS)

    Baglioni, Luca; Bonamini, Enrico

    2013-04-01

    The three dimension visualisation softwares of seismic data and the recent development of semi-automatic interpretation tools allow to define the 3D morphology of ancient depositional systems at a resolution never achieved before. This study analyses a Neogenic stratigraphic interval in the deep water of the West African margin. The purpose of the work is the understanding of the sedimentary architectures and the link with the genetic depositional processes. The study is mainly based on the interpretation of seismic geometries and amplitude/isochron maps derived from newly-interpreted seismic horizons. The seismic stratigraphy reveals abrupt changes in depositional styles and sedimentary processes. Transitions between Sediment Drifts (SD), Sediment Waves (SWs) and Mass Transport Complexes (MTCs) are here frequently observed, suggesting that cyclically either bottom-current intensity decreased or gravity-flow input overwhelmed the bottom-current signal. The lower studied interval corresponds to a SD sequence, made up of stacked individual packages and having a maximum thickness of 300 ms. The landward drift morphology is characterized by convex-upward, mounded seismic reflections. Each drift onlaps on a seaward-dipping reflection interpreted as paleo-slope. These contouritic deposits are concentrated near the base of slope, and fade out downdip. The drift appears to be grown from the deeper part of the basin and backstepped up the slope. It is inferred that the deposition of the drifts took place under the influence of a marine current, subparallel to the southern margin of West African coast. The backstepping of the onlapping architecture may have resulted from bottom current acceleration across the ramp. The intermediate studied interval represents a transitional sequence in which SW are alternated with MTDs of minor size (up to 60 ms thick). In this transition interval, onlap relationships and thickness variations suggest that gravity flow deposits preferentially

  18. IRIS Controlled Source Seismic Experiments: Continental Structure, Instrumentation, and Education

    NASA Astrophysics Data System (ADS)

    Mooney, W. D.; Keller, G. R.

    2004-12-01

    The controlled-source seismology program of IRIS/PASSCAL has made major contributions to the study of continental structure and evolution. It has also undergone major developments in seismic instrumentation. The first PASSCAL experiments (1984/85) targeted the Basin and Range Province and the Ouachita orogenic belt. The Basin and Range study provided remarkably clear images of this thin, highly-extended crust, while the Ouachita experiment tested competing hypotheses for the deep structure of this Paleozoic orogen. However, both of these projects were limited by a lack of seismic instruments. The situation improved in the late 1980's with the benefit of a mixed array of 600 seismic recorders from the USGS, Stanford, and the Geological Survey of Canada. The resolution achieved with these instruments was revolutionary. Results include the imaging of such remarkable features as crustal-scale duplexes in the Brooks Range compressional orogen of northern Alaska, and of crustal "core complexes" in the extended crust of southwest Arizona. The 3-channel PASSCAL Jr. instrument was developed, leading to experiments in which ˜1000 instruments were deployed, including three-component recording. This complex mix of instruments served the community well for several years, but required large, complex instrument centers and lots of technical support. With input from PASSCAL and the international community, a newly designed, compact instrument (the Texan) was finalized in the spring of 1998, and the first 200 instruments was delivered to the Univ. of Texas-El Paso in late 1998. The present instrument pool of Texans exceeds 1,400 and these have been used on such projects as the high-resolution imaging of the Los Angeles and San Fernando basins (LARSE I and II experiments), where active thrust faults have been imaged. Controlled-source seismic experiments are now very numerous. During calendar year 2004 alone, portable Texan instruments have traveled from Venezuela to Denmark

  19. 3D Seismic Reflection Experiment over the Galicia Deep Basin

    NASA Astrophysics Data System (ADS)

    Sawyer, D. S.; Jordan, B.; Reston, T. J.; Minshull, T. A.; Klaeschen, D.; Ranero, C.; Shillington, D. J.; Morgan, J. K.

    2014-12-01

    In June thru September, 2013, a 3D reflection and a long offset seismic experiment were conducted at the Galicia rifted margin by investigators from the US, UK, Germany, and Spain. The 3D multichannel experiment covered 64 km by 20 km (1280 km2), using the RV Marcus Langseth. Four streamers 6 km long were deployed at 12.5 m hydrophone channel spacing. The streamers were 200 m apart. Two airgun arrays, each 3300 cu in, were fired alternately every 37.5 m, to collectively yield a 400 m wide sail line consisting of 8 CMP lines at 50 m spacing. The long offset seismic experiment included 72 short period OBS's deployed below the 3D reflection survey box. Most of the instruments recorded all the shots from the airgun array shots. The 3D seismic box covered a variety of geologic features. The Peridotite Ridge (PR), is associated with the exhumation of upper mantle rocks to the seafloor during the final stage of the continental separation between the Galicia Bank and the Grand Banks of Newfoundland. The S reflector is present below most of the continental blocks under the deep Galicia basin. S is interpreted to be a low-angle detachment fault formed late in the rifting process, and a number of rotated fault block basins and ranges containing pre and syn-rift sediments. Initial observations from stacked 3D seismic data, and samples of 2D pre-stack time migrated (PSTM) 3D seismic data show that the PR is elevated above the present seafloor in the South and not exposed through the seafloor in the North. The relative smoothness of the PR surface for the entire 20 km N-S contrasts with the more complex, shorter wavelength, faulting of the continental crustal blocks to the east. The PR does not seem to show offsets or any apparent internal structure. The PSTM dip lines show substantial improvement for the structures in the deep sedimentary basin East of the PR. These seem to extend the S reflector somewhat farther to the West. The migrated data show a substantial network of

  20. Seismic tomography Technology for the Water Infiltration Experiment

    SciTech Connect

    J. Descour

    2001-04-30

    NSA Engineering, Inc., conducted seismic tomography surveys in Niche No.3 in the Exploratory Studies Facility (ESF), Yucca Mountain, Nevada, and Alcove No.8 in the Enhanced Characterization of the Repository Block (ECRB) cross drift as part of the Infiltration Experiment being conducted in Niche No.3. NSA Engineering is a direct support contractor to the Yucca Mountain Project. This report documents the work performed from August 14 through 30, 2000, prior to the beginning of the infiltration experiment. The objective of the seismic tomography survey was to investigate the flow path of water between access drifts and more specifically to (Kramer 2000): (1) Conduct a baseline seismic tomography survey prior to the infiltration experiment; (2) Produce 2-D and 3-D tomographic images of the rock volume between Alcove No.8 and Niche No.3; (3) Correlate tomography results with published structural and lithological features, and with other geophysical data such as ground penetrating radar (GPR); and (4) Results of this survey will form a baseline with which to compare subsequent changes to the rock mass. These changes may be as a result of the water infiltration tests that could be conducted in Alcove No.8 in 2001. The scope of this reported work is to use the velocity tomograms to: (a) assess the structures and lithologic features within the surveyed area and/or volume between the two access drifts; and (b) provide information on the structural state of the rock mass as inferred by the velocity signatures of the rock prior to the beginning of the infiltration experiment.

  1. Characterisation of rockfalls from seismic signal: insights from laboratory experiments

    NASA Astrophysics Data System (ADS)

    Farin, Maxime; Mangeney, Anne; Toussaint, Renaud; de Rosny, Julien; Shapiro, Nikolai; Dewez, Thomas; Hibert, Clément; Mathon, Christian; Sedan, Olivier; Berger, Frédéric

    2015-04-01

    Rockfalls, debris flows and rock avalanches represent a major natural hazard for the population in mountainous, volcanic and coastal areas but their direct observation on the field is very difficult. Recent field studies showed that gravitational instabilities can be detected, localized and characterized thanks to the seismic signal they generate. Therefore, a burning challenge for risks assessment related to these events is to obtain quantiative informations on the characteristics of the rockfalls (mass, speed, extension,...) from the properties of the signal (seismic energy, frequencies,...). Using a theoretical model of viscoelastic impact of a sphere on a plane, we develop analytical scaling laws relating the energy radiated in elastic waves, the energy dissipated in viscoelasticity during the impact and the frequencies of the generated seismic signal to the mass m and the impact speed V z of the sphere and to the elastic parameters of the involved materials. The radiated elastic energy is shown to vary as m5/3V z11/5 on plates and as mV z13/5 on blocks, regardless of the elastic parameters. The energy dissipated in viscoelasticity does not depend on the support thickness and varies as m2/3V z11/5. The mean frequency of the generated signal is inversely proportional to the impact duration. Then, we conduct simple laboratory experiments that consist in dropping spherical beads of different size and materials and small gravels on thin plates of glass and PMMA and rock blocks. In the experiments, piezoelectric accelerometers are used to record the signals in a wide frequency range: 1 Hz to 56 kHz. The experiments are also monitored optically using fast cameras. The elastic energy emitted by an impact on the supports is first quantitatively estimated and compared to the potential energy of fall and to the potential energy change during the shock. We observe a quantitative agreement between experimental data and the analytical scaling laws, even when we use small

  2. Intense convection over West Africa during AMMA SOP3 experiment

    NASA Astrophysics Data System (ADS)

    Lenouo, André; Sall, Saïdou Moustapha; Badiane, Daouda; Gaye, Amadou Thierno; Kamga Mkankam, F.

    2016-11-01

    ERA-Interim product from the European Center for Medium-Range Weather Forecast (ECMWF) assimilation of African Monsoon Multidisciplinary Analysis (AMMA) resources, Meteosat satellite images, and synoptic observations were used to study local- and regional-scale environments associated with intense convective systems during the AMMA-SOP3 experiment over West Africa in the Northern Hemisphere of summer 2006. The convective system, from the 21st to 23rd of August 2006, was more active at 0000 and 1800 UTC showing diurnal cycle of deep convection over West Africa where the African easterly waves (AEWs) are developed downstream. Downstream barotropic and baroclinic energy conversions associated with strong AEWs are important for the maintenance of AEW activity in West Africa. Barotropic energy conversions dominate south of the African easterly jet (AEJ), while baroclinic energy conversions are most important north of the AEJ. From a dynamical viewpoint, the low-level vorticity presents strong positive values over the sea and Sahara zone, indicating that exists on the cyclonic shear side of the African easterly jet, which is consistent with baroclinic growth. The 925-hPa equivalent potential temperature structure show a maximum over the Sahara which corresponds to the depression observed in this region. A mosaic of three hourly infrared (IR) satellite images, depicts a very distinct signal from an initial region of convection, developing through several stages and moving off the African coast. These observations, along with those available from the World Weather Watch, provide an opportunity to carry out numerical weather prediction (NWP) studies over West Africa utilizing high resolution limited area models.

  3. Towards a Comprehensive Seismic Velocity Model for the Broader Africa-Eurasia Collision Region, to Improve Nuclear Explosion Monitoring

    SciTech Connect

    der Lee, S v; Flanagan, M P; Rodgers, A J; Pasyanos, M E; Marone, F; Romanowicz, B

    2005-07-13

    We report on progress towards a new, comprehensive three-dimensional model of seismic velocity in a broad region encompassing the Middle East, northern Africa, the Mediterranean Sea, the Levant, the Arabian Peninsula, the Turkish-Iranian Plateau, Indus Valley, and the Hindu Kush. Our model will be based on regional waveform fits, surface wave group velocity measurements, teleseismic arrival times of S and P waves, receiver functions, and published results from active source experiments. We are in the process of assembling each of these data sets and testing the joint inversion for subsets of the data. Seismograms come from a variety of permanent and temporary seismic stations in the region. Some of the data is easily accessible through, for example, IRIS, while collection of other data is more involved. This work builds on ongoing work by Schmid et al. (GJI, 2004, and manuscript in preparation). In these proceedings we highlight our data sets and their inferences, demonstrate the proposed new data-inversion modeling methodology, discuss results from preliminary inversions of subsets of the data, and demonstrate the prediction of arrival times with three-dimensional velocity models. We compare our preliminary inversion results to the results of Schmid et al., and the predicted arrival times to ground-truth data from the NNSA Knowledge Base. Our data sets are simultaneously redundant and highly complementary. The combined data coverage will ensure that our three-dimensional model comprises the crust, the upper mantle, including the transition zone, and the top of the lower mantle, with spatially varying, but useful resolution. The region of interest is one of the most structurally heterogeneous in the world. Continental collision, rifting and sea-floor spreading, back-arc spreading, oceanic subduction, rotating micro plates, continental shelf, and stable platforms, are just some of the region's characteristics. Seismicity and the distribution of seismic stations are

  4. 3D Seismic Reflection Experiment Over the Galicia Deep Basin

    NASA Astrophysics Data System (ADS)

    Sawyer, Dale; Jordan, Brian; Tesi Sanjurjo, Mari; Alexanian, Ara; Morgan, Julia; Shillington, Donna; Reston, Timothy; Minshull, Timothy; Klaeschen, Dirk; Ranero, César

    2014-05-01

    In June thru September, 2013, a 3D reflection and a long offset seismic experiment were conducted at the Galicia rifted margin by investigators from the US, UK, Germany, and Spain. The 3D multichannel experiment covered 64 km by 20 km (1280 km2), using the RV Marcus Langseth. Four streamers 6 km long were deployed at 12.5 m hydrophone channel spacing. The streamers were 200 m apart. Two airgun arrays, each 3300 cu in, were fired alternately every 37.5 m, to collectively yield a 400 m wide sail line consisting of 8 CMP lines at 50 m spacing. The long offset seismic experiment included 72 short period OBS's deployed below the 3D reflection survey box. Most of the instruments recorded all the shots from the airgun array shots. The 3D seismic box covered a variety of geologic features. The Peridotite Ridge (PR), is associated with the exhumation of upper mantle rocks to the seafloor during the final stage of the continental separation between the Galicia Bank and the Grand Banks of Newfoundland. The S reflector is present below most of the continental blocks under the deep Galicia basin. S is interpreted to be a low-angle detachment fault formed late in the rifting process, and a number of rotated fault block basins and ranges containing pre and syn-rift sediments. Initial observations from stacked, but not yet migrated, 3D seismic data show that the PR is elevated above the present seafloor in the South and not exposed through the seafloor in the North. The relative smoothness of the PR surface for the entire 20 km N-S contrasts with the more complex, shorter wavelength, faulting of the continental crustal blocks to the east. The PR does not seem to show offsets or any apparent internal structure. However, migration will be required to see internal structure of the PR. Between the PR and the western most rifted continental crustal blocks, is a sedimentary basin about as wide as the PR and very different from the sedimentary basins bounded by the continental crustal

  5. Seismic amplification within the Seattle Basin, Washington State: Insights from SHIPS seismic tomography experiments

    USGS Publications Warehouse

    Snelson, C.M.; Brocher, T.M.; Miller, K.C.; Pratt, T.L.; Trehu, A.M.

    2007-01-01

    Recent observations indicate that the Seattle sedimentary basin, underlying Seattle and other urban centers in the Puget Lowland, Washington, amplifies long-period (1-5 sec) weak ground motions by factors of 10 or more. We computed east-trending P- and S-wave velocity models across the Seattle basin from Seismic Hazard Investigations of Puget Sound (SHIPS) experiments to better characterize the seismic hazard the basin poses. The 3D tomographic models, which resolve features to a depth of 10 km, for the first time define the P- and S-wave velocity structure of the eastern end of the basin. The basin, which contains sedimentary rocks of Eocene to Holocene, is broadly symmetric in east-west section and reaches a maximum thickness of 6 km along our profile beneath north Seattle. A comparison of our velocity model with coincident amplification curves for weak ground motions produced by the 1999 Chi-Chi earthquake suggests that the distribution of Quaternary deposits and reduced velocity gradients in the upper part of the basement east of Seattle have significance in forecasting variations in seismic-wave amplification across the basin. Specifically, eastward increases in the amplification of 0.2- to 5-Hz energy correlate with locally thicker unconsolidated deposits and a change from Crescent Formation basement to pre-Tertiary Cascadia basement. These models define the extent of the Seattle basin, the Seattle fault, and the geometry of the basement contact, giving insight into the tectonic evolution of the Seattle basin and its influence on ground shaking.

  6. Seismic studies of a massive hydraulic fracturing experiment

    SciTech Connect

    House, L.; Keppler, H.; Kaieda, H.

    1985-01-01

    During a massive hydraulic fracturing experiment carried out at Fenton Hill, New Mexico, 850 microearthquakes, ranging in magnitudes from -3 to 0, were located reliably using arrival times recorded at a set of 5 downhole geophone stations. A subset of these events were located using an upgraded hodogram technique. The seismicity defines a tabular zone with horizontal extent of 900 m, vertical extent of 800 m, and thickness of 150 m. This zone strikes N340/sup 0/E, and dips 75/sup 0/ to the east; its position indicates that no hydraulic connection between the two predrilled wells could be achieved by the fracturing. The distribution of locations obtained from arrival times shows good agreement with those derived from hodograms. Well constrained fault plane solutions were determined for 26 of the larger microearthquakes observed at a surface seismic net. Most solutions display one nearly vertical nodal plane that strikes close to N - S, and a T axis that trends roughly E - W, in agreement with regional indicators of the least principal stress direction. 9 refs., 6 figs.

  7. Drought Monitoring and Forecasting: Experiences from the US and Africa

    NASA Astrophysics Data System (ADS)

    Sheffield, Justin; Chaney, Nate; Yuan, Xing; Wood, Eric

    2013-04-01

    Drought has important but very different consequences regionally due to differences in vulnerability. These differences derive from variations in exposure related to climate variability and change, sensitivity of local populations, and coping capacity at all levels. Managing the risk of drought impacts relies on a variety of measures to reduce vulnerability that includes forewarning of drought development through early-warning systems. Existing systems rely on a variety of observing systems from satellites to local observers, modeling tools, and data dissemination methods. They range from sophisticated state-of-the-art systems to simple ground reports. In some regions, systems are virtually non-existent due to limited national capacity. This talk describes our experiences in developing and implementing drought monitoring and seasonal forecast systems in the US and sub-Saharan Africa as contrasting examples of the scientific challenges and user needs in developing early warning systems. In particular, early warning can help improve livelihoods based on subsistence farming in sub-Saharan Africa; whist reduction of economic impacts is generally foremost in the US. For the US, our national drought monitoring and seasonal forecast system has been operational for over 8 years and provides near real-time updates on hydrological states at ~12km resolution and hydrological forecasts out to 9 months. Output from the system contributes to national assessments such as from the NOAA Climate Prediction Center (CPC) and the US National Drought Monitor (USDM). For sub-Saharan Africa, our experimental drought monitoring system was developed as a translation of the US system but presents generally greater challenges due to, for example, lack of ground data and unique user needs. The system provides near real-time updates based on hydrological modeling and satellite based precipitation estimates, and has recently been augmented by a seasonal forecast component. We discuss the

  8. Africa.

    ERIC Educational Resources Information Center

    Happel, Sue; Loeb, Joyce

    Although the activities in this unit are designed primarily for students in the intermediate grades, the document's text, illustrations, and bibliographic references are suitable for anyone interested in learning about Africa. Following a brief introduction and map work, the document is arranged into six sections. Section 1 traces Africa's history…

  9. Africa.

    ERIC Educational Resources Information Center

    Martz, Carlton

    2001-01-01

    This publication explores issues related to Africa. It examines the U.S. response to the Barbary pirate states (Morocco, Algiers, Tunis, Tripoli) in the early 19th century; the current AIDS crisis in Africa; and 14th century Mali and other Islamic lands through the eyes of Ibn Battuta, who traveled throughout the Muslim world. Each article…

  10. Seismic expression of depositional systems tracts and application to hydrocarbon exploration in Bredasdorp basin, offshore South Africa

    SciTech Connect

    Beamish, G.W.J.

    1989-03-01

    Postrift Cretaceous sequences of Bredasdorp basin, offshore South Africa, were rigorously analyzed using the unified application of the latest seismic-stratigraphic, sequence-stratigraphic, and depositional systems concepts. Using 101 seismic profiles totaling 5600 km, the authors identified ten cyclic depositional sequences bounded by nine type 1 and two type 2 unconformities. Component depositional systems tracts exhibit a distinct seismic expression and can be delineated using truncation and lap-out relationships. Lowstand systems tracts developed on type 1 unconformities, which resulted from relative sea level fall below the shelf edge. In a terrigenous clastic basin such as Bredasdorp, these tracts are interpreted as being composed of basin-floor turbidite fans, channels, and/or sheets. These features formed contemporaneously with the erosion of incised valleys and submarine canyons, followed by channelized slope fans and deltaic/coastal lowstand wedges that prograded during a relative sea level rise. Subsequent flooding of the shelf as relative sea level rise accelerated resulted in poorly defined transgressive systems tracts. With the relative sea level at a highstand, extensively developed deltaic/coastal systems prograded basinward exhibiting well-defined clinoforms. The major hydrocarbon plays in the lowstand tracts occur as mounded basin-floor turbidite fans, channel fills, and draped sheets and are found in the updip pinch-out of deltaic/coastal sandstones.

  11. Overview of Results from the Endeavour Seismic Tomography Experiment

    NASA Astrophysics Data System (ADS)

    Toomey, D. R.; Hooft, E. E.; Wilcock, W. S.; Weekly, R. T.; Wells, A. E.; Soule, D. C.

    2011-12-01

    We report on our continuing analyses of a multi-scale seismic tomography experiment of the Endeavour segment of the Juan de Fuca Ridge. In August 2009 we deployed 68 four-component ocean bottom seismometers (OBSs) at 64 sites throughout a 90x50 km2 area to record seismic energy from 5567 shots of the 36-element, 6600 in.3 airgun array of the R/V Marcus G. Langseth. The experimental geometry utilized 3 nested scales and was designed to image (1) crustal thickness variations within 25 km of the axial high (0 to 900 kyr); (2) the map view heterogeneity and anisotropy of the topmost mantle beneath the spreading axis; (3) the three-dimensional structure of the crustal magmatic system and (4) the detailed three-dimensional, shallow crustal thermal structure beneath the Endeavour vent fields. The 90-km-long Endeavour segment lies between the Cobb and Endeavour overlapping spreading centers (OSCs), which are converging and thus shortening the Endeavour segment. Previous seismic reflection studies indicate that the central Endeavour segment is on a 40-km-wide plateau of greater crustal thickness that is interpreted to have developed when the ridge overrode the mantle melt anomaly associated with the Heckle seamount chain. The central Endeavour is also underlain by an axial magma chamber (AMC) reflector that is shallowest and most prominent beneath the hydrothermal fields. Geophysical studies of Endeavour thus permit investigation of the competing effects of tectonic, magmatic and hydrothermal processes on crustal structure and architecture. Ongoing analyses include tomographic inversion of first-arriving P waves that sample the upper- and mid-crustal regions, characterization of off-axis magma bodies via travel time and amplitude anomalies of crustal phases, estimation of regional-scale crustal thickness variations from analysis of PmP arrivals and imaging of mantle structure using Pn to constrain mantle flow and melt distribution [Weekly et al.; Wells et al.; Soule et al

  12. OSI Passive Seismic Experiment at the Former Nevada Test Site

    SciTech Connect

    Sweeney, J J; Harben, P

    2010-11-11

    its effectiveness for OSI purposes has yet to be determined. For this experiment, we took a broad approach to the definition of ''resonance seismometry''; stretching it to include any means that employs passive seismic methods to infer the character of underground materials. In recent years there have been a number of advances in the use of correlation and noise analysis methods in seismology to obtain information about the subsurface. Our objective in this experiment was to use noise analysis and correlation analysis to evaluate these techniques for detecting and characterizing the underground damage zone from a nuclear explosion. The site that was chosen for the experiment was the Mackerel test in Area 4 of the former Nevada Test Site (now named the Nevada National Security Site, or NNSS). Mackerel was an underground nuclear test of less than 20 kT conducted in February of 1964 (DOENV-209-REV 15). The reason we chose this site is because there was a known apical cavity occurring at about 50 m depth above a rubble zone, and that the site had been investigated by the US Geological Survey with active seismic methods in 1965 (Watkins et al., 1967). Note that the time delay between detonation of the explosion (1964) and the time of the present survey (2010) is nearly 46 years - this would not be typical of an expected OSI under the CTBT.

  13. Twentieth century seismicity of the Koffiefontein region (Free State, South Africa): consistent determination of earthquake catalogue parameters from mixed data types

    NASA Astrophysics Data System (ADS)

    Strasser, F. O.; Albini, P.; Flint, N. S.; Beauval, C.

    2015-10-01

    The preparation of earthquake catalogues for seismic hazard analysis requires the use of uniform parameters, in particular for magnitudes, although the original data include a variety of formats, such as macroseismic intensities and various instrumental magnitude scales. In regions of low seismicity, such as South Africa, data are generally sparse and not always sufficient to develop locally calibrated conversion relations. They can nevertheless be used to test the applicability of imported conversion relations, as well as their consistency. The Koffiefontein region of South Africa provides a good test case in view of its somewhat higher level of seismicity, and central geographic location within the country. This paper reviews determinations of location and magnitude parameters for a suite of moderate-to-large earthquakes that have occurred in this region between 1903 and 1985.

  14. US Geological Survey begins seismic ground response experiments in Washington State

    USGS Publications Warehouse

    Tarr, A.C.; King, K.W.

    1988-01-01

    This article briefly describes the experimental monitoring of minor seismic features caused by distant nuclear explosions, mining blasts and rhythmic human pushing against wooden homes. Some means of response prediction are outlined in Washington State and some effects of seismic amplification by weak clayey sediments are described. The results of several experiments are described. -A.Scarth

  15. Acquiring unpublished population documents in Africa: a personal experience.

    PubMed

    Kwafo-akoto, K O

    1988-04-01

    Acquiring both published and unpublished documents produced in Africa is, generally, a difficult task due to the existing poor state of bibliographic control and the publishing industry. It is even more difficult to obtain unpublished documents in a specialized area of study such as demography--a diffuse area which cuts across several disciplines. This paper discusses the problems encountered on acquisition trips to some African countries to acquire unpublished population material. To help solve the problems, the Population Association of Africa must persuade its members to send copies of their publications to population libraries and documentation centers in their individual countries for dissemination to the other users in Africa. The various organizations and institutions in Africa engaged in the teaching and research of population studies should have an agreement to exchange copies of their theses. The Economic Commission for Africa (ECA) and the Organization of African Unity (OAU) should make representations to the various African member countries on the need to disseminate the results of vital censuses and surveys conducted. Finally, the Population Information Network for Africa (POPIN-AFRICA) with its coordinating unit at the population division of ECA should ensure that all the nodes of the network have the financial and other resources to be able to acquire the relevant documents needed for their operations. PMID:12341802

  16. Risk equalisation and voluntary health insurance: The South Africa experience.

    PubMed

    McLeod, Heather; Grobler, Pieter

    2010-11-01

    South Africa intends implementing major reforms in the financing of healthcare. Free market reforms in private health insurance in the late 1980s have been reversed by the new democratic government since 1994 with the re-introduction of open enrolment, community rating and minimum benefits. A system of national health insurance with income cross-subsidies, risk-adjusted payments and mandatory membership has been envisaged in policy papers since 1994. Subsequent work has seen the design of a Risk Equalisation Fund intended to operate between competing private health insurance funds. The paper outlines the South African health system and describes the risk equalisation formula that has been developed. The risk factors are age, gender, maternity events, numbers with certain chronic diseases and numbers with multiple chronic diseases. The Risk Equalisation Fund has been operating in shadow mode since 2005 with data being collected but no money changing hands. The South African experience of risk equalisation is of wider interest as it demonstrates an attempt to introduce more solidarity into a small but highly competitive private insurance market. The measures taken to combat over-reporting of chronic disease should be useful for countries or funders considering adding chronic disease to their risk equalisation formulae. PMID:20619476

  17. Seismic while drilling: Operational experiences in Viet Nam

    SciTech Connect

    Jackson, M.; Einchcomb, C.

    1997-03-01

    The BP/Statoil alliance in Viet Nam has used seismic while drilling on four wells during the last two years. Three wells employed the Western Atlas Tomex system, and the last well, Schlumberger`s SWD system. Perceived value of seismic while drilling (SWD) lies in being able to supply real-time data linking drill bit position to a seismic picture of the well. However, once confidence in equipment and methodology is attained, SWD can influence well design and planning associated with drilling wells. More important, SWD can remove uncertainty when actually drilling wells, allowing risk assessment to be carried out more accurately and confidently.

  18. The seismicity in Kenya (East Africa) for the period 1906-2010: A review

    NASA Astrophysics Data System (ADS)

    Mulwa, J. K.; Kimata, F.; Suzuki, S.; Kuria, Z. N.

    2014-01-01

    Kenya has had a seismic station since 1963 as part of the World Wide Standardized Seismograph Network (WWSSN). In 1990, the University of Nairobi in collaboration with GeoForschungsZentrum (GFZ) started to build up a local seismological network, the Kenya National Seismic Network (KNSN), which operated for about ten years between 1993-2002. This, however, experienced a myriad of problems ranging from equipment breakdown, vandalism and lack of spares. Kenya is seismically active since the Kenya rift valley traverses through the country from north to south bisecting the country into eastern and western regions. In the central part, the Kenya rift branches to form the NW-SE trending Kavirondo (Nyanza) rift. The Kenya rift valley and the Kavirondo (Nyanza) rift are the most seismically active where earthquakes of local magnitude (Ml) in the order of ⩽2.0-5.0 occur. Furthermore, historical records show that earthquakes of magnitudes of the order of Ml ⩾ 6.0 have occurred in Kenya. Such large magnitude earthquakes include the January 6, 1928 Subukia earthquake (Ml 7.1) and an aftershock (Ml 6.2) four days later, as well as the 1913 Turkana region earthquake (Ml 6.2). Since early 1970's, numerous seismic investigations have been undertaken in Kenya in order to understand the formation and structure of the Kenyan part of the East African rift valley. Earthquake data from these studies is, however, rather disorganized and individual datasets, including that acquired during the period 1993-2002, cannot furnish us with comprehensive information on the seismicity of Kenya for the past ∼100 years. The purpose of this paper is, therefore, to review the seismicity in Kenya for the period 1906-2010 by utilizing data and results from different sources. The general seismicity of Kenya has been evaluated using historical data, data recorded by local seismic networks, the United States Geological Survey catalogue as well as earthquake data from the numerous seismic

  19. Simulation of Seismic Tunnel Detection Experiments in Heterogeneous Geological Media

    NASA Astrophysics Data System (ADS)

    Sherman, C. S.; Glaser, S. D.; Rector, J.

    2013-12-01

    Detecting covert tunnels and other underground openings is an important yet challenging problem for geophysicists, especially where geological heterogeneity is pronounced. A number of geophysical methods have been employed to solve this problem, each with varying degrees of success. We focus on the near-surface seismic techniques of surface wave backscattering, surface wave attenuation tomography, body wave diffraction imaging, and resonant imaging. We use the elastodynamic wave propagation code E3D to simulate tunnel detection experiments completed at this site for a range of synthetic fractal velocity models. The Black Diamond mine, located near Pittsburg California, is used for the field test of our analysis. Our results show that for the relatively low-frequency surface wave attenuation and backscattering methods, the maximum detectable tunnel depth in a homogenous medium is approximately equal to the wavelength of the probing Rayleigh wave. The higher-frequency body wave diffraction and resonant imaging techniques are able to locate tunnels at greater depths, but require more sophisticated analysis and are prone to greater attenuation losses. As is expected, for large values of heterogeneity amplitude, ɛ, the percent standard deviation from the mean velocity model, the average observed surface wave attenuation signal decreases and the maximum detectable tunnel depth decreases. However, for moderate values of heterogeneity amplitude (ɛ < 3%), the average surface wave attenuation signal increases and the maximum detectable tunnel depth increases. For the body wave diffraction and resonant imaging experiments, as ɛ increases the complexity of the observed signal increases, resulting in more difficult processing and interpretation. The additional scattering attenuation tends to degrade the signals significantly due to their reliance on lower amplitude and higher frequency waves.

  20. Bandung seismic experiment: Towards tomographic imaging by using ambient seismic noise

    NASA Astrophysics Data System (ADS)

    Pranata, Bayu; Yudistira, Tedy; Saygin, Erdinc; Cummins, Phil R.; Widiyantoro, Sri; Zulfakriza, Nugraha, Andri D.

    2016-05-01

    Bandung is one of the most densely populated cities in Indonesia with vital infrastructures. On the other hand, this area is surrounded by potential sources of earthquakes that make Bandung vulnerable to earthquakes. Structure of seismic velocity and sediment thickness are crucially needed in the earthquake hazard reduction program for Bandung. Based on this consideration, we deployed 64 seismic stations over the Bandung basin to record seismic ambient noise. In this study, we employed a cross-correlation method to the simultaneously recorded data to retrieve interstation Green's functions. We measured group velocity of the retrieved Green's functions by using frequency-time analysis technique. By the end of this project, the set of interstation group velocity will be inverted to image the shallow seismic velocity structure of the Bandung basin and its surrounding areas including Mt. Tangkuban Parahu and Lembang fault. As the first stage of this work, currently we focus on Green ' s function calculation as well as the interstation group velocity measurements. The general characteristics of group velocity can be evaluated from the plot of cross-correlation function as a function of its interstation distance.

  1. Local seismic events in area of Poland based on data from PASSEQ 2006-2008 experiment

    NASA Astrophysics Data System (ADS)

    Polkowski, Marcin; Plesiewicz, Beata; Wiszniowski, Jan; Wilde-Piórko, Monika; Passeq Working Group

    2014-05-01

    PASSEQ 2006-2008 (Passive Seismic Experiment in TESZ; Wilde-Piórko et al, 2008) was the biggest so far passive seismic experiment in the area of Central Europe (Poland, Germany, Czech Republic and Lithuania). 196 seismic stations (including 49 broadband seismometers) worked simultaneously for over two years. During experiment multiple types of data recorders and seismometers were used making analysis more complex and time consuming. Dataset was unified and repaired to start the detection of local seismic events. Two different approaches for detection were applied for stations located in Poland. One used standard STA/LTA triggers (Carl Johnson's STA/LTA algorithm) and grid search to classify and locate events. Result was manually verified. Other approach used Real Time Recurrent Network (RTRN) detection (Wiszniowski et al, 2014). Both methods gave similar results showing four previously unknown seismic events located in area of Gulf Of Gdańsk in southern Baltic Sea. The investigation of local seismicity is a good opportunity for verification of new seismic models of lithosphere in the area. In this paper we discuss both detection methods with their pros and cons (accuracy, efficiency, manual work required, scalability). We also show details of all detected and previously unknown events in discussed area. This work was partially supported by NCN grant UMO-2011/01/B/ST10/06653.

  2. Field experiment in Soultz-sous-Forêts, 1993: Changes of the pattern of induced seismicity

    NASA Astrophysics Data System (ADS)

    Smirnov, Vladimir; Ponomarev, Alexander; Bernard, Pascal; Bourouis, Seid

    2013-12-01

    The data of the known field experiment on water injection in the borehole were analyzed. Parameters of self-similarity of seismicity were estimated in comparison with the changes of water pressure. Changes of seismicity parameters that indicate the redistribution of the failure from lower scales to upper are revealed. The total number of earthquakes per series of the water initiation found to be depended exponentially on the water pressure and seismic activity maximum is delayed gradually relative to beginning of initiation. The growth of induced seismicity zone in time differs from diffusion model for water flow in the porous medium. Analysis carried out from laboratory data indicates that diffusion growth of the failure area may be realized in the dry specimen, without fluid. It could be assumed that both kinetic processes — water and the failure diffusion — can be significant for the development of seismicity induced by the water injection.

  3. Recent Seismic Experiments of OBS in the South China Sea

    NASA Astrophysics Data System (ADS)

    Ruan, A.; Li, J.; Wu, Z.

    2012-12-01

    Since 2006 some research institutions of China have carried out some important seismic experiments by using ocean bottom seismometer(OBS) in the South China Sea (SCS) and obtained many concrete progresses in modeling the crustal structure of SCS and also in understanding of its formation and evolution as well. In 2006 three wide-angle profiles were completed in the northern margin, named OBS2006-1 across the northwestern sub-basin, OBS2006-2 parallel to the sea basin boundary and OBS2006-3 across the Dongsha Rise and Chaoshan Depression respectively. In 2010 two wide- angle profiles were completed, named OBS2010-1 and OBS 2010-2 both perpendicular to the northern off-shore faulting system. During 2009-2011 four wide-angle profiles were completed in the southern margin, named OBS973-1 from southern margin to the southwestern sub-basin, OBS973-2 from Liyue Bank to the southwestern sub-basin and OBS973-3 from Xisha to the southwestern sub-basin, OBS2011-2 from Xisha to Hainan Island respectively. In 2011 two 3D seismic array of OBS were completed in the Zhongnan-Changlong sea mount chain and Huangyan-Zhenbei sea mount chain respectively. Here we present some primary but important results as follows. (1) The velocity model of OBS2006-1 indicates that the crust under the continental slope decreases from 21km to 11km, and to 7.7km in the northwestern sub-basin with Moho depth ascends from 21km to 11km. The tectonic geometry and velocity structure of the northwestern sub-basin and its margins on both sides shows symmetrical and conjugate and indicates pure shear mode of continental margin rifting mechanism. (2) The velocity model of OBS2006-3 reveals remarkable thickness with maximum 8 km of the Mesozoic sediment in Chaoshan Depression in which velocity increases downward from 4.4 km/s at top to 5.3 km/s at the bottom. The buried depth of Moho decreases from 24-25 km under Dongsha Rise to 17 km in the lower slope and an obviously velocity abnormal is detected in the upper

  4. Mathematics Registers in Indigenous Languages: Experiences from South Africa

    ERIC Educational Resources Information Center

    Schafer, Marc

    2010-01-01

    Through reporting on an initiative in South Africa that aimed to provide epistemological access to teachers and learners of mathematics (and science) through translating mathematical concepts into two indigenous languages, this paper argues for the urgent development of mathematical registers in indigenous languages for mathematics and …

  5. Seismic Images of the Gulf Stream Front off the Coast of North Carolina from the 2014 ENAM Community Seismic Experiment

    NASA Astrophysics Data System (ADS)

    Blacic, T. M.

    2014-12-01

    The Eastern North America Margin (ENAM) Community Seismic Experiment (CSE) is scheduled to collect on- and offshore active source seismic data including more than 2500 km of multichannel seismic (MCS) reflection profiles in the fall of 2014. The project was designed to address a wide array of questions related to the evolution and modification of the eastern North American rifted margin in conjunction with the arrival of the Earthscope transportable array on the US East Coast. The planned rifting-parallel profiles north and south of Cape Hatteras are expected to cross the front between the warm water of the Gulf Stream western boundary current and colder North Atlantic water providing the opportunity to image mesoscale features related to the front and their associated fine structure. Standard MCS data has been shown to be well-tuned to image ocean fine structure resulting from abrupt vertical changes in temperature and salinity in the ocean. Thus, the same seismic data that is collected to investigate the sub-seafloor geology can also be processed to image reflections in the water that reveal ocean processes with a horizontal resolution of ~10 m and vertical resolution of ~4 m. As an add-on to the ENAM CSE, 30 additional expendable bathythermographs and 3 conductivity temperature depth probes belonging to the University of Wyoming are planned for deployment during the collection of the MCS profiles resulting in an average hydrographic profile spacing of ~33 km. We present a first look at this new seismic oceanography data set providing 2-D images of ocean acoustic reflectivity correlated with closely spaced hydrographic measurements across the Gulf Stream front.

  6. A strategy for implementation of experience based seismic equipment qualification in IEEE and ASME industry standards

    SciTech Connect

    Adams, T.M.

    1996-12-01

    In the past 20 years, extensive data on the performance of mechanical and electric equipment during actual strong motion earthquakes and seismic qualification tests has been accumulated. Recognizing that an experience based approach provides a technically sound and cost effective method for the seismic qualification of some or certain equipment, the IEEE Nuclear Power Engineering Committee and the ASME Committee on Qualification of Mechanical Equipment established a Special Working Group to investigate the incorporation of experienced based methods into the industry consensus codes and standards currently used in the seismic qualification of Seismic Category Nuclear Power Plant equipment. This paper presents the strategy (course of action) which was developed by the Special Working Group for meeting this objective of incorporation of experience based seismic qualification standards used in the design and seismic qualification of seismic category nuclear power plant equipment. This strategy was recommended to both chartering organizations, the IEEE Nuclear Power Engineering Committee and the ASME Committee on Qualification of Mechanical Equipment for their consideration and implementation. The status of the review and implementation of the Special Working Group`s recommended strategy by the sponsoring organization is also discussed.

  7. Study of Local Seismic Events in Lithuania and Adjacent Areas Using Data from the PASSEQ Experiment

    NASA Astrophysics Data System (ADS)

    Janutyte, Ilma; Kozlovskaya, Elena; Motuza, Gediminas

    2013-05-01

    The territory of Lithuania and adjacent areas of the East European Craton have always been considered a region of low seismicity. Two recent earthquakes with magnitudes of more than 5 in the Kaliningrad District (Russian Federation) on 21 September 2004 motivated re-evaluation of the seismic hazard in Lithuania and adjacent territories. A new opportunity to study seismicity in the region is provided by the PASSEQ (Pasive Seismic Experiment) project that aimed to study the lithosphere-asthenosphere structure around the Trans-European Suture Zone. Twenty-six seismic stations of the PASSEQ temporary seismic array were installed in the territory of Lithuania. The stations recorded a number of local and regional seismic events originating from Lithuania and adjacent areas. This data can be used to answer the question of whether there exist seismically active tectonic zones in Lithuania that could be potentially hazardous for critical industrial facilities. Therefore, the aim of this paper is to find any natural tectonic seismic events in Lithuania and to obtain more general view of seismicity in the region. In order to do this, we make a manual review of the continuous data recorded by the PASSEQ seismic stations in Lithuania. From the good quality data, we select and relocate 45 local seismic events using the well-known LocSAT and VELEST location algortithms. In order to discriminate between possible natural events, underwater explosions and on-shore blasts, we analyse spatial distribution of epicenters and temporal distribution of origin times and perform both visual analysis of waveforms and spectral analysis of recordings. We show that the relocated seismic events can be grouped into five clusters (groups) according to their epicenter coordinates and origin and that several seismic events might be of tectonic origin. We also show that several events from the off-shore region in the Baltic Sea (at the coasts of the Kaliningrad District of the Russian Federation) are

  8. Integrated application of gravity and seismic methods for determining the dip angle of a fault plane: Case of Mahjouba fault (Central Tunisian Atlas Province, North Africa)

    NASA Astrophysics Data System (ADS)

    Gabtni, H.; Hajji, O.; Jallouli, C.

    2016-07-01

    A procedure for a dip angle determination of a fault plane from gravity field data is presented to constrain a seismic profile interpretation. This procedure is applied on Mahjouba normal fault at the western border of Kalaa Khesba graben (Central Tunisian Atlas Province, North Africa). Seismic and detailed gravity data, in this region, were analyzed to provide more constraints on the geometry of the fault dip angle. The Mahjouba fault is mapped as three major parallel lineaments extended for 2 km with a NW-SE to N-S trend. The dip of the Mahjouba fault is estimated from the gravity modeling data to be 45°E. This study reveals that integrating gravity and seismic data provides accurate mapping of faults geometry and such result provides useful information and constraints on the exploration of natural resources.

  9. Reduce seismic design conservatism through large-scale earthquake experiments

    SciTech Connect

    Tang, H.T.; Stepp, J.C. )

    1992-01-01

    For structures founded on soil deposits, the interaction between the soil and the structure caused by incident seismic waves modifies the foundation input motion and the dynamic characteristics of the soil-structure system. This paper reports that as a result, soil-structure interaction (SSI) plays a critical role in the design of nuclear plant structures. Recognizing that experimental validation and quantification is required, two scaled cylindrical reinforced-concrete containment models (1/4-scale and 1/12-scale of typical full-scale reactor containments) were constructed in Lotung, an active seismic region in Taiwan. Forced vibration tests (FBT) were also conducted to characterize the dynamic behavior of the soil-structure system. Based on these data, a series of round-robin blind prediction and post-test correlation analyses using various currently-available SSI methods were performed.

  10. Las Vegas Basin Seismic Response Project: Preliminary Results From Seismic Refraction Experiments, Las Vegas, NV.

    NASA Astrophysics Data System (ADS)

    Zaragoza, S. A.; Snelson, C. M.; Harder, S. H.; Kaip, G.; Luke, B.; Buck, B. J.; Hanson, A. D.

    2002-12-01

    In May and September 2002, seismic refraction data were acquired in the Las Vegas basin. Located in the southern Basin and Range province, the cities of Las Vegas, North Las Vegas, and Henderson sit atop a fault-bounded basin with a depth of up to 5 km and basin dimensions of roughly 60 km wide (east-west) by 50 km in length (north-south). Previous isostatic gravity, seismic reflection, and aeromagnetic studies indicate that a series of sub-basins exist beneath the unconsolidated basin fill, with the deepest sub-basin occurring 5 km west of the fault block bounding the eastern edge of the basin (Frenchman Mountain). The basin is significantly deeper along its northern extremity, following the path of the fault block bounding the northern edge of the basin (Las Vegas Valley Shear Zone), and along the western edge of Frenchman Mountain. Recent, paleoseismic studies have indicated that faults in the Las Vegas region have the potential for an earthquake of M6.5 to 7.0. It is estimated that a M6.9 earthquake in the basin could produce about 11 billion dollars in damage and a significant number of deaths and/or injuries. In addition, an equivalent or larger event in the Death Valley fault zone, 150 km distance, would also be devastating to the metropolitan area of approximately 1.5 million residents. Therefore, it is essential to understand the seismic hazard posed to the Las Vegas region. This project is part of a larger collaborative effort to characterize the basin and its response to ground shaking. The University of Nevada, Las Vegas with assistance from the University of Texas at El Paso, students from UNLV and UTEP, volunteers from the community and several students from Centennial High school deployed 432 portable seismic recorders ("Texans") throughout the valley. Shot point locations were located at three quarries in the valley, one to the north, one to the east and one to the southwest. The profiles cross the Las Vegas Valley Shear zone as well as a prominent

  11. Deep seismic exploration into the Arctic Lithosphere: Arctic-2012 Russian wide-angle seismic experiment

    NASA Astrophysics Data System (ADS)

    Kashubin, S.

    2013-12-01

    Integrated geological and geophysical studies of the Earth's crust and upper mantle (the Russian project 'Arctic-2012') were carried out in 2012 in the Mendeleev Rise, central Arctic. The set of studies included wide-angle seismic observations along the line crossing the Mendeleev Rise in its southern part. The DSS seismic survey was aimed at the determination of the Mendeleev Rise crust type. A high-power air gun (120 liters or 7320 cu.in) and ocean stations with multi-component recording (X, Y, Z geophone components and a hydrophone) were used for the DSS. The line was studied using a dense system of observation: bottom station spacing was from 10 to 20 km, excitation point spacing (seismic traces interval) was 315 m. Observation data were obtained in 27 location points of bottom stations, the distance between the first and the last stations was 480 km, the length of the excitation line was 740 km. In DSS wave fields, in the first and later arrivals, there are refracted and reflected waves associated with boundaries in the sedimentary cover, with the top of the basement, and with boundaries in the consolidated crust, including its bottom (Moho discontinuity). The waves could be traced for offsets up to 170-240 km. The DSS line coincides with the near-vertical CMP line worked out with the use of a 4500-m-long seismic streamer and with a 50 m shot point interval that allowed essential detalization of the upper part of the section and taking it into account in the construction of a deep crust model. The deep velocity model was constructed using ray-trace modeling of compressional, shear, and converted waves with the use of the SeisWide program. Estimates were obtained for Vp/Vs velocity ratios, which played an important role in determining the type of crust. The results of the interpretation show that the Mendeleev Rise section corresponds to sections of a thin continental crust of shelf seas and a thinned continental crust of submarine ridges and rises.

  12. Seismic sequence stratigraphy of the Lower Congo, Kwanza, and Benguela Basins, offshore Angola, Africa

    NASA Astrophysics Data System (ADS)

    Schollnberger, Elle Marie

    2001-07-01

    Sequences are recognized throughout the geologic record. The Angolan margin provides an excellent opportunity to examine the factors that control the deposition and preservation of sediments in sequences, as well as the factors that create the erosion or non-deposition along sequence boundaries. The Angolan sequences can be compared to global sequence charts and used to investigate the effects of local events versus global events on the area's sequences. Using seismic sequence stratigraphic principles, a 2D regional seismic data set covering three basins offshore Angola, the Lower Congo, Kwanza, and Benguela Basins, was interpreted. Sequences and their unconformities were correlated within each basin as well as between basins. Major sequences could be interpreted throughout and between the three basins with a high degree of confidence. Additional sequences within these major sequences were interpreted within a basin, but could not be correlated to the adjacent basin with a high degree of confidence. Detailed interpretation of the sequence stratigraphic significance of each reflector was performed on three profiles, one for each basin. Chronostratigraphic charts were constructed using the detailed interpretation of the profiles. Within the interpreted sequence stratigraphic framework, the timing and mechanics of the formation of salt structures was examined. The Angolan basins contain a variety of salt tectonic features. The reflectors of strata adjacent to the salt features were used to determine the timing and mechanics of the salt structure formation. This study accomplished several objectives. The tectonic evolution of the Angolan margin was reviewed. This study established a sequence stratigraphic framework for Angola. The process of deposition and preservation of sediments as depositional sequences was examined. The sequences were compared with the global sequence charts as well as with eustatic, tectonic, and oceanic circulation events. The formation of the

  13. Water percolation induced seismicity: evidences from low scale in-situ experiment

    NASA Astrophysics Data System (ADS)

    Saetta, V.; Amitrano, D.; Guglielmi, Y.; Senfaute, G.

    2003-04-01

    The aim of the paper is to investigate the correlation between the hydro-mechanical behaviour and the seismicity induced by hydraulic loading in a fractured rock mass. The experiments have been performed in a low scale fractured rock mass (1500 m3). The site is a small reservoir composed of a 17 m thick pile of Lower Cretaceous fractured limestone limited at the top and the bottom by a two-meter thick, impervious marl layer. A water-gate installed on the draining spring allows to artificially induce a 0.1 MPa hydraulic loading within the fracture network. Hydro - mechanical studies have pointed out different type of behaviour for rock joints thanks to punctual measurements of water pressure and deformations. The results of seismic monitoring show that the most permeable joints are aseismic whereas the low permeability joint revealed a mesurable seismicity related to water percolation. The fluid pressure increase induces instability phenomena at low scale like the rupture of crystallised zone, the formation of new micro-fractures or the sudden opening and the shearing of bedding joints. The seismic events display temporal clustering as observed for induced seismicity at larger scale (dam, gas reservoir). These results reveal that even for low water pressure variation (up to 0.1 MPa) hydraulical loading of a fractured rock masse can induce observable seismicity. These low scale (1-10 m) results could be of interest for understanding induced seismicity at larger scale (100-1000 m like dam, reservoir etc.).

  14. Computing 3-D wavefields in mantle circulations models to test hypotheses on the origin of lower mantle heterogeneity under Africa directly against seismic observations

    NASA Astrophysics Data System (ADS)

    Schuberth, Bernhard; Zaroli, Christophe; Nolet, Guust

    2015-04-01

    Of particular interest for the tectonic evolution of the Atlantic region is the influence of lower mantle structure under Africa on flow in the upper mantle beneath the ocean basin. Along with its Pacific counterpart, the large African anomaly in the lowermost mantle with strongly reduced seismic velocities has received considerable attention in seismological and geodynamic studies. Several seismological observations are typically taken as an indication that these two anomalies are being caused by large-scale compositional variations and that they are piles of material with higher density than normal mantle rock. This would imply negative buoyancy in the lowermost mantle under Africa, which has important implications for the flow at shallower depth and inferences on the processes that led to the formation of the Atlantic Ocean basin. However, a large number of recent studies argue for a strong thermal gradient across the core-mantle boundary that might provide an alternative explanation for the lower mantle anomaly through the resulting large lateral temperature variations. Recently, we developed a new joint forward modeling approach to test such geodynamic hypotheses directly against the seismic observations: Seismic heterogeneity is predicted by converting the temperature field of a high-resolution 3-D mantle circulation model into seismic velocities using thermodynamic models of mantle mineralogy. 3-D global wave propagation in the synthetic elastic structures is then simulated using a spectral element method. Being based on forward modelling only, this approach allows us to generate synthetic wavefields and seismograms independently of seismic observations. The statistics of observed long-period body wave traveltime variations show a markedly different behaviour for P- and S-waves: the standard deviation of P-wave delay times stays almost constant with ray turning depth, while that of the S-wave delay times increases strongly throughout the mantle. In an

  15. A New Generation of Large Seismic Refraction Experiments in Central Europe (1997-2003)

    NASA Astrophysics Data System (ADS)

    Guterch, A.; Grad, M.; Spicak, A.; Brueckl, E.; Hegedus, E.; Keller, G. R.; Thybo, H.

    2003-12-01

    Beginning in 1997, Central Europe has been covered by an unprecedented network of seismic refraction experiments. These experiments (POLONAISE'97, CELEBRATION 2000, ALP 2002, SUDETES 2003) have only been possible due a massive international cooperative effort. The total length of all profiles is about 19,000 km, and over 300 explosive sources were employed. The result is a network of seismic refraction profiles that extends along the Trans-European Suture Zone region of Poland and the Bohemian massif, Pannonian basin, trough the Carpathians and Alps to the Adriatic Sea and the Dinarides. As reflected in structures within these areas, Central Europe has experienced a complex tectonic history that includes the Caledonian, Variscan, and Alpine orogenies. The related TESZ region is a broad zone of deformation that extends across Europe from British Isles to the Black Sea region that formed as Europe was assembled from a complex collage of terranes during the late Palaeozoic. For example, the Bohemian massif is mostly located in the Czech Republic and is a large, complex terrane whose origin can be traced to northern Gondwana (Africa). These terranes were accreted along the margin of Baltica that was formed during the break-up of Rodinia. The tectonic evolution of this region shares many attributes with the Appalachian/Ouachita origin and is certainly of global important to studies in terrane tectonics and continental evolution. In southern Poland, several structural blocks are located adjacent to Baltica and were probably transported laterally along it similar to the Cenozoic movement of terranes along the western margin of North America. The younger Carpathian arc and Pannonian back-arc basin were also targeted by these experiments. Thickness of the crust in the area of investigations changes from 22-25 km in the Pannonian basin to about 55 km in the Trans-European Suture Zone in SE Poland. Together, these experiments are providing an unprecedented 3-D image of the

  16. Local Knowledge and Experiences of Vaccination: Implications for HIV-Preventive Vaccine Trials in South Africa

    ERIC Educational Resources Information Center

    Lindegger, Graham; Quayle, Michael; Ndlovu, Moses

    2007-01-01

    This study forms part of the preparation of communities for HIV-preventive vaccine trials in South Africa. On the basis of the assumption that attitudes to any HIV vaccine or vaccine trials will partly be influenced by experiences of vaccination in general, this study aimed to investigate knowledge of, attitudes to, and experiences of vaccination…

  17. Structural evolution beneath Sakurajima Volcano, Japan, revealed through rounds of controlled seismic experiments

    NASA Astrophysics Data System (ADS)

    Tsutsui, Tomoki; Iguchi, Masato; Tameguri, Takeshi; Nakamichi, Haruhisa

    2016-04-01

    Structural evolution beneath an active volcano is detected as the variation of seismic reflectivity through controlled seismic experiments, which is interpreted as being associated with discharging magma. The target of the present study is Sakurajima Volcano, which is one of the most active volcanoes in Japan. Six rounds of seismic experiments with controlled sources have been conducted annually at the volcano. Two seismic reflection profiles are obtained from the datasets for each successful round of experiments. The experiments reveal clear annual variation in seismic reflectivity at a depth of 6.2 km in the northeastern part of Sakurajima. The reflectivity is maximum in December 2009 upon the first intrusion of magma and decreases gradually until December 2013, which coincides with the inflation and deflation cycle of Sakurajima Volcano. Reflectivity variation occurred in the embedded clear reflector at depth. An evolving sandwiched structure in the intermediate layer is used as the reflector model. Lower-velocity magma embedded in the intermediate layer and its succeeding velocity increment explain the variation range of reflectivity. This is interpreted as a temperature decrease associated with discharging magma at depth. The present study describes a new approach for instantaneously sensing magma properties and for monitoring active volcanoes.

  18. An active seismic experiment at Tenerife Island (Canary Island, Spain): Imaging an active volcano edifice

    NASA Astrophysics Data System (ADS)

    Garcia-Yeguas, A.; Ibañez, J. M.; Rietbrock, A.; Tom-Teidevs, G.

    2008-12-01

    An active seismic experiment to study the internal structure of Teide Volcano was carried out on Tenerife, a volcanic island in Spain's Canary Islands. The main objective of the TOM-TEIDEVS experiment is to obtain a 3-dimensional structural image of Teide Volcano using seismic tomography and seismic reflection/refraction imaging techniques. At present, knowledge of the deeper structure of Teide and Tenerife is very limited, with proposed structural models mainly based on sparse geophysical and geological data. This multinational experiment which involves institutes from Spain, Italy, the United Kingdom, Ireland, and Mexico will generate a unique high resolution structural image of the active volcano edifice and will further our understanding of volcanic processes.

  19. Deltas of the Lake Malawi rift, east Africa: Seismic expression and exploration implications

    SciTech Connect

    Scholz, C.A.

    1995-11-01

    High-resolution, air-gun-sourced seismic reflection surveys over the offshore regions of five river deltas in Lake Malawi in the East African rift system reveal considerable variability in acoustic facies and stratigraphic architecture. This variability can largely be attributed to the influences of different structural settings, and to a lesser degree to high-amplitude (100-400 m) and high-frequency (1000 to 100,000 yr) fluctuations in lake level. Deltas on flexural and axial margins in the rift lake show well-developed progradational geometries. In contrast, a delta on a steep, accommodation zone margin distributes coarse sediments over a broad depositional apron, rather than concentrating sediment in discrete progradational lobes as on the other deltas. A large border fault margin river delta displays the most complex tectonic and stratigraphic architecture of all the deltas studied. It contains several delta-associated facies, including prograding clinoform packages, fan deltas stacked against a boundary fault, and extensive subaqueous fans. Flexural margin lowstand deltas may be the most prospective for hydrocarbon exploration due to their large, internally well-organized, progradational lobes and their close proximity to deep-water, high total organic carbon lacustrine source facies.

  20. A Comparison of Seismicity Characteristics and Fault Structure Between Stick-Slip Experiments and Nature

    NASA Astrophysics Data System (ADS)

    Goebel, T. H. W.; Sammis, C. G.; Becker, T. W.; Dresen, G.; Schorlemmer, D.

    2015-08-01

    Fault zones contain structural complexity on all scales. This complexity influences fault mechanics including the dynamics of large earthquakes as well as the spatial and temporal distribution of small seismic events. Incomplete earthquake records, unknown stresses, and unresolved fault structures within the crust complicate a quantitative assessment of the parameters that control factors affecting seismicity. To better understand the relationship between fault structure and seismicity, we examined dynamic faulting under controlled conditions in the laboratory by creating saw-cut-guided natural fractures in cylindrical granite samples. The resulting rough surfaces were triaxially loaded to produce a sequence of stick-slip events. During these experiments, we monitored stress, strain, and seismic activity. After the experiments, fault structures were imaged in thin sections and using computer tomography. The laboratory fault zones showed many structural characteristics observed in upper crustal faults, including zones of localized slip embedded in a layer of fault gouge. Laboratory faults also exhibited a several millimeter wide damage zone with decreasing micro-crack density at larger distances from the fault axis. In addition to the structural similarities, we also observed many similarities between our observed distribution of acoustic emissions (AEs) and natural seismicity. The AEs followed the Gutenberg-Richter and Omori-Utsu relationships commonly used to describe natural seismicity. Moreover, we observed a connection between along-strike fault heterogeneity and variations of the Gutenberg-Richter b value. As suggested by natural seismicity studies, areas of low b value marked the nucleation points of large slip events and were located at large asperities within the fault zone that were revealed by post-experimental tomography scans. Our results emphasize the importance of stick-slip experiments for the study of fault mechanics. The direct correlation of

  1. Seismic evidence for the layered mantle lithosphere: a comparsion between Zagros and South Africa

    NASA Astrophysics Data System (ADS)

    Sodoudi, Forough; Kind, Rainer

    2014-05-01

    Recent S receiver function studies present evidence for the existence of the layered mantle lithosphere beneath ancient cratons. However, the nature of these layers is still unclear. They can be attributed to the presence of accumulated melts, remnants of subduction interfaces, changes in anisotropic properties or fluids. Further characterization of these layers is needed to provide more insights into the assembly and evolution of cratons. Here we compare the mantle lithosphere of the ancient Kalahari craton with the relatively young mantle lithosphere of Zagros, which is assumed as the location of the future craton. We applied the S receiver function method to map the internal layering of the lithosphere and to image its lower limit. For this aim, we used teleseismic events recorded at 97 seismic stations within the Kalahari craton and those recorded at 61 permanent seismic stations in Iran. Our results reveal a thick and stratified mantle lithosphere beneath the Kalahari craton containing three significant negative velocity contrasts at 85, 150-200, and 260-280 km depth. Moreover, they imply that frozen-in anisotropy as well as notable compositional variations can lead to sharp Mid-Lithospheric Discontinuities (MLD) that can be clearly observed in the SRF data. We show that a 50 km thick anisotropic layer just below the Moho boundary with 3% S wave anisotropy may be responsible for producing a MLD at 85 km depth. The horizontal anisotropy in the upper lithosphere may be attributed to processes during the formation of the Kalahari Craton. Furthermore, significant correlation between the depths of an apparent boundary separating the depleted and metasomatised lithosphere, as inferred from chemical tomography, and those of our second layer led us to characterize it as a compositional boundary, most likely due to the modification of the cratonic mantle lithosphere by magma infiltration. The largest velocity contrast (3.6-4.7%) is observed at a boundary located at

  2. Large-N Seismic Deployment at the Source Physics Experiment (SPE) Site

    NASA Astrophysics Data System (ADS)

    Chen, T.; Snelson, C. M.; Mellors, R. J.; Pitarka, A.

    2015-12-01

    The Source Physics Experiment (SPE) is multi-institutional and multi-disciplinary project that consists of a series of chemical explosion experiments at the Nevada National Security Site. The goal of SPE is to understand the complicated effect of earth structures on source energy partitioning and seismic wave propagation, develop and validate physics-based monitoring, and ultimately better discriminate low-yield nuclear explosions from background seismicity. Deployment of a large number of seismic sensors is planned for SPE to image the full 3-D wavefield with about 500 three-component sensors and 500 vertical component sensors. This large-N seismic deployment will operate near the site of SPE-5 shot for about one month, recording the SPE-5 shot, ambient noise, and additional controlled-sources. This presentation focuses on the design of the large-N seismic deployment. We show how we optimized the sensor layout based on the geological structure and experiment goals with a limited number of sensors. In addition, we will also show some preliminary record sections from deployment. This work was conducted under Contract No. DE-AC52-06NA25946 with the U.S. Department of Energy.

  3. Blood Trials: Transfusions, Injections, and Experiments in Africa, 1890-1920.

    PubMed

    Sunseri, Thaddeus

    2016-07-01

    From about 1880 to 1920, a culture of medical experimentation promoted blood transfusion as a therapy for severe anemia in Europe, which was applied in German East Africa in 1892 for a case of blackwater fever, a complication of malaria afflicting mainly Europeans. This first case of blood transfusion in Africa, in which an African's blood was transfused into a German official, complicates the dominant narrative that blood transfusions in Africa came only after World War I. Medical researchers moreover experimented with blood serum therapies on human and animal subjects in Europe and Africa, injecting blood of different species, "races" and ethnicities into others to demonstrate parasite transmissibility and to discover vaccines for diseases such as malaria, sleeping sickness, and yellow fever. While research in German colonies is highlighted here, this was a transnational medical culture that crossed borders and oceans. This research is of interest as a possible early pathway for the epidemic spread of HIV and other zoonoses in Africa and the world, which biomedical researchers have identified as emerging in West-Central Africa sometime around the turn of the twentieth century. PMID:26514397

  4. Development of performance criteria for advanced Viking seismic experiments

    NASA Technical Reports Server (NTRS)

    1972-01-01

    The characteristics and requirements of the seismic instrument for mapping the internal structure of the planet Mars are briefly described. The types of signals expected to exist are microseismic background generated by wind and pressure variations and thermal effects, disturbances of or in the landed vehicle, signals caused by faulting and volcanic activity, and signals due to meteoritic impacts. The advanced instrument package should include a short-period vertical component system, a long-period or wide-band 3-component system, a high frequency vertical component system, and a system for detection and rejection of lander noises. The Viking '75, Surveyor, and Apollo systems are briefly described as potential instruments to be considered for modification. Data processing and control systems are also summarized.

  5. Recording and investigation of the seismic signal generated by hypervelocity impact experiments and numerical models

    NASA Astrophysics Data System (ADS)

    Güldemeister, N.; Moser, D.; Wünnemann, K.; Hoerth, T.; Schäfer, F.

