Central Arc Research Articles

Origin of Late Paleogene to Neogene basalts and associated coeval felsic volcanic rocks in Southwest Hokkaido, northern NE Japan arc: Constraints from Sr and Nd isotopes and major- and trace-element chemistry

Basalts and felsic volcanic rocks (mainly dacite and rhyolite) found in southwest Hokkaido, northern part of the NE Japan arc, result from protracted volcanism during the Oligocene (34–30Ma), Early Miocene (25–17Ma), Middle Miocene (16–12Ma), Late Miocene (10–5Ma), Pliocene (4Ma) and Quaternary (2Ma), thus spanning the pre-Japan Sea opening to post-opening stages.The majority of basaltic rocks after about 16Ma show depleted Sr (SrI) and Nd (NdI) isotopic signatures compared with some Middle to Early Miocene basalts, which strongly resemble, in terms of both timing and extent, the change in SrI and NdI values for back-arc basaltic rocks of the central NE Japan arc. However, significant differences exist for younger basaltic rocks, in that basaltic rocks with depleted SrI and NdI signatures are found from the Middle Miocene onwards throughout the eastern-, transitional- and western-volcanic zones in SW Hokkaido, whereas in the central NE Japan arc, basaltic rocks with similar isotopic signatures are confined to the back-arc side.Felsic volcanic rocks in southwest Hokkaido have SrI and NdI values, which overlap with coeval southwest Hokkaido basaltic rocks. Although the relationship between mafic and felsic rocks could be attributed to fractional crystallization, this process is inconsistent with REE chemistry, as total REE do not increase systematically from basaltic rocks to felsic volcanic rocks. Alternatively, lower crustal mafic rocks, represented by gabbroic and amphibolitic xenoliths found in basaltic rocks at Itinome-gata (Oga Peninsula), are a possible source for Late Paleogene to Quaternary felsic magmas, as both felsic volcanic rocks and xenoliths have similar SrI and NdI.A possible tectono-magmatic model for the production of post-Late Paleogene volcanic rocks from SW Hokkaido commences in the Oligocene (34Ma) with asthenospheric mantle upwelling followed by partial melting to generate basalt magma (Matsue basalt) with depleted SrI and NdI, followed by interaction of asthenosphere-derived basalt magmas with overlying subcontinental lithosphere. In the Early Miocene (25–17Ma), asthenospheric upwelling triggered partial melting of the overlying lithospheric mantle from which most basalts with undepleted SrI and NdI values were derived. During the Middle Miocene (16–12Ma), thinning of the overlying lithosphere due to the opening of the Japan Sea resulted in asthenospheric upwelling which reached the region beneath the present NE Japan arc volcanic front. Partial melting of the asthenosphere led to generation of voluminous basalt magma with depleted SrI and NdI values throughout southwest Hokkaido. Most basaltic rocks that erupted since the Late Miocene are considered to have also formed from asthenospheric mantle. Basaltic magmas formed since the Oligocene have either been erupted, or fluxed and heated the lower crust from which coeval felsic magmas were generated.

Uso do retalho osteocutâneo microcirúrgico de fíbula na reconstrução dos defeitos complexos de mandíbula

BACKGROUND: Free fibular osteocutaneous flap is the first choice for segmental mandible and contiguous soft-tissue defect reconstructions in most situations. OBJECTIVE: This study presents a four-year experience with free fibular osteocutaneous flap for mandibular reconstruction. METHODS: An analysis of 15 patients underwent to microsurgical reconstruction of the mandible and oral floor, with a fibular osteocutaneous flap was performed. The mean follow-up after surgery was 2 years. We studied the histopathological classification of primary tumor, location of the resected mandibular portion, vessels used for the anastomosis, associated flap, exposition to radiation, results and complications. RESULTS: The most common histological type was squamous cell carcinoma (81%) followed by osteosarcoma (13%). The mandibular portion resected with greater frequency was the central arc in 81% of patients; 87% of patients were exposed to radiation in the preoperative or postoperative. Reconstruction was immediate in 81% of cases. Pedicled or free flaps associated were used in 46%. Immediate complications were observed in 25% of patients and late complications, in 31%, with a success rate of 100%. CONCLUSIONS: The osteocutaneous free fibula flap is indicated in reconstruction of large mandibular defects, especially of its central portion. The procedure indications must be individualized, taking into account risks and benefits, as well as its impact on quality of life of patients.

