Arc Region Research Articles

Post-seismic motions after the 2006–2007 Simushir earthquakes at different stages of the seismic cycle

We analyzed long-term satellite geodesic observations after the Simushir earthquakes of 2006–2007. Application of a key model of the structure of the island arc regions combined with a model of nonstationary convective system in the upper mantle allowed us to find a consistent explanation of the motion of the Earth’s surface and distinguish the segments of the island arc at different stages of the seismic cycle.

Geochemistry and isotopic signatures of metavolcanic and metaplutonic rocks of the Faina and Serra de Santa Rita greenstone belts, Central Brazil: Evidences for a Mesoarchean intraoceanic arc

The Archean-Paleoproterozoic Terrane of Goiás, Central Brazil, is an allochthonous block within the Neoproterozoic Tocatins Province and consists of an association of Archean TTG complexes and gold-bearing Archean-Paleoproterozoic greenstone belts. The Faina and Serra Santa Rita greenstone belts, located in the southern portion of the terrane, are investigated using geochemistry and isotope geology to establish the time of magmatism and tectonic environment. Our data show that the ultramafic rocks have some chemical characteristics similar to modern boninites, whereas the amphibolites are subdivided into two groups: the type 1 basalts group are tholeiites with flat REE patterns and are similar to back-arc basin basalts; the type 2 basalts group have high Nb contents and are comparable to Nb-enriched basalts. Felsic to intermediate rocks present some of the main chemical diagnostic features of adakites, in which the metandesites and metatonalites are comparable to high-SiO2 adakites, and the metadiorites, characterized by very high MgO, Cr and Ni contents, are comparable to low-SiO2 adakites or high-Mg andesites. Metavolcanic and metaplutonic rocks show two main periods of magmatic crystallization ages with juvenile and slightly crustal contaminated rocks. The first occurred at 2.96–2.92Ga with positive ƐNd (t) values of +2.16 to +2.77, while the second formed at 2.8Ga with slightly negative ƐNd (t) value of −0.15. The volcanic and plutonic protoliths of the two greenstone belts were formed in an intraoceanic forearc-arc-back-arc system. The initial stage corresponds to ultramafic lava eruption in the forearc region of a proto-island arc, at 2.96Ga. The evolution of the island arc and subduction progression led to oceanic slab-melting and generation of adakites. At 2.92Ga, the adakitic melt was totally consumed by peridotite mantle and the subsequent melting of these hybridized mantle wedge generated high-Mg andesites that lodged in the crust as dioritic intrusions with high MgO, Cr and Ni contents. The late-stage corresponds to a continental arc formation at 2.8Ga, marked by tonalitic magmatism and amalgamation with other island arcs and continental arcs of the TTG complexes of the Archean-Paleoproterozoic Terrane of Goiás.

A30 伊豆小笠原背弧域の火成活動史 : リフティングに伴う火成活動の変化

A30 伊豆小笠原背弧域の火成活動史 : リフティングに伴う火成活動の変化

Role of the Kopili Fault in Deformation Tectonics of the Indo‐Burmese Arc Inferred from the Rupture Process of the 3 January 2016Mw 6.7 Imphal Earthquake

The Burmese arc is a peculiar plate boundary where there exists an eastward subducted Indian slab, but the current tectonics of the region are predominantly governed by a northward strike‐slip motion of the Indian plate past the Burmese plate, as evidenced by seismic and Global Positioning System data. The shallower portion of the dipping Indian slab is characterized mostly by earthquakes with strike‐slip type focal mechanisms with roughly northwest‐ and northeast‐trending fault planes, although there is no clear evidence for the choice of rupture planes. In the present study, we use teleseismic broadband waveforms to model the rupture propagation of an M w 6.7 strike‐slip earthquake of 3 January 2016 that occurred in the Indian city of Imphal, and infer the fault‐plane orientation. The result indicates a right‐lateral strike‐slip motion along a N21°W plane, which is confirmed by both waveform fitting and distribution of aftershocks. Interestingly, this earthquake occurred at the intersection of three major faults in this region—the Churachandpur Mao fault bounding the India and Burma plates, the Dauki fault south of the Shillong plateau, and the Kopili fault separating the Shillong plateau from the Brahmaputra valley. This raises various possibilities for interpreting this event. However, based on the finite‐fault inversion, we infer that this earthquake occurred on the Kopili fault running northwest–southeast from Bhutan Himalaya down to the Burmese arc, and manifested as a right‐lateral strike‐slip motion in response to the northward motion of the Indian plate and a counterclockwise rotation of the Brahmaputra valley. We further interpret that the overall deformation in the Burmese arc region is accommodated by northward slivering of the eastward subducted Indian lithospheric slab along a series of northwest‐ to north–south‐trending right‐lateral strike‐slip faults from west to east as the Indian plate moves northward past the Burma and Sunda blocks.