    2013-09-01

    Meteorite impacts can cause environmental consequences, one of which is the generation of ground motions that may exceed the magnitude of the largest earthquakes [1]. Impacts generate shock waves that attenuate with distance until they even tually turn into seismic waves. Thus, meteorite impact may be considered as a source for seismic shaking similar to earthquakes. Seismic signals have been recorded in explosion experiments [2] and in hydrocode models of large impact events such as the Chicxulub crater [3]. To determine how much of the kinetic energy Ekin of the impactoris turned into seismic energy Eseis can be investigated experimentally (by recording the acoustic emission) or by numerical models. The ratio of Eseis/Ekin is the so called seismic efficiency k. The seismic efficiency depends on material properties (porosity) and is usually estimated to range between 10-2 and 10-6 [2,4]. In the framework of the "MEMIN" (multidisciplinary experimental and modeling impact crater research network) project a suite of hypervelocity impact experiments on a decimeter scale have been carried out [5]. We use acoustic emission (AE) technique and pressure gauges in high spatiotemporal Meteorite impacts can cause environmental consequences, one of which is the generation of ground motions that may exceed the magnitude of the largest earthquakes [1]. Impacts generate shock waves that attenuate with distance until they even tually turn into seismic waves. Thus, meteorite impact may be considered as a source for seismic shaking similar to earthquakes. Seismic signals have been recorded in explosion experiments [2] and in hydrocode models of large impact events such as the Chicxulub crater [3]. To determine how much of the kinetic energy Ekin of the impactoris turned into seismic energy Eseis can be investigated experimentally (by recording the acoustic emission) or by numerical models. The ratio of Eseis/Ekin is the so called seismic efficiency k. The seismic efficiency depends

  6. Peru Subduction Zone Seismic Experiment (PeruSZE): Preliminary Results From a Seismic Network Between Mollendo and Lake Titicaca, Peru.

    NASA Astrophysics Data System (ADS)

    Guy, R.; Stubailo, I.; Skinner, S.; Phillips, K.; Foote, E.; Lukac, M.; Aguilar, V.; Tavera, H.; Audin, L.; Husker, A.; Clayton, R.; Davis, P. M.

    2008-12-01

    This work describes preliminary results from a 50 station broadband seismic network recently installed from the coast to the high Andes in Peru. UCLA's Center for Embedded Network Sensing (CENS) and Caltech's Tectonic Observatory are collaborating with the IRD (French L'Institut de Recherche pour le Developpement) and the Institute of Geophysics, in Lima Peru in a broadband seismic experiment that will study the transition from steep to shallow slab subduction. The currently installed line has stations located above the steep subduction zone at a spacing of about 6 km. In 2009 we plan to install a line of 50 stations north from this line along the crest of the Andes, crossing the transition from steep to shallow subduction. A further line from the end of that line back to the coast, completing a U shaped array, is in the planning phase. The network is wirelessly linked using multi-hop network software designed by computer scientists in CENS in which data is transmitted from station to station, and collected at Internet drops, from where it is transmitted over the Internet to CENS each night. The instrument installation in Peru is almost finished and we have been receiving data daily from 10 stations (out of total 50) since June 2008. The rest are recording on-site while the RF network is being completed. The software system provides dynamic link quality based routing, reliable data delivery, and a disruption tolerant shell interface for managing the system from UCLA without the need to travel to Peru. The near real-time data delivery also allows immediate detection of any problems at the sites. We are building a seismic data and GPS quality control toolset that would greatly minimize the station's downtime by alerting the users of any possible problems.

  7. Pre-instrumental seismicity in Central Africa using felt seisms recorded mainly at the meteorological stations of DRC, Rwanda and Burundi during the colonial period

    NASA Astrophysics Data System (ADS)

    Mulumba, J.-L.; Delvaux, D.

    2012-04-01

    Seismic hazard assessment and mitigation of catastrophes are primarily based on the identification and characterization of seismically active zones. These tasks still rely heavily on the existing knowledge of the seismic activity over the longest possible time period. The first seismic network in Equatorial Africa (IRSAC network) was operated from the Lwiro scientific base on the western shores of Lake Kivu between 1953 and 1963. Before this installation, the historical record of seismic activity in Central Africa is sparse. Even for the relatively short period concerned, spanning only 50-60 years, the historical record is far from being complete. A first attempt has been made by Herrinckx (1959) who compiled a list 960 felt seisms recorded at the meteorological stations between 1915 and 1954 in Congo, Rwanda and Burundi. They were used to draw a density map of felt seisms per square degree. We completed this data base by exploiting the meteorological archives and any available historical report to enlarge the database which now reaches 1513 entries between 1900 and 1959. These entries have been exanimate in order to identify possible historical seismic events. Those are defined by 3 or more quasi-simultaneous records observed over a relatively short distance (a few degrees of latitude/longitude) within a short time difference (few hours). A preliminary list of 115 possible historical seisms has been obtained, identified by 3 to 15 different stations. The proposed location is taken as the average latitude and longitude of the stations where the felt seisms were recorded. Some of the most important ones are associated to aftershocks that have been felt at some stations after the main shocks. The most recent felt seisms have been also recorded instrumentally, which helps to validate the procedure followed. The main difficulties are the magnitude estimation and the possible spatial incompleteness of the recording of felt seism evidence at the margin of the observation

  8. The BOrborema Deep Electromagnetic and Seismic (BODES) Experiment

    NASA Astrophysics Data System (ADS)

    Julià, J.; Garcia, X.; Medeiros, W. E.; Farias do Nascimento, A.

    2015-12-01

    The Borborema Province of NE Brazil is a large Precambrian domain of the Brazilian shield located in the Northeasternmost corner of South America. It is bounded by the Parnaíba basin to the West and by the São Francisco craton to the South. Its structuration in the Precambrian has been related to compressional processes during the Brasiliano-Pan African orogeny (600-550 Ma). In the Mesozoic, extensional stresses eventually leading to continental breakup, left a number of aborted rift basins within the Province. After continental breakup, the evolution of the Province was marked by episodes of uplift, which might have been coeval with episodes of Cenozoic volcanism. The most prominent expression of those uplift processes is the Borborema Plateau, an elliptically shaped topographic feature in the eastern half of the Province with maximum elevations of ~1200 m. The origin of uplift in the Plateau has been the focus of a number of multi-institutional and multi-disciplinary studies in the past few years, which have imaged the deep structure of the eastern Province with unprecedented detail. The origin of uplift in the western Province, which includes a superb example of basin inversion demonstrated by the ~1000 km elevations of the Chapada do Araripe, however, has been seldom investigated. With the goal of investigating the deep structure of the western Province, a temporary network of 10 collocated seismic and magnetotelluric stations was deployed in the region. The collocated stations were arranged in an approximately NS direction, with an interspation spacing of ~70 km and spanning a total length of ~600 km. The seismic stations consisted of broadband sensors (RefTek 151B-120 "Observer") sampling at 100 Hz and were deployed in January 2015; the MT stations consisted of long-period magnetotelluric (LEMI) systems, sampling at 1 Hz and 4 Hz, and were deployed in April 2015 for a period of ~2 weeks. Preliminary results based on teleseismic P-wave receiver functions

  9. Race and Assessment Practice in South Africa: Understanding Black Academic Experience

    ERIC Educational Resources Information Center

    Jawitz, Jeff

    2012-01-01

    Despite efforts to transform the racialised system of higher education in South Africa inherited from apartheid, there has been little research published that interrogates the relationship between race and the experience of academic staff within the South African higher education environment. Drawing on critical discourse analysis and critical…

  10. Enhancing Critical Consciousness through a Cross-Cultural Immersion Experience in South Africa

    ERIC Educational Resources Information Center

    Choi, Kyoung Mi; VanVoorhis, Richard W.; Ellenwood, Audrey E.

    2015-01-01

    Using phenomenological approaches, the author explored the meanings and essences of a cross-cultural immersion experience in South Africa among counseling master's-level students. Five core themes--the meaning of being American, sociopolitical awareness, engagement with South Africans and their communities, appreciation of life, and commitment to…

  11. Experiences of School Principals with Newcomers from War-Affected Countries in Africa

    ERIC Educational Resources Information Center

    Okoko, Janet Mola

    2011-01-01

    This article is based on the results of an exploratory study of experiences of 2 urban school principals about leading schools with immigrants from war-affected countries in Africa. It examines how they perceived their preparation for multicultural leadership, and explores lessons that leadership development institutions can learn from their…

  12. What Does an Inventory of Recent Innovation Experiences Tell Us about Agricultural Innovation in Africa?

    ERIC Educational Resources Information Center

    Triomphe, Bernard; Floquet, Anne; Kamau, Geoffrey; Letty, Brigid; Vodouhe, Simplice Davo; Ng'ang'a, Teresiah; Stevens, Joe; van den Berg, Jolanda; Selemna, Nour; Bridier, Bernard; Crane, Todd; Almekinders, Cornelia; Waters-Bayer, Ann; Hocde, Henri

    2013-01-01

    Purpose: Within the context of the European-funded JOLISAA project (JOint Learning in and about Innovation Systems in African Agriculture), an inventory of agricultural innovation experiences was made in Benin, Kenya and South Africa. The objective was to assess multi-stakeholder agricultural innovation processes involving smallholders. Approach:…

  13. The seismic-stratigraphic record of lake-level fluctuations in Lake Challa: Hydrological stability and change in equatorial East Africa over the last 140 kyr

    NASA Astrophysics Data System (ADS)

    Moernaut, J.; Verschuren, D.; Charlet, F.; Kristen, I.; Fagot, M.; De Batist, M.

    2010-02-01

    Seismic-reflection data from crater lake Challa (Mt. Kilimanjaro, equatorial East Africa) reveal a ˜ 210-m thick sedimentary infill containing distinct seismic-stratigraphic signatures of late-Quaternary lake-level fluctuations. Extrapolation of a well-constrained age model on the cored upper part of the sequence suggests that these lake-level fluctuations represent a detailed and continuous record of moisture-balance variation in equatorial East Africa over the last 140 kyr. This record indicates that the most severe aridity occurred during peak Penultimate glaciation immediately before ˜ 128 kyr BP (coeval with Heinrich event 11) and during a Last Interglacial 'megadrought' period between ˜ 114 and ˜ 97 kyr BP; in comparison, Last Glacial Maximum (LGM) aridity was modest. It was preceded by ˜ 75 000 years of relatively stable and moist climate conditions interrupted by eleven short-lived dry spells, five of which match the timing of Heinrich events 2 to 6. Climate history near the East African equator reflects variation in the precessional forcing of monsoon rainfall modulated by orbital eccentricity, but precession-driven moisture fluctuations were less extreme than those observed in northern and southern tropical Africa. The near-continuous moist climate from ˜ 97 to 20.5 kyr BP recorded in the Lake Challa record contrasts with the trend towards greater aridity after ˜ 70 kyr BP documented in equatorial West Africa. This long period of moist glacial climate and a short, relatively modest LGM drought can be attributed to greater independence of western Indian Ocean monsoon dynamics from northern high-latitude glaciation than those in the tropical Atlantic Ocean. This rather persistent moist glacial climate regime may have helped maintain high biodiversity in the tropical forest ecosystems of the Eastern Arc mountains in Tanzania.

  14. Imaging the deep seismic structure beneath a mid-ocean ridge: the MELT experiment

    PubMed

    1998-05-22

    The Mantle Electromagnetic and Tomography (MELT) Experiment was designed to distinguish between competing models of magma generation beneath mid-ocean ridges. Seismological observations demonstrate that basaltic melt is present beneath the East Pacific Rise spreading center in a broad region several hundred kilometers across and extending to depths greater than 100 kilometers, not just in a narrow region of high melt concentration beneath the spreading center, as predicted by some models. The structure of the ridge system is strongly asymmetric: mantle densities and seismic velocities are lower and seismic anisotropy is stronger to the west of the rise axis. PMID:9596564

  15. An Idea for an Active Seismic Experiment on Mars in 2008

    NASA Technical Reports Server (NTRS)

    Lognonne, Ph.; Banerdt, B.; Giardini, D.; Costard, F.

    2001-01-01

    The detection of liquid water is of prime interest and should have deep implications in the understanding of the Martian hydrological cycle and also in exobiology. In the frame of the 2007 joint CNES-NASA mission to Mars, a set of 4 NETLANDERS developed by an European consortium is expected to be launched in June 2007. We propose to use a second spacecraft going or landing to Mars to release near one of the Netlander a series of artificial metallic meteorites, in order to perform an active seismic experiment providing a seismic profile of the crust and subsurface.

  16. Seismicity location from analysis of a 2 years passive seismological experiment around Ulaanbaatar

    NASA Astrophysics Data System (ADS)

    Batkhuu, Battulga; Munkhuu, Ulziibat; Sebe, Olivier; Monfret, Tony; Deschamps, Anne; Gao, Mengtan; Wu, Qingju

    2014-05-01

    We analyse broadband seismological records from a 2 years temporary array deployed over a 400x600km2 region in central Mongolia, including Ulaanbaatar region, by a Sino-Mongolian cooperation. The dataset is completed with all available regional data, mostly recorded by Mongolian National Seismic Network (MNSN) operated by Research Center for Astronomy and Geophysics (RCAG). The seismic activity of the covered area is not very high, except SW of Ulaanbaatar. To obtain as good as possible image of this seismicity, we have first to determine a regional velocity model. The development of mining activity in Mongolia, allows us to record a large set of quarry blasts. Due to the very continental position of Mongolia, micro-seismic noise level is low and the signal of these human made sources are very often recorded at distances as far as 200km. Travel time information of direct, reflected and refracted waves are used to produce crustal information (Moho depth and mean crustal P wave velocity, and velocity below the Moho, Vp/Vs ratio) over the area of observation. We show that the crust of the studied area is relatively homogeneous which allows us to improve this very simple model, searching the best crustal model with Velest software. The experiment was supported by Sino-Mongolian joint project titled "The Geophysical Investigation and Deep Structure Modeling for Seismic Hazard Assessment in the Far East", Project code: 2011DFB20120.

  17. The Millikan shaking experiments and high-frequency seismic wave propagation in Southern California

    NASA Astrophysics Data System (ADS)

    Tanimoto, Toshiro; Okamoto, Taro

    2014-08-01

    In order to study high-frequency seismic wave propagation, seismic wavefields generated by resonant-shaking experiments of the Millikan Library, on the campus of California Institute Technology (Pasadena, California, USA), were analysed. Because the resonant shaking frequencies are 1.12 Hz (the east-west direction) and 1.64 Hz (the north-south direction), this active-source experiment can provide opportunities for studying high-frequency seismic wave propagation in Southern California. Because they are very narrow frequency band data, the analyses must be quite different from ordinary time-domain analyses. We show, theoretically, that the signals must be dominated by surface waves. Adopting this surface wave assumption, we proceed to make two separate analyses, one on spectral amplitude and the other on phase. We present a new method to derive group velocity from phase based on the cross correlations between the station in the Millikan Library (MIK) and stations in the regional network. Our results support that an active-source experiment by resonant shaking of a building is a feasible approach for high-frequency seismic wave studies.

  18. Seismic Properties of Partially Molten Rocks: Constraints from Experiments and Observations on Natural Rocks

    NASA Astrophysics Data System (ADS)

    Faul, U.; Jackson, I.; Garapic, G.

    2014-12-01

    The increasing resolution of seismic tomography studies as well as techniques that are sensitive to sharp, localized velocity changes indicate that melt is present in diverse tectonic settings in the upper mantle. Unresolved questions are the quantification of seismic velocities and attenuation to melt fraction, and the dynamic stability of this melt. Properties of partially molten rocks are generally sensitive to melt geometry. The melt geometry can be observed in experiments, but the experimental observations have to be extrapolated to mantle grain sizes. High resolution images of experimentally observed melt geometries (Garapic et al., 2013) indicate that the broad attenuation peak observed by forced torsional oscillation experiments (Jackson et al., 2004, Faul et al., 2004) are due to melt 'squirt'. Characterization of the inferred melt geometry in rocks recovered from mid-ocean ridges and peridotite massifs suggest that the experimental observations are applicable to the upper mantle. The data from the earlier seismic property experiments will be reprocessed with improved apparatus calibration and fitting strategies to provide a 'global' fit to the melt-bearing data as a function of grain size and melt fraction. This should allow quantification of the amount of melt imaged in seismic studies and therefore enable more accurate geodynamical models for example of arcs and backarcs, for which the highest resolution tomographic images exist. It should also provide more quantitative constraints on the amount of melt required to generate receiver functions and SS-bounces that suggest the presence of melt in the asthenosphere.

  19. Martian Ambient Seismic Noise: from the first modeling to the future data of the InSight Seismic experiment.

    NASA Astrophysics Data System (ADS)

    Lognonne, P. H.; Banerdt, W. B.; Mimoun, D.; Kobayashi, N.; Panning, M. P.; Pike, W. T.; Giardini, D.; Christensen, U. R.; Nishikawa, Y.; Murdoch, N.; Kawamura, T.; Kedar, S.; Spiga, A.

    2014-12-01

    The InSight NASA Discovery mission is expected to deploy a 3 axis VBB and a 3 axis SP seismometer on Mars by late september 2016. This seismic station will explore the Martian ambient noise, in addition to more classical science goals related to the detection of Marsquakes, Meteoritic Impacts and Tides. Mars, in contrast with the Earth (with both atmosphere and ocean) and the Moon (with no atmosphere nor ocean) is expected to have ambient noise only related to its atmosphere. Mars seismic data are therefore expecting to reveal the atmospheric coupling for a different atmospheric dynamics than Earth, especially in the 0.1-1 Hz bandwidth, dominated by oceanic microseisms on Earth. We rapidly present the expected performances of the SEIS experiment onboard InSight. This experiment is based on two 3 axis seismometers, one covering the tide and low seismic frequencies (up to 10 Hz) and a second one covering the high frequencies (from 0.1 Hz to 50 Hz). Both sensors are mounted on a sensors plateform, deployed by a robotic arm 1-2 meters from the lander and covered by thermal protection and a wind protection. The expected performances indicates that signal as low as 10**(-9) m/s**2/Hz**(1/2) will be detected in the 0.005-2 Hz bandwidth. We then focus on the modeling of this ambient atmospheric noise.This modeling has been done not only from constraints gathered by the atmospheric sensors of previous Mars missions (e.g. Viking and Pathfinder) but also by numerical modeling of the atmospheric perturbations, both at global scale and mesoscale. Theoretical estimation of the ambient noise has then been obtained for the pressure-correlated surface loading and the stochastic excitation of surface waves, at both long and very long period (e.g. Mars hum) and at medium or short period (e.g. regional and local generated surface waves). Results shows that most of these source of ambient noise will be detected, likely during the day for those generated locally and possibly during the

  20. ISIS : a formation flying ionospheric seismic imaging experiment

    NASA Astrophysics Data System (ADS)

    Mimoun, D.; Lognonné, Ph; Garcia, R.; Occhipinti, G.; Abbondanza, S.

    Today, available techniques for the lithosphere tomography are limited by the number of seismic stations that we can deploy : it is sometimes difficult to access to some remote regions, but foremost the number of stations that are deployable over the oceans is strongly reduced. If we can dispose of some sites on islands (which are all characterized by a strong background noise), and on the measurements on coastal areas borders, it is therefore difficult to inverse the fine structure of the oceanic lithosphere. A promising idea is to use a long known idea, that earthquakes have a measurable impact on the ionosphere. As a matter of fact, the decrease of the atmosphere density with respect to altitude implies an amplification of the Rayleigh waves in the atmosphere, up to a maximum at about 250 km. This effect has been quantified for the Denali earthquake (Ducic et al, 2003) though its impact on the TEC content on the ionosphere. We therefore propose to detect this effect from space, thanks to a spaceborne multistatic SAR. Our concept includes 3 satellites in formation (along the same orbit) in a MEO orbit (about 19000 km). The master satellite payload is a slightly modified SAR, which operates around two main frequencies, in order to allow the computation of the delay induced by ionospheric fluctuations. The two other satellites have a passive payload which is time-synchronized with the master SAR: the use of their crossing rays will allow a 3D reconstruction of the ionosphere. A preliminary design of the space segment proposes an implementation on a MEO-orbit compatible bus, with high peak power capabilities. In order to allow the compatibility of the payload concept with the on-board available power, we have assumed that the satellite will enter in its alert mode on ground request. When an earthquake occurs, we dispose of a ten minutes delay to "wake-up" the satellite. When not in alert mode, its nominal imaging frequency will be reduced to allow the detection of

  1. Seismic images of the Brooks Range fold and thrust belt, Arctic Alaska, from an integrated seismic reflection/refraction experiment

    USGS Publications Warehouse

    Levander, A.; Fuis, G.S.; Wissinger, E.S.; Lutter, W.J.; Oldow, J.S.; Moore, T.E.

    1994-01-01

    We describe results of an integrated seismic reflection/refraction experiment across the Brooks Range and flanking geologic provinces in Arctic Alaska. The seismic acquisition was unusual in that reflection and refraction data were collected simultaneously with a 700 channel seismograph system deployed numerous times along a 315 km profile. Shot records show continuous Moho reflections from 0-180 km offset, as well as numerous upper- and mid-crustal wide-angle events. Single and low-fold near-vertical incidence common midpoint (CMP) reflection images show complex upper- and middle-crustal structure across the range from the unmetamorphosed Endicott Mountains allochthon (EMA) in the north, to the metamorphic belts in the south. Lower-crustal and Moho reflections are visible across the entire reflection profile. Travel-time inversion of PmP arrivals shows that the Moho, at 33 km depth beneath the North Slope foothills, deepens abruptly beneath the EMA to a maximum of 46 km, and then shallows southward to 35 km at the southern edge of the range. Two zones of upper- and middle-crustal reflections underlie the northern Brooks Range above ~ 12-15 km depth. The upper zone, interpreted as the base of the EMA, lies at a maximum depth of 6 km and extends over 50 km from the range front to the north central Brooks Range where the base of the EMA outcrops above the metasedimentary rocks exposed in the Doonerak window. We interpret the base of the lower zone, at ~ 12 km depth, to be from carbonate rocks above the master detachment upon which the Brooks Range formed. The seismic data suggest that the master detachment is connected to the faults in the EMA by several ramps. In the highly metamorphosed terranes south of the Doonerak window, the CMP section shows numerous south-dipping events which we interpret as a crustal scale duplex involving the Doonerak window rocks. The basal detachment reflections can be traced approximately 100 km, and dip southward from about 10-12 km

  2. Advancing Explosion Source Theory through Experimentation: Results from Seismic Experiments Since the Moratorium on Nuclear Testing

    NASA Astrophysics Data System (ADS)

    Bonner, J. L.; Stump, B. W.

    2011-12-01

    On 23 September 1992, the United States conducted the nuclear explosion DIVIDER at the Nevada Test Site (NTS). It would become the last US nuclear test when a moratorium ended testing the following month. Many of the theoretical explosion seismic models used today were developed from observations of hundreds of nuclear tests at NTS and around the world. Since the moratorium, researchers have turned to chemical explosions as a possible surrogate for continued nuclear explosion research. This talk reviews experiments since the moratorium that have used chemical explosions to advance explosion source models. The 1993 Non-Proliferation Experiment examined single-point, fully contained chemical-nuclear equivalence by detonating over a kiloton of chemical explosive at NTS in close proximity to previous nuclear explosion tests. When compared with data from these nearby nuclear explosions, the regional and near-source seismic data were found to be essentially identical after accounting for different yield scaling factors for chemical and nuclear explosions. The relationship between contained chemical explosions and large production mining shots was studied at the Black Thunder coal mine in Wyoming in 1995. The research led to an improved source model for delay-fired mining explosions and a better understanding of mining explosion detection by the International Monitoring System (IMS). The effect of depth was examined in a 1997 Kazakhstan Depth of Burial experiment. Researchers used local and regional seismic observations to conclude that the dominant mechanism for enhanced regional shear waves was local Rg scattering. Travel-time calibration for the IMS was the focus of the 1999 Dead Sea Experiment where a 10-ton shot was recorded as far away as 5000 km. The Arizona Source Phenomenology Experiments provided a comparison of fully- and partially-contained chemical shots with mining explosions, thus quantifying the reduction in seismic amplitudes associated with partial

  3. The interface between research and policy: experience from South Africa.

    PubMed

    Gilson, Lucy; McIntyre, Di

    2008-09-01

    Increasing attention has been paid in recent years to efforts to strengthen the impact of research on policy in low- and middle-income countries. However, the processes by which such research might have policy impact remain a subject of debate. This paper presents an analysis of the research/policy interface, drawing on the experiences of two South African health policy and systems research (HPSR) units and one specific study which traced the development and implementation of three areas of health care financing policy change and debate between 1994 and 1999. The analysis is based primarily on the authors' own experiences and has been developed through a deliberate process of reflection. It suggests, first, that it is important to acknowledge the conceptual and symbolic uses and impacts of research--perhaps, particularly in relation to the system-oriented work of HPSR groups. These uses may not be verifiable by specific changes in policy and practice but are important contributions to the policy environment and do filter into policy-makers' understandings and actions. Second, achieving any form of impact on policy is linked to the attention researchers pay to the context in which the research is undertaken, the nature and credibility of the research; and the importance of nesting any single project in a broader programme of engagement with the policy environment that builds trust in the researchers. PMID:18387723

  4. Large heterogeneous structure beneath the Atotsugawa Fault, central Japan, revealed by seismic refraction and reflection experiments

    NASA Astrophysics Data System (ADS)

    Iidaka, Takashi; Kurashimo, Eiji; Iwasaki, Takaya; Arai, Ryuta; Kato, Aitaro; Katao, Hiroshi; Yamazaki, Fumihito

    2015-08-01

    A high-strain-rate zone termed the Niigata Kobe Tectonic Zone is located in central Japan and contains an active right-lateral fault called the Atotsugawa Fault. We present the results of an explosive-source seismic experiment that focused on identifying the formation mechanisms of the fault. The experiment used seven explosive sources and 1108 seismic stations, and was undertaken during October 2007 in the area of the Atotsugawa Fault. The seismic stations were set up on a survey line with a length of ~ 170 km, oriented orthogonal to the strike of the fault. The linear array was used to identify the seismic structure of the fault zone and the deeper parts of the crust in the study area, yielding fine details of the seismic structure of the crust along the profile line, including lateral variations in P-wave velocity and the configuration of layers in the crust. A relatively low P-wave velocity reflective zone was detected beneath the fault at depths of 15-25 km. This zone also has extremely low S-wave velocities, directly underlies three active faults, and contains three low-resistivity zones that underlie these faults. These reflective and low-resistivity zones are thought to represent fluid within the crust, and the data obtained during this study are consistent with a weak zone model for the formation of the active faults in the study area. This suggests that the reflective layer represents a weak zone in the lower crust that is responsible for the concentration of deformation within the upper crust. The presence of abundant fluids beneath the Atotsugawa Fault could also reduce the strength of the lower crust, again focusing deformation related to the regional stress regime in areas that overlie these fluid-containing zones. The results suggest that the reflective layer was an important factor in the formation of the Atotsugawa Fault.

  5. The structure and subsidence of Rockall Trough from two-ship seismic experiments

    SciTech Connect

    Joppen, M.; White, R.S. )

    1990-11-10

    Coincident multichannel seismic reflection and refraction profiles acquired northwest of Britain during a two-ship seismic experiment in the southern Rockall Trough provide evidence for a thin (6 km) syn-rift crust below Rockall Trough. The variation of seismic velocity with depth is consistent with either oceanic crust similar to that found in other parts of the North Atlantic or with thinned continental crust heavily intruded by syn-rift igneous rocks. The syn-rift crust beneath Rockall Trough is now buried by nearly 5 km of sediments that are intruded by Tertiary volcanics varying in extent from isolated sills to a large sill complex extending 100 km laterally. The basement imaged on seismic profiles exhibits a band of subhorizontal reflectors that extend laterally over distances of up to 40 km which they interpret as sediments intercalated with submarine lava flow generated during the opening of the Trough. Estimates of stretching from crustal thinning and from subsidence indicate that Rockall Trough has undergone extensive rifting ({beta} > 6). Upwelling asthenosphere beneath the thinned lithosphere generated at least 1-3 km thickness of melt as it decompressed. The molten rock rose upward from the mantle until it was in part extruded as lava flows and in part intruded into the crust.

  6. Crust structure across the Rif Cordillera from 'RIFSIS' seismic refraction and wide-angle reflection experiment

    NASA Astrophysics Data System (ADS)

    Gil, Alba; Gallart, Josep; Díaz, Jordi; Carbonell, Ramon; Harnafi, Mimoun; Levander, Alan

    2013-04-01

    The Rif Cordillera, located in North Morocco forms, together with the Betic Range, the Gibraltar Arc around the Alboran Sea. This asymmetric curved mountain belt originated during a Miocene continent-continent collision as a result of the westward motion of the Alboran domain between northwest Africa and Iberia. The complexity of the area favored the proposition of diverse tectonic models, such as roll-back, accompanied and followed by lithospheric convective down-welling, and delamination. In this study, we present models of crustal structure derived from a seismic refraction and wide-angle reflection experiment which took place in October 2011 within the Spanish project RIFSIS complemented by the US-PICASSO one. Two profiles oriented N-S and E-W respectively were carried out across the Rif domains. Five shots of 1 Tn each were detonated along the lines and at the crossing point, recorded by about 900 stations from US-Iris pool deployed at an average spacing of 750 m. The N-S line was extended northwards by a 70 km long segment in Spain, in the Betic Range. Southwards, this profile connects with the one recorded in 2010 across the Atlas Mountains, within the SIMA project. The interpreted crustal structure differentiates two sedimentary layers on top of the basement, inferred from the observed first arrivals at short offsets, followed by upper, mid and lower crustal levels constrained by reflected phases visible in the record sections. The bottom of the crust is well defined from PmP phases, although the absence of Pn arrivals prevents to constrain upper mantle velocities. Average velocity values for the different layers in the models are respectively: 3.5 and 4.2 km/s for the sediments, 5.9, 6.3 and 6.6 km/s within the crust, and 8 km/s below Moho. These velocity depth models obtained at the Rif Cordillera hold major variations in crustal thickness, especially along the E-W profile, that shows a rapid change of 15-20 km in Moho depths within 30 km horizontal

  7. Configuration of geological domains and geodynamic evolution of the Africa-Eurasia plate boundary off SW Iberia revisited based on seismic velocity and density models

    NASA Astrophysics Data System (ADS)

    Martínez-Loriente, Sara; Sallarès, Valentí; Gràcia, Eulàlia; Bartolome, Rafael; Ranero, César

    2015-04-01

    We present a new classification of geological (basement) domains at the Africa-Eurasia plate boundary offshore SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along two regional wide-angle seismic transects, one running NW-SE from the Tagus to the Seine abyssal plains, and the other running N-S from S Portugal to the Seine Abyssal Plain, combined with previously available information. The seismic velocity and density structure at the Seine Abyssal Plain and the internal Gulf of Cadiz indicates the presence of a highly heterogeneous oceanic crust, similar to that described in ultra-slow spreading centers, whereas in the Horseshoe and Tagus abyssal plains, the basement structure resembles that of exhumed mantle sections identified in the Northern Atlantic margin. The integration of all this new information allows defining the presence of three oceanic domains off SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE segment of the Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental break-up (Late Jurassic); and (3) the Gorringe Bank domain, mainly made of rocks exhumed from the mantle with little synchronous magmatism, which formed during the first stages of North Atlantic opening (Early Cretaceous). Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain, which coincides with the seismicity cluster nucleated in the

  8. Developing national treatment policy for falciparum malaria in Africa: Malawi experience.

    PubMed

    Malenga, Grace; Wirima, Jack; Kazembe, Peter; Nyasulu, Yohane; Mbvundula, Michael; Nyirenda, Cooper; Sungani, Francis; Campbell, Carl; Molyneux, Malcolm; Bronzan, Rachel; Dodoli, Wilfred; Ali, Doreen; Kabuluzi, Storn

    2009-04-01

    The emergence and spread across sub-Saharan Africa of Plasmodium falciparum resistant to the inexpensive antimalarials chloroquine and sulfadoxine-pyrimethamine has worsened the health and hampered the socio-economic development of affected countries, a situation that calls for urgent review of malaria treatment policies in these countries. The Roll Back Malaria (RBM) initiative promotes strong partnerships for implementing effective malaria control measures. The development of clear policies to guide such implementation at country level offers a way of assessing the achievement of set milestones in this collaborative venture. In this article we describe the policy development process for the treatment of falciparum malaria in Africa, based on experience in Malawi, where the first-line drug treatment was recently changed from sulfadoxine-pyrimethamine to an artemisinin combination therapy. PMID:19285699

  9. Martian seismicity

    NASA Technical Reports Server (NTRS)

    Phillips, Roger J.; Grimm, Robert E.

    1991-01-01

    The design and ultimate success of network seismology experiments on Mars depends on the present level of Martian seismicity. Volcanic and tectonic landforms observed from imaging experiments show that Mars must have been a seismically active planet in the past and there is no reason to discount the notion that Mars is seismically active today but at a lower level of activity. Models are explored for present day Mars seismicity. Depending on the sensitivity and geometry of a seismic network and the attenuation and scattering properties of the interior, it appears that a reasonable number of Martian seismic events would be detected over the period of a decade. The thermoelastic cooling mechanism as estimated is surely a lower bound, and a more refined estimate would take into account specifically the regional cooling of Tharsis and lead to a higher frequency of seismic events.

  10. Seismic mapping of shallow fault zones in the San Gabriel Mountains from the Los Angeles Region Seismic Experiment, southern California

    USGS Publications Warehouse

    Fuis, G.S.; Ryberg, T.; Lutter, W.J.; Ehlig, P.L.

    2001-01-01

    During the Los Angeles Region Seismic Experiment (LARSE), a reflection/refraction survey was conducted along a profile (line 1) extending from Seal Beach, California, northeastward to the Mojave Desert and crossing the Los Angeles and San Gabriel Valley basins and San Gabriel Mountains. In most shot gathers from the southern and central San Gabriel Mountains, clear secondary arrivals are seen that merge, or appear to merge, with first arrivals at three locations, including the location of the Vincent thrust fault, an exposed late Mesozoic/early Cenozoic megathrust. These secondary arrivals are interpretable as reflections in the shallow crust (<5 km depth) from a concave-upward interface that projects to the surface in the north near the Vincent thrust fault, is offset in its central part at the San Gabriel fault (an old branch of the San Andreas fault), and terminates in the south at 1 to 2 km depth at the southern mountain front. The velocity structure above and below this interface strongly suggests it is the Vincent thrust fault: intermediate velocities (6.2 km/s), consistent with mylonites overlying the Vincent thrust fault, are observed above it; lower velocities (5.8 km/s), consistent with the Pelona Schist underlying the Vincent thrust fault, are observed below it. Problems arise, however, in attempting to match this reflector to the exposed Vincent thrust fault, which is seen in outcrops east of line 1. The Vincent thrust fault is shallower than the reflector in most places. An unmapped structure (steep fault, monocline, or thrust fault) is required between line 1 and the outcrops that either drops the Vincent thrust fault down to the depths of the reflector or repeats the Vincent thrust fault beneath line 1 in the footwall of another thrust fault. An alternative interpretation of the reflector is a deep greenstone horizon within the Pelona Schist, although this alternative is not favored by the velocity structure. Copyright 2001 by the American

  11. Data report for the 1985 seismic-refraction experiment at Yucca Mountain and vicinity, southwestern Nevada

    SciTech Connect

    Sutton, V.D.

    1985-12-31

    In February 1985, the US Geological Survey (USGS) conducted a seismic-refraction survey in the vicinity of Yucca Mountain, southwestern Nevada to better define the P(compressional)-wave velocity structure of the upper crust in this area. This experiment is a continuation of seismic investigations at the Nevada Test Site (NTS) by the USGS on behalf of the Nevada Nuclear Waste Storage Investigations Project (NNWSI) to assess the feasibility of a proposed nuclear waste disposal site at Yucca Mountain. The 1985 seismic-refraction survey consisted of three separate deployments: two East-West profiles, Line A and Line B, and a North-South profile (Plate 1). Thirty-one shots were recorded by 120 portable seismographs, where recorder station spacing averaged .3 km, and the shotpoints averaged 5 to 8 km apart. Additionally, off set shots were fired at shotpoints located about 7 to 15 km from the endpoints of the deployment lines. This report includes record sections from the twenty-nine shotpoints (Plates 2 to 17), a list of seismograph locations (Appendix A), a list of shotpoint locations and shot times, DKDAT data files and Tape Grade Code (Appendix B), and a list of first-arrival traveltime picks (Appendix C). Detailed interpretation of these data will be published in a subsequent report.

  12. Near-Field High-Resolution Seismic, Strain and Displacement Measurements for Earthquake Source Studies in Deep Mines in South Africa

    NASA Astrophysics Data System (ADS)

    Johnston, M. J.; Reches, Z.; van Aswegan, G.; McGarr, A.; Lockner, D.; Sellers, E.; Ben Zion, Y.; Williams, C.

    2004-12-01

    Unique access to information on the physics of the earthquake source (earthquake nucleation, fault rupture, heat generation, stress state, seismic wave propagation, fault displacement, material properties and particularly changes in some of these parameters prior to rupture) exists in the near-field of mining-induced earthquakes in deep gold mines in South Africa. The new NSF funded Natural Earthquake Laboratory in South African Mines (NELSAM) will provide seismic velocity/acceleration, ground strain, temperature, fault displacement, acoustic emission (AE), and perhaps self-potential (SP) data in small 3-D arrays across and within active faults in two different mines. 3-component accelerometers to be installed in or near the faults have a range from micro g to 0.5 g in the band 0.05 - 500 Hz. Fault displacement meters (creepmeters) to be installed at low angles across faults within boreholes have a range of microns to 0.2 m and cover the frequency range from DC to 100 Hz. Successful measurement of total displacement will depend on the creepmeter reference length surviving the fault rupture. Temperature will be measured to millidegrees C at points within, and at increasing distances from fault zones, to capture the heat generated by future and past earthquakes. Strain transients will be measured with 3-component near-fault borehole strainmeters with capacitance displacement transducers providing a resolution < 10E-9. 3-component seismic velocity transducers will be installed together with each accelerometer and supplement the current mine seismic network. AE and SP will be measured within boreholes crossing faults if recording capability is sufficient. All data will be digitally sampled and transmitted to the surface in real-time for analysis to focus on unraveling the physics of the nucleation process, non-linear deformation prior to rupture, propagating aseismic slip, and variation in the material properties of near-fault materials (e.g. state/rate dependent

  13. Adapting existing experience with aquifer vulnerability and groundwater protection for Africa

    NASA Astrophysics Data System (ADS)

    Robins, N. S.; Chilton, P. J.; Cobbing, J. E.

    2007-01-01

    Whilst groundwater vulnerability mapping and the delineation of resource and source protection zones have become an appropriate set of management tools for Britain as incorporated in European policy, much of semi-arid Africa is still dealing with more pressing issues centred on water supply coverage. There are a number of fundamental differences with Britain which disallow conventional vulnerability mapping and land zonation in much of Africa. Firstly, the scale of groundwater occurrence in weathered basement aquifers does not encourage vulnerability mapping to be undertaken at a field scale, whereas the Karoo and some of the larger areas of unconsolidated sedimentary aquifers could more readily be zoned according to aquifer vulnerability. Secondly, analysis needs to disregard the productivity (or recharge potential) of the aquifer so that poorly productive but socially important aquifers can be assessed. Such practice also avoids the need to identify a value for effective rainfall, a problematical value in semi-arid climates given current uncertainties. Thirdly, it is difficult to protect the many small and dispersed groundwater supply sources typical of many African communities when compared with the fewer and larger sources characteristic of Britain and Europe. Some aspects of European groundwater management practice have been transferred to the African context, notably by South Africa, but there are other practices that should not be attempted. Lessons from experience in South Africa highlight capacity to implement as a key inhibiting factor. Examples of vulnerability assessment and land zonation in a variety of African settings indicate only limited success so far with standard vulnerability assessment and land zonation techniques. Alternative means of quantifying the problem of the optimum proximity of the pit latrine from the well are highlighted, with a minimum separation of 10 m suggested for typical weathered basement rocks.

  14. TOMO-ETNA MED-SUV.ISES an active seismic and passive seismic experiment at Mt. Etna volcano. An integrated marine and onland geophysical survey.

    NASA Astrophysics Data System (ADS)

    Ibáñez, Jesus. M.; Patane, Domenico; Puglisi, Guisseppe; Zuccarello, Lucciano; Bianco, Francesca; Luehr, Birger; Diaz-Moreno, Alejandro; Prudencio, Janire; Koulakov, Ivan; Del Pezzo, Edoardo; Cocina, Ornella; Coltelli, Mauro; Scarfi, Lucciano; De Gori, Pascuale; Carrion, Francisco

    2014-05-01

    An active seismic experiment to study the internal structure of Etna Volcano is going to carried out on Sicily and Aeolian islands. The main objective of the TOMO-ETNA MED-SUV.ISES experiment, beginning in summer 2014, is to perform a high resolution seismic tomography, in velocity and attenuation, in Southern Italy, by using active and passive seismic data, in an area encompassing outstanding volcanoes as Mt. Etna, and Aeolian volcanoes. The achievement of this objective is based on the integration and sharing of the in-situ marine and land experiments and observations and on the implementation of new instruments and monitoring systems. For the purpose, onshore and offshore seismic stations and passive and active seismic data generated both in marine and terrestrial environment will be used. Additionally, other geophysical data, mainly magnetic and gravimetric data will be considered to obtain a joint Upper Mantle-Crust structure that could permit to make progress in the understanding of the dynamic of the region. This multinational experiment which involves institutions from Spain, Italy, Germany, United Kingdom, Ireland, France, Malta, Portugal, Russia, USA and Mexico. During the experiment more than 6.600 air gun shots performed by the Spanish Oceanographic vessel "Sarmiento de Gamboa" will be recorder on a dense local seismic network consisting of 100 on land non-permanent stations, 70 on land permanent stations and 20-25 OBSs. Contemporaneously other marine geophysical measures will be performed using a marine Gravimeter LaCoste&Romberg Air-Sea Gravity System II and a Marine Magnetometer SeaSPY. The experiments will provide a unique data set in terms of data quantity and quality, and it will provide a detailed velocity and attenuation structural image of volcano edifice. The results will be essential in the development and interpretation of future volcanic models. It is noteworthy that this project is fully transversal, multidisciplinary and crosses several

  15. Initial Results from the 2002 Gulf of California Conjugate Margin Seismic Experiment

    NASA Astrophysics Data System (ADS)

    Holbrook, S.; Lizarralde, D.; Kent, G.; Harding, A.; Fletcher, J.; Gonzalez-Fernandez, A.; Umhoefer, P.; Axen, G.

    2003-04-01

    The Gulf of California, which marks the ongoing separation of Baja California from mainland Mexico, is one of the few locales where active continental breakup can be studied along unambiguous flow lines that join clear conjugate margin pairs. In Fall 2002, we conducted an onshore-offshore seismic experiment across the conjugate rifted margins of the Gulf of California in several rift segments. The joint U.S.-Mexico project, sponsored principally by the MARGINS program of the U.S. National Science Foundation, aimed to image crustal structure across conjugate margins of four major basins to determine the modes of extension and the influence of sedimentation and magmatism on breakup. Here we present an overview of the experiment, which was substantially altered at sea due to concerns for marine-mammal safety, and present some preliminary findings. Three flow-line transects were acquired, in the Alarcon Basin, the Guaymas Basin, and between Cabo and Tres Marias Islands. In addition, a fourth transect across the Baja Peninsula was acquired. Data acquired included (1) multichannel seismic reflection data using the R/V Ewing’s 20-gun array and 480-channel, 6-km-long streamer, (2) wide-angle reflection/refraction data recorded on ocean-bottom seismometers, from 206 deployments conducted by the R/V New Horizon, and (3) onshore-offshore data recorded on portable seismometers deployed up to 100 km inland on all transects. Initial results from the experiment include (1) clear evidence for asymmetric basement structure on the conjugate rifted margins and across the active mid-ocean spreading center, of the Guaymas Basin, (2) the suggestion of substantial magmatism in an early failed rift of the Alarcon Basin, and (3) active subduction beneath the margin at the Tres Marias islands. In addition, we will discuss new procedures for mitigating effects on marine mammals that may have a significant impact on future U.S.-sponsored seismic reflection activities.

  16. A Gravity data along LARSE (Los Angeles Regional Seismic Experiment) Line II, Southern California

    USGS Publications Warehouse

    Wooley, R.J.; Langenheim, V.E.

    2001-01-01

    The U.S. Geological Survey conducted a detailed gravity study along part of the Los Angeles Regional Seismic Experiment (LARSE) transect across the San Fernando Basin and Transverse Ranges to help characterize the structure underlying this area. 249 gravity measurements were collected along the transect and to augment regional coverage near the profile. An isostatic gravity low of 50-60 mGal reflects the San Fernando-East Ventura basin. Another prominent isostatic gravity with an amplitude of 30 mGal marks the Antelope Valley basin. Gravity highs occur over the Santa Monica Mountains and the Transverse Ranges. The highest isostatic gravity values coincide with outcrops of Pelona schist.

  17. The lived experiences of street children in Durban, South Africa: Violence, substance use, and resilience

    PubMed Central

    Hills, Frances; Meyer-Weitz, Anna; Asante, Kwaku Oppong

    2016-01-01

    South African studies have suggested that street children are resilient but also suicidal, engage in unprotected sex and other high risk sexual behaviour as a means of survival, have high rates of substance abuse and are physically abused and stigmatized due to their state of homelessness. However, few studies have explored in a more holistic manner the lived experiences of street children in South Africa. The main purpose of this study was to explore qualitatively the lived experiences of street children living on the street of Durban, in the province of KwaZulu-Natal, South Africa. Adolescents (six males and four females) between the ages of 14 and 18 years (average age=16) were purposively selected and in-depth semi-structured interviews were conducted. An interpretative phenomenological analysis of the transcribed data revealed that incidence of violence and drug and alcohol use were common experiences of street life. Yet despite these challenges survival was made possible through personal and emotional strength, cultural values, religious beliefs, supportive peer relationships, and participation in sports activities. These protective, resilience resources should be strengthened in health promotion interventions with a focus on mental health, the prevention of violence, substance use, and daily physical activities that seems to provide meaning and hope. PMID:27291160

  18. The lived experiences of street children in Durban, South Africa: Violence, substance use, and resilience.

    PubMed

    Hills, Frances; Meyer-Weitz, Anna; Asante, Kwaku Oppong

    2016-01-01

    South African studies have suggested that street children are resilient but also suicidal, engage in unprotected sex and other high risk sexual behaviour as a means of survival, have high rates of substance abuse and are physically abused and stigmatized due to their state of homelessness. However, few studies have explored in a more holistic manner the lived experiences of street children in South Africa. The main purpose of this study was to explore qualitatively the lived experiences of street children living on the street of Durban, in the province of KwaZulu-Natal, South Africa. Adolescents (six males and four females) between the ages of 14 and 18 years (average age=16) were purposively selected and in-depth semi-structured interviews were conducted. An interpretative phenomenological analysis of the transcribed data revealed that incidence of violence and drug and alcohol use were common experiences of street life. Yet despite these challenges survival was made possible through personal and emotional strength, cultural values, religious beliefs, supportive peer relationships, and participation in sports activities. These protective, resilience resources should be strengthened in health promotion interventions with a focus on mental health, the prevention of violence, substance use, and daily physical activities that seems to provide meaning and hope. PMID:27291160

  19. Preliminary Results from the iMUSH Active Source Seismic Experiment

    NASA Astrophysics Data System (ADS)

    Levander, Alan; Kiser, Eric; Palomeras, Imma; Zelt, Colin; Schmandt, Brandon; Hansen, Steve; Harder, Steven; Creagar, Kenneth; Vidale, John; Abers, Geoffrey

    2015-04-01

    iMUSH (imaging Magma Under Saint Helens) is a US NSF sponsored multi-disciplinary investigation of Mount Saint Helens (MSH), currently the most active volcano in the Cascades arc in the northwestern United States. The project consists of active and passive seismic experiments, extensive magnetotelluric sounding, and geological/geochemical studies involving scientists at 7 institutions in the U.S. and Europe. The long-term goal of the seismic project is to combine analysis of the active source data with that of data from the 70 element broadband seismograph operating from summer 2014 until 2016. Combining seismic and MT analyses with other data, we hope to image the MSH volcanic plumbing system from the surface to the subducting Juan de Fuca slab. Here we describe preliminary results of the iMUSH active source seismic experiment, conducted in July and August 2014. The active source experiment consisted of twenty-three 454 or 908 kg weight shots recorded by ~3500 seismographs deployed at ~6,000 locations. Of these instruments, ~900 Nodal Seismic instruments were deployed continuously for two weeks in an areal array within 10 km of the MSH summit. 2,500 PASSCAL Texan instruments were deployed twice for five days in 3 areal arrays and 2 dense orthogonal linear arrays that extended from MSH to distances > 80 km. Overall the data quality from the shots is excellent. The seismograph arrays also recorded dozens of micro-earthquakes beneath the MSH summit and along the MSH seismic zone, and numerous other local and regional earthquakes. In addition, at least one low frequency event beneath MSH was recorded during the experiment. At this point we have begun various types of analysis of the data set: We have determined an average 1D Vp structure from stacking short-term/long-term average ratios, we have determined the 2-D Vp structure from ray-trace inversions along the two orthogonal profiles (in the NW-SE and NE-SW directions), and we have made low-fold CMP stacks of the

  20. Field Report on the iMUSH Active Source Seismic Experiment

    NASA Astrophysics Data System (ADS)

    Kiser, E.; Levander, A.; Schmandt, B.; Palomeras, I.; Harder, S. H.; Creager, K. C.; Vidale, J. E.; Malone, S. D.

    2014-12-01

    In the second half of July we completed the iMUSH active source seismic experiment, one component of the Imaging Magma Under Saint Helens project. A team of ~75 volunteers deployed 3500 seismographs to ~5920 locations on and around Mount St. Helens over the course of 3 weeks. This instrument deployment was accompanied by 23 shots distributed around the volcano. Instrumentation consisted of ~2550 Reftek 125A (Texan) seismographs with 4.5 Hz geophones, and 920 Nodal Seismic recorders with 10 Hz geophones. The shots were also recorded by the permanent stations of the Pacific Northwest Seismograph Network and 70 iMUSH broadband seismographs. Fifteen of the shots, 424 kg each, formed two rings around Mount Saint Helens at 15 km and 30 km radius from the summit. Eight of the shots, 828 kg each, were fired at distances of 50 to 80 km from MSH on NW-SE and NE-SW azimuths. The deployment geometry consisted of two lines oriented NW/SE and NE/SW, and three arrays. The offset of the lines ranged from 150 km to 190 km with an average spacing of 200 m. The first array was centered on the volcano with a radius of 30 km, and required both driving and hiking to deploy. Arrays two and three were set out with, and centered on, the NW/SE line. These arrays had a distance range from MSH of 30-75 km and an azimuth range of about 100 degrees. In addition to this large-scale deployment, we set out 7 beamforming arrays approximately collocated with iMUSH broadband seismographs, and above clusters of seismicity in the region. The aperture of these arrays was about 1 km with an instrument spacing of 100 m. The final deployment ended only days before the AGU abstract deadline, so we have not yet examined all of the data. However, the preliminary indications are that signal to noise is excellent: The shots, several of which registered on PNSN as ML>2.1, carried across the entire array, and were recorded as far away as Seattle and Corvallis on permanent stations. The array also recorded a

  1. Telemedicine as a Tool for Europe-Africa Cooperation: A Practical Experience

    NASA Astrophysics Data System (ADS)

    Dinis, Manuel; Santiago, Fernando; Silva, Luís; Ferreira, Ricardo; Machado, José; Castela, Eduardo

    This paper presents the experience of an Europe-Africa telemedicine network, focused on the pediatric area, and involving hospitals located in Luanda (Angola), Benguela (Angola), Praia (Cape Verde) and Coimbra (Portugal). In the scope of this network, the cooperation between these hospitals goes beyond the teleconsultation sessions. Tele-training, clinical experience exchange, patient transfer agreements and health staff training to local development of new medical capabilities are some of the involved activities. It is therefore agreed that this kind of technical and knowledge network could also be expanded to other African countries with clear benefits to the local citizens, overcoming the digital-divide and improving the cooperation between developed and developing countries.

  2. Filovirus Research in Gabon and Equatorial Africa: The Experience of a Research Center in the Heart of Africa

    PubMed Central

    Leroy, Eric; Gonzalez, Jean Paul

    2012-01-01

    Health research programs targeting the population of Gabon and Equatorial Africa at the International Center for Medical Research in Franceville (CIRMF), Gabon, have evolved during the years since its inception in 1979 in accordance with emerging diseases. Since the reemergence of Ebola virus in Central Africa, the CIRMF “Emerging Viral Disease Unit” developed diagnostic tools and epidemiologic strategies and transfers of such technology to support the response of the National Public Health System and the World Health Organization to epidemics of Ebola virus disease. The Unit carries out a unique investigation program on the natural history of the filoviruses, emergence of epidemics, and Ebola virus pathogenesis. In addition, academic training is provided at all levels to regional and international students covering emerging conditions (host factors, molecular biology, genetics) that favor the spread of viral diseases. PMID:23170174

  3. The experience of cash transfers in alleviating childhood poverty in South Africa: Mothers' experiences of the Child Support Grant

    PubMed Central

    Zembe-Mkabile, Wanga; Surrender, Rebecca; Sanders, David; Jackson, Debra; Doherty, Tanya

    2015-01-01

    Cash transfer (CT) programmes are increasingly being used as policy instruments to address child poverty and child health outcomes in developing countries. As the largest cash-transfer programme in Africa, the South African Child Support Grant (CSG) provides an important opportunity to further understand how a CT of its kind works in a developing country context. We explored the experiences and views of CSG recipients and non-recipients from four diverse settings in South Africa. Four major themes emerged from the data: barriers to accessing the CSG; how the CSG is utilised and the ways in which it makes a difference; the mechanisms for supplementing the CSG; and the impact of not receiving the grant. Findings show that administrative factors continue to be the greatest barrier to CSG receipt, pointing to the need for further improvements in managing queues, waiting times and coordination between departments for applicants trying to submit their applications. Many recipients, especially those where the grant was the only source of income, acknowledged the importance of the CSG, while also emphasising its inadequacy. To maximise their impact, CT programmes such as the CSG need to be fully funded and form part of a broader basket of poverty alleviation strategies. PMID:25685927

  4. The experience of cash transfers in alleviating childhood poverty in South Africa: mothers' experiences of the Child Support Grant.

    PubMed

    Zembe-Mkabile, Wanga; Surender, Rebecca; Surrender, Rebecca; Sanders, David; Jackson, Debra; Doherty, Tanya

    2015-01-01

    Cash transfer (CT) programmes are increasingly being used as policy instruments to address child poverty and child health outcomes in developing countries. As the largest cash-transfer programme in Africa, the South African Child Support Grant (CSG) provides an important opportunity to further understand how a CT of its kind works in a developing country context. We explored the experiences and views of CSG recipients and non-recipients from four diverse settings in South Africa. Four major themes emerged from the data: barriers to accessing the CSG; how the CSG is utilised and the ways in which it makes a difference; the mechanisms for supplementing the CSG; and the impact of not receiving the grant. Findings show that administrative factors continue to be the greatest barrier to CSG receipt, pointing to the need for further improvements in managing queues, waiting times and coordination between departments for applicants trying to submit their applications. Many recipients, especially those where the grant was the only source of income, acknowledged the importance of the CSG, while also emphasising its inadequacy. To maximise their impact, CT programmes such as the CSG need to be fully funded and form part of a broader basket of poverty alleviation strategies. PMID:25685927

  5. Multichannel seismic-reflection profiling on the R/V Maurice Ewing during the Los Angeles Region Seismic Experiment (LARSE), California

    USGS Publications Warehouse

    Brocher, Thomas M.; Clayton, Robert W.; Klitgord, Kim D.; Bohannon, Robert G.; Sliter, Ray; McRaney, John K.; Gardner, James V.; Keene, J.B.

    1995-01-01

    This report describes the acquisition of deep-crustal multichannel seismic-reflection data in the Inner California Borderland aboard the R/V Maurice Ewing, conducted in October 1994 as part of the Los Angeles Regional Seismic Experiment (LARSE). LARSE is a cooperative study of the crustal structure of southern California involving earth scientists from the U.S. Geological Survey, Caltech, the University of Southern California, the University of California Los Angeles, and the Southern California Earthquake Center (SCEC). During LARSE, the R/V Ewing's 20- element air gun array, totaling 137.7 liters (8470 cu. in.), was used as the primary seismic source for wide-angle recording along three main onshore-offshore lines centered on the Los Angeles basin and the epicenters of the 1933 Long Beach and 1994 Northridge earthquakes. The LARSE onshore-offshore lines were each 200-250 km long, with the offshore portions being between 90 and 150 km long. The nearly 24,000 air gun signals generated by the Ewing were recorded by an array of 170 PASSCAL REFTEK recorders deployed at 2 km intervals along all three of the onshore lines and 9 ocean bottom seismometers (OBSs) deployed along two of the lines. Separate passes over the OBS-deployment lines were performed with a long air gun repetition rate (60 and 90 seconds) to minimize acoustic-wave interference from previous shots in the OBS data. The Ewing's 4.2-km, 160-channel, digital streamer was also used to record approximately 1250 km of 40-fold multichannel seismic-reflection data. To enhance the fold of the wide-angle data recorded onshore, mitigating against cultural and wind noise in the Los Angeles basin, the entire ship track was repeated at least once resulting in fewer than about 660 km of unique trackline coverage in the Inner Borderland. Portions of the seismic-reflection lines were repeated up to 6 times. A variety of other geophysical data were also continuously recorded, including 3.5 kHz bathymetry, multi

  6. ENAM: A community seismic experiment targeting rifting processes and post-rift evolution of the Mid Atlantic US margin

    NASA Astrophysics Data System (ADS)

    Van Avendonk, H. J.; Magnani, M. B.; Shillington, D. J.; Gaherty, J. B.; Hornbach, M. J.; Dugan, B.; Long, M. D.; Lizarralde, D.; Becel, A.; Benoit, M. H.; Harder, S. H.; Wagner, L. S.; Christeson, G. L.

    2014-12-01

    The continental margins of the eastern United States formed in the Early Jurassic after the breakup of supercontinent Pangea. The relationship between the timing of this rift episode and the occurrence of offshore magmatism, which is expressed in the East Coast Magnetic Anomaly, is still unknown. The possible influence of magmatism and existing lithospheric structure on the rifting processes along margin of the eastern U.S. was one of the motivations to conduct a large-scale community seismic experiment in the Eastern North America (ENAM) GeoPRISMS focus site. In addition, there is also a clear need for better high-resolution seismic data with shallow penetration on this margin to better understand the geological setting of submarine landslides. The ENAM community seismic experiment is a project in which a team of scientists will gather both active-source and earthquake seismic data in the vicinity of Cape Hatteras on a 500 km wide section of the margin offshore North Carolina and Virginia. The timing of data acquisition in 2014 and 2015 facilitates leveraging of other geophysical data acquisition programs such as Earthscope's Transportable Array and the USGS marine seismic investigation of the continental shelf. In April of 2014, 30 broadband ocean-bottom seismometers were deployed on the shelf, slope and abyssal plain of the study site. These instruments will record earthquakes for one year, which will help future seismic imaging of the deeper lithosphere beneath the margin. In September and October of 2014, regional marine seismic reflection and refraction data will be gathered with the seismic vessel R/V Marcus Langseth, and airgun shots will also be recorded on land to provide data coverage across the shoreline. Last, in the summer of 2015, a land explosion seismic refraction study will provide constraints on the crustal structure in the adjacent coastal plain of North Carolina and Virginia. All seismic data will be distributed to the community through IRIS

  7. Preliminary TEX86 temperatures and a lake level record of tropical climate extremes derived from sediment cores and seismic stratigraphy from Lake Turkana, East Africa

    NASA Astrophysics Data System (ADS)

    Morrissey, A. J.; Scholz, C. A.; Russell, J. M.

    2012-12-01

    Lake Turkana is the largest lake in the Eastern Branch of the East African Rift System and records hydrologic conditions of a region spanning nearly 2.5 degrees of latitude (~2.0 - 4.5 degrees N) in the African tropics. New data suggest the Turkana region likely experienced much wetter and cooler climate over several intervals since the latest Pleistocene. Lake level was extremely low twice during the latest Pleistocene, evidenced by depositional hiatuses in high-resolution CHIRP seismic reflection data that correlate with sediments that have low water-content, abundant sand, and low total organic carbon (TOC as low as <0.7%). Lake Turkana, like many lakes in northern tropical Africa, had a wetter climate during the African Humid Period. Intervals of high lake levels (up to ~440 m amsl) are indicated by flat-lying, laterally continuous, low-amplitude reflections that correlate in sediment cores to dark, fine-grained, laminated sediment with high TOC (up to ~6%). Calcium carbonate accumulation during this time period is nearly 0%, and combined with evidence of laminated, unbioturbated sediment suggests a fresh, stratified lake with anoxic bottom waters. During the early mid-Holocene, lake level began to fall to close to present levels (~365 m amsl). Sediments deposited during this time period have low but variable organic carbon content (~0.5 - ~2%) and are much higher in inorganic carbon (from fine-grained calcite precipitation). A moderate lowstand during the late Holocene is indicated by an erosional unconformity seen down to ~40 m below the current lake surface in several seismic profiles. This record of lake level extremes suggests highly variable rainfall patterns, forced by migration of the Intertropical Convergence Zone) across tropical East Africa over the last 20,000 years. More than 50 sediment samples from 3 piston cores represent a continuous record of TEX86 temperature from ~20,000 years ago to modern. The generally low (<0.25) BIT index for the

  8. The Source Physics Experiments and Advances in Seismic Explosion Monitoring Predictive Capabilities

    NASA Astrophysics Data System (ADS)

    Walter, W. R.; Ford, S. R.; Antoun, T.; Pitarka, A.; Xu, H.; Vorobiev, O.; Rodgers, A.; Pyle, M. L.

    2012-12-01

    Despite many years of study, a number of seismic explosion phenomena remain incompletely understood. These include the generation of S-waves, the variation of absolute amplitudes with emplacement media differences, and the occasional generation of reversed Rayleigh waves. Advances in numerical methods and increased computational power have improved the physics contained in the modeling software and it is possible to couple non-linear source-region effects to far-field propagation codes to predict seismic observables, thereby allowing end-to-end modeling. However, despite the many sensor records from prior nuclear tests, the data available to develop and validate the simulation codes remain limited in important ways. This is particularly the case for the range of both scaled depths of burial and of source media, especially where full near-field to far-field records are available along with key quantitative parameter data such as depth, material properties and yield. For example, two of the most widely used seismic source models, both derived from the best empirical data, Mueller and Murphy (1971) and Denny and Johnson (1989), predict very different amplitudes for greatly overburied explosions. To provide new data to advance predictive explosion modeling capabilities, the National Nuclear Security Administration (NNSA) is carrying out a series of seven chemical explosions over a range of depths and sizes in the Source Physics Experiments (SPE). These shots are taking place in the Climax Stock granite at the Nevada National Security Site, the location where reversed Rayleigh waves from a nuclear test were first observed in the 1962 HARDHAT event (e.g. Brune and Pomeroy, 1963). Three of the SPE shots have successfully occurred so far, and were well-recorded by an extensive set of instrumentation including seismic, acoustic, EM, and remote sensing. In parallel, detailed site characterization has been conducted using geologic mapping and sampling, borehole geophysics

  9. Zambian Women in South Africa: Insights Into Health Experiences of Labia Elongation.

    PubMed

    Martínez Pérez, Guillermo; Mubanga, Mwenya; Tomás Aznar, Concepción; Bagnol, Brigitte

    2015-01-01

    Labia minora elongation consists in the manual stretching of the inner lips of the external genitalia. This practice is documented in east and southern Africa. The experiences of African women in the diaspora practicing elongation are not thoroughly understood. The purpose of this qualitative study was to explore the health harms and benefits associated with this practice of Zambian women who have migrated to Cape Town, South Africa. Twenty women and seventeen men participated in this study. Between December 2013 and May 2014, in-depth interviews and natural group discussions were conducted with the participants. The focus of this article is to report on the emic of the women related to notions of health, hygiene, and well-being. Labial elongation is perceived as a practice involving minor, short-term adverse effects that can be prevented by following some basic hygiene. Overall, personal and social value is placed on this practice because of its reported benefits for the sexual health of men and women, and for women's femininity and self-image. Further research is necessary on how female genital modifications influence Zambians' sexual preferences to inform the development of culturally appropriate health promotion interventions. PMID:26147362

  10. Passive Seismic Experiment "13 BB Star" in the Margin of the East European Craton, Northern Poland

    NASA Astrophysics Data System (ADS)

    Polkowski, M.; Grad, M.; Wilde-Piórko, M.; Suchcicki, J.; Arant, T.

