Role of inherited structures and magmatism in North Tanzania from high resolution teleseismic P and S body-wave tomographies.

2021 ◽  
Author(s):  
Stéphanie Gautier ◽  
Adeline Clutier ◽  
Christel Tiberi ◽  
Fleurice Parat ◽  
Benoit Gibert ◽  
...  
Keyword(s):  
Body Wave ◽  
A Priori ◽  
Regional Scale ◽  
Velocity Model ◽  
S Wave ◽  
Fine Grid ◽  
Local Tomography ◽  
The North ◽  
Velocity Anomalies

<p>The North Tanzanian Divergence (NTD) is a zone of rift initiation. Its surface expression results from interactions between deep-mantle (mantle plume), lithospheric (inherited rheology and stratification, melting...) and crustal (dyke propagation, fault activation...) processes. However, the role of each process on the observed surface activity is still debated, because highly difficult to decorrelate.</p><p>We recently carried out a study to obtain enhanced P and S-wave tomography, from the surface down to 150-200 km depth. The particularity of our method consists in its initial velocity model. It is composed of a 1D IASP91 regional velocity model in which we inserted an a priori 3D crustal velocity model with a fine grid. This crustal model was deduced from an independent local tomography inversion.</p><p>The P and S images obtained, resulting from the teleseismic inversion of this hybrid method, show strong contrasted velocity anomalies: from 10 % of P (Vp) and S velocity (Vs) variation on the craton, to -17 % below the rift axis. The anomalies locations are consistent with the surface geology (rifting basin, border faults, volcanoes). At a regional scale, the strongest velocity contrasts correspond to the lithospheric inherited structure (Tanzanian craton and Proterozoic belts) boundaries, which control the propagation of the rift. In particular, the Masai cratonic block, south of the NTD, is inferred to have a strong influence in the rift evolution. The transition from the North-South axial valley into three diverging rift arms (Eyasi, Natron-Manyara and Pangani) is likely due to the change in rheology and to the presence of magma along inherited sutures between the craton and the mobile belts.</p><p>However, interrogations about the role of the thermal changes, the melt/fluid presence and the mantle composition in the NTD on these velocity anomalies still remain. To distinguish which parameters are acting in the rift, we realize a Vp/Vs ratio map. With this new data, and in the light of parallel petrological studies, we interpret the Vp/Vs anomalies in term of gas and/or melt concentration zones.</p>

High-resolution teleseismic body-wave tomography with a 3D initial crustal model for crust-to-upper mantle images in highly heterogeneous media.

2020 ◽  
Author(s):  
Adeline Clutier ◽  
Stéphanie Gautier ◽  
Christel Tiberi
Keyword(s):  
Upper Mantle ◽  
Heterogeneous Media ◽  
Body Wave ◽  
A Priori ◽  
Velocity Model ◽  
Low Velocity ◽  
Local Tomography ◽  
Velocity Models ◽  
The North ◽  
3D Velocity Model

<p>Local and teleseismic body wave inversions are two approaches commonly used to obtain 3D Earth velocity models for shallow and mantle scale, respectively. However, each method used separately is poorly resolved at the mantle/crust boundary while imaging that interface is important to understand the geodynamic processes (e.g. magmatic underplating, mantle delamination, crustal thinning or thickening) occurring at this depth. In order to develop a high-resolved final velocity model, the two approaches were combined. First, an irregular grid was settled, with a higher density of nodes at crustal scale (from 0 to 40 km) and an increasing node step when approaching the limits of the model. Then, an a priori 3D crustal velocity model (from an independent local tomography) was inserted within the 1D IASP91 lithospheric one. Finally, the teleseismic tomographic inversion was carried out at crust-to-upper mantle scale using this new mixed initial model and teleseismic data. We applied the method on a real case that includes both tectonic and magmatic processes, the North Tanzanian Divergence (NTD). Synthetic tests showed that we had no resolution between 0 and 35 km. However, a fine crustal grid with the 3D local model helps to better constrain ray paths, limiting the artefacts and smearing from the mantle to the crust, enhancing details, sharpening the velocity anomalies and modifying the geometry of anomalies at depth (> 150 km). Following these tests, we propose then a final scheme in which we include the a priori crustal 3D velocity model in the finer crustal grid, and we prevent the inversion from modifying it. This insertion of strong crustal constraints in teleseismic inversion provides sharper spatial resolution at both crustal and mantle scales, including areas with poor ray coverage, beneath the NTD region. Our strategy allows to counteract the degradation of the results in areas with low velocity zones (such as rift and hotspot), where the seismic rays go around these anomalies.</p>

Seismotectonics of the Ionian-Akarnania Block (IAB) and Western Greece deduced from a local seismic deployment.