The Role of Metal Vapour in Gas Metal Arc Welding and Methods of Combined Experimental and Numerical Process Analysis

Gas metal arc welding (GMAW) processes are characterized by a high number of simultaneously running physical processes. The process capability is mainly determined by the properties of a metal vapour influenced arc and the material transfer. In recent years, experimental as well as numerical methods are being used increasingly in order to understand the complex interactions between the arc and material transfer. In this paper, we discuss the influence of metal vapour on GMAW processes in spray as well as pulsed material transfer mode. With respect to the high complexity of the process, experimental and numerical methods are combined in a targeted manner in order to obtain a high level of expressive capability with moderate numerical and experimental effort. The results illustrate the high influence of the changing vaporization rate not only on the arc properties but on the arc attachment at the filler wire. It could be shown, that in many cases the metal vapour concentration in the arc region has a greater influence on the arc properties and the material transfer than different shielding gas components like oxygen, hydrogen or helium.

NOAfaults: a digital database for active faults in Greece

This paper documents the approach to compiling a digital database of fault geometry and additional attributes primarily to support seismicity monitoring at the National Observatory of Athens (NOA). A database for Greek active faults has been constructed from published fault maps in peer-reviewed journals since 1972. The standard commercial software ARC GIS has been used to design and populate the database. The fault layer was produced by on-screen digitization and is available to the scientific community in ESRI shapefile (SHP) and TXT formats in WGS84 projection. A KML file is also available to display the fault data in an Earth browser such as Google Earth. In this version of the database, we focus our attention to the active faults of the upper (Aegean + Eurasian) plate and the back-arc region of the Hellenic Arc, in general. 963 faults are included. The database is freely accessible from the Internet.

Statistical Analysis of the Spatial Distribution of Multi-Elements in an Island Arc Region: Complicating Factors and Transfer by Water Currents

The compositions and transfer processes affecting coastal sea sediments from the Seto Inland Sea and the Pacific Ocean are examined through the construction of comprehensive terrestrial and marine geochemical maps for western Japan. Two-way analysis of variance (ANOVA) suggests that the elemental concentrations of marine sediments vary with particle size, and that this has a greater effect than the regional provenance of the terrestrial material. Cluster analysis is employed to reveal similarities and differences in the geochemistry of coastal sea and stream sediments. This analysis suggests that the geochemical features of fine sands and silts in the marine environment reflect those of stream sediments in the adjacent terrestrial areas. However, gravels and coarse sands do not show this direct relationship, which is likely a result of mineral segregation by strong tidal currents and the denudation of old basement rocks. Finally, the transport processes for the fine-grained sediments are discussed, using the spatial distribution patterns of outliers for those elements enriched in silt and clay. Silty and clayey sediments are found to be transported and dispersed widely by a periodic current in the inner sea, and are selectively deposited at the boundary of different water masses in the outer sea.

Arc Shape Characteristics with Ultra-High-Frequency Pulsed Arc Welding

Arc plasma possesses a constriction phenomenon with a pulsed current. The constriction is created by the Lorentz force, the radial electromagnetic force during arc welding, which determines the energy distribution of the arc plasma. Welding experiments were carried out with ultra-high-frequency pulsed arc welding (UHFP-AW). Ultra-high-speed camera observations were produced for arc surveillance. Hue-saturation-intensity (HSI) image analysis was used to distinguish the regions of the arc plasma that represented the heat energy distribution. The measurement of arc regions indicated that, with an ultra-high-frequency pulsed arc, the constriction was not only within the decreased arc geometry, but also within the constricted arc core region. This can be checked by the ratio of the core region to the total area. The arc core region expanded significantly at 40 kHz at 60 A. A current level of 80 A caused a decrease in the total region of the arc. Meanwhile, the ratio of the core region to the total increased. It can be concluded that arc constriction depends on the increased area of the core region with the pulsed current (>20 kHz).