    2014-12-01

    Passive experiment "13 BB star" is dedicated to study deep structure of the Earth's interior in the marginal zone of the East European Craton in northern Poland. The seismic network consists of 13 broadband stations on the area of c. 120 km in diameter. The network is located in the area well recognized from the point of view velocities of sedimentary cover and crustal structure. Good records obtained since summer 2013, and expected during next 1.5 years long recording campaign, should yield images of detailed structure of the lithosphere-asthenosphere boundary (LAB), „410", "?520", and „660" km discontinuities, as well as mantle-core boundary and inner core. The LAB is investigated recently very effectively, mostly using seismic methods because their deep penetration and relatively good resolution. The nature of LAB is still debated, particularly under "cold" Precambrian shields and platforms. We show examples of local and teleseismic records, array transfer function of "13 BB star" network and preliminary noise analysis. National Science Centre Poland provided financial support for this work by NCN grant DEC- 2011/02/A/ST10/00284.

  11. High-resolution shallow-seismic experiments in sand. Part 2: Velocities in shallow unconsolidated sand

    SciTech Connect

    Bachrach, R.; Dvorkin, J.; Nur, A.

    1998-07-01

    The authors conducted a shallow high-resolution seismic reflection and refraction experiment on a sandy beach. The depth of investigation was about 2 m. They interpret the data using the Hertz-Mindlin contact theory combined with Gassmann`s equation. These were used to obtain the vertical velocity profile. Then the profile was computed from seismic data using the turning-rays approximation. The normal moveout (NMO) velocity at the depth of 2 m matches the velocity profile. As a result, they developed a method to invert measured velocity from first arrivals, i.e., velocity versus distance into velocity versus depth using only one adjustable parameter. This parameter contains all the information about the internal structure and elasticity of the sand. The lowest velocity observed was about 40 m/s. It is noteworthy that the theoretical lower bound for velocity in dry sand with air is as low as 13 m/s. The authors find that modeling sand as a quartz sphere pack does not quantitatively agree with the measured data. However, the theoretical functional form proves to be useful for the inversion.

  12. A comparative study of seismicity statistics in laboratory stick-slip experiments and nature: Implications for fault mechanics

    NASA Astrophysics Data System (ADS)

    Goebel, Thomas; Kwiatek, Grzegorz; Becker, Thorsten; Sammis, Charles; Dresen, Georg

    2016-04-01

    Fault properties can rarely be monitored under in-situ conditions at seismogenic depth. At these depths seismicity records are possibly the only high-resolution data that can provide insight into state of stress and mechanics of faulting. We analyze series of laboratory experiments on faults that developed during stick-slip on saw-cut and fractured surfaces under upper crustal stress conditions. Stick-slip experiments were performed on surfaces with varying roughness and fracture surfaces that evolved into fault zones with pronounced damage zones. We monitor and analyze acoustic emission events that exhibit many striking similarities to natural seismicity across all examined scales. These similarities include pronounced Gutenberg-Richter-type magnitude distributions, Omori-type aftershock decay, and off-fault seismicity distributions that decay as a power law with distance. In the laboratory, fault roughness and heterogeneity are critical in concentrating stresses that lead to local AE clustering, and differences in off-fault activities and lower b-values. Similar observations of earthquake clustering and b-value variations were made for natural faults such as the Parkfield segment of the San Andreas fault. In addition to seismicity statistics, we conducted a detailed analysis of moment tensors, focusing on relative contributions from isotropic and deviatoric components to laboratory seismicity. In contrast to natural seismicity, our results revealed a larger contribution from isotropic components. These contributions are a result of ongoing fracture processes within the evolving fault which are most pronounced after stick-slip events. Our study shows, that seismicity analyses in laboratory experiments can significantly advance our understanding of fault mechanics from the scale of single asperities to large fault zones.

  13. On the scalability of seismic waveform inversion: From ultrasonic experiments to global-scale tomography

    NASA Astrophysics Data System (ADS)

    Kamei, R.; Pratt, R. G.

    2012-12-01

    Seismic waveform inversion endeavors to extract high-resolution subsurface models from full seismic records by using numerical solutions of the full forward wave equation. In the last two decades, waveform inversion has been successfully applied to both active and passive seismic experiments, and has demonstrated superb resolution power over a wide-range of applications. Waveform inversion is still computationally challenging, and is well known to be a strongly non-linear and ill-conditioned inverse problem. Passive and active waveform inversions have largely been developed independently, although both originate from the work of Lailly (1983) and Tarantola (1984). In this presentation, we review a suite of past results from both active and passive source waveform inversions, and attempt to illustrate similarities and shared challenges between them. In active seismics, waveform inversion has been applied to i) ultrasonic breast cancer data to image targets of a few tens of centimeters on a side, ii) cross-well exploration data using frequencies between hundreds and a few thousands of Hz to image targets of the order of hundreds of meters on a side, iii) surface seismic for near-surface engineering problems using frequencies of tens to a few hundreds of Hz to image targets of the order of hundreds of meters to several kilometers, and iv) hydrocarbon exploration and crustal imaging using frequencies of a few, to a few tens of Hz for targets tens of kilometers on a side. In contrast, waveform inversion from passive source data uses much lower frequencies (less than 1 Hz), and images much larger target areas to retrieve iv) crustal scale structures of the order of hundreds of kilometers using data periods of one to several tens of seconds, v) upper-mantle structure on regional scales thousands of kilometers on a side using data periods of ten to a few hundred seconds, and vi) the whole-earth inversions (of order 10,000 km on a side), using a similar frequency range. Our

  14. Healthcare experiences of lesbian and bisexual women in Cape Town, South Africa.

    PubMed

    Smith, Riley

    2015-01-01

    Understanding the health needs and experiences of South African lesbian and bisexual women is imperative for implementing effective and inclusive public health strategies. Such understanding, however, is limited due to the exclusion of these women from most existing research on healthcare access in the region. This paper bridges that gap by investigating the healthcare experiences of lesbian and bisexual women in Cape Town. Data were gathered from 22 interviews with self-identified lesbian and bisexual community members and university students in the Cape Town area. Interviews explored obstacles women face in accessing affirming services, different experiences with public and private healthcare, fear of stigma/discrimination, availability of relevant sexual health information and suggestions to improve existing programmes. Findings suggest that South African lesbians and bisexual women may have a range of both positive and negative experiences in public and private health services, that they use protective strategies when 'coming out' and that they find that sexual health information pertinent to them is largely unavailable. These discussions contribute to a more inclusive understanding of the experiences of lesbian and bisexual women accessing healthcare and other services and help to inform providers, thereby enabling them to deliver more meaningful care to lesbian, gay, bisexual and transgender persons in South Africa. PMID:25291355

  15. Subsurface Seismic Record of Sediment Failures in the Neogene of Deepwater West Africa: Causal Mechanisms and Characteristics

    NASA Astrophysics Data System (ADS)

    Oluboyo, A. P.; Zhunussov, D.; Huuse, M.; Gawthorpe, R.

    2010-12-01

    Catastrophic sediment failures in deepwater margins are initiated by a wide range of triggering mechanisms including but not limited to; sea-level fluctuations, earthquakes, rapid sediment overburdening, progressive slope failures and gas hydrate destabilization. Three-dimensional seismic interpretation of a 1,400 km2 3D volume from the Neogene stratigraphic record of the Lower Congo Basin (LCB) demonstrates the existence of two major types of sediment failures within an elongate salt bound mini-basin (c. 15 km by 60 km). These slope instabilities are distinguished on the basis of their size, origin, geometries and deformational structures.Within the Middle Miocene, a regionally extensive, frontally emergent mass transport deposit occurs, and is a part of a much larger, regionally prevalent sediment failure deposit within the LCB. This deposit covers an area of ~ 750 km2 with an average thickness of ~ 60 m and a volume of 45 km3, with its lateral extent delimited by the salt diapirs which bound the mini-basin. Seismically, it exhibits chaotic, discontinuous, low amplitude semi-transparent facies with an erosive basal scour surface and an irregular upper bounding surface.The second type of sediment failure is a Pliocene aged, detached MTC with a short run out distance c. 10km. The slump is areally constrained to the flank of the western bounding salt-cored fold, with a preserved scarp along the fold crest. This deposit is frontally confined, with an average thickness of ~250 m and covers an area ~ 100 km2 (4 km by 26 km). It is defined by a high amplitude reflection at the base, with a series of syndepositional thrusts detaching off this surface at the terminal end of the deposit. Compressional structures are also seismically resolvable in strata adjacent to the distal end of the MTC. The presence of pressure ridges along the top bounding surface, coupled with the differential compaction of the slump deposits and mounded topography relative to local bathymetry

  16. Why did Arabia separate from Africa? Insights from 3-D laboratory experiments

    NASA Astrophysics Data System (ADS)

    Bellahsen, N.; Faccenna, C.; Funiciello, F.; Daniel, J. M.; Jolivet, L.

    2003-11-01

    We have performed 3-D scaled lithospheric experiments to investigate the role of the gravitational force exerted by a subducting slab on the deformation of the subducting plate itself. Experiments have been constructed using a dense silicone putty plate, to simulate a thin viscous lithosphere, floating in the middle of a large box filled with glucose syrup, simulating the upper mantle. We examine three different plate configurations: (i) subduction of a uniform oceanic plate, (ii) subduction of an oceanic-continental plate system and, (iii) subduction of a more complex oceanic-continental system simulating the asymmetric Africa-Eurasia system. Each model has been performed with and without the presence of a circular weak zone inside the subducting plate to test the near-surface weakening effect of a plume activity. Our results show that a subducting plate can deform in its interior only if the force distribution varies laterally along the subduction zone, i.e. by the asymmetrical entrance of continental material along the trench. In particular, extensional deformation of the plate occurs when a portion of the subduction zone is locked by the collisional process. The results of this study can be used to analyze the formation of the Arabian plate. We found that intraplate stresses, similar to those that generated the Africa-Arabia break-up, can be related to the Neogene evolution of the northern convergent margin of the African plate, where a lateral change from collision (Mediterranean and Bitlis) to active subduction (Makran) has been described. Second, intraplate stress and strain localization are favored by the presence of a weakness zone, such as the one generated by the Afar plume, producing a pattern of extensional deformation belts resembling the Red Sea-Gulf of Aden rift system.

  17. DHOFAR Seismic Experiment: First results to understand the breakup processes in a passive margin context

    NASA Astrophysics Data System (ADS)

    Tiberi, C.; Leroy, S.; D'Acremont, E.; Pointu, A.; Ebinger, C.; Brisbourne, A.; Denton, P.; Al-Lazki, A.; Al-Azri, H.; Bin Monshir Bahlaf, S.; Brunet, C.; Famin, V.; Labrousse, L.

    2004-12-01

    The process of strain localisation preceding the onset of seafloor spreading is still poorly understood, though extensively studied. The reason is the differences in lithospheric properties, proximity to hot spot(s) and melt generation and extraction that lead to a variety of structural styles with major differences. The eastern Gulf of Aden represents a natural laboratory to study passive continental margins for many reasons: post-rift sedimentary strata are relatively thin, both onshore and nearshore structures are well-exposed, and conjugate margins can be precisely reconstructed. A first cruise (ENCENS-SHEBA), in 2000, has established the structural and geophysical framework using bathymetric swath mapping and underway geophysics. Later on, the Dhofar seismic experiment consisted in the deployment of a network of 11 broadband seismic stations from March 2003 to March 2004 on the northern margin, in the Dhofar area, southern Oman. This experiment was dedicated to the detailed study of the crust and upper mantle beneath the northern passive margin. CMG40TD 3-components seismometers from SEIS-UK network were used. We have recorded hundreds of teleseismic events with a good azimuthal coverage. Three main studies are then attempted. First, a teleseismic image of the first 200 km depth will be established using the P- and PKP-phases. This will allow a 3D representation of crustal and upper mantle velocity structures. We present here the preliminary results from the study of the traveltime residuals. The image resolution shall be enhanced by combining gravity data. Second, a receiver function analysis will locally determine the depth of the main interfaces (eg, Moho boundary). Finally, events recorded within the 1000-6000 km distance range will improve the regional S-wave velocity structure in this area and will help to locate the main regional wide structures related to this extended area.

  18. Mantle P wave travel time tomography of Eastern and Southern Africa: New images of mantle upwellings

    NASA Astrophysics Data System (ADS)

    Benoit, M. H.; Li, C.; van der Hilst, R.

    2006-12-01

    Much of Eastern Africa, including Ethiopia, Kenya, and Tanzania, has undergone extensive tectonism, including rifting, uplift, and volcanism during the Cenozoic. The cause of this tectonism is often attributed to the presence of one or more mantle upwellings, including starting thermal plumes and superplumes. Previous regional seismic studies and global tomographic models show conflicting results regarding the spatial and thermal characteristics of these upwellings. Additionally, there are questions concerning the extent to which the Archean and Proterozoic lithosphere has been altered by possible thermal upwellings in the mantle. To further constrain the mantle structure beneath Southern and Eastern Africa and to investigate the origin of the tectonism in Eastern Africa, we present preliminary results of a large-scale P wave travel time tomographic study of the region. We invert travel time measurements from the EHB database with travel time measurements taken from regional PASSCAL datasets including the Ethiopia Broadband Seismic Experiment (2000-2002); Kenya Broadband Seismic Experiment (2000-2002); Southern Africa Seismic Experiment (1997- 1999); Tanzania Broadband Seismic Experiment (1995-1997), and the Saudi Arabia PASSCAL Experiment (1995-1997). The tomographic inversion uses 3-D sensitivity kernels to combine different datasets and is parameterized with an irregular grid so that high spatial resolution can be obtained in areas of dense data coverage. It uses an adaptive least-squares context using the LSQR method with norm and gradient damping.

  19. "We Must Believe in Ourselves": Attitudes and Experiences of Adult Learners with Disabilities in Kwazulu-Natal, South Africa

    ERIC Educational Resources Information Center

    Rule, Peter; Modipa, Taadi Ruth

    2012-01-01

    Many adults with disabilities in South Africa never had a chance to attend school or dropped out at an early age because of poverty and discrimination. This article investigates the attitudes and experiences of adults with disabilities regarding education. It draws on an interactional model of disability and an embodied understanding of cognition…

  20. Randomized Impact Evaluation of Education Interventions: Experiences and Lessons from a Reading to Learn Intervention in East Africa

    ERIC Educational Resources Information Center

    Ngware, Moses Waithanji; Abuya, Benta; Oketch, Moses; Admassu, Kassahun; Mutisya, Maurice; Musyoka, Peter

    2015-01-01

    This paper presents the experiences and lessons learnt during the design and implementation of the randomized impact evaluation (IE) of a reading to learn (RtL) intervention in early primary grades. The study was to assess the impact of RtL on literacy and numeracy among pupils in low-performing districts in East Africa. The intervention was…

  1. Africa: "Yonondio."

    ERIC Educational Resources Information Center

    Bendetson, Jane

    1996-01-01

    Recounts a teacher's experiences on a trip to Africa. Describes her pleasant moments with her fellow travelers; her appreciation of the natural setting; her visit to an impoverished native school; and her confrontation with a Maasai warrior. (TB)

  2. Experiences of leadership in health care in sub-Saharan Africa

    PubMed Central

    2012-01-01

    Background Leadership is widely regarded as central to effective health-care systems, and resources are increasingly devoted to the cultivation of strong health-care leadership. Nevertheless, the literature regarding leadership capacity building has been developed primarily in the context of high-income settings. Less research has been done on leadership in low-income settings, including sub-Saharan Africa, particularly in health care, with attention to historical, political and sociocultural context. We sought to characterize the experiences of individuals in key health-care leadership roles in sub-Saharan Africa. Methods We conducted a qualitative study using in-person interviews with individuals (n = 17) in health-care leadership roles in four countries in sub-Saharan Africa: the Federal Democratic Republic of Ethiopia, the Republic of Ghana, the Republic of Liberia and the Republic of Rwanda. Individuals were identified by their country’s minister of health as key leaders in the health sector and were nominated to serve as delegates to a global health leadership conference in June 2010, at Yale University in the United States. Interviews were audio recorded and professionally transcribed. Data analysis was performed by a five-person multidisciplinary team using the constant comparative method, facilitated by ATLAS.ti 5.0 software. Results Five key themes emerged as important to participants in their leadership roles: having an aspirational, value-based vision for improving the future health of the country, being self-aware and having the ability to identify and use complementary skills of others, tending to relationships, using data in decision making, and sustaining a commitment to learning. Conclusions Current models of leadership capacity building address the need for core technical and management competencies. While these competencies are important, skills relevant to managing relationships are also critical in the sub-Saharan African context

  3. Characterization of blocks impacts from seismic signal: insights from laboratory experiments

    NASA Astrophysics Data System (ADS)

    Farin, M.; Mangeney, A.; Toussaint, R.; de Rosny, J.; Sainte-Marie, J.; Shapiro, N.

    2014-12-01

    Rockfalls, debris flows and rock avalanches represent a major natural hazard for the population in mountainous, volcanic and coastal areas but their direct observation on the field is very difficult. Recent field studies showed that gravitational instabilities can be detected, localized and characterized thanks to the seismic signal they generate. Therefore, a burning challenge for risks assessment related to these events is to obtain quantiative informations on the characteristics of the rockfalls (mass, speed, extension,...) from the properties of the signal (seismic energy, frequencies,...). Using a theoretical model of viscoelastic impact of a sphere on a plane, we develop analytical scaling laws relating the energy radiated in elastic waves, the energy dissipated in viscoelasticity during the impact and the frequencies of the generated acoustic signal to the mass m and the impact speed Vz of the sphere and to the elastic parameters of the involved materials. The elastic energy is shown to vary as m5/3Vz11/5 on plates and as mVz13/5 on blocks, regardless of the elastic parameters. The energy dissipated in viscoelasticity does not depend on the support thickness and varies as m2/3Vz11/5. The mean frequency of the generated signal is inversely proportional to the impact duration. Then, we conduct simple laboratory experiments that consist in dropping spherical beads of different size and materials and small gravels on thin plates of glass and Plexiglass and rock blocks. The elastic energy emitted by an impact on the supports is first quantitatively estimated and compared to the potential energy of fall and to the potential energy change during the shock. We observe a quantitative agreement between experimental data and the analytical scaling laws, even when we use small gravels instead of spherical beads as impactors. These experiments allows to valid the theoretical model and to establish the energy budget of an impact. In the experiments, piezoelectric

  4. An experiment to locate cavities as strong scatterers using S-coda waves -the Cooke4 mine in South Africa-

    NASA Astrophysics Data System (ADS)

    Imagawa, S.; Kawakata, H.; Doi, I.; Yoshimitsu, N.; Murakami, O.; Nakatani, M.; Naoi, M.; Philipp, J.; Ward, A.; Visser, V.; Masakale, T.; Milev, A. M.; Durrheim, R. J.; Ribeiro, L.; Ward, M.; Ogasawara, H.

    2013-12-01

    To investigate short-wavelength heterogeneity of the crust, scattered waves contained in coda waves are useful. In general, locations of the scatterers are estimated from the travel times of scattered waves with a stochastic back-projection method, so that artifacts may emerge if seismic stations and sources are inadequately distributed. In this study, using coda waves, we try to locate well-mapped cavities such as tunnels, shafts and stopes in the Cooke4 Gold Mine in South Africa. At this mine, we have developed a dense seismic network in the vicinity of a region with high seismicity. The seismic network is narrow and the source distribution is far from being uniform, which can cause artifacts. We use 3-component accelerograms recorded at 6 stations about 1 km below surface in the shaft pillar area. The data are recorded for 6.6 ms at the sampling frequency of 500 kHz. Considering the size (2-4 m) of tunnels and shafts, a band-pass filter of 800-1600 Hz is applied. Considering the distribution of seismic sources and stations, and also the data length, an analysis volume of 300×300×260 m3 is set and divided into blocks of 4×4×4 m3. In general, the exponential decays of the coda wave amplitude from an event tend to be the same regardless of the distance from seismic source to station (Aki, 1980). If strong scatterers exist, a phase with relatively large amplitude would appear at the corresponding time. We identify such phases by looking for phases where the amplitude significantly exceeds the overall envelope of S-coda. Using the travel time of thus picked 'scattering phase', we locate the corresponding scatterer. Since our target structures are highly localized strong scatterers, we assume single scattering in the present analysis, as, for example, Matsumoto et al. (2006). The block containing the estimated scatterer location receives votes according to the amplitude of the scattering phase. By adding votes from all the traces, we have obtained a three

  5. Seismic results from DOE`s non-proliferation experiment: A comparison of chemical and nuclear explosions

    SciTech Connect

    Denny, M.; Goldstein, P.; Mayeda, K.; Walter, W.

    1995-01-01

    The basic results from the US Department of Energy`s (DOE`s) NonProliferation Experiment (NPE) for seismic signal generation are that the source function for a chemical explosion is equivalent to that of a nuclear explosion of about twice the yield and that the seismic moment measurements are consistent between freefield, local, and regional measurements. In addition, evidence was found that Pn in the Basin and Range province of the western United States is a turning ray and is simply proportional to the source function while the transfer functions for Pg and Lg are low-pass in nature.

  6. The North East Italy (NI) broadband seismic network run by OGS: experience in improving the long period performances

    NASA Astrophysics Data System (ADS)

    Pesaresi, D.

    2009-04-01

    experimented and routinely used by the world wide GEOFON seismic network and the German regional seismic network: examples and performances of a typical OGS installation will be shown.

  7. Transition from slab to slabless: Results from the 1993 Mendocino triple junction seismic experiment

    USGS Publications Warehouse

    Beaudoin, B.C.; Godfrey, N.J.; Klemperer, S.L.; Lendl, C.; Trehu, A.M.; Henstock, T.J.; Levander, A.; Holl, J.E.; Meltzer, A.S.; Luetgert, J.H.; Mooney, W.D.

    1996-01-01

    Three seismic refraction-reflection profiles, part of the Mendocino triple junction seismic experiment, allow us to compare and contrast crust and upper mantle of the North American margin before and after it is modified by passage of the Mendocino triple junction. Upper crustal velocity models reveal an asymmetric Great Valley basin overlying Sierran or ophiolitic rocks at the latitude of Fort Bragg, California, and overlying Sierran or Klamath rocks near Redding, California. In addition, the upper crustal velocity structure indicates that Franciscan rocks underlie the Klamath terrane east of Eureka, California. The Franciscan complex is, on average, laterally homogeneous and is thickest in the triple junction region. North of the triple junction, the Gorda slab can be traced 150 km inboard from the Cascadia subduction zone. South of the triple junction, strong precritical reflections indicate partial melt and/or metamorphic fluids at the base of the crust or in the upper mantle. Breaks in these reflections are correlated with the Maacama and Bartlett Springs faults, suggesting that these faults extend at least to the mantle. We interpret our data to indicate tectonic thickening of the Franciscan complex in response to passage of the Mendocino triple junction and an associated thinning of these rocks south of the triple junction due to assimilation into melt triggered by upwelling asthenosphere. The region of thickened Franciscan complex overlies a zone of increased scattering, intrinsic attenuation, or both, resulting from mechanical mixing of lithologies and/or partial melt beneath the onshore projection of the Mendocino fracture zone. Our data reveal that we have crossed the southern edge of the Gorda slab and that this edge and/or the overlying North American crust may have fragmented because of the change in stress presented by the edge.

  8. Active Source Tomography of Stromboli Volcano (Italy): Results From the 2006 Seismic Experiment.

    NASA Astrophysics Data System (ADS)

    Zuccarello, L.; Patanè, D.; Cocina, O.; Castellano, M.; Sgroi, T.; Favali, P.; de Gori, P.

    2008-12-01

    Stromboli island, located in the Southern Tyrrhenian sea, is the emerged part (about 900 m a.s.l.) of a 3km-high strato-volcano. Its persistent Strombolian activity, documented for over 2000 years, is sometimes interrupted by lava effusions or major explosions. Despite the amount of recent published geophysical studies aimed to clarifying eruption dynamics, the spatial extend and geometrical characteristics of the plumbing system remain poorly understood. In fact, the knowledge of the inner structure and the zones of magma storage is limited to the upper few hundreds meters of the volcanic edifice and P- and S-waves velocity models are available only in restricted areas. In order to obtain a more suitable internal structural and velocity models of the volcano, from 25 November to 2 December 2006, a seismic tomography experiment through active seismics using air-gun sources was carried out and the final Vp model is here presented. The data has been inverted for the Vp structure by using the code Simulps13q, considering a 3D grid of nodes spaced 0.5 km down to 2 km depth, beneath the central part of volcano. The results show a relatively high velocity zones located both in the inner part of the volcanic structure, at about 1km b.s.l. and in the last 200-300 m a.s.l. in correspondence with the volcanic conduit. Slower zones were located around the summit craters in agreement with volcanological and petrological informations for the area. The relatively high velocity zones could suggest the presence of intrusive bodies related to the plumbing system.

  9. Out of (South) Africa: Pretoria`s nuclear weapons experience. Final report

    SciTech Connect

    Horton, R.E.

    1998-04-01

    The primary focus of this paper is the impact of key South African leaders on the successful developments and subsequent rollbacks of South Africa`s nuclear weapons capability. It highlights the key milestones in the development of South Africa`s nuclear weapon capability. It also relates how different groups within South Africa (scientists, politicians, military and technocrats) interacted to successfully produce South Africa`s nuclear deterrent. It emphasizes the pivotal influence of the senior political leadership to pursue nuclear rollback given the disadvantages of its nuclear means to achieve vital national interests. The conclusions drawn from flu`s effort are the South African nuclear program was an extreme response to its own identity Crisis. Nuclear weapons became a means to achieving a long term end of a closer affiliation with the West. A South Africa yearning to be identified as a Western nation and receive guarantees of its security rationalized the need for a nuclear deterrent. The deterrent was intended to draw in Western support to counter a feared total onslaught by Communist forces in the region. Two decades later, that same South Africa relinquished its nuclear deterrent and reformed its domestic policies to secure improved economic and political integration with the West.

  10. Regional Seismic Signals from Chemical Explosions, Nuclear Explosions and Earthquakes: Results from the Arizona Source Phenomenology Experiment

    SciTech Connect

    Walter, W R; Gok, R; Mayeda, K; Sicherman, A; Bonner, J; Leidig, M

    2005-09-02

    Routine industrial mining explosions play two important roles in seismic nuclear monitoring research: (1) they are a source of background events that need to be discriminated from potential nuclear explosions; (2) as some of the only explosions occurring in the current de facto global moratoria on nuclear testing, their signals should be exploited to improve the calibration of seismic m monitoring systems. A common issue monitoring arising in both of these roles is our limited physical understanding of the causes behind observed differences and similarities in the seismic signals produced by routine industrial mining blasts and small underground nuclear tests. In 2003 a consortium (Weston, SMU, LLNL, LANL and UTEP) carried out a Source Phenomenology Experiment (SPE), a series of dedicated explosions designed to improve this physical understanding, particularly as it relates to seismic methods of discriminating between signals from three different source types: earthquakes, industrial blasts, and nuclear tests. Here we very briefly review prior field experimental work that examined the seismic relationships between these source types.

  11. The effect of deformation history on the interpretation of seismic anisotropy in the upper mantle: experiments and numerical modeling

    NASA Astrophysics Data System (ADS)

    Boneh, Y.; Skemer, P. A.; Morales, L. F. G.; Kaminski, E. C.

    2015-12-01

    The main source of seismic anisotropy in the upper mantle is the deformation-induced crystallographic preferred orientation (CPO) of olivine. The interpretation of seismic anisotropy relies on models and experiments that predict certain relationships between olivine CPO and the deformation kinematics. Under some conditions, such as the interiors of oceanic plates, these relationships may be quite simple. However, near plate boundaries flow patterns are complex and the interpretation of seismic anisotropy is not straight-forward. In this contribution we describe the effect of deformation history on the re-orientation of olivine CPO as a function of strain. High pressure and temperature deformation experiments were performed on the Åheim dunite, which exhibits a pre-existing texture. Experiments were conducted in three different configurations with the pre-existing foliation at 0°, 45°, and 90° to the axis of compression, simulating three unique deformation histories. Deformation microstructures and texture are analyzed using electron backscatter diffraction (EBSD). The experiments show that up to strains of ~0.7 the three configurations evolve differently from one another, and from models initiated with random textures. Moreover, none of the models achieved the expected textural steady-state. The experiments results are then compared to numerical simulations using a Viscoplastic Self Consistent (VPSC) approach, and D-Rex. The input for the models is the Åheim dunite CPO in the three configurations used in the experiments. It is shown that, generally, texture symmetry evolves similarly in the models and the experiments although there are notable differences in texture strength. To achieve better agreement between experiments and models, new model parameterizations are proposed. Finally, we use the new parameterization of D-Rex to simulate a range of plausible deformation histories and associated seismic anisotropy in a variety of flow settings.

  12. Children's experiences of corporal punishment: A qualitative study in an urban township of South Africa.

    PubMed

    Breen, Alison; Daniels, Karen; Tomlinson, Mark

    2015-10-01

    Exposure to violence is a serious mental and public health issue. In particular, children exposed to violence are at risk for poor developmental outcomes and physical and mental health problems. One area that has been shown to increase the risk for poor outcomes is the use of corporal punishment as a discipline method. While researchers are starting to ask children directly about their experiences of violence, there is limited research with children about their perspectives on physical punishment, particularly in low-and middle-income countries (LMIC). This paper begins to address this gap by reporting on the spontaneous data that emerged during 24 qualitative interviews that were conducted with children, aged 8-12 in South Africa. The themes that emerged indicated that corporal punishment is an everyday experience, that it has negative emotional and behavioral consequences, and that it plays a role in how children resolve interpersonal conflicts. The study highlights the challenges for violence prevention interventions in under-resourced contexts. PMID:26094159

  13. Building Geophysics Talent and Opportunity in Africa: Experience from the AfricaArray/Wits Geophysics Field School

    NASA Astrophysics Data System (ADS)

    Webb, S. J.; Manzi, M.; Scheiber-Enslin, S. E.; Durrheim, R. J.; Jones, M. Q. W.; Nyblade, A.

    2015-12-01

    There are many challenges faced by geophysics students and academic staff in Africa that make it difficult to develop effective field and research programs. Challenges to conducting field work that have been identified, and that can be tackled are: lack of training on geophysical equipment and lack of exposure to field program design and implementation. To address these challenges, the AfricaArray/Wits Geophysics field school is designed to expose participants to a wide variety of geophysical instruments and the entire workflow of a geophysical project. The AA field school was initially developed for the geophysics students at the University of the Witwatersrand. However, by increasing the number of participants, we are able to make more effective use of a large pool of equipment, while addressing challenging geophysical problems at a remote field site. These additional participants are selected partially based on the likely hood of being able start a field school at their home institution. A good candidate would have access to geophysical equipment, but may not have knowledge of how to use it or how to effectively design surveys. These are frequently junior staff members or graduate students in leadership roles. The three week program introduces participants to the full geophysical field workflow. The first week is spent designing a geophysical survey, including determining the cost. The second week is spent collecting data to address a real geophysical challenge, such as determining overburden thickness, loss of ground features due to dykes in a mine, or finding water. The third week is spent interpreting and integrating the various data sets culminating in a final presentation. Participants are given all lecture material and much of the software is open access; this is done to encourage using the material at the home institution. One innovation has been to use graduate students as instructors, thus building a pool of talent that has developed the logistic and

  14. Building on Experience: A Formative Evaluation of a Peer Education Sexual Health Project in South Africa

    ERIC Educational Resources Information Center

    Warwick, Ian; Aggleton, Peter

    2004-01-01

    In South Africa, as elsewhere in the world, the promise of peer education as a means of promoting sexual health has contributed to its increasing popularity. While structural and organisational constraints can compromise the success of peer education, many of those involved in modest local programmes in South Africa are able to address the sexual…

  15. Evaluation and developmental studies of possible active seismic experiments during the post-Apollo period

    NASA Technical Reports Server (NTRS)

    Kovach, R. L.

    1974-01-01

    Seismic velocity studies pertinent to the lunar crust and mantle are briefly summarized. The compressional and shear wave velocities in loose aggregates are discussed along with the effects of temperature on seismic velocity in compacted powders. Abstracts of papers concerning the lunar structure are included.

  16. The Seismic Aftershock Monitoring System (SAMS) for OSI - Experiences from IFE14

    NASA Astrophysics Data System (ADS)

    Gestermann, Nicolai; Sick, Benjamin; Häge, Martin; Blake, Thomas; Labak, Peter; Joswig, Manfred

    2016-04-01

    An on-site inspection (OSI) is the third of four elements of the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The sole purpose of an OSI is to confirm whether a nuclear weapon test explosion or any other nuclear explosion has been carried out in violation of the treaty and to gather any facts which might assist in identifying any possible violator. It thus constitutes the final verification measure under the CTBT if all other available measures are not able to confirm the nature of a suspicious event. The Provisional Technical Secretariat (PTS) carried out the Integrated Field Exercise 2014 (IFE14) in the Dead Sea Area of Jordan from 3 November to 9. December 2014. It was a fictitious OSI whose aim was to test the inspection capabilities in an integrated manner. The technologies allowed during an OSI are listed in the Treaty. The aim of the Seismic Aftershock Monitoring System (SAMS) is to detect and localize aftershocks of low magnitudes of the triggering event or collapses of underground cavities. The locations of these events are expected in the vicinity of a possible previous explosion and help to narrow down the search area within an inspection area (IA) of an OSI. The success of SAMS depends on the main elements, hardware, software, deployment strategy, the search logic and not least the effective use of personnel. All elements of SAMS were tested and improved during the Built-Up Exercises (BUE) which took place in Austria and Hungary. IFE14 provided more realistic climatic and hazardous terrain conditions with limited resources. Significant variations in topography of the IA of IFE14 in the mountainous Dead Sea Area of Jordan led to considerable challenges which were not expected from experiences encountered during BUE. The SAMS uses mini arrays with an aperture of about 100 meters and with a total of 4 elements. The station network deployed during IFE14 and results of the data analysis will be presented. Possible aftershocks of

  17. Siting of USArray Seismic Stations in North Carolina and southern Virginia: Experience of NC-1 Team

    NASA Astrophysics Data System (ADS)

    Martin, P.; Howard, J.; Horne, T.

    2012-12-01

    The USArray component of the EarthScope, a transportable array of 400 seismometers installed in a grid about 70 km apart, is in the next two years entering its final stage with station deployment along the Atlantic coast of the United States. Here, we present the experience of the student-faculty team from North Carolina Central University (NCCU) in finding and documenting the suitable sites for the twenty five USArray stations in North Carolina and southern Virginia. The ideal sites are easily accessible yet far from traffic and other sources of noise, with good cell phone coverage, sun exposure and out of flood-prone areas. Although the initial selection of potential locations was done using geospatial mapping and analysis software provided by EarthScope, finding and finalizing the sites involved driving more then 1,000 miles each week for over two months inspecting possible site locations. Aside from driving, the majority of time was spent talking about the EarthScope project and hosting of USArray stations to mostly reluctant landowners. In addition to facing various challenges in finding appropriate sites due to land use issues, such as suburban sprawl of central North Carolina, or topography factors, such as low lying flood prone coastal areas, by far the major challenge was finding the landowners willing to host the seismic station for the necessary three years. In addition to involving students from an HBCU in seismology related project and increasing the visibility of NCCU geophysics program in the University and local community through publicity releases in local media and on university web site, the project had an important outreach component. As North Carolina is located along the seismically quiet, passive Atlantic margin, most residents are not familiar with earthquakes and seismology and the siting experience provided students an opportunity to practice explaining the earthquake research to the general public. The dialog also highlighted science

  18. Application of a cross correlation-based picking algorithm to an active seismic experiment in Sicily and Aeolian Islands

    NASA Astrophysics Data System (ADS)

    Diaz, Alejandro; Álvarez, Isaac; De la Torre, Ángel; García, Luz; Benítez, Ma Carmen; Cortés, Guillermo

    2014-05-01

    The detection of the arrival time of seismic waves or picking is of great importance in many seismology applications. Traditionally, picking has been carried out by human operators. This process is not systematic and relies completely on the expertise and judgment of the analysts. The limitations of manual picking and the increasing amount of data daily stored in the seismic networks worldwide distributed and in active seismic experiments lead to the development of automatic picking algorithms. Current conventional algorithms work with single signals, such as the "short-term average over long-term average" (STA/LTA) algorithm, autoregressive methods or the recently developed "Adaptive Multiband Picking Algorithm" (AMPA). This work proposes a correlation-based picking algorithm, whose main advantage is the fact of using the information of a set of signals, improving the signal to noise ratio and therefore the picking accuracy. The main advantage of this approach is that the algorithm does not require to set up sophisticated parameters, in contrast to other automatic algorithms. The accuracy of the conventional STA/LTA algorithm, the recently developed AMPA algorithm, an autoregressive method, and a preliminary version of the cross correlation-based picking algorithm were assessed using a huge data set composed by active seismic signals from experiments in Tenerife Island (January 2007, Spain). The experiment consisted of the deployment of a dense seismic network on Tenerife Island (125 seismometers in total) and the shooting of air-guns around the island with the Spanish oceanographic vessel Hespérides (6459 air shots in total). Only 110937 signals (13.74% of the total) had the signal to noise ratio enough to be manually picked. Results showed that the use of the cross correlation-based picking algorithm significantly increases the number of signals that can be considered in the tomography. A new active seismic experiment will cover Sicily and Aeolian Islands (TOMO

  19. Lesser Antilles Subduction Zone Investigation by a Cluster of Large Seismic Experiments in the Forearc Region

    NASA Astrophysics Data System (ADS)

    Last, T.

    2007-12-01

    subduction mega-thrust fault plane, and which is here the main target has been localized along 3 transects to the Arc thanks to a preliminary survey in 2001, the French SISMANTILLES cuise. We will present the first results obtained during these experiments dedicated specifically to image at depth the seismic structure and activity of this region. To image faults at depth and the detailed upper-crustal structure, 3700 km of multi-beam bathymetry and multi-channel reflection seismic profiles have been collected along a grid comprising 7 strike-lines of up to 300 km long and spaced by 15 km and 12 transects of up to 150 km long and spaced by 25 km (SISMANTILLES 2). All these airgun shots dedicated to deep penetration have been recorded by the 84 OBSs and 20 OBHs deployed by the F/S Merian and N/O Atalante on the nodes of this grid of profiles. It will permit to get Vp constraints on the deep forearc region and mantle wedge by wide-angle refraction studies, as well as constraints on the updip and downdip limits of the seismogenic part of the mega-thrust fault plane. Two of these transects have been extended across the whole arc during the TRAIL survey, with up to 50 OBSs deployed along both 240 km long profiles. All these OBSs remained several months beyond the shot experiments for local earthquakes Vp and Vp/Vs tomography. They have been recovered and partly redeployed by N/O Antea during the OBSANTILLES survey. A significant number of those instruments had broadband seismometers, a notable originality in the case of the OBSs to detect low-frequency transient signals.

  20. Conceptual Design and Architecture of Mars Exploration Rover (MER) for Seismic Experiments Over Martian Surfaces

    NASA Astrophysics Data System (ADS)

    Garg, Akshay; Singh, Amit

    2012-07-01

    Keywords: MER, Mars, Rover, Seismometer Mars has been a subject of human interest for exploration missions for quite some time now. Both rover as well as orbiter missions have been employed to suit mission objectives. Rovers have been preferentially deployed for close range reconnaissance and detailed experimentation with highest accuracy. However, it is essential to strike a balance between the chosen science objectives and the rover operations as a whole. The objective of this proposed mechanism is to design a vehicle (MER) to carry out seismic studies over Martian surface. The conceptual design consists of three units i.e. Mother Rover as a Surrogate (Carrier) and Baby Rovers (two) as seeders for several MEMS-based accelerometer / seismometer units (Nodes). Mother Rover can carry these Baby Rovers, having individual power supply with solar cells and with individual data transmission capabilities, to suitable sites such as Chasma associated with Valles Marineris, Craters or Sand Dunes. Mother rover deploys these rovers in two opposite direction and these rovers follow a triangulation pattern to study shock waves generated through firing tungsten carbide shells into the ground. Till the time of active experiments Mother Rover would act as a guiding unit to control spatial spread of detection instruments. After active shock experimentation, the babies can still act as passive seismometer units to study and record passive shocks from thermal quakes, impact cratering & landslides. Further other experiments / payloads (XPS / GAP / APXS) can also be carried by Mother Rover. Secondary power system consisting of batteries can also be utilized for carrying out further experiments over shallow valley surfaces. The whole arrangement is conceptually expected to increase the accuracy of measurements (through concurrent readings) and prolong life cycle of overall experimentation. The proposed rover can be customised according to the associated scientific objectives and further

  1. Legacy, legitimacy, and possibility: an exploration of community health worker experience across the generations in Khayelitsha, South Africa.

    PubMed

    Swartz, Alison

    2013-06-01

    In South Africa, the response to HIV and TB epidemics is complex, varied, and contextually defined. "Task-shifting" and a movement toward a decentralized model of care have led to an increased reliance on community health workers (CHWs) providing health care services to residents of impoverished, peri-urban areas. Public health policy tends to present CHWs as a homogeneous group, with little attention paid to the nuances of experience, motivation, and understanding, which distinguish these care workers from one another and from other kinds of health workers. An exploration of the layered meanings of providing community health care services under financially, politically, and socially difficult conditions reveals clear distinctions of experience across the generations. Many older CHWs say that ubuntu, a notion of shared African humanity, is being "killed off" by the younger generation, whereas younger CHWs often describe older women as being "jealous" of the opportunities that this younger generation has for education, training, and employment. The structure of the South African health system, past and present responses to disease epidemics, and the legacy of apartheid's structural violence have amplified these generational differences among CHWs. Using ethnographic data collected from approximately 20 CHWS in a peri-urban settlement in Cape Town, South Africa, I explore how CHWs experience and understand legitimacy in the moral economy of care. A call for closer attention to the experiences of CHWs is critical when designing public health policies for the delivery of health care services in impoverished communities in South Africa. PMID:23804283

  2. Seismic aftershock monitoring for on-site inspection purposes. Experience from Integrated Field Exercise 2008.

    NASA Astrophysics Data System (ADS)

    Labak, P.; Arndt, R.; Villagran, M.

    2009-04-01

    One of the sub-goals of the Integrated Field Experiment in 2008 (IFE08) in Kazakhstan was testing the prototype elements of the Seismic aftershock monitoring system (SAMS) for on-site inspection purposes. The task of the SAMS is to collect the facts, which should help to clarify nature of the triggering event. Therefore the SAMS has to be capable to detect and identify events as small as magnitude -2 in the inspection area size up to 1000 km2. Equipment for 30 mini-arrays and 10 3-component stations represented the field equipment of the SAMS. Each mini-array consisted of a central 3-component seismometer and 3 vertical seismometers at the distance about 100 m from the central seismometer. The mini-arrays covered approximately 80% of surrogate inspection area (IA) on the territory of former Semipalatinsk test site. Most of the stations were installed during the first four days of field operations by the seismic sub-team, which consisted of 10 seismologists. SAMS data center comprised 2 IBM Blade centers and 8 working places for data archiving, detection list production and event analysis. A prototype of SAMS software was tested. Average daily amount of collected raw data was 15-30 GB and increased according to the amount of stations entering operation. Routine manual data screening and data analyses were performed by 2-6 subteam members. Automatic screening was used for selected time intervals. Screening was performed using the Sonoview program in frequency domain and using the Geotool and Hypolines programs for screening in time domain. The screening results were merged into the master event list. The master event list served as a basis of detailed analysis of unclear events and events identified to be potentially in the IA. Detailed analysis of events to be potentially in the IA was performed by the Hypoline and Geotool programs. In addition, the Hyposimplex and Hypocenter programs were also used for localization of events. The results of analysis were integrated

  3. Site Characterization of the Source Physics Experiment Phase II Location Using Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Sexton, E. A.; Snelson, C. M.; Chipman, V.; Emer, D. F.; White, R. L.; Emmitt, R.; Wright, A. A.; Drellack, S.; Huckins-Gang, H.; Mercadante, J.; Floyd, M.; McGowin, C.; Cothrun, C.; Bonal, N.

    2013-12-01

    An objective of the Source Physics Experiment (SPE) is to identify low-yield nuclear explosions from a regional distance. Low-yield nuclear explosions can often be difficult to discriminate among the clutter of natural and man-made explosive events (e.g., earthquakes and mine blasts). The SPE is broken into three phases. Phase I has provided the first of the physics-based data to test the empirical models that have been used to discriminate nuclear events. The Phase I series of tests were placed within a highly fractured granite body. The evolution of the project has led to development of Phase II, to be placed within the opposite end member of geology, an alluvium environment, thereby increasing the database of waveforms to build upon in the discrimination models. Both the granite and alluvium sites have hosted nearby nuclear tests, which provide comparisons for the chemical test data. Phase III of the SPE is yet to be determined. For Phase II of the experiment, characterization of the location is required to develop the geologic/geophysical models for the execution of the experiment. Criteria for the location are alluvium thickness of approximately 170 m and a water table below 170 m; minimal fracturing would be ideal. A P-wave mini-vibroseis survey was conducted at a potential site in alluvium to map out the subsurface geology. The seismic reflection profile consisted of 168 geophone stations, spaced 5 m apart. The mini-vibe was a 7,000-lb peak-force source, starting 57.5 m off the north end of the profile and ending 57.5 m past the southern-most geophone. The length of the profile was 835 m. The source points were placed every 5 m, equally spaced between geophones to reduce clipping. The vibroseis sweep was from 20 Hz down to 180 Hz over 8 seconds, and four sweeps were stacked at each shot location. The shot gathers show high signal-to-noise ratios with clear first arrivals across the entire spread and the suggestion of some shallow reflectors. The data were

  4. Transient Creep Events and the Transition from Aseismic to Seismic Faulting Observed in Laboratory Experiments

    NASA Astrophysics Data System (ADS)

    Schubnel, A.; Brantut, N.; Fortin, J.; Gueguen, Y.

    2008-12-01

    Dry triaxial compression experiments performed on Carrara marble and Volterra Gypsum at confining pressures ranging from 10 to 100MPa revealed an important dependence of the strain rate on the confining stress. At constant shear stress, transient exponential increases in axial strain, similar to transient creep events observed on the field, were observed for small decreases of the confining pressure (1-10MPa), which could eventually lead to ductile failure nucleation. In such case, rupture propagation was silent and slow (several hundreds of seconds), although accompanied by stress drops of the order of several tens of MPas and millimetric slips. However, as the slip velocity increased during failure propagation, continuous acoustic waveform recordings enabled us to illustrate the transition from aseismic to seismic faulting. These experiments provide a clear experimental case of silent, slow localized failure in rocks as a result of an interplay between intragranular plasticity and microcracking. In the case of ductile failure as in the marble, dislocation and twin accumulation is such that cracks propagation steps are small and/or slow, and thus the radiated energy release rate remains small at early stages of rupture and increases with rupture speed. This last observation clearly highlights the dependence of radiated acoustic (and microseismic?) energy during crack propagation not only on the rupture propagation speed and the slip velocity but most importantly on the rock's lithology and rheology. This could have important implications as carbonates are prevalent within sedimentary basins. At even at shallower depths and prevalent within fault gouges, clay minerals are also expected to behave in a similar way.

  5. Rock mass response to strong ground motion generated by mining induced seismic events and blasting observed at the surface of the excavations in deep level gold mines in South Africa

    NASA Astrophysics Data System (ADS)

    Milev, Alexander; Durrheim, Ray; Ogasawara, Hiroshi

    2014-05-01

    The strong ground motion generated by mining induced seismic events was studied to characterize the rock mass response and to estimate the site effect on the surface of the underground excavations. A stand-alone instruments, especially designed for recording strong ground motions, were installed underground at a number of deep level gold mines in South Africa. The instruments were recording data at the surface of the stope hangingwalls. A maximum value of 3 m/s was measured. Therefore data were compared to the data recorded in the solid rock by the mine seismic networks to determine the site response. The site response was defined as the ratio of the peak ground velocity measured at the surface of the excavations to the peak ground velocity inferred from the mine seismic data measured in the solid rocks. The site response measured at all mines studied was found to be 9 ± 3 times larger on average. A number of simulated rockbursts were conducted underground in order to estimate the rock mass response when subjected to extreme ground motion and derive the attenuation factors in near field. The rockbursts were simulated by means of large blasts detonated in solid rock close to the sidewall of a tunnel. The numerical models used in the design of the simulated rockbursts were calibrated by small blasts taking place at each experimental site. A dense array of shock type accelerometers was installed along the blasting wall to monitor the attenuation of the strong ground motion as a function of the distance from the source. The attenuation of the ground motion was found to be proportional to the distance from the source following R^-1.1 & R^-1.7 for compact rock and R^-3.1 & R^-3.4 for more fractured rock close to the surface of the tunnel. In addition the ground motion was compared to the quasi-static deformations taking place around the underground excavations. The quasi-static deformations were measured by means of strain, tilt and closure. A good correspondence

  6. Comparison of seismic and hydrodynamic yield determinations for the Soviet joint verification experiment of 1988

    PubMed Central

    Sykes, Lynn R.; Ekström, Göran

    1989-01-01

    Seismic magnitudes determined from surface and body waves for the Soviet underground nuclear explosion of September 14, 1988, are used to calculate the yield of that event from previously derived calibration curves. The yield obtained by combining the two seismic estimates is 113 kilotons, which is very close to those obtained by hydrodynamic measurements made on-site. This comparison substantiates previous conclusions about the sizes of past Soviet weapons tests and compliance with the Threshold Test Ban Treaty. The factor of uncertainty in the combined seismic yield is 1.28 at the 68% and 1.62 at the 95% confidence levels, demonstrating that accuracies considerably better than a factor of 2 can be obtained by combining seismic determinations of yield. PMID:16594040

  7. Experiments on the Brazil-nut effect due to seismic shakings

    NASA Astrophysics Data System (ADS)

    Maciel, A.; Tancredi, G.; Lluch, N.

    2014-07-01

    Size segregation processes have been identified as relevant when studying the behaviour of rocks and boulders on the surface and in the interior of a rubble-pile asteroid. The size segregation as a consequence of repeated shakings is also known as the Brazil-nut effect (BNE). These processes might be really important when studying rubble-pile -type asteroids, which may have suffered seisms as a consequence of repeated collisions; such as in the case of asteroid Itokawa. Size segregation processes can be studied using laboratory experiments as well as computational models, the first case being the one initially considered in this work. Previous studies of the BNE were performed using a sinusoidal vertical or horizontal vibration of the containers. Since we are interested in the effects of repeated seismic shakes, we have used in our experiments a sequence of repeated knocks of the container. We built a resin and polycarbonate box, which is filled with marbles of different sizes. Vacuum up to 0.5 % of ambient pressure is established inside the box. The box is subjected to repeated free-falls from heights up to 1m, with impact velocities on the ground up to 4m/s. We have chosen these low velocities since they are comparable to the escape velocities of km-size asteroids; and they are on the order of the displacement velocities of surface material as a consequence of a small impact (far from the impact point; Tancredi et al. 2012). We study the dependence of size segregation processes with the size rate among the spheres and the impact speed of the box. We observe that, when effectively occurs, size segregation mostly depends on the size rate of the particles and very little on the impact speed, even though this slight dependence has been recorded in our experiments. The laboratory experiments have been also numerically simulated using the Discrete Element Method (DEM) package known as ESyS-particle. The results of the numerical simulations are compared to the

  8. Seismic passive: an experiment for the campus of the National University of Colombia

    NASA Astrophysics Data System (ADS)

    Mateus Reyes, S. E.

    2015-12-01

    The generation of seismic image, in areas where the use of active sources it is restricted (like dynamite) or just the area where the area is an active source, it is possible to do it with passive seismic, using seismic interferometry, retrieving the impulse response (Function Green) from the cross-correlation of the ambient noise. It was cross-correlated ambient seismic noise, of a recording made along a line lying on the university campus in Bogota, on that line were located the virtual-source and the traces. For processing, the surface waves were removed and subsequently, it was applied energy normalization to each of the noise panel and were correlated each noise panels with the trace at the chosen virtual-source position. When it was retrieved common-source gathers it was made a new stacking. And with this stack, seismic image was generated. The image obtained was compared with the geological surveys of the area and found that the reflectors match, showing 2 matching reflections. It was determined from this study of seismic exploration on one line, using retrieved reflection data it posible to obtain a migrated reflection imageof the subsurface.

  9. Seismically imaging the Afar plume

    NASA Astrophysics Data System (ADS)

    Hammond, J. O.; Kendall, J. M.; Bastow, I. D.; Stuart, G. W.; Keir, D.; Ayele, A.; Ogubazghi, G.; Ebinger, C. J.; Belachew, M.

    2011-12-01

    Plume related flood basalt volcanism in Ethiopia has long been cited to have instigated continental breakup in northeast Africa. However, to date seismic images of the mantle beneath the region have not produced conclusive evidence of a plume-like structure. As a result the nature and even existence of a plume in the region and its role in rift initiation and continental rupture are debated. Previous seismic studies using regional deployments of sensors in East-Africa show that low seismic velocities underlie northeast Africa, but their resolution is limited to the top 200-300km of the Earth. Thus, the connection between the low velocities in the uppermost mantle and those imaged in global studies in the lower mantle is unclear. We have combined new data from Afar, Ethiopia with 6 other regional experiments and global network stations across Ethiopia, Eritrea, Djibouti and Yemen, to produce high-resolution models of upper mantle P- and S- wave velocities to the base of the transition zone. Relative travel time tomographic inversions show that the top 100km is dominated by focussed low velocity zones, likely associated with melt in the lithosphere/uppermost asthenosphere. Below these depths a broad SW-NE oriented sheet like upwelling extends down to the top of the transition zone. Within the transition zone two focussed sharp-sided low velocity regions exist: one beneath the Western Ethiopian plateau outside the rift valley, and the other beneath the Afar depression. The nature of the transition zone anomalies suggests that small upwellings may rise from a broader low velocity plume-like feature in the lower mantle. This interpretation is supported by numerical and analogue experiments that suggest the 660km phase change and viscosity jump may impede flow from the lower to upper mantle creating a thermal boundary layer at the base of the transition zone. This allows smaller, secondary upwellings to initiate and rise to the surface. Our images of secondary upwellings

  10. High-resolution shallow-seismic experiments in sand. Part 1: Water table, fluid flow, and saturation

    SciTech Connect

    Bachrach, R.; Nur, A.

    1998-07-01

    A high-resolution, very shallow seismic reflection and refraction experiment was conducted to investigate the seismic response of groundwater level changes in beach sand in situ. A fixed 10-m-long receiver array was used for repeated seismic profiling. Direct measurements of water level in a monitoring well and moisture content in the sand were taken as well. The water table in the well changed by about 1 m in slightly delayed response to the nearby ocean tides. In contrast, inversion of the seismic data yielded a totally different picture. The reflection from the water table at high tide appeared at a later time than the reflection at low tide. This unexpected discrepancy can be reconciled using Gassmann`s equation: a low-velocity layer must exist between the near-surface dry sand and the deeper and much faster fully saturated sand. This low-velocity layer coincides with the newly saturated zone and is caused by a combination of the sand`s high density (close to that of fully saturated sand), and its high compressibility (close to that of dry sand). This low-velocity zone causes a velocity pull-down for the high-frequency reflections, and causes a high-tide reflection to appear later in time than low-tide reflection. The calculated velocities in the dry layer show changes with time that correlate with sand dryness, as predicted by the temporal changes of the sand`s density due to changing water/air ratio. The results show that near-surface velocities in sand are sensitive to partial saturation in the transition zone between dry and saturated sand. The authors were able to extract the saturation of the first layer and the depth to the water table from the seismic velocities.

  11. Seismic Interferometry and the Spatial Auto-Correlation Method on the Regional Coda of the Non-Proliferation Experiment

    NASA Astrophysics Data System (ADS)

    de Ridder, S.; Prieto, G. A.

    2008-12-01

    A seismic recording of the non-proliferation experiment (NPE), made by a petroleum-exploration company in Railroad Valley (Nevada), contains the first break of the regional P phases followed by a three minute long coda. The transverse orientation and sign-bit recording of the array, renders distinguishing phase arrival times difficult. This motivates the use of seismic interferometry. The geometry does not permit recovering the Green's function from the first break arrival times using the stationary phase theorem, however the coda contains sufficiently equipartitioned energy. We study the result of seismic interferometry in the frequency-domain. This procedure is analogous to the spatial auto-correlation (SPAC) method, devised for studying microtremors by Aki in 1957. Cross-correlating two receiver stations retrieves, under favorable circumstances, an approximation of the Green's function between these two stations. To first order, this Green's function consists of a direct event traveling between the receivers. In the frequency domain, the lowest mode in the Green's function is a weighted and scaled zero-order Bessel function of the first kind, J0. We fit the frequency-domain of the recovered Green's functions to damped J0 functions. to recover phase velocity and estimates of the attenuation coefficients. Only energy between 1-4 Hz can be fitted unambiguously with J0 functions, because higher frequencies contain too much spurious energy. This result shows the equivalence of the SPAC method and seismic interferometry for the lowest mode in the Green's function. This study also shows how the coda of a regional event, seemingly unfavorably positioned, can contains energy useful for seismic interferometry.

  12. An overview on geophysical structures in the Eastern Alps revealed by recent seismic experiments

    NASA Astrophysics Data System (ADS)

    Behm, M.; Brueckl, E. P.; Grad, M.

    2009-12-01

    CELEBRATION 2000 and ALP 2002 were two large seismic wide-angle experiments which targeted the lithospheric structure of Central Europe. This presentation highlights crustal features of the Eastern Alps and their transition into adjacent tectonic provinces (Bohemian Massif, Carpathians, Pannonian Basin, Southern Alps and Dinarides) which were unknown prior to these experiments. The Eastern Alps result from the collision of the European platform with the Adriatic plate which got initiated in the Eocene. From the late Oligocene on, escape tectonics towards the unconstrained eastern margin contributed to the evolution of the Eastern Alps. Both processes left their imprints on the surface geology which differs significantly from the Western Alps. Considering the layout of the experiments, an innovative 3D processing scheme was implemented and supplemented by traditional 2D interpretation techniques. The 3D approach provides robust models with large spatial coverage, while the evaluation of 2D profiles allows resolving details at locations of particular interest. The P-wave velocity distribution of crust shows a clear separation into a low-velocity European plate and a high-velocity Adriatic plate. Crustal velocities below the Pannonian Basin are moderate to low. Velocity structures in the uppermost crust correlate well with surface geology and tectonic divisions. One of the most important results is a new map of the Moho discontinuity. Its depth varies between 52 and 24 km, and from its structure we deduce the new crustal fragment Pannonia. Pannonia has shallow crust and is underthrusted by both the European Moho in the North and the Adriatic Moho in the South-West. Although solely vertical component receivers were used, strong S-waves can be observed on some seismograms. Their evaluation confirms the separation into three crustal fragments and provides constraints on Poisson’s ratio. A subhorizontal mantle reflector in a depth range from approximately 55 km is found

  13. Scaling relationship between corner frequencies and seismic moments of ultra micro earthquakes estimated with coda-wave spectral ratio -the Mponeng mine in South Africa

    NASA Astrophysics Data System (ADS)

    Wada, N.; Kawakata, H.; Murakami, O.; Doi, I.; Yoshimitsu, N.; Nakatani, M.; Yabe, Y.; Naoi, M. M.; Miyakawa, K.; Miyake, H.; Ide, S.; Igarashi, T.; Morema, G.; Pinder, E.; Ogasawara, H.

    2011-12-01

    Scaling relationship between corner frequencies, fc, and seismic moments, Mo is an important clue to understand the seismic source characteristics. Aki (1967) showed that Mo is proportional to fc-3 for large earthquakes (cubic law). Iio (1986) claimed breakdown of the cubic law between fc and Mo for smaller earthquakes (Mw < 2), and Gibowicz et al. (1991) also showed the breakdown for the ultra micro and small earthquakes (Mw < -2). However, it has been reported that the cubic law holds even for micro earthquakes (-1 < Mw > 4) by using high quality data observed at a deep borehole (Abercrombie, 1995; Ogasawara et al., 2001; Hiramatsu et al., 2002; Yamada et al., 2007). In order to clarify the scaling relationship for smaller earthquakes (Mw < -1), we analyzed ultra micro earthquakes using very high sampling records (48 kHz) of borehole seismometers installed within a hard rock at the Mponeng mine in South Africa. We used 4 tri-axial accelerometers of three-component that have a flat response up to 25 kHz. They were installed to be 10 to 30 meters apart from each other at 3,300 meters deep. During the period from 2008/10/14 to 2008/10/30 (17 days), 8,927 events were recorded. We estimated fc and Mo for 60 events (-3 < Mw < -1) within 200 meters from the seismometers. Assuming the Brune's source model, we estimated fc and Mo from spectral ratios. Common practice is using direct waves from adjacent events. However, there were only 5 event pairs with the distance between them less than 20 meters and Mw difference over one. In addition, the observation array is very small (radius less than 30 m), which means that effects of directivity and radiation pattern on direct waves are similar at all stations. Hence, we used spectral ratio of coda waves, since these effects are averaged and will be effectively reduced (Mayeda et al., 2007; Somei et al., 2010). Coda analysis was attempted only for relatively large 20 events (we call "coda events" hereafter) that have coda energy

  14. Upper Mantle Structure of the Eastern Africa from Body Wave Tomography

    NASA Astrophysics Data System (ADS)

    Mulibo, G. D.; Nyblade, A.; Ferdinand, R. W.; Reusch, A. M.; Adams, A. N.; Tugume, F. A.

    2009-12-01

    This study presents preliminary results of the upper mantle structure beneath the east Africa from body wave tomography. This work is part of an on-going study aimed at investigating the origin and structure of the African Superplume. The available global tomographic studies suggest that the African Superplume is a low velocity-anomaly extending from the core-mantle boundary upward into the mid mantle beneath southern Africa and may reach the upper mantle beneath eastern Africa. However, the limited vertical resolution of global tomographic models makes it difficult to confirm a connection from the lower to the upper mantle. Previous regional studies of upper mantle structure in east Africa have found evidence of a low velocity anomaly beneath the region that has been suggested as the upper mantle expression of the Superplume. Models from previous tomographic studies in east Africa have limited resolution below ~400 km beneath the eastern rift and are less well resolved beneath the western part of the rift due to less data coverage. This study uses teleseismic data from a wider region in east Africa than previously used. Data for this study are from a 3-year (2007-2010) deployment of 40 broadband seismic stations in Uganda and Tanzania. The dataset is supplemented by data from the 1994-1995 Tanzania broadband seismic experiment, the 2001-2002 Kenya broadband seismic experiment, the permanent AfricaArray seismic stations and IRIS/GSN stations. The data have been used for body wave tomography by computing relative travel time delays using a multi-channel cross-correlation technique and then inverting them for a 3D wave speed model. Preliminary results from the inversion of the relative delay times show that there is a low wave speed anomaly beneath east Africa extending from shallow upper mantle depths to at least 500 km.

  15. Fault rupture as a series of nano-seismic events during high-velocity shear experiments

    NASA Astrophysics Data System (ADS)

    Zu, X.; Reches, Z.; Chen, X.; Chang, J. C.; Carpenter, B. M.

    2015-12-01

    The rupture process of experimental faults is investigated here by monitoring nano-seismic events (NSE) during slip in a rotary shear apparatus. Our experimental faults are made of two rock blocks with one to four miniature 3D accelerometers that are glued to the stationary block at distance of ~ 2 cm from the fault surface. Accelerations in the frequency range of 1 Hz to 200 kHz are recorded in slip-parallel (x), slip-transverse (y), and slip-vertical (z) directions. We conducted a series of 45 experiments on diorite and dolomite samples in two loading styles: classical velocity controlled loading, and power-density loading, in which the power-density (shear stress times slip velocity) is selected, and stick-slip events develop spontaneously according to the experimental fault response. The 3D accelerometer data were recorded at 106 samples/s, with acceleration resolution of 10 mV/g in recoding range of +/- 5 V. The experiments were conducted at slip-velocity of 0.001-0.8 m/s and slip distance up to 1.38 m. The accelerometer observations revealed tens to hundreds of NSEs per slip in both loading styles; peak acceleration ranged from 1g to over 500g. A typical stick-slip with tens of NSEs in Fig. 1, shows: (1) An initial NSE at ~59.72 s (green) that coincides with a small stress drop (~10%, red); (2) Simultaneous macroscopic slip initiation (blue); (3) A swarm of NSEs occur as the fault slips, each NSE lasts 1-2 milliseconds; and (4) Details of the initial NSE are shown in Fig. 2. Based on waveform cross-correlation between frequency band from 20 kHz to 70kHz, we identify several groups of NSE clusters, and apply empirical Green's function method to analyze event source spectra based on Brune-type source model. These NSEs are indicators of rupture propagation during the experimental fault slip.

  16. Moonquakes and lunar tectonism results from the Apollo passive seismic experiment.

    NASA Technical Reports Server (NTRS)

    Latham, G.; Ewing, M.; Dorman, J.; Lammlein, D.; Press, F.; Toksoz, N.; Sutton, G.; Duennebier, F.; Nakamura, Y.

