scholarly journals Simultaneous Inference of Plate Boundary Stresses and Mantle Rheology Using Adjoints: Large-Scale Two-Dimensional Models

2021 ◽  
Author(s):  
Johann Rudi ◽  
Michael Gurnis ◽  
Georg Stadler
Keyword(s):  
Large Scale ◽  
Plate Boundary ◽  
Optimization Method ◽  
Plate Motion ◽  
Rheological Parameters ◽  
Shear Stresses ◽  
Plate Boundaries ◽  
Mantle Dynamics ◽  
Motion Data ◽  
Mantle Rheology

Plate motions are a primary surface constraint on plate and mantle dynamics and rheology, plate boundary stresses, and the occurrence of great earthquakes. Within an optimization method, we use plate motion data to better constrain uncertain mantle parameters. For the optimization problem characterizing the maximum a posteriori rheological parameters we derive gradients using adjoints and expressions to approximate the posterior distributions for stresses within plate boundaries. We apply these methods to a 2-D cross section from the western to eastern Pacific, with temperature distributions and fault zone geometries developed primarily from seismic and plate motion data. We find that the best-fitting stress exponent, $n$, is about 2.8 and the yield stress about 100 MPa or less. The normal stress on the interplate fault zones is about 100 MPa and the shear stresses about 10 MPa or less.

scholarly journals Current Plate Motions

1988 ◽  
Vol 129 ◽  
pp. 351-352
Author(s):  
Richard Gordon ◽  
Charles Demets ◽  
Seth Stein ◽  
Don Argus ◽  
Dale Woods
Keyword(s):  
Subduction Zones ◽  
Continental Drift ◽  
Geophysical Data ◽  
Plate Motion ◽  
Plate Boundaries ◽  
Transform Faults ◽  
Plate Motions ◽  
Motion Data ◽  
Motion Models ◽  
Self Consistent

The standard against which VLBI measurements of continental drift and plate motions are compared are self-consistent global models of “present-day” plate motions determined from geophysical data: marine magnetic anomalies at oceanic spreading centers, azimuths of transform faults, and orientations of earthquake slip vectors on transform faults and at subduction zones. Past global plate motion models have defined regions where the assumption that plates behave rigidly has apparently lead to systematic misfits, sometimes exceeding 10 mm/yr, of plate motion data. Here, we present some of the results from NUVEL-1, a new, self-consistent global model of present-day relative plate motions determined from a compilation and analysis of existing and new geophysical data. These data and new techniques have allowed us to eliminate nearly all statistically significant systematic misfits identified by earlier models, suggesting that the rigid-plate assumption is an excellent approximation when plate motions are averaged over several million years. Beside improving estimates of the motion on previously identified plate boundaries, we have also identified and determined motions on other boundaries whose subtle morphologies, lack of seismicity, and very slow (< 10 mm/yr) relative motions have made them difficult to detect. Here we focus on the application of VLBI measurements to help resolve plate tectonic problems and then briefly outline our results for Pacific-North America motion and plate motions in the Indian Ocean.

scholarly journals Taking time to twist a continent—Multistage origin of the New Zealand orocline

Geology ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 56-60
Author(s):  
S. Lamb ◽  
N. Mortimer
Keyword(s):  
New Zealand ◽  
Large Scale ◽  
Plate Boundary ◽  
Plate Motion ◽  
West Antarctica ◽  
Alpine Fault ◽  
Plate Rotation ◽  
Dextral Shear ◽  
Plate Boundary Zone ◽  
Two Sides

Abstract In New Zealand, a giant coherent “Z” shape is defined by several curvilinear pre-Cenozoic basement terranes that extend across Zealandia for &gt;1500 km along strike. It is widely assumed that this curvature was the result of bending during the Neogene, which together with ∼450 km of dextral displacement on the Alpine fault accommodated a total of ∼750 km of dextral shear through the New Zealand plate boundary zone between the Australian and Pacific plates. This would make it a very simple form of orocline. In fact, we show that its development was surprisingly complex and protracted, with a composite origin. Its western and southern parts were bent as much as 70° in the Mesozoic. In the Late Cretaceous, the already bent terranes were offset sinistrally by ∼250 km along the cross-cutting proto–Alpine fault, which acted as a transform to the rift between East and West Antarctica. Since the Eocene, and after Zealandia had completely separated from Antarctica, the two sides of the Alpine fault have undergone 45° of relative plate rotation, further bending the terranes. However, the eastern part of what appears today to be the same oroclinal structure has been created entirely since the Eocene, and mainly during the Neogene phase of dextral shear through the plate boundary, with large-scale internal bending and shortening. We suggest that multistage and composite evolutions may be typical features of oroclines, which would be difficult to unravel without a rich tectonic and plate motion database, such as that available for the New Zealand region.