2020 ◽  
Author(s):  
Antoine Haddad ◽  
Athanassios Ganas ◽  
Ioannis Kassaras ◽  
Matteo Lupi
Keyword(s):  
Fault Zone ◽  
Velocity Model ◽  
Focal Mechanisms ◽  
Seismogenic Zone ◽  
The South ◽  
S Wave ◽  
North West ◽  
The North ◽  
Short Period ◽  
Western Greece

<p>From July 2016 to May 2017, we deployed a local seismic network composed of 15 short-period seismic stations to investigate the ongoing seismotectonic deformation of Western Greece with emphasis on the region between Ambrakikos Gulf (to the north) and Kyparissia (to the south). The network was deployed to investigate the behavior of key crustal blocks in western Greece, such as the Ionian-Akarnania Block (IAB).</p><p>After applying automatic P- and S- wave phase picking we located 1200 local earthquakes using HypoInverse and constrained five 1D velocity model by applying the error minimization technique. Events were relocated using HypoDD and 76  focal mechanisms were computed for events with magnitudes down to M<sub>L</sub> 2.3 using first motion polarities.</p><p>We combined the calculated focal mechanisms and the relocated seismicity to shed light on the IAB block boundaries. Three boundaries highlighted by previous studies were also evidenced :</p><p>-The north-west margin of the block, the Cephalonia Transform Fault, Europe‘s most active fault. NW-striking dextral strike-slip motion was recognized for this fault near the Gulf of Myrtos and the town of Fiskardo.</p><p>- The south-east margin is the Movri-Amaliada right-lateral Fault Zone, activated during the Movri Mt. M<sub>w</sub> 6.4 earthquake sequence.</p><p>- The Ambrakikos Gulf (a young E-W rift) and the NW-striking left-lateral Katouna-Stamna Fault zone depict the north and north-eastern margins of the IAB block.</p><p>Seismicity lineaments and focal mechanisms define theKyllini-Cephalonia left-lateral fault, which is also highlighted by bathymetry data. We interpret this fault as the south-western margin of IAB separating an aseismic area observed between Cephalonia and Akarnania from a seismogenic zone north of Zakynthos Island and bridging NW Peloponnese with Cephalonia.</p>

scholarly journals Influence of Circulation Patterns on Temperature Behavior at the Regional Scale: A Case Study Investigated via Neural Network Modeling

2012 ◽  
Vol 25 (6) ◽  
pp. 2123-2128 ◽  
Author(s):  
Antonello Pasini ◽  
Rocco Langone
Keyword(s):  
Neural Network ◽  
Network Modeling ◽  
Regional Scale ◽  
Neural Network Modeling ◽  
Limited Region ◽  
Temperature Changes ◽  
The North ◽  
Circulation Patterns ◽  
The North Atlantic Oscillation

Abstract An analysis of the influence of circulation patterns on temperature changes in an extended Italian Alpine area has been performed by nonlinear methods and neural network modeling. This leads to the clarification of the roles of these patterns in the various seasons and permits the development of models that are able to reconstruct in a satisfactory manner the behavior of temperature anomalies in the second half of the twentieth century in this limited region. This nonlinear analysis shows that the role of the North Atlantic Oscillation (NAO) is probably overestimated, and that European blocking and the Scandinavian pattern should be considered as prime candidates as temperature drivers in this area.

Hotspot signatures at the North American passive margin

Geology ◽  
2020 ◽  
Author(s):  
Zhongmin Tao ◽  
Aibing Li ◽  
Karen M. Fischer
Keyword(s):  
North America ◽  
New England ◽  
Velocity Model ◽  
Passive Margin ◽  
Small Scale ◽  
Low Velocity ◽  
Velocity Anomaly ◽  
The North ◽  
New Information ◽  
Velocity Anomalies