    1972-01-01

    The natural seismicity of the moon appears to be very low relative to that of the earth. However, moonquakes do occur. They are detected by the stations of the Apollo seismic network at an average rate of 1800/yr at Station 14 and at lower rates at Stations 12 and 15. All of the moonquakes are small, and in the few cases for which the foci have been located, they occur at great depth (about 800 km). The frequency of occurrence of moonquakes is strongly correlated with lunar tides. The dynamic processes that generate quakes are clearly much less vigorous within the moon than they are within the earth.

  17. Planning the improvement of seismic monitoring in a volcanic supersite: experience on Mt. Etna

    NASA Astrophysics Data System (ADS)

    D'Alessandro, Antonino; Scarfi, Luciano; Scaltrito, Antonio; Aiesi, Giampiero; Di Prima, Sergio; Ferrari, Ferruccio; Rapisarda, Salvatore

    2013-04-01

    Etna is one of the most active volcanoes in the world and one of the most intriguing natural laboratories for the understanding of eruptive processes and lava uprising in basalt-type volcanic environments; indeed, it is considered, by the scientific international community, together with the Vesuvius and the Hawaiian Islands, as a volcanic supersite. Its activity is continuously monitored by the Osservatorio Etneo of the Istituto Nazionale di Geofisica e Vulcanologia (INGV), by means of an array of integrated multidisciplinary techniques. In particular, Etna seismicity is recorded by a dense local seismic network (ESN- Etna Seismic Network), which, nowadays, consists of about 40 real-time seismic stations, many of which equipped with broadband velocity and accelerometer sensors. The data are analyzed routinely in detail by the Osservatorio Etneo staff, producing daily and periodic reports and bulletins of the earthquakes located in the whole Sicily and southern Calabria region. In the last decades, seismological observations provided important information on both the dynamics and internal structure of the volcano, in addition to their interaction with the regional tectonic structures. In the last year, in the framework of the VULCAMED project, an INGV workgroup has taken on the task of developing the existing seismic network through the installation of new measurement stations. By considering the spatial distribution of earthquakes in the area, the presence of structures known as seismically active and through extensive geological-geophysical surveys, ten potential new sites were identified. In the following months, some of these sites will complement the existing network. The choice of optimal sites must clearly be made through a careful analysis of environmental noise, of the possible logistics, technical and broadcast problems, but must also take into account the geometry of the existing seismic network. For this purpose, we applied the Seismic Network

  18. U. S. Geological Survey begins seismic ground response experiments in Washington State

    USGS Publications Warehouse

    Tarr, A.C.; King, K.W.

    1987-01-01

    The men were Denver-based U.S Geological Survey (USGS) geophysicists working on the Urban Hazards Field Investigations project. On the previous day they had recorded two events on their seismographs-a distant nuclear explosion in Nevada and a blast at amine near Centralia, Washington. On another day, they used seismic refraction equipment to locate the depth of bedrock and seismic velocity to it at several locations in West Seattle and in the Seward Park-Brighton district of southeast Seattle. 

  19. Ghana's experience in the establishment of a national digital seismic network observatory

    NASA Astrophysics Data System (ADS)

    Ahulu, Sylvanus; Danuor, Sylvester Kojo

    2015-07-01

    The Government of Ghana has established a National Digital Seismic Network Observatory in Ghana with the aim of monitoring events such as earthquakes, blasts from mining and quarrying, nuclear tests, etc. The Digital Observatory was commissioned on 19 December 2012, and was dedicated to Geosciences in Ghana. Previously Ghana did not have any operational, digital seismic network acquisition system with the capability of monitoring and analysing data for planning and research purposes. The Ghana Geological Survey has been monitoring seismic events with an analogue system which was not efficient and does not deliver real-time data. Hence, the importance of setting up the National Digital Seismic Network System which would enable the Geological Survey to constantly monitor, manage and coordinate both natural and man-made seismic activities in the country and around the globe, to some extent on real-time basis. The Network System is made up of six remote digital stations that transmit data via satellite to the central observatory. Sensors used are 3× Trillium Compact and 3× Trillium 120PA with Trident digitizers. The department has also acquired strong motion equipment: Titan accelerometers with Taurus digitizers from Nanometrics. Three of each of these instruments have been installed at the Akosombo and Kpong hydrodams, and also at the Weija water supply dam. These instruments are used to monitor dams. The peak ground acceleration (PGA) values established from the analysed data from the accelerometers will be used to retrofit or carry out maintenance work of the dam structures to avoid collapse. Apart from these, the observatory also assesses and analyses seismic waveforms relevant to its needs from the Global Seismographic Network (GSN) system operated by the US Geological Survey. The Ghana Geological Survey, through its Seismic Network Observatory makes data available to its stakeholder institutions for earthquake disaster mitigation; reports on all aspects of

  20. Parent Participation in School Governance: A Legal Analysis of Experiences in South Africa and Kentucky

    ERIC Educational Resources Information Center

    Bathon, Justin; Beckmann, Johan; Bjork, Lars G.

    2011-01-01

    This comparative study on the educational governance systems of South Africa and the Commonwealth of Kentucky examines legal evidence from judicial decisions and administrative law to understand similarities in how school-based governance structures have been developed. We found that although school-level governance structures may provide greater…

  1. Transforming Education in South Africa: Comparative Perceptions of a South African Social Work Learning Experience

    ERIC Educational Resources Information Center

    Collins, Kathleen; Millard, Maria

    2013-01-01

    The state of tertiary education in South Africa is not adequately meeting the needs of its populace. The system in place does not effectively nor appropriately target the racial group of students which forms the democratic majority. This paper portrays the reasons why these students are not succeeding on the basis of a mismatch between their…

  2. Modelling Active Faults in Probabilistic Seismic Hazard Analysis (PSHA) with OpenQuake: Definition, Design and Experience

    NASA Astrophysics Data System (ADS)

    Weatherill, Graeme; Garcia, Julio; Poggi, Valerio; Chen, Yen-Shin; Pagani, Marco

    2016-04-01

    The Global Earthquake Model (GEM) has, since its inception in 2009, made many contributions to the practice of seismic hazard modeling in different regions of the globe. The OpenQuake-engine (hereafter referred to simply as OpenQuake), GEM's open-source software for calculation of earthquake hazard and risk, has found application in many countries, spanning a diversity of tectonic environments. GEM itself has produced a database of national and regional seismic hazard models, harmonizing into OpenQuake's own definition the varied seismogenic sources found therein. The characterization of active faults in probabilistic seismic hazard analysis (PSHA) is at the centre of this process, motivating many of the developments in OpenQuake and presenting hazard modellers with the challenge of reconciling seismological, geological and geodetic information for the different regions of the world. Faced with these challenges, and from the experience gained in the process of harmonizing existing models of seismic hazard, four critical issues are addressed. The challenge GEM has faced in the development of software is how to define a representation of an active fault (both in terms of geometry and earthquake behaviour) that is sufficiently flexible to adapt to different tectonic conditions and levels of data completeness. By exploring the different fault typologies supported by OpenQuake we illustrate how seismic hazard calculations can, and do, take into account complexities such as geometrical irregularity of faults in the prediction of ground motion, highlighting some of the potential pitfalls and inconsistencies that can arise. This exploration leads to the second main challenge in active fault modeling, what elements of the fault source model impact most upon the hazard at a site, and when does this matter? Through a series of sensitivity studies we show how different configurations of fault geometry, and the corresponding characterisation of near-fault phenomena (including

  3. Passive, broad-band seismic measurements for geothermal exploration : The GAPSS experiment

    NASA Astrophysics Data System (ADS)

    Saccorotti, Gilberto; Piccinini, Davide; Zupo, Maria; Mazzarini, Francesco; Cauchie, Lena; Chiarabba, Claudio; Piana Agostinetti, Nicola

    2014-05-01

    Passive seismological imaging techniques based on either transient (earthquakes) or sustained (background noise) signals can provide detailed descriptions of subsurface attributes as seismic velocity, attenuation, and anisotropy. However, the correspondence between these parameters and the physical properties of crustal fluids is still ambiguous. Moreover, the resolving capabilities and condition of applicability of emerging techniques such as the Ambient Noise Tomography are still to be investigated thoroughly. Following these arguments, a specific project (GAPSS-Geothermal Area Passive Seismic Sources) was planned, in order to test passive exploration methods on a well-known geothermal area, namely the Larderello-Travale Geothermal Field (LTGF). This geothermal area is located in the western part of Tuscany (Italy), and it is the most ancient geothermal power field of the world. Heat flow in this area can reach local peaks of 1000 mW/m3. The deep explorations in this area showed a deeper reservoir (3000 to 4000 m depth) located within the metamorphic rocks in the contact aureole of the Pliocene-Quaternary granites; it is characterized by a wide negative gravimetric anomaly, interpreted as partially molten granite at temperatures of 800°C. From seismic surveys the K-marker K (pressurized horizons) was found at depths between 3 and 7 km. The structural grain of the geothermal field is characterized by N-W trending and N-E dipping normal faults whose activity lasts since the Pliocene. GAPSS lasted from early May, 2012, through October, 2013. It consisted of up to 20 temporary seismic stations, complemented by two permanent stations from the National Seismic Network of Italy. The resulting array has an aperture of about 50 Km, with station spacings between 2 and 50 km. Stations are equipped with either broadband (40s and 120s) or intermediate-period (5s), 3-components seismometers. LTGF is seismically active. During the first 10 months of measurements, we located

  4. Healthcare Worker Preferences for Active Tuberculosis Case Finding Programs in South Africa: A Best-Worst Scaling Choice Experiment

    PubMed Central

    O’Hara, Nathan N.; Roy, Lilla; O’Hara, Lyndsay M.; Spiegel, Jerry M.; Lynd, Larry D.; FitzGerald, J. Mark; Yassi, Annalee; Nophale, Letshego E.; Marra, Carlo A.

    2015-01-01

    Objective Healthcare workers (HCWs) in South Africa are at a high risk of developing active tuberculosis (TB) due to their occupational exposures. This study aimed to systematically quantify and compare the preferred attributes of an active TB case finding program for HCWs in South Africa. Methods A Best–Worst Scaling choice experiment estimated HCW’s preferences using a random-effects conditional logit model. Latent class analysis (LCA) was used to explore heterogeneity in preferences. Results “No cost”, “the assurance of confidentiality”, “no wait” and testing at the occupational health unit at one’s hospital were the most preferred attributes. LCA identified a four class model with consistent differences in preference strength. Sex, occupation, and the time since a previous TB test were statistically significant predictors of class membership. Conclusions The findings support the strengthening of occupational health units in South Africa to offer free and confidential active TB case finding programs for HCWs with minimal wait times. There is considerable variation in active TB case finding preferences amongst HCWs of different gender, occupation, and testing history. Attention to heterogeneity in preferences should optimize screening utilization of target HCW populations. PMID:26197344

  5. Localization of short-range acoustic and seismic wideband sources: Algorithms and experiments

    NASA Astrophysics Data System (ADS)

    Stafsudd, J. Z.; Asgari, S.; Hudson, R.; Yao, K.; Taciroglu, E.

    2008-04-01

    We consider the determination of the location (source localization) of a disturbance source which emits acoustic and/or seismic signals. We devise an enhanced approximate maximum-likelihood (AML) algorithm to process data collected at acoustic sensors (microphones) belonging to an array of, non-collocated but otherwise identical, sensors. The approximate maximum-likelihood algorithm exploits the time-delay-of-arrival of acoustic signals at different sensors, and yields the source location. For processing the seismic signals, we investigate two distinct algorithms, both of which process data collected at a single measurement station comprising a triaxial accelerometer, to determine direction-of-arrival. The direction-of-arrivals determined at each sensor station are then combined using a weighted least-squares approach for source localization. The first of the direction-of-arrival estimation algorithms is based on the spectral decomposition of the covariance matrix, while the second is based on surface wave analysis. Both of the seismic source localization algorithms have their roots in seismology; and covariance matrix analysis had been successfully employed in applications where the source and the sensors (array) are typically separated by planetary distances (i.e., hundreds to thousands of kilometers). Here, we focus on very-short distances (e.g., less than one hundred meters) instead, with an outlook to applications in multi-modal surveillance, including target detection, tracking, and zone intrusion. We demonstrate the utility of the aforementioned algorithms through a series of open-field tests wherein we successfully localize wideband acoustic and/or seismic sources. We also investigate a basic strategy for fusion of results yielded by acoustic and seismic arrays.

  6. Time-frequency-wavenumber Decomposition To Investigate Seismic Wavefield: Application To The Annot Experiment

    NASA Astrophysics Data System (ADS)

    Schissele, E.; Cansi, Y.; Gaffet, S.

    Many observations and studies as well as numerical simulations have been done in order to completely understand the whole seismogram recorded during an earthquake. At regional distances, the seismic wavefield is strongly influenced by crustal hetero- geneities. The primary wavefield constituted by Pn, Pg, Sn, Sg, Rg, Lg.... phases is diffracted and refracted by these heterogeneities and hence forms the coda of the seis- mogram. But the different mechanisms of propagation in a heterogeneous medium are not fully understood. The identification of the different phases contributing to the coda seems to be essential to progress in the comprehension of the seismic wavefield propagation. Seismic arrays are then well-adapted tools since they provide the spatio-temporal evo- lution of the wavefield. In 1998, 4 small-scales arrays were deployed for 2 months around the Annot region, located in the southern French Alps. Each array was constituted by 9 short-period seismometers, recording frequencies greater than 0.2 Hz. Its aperture was 250 meters, with a minimal distance between 2 adjacent sensors of 20 meters. That allows us to study the seismic wavefield for very low wavelength without any problem of spatial aliasing. It will be interesting to characterize in terms of wavefield deformation the signature of the different kinds of heterogeneities (fault system, topographic relief, impedance contrast...) surrounding this area. We expect the primary wavefield to be diffracted or refracted by all these heterogeneities. A time-frequency-wavenumber technique which allows us to characterize the whole coherent part of the energy which prop- agates through the seismic array has been derived. Such a characterization involves, for each coherent wavelet, an estimate of: (i) an arrival time and a frequency content and (ii) an azimuth and an apparent velocity. This way, the principal phases will be described. What will be more interesting, is the extraction of the deterministic part of the

  7. Rocky Mountain evolution: Tying Continental Dynamics of the Rocky Mountains and Deep Probe seismic experiments with receiver functions

    USGS Publications Warehouse

    Rumpfhuber, E.-M.; Keller, Gordon R.; Sandvol, E.; Velasco, A.A.; Wilson, D.C.

    2009-01-01

    In this study, we have determined the crustal structure using three different receiver function methods using data collected from the northern transect of the Continental Dynamics of the Rocky Mountains (CD-ROM) experiment. The resulting migrated image and crustal thickness determinations confirm and refine prior crustal thickness measurements based on the CD-ROM and Deep Probe experiment data sets. The new results show a very distinct and thick lower crustal layer beneath the Archean Wyoming province. In addition, we are able to show its termination at 42??N latitude, which provides a seismic tie between the CD-ROM and Deep Probe seismic experiments and thus completes a continuous north-south transect extending from New Mexico into Alberta, Canada. This new tie is particularly important because it occurs close to a major tectonic boundary, the Cheyenne belt, between an Archean craton and a Proterozoic terrane. We used two different stacking techniques, based on a similar concept but using two different ways to estimate uncertainties. Furthermore, we used receiver function migration and common conversion point (CCP) stacking techniques. The combined interpretation of all our results shows (1) crustal thinning in southern Wyoming, (2) strong northward crustal thickening beginning in central Wyoming, (3) the presence of an unusually thick and high-velocity lower crust beneath the Wyoming province, and (4) the abrupt termination of this lower crustal layer north of the Cheyenne belt at 42??N latitude. Copyright 2009 by the American Geophysical Union.

  8. Capacity building for oncology programmes in sub-Saharan Africa: the Rwanda experience.

    PubMed

    Stulac, Sara; Binagwaho, Agnes; Tapela, Neo M; Wagner, Claire M; Muhimpundu, Marie Aimee; Ngabo, Fidele; Nsanzimana, Sabin; Kayonde, Leonard; Bigirimana, Jean Bosco; Lessard, Adam J; Lehmann, Leslie; Shulman, Lawrence N; Nutt, Cameron T; Drobac, Peter; Mpunga, Tharcisse; Farmer, Paul E

    2015-08-01

    Despite an estimated 456,000 deaths caused by cancer in sub-Saharan Africa in 2012 and a cancer burden that is predicted to double by 2030, the region accounts for only 0·3% of worldwide medical expenditure for cancer. Challenges to cancer care in sub-Saharan Africa include a shortage of clinicians and training programmes, weak healthcare infrastructure, and inadequate supplies. Since 2011, Rwanda has developed a national cancer programme by designing comprehensive, integrated frameworks of care, building local human resource capacity through partnerships, and delivering equitable, rights-based care. In the 2 years since the inauguration of Rwanda's first cancer centre, more than 2500 patients have been enrolled, including patients from every district in Rwanda. Based on Rwanda's national cancer programme development, we suggest principles that could guide other nations in the development of similar cancer programmes. PMID:26248848

  9. Joint interpretation of high-precision tilt data and mining induced seismic events recorded underground in deep level gold mine in South Africa

    NASA Astrophysics Data System (ADS)

    Milev, Alexander; Share, Pieter; Durrheim, Ray; Naoi, Makoto; Nakatani, Masao; Yabe, Yasuo; Ogasawara, Hiroshi

    2013-04-01

    Seismicity associated with deep-level mining has for long been a problem, leading to rockburst and other similar hazards. Several studies have been completed in an attempt to minimize the total amount of seismicity. In this study high resolution measurements of ground tilting in combination with seismic monitoring is used to observe how the rock mass responds to mining. A good correspondence between the coseismic and the aseismic tilt was found. The rate of coseismic and aseismic tilt, as well as seismicity recorded by the mine seismic network, are approximately constant until the daily blasting time, which takes place from about 19:30 until shortly before 21:00. During the blasting time and the subsequent seismic events, the coseismic and aseismic tilt shows a rapid increase. In an attempt to distinguish between the different mechanisms of tilting two types of events were recognized. The "fast" seismic events characterized with sharp increase of the tilt during the seismic rupture and "slow" seismic events characterized by creep type post seismic deformations. Tilt behaviour before and after a seismic event was also analysed. The fact that no recognizable aftertilt was observed for more of the "fast" seismic events means that there is no gradual release of stress and an associated continuous strain rate change afterwards. It can therefore be concluded that a large seismic event causes a rapid change in the state of stress rather than a gradual change in the strain rate. The mechanism of the observed "slow" seismic events is more complicated. Although several explanations have been proposed, a suggestion for further work could be to investigate the presence of "slow" events in or after blasting time more closely. During the monitoring period a seismic event with MW 2.2 occurred in the vicinity of the instrumented site. This event was recorded by both the CSIR integrated monitoring system and JAGUARS acoustic emission network. More than 21,000 AE aftershocks were

  10. Theory and experiment of an inertia-type vertical isolation system for seismic protection of equipment

    NASA Astrophysics Data System (ADS)

    Lu, Lyan-Ywan; Chen, Pei-Rong; Pong, Kuan-Wen

    2016-03-01

    Although it has been proven that seismic isolation is an effective technology for seismic protection of structures and equipment, most existing isolation systems are for mitigating horizontal ground motions, and in practice there are very few vertical isolation systems. Part of the reason is due to the conflict with regard to the demand for isolation stiffness. In other words, a vertical isolation system must have sufficient vertical rigidity to sustain the weight of the isolated object, while it must also have sufficient flexibility in order to elongate the vibration period under seismic excitation. In order to overcome this difficulty, a novel system is proposed in this study, called an inertia-type vertical isolation system (IVIS). The primary difference between the IVIS and a traditional system is that the former has an additional leverage mechanism with a counterweight. The counterweight will provide a static uplifting force and an extra dynamic inertia force, such that the effective vertical stiffness of the IVIS becomes higher in its static state and lower in the dynamic one. The theory underlying the IVIS is developed and verified experimentally by a seismic simulation test in this work. The results show that the IVIS leads to a less static settlement and at the same time a lower effective isolation frequency. The test results also demonstrate that the isolator displacement demand of the IVIS is only about 30-40 percent that of the traditional one in all kinds of earthquakes. With regard to the reduction of acceleration response, the IVIS is particularly effective for near-fault earthquakes or near-resonant excitations, but is less effective for far-field earthquakes with more high-frequency contents, as compared with the traditional system.

  11. South Africa's early experiment in social medicine: its pioneers and politics.

    PubMed Central

    Marks, S

    1997-01-01

    The election of a democratic, nonracial government in South Africa has moved the health needs of the majority of the population to center stage. In the search for precedents, health policymakers have turned to South Africa's pioneering of health centers and social medicine in the 1940s. This paper looks at the intellectual context in which these ideas were first developed; the particular political circumstances and relationships between doctors and the state in the late 1930s, which facilitated the establishment of health centers; the role that the health centers were intended to play in South Africa's wider postwar health plans; and the reasons for the centers' failure. Contrary to conventional wisdom, it argues that the failure of the health centers and the wider health plans predated the advent of the National Party to power in 1948, and resulted mainly from the marginalization of the centers as a low-cost option for the poor, which was itself a consequence of underfunding and the vested interests of local health authorities and private practitioners. PMID:9096553

  12. Passive seismic experiment - A summary of current status. [Apollo-initiated lunar surface station data

    NASA Technical Reports Server (NTRS)

    Latham, G. V.; Dorman, H. J.; Horvath, P.; Ibrahim, A. K.; Koyama, J.; Nakamura, Y.

    1978-01-01

    The data set obtained from the four-station Apollo seismic network including signals from approximately 11,800 events, is surveyed. Some refinement of the lunar model will result, but its gross features remain the same. Attention is given to the question of a small, molten lunar core, the answer to which remains dependent on analysis of signals from a far side impact. Seventy three sources of repeating, deep moonquakes have been identified, thirty nine of which have been accurately located. Concentrated at depths from 800 to 1000 km, the periodicities of these events have led to the hypothesis that they are generated by tidal stresses. Lunar seismic data has also indicated that the meteoroid population is ten times lower than originally determined from earth based observations. Lunar seismic activity is much lower and mountainous masses show no sign of sinking, in contrast to earth, as a result of the lunar crust being four times thicker. While much work remains to be done, significant correlation between terrestrial and lunar observations can be seen.

  13. Active source seismic experiment investigating the formation of the Ontong Java Plateau

    NASA Astrophysics Data System (ADS)

    Miura, S.; Noguchi, N.; Coffin, M. F.; Kawagle, S. A.; Verave, R. T.; Kodaira, S.; Fukao, Y.

    2010-12-01

    The Ontong Java Plateau (OJP) is one of the largest oceanic plateaus and possibly the most voluminous large igneous province (LIP) on Earth, and is thought to have formed by a non-plate tectonic mechanism such as 1) a plume head, 2) a bolide impact, or 3) atypical seafloor spreading. Due to massive magmatism over short durations of geological time, formations of the OJP and LIPs in general likely have had global scale environmental impacts (e.g., Oceanic Anoxic Events). Therefore, understanding how LIPs form is important not only for illuminating solid Earth processes, but also for advancing knowledge of associated environmental, including biospheric, changes. On the basis of the OJP’s shallow bathymetry, its crust has long been thought to be thicker than normal oceanic crust. However, previous seismic and gravimetric analyses of its crustal thickness produced inconsistent results. To understand how the OJP formed, we conducted a seismic survey using a multi-channel seismic (MCS) hydrophone streamer and 100 ocean bottom seismometers (OBS) in February-March 2010 (EOS, submitted). New MCS data confirm that sediment approximately 1 s (two-way travel time) thick covers the uppermost OJP. Sediment layers are generally flat-lying, except near seamounts, in a local depression, and around some faults. Because of the flat-lying seafloor and shallow water depths, several water-bottom multiples of large amplitude characterize the MCS data, making identification of sub-basement reflections challenging. On the northernmost part of the seismic line, a reflection event at about 12 s (two-way travel time) differs unambiguously from multiple reflections, and may represent the base of the OJP’s crust. OBS data show first refraction arrivals within 100-km offsets. First arrivals with an apparent velocity of 7 km/s can be identified at offsets greater than 100 km. This may indicate a thick high velocity (~7 km/s) layer in the OJP’s lower crust. This high velocity layer may be

  14. Fault structure, stress, or pressure control of the seismicity in shale? Insights from a controlled experiment of fluid-induced fault reactivation

    NASA Astrophysics Data System (ADS)

    De Barros, Louis; Daniel, Guillaume; Guglielmi, Yves; Rivet, Diane; Caron, Hervé; Payre, Xavier; Bergery, Guillaume; Henry, Pierre; Castilla, Raymi; Dick, Pierre; Barbieri, Ernesto; Gourlay, Maxime

    2016-06-01

    Clay formations are present in reservoirs and earthquake faults, but questions remain on their mechanical behavior, as they can vary from ductile (aseismic) to brittle (seismic). An experiment, at a scale of 10 m, aims to reactivate a natural fault by fluid pressure in shale materials. The injection area was surrounded by a dense monitoring network comprising pressure, deformation, and seismicity sensors, in a well-characterized geological setting. Thirty-two microseismic events were recorded during several injection phases in five different locations within the fault zone. Their computed magnitude ranged between -4.3 and -3.7. Their spatiotemporal distribution, compared with the measured displacement at the injection points, shows that most of the deformation induced by the injection is aseismic. Whether the seismicity is controlled by the fault architecture, mineralogy of fracture filling, fluid, and/or stress state is then discussed. The fault damage zone architecture and mineralogy are of crucial importance, as seismic slip mainly localizes on the sealed-with-calcite fractures which predominate in the fault damage zone. As no seismicity is observed in the close vicinity of the injection areas, the presence of fluid seems to prevent seismic slips. The fault core acts as an impermeable hydraulic barrier that favors fluid confinement and pressurization. Therefore, the seismic behavior seems to be strongly sensitive to the structural heterogeneity (including permeability) of the fault zone, which leads to a heterogeneous stress response to the pressurized volume.

  15. Upper Mantle Structure of Eastern Africa from Body Wave Tomography

    NASA Astrophysics Data System (ADS)

    Mulibo, G.; Nyblade, A.; Fredinand, R.

    2010-12-01

    This study presents preliminary results of the upper mantle structure beneath the east Africa from body wave tomography. This work is part of an on-going study aimed at investigating the origin and structure of the African Superplume. The available global tomographic studies suggest that the African Superplume is a low velocity-anomaly extending from the core-mantle boundary upward into the mid mantle beneath southern Africa and may reach the upper mantle beneath eastern Africa. However, the limited vertical resolution of global tomographic models makes it difficult to confirm a connection from the lower to the upper mantle. Previous regional studies of upper mantle structure in east Africa have found evidence of a low velocity anomaly beneath the region that has been suggested as the upper mantle expression of the Superplume. Models from previous tomographic studies in east Africa have limited resolution below ~400 km beneath the eastern rift and are less well resolved beneath the western part of the rift due to less data coverage. This study uses teleseismic data from a wider region in east Africa than previously used. Data for this study are from a 3-year (2007-2010) deployment of 40 broadband seismic stations in Uganda and Tanzania. The dataset is supplemented by data from the 1994-1995 Tanzania broadband seismic experiment, the 2001-2002 Kenya broadband seismic experiment, the permanent AfricaArray seismic stations and IRIS/GSN stations. The data have been used for body wave tomography by computing relative travel time delays using a multi-channel cross-correlation technique and then inverting them for a 3D wave speed model. Preliminary results from the inversion of the relative delay times show that there is a broad low wave speed anomaly beneath east Africa extending from shallow upper mantle depths to at least 500 km into the mantle transition zone. The appearance and size of the low wave speed anomaly in the region indicates the presence of broad thermal

  16. Broadband seismic experiment at Merapi Volcano, Java, Indonesia: very-long-period pulses embedded in multiphase earthquakes

    NASA Astrophysics Data System (ADS)

    Hidayat, D.; Voight, B.; Langston, C.; Ratdomopurbo, A.; Ebeling, C.

    2000-07-01

    Multiphase (MP) and low frequency (LF) earthquakes with spectral peak amplitudes at 3-4 and 1 Hz, respectively, are two common types of shallow volcanic earthquakes previously recognized at Merapi Volcano. Their mechanisms are poorly understood but MPs have been temporally associated with lava dome growth. We conducted a seismic experiment in January-February 1998, using four broadband seismographs to investigate the nature of seismic activity associated with dome growth. During our experiment, Merapi experienced mild dome growth with low-level seismic activity. We compare our data to that recorded on a local short-period (SP) network, with the following preliminary results. MP and LF events as recorded and classified on the short-period network instruments were recognized on the broadband network. Frequency spectrograms revealed similar patterns in the near summit region at widely separated broadband stations. Higher frequency spectra than previously recognized were identified for both MP and LF events, and were strongly attenuated as a function of radial distance from the source. Thus the spectral characteristics of these events as recorded on far-field stations are not fully indicative of the source processes. In particular, many events classified as LF-type appear to have much high frequency energy near the source. This aspect of these so-called LF earthquakes, and their association with very-long-period (VLP) pulses, suggests that many events identified in the far-field as LF events are in actuality a variety of the MP event and involve similar source processes. Broadband records indicated that simple large-amplitude VLP pulses were embedded in MP and LF wavetrains. From event to event these pulses were similar in their waveforms and had periods of 4 s. VLP events embedded in LF and MP earthquakes were located using particle motions. The epicenters were clustered in a central region of the dome complex, and preliminary source depths were within about 100 m of

  17. Sharing perspectives and experiences of doctoral fellows in the first cohort of Consortium for Advanced Research Training in Africa: 2011–2014

    PubMed Central

    Adedokun, Babatunde; Nyasulu, Peter; Maseko, Fresier; Adedini, Sunday; Akinyemi, Joshua; Afolabi, Sulaimon; de Wet, Nicole; Sulaimon, Adedokun; Sambai, Caroline; Utembe, Wells; Opiyo, Rose; Awotidebe, Taofeek; Chirwa, Esnat; Nabakwe, Esther; Niragire, François; Uwizeye, Dieudonné; Niwemahoro, Celine; Kamndaya, Mphatso; Mwakalinga, Victoria; Otwombe, Kennedy

    2014-01-01

    Background Resolution of public health problems in Africa remains a challenge because of insufficient skilled human resource capacity. The Consortium for Advanced Research Training in Africa (CARTA) was established to enhance capacity in multi-disciplinary health research that will make a positive impact on population health in Africa. Objective The first cohort of the CARTA program describes their perspectives and experiences during the 4 years of fellowship and puts forward suggestions for future progress and direction of research in Africa. Conclusions The model of training as shown by the CARTA program is an effective model of research capacity building in African academic institutions. An expansion of the program is therefore warranted to reach out to more African academics in search of advanced research training. PMID:25280739

  18. South-South Cooperation: Brazilian experiences in South America and Africa.

    PubMed

    Santos, Roberta de Freitas; Cerqueira, Mateus Rodrigues

    2015-01-01

    Over recent years Brazil has played an increasingly active role internationally, the result of its model of integration and its foreign policy directives. The health sector is a valuable and strategic area for Brazilian technical cooperation to achieve various objectives, including its development goals. This article describes the main directives of Brazilian foreign policy, conceptually defining and characterizing South-South Cooperation, illustrated through an analysis of two Brazilian technical cooperation initiatives in healthcare: one in South America, the other in Africa. The study concludes that, irrespective of the interests and power asymmetries existing in South-South Cooperation, the objectives of this cooperation were achieved through the technical work. PMID:25742098

  19. Diagnosing GCM errors over West Africa using relaxation experiments. Part II: intraseasonal variability and African easterly waves

    NASA Astrophysics Data System (ADS)

    Pohl, Benjamin; Douville, Hervé

    2011-10-01

    A near-global grid-point nudging of the Arpege-Climat atmospheric General Circulation Model towards ECMWF reanalyses is used to diagnose the regional versus remote origin of the summer model biases and variability over West Africa. First part of this study revealed a limited impact on the monsoon climatology compared to a control experiment without nudging, but a significant improvement of interannual variability, although the amplitude of the seasonal anomalies remained underestimated. Focus is given here on intraseasonal variability of monsoon rainfall and dynamics. The reproducible part of these signals is investigated through 30-member ensemble experiments computed for the 1994 rainy season, a year abnormally wet over the Sahel but representative of the model systematic biases. In the control experiment, Arpege-Climat simulates too few rainy days that are associated with too low rainfall amounts over the central and western Sahel, in line with the seasonal dry biases. Nudging the model outside Africa tends to slightly increase the number of rainy days over the Sahel, but has little effect on associated rainfall amounts. However, results do indicate that a significant part of the monsoon intraseasonal variability simulated by Arpege-Climat is controlled by lateral boundary conditions. Parts of the wet/dry spells over the Sahel occur in phase in the 30 members of the nudging experiment, and are therefore embedded in larger-scale variability patterns. Inter-member spread is however not constant across the selected summer season. It is partly controlled by African Easterly Waves, which show dissimilar amplitude from one member to another, but a coherent phasing in all members. A lowpass filtering of the nudging fields suggests that low frequency variations in the lateral boundary conditions can lead to eastward extensions of the African Easterly Jet, creating a favorable environment for easterly waves, while high frequency perturbations seem to control their

  20. Effect of the surface roughness on the seismic signal generated by a single rock impact: insight from laboratory experiments

    NASA Astrophysics Data System (ADS)

    Bachelet, Vincent; Mangeney, Anne; de Rosny, Julien; Toussaint, Renaud

    2016-04-01

    The seismic signal generated by rockfalls, landslides or avalanches is a unique tool to detect, characterize and monitor gravitational flow activity, with strong implication in terms of natural hazard monitoring. Indeed, as natural flows travel down the slope, they apply stresses on the ground, generating seismic waves in a wide frequency band. Our ultimate objective is to relate the granular flow properties to the generated signals that result from the different physical processes involved. We investigate here the more simple process: the impact of a single bead on a rough surface. Farin et al. [2015] have already shown theoretically and experimentally the existence of a link between the properties of an impacting bead (mass and velocity) on smooth surfaces, and the emitted signal (radiated elastic energy and mean frequency). This demonstrates that the single impactor properties can be deduced from the form of the emitted signal. We extend this work here by investigating the impact of single beads and gravels on rough and erodible surfaces. Experimentally, we drop glass and steel beads of diameters from 2 mm to 10 mm on a PMMA plate. The roughness of this last is obtained by gluing 3mm-diameter glass beads on one of its face. Free beads have been also added to get erodible beds. We track the dropped impactor motion, times between impacts and the generated acoustic waves using two fast cameras and 8 accelerometers. Cameras are used in addition to estimate the impactor rotation. We investigate the energy balance during the impact process, especially how the energy restitution varies as a function of the energy lost through acoustic waves. From these experiments, we clearly observe that even if more dissipative processes are involved (friction, grain reorganization, etc.), the single bead scaling laws obtained on smooth surfaces remain valid. A main result of this work is to quantify the fluctuations of the characteristic quantities such as the bounce angle, the

  1. Magmatic underplating and crustal growth in the Emeishan Large Igneous Province, SW China, revealed by a passive seismic experiment

    NASA Astrophysics Data System (ADS)

    Chen, Yun; Xu, Yigang; Xu, Tao; Si, Shaokun; Liang, Xiaofeng; Tian, Xiaobo; Deng, Yangfan; Chen, Lin; Wang, Peng; Xu, Yihe; Lan, Haiqiang; Xiao, Fuhui; Li, Wei; Zhang, Xi; Yuan, Xiaohui; Badal, José; Teng, Jiwen

    2015-12-01

    In an attempt to characterize the subsurface structure that is related to fossil mantle plume activity, a comprehensive geophysical investigation was conducted in the Emeishan Large Igneous Province (ELIP). The nature and geometry of the crust were examined within the scheme of the domal structure of ELIP, which comprises the Inner, Intermediate and Outer zones, which are defined on the basis of the biostratigraphy of pre-volcanic sediments. The bulk crustal properties within the Inner Zone are characterized by high density, high P-wave velocity, high Vp/Vs ratios and large crustal thickness. A visible continuous seismic converter is present in the upper part of the crust in the whole Intermediate Zone and the eastern part of the Inner Zone, but it is absent in the Inner Zone, where another seismic converter is observed in the lower part of the crust. The geometric configuration of these converters is attributable to the addition of mantle-derived melts to the pre-existing crust and subsequent interaction between them. The crustal geometry, which is delineated by the migrated image of receiver functions from the passive seismic experiment, and the crustal properties collectively suggest that a mafic layer of 15-20 km thickness and 150-180 km width exists at the base of the crust in the Inner Zone. Such a mafic layer reflects a vertical crustal growth through magmatic underplating at the base of the crust and intraplating within the upper crust. The salient spatial correlation between the deep crustal structure and the dome strongly supports a genetic link between crustal thickening and plume activity, if the pre-volcanic domal uplift is generated by the Permian Emeishan mantle plume. This arrangement is further supported by the consistency of the extent of crustal uplift estimated by isostatic equilibrium modeling and sedimentary data. This study therefore characterizes and provides evidence for a plume-modified crust in a large igneous province.

  2. Results of high resolution seismic imaging experiments for defining permeable pathways in fractured gas reservoirs

    SciTech Connect

    Majer, E.L.; Peterson, J.E.; Daley, T.

    1997-10-01

    As part of its Department of Energy (DOE) Industry cooperative program in oil and gas, Berkeley Lab has an ongoing effort in cooperation with Industry partners to develop equipment, field techniques, and interpretational methods to further the practice of characterizing fractured heterogeneous reservoirs. The goal of this work is to demonstrate the combined use of state-of-the-art technology in fluid flow modeling and geophysical imaging into an interdisciplinary approach for predicting the behavior of heterogeneous fractured gas reservoirs. The efforts in this program have mainly focused on using seismic methods linked with geologic and reservoir engineering analysis for the detection and characterization of fracture systems in tight gas formations, i.e., where and how to detect the fractures, what are the characteristics of the fractures, and how the fractures interact with the natural stresses, lithology, and their effect on reservoir performance. The project has also integrated advanced reservoir engineering methods for analyzing flow in fractured systems such that reservoir management strategies can be optimized. The work at Berkeley Lab focuses on integrating high resolution seismic imaging, (VSP, crosswell, and single well imaging), geologic information and well test data to invert for flow paths in fractured systems.

  3. Local-scale cross-correlation of seismic noise from the Calico fault experiment

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Gerstoft, Peter

    2014-06-01

    Most studies of seismic noise cross-correlation (NCC) have focused on regional/continental scale imaging using empirical surface-wave Green's functions extracted from primary (0.05-0.08 Hz) and secondary (0.1-0.16 Hz) microseisms. In this work, we present the NCC results at higher frequencies (>0.5 Hz) from 6 months seismic noise recorded by a local array (~4 km aperture) deployed along the Calico fault in the Mojave Desert, California. Both fast and slow propagating waves are observed from the NCC record-sections. We compare the NCCs from sensor pairs that share a common sensor with the records of a borehole shot located very close to this common sensor. The result shows a good match of the slow surface-wave arrivals, indicating that the NCC method is able to recover unbiased surface-wave Green's functions at local scales. The strong body-wave NCC component is caused by the P waves generated offshore California. Along a SW-NE profile across the fault, we observe apparent P-wave arrivals and their reflections, which can be explained by a low-velocity-zone (LVZ) along the Calico fault. We calculate the LVZ width to be ~ 2.3 km, and the P-wave velocity reduction within the LVZ to be ~35 %. These estimates are consistent with other evidence for a relatively wide LVZ along the Calico fault.

  4. The CAFE experiment: A joint seismic and MT investigation of the Cascadia subduction system

    NASA Astrophysics Data System (ADS)

    McGary, R. Shane

    In this thesis we present results from inversion of data using dense arrays of ˙ collocated seismic and magnetotelluric stations located in the Cascadia subduction zone region of central Washington. In the migrated seismic section, we clearly image the top of the slab and oceanic Moho, as well as a velocity increase corresponding to the eclogitization of the hydrated upper crust. A deeper velocity increase is interpreted as the eclogitization of metastable gabbros, assisted by fluids released from the dehydration of upper mantle chlorite. A low velocity feature interpreted as a fluid/melt phase is present above this transition. The serpentinized wedge and continental Moho are also imaged. The magnetotelluric image further constrains the fluid/melt features, showing a rising conductive feature that forms a column up to a conductor indicative of a magma chamber feeding Mt. Rainier. This feature also explains the disruption of the continental Moho found in the migrated image. Exploration of the assumption of smoothness implicit in the standard MT inversion provides tools that enable us to generate a more accurate MT model. This final MT model clearly demonstrates the link between slab derived fluids/melting and the Mt. Rainier magma chamber. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - docs mit.edu)

  5. Termination of the Batholiths marine seismic experiment: the scientific method loses to hearsay

    NASA Astrophysics Data System (ADS)

    Hollister, L. S.

    2007-12-01

    The marine seismic component of the NSF-Continental Dynamics funded project Batholiths was terminated by Canadian authorities due to environmental concerns. Socioeconomic benefits of the project were not taken into account, nor were findings by the National Research Council on effects of ocean noise on marine mammal populations. The marine seismic component of Batholiths was to have been done using sound from airguns towed behind the R/V Langseth in order to seismically image the geologic structures below the Coast Mountains of British Columbia. The project was nearly identical in timing, location, and scope to the ACCRETE project, which was successfully permitted and done in the early fall of 1994, with no detected or known damage to the environment. However, what changed in the last 13 years was a dramatic increase of concern by eNGOs (environmental non- government organizations) that airguns produced sound that might be harmful to marine species, marine mammals in particular. The marine noise concerns were amplified by eNGO agendas and campaigns to prevent oil exploration along continental margins and to shut down naval exercises involving sonar to detect submarines. Compared to these agendas, Batholiths was an easy target because the PIs (Principal Investigators) did not have the manpower or financial or legal resources (in contrast to the Navy and oil companies) to push back against an organized campaign set on stopping Batholiths. The main concern used to mobilize public opinion against Batholiths was that, if we were permitted, then oil exploration in the nearby region would be permitted; and, if oil were found, drilling would proceed: the slippery slope argument. Thus, by stopping Batholiths with the speculation that airgun noise, as used in a marine seismic study, might damage marine life, the eNGOs believe they have stopped oil exploration in British Columbia coastal waters. It is widely recognized that everything was done right to get the permits for

  6. Use of active source geophones for passive source imaging: Examples from Bighorn Arch Seismic Experiment (BASE), USA

    NASA Astrophysics Data System (ADS)

    Sheehan, A.; O'rourke, C. T.; Haines, S. S.; Yang, Z.; Worthington, L. L.; Miller, K. C.

    2013-05-01

    In this paper we explore the variety of active and passive source deep seismic imaging that can be performed using continous wavefield recordings from a dense array of industry-style geophones. The data in this study were acquired during the 2009-10 EarthScope FlexArray Bighorn Arch Seismic Experiment(BASE) in central Wyoming, USA. In addition to traditional active and passive source seismic data acquisition, BASE included a deployment of 850 Reftek RT125 " Texan" dataloggers that produced continuous recording over 14 days. Ground motion was recorded via Geospace GS-11 4.5 Hz single channel vertical component geophones. The geophones were deployed in a grid of three E-W lines and two N-S lines across the Bighorn Mountains. We find that the high frequency geophones effectively record the P waves of teleseismic earthquakes. During the 15 days of continuous recording we observed 57 teleseismic events with pickable P-wave arrivals across the array, providing over 10,000 travel times (P, PKiKP, Pdiff, Pn) suitable for teleseismic tomography. The full waveforms can be used to extract additional information about the subsurface. We have successfully utilized teleseismic receiver-side crustal reverberation phases as virtual sources to mimic crustal reflection profiles (Yang et al., 2012). After depth conversion, we find a coherent phase that correlates well with the top of the Madison Formation under the Powder River and Bighorn Basins that flank the Bighorn Mountains. In addition, we combine the phases PpPdp from single-channel geophone recordings and Ps from three-component recordings to constrain the average Vp /Vs ratio for the sedimentary strata. Following Haines (2011), we are exploring the use of interferometric processing of active source blasts. In principle, virtual source and receiver gathers can be created through cross-correlation of full wavefields. The seismic interferometry provides a means of simulating alternative acquisition geometries, and has the

  7. Lidar Observations of Tropospheric Aerosols Over Northeastern South Africa During the ARREX and SAFARI-2000 Dry Season Experiments

    NASA Technical Reports Server (NTRS)

    Campbell, James R.; Welton, Ellsworth J.; Spinhirne, James D.; Ji, Qiang; Tsay, Si-Chee; Piketh, Stuart J.; Barenbrug, Marguerite; Holben, Brent; Starr, David OC. (Technical Monitor)

    2002-01-01

    During the ARREX-1999 and SAFARI-2000 Dry Season experiments a micropulse lidar (523 nm) instrument was operated at the Skukuza Airport in northeastern South Africa. The Mar was collocated with a diverse array of passive radiometric equipment. For SAFARI-2000 the processed Mar data yields a daytime time-series of layer mean/derived aerosol optical properties, including extinction-to-backscatter ratios and vertical extinction cross-section profile. Combined with 523 run aerosol optical depth and spectral Angstrom exponent calculations from available CIMEL sun-photometer data and normalized broadband flux measurements the temporal evolution of the near surface aerosol layer optical properties is analyzed for climatological trends. For the densest smoke/haze events the extinction-to-backscatter ratio is found to be between 60-80/sr, and corresponding Angstrom exponent calculations near and above 1.75. The optical characteristics of an evolving smoke event from SAFARI-2000 are extensively detailed. The advecting smoke was embedded within two distinct stratified thermodynamic layers, causing the particulate mass to advect over the instrument array in an incoherent manner on the afternoon of its occurrence. Surface broadband flux forcing due to the smoke is calculated, as is the evolution in the vertical aerosol extinction profile as measured by the Han Finally, observations of persistent elevated aerosol during ARREX-1999 are presented and discussed. The lack of corroborating observations the following year makes these observation; both unique and noteworthy in the scope of regional aerosol transport over southern Africa.

  8. Calibration formulae and values for velocity seismometers used in the 1998 Santa Clara Valley, California seismic experiment

    USGS Publications Warehouse

    Lindh, Allan G.; Eaton, Jerry P.; O'Neill Allen, Mary; Healy, John H.; Stewart, Samuel W.; Damerell, Lu

    1999-01-01

    Eaton (1975), Bakun and Dratler (1976), Eaton (1977), Healy and O’Neil (1977), Asten (1977), Stewart and O'Neill (1980), Liu and Peselnick (1986), Eaton (1991), Rodgers et al. (1995), and many others (see Asten (1977) for a list of earlier references) have presented formulae for calculating the damped generator constant (or motor constant), and the damping constant (or fractional damping ratio) for magnetically damped velocity seismometers. Unfortunately the notation varies between authors, and not all the formulae allow for some of the significant variables -- differences in input impedance of the recording system in particular. This has become particularly relevant because the USGS seismic networks in California have traditionally set up their velocity sensors for the 10K Ohm impedance of the standard USGS analog telemetry systems (Eaton, 1977), but modern digital recording systems are usually set up with high input impedances, often of a megaohm or greater. Thus the nominal calibration values valid for USGS velocity sensors in their “normal” configuration are incorrect when they are recorded on other systems. In this short note we have collected the relevant formulae needed, and computed the seismometer responses for the various velocity sensors used in the recent Santa Clara Valley Seismic Experiment (SCVSE, see Lindh et al., 1999).

  9. Patient experiences and health system responsiveness among older adults in South Africa

    PubMed Central

    Peltzer, Karl; Phaswana-Mafuya, Nancy

    2012-01-01

    Background As populations age, health systems must adapt and develop approaches that meet the needs of older patients with increasing multiple chronic conditions. Understanding older populations’ perceptions of quality of care is critical to developing measures to increase the utilization of primary healthcare services. Using the data from the Global Study on Ageing and Adult Health (SAGE) survey, the current study aims to evaluate the degree of perceived responsiveness with outpatient and inpatient healthcare in South Africa. Methods We conducted a national population-based cross-sectional study with a sample of 3,840 individuals aged 50 years or older in South Africa in 2008. The questionnaire included sociodemographic characteristics, healthcare utilization and responsiveness, and other health variables. Results Healthcare utilization was 9% inpatient care in the past 3 years and 50% outpatient care in the past 12 months. The overall mean perceived responsiveness score for inpatient care was 71 and for outpatient care 69. According to the evaluation of inpatient care, autonomy and prompt attention showed the lowest while quality, confidentiality, and dignity showed the highest degree of perceived responsiveness among all the areas analyzed. Regarding outpatient care, prompt attention showed the lowest while quality, confidentiality, and dignity the highest degree of perceived responsiveness scores. Overall, perceived healthcare responsiveness was higher in private than in public inpatient and outpatient healthcare facilities. Multivariate analysis found that being from the White population group (OR=3.96, CI=1.54–19.19), not a public health facility (OR=0.34, CI=0.17–0.69), poor subjective health status (OR=0.53, CI=0.38–0.75) and having health insurance paying for the outpatient care visit (OR=3.39, CI=1.24–9.27) were associated with outpatient perceived healthcare responsiveness, whereas male gender (OR=0.36, CI=0.14–0.89), 80 years or older (OR=5

  10. Seismoelectric experiments in a natural laboratory: investigating the permeability/frequency dependence of co-seismic effects at the Boise Hydrogeophysical Research Site

    NASA Astrophysics Data System (ADS)

    Butler, K. E.; West, M. T.; Barrash, W.; Hinz, E. A.

    2009-12-01

    The propagation of seismic waves through porous media generates electric fields, known as seismoelectric effects, as a consequence of electrokinetic coupling associated with movement of pore fluid relative to the solid matrix. Seismoelectric conversions generated at interfaces are of interest for their predicted sensitivity to contrasts in permeability, and pore fluid type (among other properties) although they can be very challenging to measure. Stronger, co-seismic electric fields that travel within P-waves and Stoneley waves are easier to measure and may prove useful as tools for borehole logging or investigation of lateral variations in near surface sediments. In August, 2009, we carried out seismoelectric field experiments on the surface and in boreholes penetrating an unconfined, coarse-grained sand, gravel and cobble aquifer at the Boise Hydrogeophysical Research Site. The aquifer is composed of a sequence of 4 cobble-dominated units overlain by a sand channel and underlain, at a depth of approximately 20 m, by a layer of clay. The water table was located at a depth of approximately 2 m. The main objective of our experiments was to determine whether theoretical seismic/seismoelectric transfer functions, linking various physical properties to the amplitudes of co-seismic effects associated with P-waves, would be consistent with in-situ measurements made in a well-characterized natural environment. Identifying the roles of porosity and permeability was of particular interest given that theoretical models suggest (somewhat counter-intuitively) that the co-seismic effect is dependent on the former but not the latter at frequencies below Biot’s critical frequency - estimated to lie in the range of a few hundred to a few thousand Hz at this site. Borehole experiments utilized sledgehammer and weight drop seismic sources positioned on surface, 2 - 3 m away from the borehole collar. A downhole electrode array and downhole geophone were used (separately) to measure

  11. Theoretical and practical considerations for the design of the iMUSH active-source seismic experiment

    NASA Astrophysics Data System (ADS)

    Kiser, E.; Levander, A.; Harder, S. H.; Abers, G. A.; Creager, K. C.; Vidale, J. E.; Moran, S. C.; Malone, S. D.

    2013-12-01

    The multi-disciplinary imaging of Magma Under St. Helens (iMUSH) experiment seeks to understand the details of the magmatic system that feeds Mount St. Helens using active- and passive-source seismic, magnetotelluric, and petrologic data. The active-source seismic component of this experiment will take place in the summer of 2014 utilizing all of the 2600 PASSCAL 'Texan' Reftek instruments which will record twenty-four 1000-2000 lb shots distributed around the Mount St. Helens region. The instruments will be deployed as two consecutive refraction profiles centered on the volcano, and a series of areal arrays. The actual number of areal arrays, as well as their locations, will depend strongly on the length of the experiment (3-4 weeks), the number of instrument deployers (50-60), and the time it will take per deployment given the available road network. The current work shows how we are balancing these practical considerations against theoretical experiment designs in order to achieve the proposed scientific goals with the available resources. One of the main goals of the active-source seismic experiment is to image the magmatic system down to the Moho (35-40 km). Calculating sensitivity kernels for multiple shot/receiver offsets shows that direct P waves should be sensitive to Moho depths at offsets of 150 km, and therefore this will likely be the length of the refraction profiles. Another primary objective of the experiment is to estimate the locations and volumes of different magma accumulation zones beneath the volcano using the areal arrays. With this in mind, the optimal locations of these arrays, as well as their associated shots, are estimated using an eigenvalue analysis of the approximate Hessian for each possible experiment design. This analysis seeks to minimize the number of small eigenvalues of the approximate Hessian that would amplify the propagation of data noise into regions of interest in the model space, such as the likely locations of magma

  12. Remote sensing experiment in West Africa. [drought effects on desert agriculture and vegetation in Niger

    NASA Technical Reports Server (NTRS)

    Macleod, N. H.

    1974-01-01

    There are substantial needs of the Sahelien Zone to detail the state of regional agricultural resources in the face of a sixth year of serious drought conditions. While most of the work has been done in the Republic of Niger, the principles which have emerged from the analysis seem to be applicable to much of the Sahel. The discussion relates to quite specific rehabilitation and development initiations under consideration in Niger which are based in part upon direct analysis of ERTS imagery of the country, in part on field surveys and on discussions with Nigerian officials and technicians. Again, because the entire Sahelien Zone (including Niger) has large zones of similar ecologic characteristics, modificiations of the approaches suggested for Niger are applicable to the solution of rehabilitation of the desert, the savannah and the woodlands of West Africa in general.

  13. Chemical and biogeophysical impact of four-dimensional (4D) seismic exploration in sub-Saharan Africa, and restoration of dysfunctionalized mangrove forests in the prospect areas.

    PubMed

    Osuji, Leo C; Ayolagha, G; Obute, G C; Ohabuike, H C

    2007-09-01

    Four-dimensional (4D) seismic exploration, an improved geophysical technique for hydrocarbon-data acquisition, was applied for the first time in the Nembe Creek prospect area of Nigeria. The affected soils were slightly alkaline in situ when wet (pH 7.2), but extremely acidic when dry (pH 3.0). The organic carbon content (4.6-26.8%) and other physicochemical properties of soils and water (N, P, and heavy-metal contents, etc.) were higher than the baseline values obtained in 2001 before seismic profiling. Most values also exceeded the baseline compliance standards of the Department of Petroleum Resources (DPR), the World Health Organization (WHO), and the Federal Environmental Protection Agency (FEPA). Rehabilitation of the affected areas was achieved by stabilizing the mangrove floor by liming and appropriate application of nutrients, followed by replanting the cut seismic lines over a distance of 1,372 km with different mangrove species, including juvenile Rhizophora racemosa, R. mangle, and Avicennia species, which were transferred from nursery points. Quicker post-operational intervention is recommended for future 4D surveys, because the time lag between the end of seismic activity and post-impact investigation is critical in determining the relationship between activity and impact: the longer the intervening period, the more mooted the interaction. PMID:17886833

  14. Simulation of complete seismic surveys for evaluation of experiment design and processing

    SciTech Connect

    Oezdenvar, T.; McMechan, G.A.; Chaney, P.

    1996-03-01

    Synthesis of complete seismic survey data sets allows analysis and optimization of all stages in an acquisition/processing sequence. The characteristics of available survey designs, parameter choices, and processing algorithms may be evaluated prior to field acquisition to produce a composite system in which all stages have compatible performance; this maximizes the cost effectiveness for a given level of accuracy, or for targets with specific characteristics. Data sets synthesized for three salt structures provide representative comparisons of time and depth migration, post-stack and prestack processing, and illustrate effects of varying recording aperture and shot spacing, iterative focusing analysis, and the interaction of migration algorithms with recording aperture. A final example demonstrates successful simulation of both 2-D acquisition and processing of a real data line over a salt pod in the Gulf of Mexico.

  15. The Tectonic Evolution of SE Canada: Seismic Evidence from the QM-III Experiment

    NASA Astrophysics Data System (ADS)

    Bastow, I. D.; Boyce, A.; Darbyshire, F. A.; Levin, V. L.; Menke, W. H.; Ellwood, A.

    2014-12-01

    Much of the geological record can be interpreted in the context of processes operating today at plate boundaries. This works well to explain processes and products during the Phanerozoic era; during Precambrian times when the oldest rocks were forming, however, conditions on the younger, hotter, more ductile Earth were likely very different, making analogies with modern day tectonics less certain. Gathering evidence preserved deep within the plates in the shields is thus essential to improve our understanding of the early Earth. Shields are usually underlain by thick, seismically fast roots that are absent beneath younger portions of Earth's surface. The thermochemically distinct nature of cratonic roots is often associated with Archean processes such as the extraction of komatiitic magmas. However, the cratonic core of North America does not fit easily into this Archean formation paradigm: part of the Canadian shield extends beneath the Archean Superior craton, but much of it persists beneath younger Proterozoic crust as well. We present here a relative arrival-time tomographic study of mantle seismic structure using data from a new seismograph network operating in SE Canada. Our stations extend from the Archean Superior craton around the southern tip of Hudson Bay, through Proterozoic Grenville terranes, and into Paleozoic coastal Maine and Nova Scotia. Tomographic images display three broad zones of mantle wavespeed: slow in the Appalachian terranes; fast in the Grenville Province; very fast within the Superior craton. Archean lithosphere has been modified by the Great Meteor hotspot, but we find no evidence for major plate-scale underthrusting during the Grenville orogeny. The abrupt wavespeed transition from Archean to Proterozoic mantle is thus consistent with the emerging consensus that keels form in two stages: a chemically depleted layer in Archean times followed by the thermal development of a less-depleted lithosphere during Proterozoic times.

  16. Variation of earthquake source mechanism with seismogenic structure type and with seismic moment in TauTona Gold Mine, South Africa

    NASA Astrophysics Data System (ADS)

    Kane, D. L.; Boettcher, M. S.

    2012-12-01

    We investigate the seismogenic behavior of faults, dikes, stopes, and tunnels in TauTona Gold Mine, South Africa, to study the effects of structure type on earthquake source mechanisms. Earthquakes are well monitored in TauTona Mine, where underground near-source stations record smaller events and higher frequency energy than can generally be observed using surface stations. Our dataset includes -4 < Mw < 4 earthquakes recorded at hypocentral distances of tens of meters to a few kilometers. The locations of structures in the mine, including faults, dikes, tunnels, and stopes, are well known from detailed geologic mapping and surveyed mine plans. We use data collected between 2004 and 2009 from the in-mine array (1-6 kHz), the Natural Earthquake Laboratory in South African Mines (NELSAM) project stations (6-12 kHz), and a short-term PASSCAL experiment (200 Hz) to study source mechanism variability and correlation with mapped structural heterogeneity within the mine. We compute full moment tensor solutions using amplitude measurements of individual arrival phases. Our initial results show a relationship between earthquake magnitude and the percentage of isotropic moment release, in which the smallest earthquakes (Mw < 0) tend to exhibit explosive isotropic components whereas larger (Mw > 1.5) earthquakes occur with a greater degree of implosive isotropic components. Double-couple type sources occur throughout the full magnitude range, and are often located along mapped faults and dikes. By contrast, we find that the events with significant isotropic moment release are associated with manmade structures, including tunnels and stopes. We interpret the smaller explosive events as being due to cracks that form at the edges of mining structures, which bound excavations, while the larger implosive events can be attributed to the collapse of mining excavations. Some events occur far enough from the mapped regions of the mine that they cannot be associated with any mapped

  17. Strike-slip fault Kinematics and mechanics at the seismic cycle time-scale : Results from new analogue model experiments.

    NASA Astrophysics Data System (ADS)

    Caniven, Yannick; Dominguez, Stéphane; Soliva, Roger; Cattin, Rodolphe; Peyret, Michel; Chéry, Jean; Romano, Christian

    2013-04-01

    The average seismic cycle duration extends from hundred to a few thousands years but geodetic measurements, including trilateration, GPS, Insar and seismological data extend over less than one century. This short time observation scale renders difficult, then, to constrain the role of key parameters such as fault friction and geometry, crust rheology, stress and strain rate that control the kinematics and mechanics of active faults. To solve this time scale issue, we have developed a new experimental set-up that reproduces scaled micro-earthquakes and several hundreds of seismic cycles along a strike-slip fault. The model is constituted by two polyurethane foam plates laterally in contact, lying on a basal silicone layer, which simulate the mechanical behaviour of an elastoplastic upper crust over a ductile lower crust, respectively. To simulate the boundary conditions of a strike-slip fault, a computerized motoreductor system moves the two compartments on an opposite sens and at a constant very low velocity (a few µm/s). The model spatial and temporal scaling, deduces from analog material physical and mechanical parameters, implies that 1 cm in the model represents 2-3 km in the nature and 1 s is equivalent to 5-15 years. Surface-horizontal strain field is quantified by sub-pixel correlation of digital camera pictures recorded every 16 µm of displacement. For each experience about 2000 horizontal-velocity field measurements are recorded. The analysis of model-interseismic and coseismic surface displacements and their comparison to seismogenic natural faults demonstrate that our analog model reproduces correctly both near and far-field surface strains. To compare the experiences, we have developed several algorithms that allow studying the main spatial and temporal evolution of the physical parameters and surface deformation processes that characterise the seismic cycle (magnitudes, stress, strain, friction coefficients, interseismic locking depth, recurrence

  18. An in-situ stimulation experiment in crystalline rock - assessment of induced seismicity levels during stimulation and related hazard for nearby infrastructure

    NASA Astrophysics Data System (ADS)

    Gischig, Valentin; Broccardo, Marco; Amann, Florian; Jalali, Mohammadreza; Esposito, Simona; Krietsch, Hannes; Doetsch, Joseph; Madonna, Claudio; Wiemer, Stefan; Loew, Simon; Giardini, Domenico

    2016-04-01

    A decameter in-situ stimulation experiment is currently being performed at the Grimsel Test Site in Switzerland by the Swiss Competence Center for Energy Research - Supply of Electricity (SCCER-SoE). The underground research laboratory lies in crystalline rock at a depth of 480 m, and exhibits well-documented geology that is presenting some analogies with the crystalline basement targeted for the exploitation of deep geothermal energy resources in Switzerland. The goal is to perform a series of stimulation experiments spanning from hydraulic fracturing to controlled fault-slip experiments in an experimental volume approximately 30 m in diameter. The experiments will contribute to a better understanding of hydro-mechanical phenomena and induced seismicity associated with high-pressure fluid injections. Comprehensive monitoring during stimulation will include observation of injection rate and pressure, pressure propagation in the reservoir, permeability enhancement, 3D dislocation along the faults, rock mass deformation near the fault zone, as well as micro-seismicity. The experimental volume is surrounded by other in-situ experiments (at 50 to 500 m distance) and by infrastructure of the local hydropower company (at ~100 m to several kilometres distance). Although it is generally agreed among stakeholders related to the experiments that levels of induced seismicity may be low given the small total injection volumes of less than 1 m3, detailed analysis of the potential impact of the stimulation on other experiments and surrounding infrastructure is essential to ensure operational safety. In this contribution, we present a procedure how induced seismic hazard can be estimated for an experimental situation that is untypical for injection-induced seismicity in terms of injection volumes, injection depths and proximity to affected objects. Both, deterministic and probabilistic methods are employed to estimate that maximum possible and the maximum expected induced

  19. The experience of the Antarctic Seismic Data Library System (SDLS) as a hub for researchers in antarctic crustal studies.