The possible role of magma and geothermal fluid in the episodic uplift cycles and intense seismicity beneath the Svartsengi high temperature geothermal field, Iceland 

2021 ◽  
Author(s):  
Ólafur Flóvenz ◽  
Rongjiang Wang ◽  
Gylfi Páll Hersir ◽  
Kristján Ágústsson ◽  
Magdalena Vassileva ◽  
...  
Keyword(s):  
High Temperature ◽  
Large Scale ◽  
Earthquake Swarm ◽  
Plate Boundary ◽  
Geothermal Field ◽  
Plate Boundaries ◽  
Clear Trend ◽  
Tectonic Event ◽  
Fibre Optics ◽  
Reykjanes Peninsula

&lt;p&gt;The highly productive high temperature geothermal fields in Iceland are located within active volcanic systems on the plate boundaries. When an earthquake swarm or an unusual surface uplift or subsidence occur, it is important to assess the hazards and whether the unrest is triggered or controlled by volcanic or anthropogenic processes, or a combination of both.&lt;/p&gt;&lt;p&gt;On January 22nd, 2020, a rapid, large-scale uplift (14 km x 12 km) started at the Svartsengi geothermal field on the plate boundary of the Reykjanes Peninsula, along with an intense earthquake swarm that began simultaneously about 3 km east of the centre of uplift. The centre of uplift was located about 1 km west of Mt. Thorbj&amp;#246;rn, in the middle of the Svartsengi geothermal field, close to the reinjection wells. Over a period of 6 months, three such uplift cycles occurred, each lasting for several weeks and followed by periods of relatively rapid subsidence. The duration and timing of the uplift-subsidence cycles appears to follow a clear trend where the successive inflation episodes lasted longer but with lower inflation rate.&lt;/p&gt;&lt;p&gt;The centres of uplift and the deflation cycles are the same and remained stationary. The accompanied intense earthquake swarms migrated along the 40 km long oblique plate boundary of the Reykjanes Peninsula, demonstrating a major plate tectonic event. The maximum depth of earthquakes was close to 4.5 km directly above the centre of uplift but extending to 6-7 km in the surroundings where the maximum magnitudes reached M&lt;sub&gt;W&lt;/sub&gt; 4.8.&lt;/p&gt;&lt;p&gt;A few weeks after the onset of the unrest, nine additional seismic stations were deployed to densify the local seismic network in place. In addition, complimentary data from an existing 21 km long fibre optics cable were used to monitor high-frequency linear strain rates. Both measures led to a significant improvement in the earthquake detection and location which predominantly occurred in swarms. Likewise, InSAR data analysis of temporal uplift cycles was performed, repeated gravity measurements at permanent sites were performed, and resistivity was remeasured at chosen sites. &amp;#160;&lt;/p&gt;&lt;p&gt;Multiple different elementary models were developed and tested to explain the cyclic excitation of the uplift, subsidence, and seismicity. While the individual unrest episodes might be controlled by possible magma intrusions into the lower crust, our favoured model explains the spatio-temporal pattern of ground uplift by the rise and diffusion of pore pressure in a 4-5 km deep geothermal aquifer. To distinguish between different models, we use multi-disciplinary geophysical datasets, such as deformation, seismicity, and gravity.&lt;/p&gt;

Oldest Array (Pacific Array on the oldest seafloor), the first result

2020 ◽  
Author(s):  
Hitoshi Kawakatsu ◽  
Hisashi Utada ◽  
Sang-Mook Lee ◽  
YoungHee Kim ◽  
Hajime Shiobara ◽  
...  
Keyword(s):  
Large Scale ◽  
Plate Boundary ◽  
Pacific Basin ◽  
Ocean Bottom ◽  
Full Spectrum ◽  
Decadal Time Scale ◽  
Mantle Dynamics ◽  
Deep Interior ◽  
The Pacific ◽  
The Us