Finite element analysis of a 3D moving vacuum arc for transverse magnetic field contacts based on Gundlach’s formula

A systematic numerical method for analyzing a 3D moving vacuum arc was proposed and tested in this research by using a transverse magnetic field (TMF) contact. The analysis was carried out by employing the finite element method and the experimental energy equation defined by Gundlach’s formula. In the literature, the vacuum interrupter has been widely applied to medium-voltage switching circuits. TMF-type contacts use the Lorentz force density to move a high-temperature arc so as to prevent the contacts from being melted and damaged. The material erosion caused by the arc on the electrode’s surface is an important process that results in the interruptive capabilities of these vacuum interrupters. In a classical arc model, to move the vacuum arc, it is required that the magneto-hydrodynamics be analyzed in the arc region at each step. However, with this approach convergence is difficult, resulting in a very time-consuming. Therefore, we propose a new technique to predict the behaviors of vacuum arc between two electrodes. This new approach adopts the experimental arc voltage equation between two electrodes defined by Gundlach’s formula. We verify our proposed model by comparing its results with the arcing behaviors obtained from earlier experiments.

Stress‐Drop Variations and Source‐Scaling Relations of Moderate Earthquakes of the Indian Tectonic Plate

We investigate the source characteristics of 53 earthquakes in and around the Indian subcontinent through a grid‐search technique applied to the P ‐ and S ‐wave displacement spectra of regional waveforms registered at 42 broadband seismic stations. In addition, we estimate the P ‐ and S ‐wave attenuation factors representative of the various tectonic regions that constitute the Indian shield. We discuss the sensitivity of the displacement spectrum to various parameters and demonstrate that for a Brune‐type source model, the seismic moment is the best estimated parameter compared to others, such as the corner frequency. Our estimates of moment magnitudes are within the range of 1014–1020 (N·m), with the crack radii being less than ∼12 km. The nonuniform distribution of the static stress drop along the Himalaya, Burmese arc, and the western Indian regions indicates that the central Himalayas are prone to frequent failures owing to the lesser stress drop, in contrast with the northwestern Himalaya and Burmese arc regions. Our results suggest that median stress drops are independent of the earthquake mechanism. Online Material: List of events and associated estimated parameters.

Primitive arc magma diversity: New geochemical insights in the Cascade Arc

The origin of the large range of compositional diversity encompassed by primitive arc magmas and the respective roles of mantle heterogeneity versus slab-derived contributions are the center of ongoing debate. The Cascade Arc of western North America is a global endmember hot subduction zone and an ideal setting in which to examine fundamental questions about the origin of arc magmas. Cascade Arc primitive magmas define several distinct compositional endmembers, the most widespread of which are high alumina olivine tholeiite (HAOT), calc-alkaline basalt (CAB), and intraplate-type basalt (IPB). New high precision Sr-Nd-Hf-Pb isotopic and trace element data for 49 of the most primitive magmas from seven major High Cascades volcanic centers are used to assess whether the basalt groups are derived from geochemically distinct mantle sources. Along with recently published data for the Garibaldi Volcanic Belt (GVB), the northern and other major segment of the Cascade Arc, and Mt. Rainier, the new data expand the high-precision isotopic coverage to seventeen volcanic centers spanning the ~1300km length of the arc. In all investigated isotopic systems, the new High Cascades data allow for finer resolution with much less scatter than previous data. HAOT mantle sources are systematically more depleted in incompatible elements than CAB sources, yet High Cascades CABs and HAOTs are isotopically indistinguishable, defining a remarkable linear Pb isotopic array consistent with a single mantle endmember that is similar to the source of Juan de Fuca mid-ocean ridge basalts. This mantle has been variably modified by contributions from a single subducting sediment endmember that is a close isotopic match to average Northern Cascadia basin sediment. Although Astoria Fan sediment was previously used as a proxy for the subducting sediment composition in the Cascadia subduction zone, the isotope ratios of Cascades basalts record no input from Astoria Fan sediment. High Cascades CABs and HAOTs both contain subducting sediment input in the form of a melt, but CABs also contain melts of subducting oceanic crust which is most apparent in the southern Cascades high-Sr/P suite and in the GVB. The least sediment input is recorded by GVB basalts, which also become progressively lower in 208Pb*/206Pb* and Hf isotope ratios to the north, reflecting the influx of an isotopically distinct enriched mantle component that generates IPBs at the northern slab edge. Enriched mantle with a composition trending towards HIMU is also recorded by a distinct isotopic array that is defined by IPBs from the Mt. Adams-Simcoe back arc region. We propose that slab gaps permit the influx of sub-slab asthenospheric mantle in both the northern GVB and Mt. Adams-Simcoe back-arc. Otherwise, western North America is underlain predominantly by isotopically homogeneous, MORB-type depleted mantle from which both the CAB and HAOT basalt groups are derived. Our results from the Cascades imply that most of the compositional heterogeneity encompassed by primitive arc magmas is not related to the presence of multiple mantle components but to variability in the composition and quantity of slab contributions. This study highlights the importance of high precision Sr-Nd-Hf-Pb isotope and trace element data in obtaining new insights on the petrogenesis of arc magmas.