Deep structure of the central Lesser Antilles Island Arc: Relevance for the formation of continental crust

Oceanic island arcs are sites of high magma production and contribute to the formation of continental crust. Geophysical studies may provide information on the configuration and composition of island arc crust, however, to date only few seismic profiles exist across active island arcs, limiting our knowledge on the deep structure and processes related to the production of arc crust. We acquired active-source wide-angle seismic data crossing the central Lesser Antilles island arc north of Dominica where the oceanic Tiburon Ridge subducts obliquely beneath the forearc. A combined analysis of wide-angle seismics and pre-stack depth migrated reflection data images the complex structure of the backstop and its segmentation into two individual ridges, suggesting an intricate relation between subducted basement relief and forearc deformation. Tomographic imaging reveals three distinct layers composing the island arc crust. A three kilometer thick upper crust of volcanogenic sedimentary rocks and volcaniclastics is underlain by intermediate to felsic middle crust and plutonic lower crust. The island arc crust may comprise inherited elements of oceanic plateau material contributing to the observed crustal thickness. A high density ultramafic cumulates layer is not detected, which is an important observation for models of continental crust formation. The upper plate Moho is found at a depth of 24 km below the sea floor. Upper mantle velocities are close to the global average. Our study provides important information on the composition of the island arc crust and its deep structure, ranging from intermediate to felsic and mafic conditions.

Seismic swarm associated with the 2008 eruption of Kasatochi Volcano, Alaska: Earthquake locations and source parameters

[1] An energetic seismic swarm accompanied an eruption of Kasatochi Volcano in the central Aleutian volcanic arc in August of 2008. In retrospect, the first earthquakes in the swarm were detected about 1 month prior to the eruption onset. Activity in the swarm quickly intensified less than 48 h prior to the first large explosion and subsequently subsided with decline of eruptive activity. The largest earthquake measured as moment magnitude 5.8, and a dozen additional earthquakes were larger than magnitude 4. The swarm exhibited both tectonic and volcanic characteristics. Its shear failure earthquake features were b value = 0.9, most earthquakes with impulsive P and S arrivals and higher-frequency content, and earthquake faulting parameters consistent with regional tectonic stresses. Its volcanic or fluid-influenced seismicity features were volcanic tremor, large CLVD components in moment tensor solutions, and increasing magnitudes with time. Earthquake location tests suggest that the earthquakes occurred in a distributed volume elongated in the NS direction either directly under the volcano or within 5–10 km south of it. Following the MW 5.8 event, earthquakes occurred in a new crustal volume slightly east and north of the previous earthquakes. The central Aleutian Arc is a tectonically active region with seismicity occurring in the crusts of the Pacific and North American plates in addition to interplate events. We postulate that the Kasatochi seismic swarm was a manifestation of the complex interaction of tectonic and magmatic processes in the Earth's crust. Although magmatic intrusion triggered the earthquakes in the swarm, the earthquakes failed in context of the regional stress field.

Formation of hybrid arc andesites beneath thick continental crust

Andesite magmatism at convergent margins is essential for the differentiation of silicate Earth, but no consensus exists as to andesite petrogenesis. Models proposing origin of primary andesite melts from mantle and/or slab materials remain in deadlock with the seemingly irrefutable petrographic and chemical evidence for andesite formation through mixing of basaltic mantle melts with silicic components from the overlying crust. Here we use 3He/4He ratios of high-Ni olivines to demonstrate the mantle origin of basaltic to andesitic arc magmas in the central Mexican Volcanic Belt (MVB) that is constructed on ~50km thick continental crust. We propose that the central MVB arc magmas are hybrids of high-Mg#>70 basaltic and dacitic initial mantle melts which were produced by melting of a peridotite subarc mantle interspersed with silica-deficient and silica-excess pyroxenite veins. These veins formed by infiltration of reactive silicic components from the subducting slab. Partial melts from pyroxenites, and minor component melts from peridotite, mix in variable proportions to produce high-Mg# basaltic, andesitic and dacitic magmas. Moderate fractional crystallization and recharge melt mixing in the overlying crust produces then the lower-Mg# magmas erupted. Our model accounts for the contrast between the arc-typical SiO2 variability at a given Mg# and the strong correlation between major element oxides SiO2, MgO and FeO which is not reproduced by mantle–crust mixing models. Our data further indicate that viscous high-silica mantle magmas may preferentially be emplaced as intrusive silicic plutonic rocks in the crust rather than erupt. Ultimately, our results imply a stronger turnover of slab and mantle materials in subduction zones with a negligible, or lesser dilution, by materials from the overlying crust.