The presence of localized low-velocity anomalies in the upper mantle beneath the passive Atlantic margin in North America is a puzzling geophysical observation. Whether the anomalies are caused by the remnant heat from past hotspots or ongoing asthenospheric upwelling is still debated. We addressed the formation of the anomalies based on a recent velocity model for eastern North America, which reveals new information on their shapes and anisotropic signatures. The low-velocity anomaly in New England appears as a narrow column above 90 km depth and broadens westward at depths of 120–200 km. Two slow anomalies are imaged under the central Appalachian Mountains between 140 km and 240 km. These low velocities correspond to pronounced positive radial anisotropy (Vsh > Vsv), indicating a dominantly horizontal asthenospheric flow. They also coincide with the tracks of the Great Meteor hotspot (140–115 Ma) and an inferred hidden hotspot (60–50 Ma). The anomalies in the central Appalachians could be due to lithospheric interaction with the second hotspot and subsequent lithospheric instabilities. The complex shape of the New England anomaly is consistent with interaction with both hotspots. The first hotspot could have eroded the base of the lithosphere, forming a channel, and the second hotspot could have further thinned the lithosphere and produced a localized cavity at shallow depths. Consequently, the indented lithosphere base would have filled with channelized asthenospheric flow or produced small-scale convection, helping to sustain the slow anomaly. Low-velocity anomalies at the North America passive margin are likely the consequences of prior hotspot interactions.

scholarly journals Metacognitive awareness and visualisation in the imagination: The case of the invisible circles

Pythagoras ◽  
2018 ◽  
Vol 39 (1) ◽  
Author(s):  
Divan Jagals ◽  
Martha Van der Walt
Keyword(s):  
A Priori ◽  
Metacognitive Awareness ◽  
Individual Interview ◽  
North West ◽  
Mathematical Ideas ◽  
The North ◽  
Mathematics Tasks ◽  
Rational Debate ◽  
The Mind

Awareness of one’s own strengths and weaknesses during visualisation is often initiated by the imagination – the faculty for intuitively visualising and modelling an object. Towards exploring the role of metacognitive awareness and imagination in facilitating visualisation in solving a mathematics task, four secondary schools in the North West province of South Africa were selected for instrumental case studies. Understanding how mathematical objects are modelled in the mind may explain the transfer of the mathematical ideas between metacognitive awareness and the rigour of the imaginer’s mental images. From each school, a top achiever in mathematics was invited to an individual interview (n = 4) and was video-recorded while solving a mathematics word problem. Participants also had to identify metacognitive statements from a sample of statement cards (n = 15) which provided them the necessary vocabulary to express their thinking during the interview. During their attempts, participants were asked questions about what they were thinking, what they did and why they did what they had done. Analysis with a priori coding suggests the three types of imagination consistent with the metacognitive awareness and visualisation include initiating, conceiving and transformative imaginations. These results indicate the tenets by which metacognitive awareness and visualisation are conceptually related with the imagination as a faculty of self-directedness. Based on these findings, a renewed understanding of the role of metacognition and imagination in mathematics tasks is revealed and discussed in terms of the tenets of metacognitive awareness and imagination. These tenets advance the rational debate about mathematics to promote a more imaginative mathematics.

Crust, mantle and core structure of Mars from InSight seismic data

2021 ◽  
Author(s):  
Amir Khan ◽  
Keyword(s):  
Epicentral Distance ◽  
Body Wave ◽  
Low Frequency ◽  
Distance Estimation ◽  
Velocity Model ◽  
Interior Structure ◽  
S Wave ◽  
S Waves ◽  
The Core ◽  
Radial Profiles

<p>With the deployment of a seismometer on the surface of Mars as part of NASA’s InSight mission,<br />the Seismic Experiment for Interior Structure (SEIS) has been collecting continuous data since early 2019.<br />The primary goal of InSight is to improve our understanding of the internal structure and dynamics of Mars, in<br />particular crust, mantle, and core. Here we describe constraints on the structure of the mantle of Mars based<br />on inversion of seismic body wave arrivals from a number of low-frequency marsquakes.</p> <p>We consider 8 of the largest (moment magnitude is estimated to be between 3 and 4) low-frequency events with<br />dominant energy below 1 Hz for which P- and S-waves are identifiable, enabling epicentral distance estimation.<br />The 8 events occur in the distance range 25-75 degrees. Body wave arrivals that include the main P- and S-waves,<br />surface reflections (PP, PPP, SS, SSS), and core reflections (ScS) are picked using a set of complimentary methods<br />that allows to check for consistency. The resultant set of differential travel times (PP-P, PPP-P, SS-S,...) are<br />subsequently inverted for radial profiles of seismic P- and S-wave velocity, core size and mean density, and epicentral<br />location of the events. To determine interior structure, we rely on independent methods as a means of assessing the<br />robustness of the results.</p> <p>We present a radial velocity model for the upper mantle of Mars, with implications for the thermo-chemical evolution<br />of the planet that match a cooling, differentiated body, and a thick lithosphere. Based on the location of the events,<br />we are able to constrain structure to the core-mantle-boundary, including the size of the core and its mean<br />density that point to large liquid and relatively light core, implying a significant complement of light alloying<br />elements. Our estimate of the average crustal thickness as seen by all events is compatible with the local crustal<br />thickness at the InSight landing determined from observations of converted phases.</p>

scholarly journals Homo habitus: agency, structure and the transformation of tradition in the constitution of the TRB foraging-farming communities in the North European plain (ca 4500–2000 BC)