    NASA Astrophysics Data System (ADS)

    Diviacco, Paolo; Wardell, Nigel

    2010-05-01

    The SDLS was created in April 1991 under the auspices of the Scientific Committee on Antarctic Research to provide open access to Antarctic multichannel seismic-reflection data (MCS) for use in cooperative research projects. The SDLS operates under the mandates of the Antarctic Treaty System, by which all institutions that collect MCS data in Antarctica must submit their MCS data to the SDLS. The SDLS has library branches worldwide at which researchers may view and study the MCS data. MCS data are submitted to the SDLS within 4 years of collection and remain in the library under SDLS guidelines until 8 years after collection. Thereafter, the data go to World Data Centers or equivalents for unrestricted use. The SDLS offers a clearing house, based at Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS) where data are processed when needed and georeferenced, so that the end user can be provided with usable, although basic, post-stack seismic sections. Re-processing of data is beyond the scope of the SDLS, so that if a researcher is interested in reviewing pre-stack data he/she must resort to the data owner. So far 228,000 km of seismic data have been made public in all sectors of the Antarctic region. To augment the concept of physical repositories where data can be accessed by researchers travelling to one of the branches or from where data could be copied to digital media and sent to users, in 2003 it was decided to develop a web interface where data could be searched for and accessed directly. At that moment no previous non-commercial experience was available in this data field, so that the system was designed from scratch. Several technologies were introduced, tested, and after a period of use, reviewed and tuned. Particular attention was devoted to the seismic data viewing facility, which was tailored to the needs of a community with specific practices and legacies. Seismic data are sensitive data that are very important for the E&P industry, so

  20. Seismic velocity structure and spatial distribution of reflection intensity off the Boso Peninsula, Central Japan, revealed by an ocean bottom seismographic experiment

    NASA Astrophysics Data System (ADS)

    Kono, Akihiro; Sato, Toshinori; Shinohara, Masanao; Mochizuki, Kimihiro; Yamada, Tomoaki; Uehira, Kenji; Shinbo, Takashi; Machida, Yuuya; Hino, Ryota; Azuma, Ryosuke

    2016-04-01

    Off the Boso Peninsula, central Japan, where the Sagami Trough is in the south and the Japan Trench is in the east, there is a triple junction where the Pacific plate (PAC), the Philippine Sea plate (PHS) and the Honshu island arc (HIA) meet each other. In this region, the PAC subducts beneath the PHS and the HIA, and the PHS subducts beneath the HIA. Due to the subduction of 2 oceanic plates, numerous seismic events took place in the past. In order to understand these events, it is important to image structure of these plates. Hence, many researchers attempted to reveal the substructure from natural earthquakes and seismic experiments. Because most of the seismometers are placed inland area and the regular seismicity off Boso is inactive, it is difficult to reveal the precise substructure off Boso area using only natural earthquakes. Although several marine seismic experiments using active sources were conducted, vast area remains unclear off Boso Peninsula. In order to improve the situation, a marine seismic experiment, using airgun as an active source, was conducted from 30th July to 4th of August, 2009. The survey line has 216 km length and 20 Ocean Bottom Seismometers (OBSs) were placed on it. We estimated 2-D P-wave velocity structure from the airgun data using the PMDM (Progressive Model Development Method; Sato and Kenett, 2000) and the FAST (First Arrival Seismic Tomography ; Zelt and Barton, 1998). Furthermore, we identified the probable reflection phases from the data and estimated the location of reflectors using Travel time mapping method (Fujie et al. 2006). We found some reflection phases from the data, and the reflectors are located near the region where P-wave velocity is 5.0 km/s. We interpret that the reflectors indicate the plate boundary between the PHS and the HIA. The variation of the intensity of reflection along the upper surface of PHS seems to be consistent with the result from previous reflection seismic experiment conducted by Kimura et

  1. Sickle-Cell Disease Healthcare Cost in Africa: Experience of the Congo

    PubMed Central

    Ngolet, L. O.; Moyen Engoba, M.; Kocko, Innocent; Elira Dokekias, Alexis; Mombouli, Jean-Vivien; Moyen, Georges Marius

    2016-01-01

    Background. Lack of medical coverage in Africa leads to inappropriate care that has an impact on the mortality rate. In this study, we aimed to evaluate the cost of severe acute sickle-cell related complications in Brazzaville. Methods. A retrospective study was conducted in 2014 in the Paediatric Intensive Care Unit. It concerned 94 homozygote sickle-cell children that developed severe acute sickle-cell disease related complications (average age 69 months). For each patient, we calculated the cost of care complication. Results. The household income was estimated as low (

  2. Experiences of violence and association with decreased drug abstinence among women in Cape Town, South Africa.

    PubMed

    Reed, Elizabeth; Myers, Bronwyn; Novak, Scott P; Browne, Felicia A; Wechsberg, Wendee M

    2015-01-01

    Drug abuse is a contributing factor in women's HIV risk in low-income communities in Cape Town, South Africa. This study assessed whether experiencing violence is associated with reduced drug abstinence among adult women (n = 603) participating in a randomized field trial for an HIV prevention study in Cape Town. In relation to drug abstinence at 12-month follow-up, multivariable regression models were used to assess (1) baseline partner and non-partner victimization, and (2) victimization at 12-month follow-up among participants reporting baseline victimization. Baseline partner (AOR = 0.6; 95 % CI 0.4-0.9) and non-partner victimization (AOR = 0.6; 95 % CI 0.4-0.9) were associated with a reduced likelihood of drug abstinence at follow-up. Among participants who reported victimization at baseline, those no longer reporting victimization at follow-up did not differ significantly in drug abstinence compared with those who reported victimization at follow-up. The study findings highlight the lasting impact of victimization on women's drug use outcomes, persisting regardless of whether violence was no longer reported at follow-up. Overall, the findings support the need for the primary prevention of violence to address the cycle of violence, drug use, and HIV among women in this setting. PMID:24934652

  3. Experiences in sub-Saharan Africa with GM crop risk communication: outcome of a workshop.

    PubMed

    Racovita, Monica; Obonyo, Dennis Ndolo; Abdallah, Roshan; Anguzu, Robert; Bamwenda, Gratian; Kiggundu, Andrew; Maganga, Harrison; Muchiri, Nancy; Nzeduru, Chinyere; Otadoh, Jane; Rumjaun, Anwar; Suleiman, Iro; Sunil, Manjusha; Tepfer, Mark; Timpo, Samuel; van der Walt, Wynand; Kaboré-Zoungrana, Chantal; Nfor, Lilian; Craig, Wendy

    2013-01-01

    In tackling agricultural challenges, policy-makers in sub-Saharan Africa (SSA) have increasingly considered genetically modified (GM) crops as a potential tool to increase productivity and to improve product quality. Yet, as elsewhere in the world, the adoption of GM crops in SSA has been marked by controversy, encompassing not only the potential risks to animal and human health, and to the environment, but also other concerns such as ethical issues, public participation in decision-making, socio-economic factors and intellectual property rights. With these non-scientific factors complicating an already controversial situation, disseminating credible information to the public as well as facilitating stakeholder input into decision-making is essential. In SSA, there are various and innovative risk communication approaches and strategies being developed, yet a comprehensive analysis of such data is missing. This gap is addressed by giving an overview of current strategies, identifying similarities and differences between various country and institutional approaches and promoting a way forward, building on a recent workshop with risk communicators working in SSA. PMID:23090016

  4. Experiences of Violence and Association with Decreased Drug Abstinence Among Women in Cape Town, South Africa

    PubMed Central

    Reed, Elizabeth; Myers, Bronwyn; Novak, Scott P.; Browne, Felicia A.; Wechsberg, Wendee M.

    2015-01-01

    Drug abuse is a contributing factor in women’s HIV risk in low-income communities in Cape Town, South Africa. This study assessed whether experiencing violence is associated with reduced drug abstinence among adult women (n = 603) participating in a randomized field trial for an HIV prevention study in Cape Town. In relation to drug abstinence at 12-month follow-up, multivariable regression models were used to assess (1) baseline partner and non-partner victimization, and (2) victimization at 12-month follow-up among participants reporting baseline victimization. Baseline partner (AOR = 0.6; 95 % CI 0.4–0.9) and non-partner victimization (AOR = 0.6; 95 % CI 0.4–0.9) were associated with a reduced likelihood of drug abstinence at follow-up. Among participants who reported victimization at baseline, those no longer reporting victimization at follow-up did not differ significantly in drug abstinence compared with those who reported victimization at follow-up. The study findings highlight the lasting impact of victimization on women’s drug use outcomes, persisting regardless of whether violence was no longer reported at follow-up. Overall, the findings support the need for the primary prevention of violence to address the cycle of violence, drug use, and HIV among women in this setting. PMID:24934652

  5. Adapting to climate change and disaster risk reduction through sustainable land management: Experiences in Tajikistan, East Africa, US, Argentina and Mongolia

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The special session will share and discuss experiences from different regions, namely from Tajikistan, East Africa, US, Argentina and Mongolia. Within the Pilot Program for Climate Resilience (PPCR) in Tajikistan 70 SLM technologies and approaches on how to implement SLM were documented with the Wor...

  6. An Irish Adult Learner in Sub-Saharan Africa: A Narrative Account of My Experience of Working with Teacher Educators in Lesotho

    ERIC Educational Resources Information Center

    Griffin, Rosarii

    2009-01-01

    This article presents a narrative account of the author's experience of working with teacher educators in Lesotho, Africa. It describes research projects developed in conjunction with the author's counterparts in Lesotho. Although the research project work is yet in its infancy, the author reflects on insights gained from working as an Irish…

  7. Calculation and experiment for dynamic response of bridge in deep water under seismic excitation

    NASA Astrophysics Data System (ADS)

    Liu, Chun-guang; Sun, Guo-shuai

    2014-08-01

    The fluid-structure interaction under seismic excitation is very complicated, and thus the damage identification of the bridge in deep water is the key technique to ensure the safe service. Based on nonlinear Morison equation considering the added mass effect and the fluid-structure interaction effect, the effect of hydrodynamic pressure on the structure is analyzed. A series of underwater shaking table tests are conducted in the air and in water. The dynamic characteristics affected by hydrodynamic pressure are discussed and the distribution of hydrodynamic pressure is also analyzed. In addition, the damage of structure is distinguished through the natural frequency and the difference of modal curvature, and is then compared with the test results. The numerical simulation and test of this study indicate that the effect of hydrodynamic pressure on the structure should not be neglected. It is also found that the presence of the damage, the location of the damage and the degree of the severity can be judged through the variation of structure frequency and the difference of modal curvature.

  8. Seismicity of the Earth 1900-2013 East African Rift

    USGS Publications Warehouse

    Hayes, Gavin P.; Jones, Eric S.; Stadler, Timothy J.; Barnhart, William D.; McNamara, Daniel E.; Benz, Harley M.; Furlong, Kevin P.; Villaseñor, Antonio

    2014-01-01

    Rifting in East Africa is not all coeval; volcanism and faulting have been an ongoing phenomenon on the continent since the Eocene (~45 Ma). The rifting began in northern East Africa, and led to the separation of the Nubia (Africa) and Arabia plates in the Red Sea and Gulf of Aden, and in the Lake Turkana area at the Kenya-Ethiopia border. A Paleogene mantle superplume beneath East Africa caused extension within the Nubia plate, as well as a first order topographic high known as the African superswell which now includes most of the eastern and southern sectors of the Nubia plate. Widespread volcanism erupted onto much of the rising plateau in Ethiopia during the Eocene-Oligocene (45–29 Ma), with chains of volcanoes forming along the rift separating Africa and Arabia. Since the initiation of rifting in northeastern Africa, the system has propagated over 3,000 km to the south and southwest, and it experiences seismicity as a direct result of the extension and active magmatism.

  9. Building learning catchments for integrated catchment managing: designing learning systems based on experiences in the UK and South Africa.

    PubMed

    Collins, Kevin; Colvin, John; Ison, Ray

    2009-01-01

    We examine challenges and opportunities for developing 'learning systems' for integrated catchment managing (ICMg) drawing on our experiences in two contexts: UK and South Africa (SA). Our research question is: what is it that we would have to experience to claim that a catchment was a learning catchment? We suggest that any valid answer to this question will arise in social relations in context-determined ways. From this perspective ICMg is an emergent 'performance' of stakeholders engaged in mutual action, or social learning (SL), in which understandings and practices are transformed in situation improving ways. These questions are relevant given recent reviews suggesting that implementation of the European Water Framework Directive (WFD) is not nurturing adaptive management. Our European and SA experiences demonstrate that it is possible to invest in social learning as a governance mechanism for water managing, but key constraints exist. Our SA work based on (i) appreciating the situation, especially the history, and (ii) contextual appreciation and design of learning systems (as a result of (i)) is described in response to these constraints. We conclude that more attention on developing an effective praxis for ICMg is required. PMID:19237762

  10. Lithospheric structure beneath Central Europe from the POLONAISE'97, CELEBRATION 2000, ALP 2002, and SUDETES 2003 seismic refraction experiments

    NASA Astrophysics Data System (ADS)

    Guterch, A.; Grad, M.; Keller, G. R.

    2005-12-01

    Beginning in 1997, Central Europe between the Baltic and Adriatic Seas, has been covered by an unprecedented network of seismic refraction experiments POLONAISE'97, CELEBRATION 2000, ALP 2002, and SUDETES 2003, have only been possible due to a massive international consortium consisted of more than 30 institutions from 16 countries in Europe and North America. The majority of recording instruments was provided by the IRIS/PASSCAL Instrument Center and the University of Texas at El Paso (USA), and several other countries also provided instrumentation. Total length of seismic profiles in all experiments is about 20,000 km. The main results of these experiments are: 1) the delineation of the deep structure of the southwestern margin of the East European Craton (southern Baltica) and its relationship to younger terranes; delineation of the major terranes and crustal blocks in the Trans European Suture Zone; determination of the structural framework of the Pannonian basin; elucidation of the deep structure and evolution of the Western Carpathian Mountains and Eastern Alps; determination of the structural relationships between the structural elements of the Bohemian massif and adjacent features; construction of 3-D models of the lithospheric structure; and evaluation and develop geodynamic models for the tectonic evolution of the region. Experiment Working Groups Members: K. Aric, M. Behm, E. Brueckl, W. Chwatal, H. Grassl, S. Hock, V. Hoeck, F. Kohlbeck, E.-M. Rumpfhuber, Ch. Schmid, R. Schmoller, C. Tomek, Ch. Ullrich, F.Weber (Austria), A.A. Belinsky (Belarus), I. Asudeh, R. Clowes, Z. Hajnal (Canada), F. Sumanova (Croatia), M. Broz , P. Hrubcova, M. Korn, O. Karousova, J. Malek, A. Spicak (Czech Republic), S.L. Jensen, P. Joergensen, H. Thybo (Denmark), K. Komminaho, U. Luosto, T. Tiira, J. Yliniemi (Finland), F. Bleibinhaus, R. Brinkmann, B. Forkmann, H. Gebrande, H. Geissler, A. Hemmann, G. Jentzsch, D. Kracke, A. Schulze, K. Schuster (Germany), T. Bodoky, T

  11. The Grenville Front Tectonic Zone: Results from the 1986 Great Lakes Onshore Seismic Wide-Angle Reflection and Refraction Experiment

    NASA Astrophysics Data System (ADS)

    Epili, Duryodhan; Mereu, Robert F.

    1991-09-01

    The Grenville Front, which marks the orogenic boundary between the Archean Superior Structural Province and the much younger Grenville Province to the southeast, is one of the major tectonic features of the Canadian Shield. Within Canada, it is approximately 1900 km in length extending from the north shore of Lake Huron across Ontario and Quebec to Labrador. In 1986, a major coincident onship near-vertical reflection and onshore wide-angle reflection/refraction experiment (GLIMPCE-Great Lakes International Multidisciplinary Program on Crustal Evolution) was conducted along a series of lines across the Great lakes. One of the lines, line J, ran across Georgian Bay and Lake Huron for a distance of 350 km and crossed the Grenville Front Tectonic Zone (GFTZ). The seismic signals from the air gun array source were well recorded by the onshore stations up to distances of 250 km with a seismic trace spacing of 50-62.5 m. The GFTZ had a profound effect on the nature of the reflector patterns observed on the onshore seismic sections. Data recorded by the stations on the east end of the line indicate that the crustal P phases are very complex and form a "shinglelike" pattern of reflected waves. Data recorded by stations at the center and at the western end of the line show that the Pg phases are normal and lack the shinglelike appearance. This character of arrivals was also observed on the corresponding S wave sections. A combined P and S wave forward modeling analysis shows that the GFTZ is composed of bands of reflectors dipping at angles of 20°-35° extending to the lower crust. These reflectors were also well imaged on the coincident near-vertical reflection data. Reflectors under the Britt domain to the east of the GFTZ have a shallower dip than those along the zone. The structure of the crust under the Manitoulin terrane to the west of the GFTZ is laterally homogeneous with a major intracrustal reflector at a depth of 17-20 km below the surface. Poisson's ratio is

  12. Amplitude and phase normalization of seismograms from multiple seismograph recording systems for the Yellowstone-Snake River Plain seismic refraction experiment

    SciTech Connect

    Baker, M.R.; Braile, L.W.; Smith, R.B.

    1982-04-10

    A z transform filter theory method for the normalization of the instrument responses of several seismographs is presented. In this method, an inverse filter is derived by consideration of the seismometer/recorder characteristics which may be applied to a given seismogram to convert the system frequency response to that of a reference system. Inverse filters are derived for the seismographs used on the 1978 Yellowstone-Snake River Plain seismic profiling experiment. It is shown by application to these data that the inverse filters are effective in amplitude normalization and that their use allows improvement in the amplitude and waveform character of seismic record sections.

  13. P-wave velocity structure of the southern Ryukyu margin east of Taiwan: Results from the ACTS wide-angle seismic experiment

    NASA Astrophysics Data System (ADS)

    Klingelhoefer, F.; Berthet, T.; Lallemand, S.; Schnurle, P.; Lee, C.-S.; Liu, C.-S.; McIntosh, K.; Theunissen, T.

    2012-11-01

    An active seismic experiment has been conducted across the southern Ryukyu margin east of Taiwan over the whole trench-arc-backarc system in May 2009. Twenty-four ocean bottom seismometers (OBS) were deployed from the Ryukyu trench to the southern Okinawa trough over the Ryukyu arc and forearc. Wide angle seismic data were recorded by the OBS array while coincident reflection seismic data were acquired using a 6 km long streamer and a 6600 cubic inch seismic airgun array. Results from tomographic inversion of 21091 travel time picks along this line allowed us to image crustal structures of the Ryukyu margin down to a depth of 25 km. The transect has been designed to provide a better seismic velocity structure of the subduction zone in a highly deformed area that has produced an M8 earthquake in 1920. The line crosses a seismic cluster of earthquakes which source mechanisms are still poorly understood. The subducting oceanic crust of the Huatung Basin is about 5-6 km thick. The underlying mantle exhibits low seismic velocities around 7.8 km/s suggesting some hydrothermal alterations or alteration of the upper mantle through faults generated by the flexure of the subducting plate as it enters the subduction. Low velocities, up to 4.5 km/s, associated with the accretionary wedge are well imaged from the trench back to the Nanao forearc. A major result concerns the abrupt termination of the buttress at the rear of the accretionary wedge. Despite the low resolution of the tomographic inversion near the subduction interface, several lines of evidence supporting the presence of a low velocity zone beneath the toe of the forearc buttress could be established. The Moho beneath the Ryukyu non-volcanic arc is located at a depth around 25 km depth.

  14. Scaling up delivery of contraceptive implants in sub-Saharan Africa: operational experiences of Marie Stopes International

    PubMed Central

    Duvall, Susan; Thurston, Sarah; Weinberger, Michelle; Nuccio, Olivia; Fuchs-Montgomery, Nomi

    2014-01-01

    Contraceptive implants offer promising opportunities for addressing the high and growing unmet need for modern contraceptives in sub-Saharan Africa. Marie Stopes International (MSI) offers implants as one of many family planning options. Between 2008 and 2012, MSI scaled up voluntary access to implants in 15 sub-Saharan African countries, from 80,041 implants in 2008 to 754,329 implants in 2012. This 9-fold increase amounted to more than 1.7 million implants delivered cumulatively over the 5-year period. High levels of client satisfaction were attained alongside service provision scale up by using existing MSI service delivery channels—mobile outreach, social franchising, and clinics—to implement strategies that broadened access for underserved clients and maintained service quality. Use of adaptive and context-specific service delivery models and attention to key operational components, including sufficient numbers of trained providers, strong supply chains, diverse financing mechanisms, and implant removal services, underpinned our service delivery efforts. Accounting for 70% of the implants delivered by MSI in 2012, mobile outreach services through dedicated MSI provider teams played a central role in scale-up efforts, fueled in part by the provision of free or heavily subsidized services. Social franchising also demonstrated promise for future program growth, along with MSI clinics. Continued high growth in implant provision between 2011 and 2012 in all sub-Saharan African countries indicates the region's capacity for further service delivery expansion. Meeting the expected rising demand for implants and ensuring long-term sustainable access to the method, as part of a comprehensive method mix, will require continued use of appropriate service delivery models, effective operations, and ongoing collaboration between the private, public, and nongovernmental sectors. MSI's experience can be instructive for future efforts to ensure contraceptive access and

  15. Lower crustal deformation beneath the central Transverse Ranges, southern California: Results from the Los Angeles Region Seismic Experiment

    USGS Publications Warehouse

    Godfrey, N.J.; Fuis, G.S.; Langenheim, V.; Okaya, D.A.

    2002-01-01

    We present a P wave velocity model derived from active source seismic data collected during the 1994 Los Angeles Region Seismic Experiment. Our model extends previously published upper crustal velocity models to mantle depths. Our model was developed by both ray tracing through a layered model and calculating travel times through a gridded model. It includes an 8-km-thick crustal root centered beneath the surface trace of the San Andreas fault, north of the highest topography in the San Gabriel Mountains. A simple mass balance calculation suggests that ???36 km of north-south shortening across the San Andreas fault in the central Transverse Ranges could have formed this root. If north-south compression began when the "Big Bend" in the San Andreas fault formed at ???5 Ma, 36 km of shortening implies a north-south contraction rate of ???7.1 mm/yr across the central Transverse Ranges. If, instead, north-south compression began when the Transverse Ranges formed at 3.4-3.9 Ma, 36 km of shortening implies a contraction rate of 9.2-10.6 mm/yr. North of the San Andreas fault, the Mojave Desert crust has a low-velocity (6.3 km/s) mid and lower crust and a 28-km-deep Moho. South of the San Andreas fault, beneath the Los Angeles and San Gabriel Valley basins, there is a fast (6.6-6.8 km/s), thick (10-12 km) lower crust with a 27-km-deep Moho. Farther south still, the lower crust of the Continental Borderland is fast (6.6-6.8 km/s) and thin (5 km) with a shallow (22 km deep) Moho.

  16. 'Issues of equity are also issues of rights': Lessons from experiences in Southern Africa

    PubMed Central

    London, Leslie

    2007-01-01

    Background Human rights approaches to health have been criticized as antithetical to equity, principally because they are seen to prioritise rights of individuals at the expense of the interests of groups, a core tenet of public health. The objective of this study was to identify how human rights approaches can promote health equity. Methods The Network on Equity in Health in Southern Africa undertook an exploration of three regional case studies – antiretroviral access, patient rights charters and civic organization for health. A combination of archival reviews and stakeholder interviews were complemented with a literature review to provide a theoretical framework for the empirical evidence. Results Critical success factors for equity are the importance of rights approaches addressing the full spectrum from civil and political, through to socio-economic rights, as well as the need to locate rights in a group context. Human rights approaches succeed in achieving health equity when coupled with community engagement in ways that reinforce community capacity, particularly when strengthening the collective agency of its most vulnerable groups. Additionally, human rights approaches provide opportunities for mobilising resources outside the health sector, and must aim to address the public-private divide at local, national and international levels. Conclusion Where it is clear that rights approaches are predicated upon understanding the need to prioritize vulnerable groups and where the way rights are operationalised recognizes the role of agency on the part of those most affected in realising their socio-economic rights, human rights approaches appear to offer powerful tools to support social justice and health equity. PMID:17257421

  17. Experience and challenges from clinical trials with malaria vaccines in Africa

    PubMed Central

    2013-01-01

    Malaria vaccines are considered amongst the most important modalities for potential elimination of malaria disease and transmission. Research and development in this field has been an area of intense effort by many groups over the last few decades. Despite this, there is currently no licensed malaria vaccine. Researchers, clinical trialists and vaccine developers have been working on many approached to make malaria vaccine available. African research institutions have developed and demonstrated a great capacity to undertake clinical trials in accordance to the International Conference on Harmonization-Good Clinical Practice (ICH-GCP) standards in the last decade; particularly in the field of malaria vaccines and anti-malarial drugs. This capacity is a result of networking among African scientists in collaboration with other partners; this has traversed both clinical trials and malaria control programmes as part of the Global Malaria Action Plan (GMAP). GMAP outlined and support global strategies toward the elimination and eradication of malaria in many areas, translating in reduction in public health burden, especially for African children. In the sub-Saharan region the capacity to undertake more clinical trials remains small in comparison to the actual need. However, sustainability of the already developed capacity is essential and crucial for the evaluation of different interventions and diagnostic tools/strategies for other diseases like TB, HIV, neglected tropical diseases and non-communicable diseases. There is urgent need for innovative mechanisms for the sustainability and expansion of the capacity in clinical trials in sub-Saharan Africa as the catalyst for health improvement and maintained. PMID:23496910

  18. Experience and challenges from clinical trials with malaria vaccines in Africa.

    PubMed

    Mwangoka, Grace; Ogutu, Bernhards; Msambichaka, Beverly; Mzee, Tutu; Salim, Nahya; Kafuruki, Shubis; Mpina, Maxmillian; Shekalaghe, Seif; Tanner, Marcel; Abdulla, Salim

    2013-01-01

    Malaria vaccines are considered amongst the most important modalities for potential elimination of malaria disease and transmission. Research and development in this field has been an area of intense effort by many groups over the last few decades. Despite this, there is currently no licensed malaria vaccine. Researchers, clinical trialists and vaccine developers have been working on many approached to make malaria vaccine available.African research institutions have developed and demonstrated a great capacity to undertake clinical trials in accordance to the International Conference on Harmonization-Good Clinical Practice (ICH-GCP) standards in the last decade; particularly in the field of malaria vaccines and anti-malarial drugs. This capacity is a result of networking among African scientists in collaboration with other partners; this has traversed both clinical trials and malaria control programmes as part of the Global Malaria Action Plan (GMAP). GMAP outlined and support global strategies toward the elimination and eradication of malaria in many areas, translating in reduction in public health burden, especially for African children. In the sub-Saharan region the capacity to undertake more clinical trials remains small in comparison to the actual need.However, sustainability of the already developed capacity is essential and crucial for the evaluation of different interventions and diagnostic tools/strategies for other diseases like TB, HIV, neglected tropical diseases and non-communicable diseases. There is urgent need for innovative mechanisms for the sustainability and expansion of the capacity in clinical trials in sub-Saharan Africa as the catalyst for health improvement and maintained. PMID:23496910

  19. South Africa

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This true-color image of South Africa was acquired on May 14, 2000, by NASA's Moderate-resolution Imaging Spectroradiometer, or MODIS. The image was produced using a combination of the sensor's 250-m and 500-m resolution visible wavelength bands. As part of the opening ceremony to begin the joint U.S.-South Africa SAFARI Field Experiment, NASA presented print copies of this image as GIFts to Dr. Ben Ngubane, Minister of Arts, Science and Technology, and Honorable Advocate Ngoaka Ramathlodi, Premier of the Northern Province, South Africa. The area shown in this image encompasses seven capital cities and a number of the region's distinctive geological features can be seen clearly. Toward the northern (top) central part of the image, the browns and tans comprise the Kalahari Desert of southern Botswana. The Tropic of Capricorn runs right through the heart of the Kalahari and the Botswanan capital city of Gaborone sits on the Limpopo River, southeast of the Kalahari. Along the western coastline of the continent is the country of Namibia, where the Namib Desert is framed against the sea by the Kaokoveld Mountains. The Namibian capital of Windhoek is obscured by clouds. Looking closely in the center of the image, the Orange River can be seen running from east to west, demarcating the boundary between Namibia and South Africa. On the southwestern corner of the continent is the hook-like Cape of Good Hope peninsula and Cape Town, the parliamentary capital of South Africa. Running west to east away from Cape Town are the Great Karroo Mountains. The shadow in this image conveys a sense of the very steep grade of the cliffs along the southern coast of South Africa. Port Elizabeth sits on the southeasternmost point of South Africa, and a large phytoplankton bloom can be seen in the water about 100 miles east of there. Moving northward along the east coast, the Drakensberg Mountains are visible. The two small nations of Lesotho and Swaziland are in this region, completely

  20. Problem-dependent 3-d Inversion of P-wave Arrivals From Local Events Recorded During The Svekalapko Deep Seismic Experiment In Finland

    NASA Astrophysics Data System (ADS)

    Kozlovskaya, E.; Hjelt, S.-E.; Yliniemi, J.; Korhonen, J.; Elo, S.; Svekalapko Seismic Tomography Working Group

    The SVEKALAPKO temporary seismic array was originally designed for studying the lithospheric structure beneath the southern Finland by means of teleseismic events. In addition, the high quality recordings of local seismic events (earthquakes and quarry blasts) registered by the SVEKALAPKO array contain a lot of information about the structure of the upper lithosphere beneath the southern Finland. However, the traditional local event tomography of SVEKALAPKO data cannot result in the ve- locity model valid for proper geological interpretation. The main reasons for this is the lack of the space resolution, which results in strong non-uniqueness of the to- mographic inversion. This problem can be treated by introducing various kinds of a-priori information into the inversion algorithm. The a-priori information available for the SVEKALAPKO study area includes not only the information from previous control source seismic experiments, but also potential fields data and petrophysical data. Usage of such a non-homogeneous a-priori information required a problem- dependent algorithm of seismic data inversion, which was developed on the base of non-probabilistic uncertainty measures. An example of this algorithm application to SVEKALAPKO local seismic event data is presented.

  1. High-Resolution Imaging of Tsunamigenic Structures in the Southwest Iberian Margin (Eurasia-Africa Convergence): Implications for Seismic Hazard Assessment

    NASA Astrophysics Data System (ADS)

    Gracia, E.; Danobeitia, J.

    2001-12-01

    The SW Iberian Margin hosts the present-day boundary between the European and African Plates. Convergence is accommodated trough a widespread active deformation zone, characterized by a significant seismic activity, source of the largest earthquakes in Western Europe (e.g. 1969 Horseshoe Earthquake of M8; 1755 Lisbon Earthquake and Tsunami of M8.5). During a recent marine geophysical project (EU-BIGSETS), we identified a 50 km long SE-dipping thrust (Marques de Pombal Fault, MPF), which based on tsunami numerical modelling has been suggested as a plausible source for the 1755 Lisbon earthquake. With the purpose to evaluate the seismic activity of the MPF and other active structures, we plan a detailed, high-resolution survey (HITS). The main objectives of the HITS cruise, to be carried out on board the Spanish RV Hesperides (September-October 2001), are: (a) to confirm the detected active faults, to identify small-scale structures and to determine their geometry using the high-resolution TOBI sidescan sonar, swath-bathymetry, 3.5 kHz sub-bottom profiler and a submarine camera; (b) to calculate the style and rate of slip of the active faults, in order to determine its recurrence interval and assess on the earthquake and tsunami hazard in SW Iberia. To achieve this we plan precise sediment sampling and dating (14C, 210Pb) of the turbiditic units associated with the seismic cycle of the fault; and (c) to investigate the seepage of fluids and heat flow regime along the active faults, which determine the nucleation and propagation of the ruptures. This project is supported by the "European Access to Seafloor Survey Systems (EASSS III)-TOBI sidescan sonar" (HPRI\\-CT\\-1999\\-00047) and Acción Especial MCYT (REN\\-2000\\-2150\\-E).

  2. Results from the latest SN-4 multi-parametric benthic observatory experiment (MARsite EU project) in the Gulf of Izmit, Turkey: oceanographic, chemical and seismic monitoring

    NASA Astrophysics Data System (ADS)

    Embriaco, Davide; Marinaro, Giuditta; Frugoni, Francesco; Giovanetti, Gabriele; Monna, Stephen; Etiope, Giuseppe; Gasperini, Luca; Çağatay, Namık; Favali, Paolo

    2015-04-01

    An autonomous and long-term multiparametric benthic observatory (SN-4) was designed to study gas seepage and seismic energy release along the submerged segment of the North Anatolian Fault (NAF). Episodic gas seepage occurs at the seafloor in the Gulf of Izmit (Sea of Marmara, NW Turkey) along this submerged segment of the NAF, which ruptured during the 1999 Mw7.4 Izmit earthquake. The SN-4 observatory already operated in the Gulf of Izmit at the western end of the 1999 Izmit earthquake rupture for about one-year at 166 m water depth during the 2009-2010 experiment (EGU2014-13412-1, EGU General Assembly 2014). SN-4 was re-deployed in the same site for a new long term mission (September 2013 - April 2014) in the framework of MARsite (New Directions in Seismic Hazard assessment through Focused Earth Observation in the Marmara Supersite, http://marsite.eu/ ) EC project, which aims at evaluating seismic risk and managing of long-term monitoring activities in the Marmara Sea. A main scientific objective of the SN-4 experiment is to investigate the possible correlations between seafloor methane seepage and release of seismic energy. We used the same site of the 2009-2010 campaign to verify both the occurrence of previously observed phenomena and the reliability of results obtained in the previous experiment (Embriaco et al., 2014, doi:10.1093/gji/ggt436). In particular, we are interested in the detection of gas release at the seafloor, in the role played by oceanographic phenomena in this detection, and in the association of gas and seismic energy release. The scientific payload included, among other instruments, a three-component broad-band seismometer, and gas and oceanographic sensors. We present a technical description of the observatory, including the data acquisition and control system, results from the preliminary analysis of this new multidisciplinary data set, and a comparison with the previous experiment.

  3. Experiences of Disabled Students in South Africa: Extending the Thinking behind Disability Support

    ERIC Educational Resources Information Center

    Matshedisho, K. R.

    2010-01-01

    This article argues that even though the experiences of disabled students have programmatic implications, their needs should not be isolated from other students'. Instead they should be understood as part of the student life cycle within the pluralistic paradigm of education. In demonstrating the argument this article will: (a) outline some of the…

  4. NSF RET in Southern Africa: community and research experiences in soil science

    NASA Astrophysics Data System (ADS)

    Mladenov, N.; Pollard, A.; Wellbeloved-Stone, R.; Riffel, H.; Chavarro, D.; D'Odorico, P.

    2010-12-01

    Collaborative research on belowground carbon storage in the Kalahari Desert has provided opportunities for international research experience for US middle and high school teachers, funded by the National Science Foundation Research Experience for Teachers (RET) Program. This presentation will highlight the field research experiences, international high school visit, relationships fostered with Botswana high school teachers, and new soil science curricula developed by three US environmental science teachers. New lesson plans and activities on carbon sequestration, fine and coarse root mapping, and soil organic carbon cycling and other learning tools have been incorporated into the existing Underground Safari webpage (instaar.colorado.edu/undergroundsafari) (Figure 1). An interactive blog, undergroundsafari.edublogs.org, has been developed to allow dynamic discourse between students, teachers and researchers on this project. Lessons learned from classroom trials of curriculum and use of other RET experience-motivated activities in the classroom will be discussed. Figure 1. Screen capture of the "Videos" page from the Underground Safari website for NSF DEB project, "Collaborative Research: Distribution and dynamics of belowground carbon in savannas."

  5. Disclosure of HIV status: Experiences of Patients Enrolled in an Integrated TB and HAART Pilot Programme in South Africa

    PubMed Central

    Gebrekristos, Hirut T; Lurie, Mark N; Mthethwa, Nkosinathi; Karim, Quarraisha Abdool

    2010-01-01

    The convergence between the tuberculosis (TB) and HIV epidemics has led to studies investigating strategies for integrated HIV and TB care. We present the experiences of a cohort of 17 patients enrolled in the first integrated TB and HIV treatment pilot programme, conducted in Durban, South Africa, as a precursor to a pivotal trial to answer the question of when to start antiretroviral treatment (ART) in patients co-infected with HIV and TB. Patients’ experiences with integrated TB and HIV care can provide insight about the problems or benefits of introducing HIV treatment into existing TB care in resource-constrained settings, where stigma and discrimination are often pervasive and determining factors influencing treatment uptake and coverage. Individual interviews, focus group discussions, and observations were used to understand patients’ experiences with integrated TB and HIV treatment. The patients described incorporating highly active antiretroviral therapy (HAART) into their daily routine as ‘easy’; however, the patients experienced difficulties with disclosing their HIV status. Non-disclosure to sexual partners may jeopardise safer-sex practices and enhance HIV transmission. Being on TB treatment created a safe space for all patients to conceal their HIV status from those to whom they did not wish to disclose. The data suggest that the context of directly observed therapy (DOT) for TB may have the added benefit of creating a safe space for introducing ART to patients who would benefit most from treatment initiation but who are not ready or prepared to disclose their HIV status to others. PMID:20411037

  6. Experiences of breastfeeding and vulnerability among a group of HIV-positive women in Durban, South Africa.

    PubMed

    Seidel, G; Sewpaul, V; Dano, B

    2000-03-01

    While international guidelines are currently being drawn up about HIV and infant feeding practices, and national and regional guidelines are under discussion in South Africa, there have been remarkably few studies that have sought to elicit HIV-positive mothers' experiences of breastfeeding and of paediatric infection. There is an urgent need to document this 'grass roots' knowledge in different sites, and for this data to be used to inform policy development, and for advocacy and counselling purposes. This qualitative investigation reports on the experiences and decisions taken around breastfeeding by a peer support group of 13 HIV-positive mothers meeting at King Edward VIII Hospital, Durban. In this study, the particular focus of information-giving and decision-making as to breast or formula feed is concerned with the impact on individual HIV-positive women and their babies. The most significant finding is that at no stage during their pregnancy were any of these mothers given information about the risks of HIV transmission through breastmilk. The study data were elicited in an in-depth group discussion, and individual women were invited to re-enact their stories in a follow-up discussion for clarification purposes. The women also discussed how they dealt with problems surrounding confidentiality in cases where few have been able to disclose their status to the extended family. There have been renewed calls for further investment in counsellors, with an enhanced role for community activists as peer educators. While there are severe resource constraints and low morale among many overworked nurses, one of the general problems in hospital settings remains the vertical health paradigm. This does not accommodate women's experiences, preferences, social networks and lay knowledge, and inhibits many women from becoming full participants in decisions affecting their own and their family's health. PMID:10731232

  7. Caregivers’ Experiences of Pathways to Care for Seriously Ill Children in Cape Town, South Africa: A Qualitative Investigation

    PubMed Central

    Jones, Caroline H. D.; Ward, Alison; Hodkinson, Peter W.; Reid, Stephen J.; Wallis, Lee A.; Harrison, Sian; Argent, Andrew C.

    2016-01-01

    Purpose Understanding caregivers’ experiences of care can identify barriers to timely and good quality care, and support the improvement of services. We aimed to explore caregivers’ experiences and perceptions of pathways to care, from first access through various levels of health service, for seriously ill and injured children in Cape Town, South Africa, in order to identify areas for improvement. Methods Semi-structured, qualitative interviews were conducted with primary caregivers of children who were admitted to paediatric intensive care or died in the health system prior to intensive care admission. Interviews explored caregivers’ experiences from when their child first became ill, through each level of health care to paediatric intensive care or death. A maximum variation sample of transcripts was purposively sampled from a larger cohort study based on demographic characteristics, child diagnosis, and outcome at 30 days; and analysed using the method of constant comparison. Results Of the 282 caregivers who were interviewed in the larger cohort study, 45 interviews were included in this qualitative analysis. Some caregivers employed ‘tactics’ to gain quicker access to care, including bypassing lower levels of care, and negotiating or demanding to see a healthcare professional ahead of other patients. It was sometimes unclear how to access emergency care within facilities; and non-medical personnel informally judged illness severity and helped or hindered quicker access. Caregivers commonly misconceived ambulances to be slow to arrive, and were concerned when ambulance transfers were seemingly not prioritised by illness severity. Communication was often good, but some caregivers experienced language difficulties and/or criticism. Conclusions Interventions to improve child health care could be based on: reorganising the reception of seriously ill children and making the emergency route within healthcare facilities clear; promoting caregivers’ use of

  8. Pre-registration nursing students' perceptions and experiences of violence in a nursing education institution in South Africa.

    PubMed

    de Villiers, Tania; Mayers, Pat M; Khalil, Doris

    2014-11-01

    Violence is a growing problem worldwide in the field of health care and within the nursing profession. A study comprising a survey and focus groups with nursing students, and interviews with nurse educators was conducted to examine nursing students' perceptions and experiences of violence at a nursing education institution in the Western Cape, South Africa. A self-administered questionnaire was distributed to all nursing students. Two hundred and twenty three (n = 223) respondents completed the questionnaire. Focus groups were conducted with purposively sampled student participants and semi-structured interviews with nurse educators. The findings indicated that the nature of the violent incidents experienced by students on campus, especially in the residences, ranged from verbal abuse to violation of students' property and personal space, and could be attributed primarily to substance abuse. Violence among student nurses could negatively affect learning. In a profession in which nurses are exposed to violence in the workplace, it is important that violence in the learning environment is actively prevented and respect of individual rights, tolerance and co-operation are promoted. PMID:25262064

  9. Young women's life experiences and perceptions of sexual and reproductive health in rural KwaZulu-Natal South Africa.

    PubMed

    Waxman, Aliza M; Humphries, Hilton; Frohlich, Janet; Dlamini, Sarah; Ntombela, Fanelesibonge

    2016-10-01

    Women in South Africa bear a disproportionate burden of the HIV epidemic. Female-controlled HIV prevention methods offer promising interventions to reduce this burden but cannot be effectively employed without a better understanding of young women's perceptions of their sexual and reproductive health. This study examines social, environmental and cultural factors contributing to young women's perceptions of, and experiences with, sexual and reproductive health to identify the challenges of engaging adolescent girls in HIV prevention. Twenty-five 15-19-year-old women were interviewed using semi-structured in-depth interview questions to discover their life context, future goals and relationships with men, and to understand how these factors influence their sexual and reproductive health decisions and outcomes. A thematic analysis of interview findings indicates that although participants are aware of the risks posed by engaging in risky sexual behaviour, life context shapes their perceptions and prioritisation of their health, which presents a barrier to achieving healthy behaviours and positive health outcomes. These findings may influence future research into how young women's health perceptions influence their sexual health behaviours, and how they utilise sexual and reproductive health services in a clinical setting. This has implications for introducing forms of female-controlled HIV prevention for this population. PMID:27216483

  10. The Play Experiences of Preschool Children from a Low-socio-economic Rural Community in Worcester, South Africa.

    PubMed

    Bartie, Michelle; Dunnell, Alex; Kaplan, Jesse; Oosthuizen, Dianka; Smit, Danielle; van Dyk, Anchen; Cloete, Lizahn; Duvenage, Mia

    2016-06-01

    Occupational therapists believe that play is a child's main occupation and is considered essential for healthy motor, cognitive and emotional development. However, play spaces and activities in low socio-economic areas are often different to those provided in structured occupational therapy treatment environments. The main objective was to determine play opportunities, activities, equipment, toys and the play environment for 5- to 6-year-olds living in a low-socio-economic community outside a small town in South Africa, in order to understand the nature of play in this environment better. Participant observation together with an adapted photovoice method to capture the play experience was used. Data was analysed using inductive content analysis. Two global themes emerged from the results: "neighbourhood children find ways to play" and "context influences play". Children were given ample opportunity to play and participated in extensive outdoor play. Their games were highly social and involved the imaginative use of found items as toys. Play was also used to make sense of social hazards. An understanding of play in a low-income context has implications for the development of future play assessments and the provision of play therapy in these communities. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26348391

  11. Notes on some experiments on the application of subtractive compensation to USGS seismic magnetic tape recording and playback systems

    USGS Publications Warehouse

    Eaton, Jerry P.

    1975-01-01

    The purpose of these experiments is to lay the groundwork for the implementation of subtractive compensation of the USGS seismic network tape playbacks utilizing the Develco model 6203 discriminators at a x1 playback speed. Although the Develco discriminators were designed for this application and a matching Develco compensation discriminator was purchased, effective use of this system for subtractive compensation has been blocked by the inadequate (frequency dependent) matching of the phase of the compensation signal to that of the data signal at the point compensation is carried out in the data discriminators. John Van Schaack has ameliorated the phase mismatch problem by an empirical alteration of the compensation discriminator input bandpass filter. We have selected a set (of eight) Develco discriminators and adjusted their compensation signal input levels to minimize spurious signals (noise) originating from tape speed irregularities. The sensitivity of the data discriminators was adjusted so that deviations of +125 Hz and -125 Hz produced output signals of +2.00 volts and -2.00 volts, respectively. The eight data discriminators are driven by a multiplex signal on a single tape track (subcarriers 680, 1020, 1360, 1700, 2040, 2380, 2720, and 3060 Hz). The Develco-supplied compensation discriminator requires an unmodulated 3125 Hz signal on a separate tape track.

  12. Seismic investigations of the Nansen Ridge during the FRAM I experiment

    NASA Astrophysics Data System (ADS)

    Kristoffersen, Y.; Husebye, E. S.; Bungum, H.; Gregersen, S.

    1982-02-01

    As part of the FRAM I ice station experiment in the Arctic Ocean during the period March 11-May 15, 1979, a sonobuoy array was kept in operation for about 6 weeks. During the last two days of the experiment the array drifted over the crestal mountains of the western flank of the Nansen Ridge. Here microearthquakes were recorded at a rate of 1-2 events per hour, with epicentral distances from 15 to 25 km. Two parallel epicenter lineations are found, a main one that coincides with the median valley and another less active one that follows the northwestern rift-valley wall. This activity may be related to the uplift of a fault block from the median valley onto the rift valley wall. A crustal model for the crestal mountain area was obtained from two unreversed refraction profiles, giving preliminary compressional velocities of 4.6 km/s at the sea floor, a 6.1 km/s refractor at 1.5 km depth, and a 7.9 km/s refractor at 6 km depth, while in the median valley a 7.2 km/s refractor is found at a depth of 3 km.

  13. The Seismotectonic Model of Southern Africa

    NASA Astrophysics Data System (ADS)

    Midzi, Vunganai; Mulabisana, Thifelimbulu; Manzunzu, Brassnavy

    2013-04-01

    Presented in this report is a summary of the major structures and seismotectonic zones in Southern Africa (Botswana, Lesotho, Namibia, South Africa and Swaziland), which includes available information on fault plane solutions and stress data. Reports published by several experts contributed much to the prepared zones. The work was prepared as part of the requirements for the SIDA/IGCP Project 601 titled "Seismotectonics and Seismic Hazards in Africa" as well as part of the seismic source characterisation of the GEM-Africa Seismic hazard study. The seismic data used are part of the earthquake catalogue being prepared for the GEM-Africa project, which includes historical and instrumental records as collected from various agencies. Seventeen seismic zones/sources were identified and demarcated using all the available information. Two of the identiied sources are faults with reliable evidence of their activity. Though more faults have been identified in unpublished material as being active, more work is being carried out to obtain information that can be used to characterise them before they are included in the seismotectonic model. Explanations for the selected boundaries of the zones are also given in the report. It should be noted that this information is the first draft of the seismic source zones of the region. Futher interpreation of the data is envisaged which might result in more than one version of the zones.

  14. iMUSH: The design of the Mount St. Helens high-resolution active source seismic experiment

    NASA Astrophysics Data System (ADS)

    Kiser, Eric; Levander, Alan; Harder, Steve; Abers, Geoff; Creager, Ken; Vidale, John; Moran, Seth; Malone, Steve

    2013-04-01

    Mount St. Helens is one of the most societally relevant and geologically interesting volcanoes in the United States. Although much has been learned about the shallow structure of this volcano since its eruption in 1980, important questions still remain regarding its magmatic system and connectivity to the rest of the Cascadia arc. For example, the structure of the magma plumbing system below the shallowest magma chamber under the volcano is still only poorly known. This information will be useful for hazard assessment for the southwest Washington area, and also for gaining insight into fundamental scientific questions such as the assimilation and differentiation processes that lead to the formation of continental crust. As part of the multi-disciplinary imaging of Magma Under St. Helens (iMUSH) experiment, funded by NSF GeoPRISMS and EarthScope, an active source seismic experiment will be conducted in late summer 2014. The experiment will utilize all of the 2600 IRIS/PASSCAL/USArray Texan instruments. The instruments will be deployed as two 1000-instrument consecutive refraction profiles (one N/S and one WNW/ESE). Each of these profiles will be accompanied by two 1600-instrument areal arrays at varying distances from Mount St. Helens. Finally, one 2600-instrument areal array will be centered on Mount St. Helens. These instruments will record a total of twenty-four 500-1000 kg shots. Each refraction profile will have an average station spacing of 150 m, and a total length of 150 km. The stations in the areal arrays will be separated by ~1 km. A critical step in the success of this project is to develop an experimental setup that can resolve the most interesting aspects of the magmatic system. In particular, we want to determine the distribution of shot locations that will provide good coverage throughout the entire model space, while still allowing us to focus on regions likely to contain the magmatic plumbing system. In this study, we approach this problem by

  15. Research-policy partnerships - experiences of the Mental Health and Poverty Project in Ghana, South Africa, Uganda and Zambia

    PubMed Central

    2012-01-01

    Background Partnerships are increasingly common in conducting research. However, there is little published evidence about processes in research-policy partnerships in different contexts. This paper contributes to filling this gap by analysing experiences of research-policy partnerships between Ministries of Health and research organisations for the implementation of the Mental Health and Poverty Project in Ghana, South Africa, Uganda and Zambia. Methods A conceptual framework for understanding and assessing research-policy partnerships was developed and guided this study. The data collection methods for this qualitative study included semi-structured interviews with Ministry of Health Partners (MOHPs) and Research Partners (RPs) in each country. Results The term partnership was perceived by the partners as a collaboration involving mutually-agreed goals and objectives. The principles of trust, openness, equality and mutual respect were identified as constituting the core of partnerships. The MOHPs and RPs had clearly defined roles, with the MOHPs largely providing political support and RPs leading the research agenda. Different influences affected partnerships. At the individual level, personal relationships and ability to compromise within partnerships were seen as important. At the organisational level, the main influences included the degree of formalisation of roles and responsibilities and the internal structures and procedures affecting decision-making. At the contextual level, political environment and the degree of health system decentralisation affected partnerships. Conclusions Several lessons can be learned from these experiences. Taking account of influences on the partnership at individual, organisation and contextual/system levels can increase its effectiveness. A common understanding of mutually-agreed goals and objectives of the partnership is essential. It is important to give attention to the processes of initiating and maintaining partnerships

  16. Perceptions and experiences of allopathic health practitioners on collaboration with traditional health practitioners in post-apartheid South Africa

    PubMed Central

    Hendricks, Stephen J.; Mulaudzi, Mavis F.

    2016-01-01

    Background The indigenous health system was perceived to be a threat to the allopathic health system. It was associated with ‘witchcraft’, and actively discouraged, and repressed through prohibition laws. The introduction of the Traditional Health Practitioners Act No 22 of 2007 brought hope that those centuries of disrespect for traditional health systems would change. The study examined the perceptions and experiences of allopathic health practitioners on collaboration with traditional health practitioners in post-apartheid South Africa. Methods Qualitative descriptive research methodology was used to collect data from allopathic health practitioners employed by Limpopo’s Department of Health. In-depth focus group discussions and meetings were conducted between January and August 2014. Perceptions and experiences of working with traditional health practitioners were explored. Ethical clearance was obtained from the University of Pretoria and approval from the Department’s Research Committee. Results Dominant views were that the two health systems were not compatible with respect to the science involved and the source of knowledge. Overall, quality of health care will be compromised if traditional health practitioners are allowed to work in public health facilities. Conclusion Allopathic health practitioners do not appear ready to work with traditional health practitioners, citing challenges of quality of health care, differences regarding concept of sciences and source of knowledge; and lack of policy on collaboration. Lack of exposure to traditional medicine seems to impede opportunities to accept and work with traditional healers. Exposure and training at undergraduate level regarding the traditional health system is recommended. Policy guidelines on collaborations are urgently required. PMID:27380856

  17. Does identity shape leadership and management practice? Experiences of PHC facility managers in Cape Town, South Africa.

    PubMed

    Daire, Judith; Gilson, Lucy

    2014-09-01

    In South Africa, as elsewhere, Primary Health Care (PHC) facilities are managed by professional nurses. Little is known about the dimensions and challenges of their job, or what influences their managerial practice. Drawing on leadership and organizational theory, this study explored what the job of being a PHC manager entails, and what factors influence their managerial practice. We specifically considered whether the appointment of professional nurses as facility managers leads to an identity transition, from nurse to manager. The overall intention was to generate ideas about how to support leadership development among PHC facility managers. Adopting case study methodology, the primary researcher facilitated in-depth discussions (about their personal history and managerial experiences) with eight participating facility managers from one geographical area. Other data were collected through in-depth interviews with key informants, document review and researcher field notes/journaling. Analysis involved data triangulation, respondent and peer review and cross-case analysis. The experiences show that the PHC facility manager's job is dominated by a range of tasks and procedures focused on clinical service management, but is expected to encompass action to address the population and public health needs of the surrounding community. Managing with and through others, and in a complex system, requiring self-management, are critical aspects of the job. A range of personal, professional and contextual factors influence managerial practice, including professional identity. The current largely facility-focused management practice reflects the strong nursing identity of managers and broader organizational influences. However, three of the eight managers appear to self-identify an emerging leadership identity and demonstrate related managerial practices. Nonetheless, there is currently limited support for an identity transition towards leadership in this context. Better

  18. Does identity shape leadership and management practice? Experiences of PHC facility managers in Cape Town, South Africa

    PubMed Central

    Daire, Judith; Gilson, Lucy

    2014-01-01

    In South Africa, as elsewhere, Primary Health Care (PHC) facilities are managed by professional nurses. Little is known about the dimensions and challenges of their job, or what influences their managerial practice. Drawing on leadership and organizational theory, this study explored what the job of being a PHC manager entails, and what factors influence their managerial practice. We specifically considered whether the appointment of professional nurses as facility managers leads to an identity transition, from nurse to manager. The overall intention was to generate ideas about how to support leadership development among PHC facility managers. Adopting case study methodology, the primary researcher facilitated in-depth discussions (about their personal history and managerial experiences) with eight participating facility managers from one geographical area. Other data were collected through in-depth interviews with key informants, document review and researcher field notes/journaling. Analysis involved data triangulation, respondent and peer review and cross-case analysis. The experiences show that the PHC facility manager’s job is dominated by a range of tasks and procedures focused on clinical service management, but is expected to encompass action to address the population and public health needs of the surrounding community. Managing with and through others, and in a complex system, requiring self-management, are critical aspects of the job. A range of personal, professional and contextual factors influence managerial practice, including professional identity. The current largely facility-focused management practice reflects the strong nursing identity of managers and broader organizational influences. However, three of the eight managers appear to self-identify an emerging leadership identity and demonstrate related managerial practices. Nonetheless, there is currently limited support for an identity transition towards leadership in this context. Better

  19. Micropulse lidar observations of tropospheric aerosols over northeastern South Africa during the ARREX and SAFARI 2000 dry season experiments

    NASA Astrophysics Data System (ADS)

    Campbell, James R.; Welton, Ellsworth J.; Spinhirne, James D.; Ji, Qiang; Tsay, Si-Chee; Piketh, Stuart J.; Barenbrug, Marguerite; Holben, Brent N.

    2003-07-01

    During the Aerosol Recirculation and Rainfall Experiment (ARREX 1999) and Southern African Regional Science Initiative (SAFARI 2000) dry season experiments, a micropulse lidar (523 nm) instrument was operated at the Skukuza Airport in northeastern South Africa. The lidar was colocated with a diverse array of passive radiometric equipment. For SAFARI 2000, a daytime time series of layer mean aerosol optical properties, including layer mean extinction-to-backscatter ratios and vertical extinction cross-section profiles are derived from the synthesis of the lidar data and aerosol optical depths from available AERONET Sun photometer data. Combined with derived spectral Angstrom exponents, normalized broadband flux measurements, and calculated air mass back-trajectories, the temporal evolution of the surface aerosol layer optical properties is analyzed for climatological trends. For dense biomass smoke events the extinction-to-backscatter ratio is between 50 and 90 sr, and corresponding spectral Angstrom exponent values are between 1.50 and 2.00. Observations of an advecting smoke event during SAFARI 2000 are shown. The smoke was embedded within two distinct stratified thermodynamic layers causing the particulate mass to advect over the instrument array in an incoherent manner on the afternoon of 1 September 2000. Significant surface broadband flux forcing of over -50 W/m2 was measured in this event. The evolution of the vertical aerosol extinction profile is profiled using the lidar data. Finally, observations of persistent elevated aerosol layers during ARREX 1999 are presented and discussed. Back-trajectory analyses combined with lidar and Sun photometer measurements indicate the likelihood for these aerosols being the result of long-range particulate transport from the southern and central South America.

  20. Site Characterization of the Source Physics Experiment Phase II Location Using Seismic Reflection Data

    SciTech Connect

    Sexton, Emily; Snelson, Catherine M; Chipman, Veraun D; Emer, Dudley; White, Bob; Emmit, Ryan; Wright, Al; Drellack, Sigmund; Huckins-Gang, Heather; Mercadante, Jennifer; Floyd, Michael; McGowin, Chris; Cothrun, Chris; Bonal, Nedra

    2013-12-05

    An objective of the Source Physics Experiment (SPE) is to identify low-yield nuclear explosions from a regional distance. Low-yield nuclear explosions can often be difficult to discriminate among the clutter of natural and man-made explosive events (e.g., earthquakes and mine blasts). The SPE is broken into three phases. Phase I has provided the first of the physics-based data to test the empirical models that have been used to discriminate nuclear events. The Phase I series of tests were placed within a highly fractured granite body. The evolution of the project has led to development of Phase II, to be placed within the opposite end member of geology, an alluvium environment, thereby increasing the database of waveforms to build upon in the discrimination models. Both the granite and alluvium sites have hosted nearby nuclear tests, which provide comparisons for the chemical test data. Phase III of the SPE is yet to be determined.

  1. Accessing Sexual and Reproductive Health Information and Services: A Mixed Methods Study of Young Women's Needs and Experiences in Soweto, South Africa.

    PubMed

    Lince-Deroche, Naomi; Hargey, Adila; Holt, Kelsey; Shochet, Tara

    2015-03-01

    Young women and girls in South Africa are at high risk of unintended pregnancy and HIV. Previous studies have reported barriers to contraceptive and other sexual and reproductive health (SRH) services among young women in this context. We aimed to assess young women's SRH knowledge and experiences and to determine how they get SRH information and services in Soweto, South Africa using quantitative and qualitative methods. Young women, aged 18-24, recruited from primary health clinics and a shopping mall, reported that they have access to SRH information and know where to obtain services. However there are challenges to accessing and utilizing information and services including providers' unsupportive attitudes, uneven power dynamics in relationships and communication issues with parents and community members. There is a need to assist young women in understanding the significance of SRH information. They need access to age-appropriate, youth-friendly services in order to have healthy sexual experiences. PMID:26103697

  2. Scientific and educational advancements across a socio-economic gradient: Experiences from a joint USA-South Africa project on water resources modeling

    NASA Astrophysics Data System (ADS)

    Wagener, T.; Hughes, D.

    2011-12-01

    One might be tempted to assume that joint projects between partners in developed and developing countries follow a one-way path in which scientific knowledge is passed on from developed to less developed regions of the world. However, experience shows that projects of this type are generally neither successful nor sustainable unless a strong two-way exchange can be established. We present results of a multi-year collaboration focused on establishing a water resources modeling framework for South Africa that combines local knowledge with state-of-the-art modeling strategies to improve regional decision making. The result is a modeling framework that allows for the use of diverse data sources to reduce predictive uncertainty in a data sparse environment with limited local resources. We will present scientific study results, personal experience from the interaction and a broader outlook on scientific and educational needs for hydrology in Africa.

  3. Experience Of A US Air Force Surgical And Critical Care Team Deployed In Support Of Special Operations Command Africa.

    PubMed

    Delmonaco, Brian L; Baker, Aaron; Clay, Jared; Kilbourn, James

    2016-01-01

    An eight-person team of conventional US Air Force (USAF) medical providers deployed to support US Special Operations Forces (SOF) in North and West Africa for the first time in November 2014. The predeployment training, operations while deployed, and lessons learned from the challenges of performing surgery and medical evacuations in the remote desert environment of Chad and Niger on the continent of Africa are described. The vast area of operations and far-forward posture of these teams requires cooperation between partner African nations, the French military, and SOF to make these medical teams effective providers of surgical and critical care in Africa. The continuous deployment of conventional USAF medical providers since 2014 in support of US Special Operations Command Africa is challenging and will benefit from more medical teams and effective air assets to provide casualty evacuation across the vast area of operations. PMID:27045506

  4. Ethical challenges in cluster randomized controlled trials: experiences from public health interventions in Africa and Asia

    PubMed Central

    Azad, Kishwar; Fernandez, Armida; Manandhar, Dharma S; Mwansambo, Charles W; Tripathy, Prasanta; Costello, Anthony M

    2009-01-01

    Abstract Public health interventions usually operate at the level of groups rather than individuals, and cluster randomized controlled trials (RCTs) are one means of evaluating their effectiveness. Using examples from six such trials in Bangladesh, India, Malawi and Nepal, we discuss our experience of the ethical issues that arise in their conduct. We set cluster RCTs in the broader context of public health research, highlighting debates about the need to reconcile individual autonomy with the common good and about the ethics of public health research in low-income settings in general. After a brief introduction to cluster RCTs, we discuss particular challenges we have faced. These include the nature of – and responsibility for – group consent, and the need for consent by individuals within groups to intervention and data collection. We discuss the timing of consent in relation to the implementation of public health strategies, and the problem of securing ethical review and approval in a complex domain. Finally, we consider the debate about benefits to control groups and the standard of care that they should receive, and the issue of post-trial adoption of the intervention under test. PMID:19876544

  5. Tropical forest recovery from logging: a 24 year silvicultural experiment from Central Africa

    PubMed Central

    Gourlet-Fleury, Sylvie; Mortier, Frédéric; Fayolle, Adeline; Baya, Fidèle; Ouédraogo, Dakis; Bénédet, Fabrice; Picard, Nicolas

    2013-01-01

    Large areas of African moist forests are being logged in the context of supposedly sustainable management plans. It remains however controversial whether harvesting a few trees per hectare can be maintained in the long term while preserving other forest services as well. We used a unique 24 year silvicultural experiment, encompassing 10 4 ha plots established in the Central African Republic, to assess the effect of disturbance linked to logging (two to nine trees ha−1 greater than or equal to 80 cm DBH) and thinning (11–41 trees ha−1 greater than or equal to 50 cm DBH) on the structure and dynamics of the forest. Before silvicultural treatments, above-ground biomass (AGB) and timber stock (i.e. the volume of commercial trees greater than or equal to 80 cm DBH) in the plots amounted 374.5 ± 58.2 Mg ha−1 and 79.7 ± 45.9 m3 ha−1, respectively. We found that (i) natural control forest was increasing in AGB (2.58 ± 1.73 Mg dry mass ha−1 yr−1) and decreasing in timber stock (−0.33 ± 1.57 m3 ha−1 yr−1); (ii) the AGB recovered very quickly after logging and thinning, at a rate proportional to the disturbance intensity (mean recovery after 24 years: 144%). Compared with controls, the gain almost doubled in the logged plots (4.82 ± 1.22 Mg ha−1 yr−1) and tripled in the logged + thinned plots (8.03 ± 1.41 Mg ha−1 yr−1); (iii) the timber stock recovered slowly (mean recovery after 24 years: 41%), at a rate of 0.75 ± 0.51 m3 ha−1 yr−1 in the logged plots, and 0.81 ± 0.74 m3 ha−1 yr−1 in the logged + thinned plots. Although thinning significantly increased the gain in biomass, it had no effect on the gain in timber stock. However, thinning did foster the growth and survival of small- and medium-sized timber trees and should have a positive effect over the next felling cycle. PMID:23878332

  6. Tropical forest recovery from logging: a 24 year silvicultural experiment from Central Africa.

    PubMed

    Gourlet-Fleury, Sylvie; Mortier, Frédéric; Fayolle, Adeline; Baya, Fidèle; Ouédraogo, Dakis; Bénédet, Fabrice; Picard, Nicolas

    2013-01-01

    Large areas of African moist forests are being logged in the context of supposedly sustainable management plans. It remains however controversial whether harvesting a few trees per hectare can be maintained in the long term while preserving other forest services as well. We used a unique 24 year silvicultural experiment, encompassing 10 4 ha plots established in the Central African Republic, to assess the effect of disturbance linked to logging (two to nine trees ha⁻¹ greater than or equal to 80 cm DBH) and thinning (11-41 trees ha⁻¹ greater than or equal to 50 cm DBH) on the structure and dynamics of the forest. Before silvicultural treatments, above-ground biomass (AGB) and timber stock (i.e. the volume of commercial trees greater than or equal to 80 cm DBH) in the plots amounted 374.5 ± 58.2 Mg ha⁻¹ and 79.7 ± 45.9 m³ ha⁻¹, respectively. We found that (i) natural control forest was increasing in AGB (2.58 ± 1.73 Mg dry mass ha⁻¹ yr⁻¹) and decreasing in timber stock (-0.33 ± 1.57 m³ ha⁻¹ yr⁻¹); (ii) the AGB recovered very quickly after logging and thinning, at a rate proportional to the disturbance intensity (mean recovery after 24 years: 144%). Compared with controls, the gain almost doubled in the logged plots (4.82 ± 1.22 Mg ha⁻¹ yr⁻¹) and tripled in the logged + thinned plots (8.03 ± 1.41 Mg ha⁻¹ yr⁻¹); (iii) the timber stock recovered slowly (mean recovery after 24 years: 41%), at a rate of 0.75 ± 0.51 m³ ha⁻¹ yr⁻¹ in the logged plots, and 0.81 ± 0.74 m³ ha⁻¹ yr⁻¹ in the logged + thinned plots. Although thinning significantly increased the gain in biomass, it had no effect on the gain in timber stock. However, thinning did foster the growth and survival of small- and medium-sized timber trees and should have a positive effect over the next felling cycle. PMID:23878332

  7. Building the Capacity to Build Capacity in e-Health in Sub-Saharan Africa: The KwaZulu-Natal Experience

    PubMed Central

    2012-01-01

    Abstract Background: Sub-Saharan Africa has a disproportionate burden of disease and an extreme shortage of health workers. There are already too few doctors to train doctors in specialities and sub-specialties. E-health is seen as a possible solution through distance education, telemedicine, and computerized health information systems but there are few people trained in e-health. We describe 12 years of experience at the University of KwaZulu-Natal (UKZ-N) in education and training in postgraduate medical disciplines, medical informatics, and telemedicine. Medical Education: Videoconferencing of seminars and grand rounds to regional training hospitals commenced in 2001 and has grown to 40 h of interactive conferencing taking place weekly during academic terms involving over 33,000 participants in 2010. Videoconferenced sessions are directly recorded to DVD and DVDs are sent to other medical schools in Africa that do not have the infrastructure to directly connect. E-health Education: Students and academic staff were initially sent to the United States for training in medical informatics and workshops were held in South Africa for people from sub-Saharan Africa. This led to the development of postgraduate academic programs in medical informatics and telemedicine at UKZ-N. African students were then brought to UKZ-N for training. The model was changed from UKZ-N to students and staff based at their home universities with the aim of building capacity in the staff at partner institutions so that they can in time offer their own e-health academic programs. Conclusions: The need for capacity development in all aspects of e-health in sub-Saharan Africa is great and innovative solutions are required. PMID:22150714

  8. The GLIMPCE seismic experiment: Onshore refraction and wide-angle reflection observations from a fan line over the Lake Superior Midcontinent Rift System

    NASA Astrophysics Data System (ADS)

    Epili, Duryodhan; Mereu, Robert F.