Advances in keratoconus treatment

Keratoconus is a noninflammatory, usually bilateral, progressive disease. It is a pathology characterized by a progressive thinning and ectasia of the stroma that results in a cone-shaped cornea. In advanced keratoconus with corneal opacities, keratoplasty was regarded as the only surgical alternative. Recently, new treatment alternatives were developed in keratoconus treatment, such as intracorneal ring segments and corneal crosslinking. Intracorneal ring segments act as spacer elements between the bundles of corneal lamellae, producing a shortening of the central arc length. Corneal crosslinking treatment increases the stiffness of the cornea. Several studies reported that collagen crosslinking can delay or stop keratoconus progression and produce a better quality of vision. A combination of crosslinking and intracorneal ring segments shows a positive, synergistic effect. Keratoconus is a disease of the corneal stroma and that usually presents itself in patients at an early age, thus the endothelial cell layer in eyes with keratoconus is young and almost healthy. Full-thickness penetrating keratoplasty has been a well-accepted surgical treatment for advanced keratoconus. Recently, great advances have been seen and new techniques of keratoplasty have been introduced in the treatment of keratoconus. These are mainly the lamellar keratoplasty techniques and the advanced shaped side-cut techniques, particularly with the use of femtosecond lasers.

Oribatid fauna (Acari, Oribatida) from the Kumaya cave of Iheya village in Central Ryukyu arc, south Japan, with a description of several new species

Eleven oribatid species were collected from the Kumaya Cave of Iheya village in Central Ryukyu Arc, South Japan. The cave is a descending horizontal tunnel of a deep-sea abysmal quartziferous deposit formed in the Permian period of the Palaeozoic era and excavated by sea erosion. The floor of the cave was covered with sand, three to four meters deep. Fragments of psephite are found at the end of the cave. Each sample of about 200 ml was collected by hand from the following five marked points of the cave on 17 March 2010: A, Sand and a fragment of psephite; B, Sand and a fragment of psephite; C, Sand, a fragment of psephite, and litter of Ficus microcarpa; D, Litter and humus of F. microcarpa and Cassytha filiformis, and sand; E, Litter and humus of F. microcarpa and C. filiformis, and sand. All species belonged to Brachypylina: Oppiella (<I>O.</I>) nova from A; Mabulatrichus kumayaensis sp. nov., Protoribates kumayaensis sp. nov. and Zygoribatula iheyaensis sp. nov. from B; Tectocepheus kumayaensis sp. nov. from C; Tectocepheus iheyaensis sp. nov., Oribatula kumayaensis sp. nov., Protoribates hirokous sp. nov. and Haplozetes makii sp. nov. from D; Eupelops kumayaensis sp. nov. from E; Neoliodes iheyaensis sp. nov. from C, D and E.

Tectonic control on sediment accretion and subduction off south central Chile: Implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes

Based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central Chile margin (33°–46°S), we study the processes of sediment accretion and subduction and their implications on megathrust seismicity. In terms of the frontal accretionary prism (FAP) size, the marine south central Chile fore arc can be divided in two main segments: (1) the Maule segment (south of the Juan Fernandez Ridge and north of the Mocha block) characterized by a relative large FAP (20–40 km wide) and (2) the Chiloe segment (south of the Mocha block and north of the Nazca-Antarctic-South America plates junction) characterized by a small FAP (≤10 km wide). In addition, the Maule and Chiloe segments correlate with a thin (<1 km thick) and thick (∼1.5 km thick) subduction channel, respectively. The Mocha block lies between ∼37.5° and 40°S and is configured by the Chile trench, Mocha and Valdivia fracture zones. This region separates young (0–25 Ma) oceanic lithosphere in the south from old (30–35 Ma) oceanic lithosphere in the north, and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction, respectively. A process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down-deflected oceanic lithosphere under trench sediment loading. On the other hand, a small FAP along the Chiloe segment is coincident with the rupture area of the trans-Pacific tsunamigenic 1960 earthquake (Mw = 9.5), while a relatively large FAP along the Maule segment is coincident with the rupture area of the 2010 earthquake (Mw = 8.8). Differences in earthquake and tsunami magnitudes between these events can be explained in terms of the FAP size along the Chiloe and Maule segments that control the location of the updip limit of the seismogenic zone. The rupture area of the 1960 event also correlates with a thick subduction channel (Chiloe segment) that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation.