&lt;p&gt;With a simple crustal structure and short geological history, ocean basins provide an unblemished view into mantle dynamics, including convective flow and melting processes that control deformation and evolution of Earth&amp;#8217;s surface. With the full spectrum of plate-boundary processes and abundant mid-plate volcanism sourced deep in the mantle, the Pacific basin provides an outstanding setting to explore connections between shallow dynamics and the deep interior. Exploiting advances in seafloor instrumentation, research groups in Japan, the US, and elsewhere have demonstrated the utility of broadband ocean-bottom seismic and EM arrays for providing new, high-resolution constraints on mantle structure and dynamics. These activities have coalesced into the international collaboration Pacific Array, which seeks to merge individual efforts into a large-scale &quot;array of arrays&quot; that will effectively cover the entire Pacific basin diachronously over a decadal time scale.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160; As a part of the Pacific Array initiative, a team comprised of scientists from Japan and South Korea has completed the Oldest Array observation on the oldest seafloor in the western Pacific. Oldest Array consists of 12-seismic and 7-EM array that was deployed in Oct-Nov, 2018, for a duration of 12 months, followed by a successfully recovered in Oct-Nov, 2019. The instruments and vessels are respectively provided by ERI and KIOST. The array covers the northwestern side of the ~170Ma old magnetic lineation triangle aiming to delineate the lithosphere-asthenosphere system beneath the oldest Pacific basin to elucidate the enigma of seafloor flattening, as well as the dynamics of the birth of Pacific plate. The initial look at data indicates beautiful recordings, and we plan to report the first analysis results at the meeting.&lt;/p&gt;

Plate tectonic chain reaction constrained from noise in the Cretaceous Quiet Zone

2020 ◽  
Author(s):  
Derya Gürer ◽  
Roi Granot ◽  
Douwe J.J. van Hinsbergen
Keyword(s):  
Subduction Zones ◽  
Kinematic Model ◽  
Plate Boundary ◽  
Western Mediterranean ◽  
Plate Motion ◽  
Plate Boundaries ◽  
Plate Tectonic ◽  
Test Bed ◽  
Chain Reaction ◽  
Tectonic Plates

&lt;p&gt;The relative motions of the tectonic plates show remarkable variation throughout Earth&amp;#8217;s history. Major changes in relative motion between the tectonic plates are traditionally viewed as spatially and temporally isolated events linked to forces acting on plate boundaries (i.e., formation of same-dip double subduction zones, changes in the strength of the boundary), or thought to be associated with mantle dynamics. A Cretaceous global plate reorganization event has been postulated to have affected all major plates. The Cretaceous &amp;#8216;swing&amp;#8217; in Africa-Eurasia relative plate motion provides an ideal test-bed for assessing the temporal and spatial evolution of both relative plate motions and surrounding geological markers. Here we show a novel plate kinematic model for the closure of the Tethys Ocean by implementing intra-Cretaceous Quiet Zone time markers and combine the results with the geological constraints found along the convergent plate boundary. Our results allow to assess the order, causes and consequences of geological events and unravel a chain of tectonic events that set off with the onset of horizontally-forced double subduction ~105 Myr ago, followed by a 40 Myr long period of acceleration of the Africa relative to Eurasia that peaked at 80 Myr ago (at rates four times as high as previously predicted). This acceleration, which was likely caused by the pull of two same-dip subduction zones was followed by a sharp decrease in plate velocity, when double subduction terminated with ophiolite obduction onto the African margin. These tectonic forces acted on the eastern half of the Africa-Eurasia plate boundary, which led to counterclockwise rotation of Africa and sparked new subduction zones in the western Mediterranean region. Our analysis identifies the Cretaceous double subduction episode between Africa and Eurasia as a link in the global plate tectonic chain reaction and provides a dynamic view on plate reorganizations.&lt;/p&gt;

Effects of strain weakening in self-consistent models of mantle convection with plate-like behavior and continental drift

2020 ◽  
Author(s):  
Tobias Rolf ◽  
Maëlis Arnould
Keyword(s):  
Mantle Convection ◽  
Previous History ◽  
Plate Boundary ◽  
Continental Drift ◽  
Rheological Parameters ◽  
Plate Boundaries ◽  
The Earth ◽  
Cumulative Strain ◽  
First Results ◽  
Long Time

