Neighboring Plates Research Articles

Interaction leads to symmetry breaking in an array of cantilever plates in oscillatory cross flow

By using a computational model based on the immersed-boundary framework, a new mode of symmetry breaking is discovered in a fluid–structure interaction problem featuring an array of cantilever plates in a cross flow whose strength and direction varies sinusoidally with time. Specifically, within the physical parameters considered in this study, the motion of a single plate remains symmetric, whereas a system containing multiple plates can move asymmetrically so that the symmetry-breaking instability comes from fluid-dynamic interactions among individual plates. Further examination suggests that vortices shed from the free ends of the plates play an important role. Indeed, symmetry breaking occurs only when these vortices are sufficiently strong and when the distance between plates lies within certain range. If the distance is too small, a vortex shed from one plate can only stay in the gap between this plate and its neighboring plate for a short time so that it does not have the chance to interact extensively with the neighbor. On the other hand, if the distance is too large it is also difficult for this vortex to interact with the neighbor since it has to travel a long distance to reach there while the background flow keeps changing its direction. In either case, the system does not display asymmetric behavior.

A critical reappraisal of paleomagnetic evidence for Philippine Sea Plate rotation

The kinematic history of the Philippine Sea Plate (PSP) is crucial for interpreting its geological record related to subduction initiation processes and the paleogeography of the junction between the Paleo-Pacific and Tethyan oceanic realms. However, reconstructing PSP's kinematic history is difficult because the plate has been surrounded by subduction zones for most of its history. In absence of marine magnetic anomalies to constrain PSP's motion relative to its neighboring plates, paleomagnetic data may be used as quantitative constraints on its motion. Previous paleomagnetic studies interpreted easterly deflected declinations to infer clockwise rotations of up to 90° since the Eocene. However, rotations inferred from these datasets may also reflect local block rotations related to plate margin deformation. We here re-evaluate to what extent paleomagnetic data from the PSP unequivocally demonstrate plate motion rather than local rotation. To this end, we provide new data from Guam, in the Mariana forearc, and reassess published paleomagnetic data. Our new data from Guam come from two localities in the Eocene, two in the Oligocene, and two in the Miocene. Our compilation assesses data quality against recently defined criteria. Our new results demonstrate that in Guam, declination differences of up to 35° exist in rocks of Eocene age, indicating local rotations. Our compilation identifies both clockwise and counterclockwise rotations from the plate margins, with little confidence which of these would reflect plate-wide rotation. We compiled paleolatitude data from igneous rocks, which we correct for microplate rotation constrained by intra-PSP marine magnetic anomalies and show a northward drift of the PSP of ∼15° since the Eocene, but without a paleomagnetic necessity for major vertical axis rotation. Hence, with the currently available data, rotations of the PSP may be permitted, but are not required. Plate motion is currently better reconstructed from geological constraints contained in circum-PSP orogenic belts.

Generalized Damping Model for MEMS Oscillators from Molecular to Viscous Flow Regime

In this study, we investigate the damping phenomena acting on piezoelectrically driven MEMS oscillators. Three different geometrical shapes of MEMS oscillators are presented, including cantilevers, bending oscillators, and paddle oscillators. An analytical model for their resonance frequencies is derived. The bending modes of these micro-oscillator structures are characterized regarding their resonance frequency and their quality factor as a function of the ambient pressure in a nitrogen atmosphere as well as the dependence on the distance to a neighboring plate representing a geometrical boundary (e.g., to the package or to the mounting). The investigations cover a pressure range from 10−3 mbar up to 900 mbar and a gap width from 150 µm to 3500 µm. Consequently, a Knudsen number range over six orders of magnitude from 100 to 10−4 is covered. The measurement data are evaluated with a generalized damping model consisting of four parts representing the individual damping mechanisms (intrinsic, molecular, transitional, and viscous). The evaluated parameters are analyzed as a function of the resonance frequency and the gap width. The data reveal an exponential growing saturation behavior, which is determined by two characteristic lengths, being correlated with the viscous and the thermal boundary layer thickness, respectively. This leads to an estimation of the strength and of the range of the damping effect just by calculating the boundary layer thicknesses given by the resonance frequency and the gas properties. From these results, we gain fundamental insights on the viscous and transitional damping mechanisms as well as on the intrinsic losses. In conclusion, a basic concept is provided to reduce the damping of micro-oscillator bending modes and thus increase the quality factor. Additionally, the results are supported by finite element simulations revealing the temperature and pressure distribution within the gap.

