scholarly journals Subduction-transition zone interaction: A review

Geosphere ◽  
2017 ◽  
Vol 13 (3) ◽  
pp. 644-664 ◽  
Author(s):  
Saskia Goes ◽  
Roberto Agrusta ◽  
Jeroen van Hunen ◽  
Fanny Garel
Keyword(s):  
Transition Zone ◽  
Lower Mantle ◽  
Dynamic Models ◽  
Flat Slabs ◽  
Mantle Silicates ◽  
Effective Yield ◽  
Current Transition ◽  
Clapeyron Slope ◽  
Plate Subduction

Abstract As subducting plates reach the base of the upper mantle, some appear to flatten and stagnate, while others seemingly go through unimpeded. This variable resistance to slab sinking has been proposed to affect long-term thermal and chemical mantle circulation. A review of observational constraints and dynamic models highlights that neither the increase in viscosity between upper and lower mantle (likely by a factor 20–50) nor the coincident endothermic phase transition in the main mantle silicates (with a likely Clapeyron slope of –1 to –2 MPa/K) suffice to stagnate slabs. However, together the two provide enough resistance to temporarily stagnate subducting plates, if they subduct accompanied by significant trench retreat. Older, stronger plates are more capable of inducing trench retreat, explaining why backarc spreading and flat slabs tend to be associated with old-plate subduction. Slab viscosities that are ∼2 orders of magnitude higher than background mantle (effective yield stresses of 100–300 MPa) lead to similar styles of deformation as those revealed by seismic tomography and slab earthquakes. None of the current transition-zone slabs seem to have stagnated there more than 60 m.y. Since modeled slab destabilization takes more than 100 m.y., lower-mantle entry is apparently usually triggered (e.g., by changes in plate buoyancy). Many of the complex morphologies of lower-mantle slabs can be the result of sinking and subsequent deformation of originally stagnated slabs, which can retain flat morphologies in the top of the lower mantle, fold as they sink deeper, and eventually form bulky shapes in the deep mantle.

scholarly journals The Pice Effects of Competition from Parallel Imports and Therapeutic Alternatives: Using Dynamic Models to Estimate the Causal Effect on the Extensive and Intensive Margins

2021 ◽  
Author(s):  
David Granlund
Keyword(s):  
Dynamic Models ◽  
Causal Effect ◽  
The Other ◽  
Causal Effects ◽  
Parallel Imports ◽  
Extensive And Intensive Margins ◽  
Price Effects ◽  
Short And Long Term ◽  
Therapeutic Alternatives

AbstractThis paper studies responses to competition with the use of dynamic models that distinguish between short- and long-term price effects. The dynamic models also allow lagged numbers of competitors to become valid and strong instruments for the current numbers, which enables studying the causal effects using flexible specifications. A first parallel trader is found to decrease prices of exchangeable products by 7% in the long term. On the other hand, prices do not respond to the first competitor that sells therapeutic alternatives; but competition from four or more competitors that sell on-patent therapeutic alternatives decreases prices by about 10% in the long term.

scholarly journals Stability of dense hydrous magnesium silicate phase G in the transition zone and the lower mantle.

1998 ◽  
Vol 20 (4) ◽  
pp. 163-169 ◽  
Author(s):  
Eiji OHTANI ◽  
Yasuhiro KUDOH ◽  
Hiroshi NAITO ◽  
Haruo ARASHI
Keyword(s):  
Transition Zone ◽  
Lower Mantle ◽  
Magnesium Silicate ◽  
Silicate Phase

scholarly journals Long-Term Effects of Vegetation Treatments in the Chaparral Transition Zone

Rangelands ◽  
2001 ◽  
Vol 23 (1) ◽  
Author(s):  
Kelly N. Fuhrmann ◽  
Timothy E. Crews ◽  
Keyword(s):  
Transition Zone ◽  
Long Term Effects

scholarly journals Carbonates from the lower part of transition zone or even the lower mantle

2007 ◽  
Vol 260 (1-2) ◽  
pp. 1-9 ◽  
Author(s):  
Frank E. Brenker ◽  
Christian Vollmer ◽  
Laszlo Vincze ◽  
Bart Vekemans ◽  
Anja Szymanski ◽  
...  
Keyword(s):  
Transition Zone ◽  
Lower Mantle

scholarly journals Self-Assisted First-Fix Method for A-BDS Receivers with Medium- and Long-Term Ephemeris Extension

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Zilong Shen ◽  
Jing Peng ◽  
Wenxiang Liu ◽  
Feixue Wang ◽  
Shibing Zhu ◽  
...  
Keyword(s):  
Dynamic Models ◽  
Rapid Development ◽  
Real Data ◽  
Satellite System ◽  
Time Interval ◽  
Signal Acquisition ◽  
Positioning Accuracy ◽  
Broadcast Ephemeris ◽  
Intelligent Logistics