&lt;p&gt;It is now well-established that the Earth&amp;#8217;s mantle and lithosphere form an integrated, dynamically self-regulating system. Numerical convection models that self-consistently generate plate-like behavior are a powerful tool to investigate this system, but have only recently reached a level at which they can be linked to the geodynamics of the Earth. Strongly temperature-dependent and viscoplastic rheology is known to be a key ingredient for these models to be successful. Such rheologies, however, are typically time-independent and lack a memory on the previous history of deformation. Yet, it is known that the Earth&amp;#8217;s geodynamic evolution is somewhat guided by structures of pre-existing weakness, which was initiated a potentially long time before.&lt;/p&gt;&lt;p&gt;As a step forward we implement a simple form of rheological memory in the mantle convection code &lt;em&gt;StagYY&lt;/em&gt;: strain weakening [&lt;em&gt;Fuchs &amp; Becker, 2019,&lt;/em&gt; &lt;em&gt;Role of strain-dependent weakening memory on the style of mantle convection and plate boundary stability&lt;/em&gt;, &lt;em&gt;Geophys. J. Int., 218, 601-618&lt;/em&gt;]. We present calculations in 2D cases with and without continents, and also selected 3D cases. By varying the governing parameters for plate-like behavior as well as the rates of rheological damage and healing, we examine how strain weakening modifies the generation of plate-like behavior and its time dependence as well as the drift of continents.&lt;/p&gt;&lt;p&gt;First results indicate the importance of the balance of weakening (via the critical strain) and thermal healing. The averaged cumulative strain (effectively the degree of lithospheric weakening) is lower when healing is more effective, so that plastic failure of the lithospheric and the formation of new plate boundaries is complicated, as expected. In initial models with strong, long-living continents, accumulated strain is very small within the continents and seems insufficient to induce substantial weakening, even if the memory on previous deformation is infinite (i.e. no healing with continents). Further models with weaker continents and different rheological parameters will be presented.&lt;/p&gt;

scholarly journals Pacific Plate slab pull and intraplate deformation in the early Cenozoic

2014 ◽  
Vol 6 (1) ◽  
pp. 145-190 ◽  
Author(s):  
N. P. Butterworth ◽  
R. D. Müller ◽  
L. Quevedo ◽  
J. M.O'Connor ◽  
K. Hoernle ◽  
...  
Keyword(s):  
Large Scale ◽  
Driving Forces ◽  
Plate Boundary ◽  
Pacific Plate ◽  
Plate Motion ◽  
Age Progression ◽  
Intraplate Volcanism ◽  
Intraplate Deformation ◽  
Lithospheric Extension ◽  
Early Cenozoic

Abstract. Large tectonic plates are known to be susceptible to internal deformation, leading to a range of phenomena including intraplate volcanism. However, the space and time dependence of intraplate deformation and its relationship with changing plate boundary configurations, subducting slab geometries, and absolute plate motion is poorly understood. We utilise a buoyancy driven Stokes flow solver, BEM-Earth, to investigate the contribution of subducting slabs through time on Pacific Plate motion and plate-scale deformation, and how this is linked to intraplate volcanism. We produce a series of geodynamic models from 62 to 42 Ma in which the plates are driven by the attached subducting slabs and mantle drag/suction forces. We compare our modelled intraplate deformation history with those types of intraplate volcanism that lack a clear age progression. Our models suggest that changes in Cenozoic subduction zone topology caused intraplate deformation to trigger volcanism along several linear seafloor structures, mostly by reactivation of existing seamount chains, but occasionally creating new volcanic chains on crust weakened by fracture zones and extinct ridges. Around 55 Ma subduction of the Pacific-Izanagi ridge reconfigured the major tectonic forces acting on the plate by replacing ridge push with slab pull along its north-western perimeter, causing lithospheric extension along pre-existing weaknesses. Large scale deformation observed in the models coincides with the seamount chains of Hawaii, Louisville, Tokelau, and Gilbert during our modelled time period of 62 to 42 Ma. We suggest that extensional stresses between 72 and 52 Ma are the likely cause of large parts of the formation of the Gilbert chain and that localised extension between 62 and 42 Ma could cause late-stage volcanism along the Musicians Volcanic Ridges. Our models demonstrate that early Cenozoic changes in Pacific plate driving forces only cause relatively minor changes in Pacific absolute plate motions, and cannot be responsible for the Hawaii-Emperor Bend (HEB), confirming previous interpretations that the 47 Ma HEB does not reflect an absolute plate motion event.

scholarly journals Beyond Plate Tectonics: Looking at Plate Deformation with Space Geodesy

1988 ◽  
Vol 129 ◽  
pp. 341-350
Author(s):  
Thomas H. Jordan ◽  
J. Bernard Minster
Keyword(s):  
Plate Tectonics ◽  
Plate Boundary ◽  
Point Of View ◽  
Space Geodesy ◽  
Plate Motion ◽  
Plate Boundaries ◽  
Measurement Systems ◽  
Motion Models ◽  
Plate Deformation ◽  
Continental Plate