The Effects of Desferroxamine on Bone and Bone Graft Healing in Critical-Size Bone Defects.

Autogenous bone grafts are still the criterion standard treatment option in critical-size bone defect reconstructions, and many therapies can affect its incorporation. In this study, it was aimed to research the effects of desferroxamine (DFO) application on bone and bone graft healing due to the effects of osteoblast and osteoclast regulation and stimulation of angiogenesis. Rat zygomatic arch critical-size bone defect model (5 mm) was used as the experimental model. Thirty-two Sprague-Dawley rats (64 zygomatic arches) were divided into 4 groups (16 zygomatic arches in each). In groups 1 and 2, defects were reconstructed with the bone grafts harvested from the other side, and the right arc was named as group 1, and the left was group 2. At group 1, 200 μM/300 μL dosage of DFO was injected at the zygomatic arch region starting at the seventh day preoperatively and lasting until the 45th day postoperatively. Group 2 animals were defined as the control group of group 1, and 0.9% NaCl injection was applied. In groups 3 and 4, there was no repair after the formation of defects, and the right arc region was treated with DFO, and left was treated with 0.9% NaCl for postoperative 45 days, respectively. Radiological (computed tomography), histological (hematoxylin-eosin), and biomechanical (3-point bending test) tests were used for the evaluation. In radiological evaluation, there was a statistically significant decrease (P < 0.05) in bone defect size in group 3 animals at the 4th, 8th, and 12th weeks, and bone graft volume showed a statistical difference at all weeks (P < 0.05). In histological evaluation, it was observed that there was an increase in osteoblast number and vascularity rates (P < 0.05) in the DFO-treated groups at all weeks. Biomechanical evaluation of the subjects showed increase in bone strength in group 1 animals at 12 weeks. In this study, it was shown that DFO treatment increased bone graft incorporation and healing in critical-size bone defects. In this aspect, we suggest that DFO can be used to increase graft incorporation in risky areas and reduce the defect size in patients who are not suitable for vascularized bone graft transfer.

Seismogenic stress field estimation in the Calabrian Arc region (south Italy) from a Bayesian approach

AbstractA new high‐quality waveform inversion focal mechanism database of the Calabrian Arc region has been compiled by integrating 292 mechanisms selected from literature and catalogs with 146 newly computed solutions. The new database has then been used for computation of posterior density distributions of stress tensor components by a Bayesian method never applied in south Italy before the present study. The application of this method to the enhanced database has allowed us to provide a detailed picture of seismotectonic stress regimes in this very complex area where lithospheric unit configuration and geodynamic engines are still strongly debated. Our results well constrain the extensional domain of Calabrian Arc and the compressional one of the southernmost Tyrrhenian Sea. In addition, previously undetected transcurrent regimes have been identified in the Ionian offshore. The new information released here will furnish useful tools and constraints for future geodynamic investigations.