    The 1986 GLIMPCE experiment (Great Lakes International Multidisciplinary Program for Crustal Evolution) was a combined on-ship seismic reflection and onshore seismic refraction experiment designed to determine the structure of the crust beneath the Great Lakes. The main tectonic targets of interest were the Midcontinent Rift System, the Grenville Front, the Penokean and Huronian Fold Belts and the Michipicoten Greenstone Belt. The source of the seismic energy came from a large air gun array fired at closely spaced intervals (50-350 m) over several long lines (150-350 km) crossing the lakes. Major participants of this experiment were the Geological Survey of Canada, the United States Geological Survey and a number of universities and research institutes on both sides of the border. The University of Western Ontario (UWO) collected data at five separate land stations using portable seismic refraction instruments. In this paper we present the results of a fan profile which was recorded from a UWO station on Michipicoten Island for the N-S line A which crossed the axis of the Lake Superior Synclinal Basin. The azimuth and distance ranges for this profile were 237 to 321 degrees and 120 to 170 km respectively. Detailed observations of the record sections show that p. is not a simple arrival but forms a rather complex pattern of irregular multiple arrivals. The wide-angle PmP reflection signals from the Moho are strong and well obilerved only for the shots fired near the ends of the line. The signals from the middle of the profile arrive relatively late and form very weak complex wave trains. These results indicate that the Moho in that area is probably greatly disrupted and gives added support to the rift theory for the structure under the lake. The observations also support the results of earlier crustal studies of Lake Superior which showed that the crust under the eastern part of the lake was exceedingly thick.

  9. Testing Models of Magmatic and Hydrothermal Segmentation: A Three-Dimensional Seismic Tomography Experiment at the Endeavour Ridge (Invited)

    NASA Astrophysics Data System (ADS)

    Wilcock, W. S.; Toomey, D. R.; Hooft, E. E.; Weekly, R. T.; Wells, A. E.

    2010-12-01

    Competing models for what controls the segmentation and intensity of ridge crest processes are at odds on the scale of mantle and crustal magmatic segmentation, the distribution of hydrothermal venting with respect to a volcanic segment and the properties of the thermal boundary layer that transports energy between the magmatic and hydrothermal systems. The presence of an axial magma chamber (AMC) reflector beneath the central portion of the Endeavour segment of the Juan de Fuca ridge, as well as systematic along axis changes in seafloor depth, ridge crest morphology and hydrothermal venting provide an ideal target for testing conflicting hypotheses. In late summer 2009, we conducted an active source seismic experiment on the Endeavour segment of the Juan de Fuca Ridge. A total of 5,567 airgun shots from the 36-gun, 6,600 in3 airgun array of the R/V Marcus G. Langseth were recorded by 68 short-period ocean bottom seismometers (OBSs) deployed at 64 sites. The experimental geometry utilized 3 nested scales and was designed to image (1) crustal thickness variations within 25 km of the axial high (0 to 900 kyr); (2) the map view heterogeneity and anisotropy of the topmost mantle beneath the spreading axis; (3) the three-dimensional structure of the crustal magmatic system and (4) the detailed three-dimensional, shallow crustal thermal structure beneath the Endeavour vent fields. At the segment scale, six 100-km-long ridge-parallel shot lines were obtained at distances of 16, 23 and 30 km to both sides of the ridge axis with OBSs on all but the outer lines. At the along-axis scale of the AMC reflector, shot lines are spaced 1 km apart and OBSs 8 km apart within a 60 x 20 km2 region. At the vent field scale, shots were obtained on a 500 x 500 m2 grid and OBSs spaced 5 km apart within a 20 x 10 km2 region. All the shooting lines were collected with a 9 m source depth to obtain impulsive arrivals at shorter ranges but the outer lines were also shot with a 15 m source depth

  10. Monitoring of glacial seismic events from Greenland at regional distances: experience from the POLENET/LAPNET experiment during the IPY 2007-2009

    NASA Astrophysics Data System (ADS)

    Kozlovskaya, E.; Pedersen, H.; Plomerova, J.; Achauer, U.; Kissling, E. H.; Sanina, I.; Jämsen, T.; Silvennoinen, H.; Pequegnat, C.; Hurskainen, R.; Hausmann, H.; Jedlicka, P.; Aleshine, I.; Bourova, E.; Bodvarsson, R.; Brueckl, E. P.; Eken, T.; Heikkinen, P. J.; Houseman, G. A.; Johnsen, H.; Kari, K.; Munzarova, H.; Roberts, R.; Ruzek, B.; Hosein Shomali, Z.; Schweitzer, J.; Shaumyan, A.; Vecsey, L.; Volosov, S.

    2010-12-01

    Monitoring of glacial earthquakes from Greenland was one of the major targets of the POLENET/LAPNET passive seismic experiment in northern Fennoscandia (northern parts of Finland, Sweden, Norway and Russian Karelia) during the IPY 2007-2009. The POLENET/LAPNET array, with the average spacing between stations of 70 km, was designed to solve specific tasks of polar seismology. The collected POLENET/LAPNET dataset includes high-frequency continuous data (sampling rate from 50 to 100 sps) of 37 temporary stations, which were in operation during the time frame from 01.05.2008 to 31.09.2009, and of 21 stations of selected permanent networks in Fennoscandia. The first results of the experiment have shown that the POLENET/LAPNET array, located at regional distances from Greenland, recorded more such events than it has been recorded by the Global Seismographic Network during the same observation period. The waveforms of events recorded by the array differ from both long-period waveforms of glacial earthquakes recorded at teleseismic distances and from short-period glacial rumblings recorded at local distances. Recordings of glacial earthquakes obtained by the array contain the long-period energy only. In many cases the events were recorded in groups within the time interval of up to 1 hour. Generally, the waveforms of events within the same group are different and the events not always originate from the same location. For some of the events it was possible to recognize not only dispersed long-period surface wave, but also the first arrival of a long-period P-wave. This suggests that source duration of these events was long. Diversity of the waveforms of glacial events recorded by the POLENET/LAPNET array can be considered as evidence for diversity of source mechanisms of these events.

  11. 1978 Yellowstone-eastern Snake River Plain seismic profiling experiment: Data and upper crustal structure of the Yellowstone region

    SciTech Connect

    Schilly, M.M.; Smith, R.B.; Braile, L.W.; Ansorge, J.

    1982-04-10

    Eleven in-line refraction profiles, recorded to distances of 300 km, and one azimuthal fan plot were constructed from data recorded with a 150-station array in the Yellowstone National Park area during the 1978 Yellowstone-Snake River Plain seismic experiment. Interpretations of the data suggest that the crustal P wave velocity model for the Yellowstone region is characterized by (1) an averaged 10-km-thick upper crustal layer, V/sub p/ = 6.0 km/s, (2) an average crustal velocity of 6.3 km/s, and (3) a total crustal thickness of 44 km. Velocity models are presented for profiles that emphasize the upper crust and show (1) a decrease in the depth to the top of the upper crustal crystalline basement from 5 km in southwestern Yellowstone near Island Park to 1 km at the northeast side of the Yellowstone Plateau that is interpreted as a progressive thinning of the silicic surface volcanic layer to the northeast and (2) evidence for a large lateral inhomogeneity interpreted to be a low-velocity body, with a decrease of at least 10% in P wave velocity, located beneath the northeast corner of the Yellowstone Plateau. The low-velocity zone coincides with a local -30-mgal residual gravity anomaly and is located beneath part of the Sour Creek resurgent dome and part of the Hot Springs Basin, the largest hydrothermal system in Yellowstone. The low-velocity body has a maximum depth to the top of 3 km and a minimum depth to the bottom of 9 km and may represent a zone of partial melt. In comparison to the thermally undisturbed upper crust of the surrounding Rocky Mountains the upper crust of the northeastern Yellowstone plateau appears laterally inhomogeneous in velocity and layer thickness, suggesting effects of thermal and magma intrusion, whereas the lower crust appears relatively homogeneous.

  12. Seismic moment tensors of acoustic emissions recorded during laboratory rock deformation experiments: sensitivity to attenuation and anisotropy

    NASA Astrophysics Data System (ADS)

    Stierle, Eva; Vavryčuk, Václav; Kwiatek, Grzegorz; Charalampidou, Elli-Maria; Bohnhoff, Marco

    2016-04-01

    Seismic moment tensors can provide information on the size and orientation of fractures producing acoustic emissions (AEs) and on the stress conditions in the sample. The moment tensor inversion of AEs is, however, a demanding procedure requiring carefully calibrated sensors and accurate knowledge of the velocity model. In field observations, the velocity model is usually isotropic and time independent. In laboratory experiments, the velocity is often anisotropic and time dependent and attenuation might be significant due to opening or closure of microcracks in the sample during loading. In this paper, we study the sensitivity of the moment tensor inversion to anisotropy of P-wave velocities and attenuation. We show that retrieved moment tensors critically depend on anisotropy and attenuation and their neglect can lead to misinterpretations of the source mechanisms. The accuracy of the inversion also depends on the fracturing mode of AEs: tensile events are more sensitive to P-wave anisotropy and attenuation than shear events. We show that geometry of faulting in anisotropic rocks should be studied using the source tensors, since the P- and T-axes of the moment tensors are affected by velocity anisotropy and deviate from the true orientation of faulting. The stronger the anisotropy is, the larger the deviations are. Finally, we prove that the moment tensor inversion applied to a large dataset of AEs can be utilized to provide information on the attenuation parameters of the rock sample. The method is capable of measuring anisotropic attenuation in the sample and allows for detection of dilatant cracking according to the stress regime.

  13. Seafloor surface processes and subsurface paleo-channel unconformities mapped using multi-channel seismic and multi-beam sonar data from the Galicia 3D seismic experiment.

    NASA Astrophysics Data System (ADS)

    Gibson, J. C.; Shillington, D. J.; Sawyer, D. S.; Jordan, B.; Morgan, J. K.; Ranero, C.; Reston, T. J.

    2015-12-01

    In this study we use geophysical methods, stratigraphic relationships, and coring/drilling leg results to assess possible controls on deep-sea channel formation in order to further constrain paleo-channel (PC) and associated unconformity timing/source processes. A series of cut and fill PC are mapped in 3D multi-channel seismic (MCS) data and compared with multi-beam (MB) sonar bathymetry/backscatter data collected during the Galicia 3D survey with the R/V Marcus G. Langseth (2013). The MCS data were collected using four 6 km streamers spaced at 200 m resulting in 25 m x 25 m common mid-point bins within the ~67 km x 20 km 3D volume. The MB data were collected at an average depth of ~4900 m with a constrained swath width of 4.5 km resulting in 11.25x overlap while enabling 25-m bathymetry and 10-m backscatter grids. The PC lie below the mouth of a submarine canyon at the edge of the Galicia abyssal plain and cut pre/syn-rift sediments; they are bound by a rift block to the north and paleo-levees to the south (maximum height of ~180m). From drilling results, the most recent PC is late Miocene in age. In this study, four PC are traced into the basin as unconformities. Several of the PC/unconformities are tentatively correlated with previously interpreted Pyrenean orogeny/compressional Miocene/Oligocene tectonic events. However, one PC/unconformity within this interval has not been previously interpreted. In order test the hypothesis that the unconformities are the result of a significant change in base level indicated by a low shale/sand (SS) ratio, we use seismic surface attributes to calculate the SS ratio and trace the horizontal extent of the unconformities. Additionally, the MB/MCS seafloor morphology reveals sedimentary waves outboard of the canyon mouth. We use backscatter data to compare the extent of recent processes (e.g., Pleistocene glaciation/de-glaciation) with the unconformities by mapping the surface/shallow subsurface SS ratio (volume scattering).

  14. Seismic structure of uppermost mantle and crust beneath West Philippine Basin and Kyusyu-Palau ridge by seafloor borehole seismometer, OBS and airgun experiment

    NASA Astrophysics Data System (ADS)

    Arisaka, M.; Shinohara, M.; Yamada, T.; Mochizuki, K.; Kaiho, Y.; Araki, E.; Nakahigashi, K.; Ito, M.; Shiobara, H.; Suehiro, K.; Kanazawa, T.

    2003-12-01

    The western Pacific area including the Philippine Sea plate is characterized by many island-arc and trench systems and back-arc basins, which are estimated to correspond to subduction of oceanic plates. The Philippine Sea plate is divided into two regions by the Kyushu-Palau Ridge running from north to south. There are the Shikoku basin and the Parece-Vela basin in the eastern part, and the West Philippine basin exists in the western part. It is important to study an uppermost mantle and crustal seismic structure of the Philippine Sea plate to consider the formation process and to estimate the development process of an island-arc and trench system. In addition, the borehole broadband seismic station (WP-1) was installed in the easternmost part of the West Philippine basin in 2001 and is in operation. To obtain the seismic structure is also important for analyses of the data retrieved from the WP-1. We conducted seismic surveys with ocean bottom seismometers (OBS), the WP-1 and controlled sources to obtain the seismic crustal structure around the WP-1 observatory March 2002, October 2002 and May 2003 using the R/V KAIREI, JAMSTEC. The total length of the profile parallel to the ridge (NS line) is about 100 km. The profile perpendicular to the ridge (EW line) has approximately 120 km long in total and crosses the ridge and the WP-1 borehole seismometer. As the controlled sources, we used a GI gun (3 liters) and Bolt 1500LL type (1500cu.in.) airguns. Number and kind of airguns differed in each experiment. Total 12 OBSs were deployed at an average interval of 10km(NS line) and 15km (EW line) for the experiments. A seismic velocity model for shallow structure is derived from using a tau-p inversion of individual OBS records. A deep structure beneath the profile is estimated by using a two-dimensional ray tracing method. The preliminary results for the NS line are obtained. P-wave velocity of the sedimentary layer is 2.7 km/s and the thickness is about 500 m. These

  15. Passive seismic experiment and receiver functions analysis to determine crustal structure at the contact of the northern Dinarides and southwestern Pannonian Basin

    NASA Astrophysics Data System (ADS)

    Šumanovac, Franjo; Hegedűs, Endre; Orešković, Jasna; Kolar, Saša; Kovács, Attila C.; Dudjak, Darko; Kovács, István J.

    2016-06-01

    Passive seismic experiment was carried out at the SW contact of the Dinarides and Pannonian basin to determine the crustal structure and velocity discontinuities. The aim of the experiment was to define the relationship between the Adriatic microplate and the Pannonian segment as a part of the European plate. Most of the temporary seismic stations were deployed in Croatia along the Alp07 profile-a part of the active-source ALP 2002 project. About 300-km-long profile stretches from Istra peninsula to the Drava river, in a WSW-ESE direction. Teleseismic events recorded on 13 temporary seismic stations along the profile were analysed by P-receiver function method. Two types of characteristic receiver functions (RF) have been identified, belonging to Dinaridic and Pannonian crusts as defined on the Alp07 profile, while in transitional zone there are both types. Three major crustal discontinuities can be identified for the Dinaridic type: sedimentary basement, intracrustal discontinuity and Mohorovičić discontinuity, whereas the Pannonian type revealed only two discontinuities. The intracrustal discontinuity was not observed in the Pannonian type, thus pointing to a single-layered crust in the Pannonian basin. Two interpretation methods were applied: forward modelling of the receiver functions and H-κ stacking method, and the results were compared with the active-source seismic data at deep refraction profile Alp07. The receiver function modelling has given reliable results of the Moho depths that are in accordance with the seismic refraction results at the end of the Alp07 profile, that is in the area of Pannonian crust characterized by simple crustal structure and low seismic velocities (Vp between 5.9 and 6.2 km s-1). In the Dinarides and its peripheral parts, receiver function modelling regularly gives greater Moho depths, up to +15 per cent, due to more complex crustal structure. The depths of the Moho calculated by the H-κ stacking method vary within wide

  16. Passive seismic experiment and receiver functions analysis to determine crustal structure at the contact of the northern Dinarides and southwestern Pannonian Basin

    NASA Astrophysics Data System (ADS)

    Šumanovac, Franjo; Hegedűs, Endre; Orešković, Jasna; Kolar, Saša; Kovács, Attila C.; Dudjak, Darko; Kovács, István J.

    2016-03-01

    Passive seismic experiment was carried out at the SW contact of the Dinarides and Pannonian basin to determine the crustal structure and velocity discontinuities. The aim of the experiment was to define the relationship between the Adriatic microplate and the Pannonian segment as a part of the European plate. Most of the temporary seismic stations were deployed in Croatia along the Alp07 profile - a part of the active-source ALP 2002 project. About 300 km long profile stretches from Istra peninsula to the Drava river, in a WSW-ESE direction. Teleseismic events recorded on 13 temporary seismic stations along the profile were analysed by P-receiver function method. Two types of characteristic receiver functions (RF) have been identified, belonging to Dinaridic and Pannonian crusts as defined on the Alp07 profile, while in transitional zone there are both types. Three major crustal discontinuities can be identified for the Dinaridic type: sedimentary basement, intracrustal discontinuity and Mohorovičić discontinuity, whereas the Pannonian type revealed only two discontinuities. The intracrustal discontinuity was not observed in the Pannonian type, thus pointing to a single-layered crust in the Pannonian basin. Two interpretation methods were applied: forward modelling of the receiver functions and H-κ stacking method, and the results were compared with the active-source seismic data at deep refraction profile Alp07. The receiver function modelling has given reliable results of the Moho depths that are in accordance with the seismic refraction results at the end of the Alp07 profile, i.e. in the area of Pannonian crust characterised by simple crustal structure and low seismic velocities (Vp between 5.9 and 6.2 km s-1). In the Dinarides and its peripheral parts, receiver function modelling regularly gives greater Moho depths, up to +15%, due to more complex crustal structure. The depths of the Moho calculated by the H-κ stacking method vary within wide limits (±13

  17. West Africa

    Atmospheric Science Data Center

    2013-04-16

    ... article title:  Hazy and Dusty Skies over Western Africa     View Larger Image ... of agricultural fires that were burning throughout western Africa during December and early January, and was likely to have been ...

  18. Report for borehole explosion data acquired in the 1999 Los Angeles Region Seismic Experiment (LARSE II), Southern California; Part II, Data tables and plots

    USGS Publications Warehouse

    Murphy, Janice M.; Fuis, Gary S.; Okaya, D.A.; Thygesen, Kristina; Baher, Shirley A.; Rybert, Trond; Kaip, Galen; Fort, Michael D.; Asudeh, Isa; Sell, Russell

    2002-01-01

    The Los Angeles Region Seismic Experiment (LARSE), a joint project of the U.S. Geological Survey (USGS) and the Southern California Earthquake Center (SCEC), was conducted to produce seismic images of the subsurface in the Los Angeles region. Primary targets were major fault systems and sedimentary basins; the goal of the project was to address the earthquake hazard posed by these geologic features. The first phase of data collection (LARSE 1) was completed in 1994; the second phase (LARSE 2) was completed in 1999. A description of the 1999 survey and an overview of both phase I and II is given in Fuis and others (2001). In this report, we present the technical details for the explosion data collected in 1999.

  19. Post-Gondwana geomorphic evolution of southwestern Africa: Implications for hte controls on landscape development from observations and numerical experiments

    NASA Technical Reports Server (NTRS)

    Gilchrist, Alan R.; Kooi, Henk; Beaumont, Christopher

    1994-01-01

    The relationship between morphology and surficial geology is used to quantify the denudation that has occurred across southwestern Africa sicne the fragmentation of Gondwana during the Early Mesozoic. Two main points emerge. Signficant denudation, of the order of kilometers, is widespread except in the Kalahari region of the continental interior. The denudation is systematically distributed so that the continental exterior catchment, draining directly to the Cape basin, is denuded to a greater depth than the interior catchment inland of the Great Escarpment. The analysis also implies tha the majority of the denudation occurred before the beginning of the Cenozoic for both teh exerior and interior catchments. Existing models of landscape development are reviewed, and implications of the denudation chronology are incorporated into a revised conceptual model. This revision implies tha thte primary effect of rifting on the subsequent landscape evolution is that it generates two distinct drainage regimes. A marginal upwarp, or rift flank uplift, separates rejuvenated rivers that drain into the subsiding rift from rivers in the continetal interior that are deflected but not rejuvenated. The two catchments evolve independently unless they are integrated by breaching of hte marginal upwarp. If this occurs, the exterior baselevel is communicated to the interior catchment that is denuded accordingly. Denudation rates generally decrease as the margin evolves, and this decrease is reinforced by the exposure of substrate that is resistant to denudation and/or a change to a more arid climate. The observations do not reveal a particular style of smaller-scale landscape evolution, sucha s escarpment retreat, that is responsible for the differential denudation across the region. It is proposed that numerical model experiments, which reflect the observational insights at the large scale, may identify the smaller-scale controls on escarpment development if the model and natural

  20. Crust Structure across the Longmen Shan Thrust Belt from Seismic Refraction and Wide-angle Reflection Experiment of Sinoprobe02

    NASA Astrophysics Data System (ADS)

    Zhu, X.; Gao, R.; Keller, R. G.; Li, Q.; Guan, Y.; Li, Y.; Li, W.; Lu, Z.; Wang, H.; Xiong, X.; Hou, H.; Dong, J.; Guo, X.; Ye, Z.; Xu, X.; Holloway, S. D.; Chang, J. C.; Kaip, G.; Ingate, S. F.

    2012-12-01

    In this study the seismic refraction and wide-angle reflection experiment has been carried out along a profile (~430 km) across the Songpan-Ganzê block of Eastern Tibet, the Longmen Shan orogenic belt to Sichuan block of the Yangtze craton. Combining with 5 wide-angle refraction seismic profiles of the Global Geoscience Transects (GGT) project carried out in 1986, a velocity model based on traveltime tomography using only the first arrivals of phases Pg and Pn has been obtained and its relative tectonic interpretation has been presented. There are strong deformations of the crust structure in the model from southern part of Songpan-Ganzê block of Eastern Tibet to the northern part of Sichuan block of the Yangtze craton. The thickness of crust varies along the profile as follow: 61~62 km in the area of Songpan-Ganzê block due to the subduction of the Tibetan plateau, 44~47 km beneath Longmen Shan orogenic belt and ~43km in the north part of the Sichuan basin. The thickness of upper crust of the Songpan-Ganzê fold belt changes regularly from the ~20km in the northwest to ~10km in the southeast. However, it is very stable in the Sichuan basin and the thickness is 16~18 km. The total thicknesses of the middle and lower crust beneath the Songpan-Ganzê fold belt change from ~50km in the Eastern Tibetan plateau to ~40km in the Western Yangtze plateau. In the frontal of Sichuan basin the thickness of them decreases to ~30km and is very stable. From the northwest to southeast , the depth of Moho varies from ~62km in the Tibetan plateau, ~60km beneath the Songpan-Ganzê fold belt in the Yangtze plateau, ~45km beneath the Longmen Shan orogenic belt, to ~43km in the Sichuan basin. The discontinuous Moho and existence of double-Moho beneath the Longmen Shan orogenic belt indicate that parts of Moho have been detached from the other parts and escaped downward from their original locations, and it has caused the uplifting and intrusion of magma from the mantle. The velocity

  1. Application of a cross correlation-based picking algorithm to active seismic signals from experiments in Tenerife Island (Canary Islands, Spain)

    NASA Astrophysics Data System (ADS)

    Garcia-Yeguas, A.; Granados, M.; Garcia, L.; Benitez, C.; De la Torre, A.; Alvarez, I.; Diaz, A.; Ibañez, J.

    2013-12-01

    The detection of the arrival time of seismic waves or picking is of great importance in many seismology applications. Traditionally, picking has been carried out by human operators. This process is not systematic and relies completely on the expertise and judgment of the analysts. The limitations of manual picking and the increasing amount of data daily stored in the seismic networks worldwide distributed led to the development of automatic picking algorithms. The accuracy of conventional 'short-term average over long-term average' (STA/LTA) algorithm, the recently developed 'Adaptive Multiband Picking Algorithm' (AMPA) and the proposed cross correlation-based picking algorithm have been assessed using a huge data set composed by active seismic signals from experiments in Tenerife Island (Canary Islands, Spain). The experiment consisted of the deployment of a dense seismic network on Tenerife Island (125 seismometers in total) and the shooting of air-guns around the island with the Spanish Oceanographic Vessel Hespérides (6459 air shots in total). Thus, more than 800.000 signals were recorded and subsequently manually picked. Since the sources and receivers locations are known and considering that the ship travelled a small distance between two consecutive shots, a picking algorithm based on cross-correlation has been proposed. The main advantage of this approach is that the algorithm does not require to set up sophisticated parameters, in contrast to other automatic algorithms. This work was supported in part by the CEI BioTic Granada project (COD55), the Spanish mineco project APASVO (TEC2012-31551), the Spanish micinn project EPHESTOS (CGL2011-29499-C02-01) and the EU project MED-SUV.

  2. The RAMESSES experiment-II. Evidence for accumulated melt beneath a slow spreading ridge from wide-angle refraction and multichannel reflection seismic profiles

    NASA Astrophysics Data System (ADS)

    Navin, D. A.; Peirce, C.; Sinha, M. C.

    1998-12-01

    The RAMESSES study (Reykjanes Axial Melt Experiment: Structural Synthesis from Electromagnetics and Seismics) targeted an apparently magmatically active axial volcanic ridge (AVR), centred on 57°45'N at the Reykjanes Ridge, with the aim of investigating the processes of crustal accretion at a slow spreading mid-ocean ridge. As part of this multicomponent experiment, airgun and explosive wide-angle seismic data were recorded by 10 digital ocean-bottom seismometers (OBSs) along profiles oriented both across- and along-axis. Coincident normal-incidence seismic, bathymetry and underway gravity and magnetic data were also collected. Forward modelling of the seismic and gravity data has revealed layer thicknesses, velocities and densities similar to those observed elsewhere within the oceanic crust near mid-ocean ridges. At 57°45'N, the Reykjanes Ridge has a crustal thickness of approximately 7.5 km on-axis. However, the crust is modelled to decrease in thickness slightly off-axis (i.e. with age), which implies that full crustal thickness is achieved on-axis and that it is subsequently thinned, most likely, by off-axis extension. Modelling also indicates that the AVR is underlain by a thin (~100 m), narrow (~4 km) melt lens some 2.5 km beneath the seafloor, which overlies a broader zone of partial melt approximately 8 km in width. Thus the results of this study provide the first clear evidence for a crustal magma chamber beneath any slow spreading ridge. The size and depth of this magma chamber (the melt lens and underlying zone of partial melt) are similar to those observed beneath fast and intermediate spreading ridges, which implies that the processes of crustal accretion are similar at all spreading rates. Hence the lack of previous observations of magma chambers beneath slow spreading ridges is probably temporally related to the periods of magmatic activity being considerably shorter and more widely spaced in time than at fast and intermediate spreading ridges.

  3. Change Detection via Cross-Borehole and VSP Seismic Surveys for the Source Physics Experiments (SPE) at the Nevada National Security Site (NNSS)

    NASA Astrophysics Data System (ADS)

    Knox, H. A.; Abbott, R. E.; Bonal, N. D.; Aldridge, D. F.; Preston, L. A.; Ober, C.

    2012-12-01

    In support of the Source Physics Experiment (SPE) at the Nevada National Security Site (NNSS), we have conducted two cross-borehole seismic experiments in the Climax Stock. The first experiment was conducted prior to the third shot in this multi-detonation program using two available boreholes and the shot hole, while the second experiment was conducted after the shot using four of the available boreholes. The first study focused on developing a well-characterized 2D pre-explosion Vp model including two VSPs and a seismic refraction survey, as well as quantifying baseline waveform similarity at reoccupied sites. This was accomplished by recording both "sparker" and accelerated weight drop sources on a hydrophone string and surface geophones. In total more than 18,500 unique source-receiver pairs were acquired during this testing. In the second experiment, we reacquired aproximately 8,800 source-receiver pairs and performed a cross-line survey allowing for a 3D post-explosion Vp model. The data acquired from the reoccupied sites was processed using cross-correlation methods and change detection methodologies, including comparison of the tomographic images. The survey design and subsequent processing provided an opportunity to investigate seismic wave propagation through damaged rock. We also performed full waveform forward modelling for a granitic body hosting a perched aquifer. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  4. Southern Africa

    Atmospheric Science Data Center

    2013-04-16

    article title:  Southern Africa     View larger JPEG image ... These Multi-angle Imaging SpectroRadiometer (MISR) images of Africa were acquired on August 25, 2000, during Terra orbit 3655. The left ... of smoke plumes and haze. The southern tip of South Africa is at the bottom of the image, and Zambia is at the top. Distinctive ...

  5. Stress control of seismicity patterns observed during hydraulic fracturing experiments at the Fenton Hill hot dry rock geothermal energy site, New Mexico

    SciTech Connect

    Fehler, M.C.

    1987-04-13

    Seismicity accompanying hydraulic injections into granitic rock is often diffuse rather than falling along a single plane. This diffuse zone of seismicity cannot be attributed to systematic errors in locations of the events. It has often been asserted that seismicity occurs along preexisting joints in the rock that are favorably aligned with the stress field so that slip can occur along them when effective stress is reduced by increasing pore fluid pressure. A new scheme for determining orientations and locations of planes along which the microearthquakes occurred was recently developed. The basic assumption of the method, called the three point method, is that many of the events fall along well defined planes; these planes are often difficult to identify visually in the data because planes of many orientations are present. The method has been applied to four hydraulic fracturing experiments conducted at Fenton Hill as part of a hot dry rock geothermal energy project. While multiple planes are found for each experiment; one plane is common to all experiments. The ratio of shear to normal stress along planes of all orientations is calculated using a best estimate of the current stress state at Fenton Hill. The plane common to all experiments has the highest ratio of shear to normal stress acting along it, so it is the plane most likely to slip. The other planes found by the three point method all have orientations with respect to current principal stresses that are favorable for slip to occur along preexisting planes of weakness. These results are consistent with the assertion that the rock contains pre-existing joints which slip when the effective stress is reduced by the increased pore fluid pressure accompanying the hydraulic injection. Microearthquakes occur along those planes that are favorably aligned with respect to the current stress field.

  6. Lessons from New Experiences in Extension in West Africa: Management Advice for Family Farms and Farmers' Governance

    ERIC Educational Resources Information Center

    Faure, Guy; Kleene, Paul

    2004-01-01

    The emergence of Management Advice for Family Farms in West Africa is closely related to the increased integration of farmers into an open market economy. This is creating a strong demand from farmers for advisory support services, focusing on management of the farm. With the gradual withdrawal of the State from extension services delivery, a…

  7. Detecting weak seismicity in urban areas using waveform stacking and cross correlation: Application to a stimulation experiment

    NASA Astrophysics Data System (ADS)

    Plenkers, K.; Ritter, J.; Schindler, M.

    2012-04-01

    Urban noise often prevents the detection of microseismicity (ML < 2). The problem is well known from many geotechnical production sites, where the need to perform reliable hazard assessment has increased the interest in small seismic events. We study the microseismicity (ML < 2) in the region of Landau, SW Germany. Here, due to thick sediments ( approx. 3 km) and high cultural seismic noise, the signal-to-noise ratio is in general very low for small earthquakes. To gain new insights into the occurrence of very small seismic events we developed a 3-step detection approach and are thus able to identify 207 formerly unknown microseismic events (-1 < ML < 1) with signal-to-noise ratios smaller than three. We use the recordings from a unfavourable broadband network installed for a teleseismic study with station distances of approximately 10 km. First, we apply a short term average to long term average detection algorithm for data reduction. The detection algorithm is affected severely by transient noise signals that do not differ in frequency content, duration and amplitude from the microseismic events searched for. Therefore, the most promising detections, selected by coinciding triggers and high amplitude measures, are reviewed manually. In this way we are able to identify 13 seismic events. Finally, we conduct a cross correlation analysis. As master template we use the stacked waveforms of five manually detected seismic events with a repeating waveform. This search reveals additional 194 events with a cross correlation coefficient exceeding 0.65 which ensures a stable identification. Our analysis shows that the repeating events occurred during the stimulation of a geothermal reservoir within a source region of only about (0.5 km)3.

  8. Towards 4-D Noise-based Seismic Probing of Volcanoes: Perspectives from a Large-N Nodal Experiment on Piton de la Fournaise Volcano

    NASA Astrophysics Data System (ADS)

    Brenguier, F.; Ackerley, N. J.; Nakata, N.; Boué, P.; Campillo, M.; Roux, P.; Shapiro, N.

    2015-12-01

    Noise-based seismology is proving to be a complementary approach to active source or earthquake-based methods for imaging and monitoring the Earth's interior and in particular volcanoes and active faults. Until recently, noise-based imaging and monitoring relied only on the inversion of surface waves reconstructed from correlations of mostly microseismic seismic noise. Compared to body-wave tomography, surface wave tomography succeeds in retrieving lateral sub-surface velocity contrasts but is less efficient in resolving velocity perturbations at depth. Moreover reflected body-waves can carry direct information about sharp interfaces at depth. Extracting body-waves from noise correlations is challenging and the use of Large-N seismic arrays proves to be of great benefit for extracting noisy body-waves from noise-correlations by stacking over a large number of receiver pairs and by applying array processing. The purpose of VolcArray Large-N seismic experiment on Piton de la Fournaise Volcano is to extract body-waves travelling directly through the active magma reservoir located at ~2.5 km depth below the summit crater using noise correlations between arrays of seismic nodes. By beamforming noise on individual arrays, we found an unusual strong directional source of body-wave noise. This is thus a favorable context for retrieving the body-wave component of the Green's function between arrays. However, standard correlation techniques between nodes do not allow deciphering between the reconstructed Green's function and artifacts from the correlation of the strong directional source of body-waves. By applying double beamforming to the noise correlations between arrays, we are able to isolate ballistic body-waves travelling across the magma storage zone at depth. The stability of these reconstructed waves over time is encouraging in the perspectives of high resolution monitoring of the volcano feeding system.

  9. Realizing or relinquishing rights? Homeless youth, their life on the streets and their knowledge and experience of health and social services in Hillbrow, South Africa.

    PubMed

    Mathebula, Sibusiso Donald; Ross, Eleanor

    2013-01-01

    Poverty and youth unemployment are critical issues in South Africa with homeless persons begging at traffic light intersections in all major cities. Support services represent one way of empowering homeless youth. The study therefore examined the experiences of 10 homeless young adult males in Hillbrow, Johannesburg and whether they were aware of local health and social services. Qualitative interviews revealed that participants experienced poor health, addiction, physical violence, psychological trauma, and public hostility. Despite limited education, they were aware of and utilized local health and social services. Findings are discussed in terms of their implications for social work. PMID:23701578

  10. Health policy for sickle cell disease in Africa: experience from Tanzania on interventions to reduce under-five mortality.

    PubMed

    Makani, Julie; Soka, Deogratias; Rwezaula, Stella; Krag, Marlene; Mghamba, Janneth; Ramaiya, Kaushik; Cox, Sharon E; Grosse, Scott D

    2015-02-01

    Tanzania has made considerable progress towards reducing childhood mortality, achieving a 57% decrease between 1980 and 2011. This epidemiological transition will cause a reduction in the contribution of infectious diseases to childhood mortality and increase in contribution from non-communicable diseases (NCDs). Haemoglobinopathies are amongst the most common childhood NCDs, with sickle cell disease (SCD) being the commonest haemoglobinopathy in Africa. In Tanzania, 10,313 children with SCD under 5 years of age (U5) are estimated to die every year, contributing an estimated 7% of overall deaths in U5 children. Key policies that governments in Africa are able to implement would reduce mortality in SCD, focusing on newborn screening and comprehensive SCD care programmes. Such programmes would ensure that interventions such as prevention of infections using penicillin plus prompt diagnosis and treatment of complications are provided to all individuals with SCD. PMID:25365928

  11. Alignment silkworms as seismic animal anomalous behavior (SAAB) and electromagnetic model of a fault: a theory and laboratory experiment

    NASA Astrophysics Data System (ADS)

    Ikeya, Motoji; Matsumoto, Hiroshi; Huang, Qing-Hua

    1998-05-01

    Alignment of silkworms and fish, observed as seismic anomalous animal behavior (SAAB) prior to the Kobe earthquake, were duplicated in a laboratory by applying a pulsed electric field assuming SAAB as electrophysiological responses to the stimuli of seismic electric signals (SES). The animals became aligned perpendicularly to the field direction since their skeletal muscle had a higher resistivity perpendicular to the field direction than parallel to it. An electromagnetic model of a fault is proposed in which dipolar charges, ±q are generated due to the change of seismic stress, σ(t). From a mathematical model, dq/dt=-α(dσ/dt) - q/ɛρ, where α is the charge generation constant like a piezoelectric coefficient, ɛ, the dielectric constant and ρ, the resistivity of bedrock granite. A fault having a length 2a and a displacement or rock rupture time τ, during which the stress is changed, gives pulsed dipolar charge surface densities, +q(t, x) and -q(t, x+2a), or an apparent electric dipole moment of P(t)=2aQ(t)=2aAq(t)=aM 0[ɛρ/(τ-ɛρ)](e-1/τ-e-1/σρ) using the earthquake moment M 0. The fault displacement, D, its initial velocity, D‧ and the stress drop, Δσ give τ=D/D‧=(Δσ/σ 0)(α/β). The field fintensity, F, and seismic current density at a fault zone, J were calculated as F=q/ɛ and J=F/ρ‧ using ρ‧ of water as to give J=0.1-1 A/m2 sufficient to cause SAAB experimentally. The near-field ultra low frequency (ULF) waves generated by P(t) give SES reciprocally proportional to the distance R.

  12. Seismic Ecology

    NASA Astrophysics Data System (ADS)

    Seleznev, V. S.; Soloviev, V. M.; Emanov, A. F.

    The paper is devoted to researches of influence of seismic actions for industrial and civil buildings and people. The seismic actions bring influence directly on the people (vibration actions, force shocks at earthquakes) or indirectly through various build- ings and the constructions and can be strong (be felt by people) and weak (be fixed by sensing devices). The great number of work is devoted to influence of violent seismic actions (first of all of earthquakes) on people and various constructions. This work is devoted to study weak, but long seismic actions on various buildings and people. There is a need to take into account seismic oscillations, acting on the territory, at construction of various buildings on urbanized territories. Essential influence, except for violent earthquakes, man-caused seismic actions: the explosions, seismic noise, emitted by plant facilities and moving transport, radiation from high-rise buildings and constructions under action of a wind, etc. can exert. Materials on increase of man- caused seismicity in a number of regions in Russia, which earlier were not seismic, are presented in the paper. Along with maps of seismic microzoning maps to be built indicating a variation of amplitude spectra of seismic noise within day, months, years. The presence of an information about amplitudes and frequencies of oscillations from possible earthquakes and man-caused oscillations in concrete regions allows carry- ing out soundly designing and construction of industrial and civil housing projects. The construction of buildings even in not seismically dangerous regions, which have one from resonance frequencies coincident on magnitude to frequency of oscillations, emitted in this place by man-caused objects, can end in failure of these buildings and heaviest consequences for the people. The practical examples of detail of engineering- seismological investigation of large industrial and civil housing projects of Siberia territory (hydro power

  13. Seismotectonics and crustal deformation in Africa

    NASA Astrophysics Data System (ADS)

    Ayadi, Abdelhakim

    2016-04-01

    We present the Seismotectonic Map of Africa based on a geological, geophysical and geodetic database including the instrumental seismicity and re-appraisal of large historical events, and harmonization and homogenization of earthquake parameters in catalogues. Although the seismotectonic framework of the African continent is a difficult task, several previous and ongoing projects provide a wealth of data and outstanding results. The database of large and moderate earthquakes in different geological domains includes the coseismic and Quaternary faulting that reveals the complex nature of the active tectonics in Africa. The map benefits from previous works on local and regional seismotectonic maps that needed to be integrated with the lithospheric and upper mantle structures, seismic anisotropy tomography and gravity anomaly, into a continental framework. The synthesis of earthquake and volcanic studies obtained from the analysis of late Quaternary faulting and geodetic data will serve as a basis for hazard calculations and the reduction of seismic risks. The map will be useful for the seismic hazard assessment and earthquake risk mitigation for significant infrastructures and their socio-economic implications in Africa. The constant population increase and infrastructure growth in the continent that exacerbate the earthquake risk justify the necessity for a continuous updating of this map. The database and related map are prepared in the framework of the IGC Project-601 "Seismotectonics and Seismic Hazards in Africa" of UNESCO-IUGS, funded by the Swedish International Development Agency and UNESCO-Nairobi for a period of 4 years (2011 - 2014, now extended to 2016).

  14. Delineating Crustal Deformation by Onshore/Offshore Seismic Experiments in the Backstop Region of the Mediterranean Ridge

    NASA Astrophysics Data System (ADS)

    Papoulia, J. E.; Makris, J.

    2009-12-01

    In order to define the velocity structure of the crust and the sedimentary basins offshore western Peloponnese,we observed 5 seismic profiles. We used 65 4-Component Ocean Bottom Seismographs (OBS) and spaced them inline at 3 Km intervals. Line lengths varied between 60 and 180 Km. Four lines were oriented perpendicular to the coast (NE-SW orientation) and one parallel to it (NW-SE orientation) crossing three out of four NE-SW lines. The seismic energy was generated by a tuned 42 l air gun array that was fired at 125 m intervals. The evaluation procedure of the velocity modeling followed the sequence: First break tomography, layered tomography, forward modeling by two-point ray tracing and finally the Common Station Gathers were depth migrated using the velocity models. In this way we were able to develop the geometry of the crust and sediments and also map the major faults. The crust in the complete area is continental ranging between 27 Km in the north (island of Zakynthos), and 22 to 24 Km in the Kyparissiakos and Messiniakos gulfs to the south. Sedimentary thickness in these basins is significant and in the order of 8 to 10 Km. The “backstop” area that extends to the eastern limit of the Mediterranean Ridge is floored by thinned continental crust of about 20 Km, thickening to about 22 Km to the east. The sediments here are less thick and vary between 5 and 7 Km. Oceanic crust was mapped only along the western part of the two southern lines, beyond the backstop limit, under the Mediterranean Ridge. In the oceanic domain crustal thickness is about 16 Km in water depth of nearly 4 Km. The down dipping of the oceanic layer at the beginning of the subduction has strong reflectivity and clearly marks the border of the continental to the oceanic domains. The Preapulian zone is exposed on Zakynthos and the Strophades islands that tectonically build large thrusts and define the western limit of the offshore folded Ionian zone. High velocity limestone marking the

  15. Research ethics review practices: experiences of the Armauer Hansen Research Institute/All Africa Leprosy and Tuberculosis Rehabilitation and Training Center Ethics Review Committee, Ethiopia.

    PubMed

    Wassie, Liya; Woldeamanuel, Yimtubezinash; Gebre-Mariam, Senkenesh; Feleke, Yeweyenhareg; Temam, Fuad; Hailu, Abebe; Abay, Hiwot; Zerihun, Zeyin; Bussa, Solomon; Aberra, Lensa; Tarekegne, Geremew; Gebre-Yohannes, Asfawessen; Aseffa, Abraham

    2015-01-01

    The need for ethics review committees (ERCs) is imperative in the conduct of research to ensure the protection of the rights, safety and well-being of research participants. However, the capacities of most ERCs in Africa are limited in terms of trained experts, competence, resources as well as standard operating procedures. The aim of this report is to share experiences of one of the local institutional ERCs, the Armauer Hansen Research Institute (AHRI)/All Africa Leprosy and Tuberculosis Rehabilitation and Training Center (ALERT) Ethics Review Committee (AAERC), to other ERCs found in academic and research institutions in the Country. In this report, we used an empirical approach to review archived documents of the AAERC Secretariat to assess the Committee's strengths and weaknesses. The experiences of the AAERC in terms of its composition, routine work activities, learning practices and pitfalls that require general attention are summarized. In spite of this summary, the Committee strongly acknowledges the functions and roles of other ERCs in the Country. In addition, an independent assessment of the Committee's activity in general is warranted to evaluate its performance and further assess the level of awareness or oversights among researchers about the roles of ERCs. PMID:25816497

  16. Seismic reflection data imaging and interpretation from Braniewo2014 experiment using additional wide-angle refraction and reflection and well-logs data

    NASA Astrophysics Data System (ADS)

    Trzeciak, Maciej; Majdański, Mariusz; Białas, Sebastian; Gaczyński, Edward; Maksym, Andrzej

    2015-04-01

    Braniewo2014 reflection and refraction experiment was realized in cooperation between Polish Oil and Gas Company (PGNiG) and the Institute of Geophysics (IGF), Polish Academy of Sciences, near the locality of Braniewo in northern Poland. PGNiG realized a 20-km-long reflection profile, using vibroseis and dynamite shooting; the aim of the reflection survey was to characterise Silurian shale gas reservoir. IGF deployed 59 seismic stations along this profile and registered additional full-spread wide-angle refraction and reflection data, with offsets up to 12 km; maximum offsets from the seismic reflection survey was 3 km. To improve the velocity information two velocity logs from near deep boreholes were used. The main goal of the joint reflection-refraction interpretation was to find relations between velocity field from reflection velocity analysis and refraction tomography, and to build a velocity model which would be consistent for both, reflection and refraction, datasets. In this paper we present imaging results and velocity models from Braniewo2014 experiment and the methodology we used.

  17. Emergency preparedness activities during an ongoing seismic swarm: the experience of the 2011-2012 Pollino (Southern Italy) sequence

    NASA Astrophysics Data System (ADS)

    Masi, A.; Mucciarelli, M.; Chiauzzi, L.; De Costanzo, G.; Loperte, G.

    2012-04-01

    Facing natural disasters effects can be a very difficult task lacking suitable activities and tools to preventively prepare the involved community (people, authorities, professionals, …) to the expected events. Therefore, a suite of preventive actions should be carried out to mitigate natural risks, in particular working to reduce the territorial vulnerability with respect to the specific natural hazard at hand, and to increase people response capacity. In fact, building social capacity helps to increase the risk perception and the people capacity to adapt to and cope with natural hazards. Since October 2011 a seismic swarm is affecting the Pollino mountain range, Southern Italy. At present the sequence is still ongoing, with more than 500 events with M>1, at least 40 well perceived by the population and a maximum magnitude at 3.6. The area mainly affected by the seismic sequence includes 12 villages, with a total population of about 50.000 inhabitants and, according to the current seismic hazard map it has high seismicity level. Such area was hit by a magnitude Ml=5.7 event in 1998 that produced macroseismic intensity not higher that VII-VIII degree of MCS scale and caused one dead, some injured and widespread damage in at least six municipalities. During the sequence, the National Department of Civil Protection (DPC) and the Civil Protection of Basilicata Region decided to put in action some measures aimed at verifying and enhancing emergency preparedness. These actions have been carried out with a constant and fruitful collaboration among the main stakeholders involved (scientific community, local and national governmental agencies, civil protection volunteers, etc) trough the following main activities: 1. collaboration between scientific community and the local and national offices of Civil Protection especially in the relationship with local authorities (e.g. mayors, which are civil protection authorities in their municipality); 2. interaction between DPC

  18. Disclosure of HIV status: experiences and perceptions of persons living with HIV/AIDS and nurses involved in their care in Africa.

    PubMed

    Greeff, Minrie; Phetlhu, Rene; Makoae, Lucia N; Dlamini, Priscilla S; Holzemer, William L; Naidoo, Joanne R; Kohi, Thecla W; Uys, Leana R; Chirwa, Maureen L

    2008-03-01

    Most people with HIV have disclosed their status to someone, often with mixed results. Most health literature seems to favor disclosure by persons living with acquired immunodeficiency syndrome (AIDS), but it could be that to disclose is not always a good thing. We used a descriptive, qualitative research design to explore the experience of human immunodeficiency virus (HIV) and AIDS stigma of people living with HIV or AIDS and nurses involved in their care in Africa. Focus group discussions were held with respondents. We asked them to relate incidents that they themselves observed, and those that they themselves experienced in the community and in families. Thirty-nine focus groups were conducted in five countries in both urban and rural settings. This article is limited to a discussion of data related to the theme of disclosure only. The sub-themes of disclosure were experiences before the disclosure, the process of disclosure, and responses during and after disclosure. PMID:18235155

  19. Next-generation seismic experiments: wide-angle, multi-azimuth, three-dimensional, full-waveform inversion

    NASA Astrophysics Data System (ADS)

    Morgan, Joanna; Warner, Michael; Bell, Rebecca; Ashley, Jack; Barnes, Danielle; Little, Rachel; Roele, Katarina; Jones, Charles

    2013-12-01

    Full-waveform inversion (FWI) is an advanced seismic imaging technique that has recently become computationally feasible in three dimensions, and that is being widely adopted and applied by the oil and gas industry. Here we explore the potential for 3-D FWI, when combined with appropriate marine seismic acquisition, to recover high-resolution high-fidelity P-wave velocity models for subsedimentary targets within the crystalline crust and uppermost mantle. We demonstrate that FWI is able to recover detailed 3-D structural information within a radially faulted dome using a field data set acquired with a standard 3-D petroleum-industry marine acquisition system. Acquiring low-frequency seismic data is important for successful FWI; we show that current acquisition techniques can routinely acquire field data from airguns at frequencies as low as 2 Hz, and that 1 Hz acquisition is likely to be achievable using ocean-bottom hydrophones in deep water. Using existing geological and geophysical models, we construct P-wave velocity models over three potential subsedimentary targets: the Soufrière Hills Volcano on Montserrat and its associated crustal magmatic system, the crust and uppermost mantle across the continent-ocean transition beneath the Campos Basin offshore Brazil, and the oceanic crust and uppermost mantle beneath the East Pacific Rise mid-ocean ridge. We use these models to generate realistic multi-azimuth 3-D synthetic seismic data, and attempt to invert these data to recover the original models. We explore resolution and accuracy, sensitivity to noise and acquisition geometry, ability to invert elastic data using acoustic inversion codes, and the trade-off between low frequencies and starting velocity model accuracy. We show that FWI applied to multi-azimuth, refracted, wide-angle, low-frequency data can resolve features in the deep crust and uppermost mantle on scales that are significantly better than can be achieved by any other geophysical technique, and

  20. South Africa

    Atmospheric Science Data Center

    2013-04-16

    ... atmospheric and oceanic conditions. At Elands Bay in South Africa's Western Cape province, about 1000 tons of rock lobsters beached ... red tide. At the same time, people came from across South Africa to gather the undersized creatures for food. The effects of the losses ...

  1. seismicity and seismotectonics of Libya

    NASA Astrophysics Data System (ADS)

    Ben Suleman, abdunnur

    2015-04-01

    Libya, located at the central Mediterranean margin of the African shield, underwent many episodes of orogenic activity that shaped its geological setting. The present day deformation of Libya is the result of the Eurasia-Africa continental collision. The tectonic evolution of Libya has yielded a complex crustal structure that is composed of a series of basins and uplifts. This study aims to explain in detail the seismicity and seismotectonics of Libya using new data recorded by the recently established Libyan National Seismograph Network (LNSN) incorporating other available geophysical and geological information. Detailed investigations of the Libyan seismicity indicates that Libya has experienced earthquakes of varying magnitudes The seismic activity of Libya shows dominant trends of Seismicity with most of the seismic activity concentrated along the northern coastal areas. Four major clusters of Seismicity were quit noticeable. Fault plane solution was estimated for 20 earthquakes recorded by the Libyan National Seismograph Network in northwestern and northeastern Libya. Results of fault plane solution suggest that normal faulting was dominant in the westernmost part of Libya; strike slip faulting was dominant in northern-central part of Libya. The northern-eastern part of the country suggests that dip-dip faulting were more prevalent.

  2. Increasing diversity in the geosciences through the AfricaArray geophysics field course

    NASA Astrophysics Data System (ADS)

    Vallejo, G.; Emry, E.; Galindo, B. L.; Carranza, V.; Gomez, C. D.; Ortiz, K.; Castro, J. G.; Guandique, J.; Falzone, C.; Webb, S. J.; Manzi, M.; Mngadi, S. B.; Stephens, K.; Chinamora, B.; Whitehead, R.; de Villiers, D. P.; Tshitlho, K.; Delhaye, R. P.; Smith, J. A.; Nyblade, A.

    2014-12-01

    For the past nine years, the AfricaArray diversity program, sponsored by industry, the National Science Foundation, and several partnering universities have supported outstanding U.S. STEM underrepresented minority undergraduates to gain field experience in near-surface geophysical techniques during an 8-week summer program at Penn State University and the University of Witwatersrand (Wits). The AfricaArray geophysics field school, which is run by Wits, has been teaching field-based geophysics to African students for over a decade. In the first 2-3 weeks of the program, the U.S. students are given basic instruction in near-surface geophysics, South African geology, and South African history and culture. The students then join the Wits AfricaArray geophysics field school - working alongside Wits students and students from several other African universities to map the shallow subsurface in prospective areas of South Africa for platinum mining. In addition to the primary goals of collecting and interpreting gravity, magnetic, resistivity, seismic refraction, seismic reflection, and EM data, students spend time mapping geologic units and gathering information on the physical properties of the rocks in the region (i.e. seismic velocity, density, and magnetic susceptibility). Subsurface targets include mafic dikes, faults, the water table, and overburden thickness. Upon returning to the U.S., students spend 2-3 weeks finalizing their project reports and presentations. The program has been effective at not only providing students with fundamental skills in applied geophysics, but also in fostering multicultural relationships, preparing students for graduate work in the geosciences, and attracting STEM students into the geosciences. Student presenters will discuss their experiences gained through the field school and give their impressions about how the program works towards the goal of increasing diversity in the geosciences in the U.S.

  3. Crustal thickness and velocity structure across the Moroccan Atlas from long offset wide-angle reflection seismic data: The SIMA experiment

    NASA Astrophysics Data System (ADS)

    Ayarza, P.; Carbonell, R.; Teixell, A.; Palomeras, I.; Martí, D.; Kchikach, A.; Harnafi, M.; Levander, A.; Gallart, J.; Arboleya, M. L.; Alcalde, J.; Fernández, M.; Charroud, M.; Amrhar, M.

    2014-05-01

    crustal structure and topography of the Moho boundary beneath the Atlas Mountains of Morocco has been constrained by a controlled source, wide-angle seismic reflection transect: the SIMA experiment. This paper presents the first results of this project, consisting of an almost 700 km long, high-resolution seismic profile acquired from the Sahara craton across the High and the Middle Atlas and the Rif Mountains. The interpretation of this seismic data set is based on forward modeling by raytracing, and has resulted in a detailed crustal structure and velocity model for the Atlas Mountains. Results indicate that the High Atlas features a moderate crustal thickness, with the Moho located at a minimum depth of 35 km to the S and at around 31 km to the N, in the Middle Atlas. Upper crustal shortening is resolved at depth through a crustal root where the Saharan crust underthrusts the northern Moroccan crust. This feature defines a lower crust imbrication that, locally, places the Moho boundary at ˜40-41 km depth in the northern part of the High Atlas. The P-wave velocity model is characterized by relatively low velocities, mostly in the lower crust and upper mantle, when compared to other active orogens and continental regions. These low deep crustal velocities together with other geophysical observables such as conductivity estimates derived from MT measurements, moderate Bouguer gravity anomaly, high heat flow, and surface exposures of recent alkaline volcanism lead to a model where partial melts are currently emplaced at deep crustal levels and in the upper mantle. The resulting model supports the existence of a mantle upwelling as mechanism that would contribute significantly to sustain the High Atlas topography. However, the detailed Moho geometry deduced in this work should lead to a revision of the exact geometry and position of this mantle feature and will require new modeling efforts.

  4. Deep seismic reflection data of EDGE U.S. mid-Atlantic continental-margin experiment: Implications for Appalachian sutures and Mesozoic rifting and magmatic underplating

    NASA Astrophysics Data System (ADS)

    Sheridan, Robert E.; Musser, Douglas L.; Glover, Lynn, III; Talwani, Manik; Ewing, John I.; Holbrook, W. Steven; Purdy, G. Michael; Hawman, Robert; Smithson, Scott

    1993-06-01

    The EDGE seismic experiment across the Virginia continental margin delineated a Paleozoic suture, buried Appalachian terranes, and Mesozoic rifting and magmatic events. The seismic grid revealed that the Mesozoic Norfolk rift basin exists only in the northern one-third of the previously mapped area. The north-striking listric border fault of the Norfolk basin half-graben parallels seismic laminations in the basement. The Jurassic volcanic wedge pinches out just landward of the Baltimore Canyon trough hinge zone and downlaps on the hummocky oceanic basement under the continental rise. Under the continental slope, the volcanic wedgereaches depths >9 s (20 km). Two distinct intracrustal reflections at 4.0-5.0 s and at 7.0 s TWIT (two-way traveltime) dip southeastward at low angles (˜15°). The Moho reflection is disrupted where it is intersected by the 7.0 s reflection. Northwest of this point the Moho dips landward; seaward it is horizontal. Seaward of this point, the lower-crustal boundary laminations exist in a narrow interval (10.5-11.0 s) and are of strong amplitude. These changes in the Moho and lower crust represent the seaward edge of the Grenville-age North American crust and the landward edge of Jurassic magmatic underplating. A northwest-dipping reflection observed for the first time on the U.S. Atlantic margin may be the top of the Jurassic magmatic- underplating layer; the northwest-dipping reflection truncates the southeast- dipping 7.0 s TWTT reflection. Landward projection of the 7.0 s reflection yields a north-south trace on the postrift unconformity under the center of lower Chesapeake Bay. This trace is near a basement fault between low-grade metamorphic rocks (Carolina slate-Avalonia) on the east and high-grade rocks (Goochland terrane) on the west. This fault boundary and the southeastdipping 7.0 s reflection probably represent the Taconic suture.

  5. The cost implications of participatory research. Experience of a health services review in a rural region in South Africa

    PubMed

    Doherty; Price

    1998-03-01

    OBJECTIVES: The study objectives were to estimate the total costs incurred by a comprehensive review of primary health care services in a rural region in South Africa, and to determine which of these costs were incurred because of the participatory research techniques employed by the review. DESIGN: The costing study estimated the direct and indirect costs of each component of the review in order to determine total costs. Costs that were linked to participatory research activities were aggregated separately. SETTING: The review that was costed was conducted in an area that included the former 'homeland' KaNgwane and the adjacent areas of 'white' South Africa, in part of what is now known as Mpumalanga Province. SUBJECTS: Not relevant. OUTCOME MEASURES: Direct, indirect, total, research and participation costs were used as outcome measures. RESULTS: Expenditure generated by participatory research techniques was estimated to be almost 14% of the total (direct and indirect) costs. CONCLUSIONS: Despite these costs, participatory research techniques are invaluable in terms of the many benefits they have for a research project. However, because of these costs, it is important that the financing of participatory research should be carefully planned. Projects must budget for the direct costs of participatory techniques, participating organisations and individuals must be committed to bearing the indirect costs of participation, and, increasingly, funders must consider funding these indirect costs. This is important in the South African situation, where public health research relies increasingly on the participation of relevant stakeholders. PMID:9608312

  6. Strengthening public health education in population and reproductive health through an innovative academic partnership in Africa: the Gates partners experience.

    PubMed

    Oni, Gbolahan; Fatusi, Adesegun; Tsui, Amy; Enquselassie, Fikre; Ojengbede, Oladosu; Agbenyega, Tsiri; Ojofeitimi, Ebenezer; Taulo, Frank; Quakyi, Isabella

    2011-01-01

    Poor reproductive health constitutes one of the leading public health problems in the world, particularly in sub-Saharan Africa (SSA). We report here an academic partnership that commenced in 2003 between a US institution and six universities in SSA. The partnership addresses the human resources development challenge in Africa by strengthening public health education and research capacity to improve population and reproductive health (PRH) outcomes in low-resource settings. The partnership's core activities focused on increasing access to quality education, strengthening health research capacity and translating scholarship and science into policy and practices. Partnership programmes focused on the educational dimension of the human resources equation provide students with improved learning facilities and enhanced work environments and also provide faculty with opportunities for professional development and an enhanced capacity for curriculum delivery. By 2007, 48 faculty members from the six universities in SSA attended PRH courses at Johns Hopkins University, 93 PRH courses were offered across the six universities, 625 of their master's students elected PRH concentrations and 158 had graduated. With the graduation of these and future student cohorts, the universities in SSA will systematically be expanding the number of public health practitioners and strengthening programme effectiveness to resolve reproductive health needs. Some challenges facing the partnership are described in this article. PMID:20614360

  7. Investigating the lithospheric structure of Queen Maud Land, East-Antarctica: a year-round seismic experiment

    NASA Astrophysics Data System (ADS)

    Lombardi, Denis; Camelbeeck, Thierry; Rapagnani, Giovanni

    2014-05-01

    The recently launched LISSA project is dedicated to imaging the lithospheric structure of East-Antarctica in relation with the past geodynamics of Gondwana by probing the Sør Rondane Mountains, Queen Maud Land, a belt formed from various metamorphosed terranes mobilized during the Proterozoic Pan-African orogeny. The project benefits from the establishment in 2009 of the Belgian Princess Elisabeth base built at the northern tip of the mountain chain. Our aim is to investigate the deep lithospheric structure of the region by setting up in January 2014 6 broadband seismic stations along a 100 km long North-South profile through the mountain belt striking perpendicular to the various geological terranes. All stations are set up to be year-round autonomously powered, all but one being on rock outcrops and only one being remotely accessible. We describe the technical developpment for year-round operation and the installation site conditions. Then we present the first collected data by analyzing the background seismic noise providing data quality and finally we provide a first inventory of a 1 month event dataset.

  8. Evidence of the impact of deep convection on reactive Volatile Organic Compounds in the upper tropical troposphere during the AMMA experiment in West Africa

    NASA Astrophysics Data System (ADS)

    Bechara, J.; Borbon, A.; Jambert, C.; Colomb, A.; Perros, P. E.

    2010-11-01

    A large dataset of reactive trace gases was collected for the first time over West Africa during the African Monsoon Multidisciplinary Analysis (AMMA) field experiment in August 2006. Volatile Organic Compounds (VOC from C5-C9) were measured onboard the two French aircrafts the ATR-42 and the Falcon-20 by a new instrument AMOVOC (Airborne Measurement Of Volatile Organic Compounds). The goal of this study is (i) to characterize VOC distribution in the tropical region of West Africa (ii) to determine the impact of deep convection on VOC distribution and chemistry in the tropical upper troposphere (UT) and (iii) to characterize its spatial and temporal extensions. Experimental strategy consisted in sampling at altitudes between 0 and 12 km downwind of Mesoscale Convective Systems (MCS) and at cloud base. Biogenic and anthropogenic VOC distribution in West Africa is clearly affected by North to South emission gradient. Isoprene, the most abundant VOC, is at maximum level over the forest (1.26 ppb) while benzene reaches its maximum over the urban areas (0.11 ppb). First, a multiple physical and chemical tracers approach using CO, O3 and relative humidity was implemented to distinguish between convective and non-convective air masses. Then, additional tools based on VOC observations (tracer ratios, proxy of emissions and photochemical clocks) were adapted to characterize deep convection on a chemical, spatial and temporal basis. VOC vertical profiles show a "C-shaped" trend indicating that VOC-rich air masses are transported from the surface to the UT by deep convective systems. VOC mixing ratios in convective outflow are up to two times higher than background levels even for reactive and short-lived VOC (e.g. isoprene up to 0.19 ppb at 12 km-altitude) and are dependent on surface emission type. As a consequence, UT air mass reactivity increases from 0.52 s-1 in non-convective conditions to 0.95 s-1 in convective conditions. Fractions of boundary layer air contained in

  9. Evidence of the impact of deep convection on reactive volatile organic compounds in the upper tropical troposphere during the AMMA experiment in West Africa

    NASA Astrophysics Data System (ADS)

    Bechara, J.; Borbon, A.; Jambert, C.; Colomb, A.; Perros, P. E.