Designing Multishape Dual-Gas Initial Conditions for the Study of Hydrodynamic Instabilities

Abstract The flow resulting from the rotation of a series of thin plates that initially separate two gases of different densities is analyzed using direct numerical simulations (DNSs). The 90-deg plates' rotation forms a vorticity shear layer and a density interface in between the tips of two neighboring plates. Results of this study show that the shape of these layers strongly depends on the plate's tip-based Reynolds number that can be varied thanks to a parametrization of the plates' opening law. Different regimes are identified corresponding to single- or multimode initial interfaces, with or without the occurrence of starting vortices during the formation of the shear layer. The density interfaces resulting from this procedure are particularly well-suited to serve as initial conditions for the study of the Richtmyer–Meshkov (RM) instability-induced mixing. Results of this study also provide a description of vortex formation in stratified flows.

Episodic back-arc spreading centre jumps controlled by transform fault to overriding plate strength ratio

Spreading centre jumps are a common feature of oceanic back-arc basins. Jumps are conventionally suggested to be triggered by plate velocity changes, pre-existing weaknesses, or punctuated events such as the opening of slab windows. Here, we present 3D numerical models of back-arc spreading centre jumps evolving naturally in a homogeneous subduction system surrounded by continents without a trigger event. Spreading centres jump towards their subduction zone if the distance from trench to spreading centre becomes too long. In particular, jumps to a new spreading centre occur when the resistance on the boundary transform faults enabling relative motion of back-arc and neighbouring plates is larger than the resistance to break the overriding plate closer to trench. Time and distance of spreading centres jumps are, thus, controlled by the ratio between the transform fault and overriding plate strengths. Despite being less complex than natural systems, our models explain why narrow subducting plates (e.g. Calabrian slab), have more frequent and closely-spaced spreading jumps than wider subduction zones (e.g. Scotia). It also explains why wide back-arc basins undergo no spreading centre jumps in their life cycle.

Tectonic constraints on formation and evolution of microplates in the Indian and Pacific Oceans: reviews and statistical inferences

Oceanic plates are growing through narrow boundaries, such as mid-ocean ridges and transform faults. However, the discovery of diffuse plate boundary suggests another type of plate boundary that accommodates difference in plate motion via internal deformation. Along the Central and Southeast Indian ridges, for example, the Capricorn and Macquarie microplates exhibit widespread diffuse boundaries and hence divide the Indo-Australian Plate further into the Indian, Australian, Capricorn, and Macquarie plates. As for microplates distributed along the East Pacific Rise and Pacific-Antarctic Ridge in the Pacific Ocean, however, the typical plate boundaries surrounding the given microplate are distinctly established. Global plate reorganization involving the changes in plate motion or in spreading direction can be accommodated by forming a microplate through ridge extinction, ridge propagation, and pseudofault formation. However, relations between these tectonic processes have not been quantitatively assessed. In particular, we aim to examine tectonic constrains on the formation processes of microplates with diffuse plate boundary. In this study, we compare plate size, plate age, full-spreading rates, thermal structures, total rotation, and rotation rate for the 9 microplates including extinct plates (i.e., Capricorn, Macquarie, and Mammerickx* microplates in the Indian and Southern Oceans; Galapagos, Easter, Juan Fernandez, Bauer*, Friday*, and Selkirk* microplates in the Pacific Ocean; extinct plates are denoted with asterisks). From this comparison, we find that the microplate formation would require certain tectonic conditions (e.g., full-spreading rates faster than 70–80 mm/yr and rotation rates faster than 5–6°/m.y.) to evolve into an independent and rigid plate with respect to the neighboring plates. If the conditions are not met, the same tectonic reorganization would result in a microplate with diffuse plate boundaries.

Victoria continental microplate dynamics controlled by the lithospheric strength distribution of the East African Rift

The Victoria microplate between the Eastern and Western Branches of the East African Rift System is one of the largest continental microplates on Earth. In striking contrast to its neighboring plates, Victoria rotates counterclockwise with respect to Nubia. The underlying cause of this distinctive rotation has remained elusive so far. Using 3D numerical models, we investigate the role of pre-existing lithospheric heterogeneities in continental microplate rotation. We find that Victoria’s rotation is primarily controlled by the distribution of rheologically stronger zones that transmit the drag of the major plates to the microplate and of the mechanically weaker mobile belts surrounding Victoria that facilitate rotation. Our models reproduce Victoria’s GPS-derived counterclockwise rotation as well as key complexities of the regional tectonic stress field. These results reconcile competing ideas on the opening of the rift system by highlighting differences in orientation of the far-field divergence, local extension, and the minimum horizontal stress.