SOUTHERN COSMOLOGY SURVEY. II. MASSIVE OPTICALLY SELECTED CLUSTERS FROM 70 SQUARE DEGREES OF THE SUNYAEV–ZEL'DOVICH EFFECT COMMON SURVEY AREA

We present a catalog of 105 rich and massive ($M>3\times10^{14}M_{\sun}$) optically-selected clusters of galaxies extracted from 70 square-degrees of public archival griz imaging from the Blanco 4-m telescope acquired over 45 nights between 2005 and 2007. We use the clusters' optically-derived properties to estimate photometric redshifts, optical luminosities, richness, and masses. We complement the optical measurements with archival XMM-Newton and ROSAT X-ray data which provide additional luminosity and mass constraints on a modest fraction of the cluster sample. Two of our clusters show clear evidence for central lensing arcs; one of these has a spectacular large-diameter, nearly-complete Einstein Ring surrounding the brightest cluster galaxy. A strong motivation for this study is to identify the massive clusters that are expected to display prominent signals from the Sunyaev-Zeldovich Effect (SZE) and therefore be detected in the wide-area mm-band surveys being conducted by both the Atacama Cosmology Telescope and the South Pole Telescope. The optical sample presented here will be useful for verifying new SZE cluster candidates from these surveys, for testing the cluster selection function, and for stacking analyzes of the SZE data.

The Lami pyroclastic succession (Lipari, Aeolian Islands): A clue for unravelling the eruptive dynamics of the Monte Pilato rhyolitic pumice cone

The Lami succession piled up during the explosive activity of the Monte Pilato on Lipari Island (Central Aeolian Arc, Italy). It comprises a repetitive alternation of fall and pyroclastic density current beds, which define 13 Units separated by fine ash beds. Despite the homogeneous rhyolitic composition the juveniles fragments show strong textural heterogeneities from highly vesicular pumice to dense black obsidians. The pumice types are termed: i) “tube”, which shows elongated tubular vesicles, ii) “frothy”, highly vesicular with large, sub-rounded vesicles, and iii) agglomerated and welded. Two types of obsidian pyroclasts are recognized: i) aphyric black obsidian, and ii) grey obsidian showing spherulitic texture. All these pyroclastic types occur throughout the stratigraphic succession, and mixed in the same bed. They account for changing physical conditions along the conduit, which is hypothesised to be filled by a melt plug during the eruption of 12 out of 13 Units. The strong textural heterogeneities of the juvenile fragments testify for the existence of differential shear rates, which can be explained though two shear mechanism: i) simple shear, producing horizontal zonation of texture in the conduit with black obsidians along the conduit walls passing to tube and frothy pumice to the centre, and ii) pure shear, producing a vertical zonation in the conduit, with black obsidians at the top overlying frothy pumice. Agglomerated and welded pumice of Unit 13 is thought to represent the portion of magma heated by a batch of hotter melt that entered the magma chamber and triggered the eruption. The deposits of Unit 13 represent a unique case of spatter accretion due to accumulation of hot, low-viscous rhyolitic pumice fragments, emplaced from pyroclastic fountaining.

Metal Vapour in MIG Arcs Can Cause (1) Minima in Central Arc Temperatures and (2) Increased Arc Voltages

Radiation emission coefficients of plasmas from high temperature metal iron vapour are about a factor of a hundred larger than emission coefficients of high temperature argon plasmas as occur in argon welding arcs. Iron vapour can be easily introduced into the central region of such a welding arc due to melting of an electrode containing iron. The high radiation emission can produce several effects contrary to the usual behaviour of arcs in pure argon. Firstly, a central cylindrical core of iron vapour will be highly radiating and calculations show that the central core can consequently be at a lower temperature than the surrounding argon plasma. Because this central core has higher radiation emission it can give the appearance of having a higher central temperature. Secondly, it is predicted that radiation cooling of the arc due to iron vapour reduces the arc temperature and has the effect of increasing the arc voltage. The effect of increased radiation in the main arc column outweighs the effect of iron vapour increasing the electrical conductivity of the plasma at low temperatures which has the effect of reducing the arc voltage. This latter effect is limited to a small region near the electrodes.

Water-saturated magmas in the Panama Canal region: a precursor to adakite-like magma generation?