    2009-09-01

    A large dataset of reactive trace gases was collected for the first time over West Africa during the African Monsoon Multidisciplinary Analysis (AMMA) field experiment in August 2006. Volatile Organic Compounds (VOC from C5-C9) were measured onboard the two French aircrafts the ATR-42 and the Falcon-20 by a new instrument AMOVOC. The goal of this study is (i) to characterize VOC distribution in the tropical region of West Africa (ii) to determine the impact of deep convection on VOC distribution and chemistry in the tropical upper troposphere (UT) and (iii) to characterize its spatial and temporal extensions. Experimental strategy consisted in sampling at altitudes between 0 and 12 km downwind of Mesoscale Convective Systems (MCS) and at cloud base. Biogenic and anthropogenic VOC distribution in West Africa is clearly affected by North to South emission gradient. Isoprene, the most abundant VOC, is at maximum level over the forest (1.26 ppb) while benzene reaches its maximum over the urban areas (0.11 ppb). First, a multiple physical and chemical tracers approach using CO, O3 and relative humidity was implemented to distinguish between convective and non-convective air masses. Then, additional tools based on VOC observations (tracer ratios, proxy of emissions and photochemical clocks) were adapted to characterize deep convection on a chemical, spatial and temporal basis. VOC vertical profiles show a "C-shaped" trend indicating that VOC-rich air masses are transported from the surface to the UT by deep convective systems. VOC mixing ratios in convective outflow are up to two times higher than background levels even for reactive and short-lived VOC (e.g. isoprene up to 0.19 ppb at 12 km-altitude) and are dependent on surface emission type. As a consequence, UT air mass reactivity increases from 0.52 s-1 in non-convective conditions to 0.95 s-1 in convective conditions. Fractions of boundary layer air contained in convective outflow are estimated to be 40±15

  10. The SOUTHERN PUNA Seismic Experiment: Shape of the Subducting Nazca Plate, Areas of Concentrated Mantle and Crustal Earthquakes, and Crustal Focal Mechanisms

    NASA Astrophysics Data System (ADS)

    Mulcahy, P.; Chen, C.; Kay, S. M.; Brown, L. D.; Alvarado, P. M.; Sandvol, E. A.; Heit, B.; Yuan, X.

    2010-12-01

    The SOUTHERN PUNA Seismic Experiment in the Central Andes between 25° - 28°S and 70° - 65°W recorded data in a 74-instrument array from Dec 07 to Nov 09 with the purpose of evaluating the structure and seismic character of the mantle and crust at the southern end of the Puna-Antiplano Plateau. Hypocenter locations for local and regional mantle earthquakes from 16 months of continuous recording confirm the persistence of the backarc teleseismic Antofalla Gap in intermediate depth mantle seismicity between 25.5° and 27.5°S consistent with the interpretation of a hot mantle wedge under this region. The best located Wadati Benioff Zone events agree with the subducting Nazca Plate contours of Cahill and Isacks (1992) north of 27°S, but show a more abrupt southward shallowing of contours in agreement with the Anderson et al. (2007) contours outlining the projected path of the already subducted Juan Fernandez Ridge. Another prominent feature in the data is the concentration of hypocenters in the Pipanaco nest to the south of the Antofalla Gap between 27° and 29°S. New PUNA results together with available HCMT solutions indicate NW oriented normal and strike-slip faulting in three general clusters within this nest at ~130km, 150km and 180km depth. Hypocenter locations and fault solutions for the Pipanaco Nest suggest flexure associated with steepening of the subducting slab consistent with the revised Wadati Benioff Zone contours. In an area of little to no crustal seismicity in global catalogs over the same time period, hundreds of well-located crustal earthquakes at depths less than 15km were recorded by the PUNA array. Among these earthquakes are three distinct clusters near relatively young volcanic centers. One cluster defines a nest northeast of the < 1 Ma Cerro Blanco caldera. The other two clusters are characterized by large quantities of earthquakes within 24-36 hours (swarms) near the Cerro Galan caldera that last erupted at ~2 Ma and near a ~1 Ma or

  11. Individual and community-level socioeconomic position and its association with adolescents experience of childhood sexual abuse: a multilevel analysis of six countries in Sub-Saharan Africa

    PubMed Central

    Yahaya, Ismail; Ponce de Leon, Antonio; Uthman, Olalekan A.; Soares, Joaquim; Macassa, Gloria

    2014-01-01

    Abstract: Background: Childhood sexual abuse (CSA) is a substantial global health and human rights problem and consequently a growing concern in sub-Saharan Africa. We examined the association between individual and community-level socioeconomic status (SES) and the likelihood of reporting CSA. Methods: We applied multiple multilevel logistic regression analysis on Demographic and Health Survey data for 6,351 female adolescents between the ages of 15 and 18 years from six countries in sub-Saharan Africa, between 2006 and 2008. Results: About 70% of the reported cases of CSA were between 14 and 17 years. Zambia had the highest proportion of reported cases of CSA (5.8%). At the individual and community level, we found that there was no association between CSA and socioeconomic position. This study provides evidence that the likelihood of reporting CSA cut across all individual SES as well as all community socioeconomic strata. Conclusions: We found no evidence of socioeconomic differentials in adolescents’ experience of CSA, suggesting that adolescents from the six countries studied experienced CSA regardless of their individual and community-level socioeconomic position. However, we found some evidence of geographical clustering, adolescents in the same community are subject to common contextual influences. Further studies are needed to explore possible effects of countries’ political, social, economic, legal, and cultural impact on childhood sexual abuse. PMID:23797565

  12. Dynamic Assessment of Seismic Risk (DASR) by Multi-parametric Observations: Preliminary Results of PRIME experiment within the PRE-EARTHQUAKES EU-FP7 Project

    NASA Astrophysics Data System (ADS)

    Tramutoli, V.; Inan, S.; Jakowski, N.; Pulinets, S. A.; Romanov, A.; Filizzola, C.; Shagimuratov, I.; Pergola, N.; Ouzounov, D. P.; Papadopoulos, G. A.; Parrot, M.; Genzano, N.; Lisi, M.; Alparlsan, E.; Wilken, V.; Tsybukia, K.; Romanov, A.; Paciello, R.; Zakharenkova, I.; Romano, G.

    2012-12-01

    The integration of different observations together with the refinement of data analysis methods, is generally expected to improve our present knowledge of preparatory phases of earthquakes and of their possible precursors. This is also the main goal of PRE-EARTHQUAKES (Processing Russian and European EARTH observations for earthQUAKE precursors Studies) the FP7 Project which, to this aim, committed together, different international expertise and observational capabilities, in the last 2 years. In the learning phase of the project, different parameters (e.g. thermal anomalies, total electron content, radon concentration, etc.), measured from ground and satellite systems and analyzed by using different data analysis approaches, have been studied for selected geographic areas and specific seismic events in the past. Since July 2012 the PRIME (PRE-EARTHQUAKES Real-time Integration and Monitoring Experiment) started attempting to perform, on the base of independent observations collected and integrated in real-time through the PEG (PRE-EARTHQUAKES Geo-portal), a Dynamic Assessment of Seismic Risk (DASR) on selected geographic areas of Europe (Italy-Greece-Turkey) and Asia (Kamchatka, Sakhalin, Japan). In this paper, results so far achieved as well as the potential and opportunities they open for a worldwide Earthquake Observation System (EQuOS) - as a dedicated component of GEOSS (Global Earth Observation System of Systems) - will be presented.

  13. SinoProbe-02:Deep Seismic Reflection Profile (480km) experiment in North China:Acquisition and the Preliminary Processing result

    NASA Astrophysics Data System (ADS)

    Hou, H.; Gao, R.; Li, Q.; Li, W.; Kuang, Z.; Liu, J.; Zhang, J.; Guan, Y.; Keller, G.; Liu, M.; Cox, C. M.; Holloway, S.; Chang, J. C.; Kaip, G. M.; Zhang, S.

    2010-12-01

    An active-source deep seismic reflection experiment was recorded across the Central Asian and Trans-North China orogens (see Figure) last winter as part of the SinoProbe-02 program. This profile extended southeastward from Erenhot and ended in the Huailai basin near Beijing. The shot depth was 25m; the shot size was 30-50kg; and the nominal shot interval was 250 km. Additional 200-kg charges were set off every 1 km and 1 ton shots were placed at intervals of 50 km. A Sercel 408 XL recording system and 2000 strings of SM-24 geophones were deployed at a spacing of 50m. Recording was at a 2ms sample interval for a total of 30s.The typical processing stream included crooked-line binning, refraction statics, true amplitude recovery, deconvolution, detailed velocity analyses, residual statics corrections and NMO stack (see Table). To the south, a transparent granite body is indicated in the middle crust with a series of north dipping reflections structures in the lower crust. The complex structures near Sonid Youqi suggest a transparent crust due to the Solonker suture zone. Map showing deep seismic reflection profile (solid black line) across North China. Processing Parameters

  14. Addiction and treatment experiences among active methamphetamine users recruited from a township community in Cape Town, South Africa: a mixed-methods study

    PubMed Central

    Meade, Christina S.; Towe, Sheri L.; Watt, Melissa H.; Lion, Ryan R.; Myers, Bronwyn; Skinner, Donald; Kimani, Stephen; Pieterse, Desiree

    2015-01-01

    Background Since 2000, there has been a dramatic increase in methamphetamine use in South Africa, but little is known about the experiences of out-of-treatment users. This mixed-methods study describes the substance use histories, addiction symptoms, and treatment experiences of a community-recruited sample of methamphetamine users in Cape Town. Methods Using respondent driven sampling, 360 methamphetamine users (44% female) completed structured clinical interviews to assess substance abuse and treatment history and computerized surveys to assess drug-related risks. A sub-sample of 30 participants completed in-depth interviews to qualitatively explore experiences with methamphetamine use and drug treatment. Results Participants had used methamphetamine for an average of 7.06 years (SD=3.64). They reported using methamphetamine on an average of 23.49 of the past 30 days (SD=8.90); 60% used daily. The majority (90%) met ICD-10 criteria for dependence, and many reported severe social, financial, and legal consequences. While only 10% had ever received drug treatment, 90% reported that they wanted treatment. In the qualitative interviews, participants reported multiple barriers to treatment, including beliefs that treatment is ineffective and relapse is inevitable in their social context. They also identified important motivators, including desires to be drug free and improve family functioning. Conclusion This study yields valuable information to more effectively respond to emerging methamphetamine epidemics in South Africa and other low- and middle-income countries. Interventions to increase uptake of evidence-based services must actively seek out drug users and build motivation for treatment, and offer continuing care services to prevent relapse. Community education campaigns are also needed. PMID:25977205

  15. Lithospheric sutures, continental fragments and hot spots revealed by a transportable seismic array experiment in southeast Australia

    NASA Astrophysics Data System (ADS)

    Rawlinson, N.; Vanacore, E. A.; Pozgay, S.

    2011-12-01

    Beginning in 1998, passive seismic arrays have been progressively deployed throughout southeast Australia in an attempt to image the 3-D seismic structure of the underlying lithosphere at high resolution. To date, over 600 stations have been deployed as part of 14 separate arrays. Station spacing on the mainland is ˜50 km, which reduces to ˜20 km in Tasmania, an island that lies at the southern tip of the continent. The majority of stations use 3-component short period sensors (1 Hz natural frequency), but several of the early arrays use vertical component short period sensors, and a number of 3-component broadband sensors are distributed throughout. In the past, teleseismic traveltime tomography has been separately applied to data from most of the arrays. More recently, the emphasis has been on joint treatment of the data, with ambient noise tomography and teleseismic traveltime tomography being applied to multiple array data. The latest developments involve the use of an irregular grid approach for traveltime tomography which incorporates global ISC traveltimes as well as relative arrival times obtained from each array, thus enabling high resolution recovery of structure where justified by the path coverage. Differential attenuation tomography is also beginning to be applied, which complements the results obtained from the traveltime tomography. To date, a wealth of features have been revealed by 3-D seismic tomography, the most significant being: (1) an easterly dipping velocity transition zone which suggests that the older Delamerian Orogen extends beneath the younger Western Subprovince of the Lachlan Orogen; (2) a distinct region of low velocity in the upper mantle north of Melbourne, which can be associated with recent Quaternary hot-spot volcanism; (3) a gradual east-southeast decrease in velocity towards the coast, which is consistent with lithospheric stretching and thinning near a passive margin; (4) a zone of high velocity north of Adelaide that may

  16. Next-generation seismic experiments: wide-angle, multi-azimuth, three-dimensional, full-waveform inversion

    NASA Astrophysics Data System (ADS)

    Bell, Rebecca; Morgan, Joanna; Warner, Michael

    2016-04-01

    There are many outstanding plate-tectonic scale questions that require us to know information about sub-surface physical properties, for example ascertaining the geometry and location of magma chambers and estimating the effective stress along plate boundary faults. These important scientific targets are often too deep, impractical and expensive for extensive academic drilling. Full-waveform inversion (FWI) is an advanced seismic imaging technique that has recently become feasible in three dimensions, and has been widely adopted by the oil and gas industry to image reservoir-scale targets at shallow-to-moderate depths. In this presentation we explore the potential for 3-D FWI, when combined with appropriate marine seismic acquisition, to recover high-resolution high-fidelity P-wave velocity models for sub-sedimentary targets within the crystalline crust and uppermost mantle. Using existing geological and geophysical models, we construct P-wave velocity models over three potential sub-sedimentary targets: the Soufrière Hills Volcano on Montserrat and its associated crustal magmatic system, the downgoing oceanic plate beneath the Nankai subduction margin, and the oceanic crust-uppermost mantle beneath the East Pacific Rise mid-ocean ridge. We use these models to generate realistic multi-azimuth 3-D synthetic seismic data, and attempt to invert these data to recover the original models. We explore the resolution and accuracy, sensitivity to noise and acquisition geometry, ability to invert elastic data using acoustic inversion codes, and the trade-off between low frequencies and starting velocity model accuracy. We will show that FWI applied to multi-azimuth, refracted, wide-angle, low-frequency data can resolve features in the deep crust and uppermost mantle on scales that are significantly better than can be achieved by any other geophysical technique, and that these results can be obtained using relatively small numbers (60-90) of ocean-bottom receivers combined

  17. Impediments to media communication of social change in family planning and reproductive health: experiences from East Africa.

    PubMed

    Kagurusi, Patrick T

    2013-09-01

    The media has been employed to increase uptake of Family Planning through behaviour change communication (BCC). Understanding the barriers encountered in effectively undertaking this function would increase the strategy's effectiveness. Sixty journalists from East Africa participated in trainings to enhance their BCC skills for Family Planning in which a qualitative study was nested to identify barriers to effective Family Planning BCC in the region's media. The barriers were observed to be insufficient BCC skills, journalists' conflict of interest, interests of media houses, inaccessible sources of family planning information, editorial ideologies and absence of commercially beneficial demand. Coupled with the historical ideologies of the media in the region, the observed barriers have precipitated ineffective family planning BCC in the regions media. Effective BCC for family planning in the regions media requires capacity building among practitioners and alignment of the concept to the media's and consumers' aspirations. PMID:24069769

  18. How can community health programmes build enabling environments for transformative communication? Experiences from India and South Africa.

    PubMed

    Campbell, Catherine; Cornish, Flora

    2012-05-01

    Much research has examined how to empower the poor to articulate demands for health-enabling living conditions. Less is known about creating receptive social environments where the powerful heed the voices of the poor. We explore the potential for 'transformative communication' between the poor and the powerful, through comparing two well-documented case studies of HIV/AIDS management. The Entabeni Project in South Africa sought to empower impoverished women to deliver home-based nursing to people with AIDS. It successfully provided short-term welfare, but did not achieve local leadership or sustainability. The Sonagachi Project in India, an HIV-prevention programme targeting female sex workers, became locally led and sustainable. We highlight the strategies through which Sonagachi, but not Entabeni, altered the material, symbolic and relational contexts of participants' lives, enabling transformative communication and opportunities for sexual health-enabling social change. PMID:21604108

  19. Biomedical infertility care in sub-Saharan Africa: a social science review of current practices, experiences and view points

    PubMed Central

    Gerrits, T.; Shaw, M.

    2010-01-01

    Some sort of infertility treatments, including the use of advanced reproductive technologies (ARTs), is nowadays provided at several places in sub-Saharan Africa. Yet, to date only a few studies have actually looked into the way these treatments are offered, used and experienced. In this review article the authors present and discuss empirical study findings that give insight into the way biomedical infertility care is provided, considered, experienced and/or used in sub-Saharan African countries. They concentrate on four themes that were often referred to in the reviewed studies and underline the importance of taking into account the local sociocultural context and notions when developing and implementing infertility care, namely: counselling, male involvement, acceptability of ARTs and the use of donor material (semen and embryos). In the conclusion the authors emphasize the importance of preventing infertility as part of integrated reproductive health programs and the need to improve the quality of (low tech) infertility care in the public health sector by means of standardized guidelines, training of health staff and improved counselling. In addition, from a reproductive rights perspective, they support initiatives to introduce low cost ARTs to treat tubal factor related infertility. They also point to potential unintended side effects of the introduction of ARTs and the use of donor material in the sub-Saharan African context, affecting gender inequity and inequity between citizens from different social classes, and argue that such effects should be acknowledged and avoided by all possible means. Finally, they present an agenda for future social science research on this topic in sub-Saharan Africa. PMID:25013712

  20. Imaging the Carboneras fault zone at depth: preliminary results from reflection/refraction seismic tomography

    NASA Astrophysics Data System (ADS)

    Nippress, S.; Rietbrock, A.; Faulkner, D. R.; Rutter, E.; Haberland, C. A.; Teixido, T.

    2009-12-01

    Understanding and characterizing fault zone structure at depth is vital to predicting the slip behaviour of faults in the brittle crust. We aim to combine detailed field mapping and laboratory velocity/physical property determinations with seismic measurements on the Carboneras fault zone (S.E. Spain) to improve our knowledge of how fault zone structure affects seismic signals. The CFZ is a large offset (10s of km) strike-slip fault that constitutes part of the diffuse plate boundary between Africa and Iberia. It has been largely passively exhumed from ca. 4 to 6 km depth. The friable fault zone components are excellently preserved in the region’s semi-arid climate, and consist of multiple strands of phyllosilicate-rich fault gouge ranging from 1 to 20 m in thickness. In May 2009 we conducted 4 high-resolution seismic reflection and refraction/first break tomography lines. Two of these lines (~1km long) crossed the entire fault zone while the remaining lines (~150 and ~300m long) concentrated on individual fault strands and associated damage zones. For each of the lines a 2 m-geophone spacing was used with a combination of accelerated drop weight, sledgehammer and 100g explosives as seismic sources. Initial seismic reflection processing has been carried out on each of the 4 lines. First breaks have been picked for each of the shot gathers and inputted into a 2D traveltime inversion and amplitude-modeling package (Zelt & Smith, 1992) to obtain first break tomography images. During this field campaign we also carried out numerous fault zone guided wave experiments on two of the dense seismic lines. At the larger offsets (~600-700m) we observe low frequency guided waves. These experiments will capture the various length scales involved in a mature fault zone and will enable the surface mapping and petrophysical studies to be linked to the seismic field observations.

  1. Nonstructural seismic restraint guidelines

    SciTech Connect

    Butler, D.M.; Czapinski, R.H.; Firneno, M.J.; Feemster, H.C.; Fornaciari, N.R.; Hillaire, R.G.; Kinzel, R.L.; Kirk, D.; McMahon, T.T.

    1993-08-01

    The Nonstructural Seismic Restraint Guidelines provide general information about how to secure or restrain items (such as material, equipment, furniture, and tools) in order to prevent injury and property, environmental, or programmatic damage during or following an earthquake. All SNL sites may experience earthquakes of magnitude 6.0 or higher on the Richter scale. Therefore, these guidelines are written for all SNL sites.

  2. Developing Ethical Practices for Public Health Research Data Sharing in South Africa: The Views and Experiences From a Diverse Sample of Research Stakeholders.

    PubMed

    Denny, Spencer G; Silaigwana, Blessing; Wassenaar, Douglas; Bull, Susan; Parker, Michael

    2015-07-01

    The abundance of South African clinical and public health research data has the potential to unlock important and valuable future advances in biomedical science. Amid increasing calls for more effective sharing of individual-level data, commitment to promote access to research data is evident within South Africa's public research sector, but national guidance and regulation are absent. This qualitative study examined the perceptions, experiences and concerns of 32 research stakeholders about data-sharing practices. There was consensus about the utility of data sharing in publicly funded health research. However, disparate views emerged about the possible harms and benefits of sharing data and how these should be weighed. The relative dearth of policies governing data-sharing practices needs to be addressed and a framework of support developed that incentivizes data-sharing practices for researchers that are both ethical and effective. PMID:26297750

  3. Shear wave velocity structure of the southern African upper mantle with implications for the uplift of southern Africa

    NASA Astrophysics Data System (ADS)

    Adams, Aubreya; Nyblade, Andrew

    2011-08-01

    Broad-band seismic data from the southern African seismic experiment and the AfricaArray network are used to investigate the seismic velocity structure of the upper mantle beneath southern Africa, and in particular beneath the Kaapvaal Craton. A two-plane approximation method that includes a finite frequency sensitivity kernel is employed to measure Rayleigh wave phase velocities, which are inverted to obtain a quasi-3-D shear wave velocity model of the upper mantle. We find phase velocities for the Kaapvaal Craton and surrounding mobile belts that are comparable to those reported by previous studies, and we find little evidence for variation from east to west across the Namaqua-Natal Belt, a region not well imaged in previous studies. A high-velocity upper-mantle lid is found beneath the Kaapvaal Craton and most of southern Africa. For the Kaapvaal Craton, the thickness of the lid (˜150-200 km) is consistent with the lid thicknesses reported in many previous studies. The cratonic lid is underlain by a ˜100-km thick low-velocity zone with a 3.9 per cent maximum velocity reduction. By comparing the velocity model to those published for other Archean cratons, we find few differences, and therefore conclude that there is little evidence in the shear wave velocity structure of the mantle to indicate that the southern African plateau is supported by an upper-mantle thermal anomaly.

  4. Juan de Fuca Plate Ridge-to-Trench Experiment: initial results from active source seismic imaging of the Juan de Fuca plate and Cascadia fore-arc (Invited)

    NASA Astrophysics Data System (ADS)

    Carbotte, S. M.; Canales, J.; Carton, H. D.; Han, S.; Gibson, J. C.; Janiszewski, H. A.; Horning, G.; Nedimovic, M. R.; Abers, G. A.; Trehu, A. M.

    2013-12-01

    Active source seismic data were acquired during the Juan de Fuca Ridge-to-Trench experiment (June-July 2012) to characterize the evolution and structure of the Juan de Fuca plate from formation at the ridge, through evolution in the plate interior, to subduction at the Cascadia trench. The survey provides plate-scale images of the sediments, crust, and shallowest mantle along two ridge-perpendicular transects, one extending from Axial seamount to the Oregon margin near Hydrate Ridge and the other from near Endeavour segment to Grays Harbor offshore Washington. In addition, a 450 km long trench-parallel line ~10 km seaward of the Cascadia deformation front was acquired to characterize variations in plate structure along the margin. Coincident long-streamer (8 km) multi-channel seismic (MCS) and wide-angle ocean bottom seismometer (OBS) data were collected along each transect. Using these data, our current investigations focus on the properties of the thick sediment blanket covering the Juan de Fuca plate and evidence for fluid flow at the deformation front, crustal structure within the plate interior and near the deformation front, and tracking the downgoing plate beneath the margin. Highlights include the discovery of numerous pockmarks on the seafloor providing evidence of active fluid flow up to 60 km west of the deformation front. Along the Oregon transect, a bright decollement horizon is imaged at ~1sec twtt above basement whereas at the Washington margin, protothrusts of the deformation front reach to the top of the oceanic crust. Variations in sediment properties are documented within the margin-parallel transect with changes in the stratigraphic level of decollement. While crustal thickness is quite uniform along the margin (~ 6 km), variations in crustal reflectivity and in shallowest mantle velocities are observed over ~30-50 km length scales that could be related to structural variations in the Cascadia subduction zone. Further landward, the top of the

  5. ‘We keep her status to ourselves’: Experiences of stigma and discrimination among HIV-discordant couples in South Africa, Tanzania and Ukraine

    PubMed Central

    Rispel, Laetitia C.; Cloete, Allanise; Metcalf, Carol A.

    2015-01-01

    Abstract In HIV-discordant relationships, the HIV-negative partner also carries the burden of a stigmatised disease. For this reason, couples often hide their HIV-discordant status from family, friends and community members. This perpetuates the silence around HIV-discordant relationships and impacts on targeted HIV prevention, treatment and counselling efforts. This article reports on experiences of stigma and discrimination among HIV-discordant couples in South Africa, Tanzania and Ukraine. During 2008, HIV-discordant couples who had been in a relationship for at least one year were recruited purposively through health-care providers and civil society organisations in the three countries. Participants completed a brief self-administered questionnaire, while semi-structured interviews were conducted with each partner separately and with both partners together. Interviews were analysed using thematic content analysis. Fifty-one couples were recruited: 26 from South Africa, 10 from Tanzania, and 15 from Ukraine. Although most participants had disclosed their HIV status to someone other than their partner, few were living openly with HIV discordance. Experiences of stigma were common and included being subjected to gossip, rumours and name-calling, and HIV-negative partners being labelled as HIV-positive. Perpetrators of discrimination included family members and health workers. Stigma and discrimination present unique and complex challenges to couples in HIV sero-discordant relationships in these three diverse countries. Addressing stigmatisation of HIV-discordant couples requires a holistic human rights approach and specific programme efforts to address discrimination in the health system. PMID:25778765

  6. 'We keep her status to ourselves': experiences of stigma and discrimination among HIV-discordant couples in South Africa, Tanzania and Ukraine.

    PubMed

    Rispel, Laetitia C; Cloete, Allanise; Metcalf, Carol A

    2015-01-01

    In HIV-discordant relationships, the HIV-negative partner also carries the burden of a stigmatised disease. For this reason, couples often hide their HIV-discordant status from family, friends and community members. This perpetuates the silence around HIV-discordant relationships and impacts on targeted HIV prevention, treatment and counselling efforts. This article reports on experiences of stigma and discrimination among HIV-discordant couples in South Africa, Tanzania and Ukraine. During 2008, HIV-discordant couples who had been in a relationship for at least one year were recruited purposively through health-care providers and civil society organisations in the three countries. Participants completed a brief self-administered questionnaire, while semi-structured interviews were conducted with each partner separately and with both partners together. Interviews were analysed using thematic content analysis. Fifty-one couples were recruited: 26 from South Africa, 10 from Tanzania, and 15 from Ukraine. Although most participants had disclosed their HIV status to someone other than their partner, few were living openly with HIV discordance. Experiences of stigma were common and included being subjected to gossip, rumours and name-calling, and HIV-negative partners being labelled as HIV-positive. Perpetrators of discrimination included family members and health workers. Stigma and discrimination present unique and complex challenges to couples in HIV sero-discordant relationships in these three diverse countries. Addressing stigmatisation of HIV-discordant couples requires a holistic human rights approach and specific programme efforts to address discrimination in the health system. PMID:25778765

  7. Topography and tectonics of the central New Madrid seismic zone: Results of numerical experiements using a three-dimensional boundary element program

    NASA Technical Reports Server (NTRS)

    Gomberg, Joan; Ellis, Michael

    1994-01-01

    We present results of a series of numerical experiments designed to test hypothetical mechanisms that derive deformation in the New Madrid seismic zone. Experiments are constrained by subtle topography and the distribution of seismicity in the region. We use a new boundary element algorithm that permits calcuation of the three-dimensional deformation field. Surface displacement fields are calculated for the New Madrid zone under both far-field (plate tectonics scale) and locally derived driving strains. Results demonstrate that surface displacement fields cannot distinguish between either a far-field simple or pure shear strain field or one that involves a deep shear zone beneath the upper crustal faults. Thus, neither geomorphic nor geodetic studies alone are expected to reveal the ultimate driving mechanism behind the present-day deformation. We have also tested hypotheses about strain accommodation within the New Madrid contractional step-over by including linking faults, two southwest dipping and one vertical, recently inferred from microearthquake data. Only those models with step-over faults are able to predict the observed topography. Surface displacement fields for long-term, relaxed deformation predict the distribution of uplift and subsidence in the contractional step-over remarkably well. Generation of these displacement fields appear to require slip on both the two northeast trending vertical faults and the two dipping faults in the step-over region, with very minor displacements occurring during the interseismic period when the northeast trending vertical faults are locked. These models suggest that the gently dippling central step-over fault is a reverse fault and that the steeper fault, extending to the southeast of the step-over, acts as a normal fault over the long term.

  8. Geoid, elevation and crustal thickness: Investigating the lithospheric structure of Africa

    NASA Astrophysics Data System (ADS)

    Globig, Jan; Fernandez, Manel; Torné, Montserrat; Faccenna, Claudio

    2014-05-01

    The African continent shows striking topographic features and has recently been target of numerous geophysical and seismic studies to determine its crustal structure, locally and regionally. Observation of surface tectonics coupled with knowledge of variations in crustal thickness provide a top to bottom frame to investigate sub-crustal processes, which affect the uppermost lithosphere and control today's African topography. As the significance of previous models of crustal thickness in Africa is debatable and favors premature conclusions here our motivation is to address the detailed structure of the African lithosphere revealing Moho and LAB geometry using 1D modeling of elevation, geoid and thermal data including the thermotectonic age of the crust as well as age and thickness of sediments to better account for lateral variations in crustal density. The four-layered model is composed of crust and lithospheric mantle plus sea water and asthenosphere, assuming Airy isostasy and is benchmarked against a detailed compilation of seismic Moho data from active and passive seismic experiments across the continent and its margins. Relating better surface topography with the depth of the Moho and the LAB contributes to improve knowledge on the lithospheric structure in Africa that mainly comes from global models, such as CRUST1.0, regional tomography models and gravity modeling, which unfortunately miss a proper relation between elevation, mean crustal density and crustal thickness. Our approach therefore is seen to support the discussion around the strongly debated processes responsible for the anomalous high elevation especially in the south eastern part of Africa and the observed undulations in Moho depth from about 20 km below the extended regions of the East African Rift System to 50 kilometers underneath the thickest Proterozoic belts. By linking differences in age, density and thermal state of the lithosphere with topography and geoid we want to provide new

  9. Wide-angle seismic constraints on the nature and limits between geological domains in the Tyrrhenian basin (MEDOC-2010 experiment)

    NASA Astrophysics Data System (ADS)

    Sallares, V.; Prada, M.; Moeller, S.; Guzman, M.; Ranero, C. R.; Grevemeyer, I.; Zitellini, N.; de Franco, R.

    2012-12-01

    The Tyrrhenian Sea is a back-arc basin that opened between Neogene and present as a response to the roll-back of the subducted slab beneath the Apennines (to the West) and the Calabrian Arc (to the South). It underwent comparatively less extension in the North (offshore Corsica) than in the South, where it evolved until full continental breakup. The combination of geological observations (e.g. ODP drilling) and geophysical data (bathymetric, multichannel seismics) has provided a good background knowledge on the tectonic structure and geodynamic evolution of the basin, but the nature of the different geological domains and the limits between them remain poorly constrained. To partially overcome this issue, five wide-angle seismic (WAS) transects across the whole basin recorded by a dense array of OBH/S and landstations, were acquired in the framework of the MEDOC-2010 survey. The northernmost profile (AB) runs E-W from Southern Corsica to mainland Italy, whereas the southernmost one (MN) runs NW-SE from Southern Sardinia to Western Sicily. We present a compilation of seismic velocity models obtained by joint refraction and reflection travel-time inversion along these five profiles. The inverted models include maps of the P-wave velocity field together with the geometry of the crust-mantle boundary, providing clues on the nature of the rocks along the different transects, a key to define the parameters controlling extension. The continental crust beneath the coast in Corsica and Sardinia is similar in terms of thickness (23±2 km) and velocity. The crustal structure is clearly continental along the two northern profiles. Sediments mostly concentrate in small, isolated basins. An exception is the ~5 km-thick Corsica basin. A similar, but considerable narrower and less defined structure can also be observed offshore Sardinia. The minimum crustal thickness along profile AB is 18 km, so the corresponding stretching factor (β) is ~1.3; whereas along profile CD, it is 13

  10. Missed Opportunities for TB Investigation in Primary Care Clinics in South Africa: Experience from the XTEND Trial

    PubMed Central

    Chihota, Violet N.; Ginindza, Sibuse; McCarthy, Kerrigan; Grant, Alison D.; Churchyard, Gavin; Fielding, Katherine

    2015-01-01

    Setting 40 primary health clinics (PHCs) in four provinces in South Africa, June 2012 –February 2013. Objective To determine whether health care worker (HCW) practice in investigating people with TB symptoms was altered when the initial test for TB was changed from smear microscopy to Xpert MTB/RIF. Design Cross-sectional substudy at clinics participating in a pragmatic cluster randomised trial, Xpert for TB: Evaluating a New Diagnostic "XTEND", which evaluated the effect of Xpert MTB/RIF implementation in South Africa. Methods Consecutive adults exiting PHCs reporting at least one TB symptom (defined as any of cough, weight loss, night sweats and fever) were enrolled. The main outcome was the proportion who self-reported having sputum requested by HCW during the clinic encounter just completed. Results 3604 adults exiting PHCs (1676 in Xpert arm, 1928 in microscopy arm) were enrolled (median age 38 years, 71.4% female, 38.8% reported being HIV-positive, 70% reported cough). For 1267 participants (35.2%) the main reason for attending the clinic was TB symptom(s). Overall 2130/3604 (59.1%) said they reported their symptom(s) to HCW. 22.7% (818/3604) reported having been asked to give sputum for TB investigation. Though participants in the Xpert vs. microscopy arm were more likely to have sputum requested by HCW, this was not significantly different: overall (26.0% [436/1676] vs 19.8% [382/1928]; adjusted prevalence ratio [aPR] 1.31, [95% CI 0.78–2.20]) and when restricted to those presenting at clinics due to symptoms (49.1% [260/530] vs 29.9% [220/737]; aPR 1.38 [0.89–2.13]) and those reporting being HIV-positive (29.4% [190/647] vs 20.8% [156/749]; aPR 1.38[0.88–2.16]). Those attending clinic due to TB symptoms, were more likely to have sputum requested if they had increasing number of symptoms; longer duration of cough, unintentional weight loss and night sweats and if they reported symptoms to HCW. Conclusions A large proportion of people exiting PHCs

  11. The CIFALPS seismic experiment: first high-resolution data on the crust and upper mantle structures of the southwestern Alps

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Paul, A.; Solarino, S.; Aubert, C.; Zheng, T.; Salimbeni, S.; Guillot, S.; Zhu, R.; Wang, Q.

    2013-12-01

    The Alpine belt, being a most studied mountain belt by geologists, is an ideal natural laboratory for understanding the processes and mechanism of orogeny. A number of questions on the dynamics of the Alps, however, remain open due to the lack of detailed data on its lithospheric and sublithospheric structures. This is particular true for the very arcuate southwestern part of the belt. In order to improve images of the crust and upper mantle beneath the southwestern Alps, we have installed a temporary broadband seismic array across the belt from the Rhone valley (France) to the Po plain (Italy). The main sub-array of the CIFALPS (China-Italy-France Alps seismic survey) project is a 350-km long roughly linear profile of 46 stations trending WSW-ENE from Bollène (France) to the north of Alessandria (Italy). Its average station spacing is smaller than 10 km, with a densification to 5 km in the internal Alps. Nine additional temporary stations located ~40 km to the north and south of the main profile complement the adjacent permanent broadband networks to improve the 3-D constraints on the deep structures. Most stations are equipped with three-component broadband sensors (50Hz -120s). The array was installed in the summer of 2012 and will be operated till to September 2013. We used available dataset to compute receiver functions and analyze shear-wave splitting from SKS phases. A common-conversion point migrated receiver function section displays a strong Moho P-to-S conversion beneath the western end of the profile, which fluctuates in amplitude and depth from beneath the Vocontian basin to the Penninic front, and becomes hardly distinguishable beneath the internal zones. This image is consistent with the results of the controlled-source ECORS-CROP profile in the northwestern Alps. The lateral change in Moho signature on the ECORS-CROP line was interpreted as the result of signal attenuation across the very heterogeneous upper crust of the internal zones. We however

  12. Seismicity of southern Lake Tanganyika

    NASA Astrophysics Data System (ADS)

    Lavayssiere, A.; Gallacher, R. J.; Keir, D.; Ebinger, C. J.; Drooff, C.; Khalfan, M.; Bull, J. M.

    2015-12-01

    Global seismic networks document frequent and unusually deep earthquakes in East African rift sectors lacking central volcanoes. The deep seismicity means that we can use earthquakes to probe the geometry and kinematics of fault systems throughout the crust, and to understand the distribution of strain between large offset border fault systems and intrabasinal faults. The southern Tanganyika rift zone has the highest seismicity rate within East Africa during the period 1973-present, yet earlier temporary seismometer networks have been too sparse in space and time to relocate earthquakes with location and depth errors of < 5-10 km. We address this issue by recording seismicity of southern Lake Tanganyika since June 2014 using a network at 12 broadband seismic stations. The distribution of earthquakes shows that deformation primarily occurs on large offset border faults beneath the lake. Subsidiary earthquake activity occurs along the subparrallel Rukwa graben, and beneath the NE-SW striking Mweru rift. The distribution of earthquakes suggests the southern end of lake Tanganyika is characterized by a network of intersecting NNW and NE striking faults. The depths of earthquakes are distributed throughout the crust, consistent with the relatively strong lithosphere.

  13. Community perceptions of repeat HIV-testing: experiences of the ANRS 12249 Treatment as Prevention trial in rural South Africa.

    PubMed

    Orne-Gliemann, Joanna; Zuma, Thembelihle; Chikovore, Jeremiah; Gillespie, Natasha; Grant, Merridy; Iwuji, Collins; Larmarange, Joseph; McGrath, Nuala; Lert, France; Imrie, John

    2016-01-01

    In the context of the ANRS 12249 Treatment as Prevention (TasP) trial, we investigated perceptions of regular and repeat HIV-testing in rural KwaZulu-Natal (South Africa), an area of very high HIV prevalence and incidence. We conducted two qualitative studies, before (2010) and during the early implementation stages of the trial (2013-2014), to appreciate the evolution in community perceptions of repeat HIV-testing over this period of rapid changes in HIV-testing and treatment approaches. Repeated focus group discussions were organized with young adults, older adults and mixed groups. Repeat and regular HIV-testing was overall well perceived before, and well received during, trial implementation. Yet community members were not able to articulate reasons why people might want to test regularly or repeatedly, apart from individual sexual risk-taking. Repeat home-based HIV-testing was considered as feasible and convenient, and described as more acceptable than clinic-based HIV-testing, mostly because of privacy and confidentiality. However, socially regulated discourses around appropriate sexual behaviour and perceptions of stigma and prejudice regarding HIV and sexual risk-taking were consistently reported. This study suggests several avenues to improve HIV-testing acceptability, including implementing diverse and personalised approaches to HIV-testing and care, and providing opportunities for antiretroviral therapy initiation and care at home. PMID:27421048

  14. Seismic bearing

    NASA Astrophysics Data System (ADS)

    Power, Dennis

    2009-05-01

    Textron Systems (Textron) has been using geophones for target detection for many years. This sensing capability was utilized for detection and classification purposes only. Recently Textron has been evaluating multiaxis geophones to calculate bearings and track targets more specifically personnel. This capability will not only aid the system in locating personnel in bearing space or cartesian space but also enhance detection and reduce false alarms. Textron has been involved in the testing and evaluation of several sensors at multiple sites. One of the challenges of calculating seismic bearing is an adequate signal to noise ratio. The sensor signal to noise ratio is a function of sensor coupling to the ground, seismic propagation and range to target. The goals of testing at multiple sites are to gain a good understanding of the maximum and minimum ranges for bearing and detection and to exploit that information to tailor sensor system emplacement to achieve desired performance. Test sites include 10A Site Devens, MA, McKenna Airfield Ft. Benning, GA and Yuma Proving Ground Yuma, AZ. Geophone sensors evaluated include a 28 Hz triax spike, a 15 Hz triax spike and a hybrid triax spike consisting of a 10 Hz vertical geophone and two 28 Hz horizontal geophones. The algorithm uses raw seismic data to calculate the bearings. All evaluated sensors have triaxial geophone configuration mounted to a spike housing/fixture. The suite of sensors also compares various types of geophones to evaluate benefits in lower bandwidth. The data products of these tests include raw geophone signals, seismic features, seismic bearings, seismic detection and GPS position truth data. The analyses produce Probability of Detection vs range, bearing accuracy vs range, and seismic feature level vs range. These analysis products are compared across test sites and sensor types.

  15. SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION

    SciTech Connect

    Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin

    2002-10-01

    RSI has access to two synthetic seismic programs: Osiris seismic modeling system provided by Odegaard (Osiris) and synthetic seismic program, developed by SRB, implementing the Kennett method for normal incidence. Achieving virtually identical synthetic seismic traces from these different programs serves as cross-validation for both. The subsequent experiments have been performed with the Kennett normal incidence code because: We have access to the source code, which allowed us to easily control computational parameters and integrate the synthetics computations with our graphical and I/O systems. This code allows to perform computations and displays on a PC in MatLab or Octave environment, which is faster and more convenient. The normal incidence model allows us to exclude from the synthetic traces some of the physical effects that take place in 3-D models (like inhomogeneous waves) but have no relevance to the topic of our investigation, which is attenuation effects on seismic reflection and transmission.

  16. Engaging media in communicating research on sexual and reproductive health and rights in sub-Saharan Africa: experiences and lessons learned

    PubMed Central

    2011-01-01

    Background The mass media have excellent potential to promote good sexual and reproductive health outcomes, but around the world, media often fail to prioritize sexual and reproductive health and rights issues or report them in an accurate manner. In sub-Saharan Africa media coverage of reproductive health issues is poor due to the weak capacity and motivation for reporting these issues by media practitioners. This paper describes the experiences of the African Population and Health Research Center and its partners in cultivating the interest and building the capacity of the media in evidence-based reporting of reproductive health issues in sub-Saharan Africa. Methods The paper utilizes a case study approach based primarily on the personal experiences and reflections of the authors (who played a central role in developing and implementing the Center’s communication and policy engagement strategies), a survey that the Center carried out with science journalists in Kenya, and literature review. Results The African Population and Health Research Center’s media strategy evolved over the years, moving beyond conventional ways of communicating research through the media via news releases and newspaper stories, to varying approaches that sought to inspire and build the capacity of journalists to do evidence-based reporting of reproductive health issues. Specifically, the approach included 1) enhancing journalists’ interest in and motivation for reporting on reproductive health issues through training and competitive grants for outstanding reporting ; 2) building the capacity of journalists to report reproductive health research and the capacity of reproductive health researchers to communicate their research to media through training for both parties and providing technical assistance to journalists in obtaining and interpreting evidence; and 3) establishing and maintaining trust and mutual relationships between journalists and researchers through regular informal

  17. GHYRAF (Gravity and HYdrology in AFrica): a New Experiment Combining Hydrology and Geodesy to Investigate Water Storage Changes from the Sahara to the Equatorial Monsoon Zone.

    NASA Astrophysics Data System (ADS)

    de Linage, C.; Hinderer, J.; Boy, J.; Masson, F.; Gegout, P.; Diament, M.; de Viron, O.; Bayer, R.; Balmino, G.; Biancale, R.; Bonvalot, S.; Genthon, P.

    2007-12-01

    We present a new project using multi-disciplinary data (gravity, geodesy, hydrology, and meteorology) to determine seasonal changes in water storage in Africa. We foresee to concentrate on two areas: the desert zone in the Sahara (Tamanrasset, Algeria) where almost no hydrological change is present, and the equatorial monsoon band (Niger, Benin Republic) that provides on the contrary a large rainfall signal. This project will be a first attempt to do a ground validation of satellite-derived gravity observations such as GRACE or GOCE in Africa. We will pay attention to the various length scales involved in hydrological processes that are differently retrieved whether gravity is measured at the ground or by satellite. Our experience includes two types of ground-based gravity measurements. First we will perform a repeated survey with absolute gravimeters (AG) on a North-South profile during 2-3 years (2008-2010) to assess the large soil moisture changes as predicted by existing hydrological models such as GLDAS or LadWorld. Second we plan to establish a superconducting gravimeter (SG) to act as a continuously monitored base station in a region of large soil moisture changes. In addition, continuous geodetic GPS measurements will be made along the gravity profile to assess the vertical deformation which acts to alter ground gravity but not satellite gravity. In-situ measurements of hydrological parameters at each station will assist us in modelling local gravity effects. The goal is a better characterization of continental water storage, particularly in the critical areas of water management in the north and central parts of the African continent.

  18. Next-generation seismic experiments - II: wide-angle, multi-azimuth, 3-D, full-waveform inversion of sparse field data

    NASA Astrophysics Data System (ADS)

    Morgan, Joanna; Warner, Michael; Arnoux, Gillean; Hooft, Emilie; Toomey, Douglas; VanderBeek, Brandon; Wilcock, William

    2016-02-01

    3-D full-waveform inversion (FWI) is an advanced seismic imaging technique that has been widely adopted by the oil and gas industry to obtain high-fidelity models of P-wave velocity that lead to improvements in migrated images of the reservoir. Most industrial applications of 3-D FWI model the acoustic wavefield, often account for the kinematic effect of anisotropy, and focus on matching the low-frequency component of the early arriving refractions that are most sensitive to P-wave velocity structure. Here, we have adopted the same approach in an application of 3-D acoustic, anisotropic FWI to an ocean-bottom-seismometer (OBS) field data set acquired across the Endeavour oceanic spreading centre in the northeastern Pacific. Starting models for P-wave velocity and anisotropy were obtained from traveltime tomography; during FWI, velocity is updated whereas anisotropy is kept fixed. We demonstrate that, for the Endeavour field data set, 3-D FWI is able to recover fine-scale velocity structure with a resolution that is 2-4 times better than conventional traveltime tomography. Quality assurance procedures have been employed to monitor each step of the workflow; these are time consuming but critical to the development of a successful inversion strategy. Finally, a suite of checkerboard tests has been performed which shows that the full potential resolution of FWI can be obtained if we acquire a 3-D survey with a slightly denser shot and receiver spacing than is usual for an academic experiment. We anticipate that this exciting development will encourage future seismic investigations of earth science targets that would benefit from the superior resolution offered by 3-D FWI.

  19. Drill-rig noise suppression using the Karhunen-Loéve transform for seismic-while-drilling experiment at Brukunga, South Australia

    NASA Astrophysics Data System (ADS)

    Sun, Baichun; Bóna, Andrej; Zhou, Binzhong; King, Andrew; Dupuis, Christian; Kepic, Anton

    2016-02-01

    Diamond-impregnated drill bits are known to be low energy vibration seismic sources. With the strong interference from the drill rig, it is difficult to obtain the drill-bit wavefield with a surface receiver array. To overcome the challenge of surface wave interference generated from the rig for seismic-while-drilling (SWD), we need to separate the rig- and bit-generated signals. To this end, we apply two wavefield separation methods, the Karhunen-Loéve (KL) transform and the f - k filter, and compare their performance. The applicability of these methods is based on the drill rig and drill bit having different spatial positions. While the drill-bit spatial position changes during the process of drilling, the drill rig remains stationary. This results in the source wavefields from the drill rig and the drill-bit having different characteristics, and allows us to separate and extract the drill-bit signal. We use a synthetic model to compare the KL transform and f - k filter. Both techniques are robust when the noise wavefield has consistent amplitude moveout. However, for changing amplitudes, such as the rig noise, which has an unrepeatable wavefield due to power amplitude variation, we show that the KL transform performs better in such situations. We also show the results of signal analysis of the SWD experiment data acquired from Brukunga, South Australia. We demonstrate the feasibility of the KL transform in separating the coherent noises from the stationary drill rig in a hard rock drilling environment, particularly emphasising the suppression of the surface and direct waves from the rig. The results show that drill-rig noise can be effectively suppressed in the correlation domain.

  20. Assessing participatory practices in community-based natural resource management: experiences in community engagement from southern Africa.

    PubMed

    Dyer, J; Stringer, L C; Dougill, A J; Leventon, J; Nshimbi, M; Chama, F; Kafwifwi, A; Muledi, J I; Kaumbu, J-M K; Falcao, M; Muhorro, S; Munyemba, F; Kalaba, G M; Syampungani, S

    2014-05-01

    The emphasis on participatory environmental management within international development has started to overcome critiques of traditional exclusionary environmental policy, aligning with shifts towards decentralisation and community empowerment. However, questions are raised regarding the extent to which participation in project design and implementation is meaningful and really engages communities in the process. Calls have been made for further local-level (project and community-scale) research to identify practices that can increase the likelihood of meaningful community engagement within externally initiated projects. This paper presents data from three community-based natural resource management (CBNRM) project case studies from southern Africa, which promote Joint Forest Management (JFM), tree planting for carbon and conservation agriculture. Data collection was carried out through semi-structured interviews with key stakeholders, community-level meetings, focus groups and interviews. We find that an important first step for a meaningful community engagement process is to define 'community' in an open and participatory manner. Two-way communication at all stages of the community engagement process is shown to be critical, and charismatic leadership based on mutual respect and clarity of roles and responsibilities is vital to improve the likelihood of participants developing understanding of project aims and philosophy. This can lead to successful project outcomes through community ownership of the project goals and empowerment in project implementation. Specific engagement methods are found to be less important than the contextual and environmental factors associated with each project, but consideration should be given to identifying appropriate methods to ensure community representation. Our findings extend current thinking on the evaluation of participation by making explicit links between the community engagement process and project outcomes, and by

  1. A regional and multi-faceted approach to postgraduate water education - the WaterNet experience in Southern Africa

    NASA Astrophysics Data System (ADS)

    Jonker, L.; van der Zaag, P.; Gumbo, B.; Rockström, J.; Love, D.; Savenije, H. H. G.

    2012-11-01

    This paper reports the experience of a regional network of academic departments involved in water education that started as a project and evolved, over a period of 12 yr, into an independent network organisation. The paper pursues three objectives. First, it argues that it makes good sense to organise postgraduate education and research on water resources on a regional scale and presents the WaterNet experience as an example that a regional approach can work. Second, it presents preliminary findings and conclusions that the regional approach presented by WaterNet did make a contribution to the capacity needs of the region both in terms of management and research capacity. Third, it draws two generalised lessons from the WaterNet experience. Lesson one pertains to the importance of legitimate ownership and an accountability structure for network effectiveness. Lesson two is related to the financial and intellectual resources required to jointly developing educational programmes through shared experience.

  2. Seismic Studies

    SciTech Connect

    R. Quittmeyer

    2006-09-25

    This technical work plan (TWP) describes the efforts to develop and confirm seismic ground motion inputs used for preclosure design and probabilistic safety 'analyses and to assess the postclosure performance of a repository at Yucca Mountain, Nevada. As part of the effort to develop seismic inputs, the TWP covers testing and analyses that provide the technical basis for inputs to the seismic ground-motion site-response model. The TWP also addresses preparation of a seismic methodology report for submission to the U.S. Nuclear Regulatory Commission (NRC). The activities discussed in this TWP are planned for fiscal years (FY) 2006 through 2008. Some of the work enhances the technical basis for previously developed seismic inputs and reduces uncertainties and conservatism used in previous analyses and modeling. These activities support the defense of a license application. Other activities provide new results that will support development of the preclosure, safety case; these results directly support and will be included in the license application. Table 1 indicates which activities support the license application and which support licensing defense. The activities are listed in Section 1.2; the methods and approaches used to implement them are discussed in more detail in Section 2.2. Technical and performance objectives of this work scope are: (1) For annual ground motion exceedance probabilities appropriate for preclosure design analyses, provide site-specific seismic design acceleration response spectra for a range of damping values; strain-compatible soil properties; peak motions, strains, and curvatures as a function of depth; and time histories (acceleration, velocity, and displacement). Provide seismic design inputs for the waste emplacement level and for surface sites. Results should be consistent with the probabilistic seismic hazard analysis (PSHA) for Yucca Mountain and reflect, as appropriate, available knowledge on the limits to extreme ground motion at

  3. Increasing Use of Postpartum Family Planning and the Postpartum IUD: Early Experiences in West and Central Africa.

    PubMed

    Pleah, Tsigue; Hyjazi, Yolande; Austin, Suzanne; Diallo, Abdoulaye; Dao, Blami; Waxman, Rachel; Karna, Priya

    2016-08-11

    A global resurgence of interest in the intrauterine device (IUD) as an effective long-acting reversible contraceptive and in improving access to a wide range of contraceptive methods, as well as an emphasis on encouraging women to give birth in health care facilities, has led programs to introduce postpartum IUD (PPIUD) services into postpartum family planning (PPFP) programs. We describe strategic, organizational, and technical elements that contributed to early successes of a regional initiative in West and Central Africa to train antenatal, maternity, and postnatal care providers in PPFP counseling for the full range of available methods and in PPIUD service delivery. In November 2013, the initiative provided competency-based training in Guinea for providers from the main public teaching hospital in 5 selected countries (Benin, Chad, Côte d'Ivoire, Niger, and Senegal) with no prior PPFP counseling or PPIUD capacity. The training was followed by a transfer-of-learning visit and monitoring to support the trained providers. One additional country, Togo, replicated the initiative's model in 2014. Although nascent, this initiative has introduced high-quality PPFP and PPIUD services to the region, where less than 1% of married women of reproductive age use the IUD. In total, 21 providers were trained in PPFP counseling, 18 of whom were also trained in PPIUD insertion. From 2014 to 2015, more than 15,000 women were counseled about PPFP, and 2,269 women chose and received the PPIUD in Benin, Côte d'Ivoire, Niger, Senegal, and Togo. (Introduction of PPIUD services in Chad has been delayed.) South-South collaboration has been central to the initiative's accomplishments: Guinea's clinical centers of excellence and qualified trainers provided a culturally resonant example of a PPFP/PPIUD program, and trainings are creating a network of regional trainers to facilitate expansion. Two of the selected countries (Benin and Niger) have expanded their PPFP/PPUID training

  4. Increasing Use of Postpartum Family Planning and the Postpartum IUD: Early Experiences in West and Central Africa

    PubMed Central

    Pleah, Tsigue; Hyjazi, Yolande; Austin, Suzanne; Diallo, Abdoulaye; Dao, Blami; Waxman, Rachel; Karna, Priya

    2016-01-01

    ABSTRACT A global resurgence of interest in the intrauterine device (IUD) as an effective long-acting reversible contraceptive and in improving access to a wide range of contraceptive methods, as well as an emphasis on encouraging women to give birth in health care facilities, has led programs to introduce postpartum IUD (PPIUD) services into postpartum family planning (PPFP) programs. We describe strategic, organizational, and technical elements that contributed to early successes of a regional initiative in West and Central Africa to train antenatal, maternity, and postnatal care providers in PPFP counseling for the full range of available methods and in PPIUD service delivery. In November 2013, the initiative provided competency-based training in Guinea for providers from the main public teaching hospital in 5 selected countries (Benin, Chad, Côte d’Ivoire, Niger, and Senegal) with no prior PPFP counseling or PPIUD capacity. The training was followed by a transfer-of-learning visit and monitoring to support the trained providers. One additional country, Togo, replicated the initiative’s model in 2014. Although nascent, this initiative has introduced high-quality PPFP and PPIUD services to the region, where less than 1% of married women of reproductive age use the IUD. In total, 21 providers were trained in PPFP counseling, 18 of whom were also trained in PPIUD insertion. From 2014 to 2015, more than 15,000 women were counseled about PPFP, and 2,269 women chose and received the PPIUD in Benin, Côte d’Ivoire, Niger, Senegal, and Togo. (Introduction of PPIUD services in Chad has been delayed.) South–South collaboration has been central to the initiative’s accomplishments: Guinea’s clinical centers of excellence and qualified trainers provided a culturally resonant example of a PPFP/PPIUD program, and trainings are creating a network of regional trainers to facilitate expansion. Two of the selected countries (Benin and Niger) have expanded their PPFP

  5. Report for borehole explosion data acquired in the 1999 Los Angeles Region Seismic Experiment (LARSE II), Southern California: Part I, description of the survey

    USGS Publications Warehouse

    Fuis, Gary S.; Murphy, Janice M.; Okaya, David A.; Clayton, Robert W.; Davis, Paul M.; Thygesen, Kristina; Baher, Shirley A.; Ryberg, Trond; Benthien, Mark L.; Simila, Gerry; Perron, J. Taylor; Yong, Alan K.; Reusser, Luke; Lutter, William J.; Kaip, Galen; Fort, Michael D.; Asudeh, Isa; Sell, Russell; Van Schaack, John R.; Criley, Edward E.; Kaderabek, Ronald; Kohler, Will M.; Magnuski, Nickolas H.

    2001-01-01

    The Los Angeles Region Seismic Experiment (LARSE) is a joint project of the U.S. Geological Survey (USGS) and the Southern California Earthquake Center (SCEC). The purpose of this project is to produce seismic images of the subsurface of the Los Angeles region down to the depths at which earthquakes occur, and deeper, in order to remedy a deficit in our knowledge of the deep structure of this region. This deficit in knowledge has persisted despite over a century of oil exploration and nearly 70 years of recording earthquakes in southern California. Understanding the deep crustal structure and tectonics of southern California is important to earthquake hazard assessment. Specific imaging targets of LARSE include (a) faults, especially blind thrust faults, which cannot be reliably detected any other way; and (b) the depths and configurations of sedimentary basins. Imaging of faults is important in both earthquake hazard assessment but also in modeling earthquake occurrence. Earthquake occurrence cannot be understood unless the earthquake-producing "machinery" (tectonics) is known (Fuis and others, 2001). Imaging the depths and configurations of sedimentary basins is important because earthquake shaking at the surface is enhanced by basin depth and by the presence of sharp basin edges (Wald and Graves, 1998, Working Group on California Earthquake Probabilities, 1995; Field and others, 2001). (Sedimentary basins are large former valleys now filled with sediment eroded from nearby mountains.) Sedimentary basins in the Los Angeles region that have been investigated by LARSE include the Los Angeles, San Gabriel Valley, San Fernando Valley, and Santa Clarita Valley basins. The seismic imaging surveys of LARSE include recording of earthquakes (both local and distant earthquakes) along several corridors (or transects) through the Los Angeles region and also recording of man-made sources along these same corridors. Man-made sources have included airguns offshore and borehole

  6. Initial constraints on crustal structure across the Suwanee Suture and South Georgia Basin from the SUGAR seismic refraction experiment

    NASA Astrophysics Data System (ADS)

    Shillington, D. J.; Lizarralde, D.; Harder, S. H.

    2014-12-01

    Some of the most important unresolved questions in plate tectonics concern the formation and rupture of continents. How does the accretion of terranes contribute to the construction of continental lithosphere, and what processes enable continental lithosphere to rupture? The South Georgia Basin was at the center of the most recent sequence of continental collision and rifting events to shape eastern North America. It is the largest of the failed Mesozoic rift basins that formed during the breakup of Pangea. It straddles the Suwannee Suture, the only well-defined remnant of the Alleghenian suture that joined North America and Gondwana, forming Pangea. The South Georgia Basin also lies at the center of the Central Atlantic Magmatic Province (CAMP). Here we present initial results from the first phase of the SUwanee Suture and GA Rift basin (SUGAR) project, an active-source seismic refraction project to image the crustal structure across these features. During March 2014, we acquired data along a ~325-km-long, NW-SE oriented profile that crossed the Suwanne Suture and western part of South Georgia Basin, extending from north of Columbus, GA to northernmost Florida east of Jasper, FL. The profile was densely instrumented with single-channel RekTek 125A seismometers ("Texans") spaced at ~250 m and deployed along state and country roads, yielding a total of 1193 seismometers along the profile. Thirty-three students and young scientists were involved in the deployment and recovery. The sources were 100 to 1800 lb shots spaced at ~20-50 km. The data are of exceptionally high quality. On nearly all shots, we observe arrivals out to the largest shot-receiver offsets. Within the basin, refractions through the sedimentary section with apparent velocities of ~3-4 km/s are observed to maximum offsets of 7 km. Crustal refractions are observed at a wide-range of offsets with apparent velocities increasing from ~5.5 km/s to as high as ~7.25 km/s. At offsets greater than 150-180 km

  7. Seismic sequences in the Sombrero Seismic Zone

    NASA Astrophysics Data System (ADS)

    Pulliam, J.; Huerfano, V. A.; ten Brink, U.; von Hillebrandt, C.

    2007-05-01

    The northeastern Caribbean, in the vicinity of Puerto Rico and the Virgin Islands, has a long and well-documented history of devastating earthquakes and tsunamis, including major events in 1670, 1787, 1867, 1916, 1918, and 1943. Recently, seismicity has been concentrated to the north and west of the British Virgin Islands, in the region referred to as the Sombrero Seismic Zone by the Puerto Rico Seismic Network (PRSN). In the combined seismicity catalog maintained by the PRSN, several hundred small to moderate magnitude events can be found in this region prior to 2006. However, beginning in 2006 and continuing to the present, the rate of seismicity in the Sombrero suddenly increased, and a new locus of activity developed to the east of the previous location. Accurate estimates of seismic hazard, and the tsunamigenic potential of seismic events, depend on an accurate and comprehensive understanding of how strain is being accommodated in this corner region. Are faults locked and accumulating strain for release in a major event? Or is strain being released via slip over a diffuse system of faults? A careful analysis of seismicity patterns in the Sombrero region has the potential to both identify faults and modes of failure, provided the aggregation scheme is tuned to properly identify related events. To this end, we experimented with a scheme to identify seismic sequences based on physical and temporal proximity, under the assumptions that (a) events occur on related fault systems as stress is refocused by immediately previous events and (b) such 'stress waves' die out with time, so that two events that occur on the same system within a relatively short time window can be said to have a similar 'trigger' in ways that two nearby events that occurred years apart cannot. Patterns that emerge from the identification, temporal sequence, and refined locations of such sequences of events carry information about stress accommodation that is obscured by large clouds of

  8. Clear the Mind of Pre-Conceived Ideas and Get Your Hands Dirty! An Approach to Field-Based Courses: The SLUSE-Southern Africa Experience

    ERIC Educational Resources Information Center

    Hill, Trevor R.; Traynor, Catherine H.; Birch-Thomsen, Torben; De Neergaard, Andreas; Bob, Urmilla; Manyatsi, Absalom M.; Sebego, Reuben J.

    2008-01-01

    This paper explores an approach to problem-oriented, interdisciplinary field-based courses devised by university consortia in southern Africa and Denmark. The SLUSE (Sustainable Land Use and Natural Resource Management) model has been applied on six three-week field courses within southern Africa and trained over 200 students. Student groups…

  9. Key aspects governing induced seismicity

    NASA Astrophysics Data System (ADS)

    Buijze, Loes; Wassing, Brecht; Fokker, Peter

    2013-04-01

    In the past decades numerous examples of earthquakes induced by human-induced changes in subsurface fluid pressures have been reported. This poses a major threat to the future development of some of these operations and calls for an understanding and quantification of the seismicity generated. From geomechanical considerations and insights from laboratory experiments the factors controlling induced seismicity may be grouped into 4 categories; the magnitude of the stress disturbance, the pre-existing stress conditions, the reservoir/fault rock properties and the local geometry. We investigated whether the (relative) contributions of these factors and their influence on magnitudes generated could be recognized by looking at the entire dataset of reported cases of induced seismicity as a whole, and what this might imply for future developments. An extensive database has been built out of over a 160 known cases of induced seismicity worldwide, incorporating the relevant geological, seismological and fluid-related parameters. The cases studied include hydrocarbon depletion and secondary recovery, waste water injection, (enhanced) geothermal systems and hydraulic fracturing with observed magnitudes ranging from less than -1.5 to 7. The parameters taken into account were based on the theoretical background of the mechanisms of induced seismicity and include the injection/depletion-related parameters, (spatial) characteristics of seismicity, lithological properties and the local stress situation. Correlations between the seismic response and the geological/geomechanical characteristics of the various sites were investigated. The injected/depleted volumes and the scale of the activities are major controlling factors on the maximum magnitudes generated. Spatial signatures of seismicity such as the depth and lateral spread of the seismicity were observed to be distinct for different activities, which is useful when considering future operations. Where available the local

  10. A little bit of Africa in Brazil: ethnobiology experiences in the field of Afro-Brazilian religions.

    PubMed

    Albuquerque, Ulysses Paulino

    2014-01-01

    This essay, which is the fourth in the series "Recollections, Reflections, and Revelations: Ethnobiologists and Their First Time in the Field", is a personal reflection by the researcher on his first field experience with ethnobiology of so called Afro-Brazilian cults. The author recounts his feelings and concerns associated with initial fieldwork. PMID:24467714

  11. A little bit of Africa in Brazil: ethnobiology experiences in the field of Afro-Brazilian religions

    PubMed Central

    2014-01-01

    This essay, which is the fourth in the series “Recollections, Reflections, and Revelations: Ethnobiologists and Their First Time in the Field”, is a personal reflection by the researcher on his first field experience with ethnobiology of so called Afro-brazilian cults. The author recounts his feelings and concerns associated with initial fieldwork. PMID:24467714

  12. Capacity Building in Southern Africa: Experiences and Reflections--Towards Joint Knowledge Production and Social Change in International Development Cooperation

    ERIC Educational Resources Information Center

    Zeelen, Jacques; van der Linden, Josje

    2009-01-01

    The intent of capacity building in international development cooperation is to enable people to control their own development. Important premises are ownership, choice and self-esteem. The authors analyse the dynamics of the enabling process in practice, based on their own experiences working for several years in universities in developing…

  13. Using ICT at an Open Distance Learning (ODL) Institution in South Africa: The Learning Experiences of Students with Visual Impairments

    ERIC Educational Resources Information Center

    Mokiwa, S. A.; Phasha, T. N.