Modeling the damping mechanism of MEMS oscillators in the transitional flow regime with thermal waves

This paper investigates the damping behavior of a vibrating micro-oscillator caused by a surrounding gas in the transitional flow regime (0.01 < Kn < 0.1). In this regime, neither the continuum theory given by the Navier-Stokes equations nor the Boltzmann equation for the molecular flow regime can be applied to describe the damping effects correctly. We propose that the well-known Zener formalism developed for describing thermoelastic damping in solid oscillators can be adapted to include thermoacoustic effects in gases. In this newly proposed model, the damping is caused by thermal waves traveling from the micro-oscillator to a neighboring plate which is placed with a gap width ranging from 150 to 750 μm. This theoretical approach can be brought to a nearly perfect fit with the experimental data, including the observed concave zone of the quality factor plot within the transitional flow regime. The resonance frequency of thermal waves of gas within the gap is derived from standard wave theory, verifying the proportionalities extracted from the experimental results. Consequently, the theory in the transitional flow regime can be expanded by the thermal wave concept and the usage of MEMS oscillators for the thermal wave resonator cavity method (TWRC) is feasible.

Thermal performance evaluation for solidification process of latent heat thermal energy storage in a corrugated plate heat exchanger

This study used latent heat thermal energy storage (LHTES) within a commercial plate-type heat exchanger (PHE) to numerically investigate the solidification process of phase change material (PCM). PCM fills the space between corrugated steel plates, and water at a certain temperature passes from top to bottom between two neighboring plates as heat transfer fluid (HTF). To determine the optimum geometry and operating conditions for the solidification process, the phase change process was investigated with three different plate geometries, different heat transfer fluid input temperatures (12 °C, 17 °C, and 22 °C), different steel plate thicknesses (0.4 mm, 0.6 mm, and 0.8 mm) and different Phase Change Materials (RT-35 and n-octadecane). Numerical analyses were simplified to two dimensions based on the finite volume method. The study results show that using the same phase change material, boundary conditions, and geometric features, the time for full solidification of phase change material decreased by a maximum of 63% in the plate heat exchanger-latent heat thermal energy storage system designed with geometry-A as phase change material layer compared to a cylindrical latent heat thermal energy storage system with the same volume of phase change material.

Effects of coupling in piezoelectric multi-beam structure

MEMS-based piezoelectric energy harvesters utilize the principle of piezoelectricity for harvesting energy from the ambient vibrations of the environment. These energy harvesters are popular because of their small size. Most of these energy harvesters are constructed using a cantilever beam or plate structure comprising of single or multiple beam or plates. This paper presents the idea of coupling effect present in the piezoelectric multiple-plate cantilever structures. In these multi-plate structures, the fixed ends of plates are connected by a metal layer. We observe that the vibrations of one plate tend to affect the vibrations and output of the neighboring plate. In this paper, we present a qualitative explanation of this coupling effect among the neighboring plates in terms of their electrical and mechanical interaction. Then we present a Finite Element Method Analysis of these multi-plate cantilever structures on COMSOL Multiphysics platform to verify our proposed hypothesis of coupling effect occurring in these structures.

SEISMIC STRAIN MAP IN MALAYSIA DERIVED FROM LONG-TERM GLOBAL POSITIONING SYSTEM DATA

Abstract. Series of major earthquakes struck the Sundaland plate as a result of convergence with neighboring plates such as Indian, Australian and Philippine plates. Since then, the Sundaland is experiencing significant crustal deformation that implicate reactivation of local fault and embark question on the status of geohazard and seismic risk. In Malaysia, crustal deformation study by using Global Positioning System (GPS) has been conducted for many years. However, the information of crustal deformation was reported separately and difficult to be archived. In addition, continuous estimation of crustal deformation derived from GPS has to be carried out in order to provide present day seismic status. This study aims at generating a seismic catalog map in Malaysia derived from approximately nine (9) years of GPS data. In this study, derived long-term crustal deformation in the form of coordinate time series (CTS) were converted into yearly strain map. The changes of strain with respect to location of old and active fault line in Malaysia were properly analysed. From the result, the highest changes of strain rate for Peninsular Malaysia happened in 2004 until 2005 and 2012 until 2013 prior to 2004 Acheh earthquake event with the moment magnitude (Mw) and 2012 two strike-slip events in Northern Sumatera with the magnitude of 8.2Mw and 8.6Mw. In North Borneo region, the most significant changes of strain rate happened from 2007 to 2009 and 2011 to 2013. It can be expected that the results will be beneficial in augmenting geohazard mitigation in Malaysia.