We address the requirements that must be met by space-geodetic systems to place useful, new constraints on horizontal secular motions associated with the geological deformation of the earth's surface. Plate motions with characteristic speeds of about 50 mm/yr give rise to displacements that are easily observed by space geodesy. However, in order to improve the existing plate-motion models, the tangential components of relative velocities on interplate baselines must be resolved to an accuracy of < 3 mm/yr. Because motions considered small from a geodetic point of view have rather dramatic geological effects, especially when taken up as compression or extension of continental crust, detecting plate deformation by space-geodetic methods at a level that is geologically unresolvable places rather stringent requirements on the precision of the measurement systems: the tangential components on intraplate baselines must be observed with an accuracy of < 1 mm/yr. Among the measurements of horizontal secular motions that can be made by space geodesy, those pertaining to the rates within the broad zones of deformation characterizing the active continental plate boundaries are the most difficult to obtain by conventional ground-based geodetic and geological techniques. Measuring the velocities between crustal blocks to ± 5 mm/yr on 100-km to 1000-km length scales can yield geologically significant constraints on the integrated deformation rates across continental plate-boundary zones such as the western United States. However, baseline measurements in geologically complicated zones of deformation are useful only to the extent that the endpoints can be fixed in a local kinematical frame that includes major crustal blocks. For this purpose, the establishment of local geodetic networks around major VLBI and SLR sites in active areas should receive high priority.

Plate tectonics and Earth System Science

2021 ◽  
Author(s):  
Dietmar Müller
Keyword(s):  
Plate Tectonics ◽  
Plate Boundary ◽  
Plate Motion ◽  
Plate Boundaries ◽  
Earth System ◽  
Dynamic Topography ◽  
Lithospheric Deformation ◽  
The Earth ◽  
Plate Models ◽  
Reconstruction Software

&lt;p&gt;Over the last 25 years the theory of plate tectonics and a growing set of geo-databases have been used to develop global plate models with increasing sophistication, enabled by open-source plate reconstruction software, particularly GPlates. Today&amp;#8217;s editable open-access community models include networks of evolving plate boundaries and deforming regions, reflecting the fact that tectonic plates are not always rigid. The theory of plate tectonics was originally developed primarily based on magnetic anomaly and fracture zone data from the ocean basins. As a consequence there has been a focus on applying plate tectonics to modelling the Jurassic to present-day evolution of the Earth based on the record of preserved seafloor, or only modelling the motions of continents at earlier times. Modern plate models are addressing this shortcoming with recently developed technologies built upon the pyGPlates python library, utilising evolving plate boundary topologies to reconstruct entirely destroyed seafloor for the entire Phanerozoic. Uncertainties in these reconstructions are large and can represented with end-member scenarios. These models are paving the way for a multitude of applications aimed at better understanding Earth system evolution, connecting surface processes with the Earth&amp;#8217;s mantle via plate tectonics. These models allow us to address questions such as: What are the causes of major perturbations in the interplay between tectonic plate motion and Earth&amp;#8217;s deep interior? How do lithospheric deformation, mantle convection driven dynamic topography and climate change together drive regional changes in erosion and sedimentation? How are major perturbations of the plate-mantle system connected to environmental change, biological extinctions and species radiation?&lt;/p&gt;

scholarly journals Earthquakes in Greenland

1982 ◽  
Vol 31 ◽  
pp. 11-27
Keyword(s):  
Plate Boundary ◽  
Ice Age ◽  
Plate Motion ◽  
The Arctic ◽  
Plate Boundaries ◽  
Earthquake Activity ◽  
Tectonic Plate ◽  
Intraplate Earthquakes ◽  
Ice Cap ◽  
Ocean Ridge

Data on earthquakes in Greenland from the international and Canadian seismological bulletins have been checked against the seismograms of the seismological stations in Greenland. A few new earthquakes have also been located based on seismograms from Greenland and Canada. A total of 103 reliable earthquakes have been confirmed, located and relocated. The earthquakes occur mainly along the coasts of eastern, northern and western Greenland. The largest earthquakes in Greenland have magnitudes around 5. There is no tectonic plate boundary in Greenland. The intraplate earthquake zones in north-eastern and in northern Greenland are situated as linear continuations of the plate boundaries near the bend of the mid ocean ridge close to Station Nord, between Spitzbergen and Greenland. Under the ice cap only a few earthquakes have occurred. In eastern and in northern Greenland a few swarms of earthquakes have been found. In western Greenland a sequence of seismic signals is noticed at a distance of 17 5 km from Godhavn. Its origin may be small earthquakes. The time sequence of the earthquakes in Greenland shows two time intervals of increased earthquake activity after the two largest earthquakes. This indicates that stress adjustments in the largest earthquakes give rise to stress adjust­ments in the smaller earthquakes more than 1000 km away, in other parts of Greenland. There is only limited correlation between earthquake activity and surface geology. It can not be determined whether the main cause of the intraplate earthquakes in Greenland is isostatic uplift following the latest ice age or tectonic plate motion in connection with sea floor spreading in the Norwegian-Greenland Sea and in the Arctic Ocean.

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