    2012-01-01

    For students with visual impairments, Information and Communication Technology (ICT) has become an important means through which they can learn and access learning materials at various levels of education. However, their learning experiences in using such form of technologies have been rarely documented, thus suggests society's lack of…

  14. Seismic Tomography.

    ERIC Educational Resources Information Center

    Anderson, Don L.; Dziewonski, Adam M.

    1984-01-01

    Describes how seismic tomography is used to analyze the waves produced by earthquakes. The information obtained from the procedure can then be used to map the earth's mantle in three dimensions. The resulting maps are then studied to determine such information as the convective flow that propels the crustal plates. (JN)

  15. Evaluating computerized health information systems: hardware, software and human ware: experiences from the Northern Province, South Africa.

    PubMed

    Herbst, K; Littlejohns, P; Rawlinson, J; Collinson, M; Wyatt, J C

    1999-09-01

    Despite enormous investment world-wide in computerized health information systems their overall benefits and costs have rarely been fully assessed. A major new initiative in South Africa provides the opportunity to evaluate the introduction of information technology from a global perspective and assess its impact on public health. The Northern Province is implementing a comprehensive integrated hospital information system (HIS) in all of its 42 hospitals. These include two mental health institutions, eight regional hospitals (two acting as a tertiary complex with teaching responsibilities) and 32 district hospitals. The overall goal of the HIS is to improve the efficiency and effectiveness of health (and welfare) services through the creation and use of information, for clinical, administrative and monitoring purposes. This multi-site implementation is being undertaken as a single project at a cost of R130 million (which represents 2.5 per cent of the health and welfare budget on an annual basis). The implementation process commenced on 1 September 1998 with the introduction of the system into Mankweng Hospital as the pilot site and is to be completed in the year 2001. An evaluation programme has been designed to maximize the likelihood of success of the implementation phase (formative evaluation) as well as providing an overall assessment of its benefits and costs (summative evaluation). The evaluation was designed as a form of health technology assessment; the system will have to prove its worth (in terms of cost-effectiveness) relative to other interventions. This is more extensive than the traditional form of technical assessment of hardware and software functionality, and moves into assessing the day-to-day utility of the system, the clinical and managerial environment in which it is situated (humanware), and ultimately its effects on the quality of patient care and public health. In keeping with new South African legislation the evaluation process sought to

  16. Seismic Symphonies

    NASA Astrophysics Data System (ADS)

    Strinna, Elisa; Ferrari, Graziano

    2015-04-01

    The project started in 2008 as a sound installation, a collaboration between an artist, a barrel organ builder and a seismologist. The work differs from other attempts of sound transposition of seismic records. In this case seismic frequencies are not converted automatically into the "sound of the earthquake." However, it has been studied a musical translation system that, based on the organ tonal scale, generates a totally unexpected sequence of sounds which is intended to evoke the emotions aroused by the earthquake. The symphonies proposed in the project have somewhat peculiar origins: they in fact come to life from the translation of graphic tracks into a sound track. The graphic tracks in question are made up by copies of seismograms recorded during some earthquakes that have taken place around the world. Seismograms are translated into music by a sculpture-instrument, half a seismograph and half a barrel organ. The organ plays through holes practiced on paper. Adapting the documents to the instrument score, holes have been drilled on the waves' peaks. The organ covers about three tonal scales, starting from heavy and deep sounds it reaches up to high and jarring notes. The translation of the seismic records is based on a criterion that does match the highest sounds to larger amplitudes with lower ones to minors. Translating the seismogram in the organ score, the larger the amplitude of recorded waves, the more the seismogram covers the full tonal scale played by the barrel organ and the notes arouse an intense emotional response in the listener. Elisa Strinna's Seismic Symphonies installation becomes an unprecedented tool for emotional involvement, through which can be revived the memory of the greatest disasters of over a century of seismic history of the Earth. A bridge between art and science. Seismic Symphonies is also a symbolic inversion: the instrument of the organ is most commonly used in churches, and its sounds are derived from the heavens and

  17. Assessing the role of fluids in episodic tremor and slip events using active seismic sources: results from a prototype experiment in Cascadia (Invited)

    NASA Astrophysics Data System (ADS)

    Niu, F.; Silver, P. G.; Nigbor, R.

    2009-12-01

    Recently, the so-called episodic tremor and slip (ETS) that consist of seismically recorded tremor events with characteristic frequencies of 1-15 Hz and slow slip events observed by GPS and strainmeters with durations of order weeks were widely observed in a variety of environments worldwide. While the community continues to make interesting observations, the underlying physical process remains poorly understood. There have been many proposed mechanisms, most of which invoke fluids. Many observations suggest that ETS can be triggered by very small stresses despite the high confining pressures at the depth of ETS, which has led many to conclude that fluids at the slab interface are under lithostatic pressure, and that furthermore there is likely fluid flow at the time of ETS events. Thus far, there is little data with which to evaluate these ideas. We have been interested in determining whether or not there are spatiotemporal structural changes in the crust and upper-most mantle associated with this phenomenon. We conducted a control-source experiment in Cascadia to examine the feasibility of using the reflection/scattering waves from the slab interface to look for structural changes that may reflect the migration of fluids. We selected a highly repeatable source, an eccentric-mass “shaker” designed for engineering studies, as the seismic source. The shaker was provided by NEES@UCLA. A 15’x15’ cement pad for installing the shaker was built on basaltic bedrock that is part of the Tertiary volcanic rocks of the Crescent Formation. We deployed arrays of short period instruments at two distances from the source: 30km and 90km away. The 90km array was deployed at the site of a previous deployment of the A of A team at Big Skidder Hill. Including our stations and those of A of A, we had 32 seismometers in all. The array has a station spacing of 60-100 m and an aperture about 1 to 1.5 km. During our experiment period, we were able to record a quarry blast near our

  18. The Seismotectonic Map of Africa

    NASA Astrophysics Data System (ADS)

    Meghraoui, Mustapha

    2015-04-01

    We present the Seismotectonic Map of Africa based on a geological, geophysical and geodetic database including the instrumental seismicity and re-appraisal of large historical events with harmonization and homogenization of earthquake parameters in catalogues. Although the seismotectonic framework and mapping of the African continent is a difficult task, several previous and ongoing projects provide a wealth of data and outstanding results. The database of large and moderate earthquakes in different geological domains includes the coseismic and Quaternary faulting that reveals the complex nature of the active tectonics in Africa. The map also benefits from previous works on local and regional seismotectonic maps that needed to be integrated with the lithospheric and upper mantle structures from tomographic anisotropy and gravity anomaly into a continental framework. The synthesis of earthquake and volcanic studies with the analysis of long-term (late Quaternary) and short-term (last decades and centuries) active deformation observed with geodetic and other approaches presented along with the seismotectonic map serves as a basis for hazard calculations and the reduction of seismic risks. The map may also be very useful in the assessment of seismic hazard and mitigation of earthquake risk for significant infrastructures and their implications in the socio-economic impact in Africa. In addition, the constant population increase and infrastructure growth in the continent that exacerbate the earthquake risk justify the necessity for a continuous updating of the seismotectonic map. The database and related map are prepared in the framework of the IGC Project-601 "Seismotectonics and Seismic Hazards in Africa" of UNESCO-IUGS, funded by the Swedish International Development Agency and UNESCO-Nairobi for a period of 4 years (2011 - 2014), extended to 2016. * Mustapha Meghraoui (Coordinator) EOST - IPG Strasbourg CNRS-UMR 7516 m.meghraoui@unistra.fr corresponding author

  19. Smoke in Southern Africa

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This SeaWiFS true-color image acquired over Southern Africa on Sept. 4, 2000, shows a thick shroud of smoke and haze blanketing much of the southern half of the continent. The smoke in this scene is being generated by a tremendous number of fires burning over a large area across the countries of Angola, Zambia, Mozambique, Zimbabwe, Botswana, and the Northern Province of South Africa. In this image, the smoke (grey pixels) is easily distinguished from clouds (bright white pixels). Refer to the Images and Data section for a larger scale view of the fires in Southern Africa. Data from both the SeaWiFS and Terra satellites are being used by an international team of scientists participating in the SAFARI field experiment. The objective of SAFARI is to measure the effects of windblown smoke and dust on air quality and the Earth's radiant energy budget. This image was produced using SeaWiFS channels 6, 5, and 1 (centered at 670 nm, 555 nm , and 412 nm, respectively). The data were acquired and provided by the Satellite Applications Center in Pretoria, South Africa. Image courtesy Gene Feldman, SeaWiFS Project and Orbital Sciences

  20. Why a regional approach to postgraduate water education makes sense - the WaterNet experience in Southern Africa

    NASA Astrophysics Data System (ADS)

    Jonker, L.; van der Zaag, P.; Gumbo, B.; Rockström, J.; Love, D.; Savenije, H. H. G.

    2012-03-01

    This paper reports the experience of a regional network of academic departments involved in water education that started as a project and evolved, over a period of 12 yr, into an independent network organisation. The paper pursues three objectives. First, it argues that it makes good sense to organise postgraduate education and research on water resources on a regional scale. This is because water has a transboundary dimension that poses delicate sharing questions, an approach that promotes a common understanding of what the real water-related issues are, results in future water specialists speaking a common (water) language, enhances mutual respect, and can thus be considered an investment in future peace. Second, it presents the WaterNet experience as an example that a regional approach can work and has an impact. Third, it draws three generalised lessons from the WaterNet experience. Lesson 1: For a regional capacity building network to be effective, it must have a legitimate ownership structure and a clear mandate. Lesson 2: Organising water-related training opportunities at a regional and transboundary scale makes sense - not only because knowledge resources are scattered, but also because the topic - water - has a regional and transboundary scope. Lesson 3: Jointly developing educational programmes by sharing expertise and resources requires intense intellectual management and sufficient financial means.

  1. Analysis of the seismic signals generated by controlled single-block rockfalls on soft clay shales sediments: the Rioux Bourdoux slope experiment (French Alps).

    NASA Astrophysics Data System (ADS)

    Hibert, Clément; Provost, Floriane; Malet, Jean-Philippe; Bourrier, Franck; Berger, Frédéric; Bornemann, Pierrick; Borgniet, Laurent; Tardif, Pascal; Mermin, Eric

    2016-04-01

    Understanding the dynamics of rockfalls is critical to mitigate the associated hazards but is made very difficult by the nature of these natural disasters that makes them hard to observe directly. Recent advances in seismology allow to determine the dynamics of the largest landslides on Earth from the very low-frequency seismic waves they generate. However, the vast majority of rockfalls that occur worldwide are too small to generate such low-frequency seismic waves and thus these methods cannot be used to reconstruct their dynamics. However, if seismic sensors are close enough, these events will generate high-frequency seismic signals. Unfortunately we cannot yet use these high-frequency seismic records to infer parameters synthetizing the rockfall dynamics as the source of these waves is not well understood. One of the first steps towards understanding the physical processes involved in the generation of high-frequency seismic waves by rockfalls is to study the link between the dynamics of a single block propagating along a well-known path and the features of the seismic signal generated. We conducted controlled releases of single blocks of limestones in a gully of clay-shales (e.g. black marls) in the Rioux Bourdoux torrent (French Alps). 28 blocks, with masses ranging from 76 kg to 472 kg, were released. A monitoring network combining high-velocity cameras, a broadband seismometer and an array of 4 high-frequency seismometers was deployed near the release area and along the travel path. The high-velocity cameras allow to reconstruct the 3D trajectories of the blocks, to estimate their velocities and the position of the different impacts with the slope surface. These data are compared to the seismic signals recorded. As the distance between the block and the seismic sensors at the time of each impact is known, we can determine the associated seismic signal amplitude corrected from propagation and attenuation effects. We can further compare the velocity, the

  2. South Africa's Unintended Experiment in School Choice: How the National Education Policy Act, the South Africa Schools Act and the Employment of Educators Act Create the Enabling Conditions for Quasi-Markets in Schools

    ERIC Educational Resources Information Center

    Woolman, Stuart; Fleisch, Brahm

    2006-01-01

    School choice is often identified with right-leaning, voucher-happy, market-oriented public school systems like those found in the United States. Thus, the proposition that a social democratic state such as South Africa will offer many primary and secondary school learners far greater choice strikes many as counter-intuitive and implausible. The…

  3. Lunar seismic data analysis

    NASA Technical Reports Server (NTRS)

    Nakamura, Y.; Latham, G. V.; Dorman, H. J.

    1982-01-01

    The scientific data transmitted continuously from all ALSEP (Apollo Lunar Surface Experiment Package) stations on the Moon and recorded on instrumentation tapes at receiving stations distributed around the Earth were processed. The processing produced sets of computer-compatible digital tapes, from which various other data sets convenient for analysis were generated. The seismograms were read, various types of seismic events were classified; the detected events were cataloged.

  4. Development and preliminary validation of a screen for interpersonal childhood trauma experiences among school-going youth in Durban, South Africa.

    PubMed

    Collings, Steven J; Valjee, Sachet R; Penning, Susan L

    2013-01-01

    This paper describes the development and preliminary validation of the Developmental Trauma Inventory (DTI), which is a 36-item, retrospective, self-administered screen for interpersonal childhood trauma experiences developed specifically for the South African context. Preliminary validation of the inventory was conducted using a sample of 720 school-going adolescents attending a high school in the Durban Metropolitan area (South Africa). Factor analysis produced the best fit for a 10-factor model (emotional abuse, community assault, domestic assault, poverty, witnessing community violence, witnessing domestic violence, indecent assault, domestic neglect, rape, and domestic injury). Contrary to expectations, items relating to loss and separation (e.g. death of a parent) did not produce a clear factor structure. Identified scales had good internal consistency (0.70 to 0.81), low factor inter-correlations, and high concurrent criterion-related validity in the sense that all scales were significantly correlated with scores on clinical measures of post-traumatic stress disorder (PTSD) and/or complex PTSD. These findings provide preliminary support for the utility of DTI in the South African context. PMID:25860304

  5. Pregnant women's experiences of male partner involvement in the context of prevention of mother-to-child transmission in Khayelitsha, South Africa.

    PubMed

    Brittain, Kirsty; Giddy, Janet; Myer, Landon; Cooper, Diane; Harries, Jane; Stinson, Kathryn

    2015-01-01

    Male partner involvement (MPI) has been identified as a priority intervention in programmes for the prevention of mother-to-child transmission (PMTCT) of HIV, but rates of MPI remain low worldwide. This study used a quantitative survey (n=170) and two focus group discussions (FGDs) with 16 HIV-positive pregnant women attending a public sector antenatal care service in Khayelitsha, South Africa, to examine the determinants of high levels of involvement and generate a broader understanding of women's experiences of MPI during pregnancy. Among survey participants, 74% had disclosed their status to their partner, and most reported high levels of communication around HIV testing and preventing partner transmission, as well as high levels of MPI. High MPI was significantly more likely among women who were cohabiting with their partner; who had reportedly disclosed their HIV status to their partner; and who reported higher levels of HIV-related communication with their partner. FGD participants discussed a range of ways in which partners can be supportive during pregnancy, not limited to male attendance of antenatal care. MPI appears to be a feasible intervention in this context, and MPI interventions should aim to encourage male partner attendance of antenatal care as well as greater involvement in pregnancy more generally. Interventions that target communication are needed to facilitate HIV-related communication and disclosure within couples. MPI should remain a priority intervention in PMTCT programmes, and increased efforts should be made to promote MPI in PMTCT. PMID:25738960

  6. Separate Schools and Separate People of South Africa

    ERIC Educational Resources Information Center

    Parker, Franklin

    1972-01-01

    After reviewing the historical and legal background of race relations in South Africa, the author reviews his experiences at a recent conference on Accelerated Development in Southern Africa,'' held in Johannesburg. (JM)

  7. Diagnosing GCM errors over West Africa using relaxation experiments. Part I: summer monsoon climatology and interannual variability

    NASA Astrophysics Data System (ADS)

    Pohl, Benjamin; Douville, Hervé

    2011-10-01

    The CNRM atmospheric general circulation model Arpege-Climat is relaxed towards atmospheric reanalyses outside the 10°S-32°N 30°W-50°E domain in order to disentangle the regional versus large-scale sources of climatological biases and interannual variability of the West African monsoon (WAM). On the one hand, the main climatological features of the monsoon, including the spatial distribution of summer precipitation, are only weakly improved by the nudging, thereby suggesting the regional origin of the Arpege-Climat biases. On the other hand, the nudging technique is relatively efficient to control the interannual variability of the WAM dynamics, though the impact on rainfall variability is less clear. Additional sensitivity experiments focusing on the strong 1994 summer monsoon suggest that the weak sensitivity of the model biases is not an artifact of the nudging design, but the evidence that regional physical processes are the main limiting factors for a realistic simulation of monsoon circulation and precipitation in the Arpege-Climat model. Sensitivity experiments to soil moisture boundary conditions are also conducted and highlight the relevance of land-atmosphere coupling for the amplification of precipitation biases. Nevertheless, the land surface hydrology is not the main explanation for the model errors that are rather due to deficiencies in the atmospheric physics. The intraseasonal timescale and the model internal variability are discussed in a companion paper.

  8. A global approach to the management of EMR (Electronic Medical Records) of patients with HIV/AIDS in Sub-Saharan Africa: the experience of DREAM Software

    PubMed Central

    2009-01-01

    Background The DREAM Project operates within the framework of the national health systems of several sub-Saharan African countries and aims to introduce the essential components of an integrated strategy for the prevention and treatment of HIV/AIDS. The project is intended to serve as a model for a wide-ranging scale-up in the response to the epidemic. This paper aims to show DREAM's challenges and the solutions adopted. One of the solutions is the efficient management of the clinical data regarding the treatment of the patients and epidemiological analyses. Methods Specific software for the management of the patients' EMR has been created within the DREAM programme in order to deal with the challenges deriving from the context in which DREAM operates. Setting up a computer infrastructure in health centres, providing a power supply, as well as managing the data and the project resources efficiently and reliably, are some of the questions that have been analysed in this study. Results Over the years this software has proved that it is able to respond to the need for efficient management of the clinical data and organization of the health centres. Today it is used in 10 countries in sub-Saharan Africa by thousands of professionals and by now it has reached its fourth version. The medical files of over 73,000 assisted patients are managed by this software and the data collected with it have become essential for the epidemiological research that is carried out to improve the effectiveness of the therapy. Conclusion Sub-Saharan Africa is the region hardest hit by HIV and AIDS in the world. However, the resources and responses adopted so far, to confront the epidemic, have at times been rather minimalist. The DREAM project has faced the battle against the epidemic by equipping itself with qualitative standards comparable to Western ones. The experience of DREAM has revealed that it is indeed possible to guarantee levels of excellence in developing countries, also in the

  9. Crustal architecture of the southern Uralides from true amplitude processing of the Urals Seismic Experiment and Integrated Studies (URSEIS) vibroseis profile

    NASA Astrophysics Data System (ADS)

    Tryggvason, A.; Brown, D.; PéRez-Estaún, A.

    2001-12-01

    True amplitude processing of the Urals Seismic Experiment and Integrated Studies (URSEIS) vibroseis deep reflection seismic data acquired by the URSEIS consortium shows the southern Uralide crust to be composed of four major blocks with distinctive reflection characteristics. These blocks are juxtaposed along crustal-scale boundaries. The foreland thrust and fold belt, developed from the East European craton crust, is imaged as subhorizontal to east dipping reflectivity that can be related to its Paleozoic and older tectonic history. The Moho beneath the foreland thrust and fold belt is not imaged in the vibroseis data set. The Main Uralian fault (the major arc-continent suture) is unreflective, but its subsurface location can be inferred by the truncation of the reflection pattern of the East European craton and its contrast with that of the Magnitogorsk arc. The Magnitogorsk arc reflectivity is characterized by patchy, noncoherent to coherent reflections in the upper ˜10 - 15 km that are interpreted to be related to the arc volcanic rocks. Below this, reflectivity is diffuse, or the arc crust is transparent, and the Moho is not imaged. The East Magnitogorsk fault zone, which juxtaposes the arc against the East Uralian zone, is not imaged by the data. The upper 5 to 6 km of the East Uralian zone, corresponding to the Dzhabyk granite, is transparent. Below the granite the crust is characterised by east dipping patches of moderately coherent, high-amplitude reflections that in the east become shallowly west-dipping. A ˜10 km thick, west dipping band of coherent, high amplitude reflections between 12 and 35 km depth, corresponding to the Kartaly Reflection Sequence, extends beneath almost the entire East Uralian zone. The crust beneath the easternmost East Uralian zone reaches 53 km in thickness. The upper and middle crust of the Trans-Uralian zone is characterized by a series of east and west dipping, concave upward, moderately coherent, high-amplitude reflections

  10. High Voltage Seismic Generator

    NASA Astrophysics Data System (ADS)

    Bogacz, Adrian; Pala, Damian; Knafel, Marcin

    2015-04-01

    This contribution describes the preliminary result of annual cooperation of three student research groups from AGH UST in Krakow, Poland. The aim of this cooperation was to develop and construct a high voltage seismic wave generator. Constructed device uses a high-energy electrical discharge to generate seismic wave in ground. This type of device can be applied in several different methods of seismic measurement, but because of its limited power it is mainly dedicated for engineering geophysics. The source operates on a basic physical principles. The energy is stored in capacitor bank, which is charged by two stage low to high voltage converter. Stored energy is then released in very short time through high voltage thyristor in spark gap. The whole appliance is powered from li-ion battery and controlled by ATmega microcontroller. It is possible to construct larger and more powerful device. In this contribution the structure of device with technical specifications is resented. As a part of the investigation the prototype was built and series of experiments conducted. System parameter was measured, on this basis specification of elements for the final device were chosen. First stage of the project was successful. It was possible to efficiently generate seismic waves with constructed device. Then the field test was conducted. Spark gap wasplaced in shallowborehole(0.5 m) filled with salt water. Geophones were placed on the ground in straight line. The comparison of signal registered with hammer source and sparker source was made. The results of the test measurements are presented and discussed. Analysis of the collected data shows that characteristic of generated seismic signal is very promising, thus confirms possibility of practical application of the new high voltage generator. The biggest advantage of presented device after signal characteristics is its size which is 0.5 x 0.25 x 0.2 m and weight approximately 7 kg. This features with small li-ion battery makes

  11. Gambian-British and Nigerian-British Children's and Families' Experiences of Migration "Back" to West Africa. Research Briefing No. 13

    ERIC Educational Resources Information Center

    Roberts-Holmes, Guy

    2013-01-01

    This research looks at the factors motivating Gambian-British and Nigerian-British parents to send their children "back" to West Africa and what this means for parents, children and families on both continents.

  12. Integrated verification experiment data collected as part of the Los Alamos National Laboratory`s Source Region program. Appendix F: Regional data from Lawrence Livermore National Laboratory and Sandia National Laboratory Seismic Networks

    SciTech Connect

    Taylor, S.R.

    1993-06-11

    A dataset of regional seismograms assembled for a series of Integrated Verification Experiments conducted by the Los Alamos National Laboratory Source Region program is described. The seismic data has been assembled from networks operated by Lawrence Livermore National Laboratory and Sandia National Laboratory. Examples of the data are shown and basic recording characteristics of the network are described. The seismograms are available on a data tape in SAC format upon request.

  13. Surveying World Heritage Islamic Monuments in North Africa: Experiences with Simple Photogrammetric Tools and no Previous Planning

    NASA Astrophysics Data System (ADS)

    Almagro, A.

    2013-07-01

    Different experiences of surveys of Islamic monuments from different sites of Tunisia, Algeria and Morocco are presented. They have been made with simple tools: one photographic camera and a laser meter, without a previous planning or prevision for the survey, profiting from visits organized during scientific meetings to which the author was invited. Some of these monuments belong to sites included in the World Heritage List, but no metric documents or only low quality information is available. Monumental Almohad gates from Rabat and Marrakech, the al-Badi palace of Marrakech, the minarets of Mansura and the Qala of Beni Hammad, the dome in front of the mihrab of the mosque of Tlemcen are some of the examples to be presented. The methodology applied is based on ideas and tools acquired in CIPA meetings proving the usefulness of these encounters but supporting the idea that "providers" should provide tools and methods and "users" should be responsible for documentation, never missing the opportunity of acquiring knowledge from the heritage during the survey process.

  14. Precise determination of phase relations in pyrolite across the 660 km seismic discontinuity by in situ X-ray diffraction and quench experiments

    NASA Astrophysics Data System (ADS)

    Nishiyama, Norimasa; Irifune, Tetsuo; Inoue, Toru; Ando, Jun-ichi; Funakoshi, Ken-ichi

    2004-06-01

    Mineral assemblage changes in a pyrolite composition with increasing pressure were observed by in situ X-ray diffraction and quench experiments at pressures near that of the 660 km seismic discontinuity and at a fixed temperature of 1600 °C. According to results obtained by in situ X-ray diffraction experiments, ringwoodite (Rw) was observed with majorite garnet and CaSiO 3-rich perovskite at pressures of about 20-22 GPa. Dissociation of ringwoodite to MgSiO 3-rich perovskite and magnesiowüstite (Mw) was completed at 22.0±0.2 GPa according to Matsui et al.'s periclase pressure scale, and at 21.7±0.1 GPa according to Shim et al.'s gold pressure scale. Majorite garnet persisted to about 24 GPa where pyrolite transformed to a lower mantle mineral assemblage, i.e. MgSiO 3-perovskite, CaSiO 3-rich perovskite, and magnesiowüstite. Thus, majorite garnet coexists with the lower mantle assemblage at pressures of about 22-24 GPa. In the quench experiments, an assemblage of MgSiO 3-perovskite, magnesiowüstite, CaSiO 3-rich perovskite, and majorite garnet was synthesized at 22.5 GPa and 1600 °C, in which Mg-perovskite contained 2.8 wt.% Al 2O 3, and was significantly poorer in Fe than coexisting magnesiowüstite. The Fe-Mg partition coefficient between Mg-perovskite and magnesiowüstite including ferric iron ( Kapp=0.27±0.06) is very close to that in the Al-free system, which suggests that these P- T conditions are in the vicinity of those of ringwoodite decomposition. Both the results of in situ X-ray diffraction and quench experiments in the present study yield a convergent result that ringwoodite decomposes into Mg-perovskite and magnesiowüstite before the garnet-to-perovskite transition at 1600 °C in pyrolite. The relation between the Al content in Mg-perovskite and Kapp in pyrolite is non-linear, which is consistent with the Fe-Mg partitioning between Mg-perovskite and magnesiowüstite previously reported for a simpler MgO-FeO-Al 2O 3-SiO 2 system.

  15. The role of fluid pressure in induced vs. triggered seismicity: insights from rock deformation experiments on carbonates.

    PubMed

    Scuderi, Marco M; Collettini, Cristiano

    2016-01-01

    Fluid overpressure is one of the primary mechanisms for tectonic fault slip, because fluids lubricate the fault and fluid pressure reduces the effective normal stress that holds the fault in place. However, current models of earthquake nucleation, based on rate- and state- friction laws, imply that stable sliding is favoured by the increase of pore fluid pressure. Despite this controversy, currently, there are only a few studies on the role of fluid pressure under controlled, laboratory conditions. Here, we use laboratory experiments, to show that the rate- and state- friction parameters do change with increasing fluid pressure. We tested carbonate gouges from sub hydrostatic to near lithostatic fluid pressure conditions, and show that the friction rate parameter (a - b) evolves from velocity strengthening to velocity neutral behaviour. Furthermore, the critical slip distance, Dc, decreases from about 90 to 10 μm. Our data suggest that fluid overpressure plays an important role in controlling the mode of fault slip. Since fault rheology and fault stability parameters change with fluid pressure, we suggest that a comprehensive characterization of these parameters is fundamental for better assessing the role of fluid pressure in natural and human induced earthquakes. PMID:27112408

  16. The role of fluid pressure in induced vs. triggered seismicity: insights from rock deformation experiments on carbonates

    PubMed Central

    Scuderi, Marco M.; Collettini, Cristiano

    2016-01-01

    Fluid overpressure is one of the primary mechanisms for tectonic fault slip, because fluids lubricate the fault and fluid pressure reduces the effective normal stress that holds the fault in place. However, current models of earthquake nucleation, based on rate- and state- friction laws, imply that stable sliding is favoured by the increase of pore fluid pressure. Despite this controversy, currently, there are only a few studies on the role of fluid pressure under controlled, laboratory conditions. Here, we use laboratory experiments, to show that the rate- and state- friction parameters do change with increasing fluid pressure. We tested carbonate gouges from sub hydrostatic to near lithostatic fluid pressure conditions, and show that the friction rate parameter (a − b) evolves from velocity strengthening to velocity neutral behaviour. Furthermore, the critical slip distance, Dc, decreases from about 90 to 10 μm. Our data suggest that fluid overpressure plays an important role in controlling the mode of fault slip. Since fault rheology and fault stability parameters change with fluid pressure, we suggest that a comprehensive characterization of these parameters is fundamental for better assessing the role of fluid pressure in natural and human induced earthquakes. PMID:27112408

  17. The role of fluid pressure in induced vs. triggered seismicity: insights from rock deformation experiments on carbonates

    NASA Astrophysics Data System (ADS)

    Scuderi, Marco M.; Collettini, Cristiano

    2016-04-01

    Fluid overpressure is one of the primary mechanisms for tectonic fault slip, because fluids lubricate the fault and fluid pressure reduces the effective normal stress that holds the fault in place. However, current models of earthquake nucleation, based on rate- and state- friction laws, imply that stable sliding is favoured by the increase of pore fluid pressure. Despite this controversy, currently, there are only a few studies on the role of fluid pressure under controlled, laboratory conditions. Here, we use laboratory experiments, to show that the rate- and state- friction parameters do change with increasing fluid pressure. We tested carbonate gouges from sub hydrostatic to near lithostatic fluid pressure conditions, and show that the friction rate parameter (a ‑ b) evolves from velocity strengthening to velocity neutral behaviour. Furthermore, the critical slip distance, Dc, decreases from about 90 to 10 μm. Our data suggest that fluid overpressure plays an important role in controlling the mode of fault slip. Since fault rheology and fault stability parameters change with fluid pressure, we suggest that a comprehensive characterization of these parameters is fundamental for better assessing the role of fluid pressure in natural and human induced earthquakes.

  18. Qualitative soil moisture assessment in semi-arid Africa: the role of experience and training on inter-rater reliability

    NASA Astrophysics Data System (ADS)

    Rinderer, M.; Komakech, H.; Müller, D.; Seibert, J.

    2015-03-01

    Soil and water management is particularly relevant in semi-arid regions to enhance agricultural productivity. During periods of water scarcity soil moisture differences are important indicators of the soil water deficit and are traditionally used for allocating water resources among farmers of a village community. Here we present a simple, inexpensive soil wetness classification scheme based on qualitative indicators which one can see or touch on the soil surface. It incorporates the local farmers' knowledge on the best soil moisture conditions for seeding and brick making in the semi-arid environment of the study site near Arusha, Tanzania. The scheme was tested twice in 2014 with farmers, students and experts (April: 40 persons, June: 25 persons) for inter-rater reliability, bias of individuals and functional relation between qualitative and quantitative soil moisture values. During the test in April farmers assigned the same wetness class in 46% of all cases while students and experts agreed in about 60% of all cases. Students who had been trained in how to apply the method gained higher inter-rater reliability than their colleagues with only a basic introduction. When repeating the test in June, participants were given improved instructions, organized in small sub-groups, which resulted in a higher inter-rater reliability among farmers. In 66% of all classifications farmers assigned the same wetness class and the spread of class assignments was smaller. This study demonstrates that a wetness classification scheme based on qualitative indicators is a robust tool and can be applied successfully regardless of experience in crop growing and education level when an in-depth introduction and training is provided. The use of a simple and clear layout of the assessment form is important for reliable wetness class assignments.

  19. Qualitative soil moisture assessment in semi-arid Africa - the role of experience and training on inter-rater reliability

    NASA Astrophysics Data System (ADS)

    Rinderer, M.; Komakech, H. C.; Müller, D.; Wiesenberg, G. L. B.; Seibert, J.

    2015-08-01

    Soil and water management is particularly relevant in semi-arid regions to enhance agricultural productivity. During periods of water scarcity, soil moisture differences are important indicators of the soil water deficit and are traditionally used for allocating water resources among farmers of a village community. Here we present a simple, inexpensive soil wetness classification scheme based on qualitative indicators which one can see or touch on the soil surface. It incorporates the local farmers' knowledge on the best soil moisture conditions for seeding and brick making in the semi-arid environment of the study site near Arusha, Tanzania. The scheme was tested twice in 2014 with farmers, students and experts (April: 40 persons, June: 25 persons) for inter-rater reliability, bias of individuals and functional relation between qualitative and quantitative soil moisture values. During the test in April farmers assigned the same wetness class in 46 % of all cases, while students and experts agreed on about 60 % of all cases. Students who had been trained in how to apply the method gained higher inter-rater reliability than their colleagues with only a basic introduction. When repeating the test in June, participants were given improved instructions, organized in small subgroups, which resulted in a higher inter-rater reliability among farmers. In 66 % of all classifications, farmers assigned the same wetness class and the spread of class assignments was smaller. This study demonstrates that a wetness classification scheme based on qualitative indicators is a robust tool and can be applied successfully regardless of experience in crop growing and education level when an in-depth introduction and training is provided. The use of a simple and clear layout of the assessment form is important for reliable wetness class assignments.

  20. The experiences of Batswana families regarding hospice care of AIDS patients in the Bophirima district, North West province, South Africa.

    PubMed

    Makhele, M F; Mulaudzi, F M

    2012-01-01

    The HIV/AIDS pandemic put significant strain on healthcare services in the country. Hospitals were no longer coping with the escalating number of AIDS patients. This resulted in the early discharge of patients, with some patients, too ill to be nursed at home, being sent to hospices for continued care. The Batswana had mixed feelings about hospice care, because their beliefs on patient care are based on the ubuntu philosophy, which emphasises the principle of caring for one another. The purpose of this study was to explore and describe the experiences of Batswana families regarding hospice care for patients in the Thlabane township in the province of the North West as well as to make recommendations to policy-makers to ensure that hospices are accepted by community members and utilised effectively. A qualitative, explorative, descriptive research design was applied. Purposive sampling was applied to select study participants with whom in-depth unstructured interviews were conducted. A qualitative data analysis was done by categorising, ordering, and summarising the data, and describing the findings. The findings indicated that families of patients in hospice care experienced such care as foreign to their culture. These families also experienced stigmatisation, firstly owing to the stigma associated with AIDS and secondly because they opted for hospice care. However, they also observed the high quality of care provided by the hospice and understood its benefits for AIDS patients. The study concluded that hospice care relieved families of terminally ill AIDS patients of the burden of care and enabled them to keep on working and earning a living. Recommendations to policy-makers included enhancing hospice care and ensuring the provisioning of culturally safe hospice care. PMID:23237045

  1. Seismic properties of the Earth's upper mantle in various geodynamic settings derived from experiments on olivine-orthopyroxene aggregates deformed up to 8 GPa and 1500 °C

    NASA Astrophysics Data System (ADS)

    Soustelle, V.; Manthilake, G.

    2015-12-01

    We present here HP and HT deformation experiments on olivine-orthopyroxene aggregates and discuss the effect of pressure, temperature and composition on the development of olivine CPO and the resulting seismic properties. The experiments were prepared, synthesized, deformed and analysed at the Bayerisches Geoinstitut (University of Bayreuth,Germany). The sample consisted of hot-pressed powders composed of an olivine-orthopyroxene mix (87.5-12.5, 75-25 and 50-50 %) that were then placed in a simple-shear geometry assembly and deformed in a multi-anvil press employing 6 independently acting hydraulic rams at a constant strain-rate of 10-4 s-1 and 3 GPa-1300°C, 5 GPa-1400°C and 8 GPa-1500°C. The achieved shear strain ranged between 1 and 2. The sample were then analysed under SEM-EBSD. At 3 GPa, the observed CPO are similar to those predicted in previous studies, while the one developed at 5 and 8 GPa varies according to the orthopyroxene content: 1) Experiments with 12.5% orthopyroxene display annealing textures and random CPO; 2) the ones with 25% orthopyroxene display B-type olivine CPO consistent with high pressure dislocation creep deformation experiments; and 3) the experiments with 50% orthopyroxenes display A-type olivine CPO consistent with olivine-pyroxene aggregates deformed at high temperature in diffusion creep regime. The resulting seismic properties could therefore explain the seismic anisotropy observations in the mid and lower part of the Earth's upper mantle in different geodynamic contexts. For example, the mantle wedge above subduction which has pyroxene content corresponding to our 25% orthopyroxene experiments and often display the olivine fast-axis normal to the expected mantle flow. On the other hand, a more pristine intraplate mantle most often predict olivine fast-axis parallel to the mantle flow and would have an olivine-pyroxene ratio close to our experiment with 50% orthopyroxene.

  2. West Africa

    NASA Technical Reports Server (NTRS)

    2002-01-01

    With its vast expanses of sand, framed by mountain ranges and exposed rock, northwestern Africa makes a pretty picture when viewed from above. This image was acquired by the Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard NASA's Terra spacecraft. The Canary Islands can be seen on the left side of the image just off Africa's Atlantic shore. The light brown expanse running through the northern two thirds of the image is the Sahara Desert. The desert runs up against the dark brown Haut Atlas mountain range of Morocco in the northwest, the Atlantic Ocean to the west and the semi-arid (light brown pixels) Sahelian region in the South. The Sahara, however, isn't staying put. Since the 1960s, the desert has been expanding into the Sahelian region at a rate of up to 6 kilometers per year. In the 1980s this desert expansion, combined with over cultivation of the Sahel, caused a major famine across west Africa. Over the summer months, strong winds pick up sands from the Sahara and blow them across the Atlantic as far west as North America, causing air pollution in Miami and damaging coral reefs in the Bahamas and the Florida Keys. The white outlines on the map represent country borders. Starting at the top-most portion of the map and working clockwise, the countries shown are Morocco, Western Sahara, Mauritania, Senegal, Mali, Burkina Fasso, Nigeria, Mali (again), and Algeria. Image by Reto Stockli, Robert Simmon, and Brian Montgomery, NASA Earth Observatory, based on data from MODIS

  3. The Impact of Inventory Management on Stock-Outs of Essential Drugs in Sub-Saharan Africa: Secondary Analysis of a Field Experiment in Zambia

    PubMed Central

    Leung, Ngai-Hang Z.; Chen, Ana; Yadav, Prashant; Gallien, Jérémie

    2016-01-01

    Objective To characterize the impact of widespread inventory management policies on stock-outs of essential drugs in Zambia’s health clinics and develop related recommendations. Methods Daily clinic storeroom stock levels of artemether-lumefantrine (AL) products in 2009–2010 were captured in 145 facilities through photography and manual transcription of paper forms, then used to determine historical stock-out levels and estimate demand patterns. Delivery lead-times and estimates of monthly facility accessibility were obtained through worker surveys. A simulation model was constructed and validated for predictive accuracy against historical stock-outs, then used to evaluate various changes potentially affecting product availability. Findings While almost no stock-outs of AL products were observed during Q4 2009 consistent with primary analysis, up to 30% of surveyed facilities stocked out of some AL product during Q1 2010 despite ample inventory being simultaneously available at the national warehouse. Simulation experiments closely reproduced these results and linked them to the use of average past monthly issues and failure to capture lead-time variability in current inventory control policies. Several inventory policy enhancements currently recommended by USAID | DELIVER were found to have limited impact on product availability. Conclusions Inventory control policies widely recommended and used for distributing medicines in sub-Saharan Africa directly account for a substantial fraction of stock-outs observed in common situations involving demand seasonality and facility access interruptions. Developing central capabilities in peripheral demand forecasting and inventory control is critical. More rigorous independent peer-reviewed research on pharmaceutical supply chain management in low-income countries is needed. PMID:27227412

  4. The national portfolio of learning for postgraduate family medicine training in South Africa: experiences of registrars and supervisors in clinical practice

    PubMed Central

    2013-01-01

    Background In South Africa the submission of a portfolio of learning has become a national requirement for assessment of family medicine training. A national portfolio has been developed, validated and implemented. The aim of this study was to explore registrars’ and supervisors’ experience regarding the portfolio’s educational impact, acceptability, and perceived usefulness for assessment of competence. Methods Semi-structured interviews were conducted with 17 purposively selected registrars and supervisors from all eight South African training programmes. Results The portfolio primarily had an educational impact through making explicit the expectations of registrars and supervisors in the workplace. This impact was tempered by a lack of engagement in the process by registrars and supervisors who also lacked essential skills in reflection, feedback and assessment. The acceptability of the portfolio was limited by service delivery demands, incongruence between the clinical context and educational requirements, design of the logbook and easy availability of the associated tools. The use of the portfolio for formative assessment was strongly supported and appreciated, but was not always happening and in some cases registrars had even organised peer assessment. Respondents were unclear as to how the portfolio would be used for summative assessment. Conclusions The learning portfolio had a significant educational impact in shaping work-place based supervision and training and providing formative assessment. Its acceptability and usefulness as a learning tool should increase over time as supervisors and registrars become more competent in its use. There is a need to clarify how it will be used in summative assessment. PMID:24207009

  5. The deep Algerian margin structure revisited by the Algerian-French SPIRAL research program, stage 2 : Wide-ange seismic experiment

    NASA Astrophysics Data System (ADS)

    Klingelhoefer, Frauke; Yellès, Abdelkarim; Bracène, Rabah; Graindorge, David; Ouabadi, Aziouz; Schnürle, Philippe; Scientific Party, Spiral

    2010-05-01

    During the second leg of the Algerien - French SPIRAL (Sismique Profonde et Investigation Regionale du Nord de l'ALgerie) cruise conducted on the R/V Atalante in October and November 2009 an extensive wide-angle seismic data-set was acquired on 5 regional transects off Algeria, from Arzew bay to the west, to Annaba to the east. The profiles are between 80 and 180 km in length and around 40 ocean-bottom seismometers were deployed on each profile. A 8350 cu. inch tuned airgun array consisting of 10 Bolt airguns was used to generate of deep frequency to allow for a good penetration. All profiles were extended on land up to 150 km by land-stations to better constrain the structure of the margin and the nature of the ocean-continent transition zone. Coincident reflection seismic, gravity and magnetic data were acquired on all profiles during the first leg of the cruise. The resulting data quality is very good with deep penetrating arrivals on most of the instruments. Only on very few instruments a deep salt layer inhibits deeper penetration of the seismic energy. Two instruments were lost and all other yielded useful information on geophone and hydrophone channels. Instruments located close to the coast show arrivals from thick sedimentary layers. Instruments located on oceanic crust indicate a relatively thin crust overlying a mantle layer characterised by seismic velocities of 8 km/s. Forward and inverse modelling of the wide-angle seismic data will help constrain the deep structure of the margin, the nature of the crust and might help to constrain possible existence of a detached slab in the upper mantle. Integration of the wide-angle seismic data with multichannel seismic, gravity and magnetic data will enable us to better understand the tectonic history and the structure of the Algerian margin.

  6. Seismic velocity anisotropy and heterogeneity beneath the Mantle Electromagnetic and Tomography Experiment (MELT) region of the East Pacific Rise from analysis of P and S body waves

    USGS Publications Warehouse

    Hammond, W.C.; Toomey, D.R.

    2003-01-01

    We use teleseismic P and S delay times and shear wave splitting measurements to constrain isotropic and anisotropic heterogeneity in the mantle beneath the southern East Pacific Rise (SEPR). The data comprise 462 P and S delay times and 18 shear wave splitting observations recorded during the Mantle Electromagnetic and Tomography (MELT) Experiment. We estimate the mantle melt content (F) and temperature (T) variation from the isotropic velocity variation. Our results indicate that the maximum variation in F beneath our array is between zero and ???1.2%, and maximum variation in T is between zero and ???100 K. We favor an explanation having partial contributions from both T and F. We approximate the seismic anisotropy of the upper mantle with hexagonal symmetry, consistent with the assumption of two dimensionality of mantle flow. Our new tomographic technique uses a nonlinear inversion of P and slow S polarization delay times to simultaneously solve for coupled VP and VS heterogeneity throughout the model and for the magnitude of anisotropy within discrete domains. The domain dimensions and the dip of the anisotropy are fixed for each inversion but are varied in a grid search, obtaining the misfit of the models to the body wave delay data and to split times of vertically propagating S waves. The data misfit and the isotropic heterogeneity are sensitive to domain dimensions and dip of anisotropy. In a region centered beneath the SEPR the best average dip of the hexagonal symmetry axis is horizontal or dipping shallowly (<30??) west. Given the resolution of our data, a subaxial region characterized by vertically aligned symmetry axes may exist but is limited to be <80 km deep. We infer that the mantle flow beneath the SEPR is consistent with shallow asthenospheric return flow from the direction of the South Pacific superswell.

  7. Infrasound Generation from the HH Seismic Hammer.

    SciTech Connect

    Jones, Kyle Richard

    2014-10-01

    The HH Seismic hammer is a large, "weight-drop" source for active source seismic experiments. This system provides a repetitive source that can be stacked for subsurface imaging and exploration studies. Although the seismic hammer was designed for seismological studies it was surmised that it might produce energy in the infrasonic frequency range due to the ground motion generated by the 13 metric ton drop mass. This study demonstrates that the seismic hammer generates a consistent acoustic source that could be used for in-situ sensor characterization, array evaluation and surface-air coupling studies for source characterization.

  8. Near-surface Fun with Seismic Data

    NASA Astrophysics Data System (ADS)

    Clapp, M.

    2015-12-01

    What is happening in the near-surface often has a direct effect on human activity. Seismic exploration has routinely targeted geology at depths of kilometers to tens of kilometers. However, these techniques can be applied to answer questions about shallower targets. Several recent experiments demonstrate seismic applicability to near-surface problems. One example is passive seismic monitoring using ambient noise to identify shallow changes and potential hazards in a producing hydrocarbon field. Another example is the use of seismic reflection data from within the water column to determine layering caused by temperature and salinity differences in depth. A third example is identifying historical elevation changes along coast lines using seismic reflection data. These examples show that exploration seismic methods can be effectively used for a variety of near-surface applications.

  9. High resolution seismic data coupled to Multibeam bathymetry of Stromboli island collected in the frame of the Stromboli geophysical experiment: implications with the marine geophysics and volcanology of the Aeolian Arc volcanic complex (Sicily, Southern Tyrrhenian sea, Italy).

    PubMed

    Aiello, Gemma; Di Fiore, Vincenzo; Marsella, Ennio; Passaro, Salvatore

    2014-01-01

    New high resolution seismic data (Subbottom Chirp) coupled to high resolution Multibeam bathymetry collected in the frame of the Stromboli geophysical experiment aimed at recording active seismic data and tomography of the Stromboli Island are here presented. The Stromboli geophysical experiment has been already carried out based on onshore and offshore data acquisition in order to investigate the deep structure and the location of the magma chambers of the Stromboli volcano. A new detailed swath bathymetry of Stromboli Island is here shown and discussed to reconstruct an up-to-date morpho-bathymetry and marine geology of the area compared to the volcanologic setting of the Aeolian Arc volcanic complex. Due to its high resolution the new Digital Terrain Model of the Stromboli Island gives interesting information about the submerged structure of the volcano, particularly about the volcano-tectonic and gravitational processes involving the submarine flanks of the edifice. Several seismic units have been identified based on the geologic interpretation of Subbottom Chirp profiles recorded around the volcanic edifice and interpreted as volcanic acoustic basement pertaining to the volcano and overlying slide chaotic bodies emplaced during its complex volcano-tectonic evolution. They are related to the eruptive activity of Stromboli, mainly poliphasic and to regional geological processes involving the intriguing geology of the Aeolian Arc, a volcanic area still in activity and needing improved research interest. PMID:24860717

  10. South Africa.

    PubMed

    1985-05-01

    The 1983 population of South Africa was estimated at 31.1 million, with an annual growth rate of 2.5% (0.8% for whites, 1.8% for blacks and "coloreds," 1.8% for Asians, and 2.8% for Africans). The infant mortality rate was 14.9/1000 live births among whites, 80.6/1000 among blacks and coloreds, and 25.3/1000 among Asians. Life expectancy was 70 years for whites, 59 years for blacks and coloreds, 66 years for Asians, and 55 years for Africans. Racial discrimination has become increasingly institutionalized in South Africa since the ruling National Party came to power in 1948. The policy of apartheid calls for separate political institutions for the 4 major racial groups in the population. Africans are considered citizens of the homelands to which their tribal group is assigned, not permanent citizens of the country. Coloreds and Asians are considered citizens and given some political expression. The new political system envisions broad consensus among whites, coloreds, and Indians, and a parliamentary committee is considering possible abolition of laws against multiracial political activity. The work force totals 11 million, 30% of whom are engaged in agriculture, 29% are employed in industry and commerce, 34% work in the services sector, and 7% work in mining. The GNP in 1983 totalled US$75.5 billion and the GDP stood at US$73.2 billion. Per capita GNP was US$5239. PMID:12178120

  11. Teaching Reflection Seismic Processing

    NASA Astrophysics Data System (ADS)

    Forel, D.; Benz, T.; Pennington, W. D.

    2004-12-01

    Without pictures, it is difficult to give students a feeling for wave propagation, transmission, and reflection. Even with pictures, wave propagation is still static to many. However, when students use and modify scripts that generate wavefronts and rays through a geologic model that they have modified themselves, we find that students gain a real feeling for wave propagation. To facilitate teaching 2-D seismic reflection data processing (from acquisition through migration) to our undergraduate and graduate Reflection Seismology students, we use Seismic Un*x (SU) software. SU is maintained and distributed by Colorado School of Mines, and it is freely available (at www.cwp.mines.edu/cwpcodes). Our approach includes use of synthetic and real seismic data, processing scripts, and detailed explanation of the scripts. Our real data were provided by Gregory F. Moore of the University of Hawaii. This approach can be used by any school at virtually no expense for either software or data, and can provide students with a sound introduction to techniques used in processing of reflection seismic data. The same software can be used for other purposes, such as research, with no additional expense. Students who have completed a course using SU are well equipped to begin using it for research, as well. Scripts for each processing step are supplied and explained to the students. Our detailed description of the scripts means students do not have to know anything about SU to start. Experience with the Unix operating system is preferable but not necessary -- our notes include Computer Hints to help the beginner work with the Unix operating system. We include several examples of synthetic model building, acquiring shot gathers through synthetic models, sorting shot gathers to CMP gathers, gain, 1-D frequency filtering, f-k filtering, deconvolution, semblance displays and velocity analysis, flattening data (NMO), stacking the CMPs, and migration. We use two real (marine) data sets. One

  12. Somalian Earthquakes of May, 1980, East Africa

    SciTech Connect

    Ruegg, J.C.; Lepine, J.C.; Tarantola, A.; Leveque, J.J.

    1981-04-01

    A seismic crisis, with a m/sub b/ = 5.3 main shock, occured in the Somali Republic East Africa (10 /sup 0/N, 43 /sup 0/E) from April to November 1980. Up to 2000 earthquakes with M/sub L/>2 have been recorded during this period. This earthquake sequence is of particular interest because it occurred in a seismically inactive zone and include a rather long aftershock sequence. Two groups of epicenters were identified using a relative location procedure. Aftershocks observed during the first two weeks fall very close to the Borama City, while latter shocks are situated 10km west. This may suggest that the second group of earthquakes has been induced continental margin between the Somalian Plateau shield and the quasi-oceanic crust of the Afar-Gulf of Aden region, remains active to day and is relevant to intraplate seismicity.

  13. Opportunities for CD-ROM Information Services in Africa.

    ERIC Educational Resources Information Center

    Compton, Anne W.

    1992-01-01

    Discusses the use of CD-ROMs in Africa based on experiences of the Population Information Program (PIP) at Johns Hopkins University. Topics addressed include available CD-ROM hardware; how CD-ROMs can help alleviate information problems in Africa; and how to market CD-ROMs in Africa. (10 references) (LRW)

  14. Validation of seismic soil-structure interaction analysis methods: EPRI (Electric Power Research Institute)/NRC (Nuclear Regulatory Commission) cooperation in Lotung, Taiwan, experiments

    SciTech Connect

    Kot, C.A.; Srinivasan, M.G.; Hsieh, B.J.; Tang, Y.K.; Kassawara, R.P.

    1986-10-31

    The cooperative program between NRC/ANL and EPRI on the validation of soil-structure interaction analysis methods with actual seismic response data is described. A large scale-model of a containment building has been built by EPRI/Taipower in a highly seismic region of Taiwan. Vibration tests were performed, first on the basemat before the superstructure was built and then on the completed structure. Since its completion, the structure has experienced many earthquakes. The site and structural response to these earthquakes have been recorded with field (surface and downhole) and structural instrumentation. The validation program involves blind predictions of site and structural response during vibration tests and a selected seismic event, and subsequent comparison between the predictions and measurements. The predictive calculations are in progress. The results of the correlation are expected to lead to the evaluation of the methods as to their conservatisms and sensitivities.

  15. Otrag rocket experiments in Africa

    NASA Technical Reports Server (NTRS)

    1978-01-01

    West German rocket manufacturers are testing their products in Zaire. Hundreds of pipes (12 m x 80 cm) are bundled together inside the test missiles, which are fired into Zaire's prairie. The reactions of neighboring nations, as well as leading countries of the world, are presented concerning the rocket tests.

  16. Seismic sources

    DOEpatents

    Green, M.A.; Cook, N.G.W.; McEvilly, T.V.; Majer, E.L.; Witherspoon, P.A.

    1987-04-20

    Apparatus is described for placement in a borehole in the earth, which enables the generation of closely controlled seismic waves from the borehole. Pure torsional shear waves are generated by an apparatus which includes a stator element fixed to the borehole walls and a rotor element which is electrically driven to rapidly oscillate on the stator element to cause reaction forces transmitted through the borehole walls to the surrounding earth. Longitudinal shear waves are generated by an armature that is driven to rapidly oscillate along the axis of the borehole, to cause reaction forces transmitted to the surrounding earth. Pressure waves are generated by electrically driving pistons that press against opposite ends of a hydraulic reservoir that fills the borehole. High power is generated by energizing the elements for more than about one minute. 9 figs.

  17. The Eastern Alpine Seismic Investigation (EASI) project

    NASA Astrophysics Data System (ADS)

    Plomerova, Jaroslava; Bianchi, Irene; Hetényi, György; Munzarova, Helena; Bokelmann, Götz; Kissling, Edi; AlpArray-EASI Working Group; AlpArray-EASI Field Team

    2015-04-01

    AlpArray (http://www.seismo.ethz.ch/research/groups/alrt/projects/alparray/) is a large European initiative to study the entire Alpine orogen at high resolution and in 3D with a large variety of methods. The core element of the initiative is an extensive and dense broadband seismological network. In addition, a number of Complementary Experiments will be conducted to focus on targeted problems. The first implemented AlpArray Complementary Experiment is called Eastern Alpine Seismic Investigation (EASI). The Eastern, "straight" part of the Alps is home to a number of open questions, e.g., the origin of the hanging lithospheric slab (Adriatic or European?), the nature of the Moho "hole" between the two plates, the anisotropic nature of the lower crust, and the relationship of the Alpine orogen to the adjacent foreland basin and the lithospheric blocks of the Bohemian Massif. Our research methods include tomography, ambient noise analysis and receiver functions, with anisotropy included in all three types of investigations as well as in shear-wave splitting analyses. The depth range of investigations encompasses the crust and the mantle lithosphere, down to the LAB. In this presentation we detail the design of the experiment. EASI is composed of 55 broadband seismic stations, deployed in a zig-zag pattern on either side of the central longitude line of 13.35°E. The planned north-south distance between stations was 10 km, the distance of each station to either side of the central line was 6 km. We aimed to keep the stations within 1.5 km of the target location, as much as topographic, field and infrastructure condition allowed. The result: with respect to the original deployment plans the closest match is 164m, 10 stations are within 500m, 31 stations are within 1.5km which is also the average match, and the farthest is 4.4km. The overall result remained a very linear and regularly spaced array, spanning 540 km from the Czech-German border to the Adriatic Sea. The

  18. Water harvesting experience in sub-Saharan Africa - lessons for sustainable intensification of rainfed agriculture and the influence of available soils and rainfall data

    NASA Astrophysics Data System (ADS)

    Gowin, John; Bunclark, Lisa

    2013-04-01

    Africa is seen by many as the continent with the greatest potential for agricultural growth, but land degradation and environmental change threaten the African soil resource more severely than in many other regions of the planet. Achieving future food security will depend mainly on increasing production from rainfed agriculture. The challenge of delivering the required sustainable intensification in rainfed agriculture is most acute in the drylands - the semi-arid and dry sub-humid climatic regions. There are two broad strategies for increasing yields under these circumstances: (1) capturing more rainwater and storing it (increasing water availability), and (2) using the available water more effectively by increasing the plant growth and/or reducing non-productive soil evaporation (increasing water productivity). We focus on the first of these options - water harvesting, which is defined as, "the collection and concentration of rainfall runoff, or floodwaters, for plant production". The benefits of water harvesting have been documented from small scale experimental plot studies, but evidence of successful adoption and impact is weak. As a contribution to improving the evidence base, we present results from an investigation conducted in SSA to gather information on progress with efforts to promote adoption of water harvesting. The intention was to investigate in detail the processes and outcomes on a large enough sample area to draw some common conclusions. This was not a comprehensive analysis of all that is happening in each country, nor was it a random sample; this was a purposive sample guided by available baseline information to permit comparative analysis. Water harvesting seems to have made the most progress where techniques can be adopted by individual farmers: in Burkina Faso and Niger micro- scale zaï /tassa and demi-lune systems; in Sudan and Tanzania meso-scale majaruba and teras systems. Macro-scale systems requiring social organisation may offer

  19. The transpressive tectonics and large earthquake distribution along the plate boundary in North Africa

    NASA Astrophysics Data System (ADS)

    Meghraoui, Mustapha; Pondrelli, Silvia

    2010-05-01

    The Tell Atlas and Rif Mountains of northern Africa have been the site of several large and moderate seismic events in the last decades. However, the thrust and fold system of NW Algeria experienced the largest earthquakes in the last centuries along the Africa-Eurasia plate boundary. This shallow seismic activity was very often associated with surface faulting and deformation as for the Mw 7.3 El Asnam (10/10/1980) and the Mw 6.8 Zemmouri-Boumerdes (21/05/2003) earthquakes. We study the active tectonics along the plate boundary in North Africa from the seismicity database, individual large and moderate earthquakes, the seismic moment tensor summation, the geodetic measurements (GPS and InSAR) and the structural and kinematic of active faults. Neotectonic structures and significant seismicity (Mw>5) indicate that coeval east-west trending right-lateral faulting and NE-SW thrust-related folding result from the oblique convergence at the plate boundary. A simple modeling of block tectonics suggests that transpression and block rotation govern the mechanics of the Africa - Eurasia plate boundary in the Tell Atlas and Rif Mountains. The tectonic restraining bend of NW Algeria combined with the ~ 5 mm/yr convergence between Africa and Eurasia justify the large seismic activity on the thrust and fold system of the Tell Atlas and the relatively passive active deformation along the adjacent sections of the plate boundary.

  20. Seismic refraction exploration

    SciTech Connect

    Ruehle, W.H.

    1980-12-30

    In seismic exploration, refracted seismic energy is detected by seismic receivers to produce seismograms of subsurface formations. The seismograms are produced by directing seismic energy from an array of sources at an angle to be refracted by the subsurface formations and detected by the receivers. The directivity of the array is obtained by delaying the seismic pulses produced by each source in the source array.

  1. How Forgetful are Seismic Waves ?

    NASA Astrophysics Data System (ADS)

    Milkereit, B.

    2005-05-01

    3D surface seismic and vertical seismic profiling (VSP) techniques can be employed to image crustal structures in complex geological settings. The effects of heterogeneities on seismic wave propagation can be described in terms of different propagation regimes (Wu, 1989): quasi-homogeneous for heterogeneities too small to be seen by seismic waves, Rayleigh scattering, Mie scattering and small-angle scattering. These scattering regimes cause characteristic amplitude, phase and travel time fluctuation, which can be used to obtain estimates of scale length. Horizontal resolution of exploration seismic data is often discussed in terms of Fresnel zone. For surface and VSP data, the Fresnel radius increases with increasing depth of investigation. In addition, the lateral resolution is limited by the effective frequency content of the seismic signal. Based on strong contrast in petrophysical data, crustal exploration targets (such as gas-hydrates, permafrost or massive sulfide ores) should make strong P-wave, S-wave and converted wave reflectors against most background velocity models. In the context of realistic geological models, 3D numerical simulations are required to better assess elastic wave interactions with high acoustic impedance targets. In addition, it is important to study the influence of composition and shape of high acoustic impedance targets on the full scattered wavefield through a series of numerical modeling experiments based on the 3D elastic finite-difference (FD) method. Massive sulfide ores consisting of the end-member sulfide minerals pyrite, sphalerite, and galena, which span the full range of observed P- and S- wave velocities and densities in ore rocks, as well as gabbro inclusions, are investigated for different shapes which represent the complex morphologies often observed for ore deposits. 3D FD modeling reveals that large ore deposits lead to a strong and complex scattering response that is often dominated by shear-wave events (Bohlen et al

  2. Fennoscandian lithosphere - electromagnetic and seismic constraints

    NASA Astrophysics Data System (ADS)

    Korja, T.; Kozlovskaya, E.; Smirnov, M.

    2009-04-01

    Knowledge of the present-day structure of the Earth's mantle is essential to our understanding of plate tectonics as well as Earth's thermomechanical evolution over long periods of geological time. Several factors including temperature, chemical composition, presence of partial melt or water influence seismic velocities and electrical conductivity in the upper mantle. Similarly, anisotropy may have a profound effect on seismic and magnetotelluric observations. During last ten years, several large scale multinational and national seismic and magnetotelluric experiments have been carried out in Fennnoscandia including e.g. the SVEKALAPKO seismic tomography experiment, Swedish National Seismic Network (SNSN) array monitoring, BEAR and EMMA magnetotelluric array studies and magnetotelluric profiling such as TOR and Jamtland. Altogether these studies cover most of Fennoscandia and make it possible to correlate two different data sets and to study lithospheric structures in Fennoscandia. In particular, we will compare the thickness of the lithosphere obtained from seismic anisotropy studies and from magnetotelluric studies. We will also correlate spatially sparse indications on seismic reflectors and electrically conducting layers in the mantle lithosphere. Finally, we aim to compare directly absolute values of seismic velocity and electrical conductivity.

  3. Borehole seismic modeling

    NASA Astrophysics Data System (ADS)

    Zhen, Tao

    In many borehole seismic experiments, the velocity of the tube wave is higher than that of the surrounding rock shear wave. This fast tube wave creates a strong conical shear wave in the surrounding rock, similar to the Mach wave in supersonic aviation and the Cherenkov radiation in electrodynamics. Many geophysicists have tried to utilize the conical signal in VSP (vertical seismic profiling) and cross borehole data interpretation, using quasi static approximations to model the borehole effect. Two popular quasi static approximations are: the effective source array method for source borehole modeling and the squeeze strain method for receiver borehole modeling. These quasi static approximations are sensible as they qualitatively conform to Hueygen's principle and the typical wavelength of a VSP or a cross borehole seismic experiment is much larger than the borehole radius. However, they have not been quantitatively benchmarked against other non approximation method such as the frequency wave number method. The frequency wave number method is a rigorous, non approximation method for modeling straight boreholes without lengthwise variation. The boreholes may consist of many coaxial, homogeneous and axially symmetric shells. In this thesis, the results of the quasi static approximations are compared to the results obtained from the frequency wave number method. The comparison demonstrates that both the effective source array method and squeeze strain method gives the correct arrival time. The effective source array method gives incorrect amplitude and waveform for direct arrivals and tube waves due to its arbitrary assumption of the elementary source radiation pattern. The squeeze strain method gives fairly accurate amplitude and waveform for P and S direct arrivals but it fails to match the tube wave results obtained from the frequency wave number method. The omission of tube wave dispersion and amplitude loss by the quasi static approximation methods also

  4. Static behaviour of induced seismicity

    NASA Astrophysics Data System (ADS)

    Mignan, Arnaud

    2016-04-01

    The standard paradigm to describe seismicity induced by fluid injection is to apply non-linear diffusion dynamics in a poroelastic medium. I show that the spatio-