Polyatomic degrees of freedom and their temporal evolution extracted from the damping of micro-oscillators

This paper investigates for the first time the influence of molecular degrees of freedom (DOF) on the damping behavior of micro-oscillators in the molecular flow regime. None of the existing theories of damping does take this aspect into account. The damping of piezoelectrically driven bending oscillators is determined by measuring the pressure dependent quality factor Q in an atmosphere consisting of noble gases or polyatomic gases. A neighboring plate with an adjustable gap width ranging from 150 to 3500 μm was mounted above the oscillator, limiting the time of flight of the gas molecules in between the delimitation to several microseconds. Taking the behavior of the noble gases with three translational DOF as a reference, the development of additional rotational and vibrational DOF of polyatomic gas molecules is determined as a function of the gap width, which can be correlated to the time of flight. The determined relaxation times and collision numbers of the DOF are compared to existing theories and to experimental results explored by other methods. Based on the experimental evidence, additions to the existing molecular damping theory are derived by including the higher DOF and adapting an existing thermodynamic excitation model.

Reducing tonal sound from a cascade of flat plates by varying the thickness ratio of neighboring plates

To mitigate the tonal noise from air flow around a cascade of flat plates, such as the grills in front of automobile engines, the thickness ratio of neighboring plates was varied in numerical simulations. Direct aeroacoustic simulations were based on compressible Navier-Stokes equations. For the baseline case with all plates at the thickness ratio of 1.0, the tonal sound is radiated because of the acoustic resonance occurring between the plates. In a controlled flow with plates alternating between large and small thicknesses, the width of the wake behind each plate varies between the neighboring plates. This indicates that the flow around the cascade of flat plates becomes biased. Simulated sound-pressure spectra show that the intensity of tonal sound at the fundamental frequency is reduced by the large thickness ratio between neighboring plates. Also, a secondary intensity peak appears at a frequency higher than the fundamental frequency. This peak appears because vortex shedding occurs at this higher frequency in the wakes behind the thin plates, whereas it occurs at the fundamental frequency in the wakes behind the thick plates. To elucidate the flow and sound related to the tonal sound at the fundamental frequency, the flow fields were phase-averaged with reference to the vortex shedding from the thick plates. With all plates of the same size, two-dimensional large-scale vortices are formed in the wakes of all the plates. Moreover, vortex shedding occurs in the anti-phase mode between the neighboring plates, which reinforces acoustic resonance. Meanwhile, for controlled flow with the plates of alternating thickness, the vortices lose their structure and spread into finer-scale vortices. The synchronization of vortex shedding between the neighboring plates is suppressed, which weakens the tonal sound from acoustic resonance.

Seismic Environments of Prehistoric Settlements in Northern Mesopotamia: A Review of Current Knowledge

Historical archives, modern instruments, and archaeological excavations at plate-boundary sites have recorded an intricate—at times, seemingly relentless—recurrence of severe earthquakes related to the northward movement and convergence of the Arabian tectonic plate with neighboring plates. Based on such information, it is possible to contour average earthquake frequency and/or severity across the northern Mesopotamian region within about 200 km from the plate boundaries.The environments of the Late Neolithic and Chalcolithic habitations of this area range seismically from very active to nearly quiescent; however, not a single excavation report from sites therein considers seismic hypotheses for recorded damage. Exceptionally detailed excavation reports of tells located in two contrasting seismic environments nevertheless show some evidence more consistent with seismic damage than with other causes. The record for Tepe Gawra in the more active area suggests severe earthquakes closely clustered in time. In both areas, there is evidence of some earthquake damage averaging every 500 years or less, and almost all Halaf sites and Halaf-to-Ubaid transitions in northern Mesopotamia plot in areas where such frequencies are expected. Expected seismicity derived from the voluminous historical and instrumental records should play a prominent part in the interpretation of archaeological evidence of this region, as in others near tectonic plate margins.