Temporal variation of the stress field during the construction of the central Andes: Constrains from the volcanic arc region (22-26°S), Western Cordillera, Chile, during the last 20 Ma

In order to understand the response of the stress field state to intrinsic processes during the construction of the Andes, such as thickening of the continental crust, lithospheric delamination, and/or thermal weakening, we investigate the stress field evolution of the arc region since the last 20 my, in the Central Andes (22°-26.5°S). The 43 reduced paleostress tensors derived from inversion of 682 fault-slip data reveal a complex pattern of stress states during the last episode of orogenic construction and topographic uplift. We identify two geodynamic stages; the first stage corresponds to the construction of the Altiplano/Puna plateau and the second one to its gravitational collapse. Four stress states that have prevailed in the Altiplano/Puna plateau since middle Miocene times, characterize the transition from one stage to the other. Along the study latitudes, a spatiotemporal change in stress state is clearly observed, which led to an understanding that a change in the stress field may be related not only to the boundary conditions but also to intrinsic factors associated with the construction of the Andean orogeny. Our results suggest that ca. 13-10 Ma and ca. 8-5 Ma, in the southern Altiplano and northern Puna, and in the southern Puna, respectively, regional elevation and crustal thicknesses reached threshold values necessary to generate the orogenic collapse.

Stimulated emission of Cooper pairs in a high-temperature cuprate superconductor.

The concept of stimulated emission of bosons has played an important role in modern science and technology, and constitutes the working principle for lasers. In a stimulated emission process, an incoming photon enhances the probability that an excited atomic state will transition to a lower energy state and generate a second photon of the same energy. It is expected, but not experimentally shown, that stimulated emission contributes significantly to the zero resistance current in a superconductor by enhancing the probability that scattered Cooper pairs will return to the macroscopically occupied condensate instead of entering any other state. Here, we use time- and angle-resolved photoemission spectroscopy to study the initial rise of the non-equilibrium quasiparticle population in a Bi2Sr2CaCu2O8+δ cuprate superconductor induced by an ultrashort laser pulse. Our finding reveals significantly slower buildup of quasiparticles in the superconducting state than in the normal state. The slower buildup only occurs when the pump pulse is too weak to deplete the superconducting condensate, and for cuts inside the Fermi arc region. We propose this is a manifestation of stimulated recombination of broken Cooper pairs, and signals an important momentum space dichotomy in the formation of Cooper pairs inside and outside the Fermi arc region.

Forecast of Large Earthquakes Through Semi-periodicity Analysis of Labeled Point Processes

Large earthquakes have semi-periodic behavior as a result of critically self-organized processes of stress accumulation and release in seismogenic regions. Hence, large earthquakes in a given region constitute semi-periodic sequences with recurrence times varying slightly from periodicity. In previous papers, it has been shown that it is possible to identify these sequences through Fourier analysis of the occurrence time series of large earthquakes from a given region, by realizing that not all earthquakes in the region need belong to the same sequence, since there can be more than one process of stress accumulation and release in the region. Sequence identification can be used to forecast earthquake occurrence with well determined confidence bounds. This paper presents improvements on the above mentioned sequence identification and forecasting method: the influence of earthquake size on the spectral analysis, and its importance in semi-periodic events identification are considered, which means that earthquake occurrence times are treated as a labeled point process; a revised estimation of non-randomness probability is used; a better estimation of appropriate upper limit uncertainties to use in forecasts is introduced; and the use of Bayesian analysis to evaluate the posterior forecast performance is applied. This improved method was successfully tested on synthetic data and subsequently applied to real data from some specific regions. As an example of application, we show the analysis of data from the northeastern Japan Arc region, in which one semi-periodic sequence of four earthquakes with M ≥ 8.0, having high non-randomness probability was identified. We compare the results of this analysis with those of the unlabeled point process analysis.

Molecular and ionized gas kinematics in the GC Radio Arc

AbstractWe present NH3 and H64α+H63α VLA observations of the Radio Arc region, including the M0.20 – 0.033 and G0.10 – 0.08 molecular clouds. These observations suggest the two velocity components of M0.20 – 0.033 are physically connected in the south. Additional ATCA observations suggest this connection is due to an expanding shell in the molecular gas, with the centroid located near the Quintuplet cluster. The G0.10 – 0.08 molecular cloud has little radio continuum, strong molecular emission, and abundant CH3OH masers, similar to a nearby molecular cloud with no star formation: M0.25+0.01. These features detected in G0.10 – 0.08 suggest dense molecular gas with no signs of current star formation.