As a sensor for standalone position and velocity determination, the BeiDou Navigation Satellite System (BDS) receiver is becoming an important part of the intelligent logistics systems under rapid development in China. The applications in the mass market urgently require the BDS receivers to improve the performance of such functions, that is, shorter Time to First Fix (TTFF) and faster navigation signal acquisition speed with Ephemeris Extension (EE) in standalone mode. As a practical way to improve such functions of the Assisted BDS (A-BDS) receivers without the need for specialized hardware support, a Self-Assisted First-Fix (SAFF) method with medium- and long-term EE is proposed in this paper. In this SAFF method, the dynamic Medium- and Long-Term Orbit Prediction (MLTOP) method, which uses the historical broadcast ephemeris data with the optimal configuration of the dynamic models and orbit fitting time interval, is utilized to generate the extended ephemeris. To demonstrate the performance of the MLTOP method used in the SAFF method, a suit of tests, which were based on the real data of broadcast ephemeris and precise ephemeris, were carried out. In terms of the positioning accuracy, the overall performance of the SAFF method is illustrated. Based on the characteristics of the medium- and long-term EE, the simulation tests for the SAFF method were conducted. Results show that, for the SAFF method with medium- and long-term EE of the BeiDou MEO/IGSO satellites, the horizontal positioning accuracy is about 12 meters, and the overall positioning accuracy is about 25 meters. The results also indicate that, for the BeiDou satellites with different orbit types, the optimal configurations of the MLTOP method are different.

Sp phases from the transition zone between the upper and lower mantle

1980 ◽  
Vol 70 (2) ◽  
pp. 487-508
Author(s):  
Sonja Faber ◽  
Gerhard MÜller
Keyword(s):  
United States ◽  
Transition Zone ◽  
Lower Mantle ◽  
The United States ◽  
P Wave ◽  
Western United States ◽  
Nodal Plane ◽  
Transition Zones ◽  
Velocity Models ◽  
Long Period

abstract Precursors to S and SKS were observed in long-period SRO and WWSSN seismograms of the Romanian earthquake of March 4, 1977, recorded in the United States at distances from 68° to 93°. According to the fault-plane solution, the stations were close to a nodal plane and SV radiation was optimum in their direction. Particle-motion diagrams, constructed from the digital data of the SRO station ANMO (distance 89.1°), show the P-wave character of the precursors. Several interpretations are discussed; the most plausible is that the precursors are Sp phases generated by conversion from S to P below the station. The travel-time differences between S or SKS and Sp are about 60 sec and indicate conversion in the transition zone between the upper and lower mantle. Sp conversions were also observed at long-period WWSSN stations in the western United States for 2 Tonga-Fiji deep-focus earthquakes (distances from 82° to 96°). Special emphasis is given in this paper to the calculation of theoretical seismograms, both for Sp precursors and the P-wave coda, including high-order multiples such as sP4 which may arrive simultaneously with Sp. The Sp calculations show: (1) the conversions produced by S, ScS, and SKS at interfaces or transition zones between the upper and lower mantle form a complicated interference pattern, and (2) conversion at transition zones is less effective than at first-order discontinuities only if their thickness is greater than about half a wavelength of S waves. As a consequence, details of the velocity structure between the upper and lower mantle can only be determined within these limits from long-period Sp observations. Our observations are compatible with velocity models having pronounced transition zones at depths of 400 and 670 km as have been proposed for the western United States, and they exclude much smoother structures. Our study suggests that long-period Sp precursors from pure thrust or normal-fault earthquakes, observed at distances from 70° to 95° close to a nodal plane and at azimuths roughly perpendicular to its strike, offer a simple means for qualitative mapping of the sharpness of the transition zones between the upper and lower mantle.

scholarly journals Evidence for the stability of ultrahydrous stishovite in Earth’s lower mantle

2019 ◽  
Vol 117 (1) ◽  
pp. 184-189 ◽  
Author(s):  
Yanhao Lin ◽  
Qingyang Hu ◽  
Yue Meng ◽  
Michael Walter ◽  
Ho-Kwang Mao
Keyword(s):  
Transition Zone ◽  
Lower Mantle ◽  
Water Reservoir ◽  
Weight Percent ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mineral Components ◽  
The Stability ◽  
Stability Of Water

The distribution and transportation of water in Earth’s interior depends on the stability of water-bearing phases. The transition zone in Earth’s mantle is generally accepted as an important potential water reservoir because its main constituents, wadsleyite and ringwoodite, can incorporate weight percent levels of H2O in their structures at mantle temperatures. The extent to which water can be transported beyond the transition zone deeper into the mantle depends on the water carrying capacity of minerals stable in subducted lithosphere. Stishovite is one of the major mineral components in subducting oceanic crust, yet the capacity of stishovite to incorporate water beyond at lower mantle conditions remains speculative. In this study, we combine in situ laser heating with synchrotron X-ray diffraction to show that the unit cell volume of stishovite synthesized under hydrous conditions is ∼2.3 to 5.0% greater than that of anhydrous stishovite at pressures of ∼27 to 58 GPa and temperatures of 1,240 to 1,835 K. Our results indicate that stishovite, even at temperatures along a mantle geotherm, can potentially incorporate weight percent levels of H2O in its crystal structure and has the potential to be a key phase for transporting and storing water in the lower mantle.

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