Instability of a parallel array of orthotropic simply-supported rectangular microplates with interactions

We study the structural instability of a parallel array of identical elastically orthotropic simply-supported rectangular microplates, each of which interacts with two neighboring plates through surface attractive forces. By means of a Stroh-type formalism and by considering the fact that the shear stress on the surfaces of each plate is zero, a 2×2 transfer matrix for a plate is derived. The transfer matrix can be directly obtained from the 6×6 fundamental elasticity matrix without resolving the Stroh eigenvalue problem. A generalized eigenvalue problem can then be conveniently constructed to determine the critical interaction coefficient. The in-plane edge compression acting on the four sides of each plate can also be incorporated in our analysis. Numerical results are presented to demonstrate the effects of material and geometric parameters and edge compression on the critical interaction coefficient and meanwhile to validate the correctness of the solution.

Exact solution to the structural instability of a parallel array of mutually attracting identical simply-supported plates

By means of the theory of elasticity, we investigate the structural instability of a parallel array of identical simply-supported plates. One plate interacts with the neighboring plates through surface attractive forces. The proposed method is based on the 2 × 2 transfer matrix for a plate and on the solution of the generalized eigenvalue problem for the plate array. Analytical expressions of the critical interaction coefficients for two, three and four interacting plates are obtained when the end-effect of the plates at the ends of the parallel array and the surface energy of the plates are ignored. The influence of the end-effect and surface energy on the critical interaction coefficient is also numerically studied. Our solution is valid whether the plates are thin or extremely thick.

Revision of Paleogene plate motions in the Pacific and implications for the Hawaiian-Emperor bend: REPLY

Understanding the relative motion between the Pacific plate and its neighboring plates in the Paleogene has important consequences for deciphering the relationship between absolute and relative plate motions in the Pacific Ocean basin, the history of circum-Pacific subduction, and the cause of the Hawaiian-Emperor bend (HEB). We quantitatively model the Farallon/Vancouver-Pacific-Antarctic seafloor spreading history from 67 to 33 Ma based on a comprehensive synthesis of magnetic anomaly and fracture identifications. We find a well-constrained increase from 75 ± 5 mm/yr to 101 ± 5 mm/yr in Pacific-Farallon full spreading rates between 57.6 Ma and 55.9 Ma, followed by a stepwise increase to 182 ± 2 mm/yr from 49.7 to 40.1 Ma. The increases in Pacific-Farallon spreading rates are not accompanied by any statistically significant change in spreading direction. The 57.6–55.9 Ma surge of Pacific-Farallon spreading reflects an eastward acceleration in Farallon plate motion, as it precedes west Pacific subduction initiation and is not associated with any significant change in Pacific-Antarctic spreading. We interpret the increase in Pacific-Farallon spreading rates after ca. 50 Ma as a consequence of further acceleration in Farallon plate motion. We find no indication of a major change in Pacific plate absolute motion at this time. Our model suggests that changes in relative motion direction between the Pacific and Farallon and Pacific and Antarctic plates were insignificant around the formation time of the HEB (ca. 47.5 Ma), and the bend is largely a consequence of Hawaiian hotspot motion, which ceased rapid motion after 47 Ma.

Revision of Paleogene plate motions in the Pacific and implications for the Hawaiian-Emperor bend

Research Article| May 01, 2015 Revision of Paleogene plate motions in the Pacific and implications for the Hawaiian-Emperor bend Nicky M. Wright; Nicky M. Wright EarthByte Group, School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia Search for other works by this author on: GSW Google Scholar R. Dietmar Müller; R. Dietmar Müller EarthByte Group, School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia Search for other works by this author on: GSW Google Scholar Maria Seton; Maria Seton EarthByte Group, School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia Search for other works by this author on: GSW Google Scholar Simon E. Williams Simon E. Williams EarthByte Group, School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia Search for other works by this author on: GSW Google Scholar Geology (2015) 43 (5): 455–458. https://doi.org/10.1130/G36303.1 Article history received: 23 Sep 2014 rev-recd: 25 Feb 2015 accepted: 03 Mar 2015 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Nicky M. Wright, R. Dietmar Müller, Maria Seton, Simon E. Williams; Revision of Paleogene plate motions in the Pacific and implications for the Hawaiian-Emperor bend. Geology 2015;; 43 (5): 455–458. doi: https://doi.org/10.1130/G36303.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Understanding the relative motion between the Pacific plate and its neighboring plates in the Paleogene has important consequences for deciphering the relationship between absolute and relative plate motions in the Pacific Ocean basin, the history of circum-Pacific subduction, and the cause of the Hawaiian-Emperor bend (HEB). We quantitatively model the Farallon/Vancouver-Pacific-Antarctic seafloor spreading history from 67 to 33 Ma based on a comprehensive synthesis of magnetic anomaly and fracture identifications. We find a well-constrained increase from 75 ± 5 mm/yr to 101 ± 5 mm/yr in Pacific-Farallon full spreading rates between 57.6 Ma and 55.9 Ma, followed by a stepwise increase to 182 ± 2 mm/yr from 49.7 to 40.1 Ma. The increases in Pacific-Farallon spreading rates are not accompanied by any statistically significant change in spreading direction. The 57.6–55.9 Ma surge of Pacific-Farallon spreading reflects an eastward acceleration in Farallon plate motion, as it precedes west Pacific subduction initiation and is not associated with any significant change in Pacific-Antarctic spreading. We interpret the increase in Pacific-Farallon spreading rates after ca. 50 Ma as a consequence of further acceleration in Farallon plate motion. We find no indication of a major change in Pacific plate absolute motion at this time. Our model suggests that changes in relative motion direction between the Pacific and Farallon and Pacific and Antarctic plates were insignificant around the formation time of the HEB (ca. 47.5 Ma), and the bend is largely a consequence of Hawaiian hotspot motion, which ceased rapid motion after 47 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Flows around a cascade of flat plates with acoustic resonance