2005 ◽  
Vol 32 ◽  
pp. 87-101 ◽  
Author(s):  
Marek Zvelebil
Keyword(s):  
Eastern Mediterranean ◽  
Regional Scale ◽  
Transition Process ◽  
Regional Level ◽  
General View ◽  
Hunter Gatherers ◽  
Farming Communities ◽  
The North ◽  
Theory Of Structuration

The current generally accepted view of the dispersal of farming into Europe is that farming groups in the eastern Mediterranean colonised selectively optimal farming areas. The role of contact between indigenous hunter-gatherers and incoming farmers was very important to the operation of this process. This general view of the spread of farming at a broad inter-regional scale gives us our understanding of the origins of the Neolithic but merits closer examination at the local and regional level, as increasingly it is becoming apparent that the causes and motivations may have differed. In this paper, Mesolithic to Neolithic communities with evidence of the transition from hunter-gatherer to farmer will be examined at a regional scale, in the central part of the north European plain, focussing on Kujavia. Additionally, the theory of structuration will be applied in order to elucidate the transition process at this level.

scholarly journals Gadfly petrels use knowledge of the windscape, not memorized foraging patches, to optimize foraging trips on ocean-wide scales

2020 ◽  
Vol 287 (1918) ◽  
pp. 20191775 ◽  
Author(s):  
Francesco Ventura ◽  
José Pedro Granadeiro ◽  
Oliver Padget ◽  
Paulo Catry
Keyword(s):  
A Priori ◽  
Regional Scale ◽  
Foraging Strategy ◽  
Gps Tracking ◽  
Flight Behaviour ◽  
Dynamic Soaring ◽  
Soaring Flight ◽  
Wind Regimes ◽  
Fine Tune

Seabirds must often travel vast distances to exploit heterogeneously distributed oceanic resources, but how routes and destinations of foraging trips are optimized remains poorly understood. Among the seabirds, gadfly petrels ( Pterodroma spp.) are supremely adapted for making efficient use of wind energy in dynamic soaring flight. We used GPS tracking data to investigate the role of wind in the flight behaviour and foraging strategy of the Desertas petrel, Pterodroma deserta . We found that rather than visiting foraging hotspots, Desertas petrels maximize prey encounter by covering some of the longest distances known in any animal in a single foraging trip (up to 12 000 km) over deep, pelagic waters. Petrels flew with consistent crosswind (relative wind angle 60°), close to that which maximizes their groundspeed. By combining state–space modelling with a series of comparisons to simulated foraging trips (reshuffled-random, rotated, time-shifted, reversed), we show that this resulted in trajectories that were close to the fastest possible, given the location and time. This wind use is thus consistent both with birds using current winds to fine-tune their routes and, impressively, with an a priori knowledge of predictable regional-scale wind regimes, facilitating efficient flight over great distances before returning to the home colony.

Collection of Ego-Centered Network Data with Computer-Assisted Interviews

Methodology ◽  
2006 ◽  
Vol 2 (1) ◽  
pp. 7-15 ◽  
Author(s):  
Joachim Gerich ◽  
Roland Lehner
Keyword(s):  
Survey Methods ◽  
A Priori ◽  
Dynamic Structure ◽  
Computer Assisted ◽  
Network Data ◽  
Great Effort ◽  
Self Administration ◽  
Face To Face ◽  
Full Network

Although ego-centered network data provide information that is limited in various ways as compared with full network data, an ego-centered design can be used without the need for a priori and researcher-defined network borders. Moreover, ego-centered network data can be obtained with traditional survey methods. However, due to the dynamic structure of the questionnaires involved, a great effort is required on the part of either respondents (with self-administration) or interviewers (with face-to-face interviews). As an alternative, we will show the advantages of using CASI (computer-assisted self-administered interview) methods for the collection of ego-centered network data as applied in a study on the role of social networks in substance use among college students.

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