The Lower Cretaceous Atzompa Formation In South-Central Mexico: Record of Evolution From Extensional Backarc Basin Margin To Carbonate Platform

Abstract: Lower Cretaceous depositional systems of southwestern Oaxaquia, in south-central Mexico, were influenced by initiation of a continental arc on mainland Mexico and subsequent accretion of the Guerrero composite arc terrane to mainland Mexico. The Atzompa Formation, defined herein, which crops out in the Sierra de Tentzo, constitutes a succession of conglomerate, sandstone, siltstone, and limestone with Early Cretaceous fauna and detrital zircon maximum depositional ages that range 126–123 Ma (late Barremian to early Aptian). The lower part of the Atzompa records a transition from alluvial to deep lacustrine depositional environments, suggesting the early stages of an extensional basin; overlying deposits of anabranching axial fluvial systems that flowed to the NE–SE accumulated after a period of rapid subsidence in the Tentzo basin, also formerly undescribed. Fluvial facies grade up-section to tidal deposits overlain in turn by a carbonate ramp succession that contains late Barremian to early Aptian fossils. The ramp deposits of the uppermost Atzompa Formation are overlain on a sharp contact by basinal carbonates of early Albian age.The Tentzo basin, formed due to crustal extension of the overriding plate in a backarc setting, was characterized by very high rates of sedimentation (3.6 mm/yr) during the early stages of basin formation (rift initiation and rift climax), and slower rates during the development of tidal systems and the carbonate ramp (post-rift stage). Regional and local subsidence took place in the backarc region of the Zicapa magmatic arc, which was established in the western margin of Mexico by Hauterivian time. Abrupt deepening following Atzompa Formation deposition is attributed to flexural subsidence related to collision of the Guerrero composite volcanic terrane with the western margin of Mexico. Following late Aptian accretion of the Guerrero terrane to Oaxaquia, the carbonate basin eventually shallowed to become a carbonate platform that faced the Gulf of Mexico.

Diverse roles of assembly factors revealed by structures of late nuclear pre-60S ribosomes.

Ribosome biogenesis is a highly complex process in eukaryotes, involving temporally and spatially regulated ribosomal protein (r-protein) binding and ribosomal RNA remodelling events in the nucleolus, nucleoplasm and cytoplasm. Hundreds of assembly factors, organized into sequential functional groups, facilitate and guide the maturation process into productive assembly branches in and across different cellular compartments. However, the precise mechanisms by which these assembly factors function are largely unknown. Here we use cryo-electron microscopy to characterize the structures of yeast nucleoplasmic pre-60S particles affinity-purified using the epitope-tagged assembly factor Nog2. Our data pinpoint the locations and determine the structures of over 20 assembly factors, which are enriched in two areas: an arc region extending from the central protuberance to the polypeptide tunnel exit, and the domain including the internal transcribed spacer 2 (ITS2) that separates 5.8S and 25S ribosomal RNAs. In particular, two regulatory GTPases, Nog2 and Nog1, act as hub proteins to interact with multiple, distant assembly factors and functional ribosomal RNA elements, manifesting their critical roles in structural remodelling checkpoints and nuclear export. Moreover, our snapshots of compositionally and structurally different pre-60S intermediates provide essential mechanistic details for three major remodelling events before nuclear export: rotation of the 5S ribonucleoprotein, construction of the active centre and ITS2 removal. The rich structural information in our structures provides a framework to dissect molecular roles of diverse assembly factors in eukaryotic ribosome assembly.

Novel non-equilibrium modelling of a DC electric arc in argon

A novel non-equilibrium model has been developed to describe the interplay of heat and mass transfer and electric and magnetic fields in a DC electric arc. A complete diffusion treatment of particle fluxes, a generalized form of Ohm’s law, and numerical matching of the arc plasma with the space-charge sheaths adjacent to the electrodes are applied to analyze in detail the plasma parameters and the phenomena occurring in the plasma column and the near-electrode regions of a DC arc generated in atmospheric pressure argon for current levels from 20 A up to 200 A. Results comprising electric field and potential, current density, heating of the electrodes, and effects of thermal and chemical non-equilibrium are presented and discussed. The current–voltage characteristic obtained is in fair agreement with known experimental data. It indicates a minimum for arc current of about 80 A. For all current levels, a field reversal in front of the anode accompanied by a voltage drop of (0.7–2.6) V is observed. Another field reversal is observed near the cathode for arc currents below 80 A.