In order to better understand the effects of acoustic resonance on flows around a cascade of flat plates, fluid structures and acoustic fields were examined by aeroacoustic direct simulations and wind tunnel experiments. Computations and experiments were performed for the flows around five parallel plates with and without the acoustic resonance changing the freestream velocity. The aspect ratio of the plates, C/b, is 15.0, and the separation-to-thickness ratio, s/b, is 6.0. For the resonant condition of a freestream velocity of 44 m/s, the Reynolds number based on the plate thickness, b, and the freestream velocity is 5.8 × 103. The computational results revealed that large-scale vortices composed of fine-scale vortices are shed in the wake of the plates. Both experimental and computational results indicated that the shedding of the large-scale vortices is more synchronized in the spanwise direction for the resonant condition. Moreover, the shedding of the large-scale vortices from one plate and those from the neighboring plates become more synchronized in the resonant condition. The mode of this synchronization was found to be an anti-phase mode, in which the vortex is shed from the upper or lower face of one plate when the vortex is shed from the lower or upper faces of the neighboring plates. Computation of the flow around a single plate was also performed, and the radiation of the acoustic waves from the downstream edge due to vortex shedding from the plate was indicated. When acoustic resonance occurs in the flows around the cascade of flat plates, vortex shedding in the above-mentioned mode contributes to the intensification of the standing waves between the plates. Moreover, standing waves were demonstrated to induce new vortices around the upstream edges of the plates in synchronization.

Re-evaluation of the kinematics of Victoria Block using continuous GNSS data

The divergent boundary between the Somalia and Nubia plates is a complex tectonic domain where extensional processes are localized along narrow rift structures isolating small plates imbedded within the East African Rift. One of these tectonic units is the Victoria plate, which is the subject of this study. Here we process space geodetic data for 37 permanent GNSS stations distributed along the Nubia, Somalia and Victoria plates to (1) compute the motion of the three plates in the ITRF2008 reference frame and (2) deduce the relative motion of Victoria with respect to its neighboring plates. The Nubia plate motion is computed from a set of 25 stations, the Somalia plate motion from a set of 7 stations, and the Victoria plate motion from a set of 5 stations. The instantaneous relative Euler poles for the Nubia-Victoria and Somalia-Victoria pairs are now evaluated as 10.6582oN, 32.9752Eo, 0.1196o/Myr and 8.0164oS, 32.2869oE, 0.1589o/Myr, respectively. The computation of the relative inter-plate velocities along Victoria s plate boundary is straightforward in most situations because the western and northeastern boundary segments correspond to well-developed rift basins, where extension is mostly normal to rift basin flanks and seismicity concentrates along narrow structures. This is particular evident on the western branch between Victoria and Nubia. The southeastern limit of the Victoria plate is poorly defined, and geodetic data indicates that differential motion between Somalia and Victoria may be accommodated by a complex plate boundary area, which roughly encompasses the Masai terrain. Geodetic observations of the Victoria-Somalia boundary along the Eastern Branch, particularly in the Manyara rift, reveal highly oblique horizontal extension. In this region seismicity is sparse which suggests that strain is accommodated by magmatic processes.