Amphibole, while uncommon as a phenocryst in arc lavas, is increasingly recognized as a key constituent in the petrogenesis of arc magmas. Fractional crystallization of water-saturated arc magmas in the lower crust can yield substantial volumes of amphibole cumulates that, depending on the pressure of crystallization, may also contain garnet. Fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production of magmas that contain an adakitic signature. This study examines newly dated Late-Oligocene (25.37 ± 0.13 Ma) hypabyssal amphibole-rich andesites from Cerro Patacon in the Panama Canal region. These andesites contain nodules of amphibole cumulates that are ~4–6 cm in diameter and are almost entirely composed of 5–10-mm amphibole crystals (dominantly ferri-tschermakite). Geochemical variations, optical and chemical zoning of the Cerro Patacon amphiboles are consistent with their evolution in a crystal mush environment that had at least one recharge event prior to entrainment in the host andesite. Amphiboles hosted within the cumulate nodules differ from those hosted in the Cerro Patacon andesite and contain consistently higher values of Ti. We suggest these nodules represent the early stages of fractionation from a water-saturated magma. Cerro Patacon andesites have REE concentrations that plot at the most depleted end of Central American Arc magmas and exhibit a distinctive depletion in the middle REE. These geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the Cerro Patacon andesite, consistent with the petrographic evidence. Fractionation of water-saturated magmas is a mechanism by which adakitic compositions may be produced, and the Cerro Patacon andesites do exhibit adakite-like geochemical characteristics (e.g., elevated Sr/Y; 28–34). However, the relatively elevated concentrations of Y and HREE indicate garnet was not stable in the fractionating assemblage during this early stage of arc development.

Functional interaction between baroreflex and vestibulo‐sympathetic reflex upon head‐up tilt

Head‐up tilt (HUT) elicits gravitational fluid shift and a decrease in arterial pressure (AP), which is thought to be buffered by baroreflex and vestibulo‐sympathetic reflex. However, functional interaction between these reflexes has not been clear. To examine this, renal sympathetic nerve activity (SNA) and AP were measured in anesthetized, vagotomized, and aortic denervated rats with or without vestibular lesion (VL). Isolated carotid sinus pressure (CSP) was increased stepwise from 60 to 180 mmHg with increments of 20 mmHg (30–60 s for each CSP level) while the rat was placed prone flat position and at 60° HUT. HUT shifted the CSP‐SNA relationship (the baroreflex central arc) to a higher SNA, shifted the SNA‐AP relationship (the baroreflex peripheral arc) to a lower AP, and consequently moved the operating point to high SNA while maintaining AP. In VL rats, the HUT‐induced central arc shift was completely abolished, while the peripheral arc shifted to a lower AP; the operating point moved to a lower AP (−26 mmHg). These results indicate that the vestibular system elicits sympathoexcitation upon HUT and shifts the baroreflex central arc to a higher SNA and then maintain baroreflex operating AP.

Nitrogen sources and recycling at subduction zones: Insights from the Izu‐Bonin‐Mariana arc

We report new chemical and nitrogen isotopic data from 29 volcanic and hydrothermal gas samples covering eight centers in the Izu‐Bonin‐Mariana (IBM) arc to investigate the sources, flux, and mass balance of nitrogen at a “cool” convergent margin. The majority of samples have high N2/He (1217–17,300) and low CO2/N2,exc. (78–937), implying addition of nitrogen from the subducting slab. This inference is supported by positive (i.e., sediment‐like) δ15N values (up to 5.5‰) in most samples. The exception to these trends is Agrigan in the Mariana arc, with low N2/He (∼200), high CO2/N2,exc. (∼1500), and negative δ15N. Mixing calculations suggest an average of 34% of the nitrogen in our samples is derived from subducted sediment, or 75% after correction for atmospheric contamination. Sediment‐derived N2 fluxes estimated by three different methods range from 0.25 × 108 to 1.11 × 108 mol yr−1 N2, representing 4%–17% of the total nitrogen input flux or 11%–51% of the sedimentary nitrogen input flux. The altered oceanic crust is identified as an important contributor to the arc nitrogen budget, and the δ15N of the residual nitrogen subducted into the mantle is estimated at approximately −1.9‰. Despite similarities in gas chemistry and δ15N values, our conclusions regarding nitrogen recycling for IBM are markedly different than those for the Nicaraguan segment of the Central American arc, and we suggest that thermal regime is the major control on nitrogen recycling within subduction zones. The global nitrogen cycle is estimated to be in steady state, suggesting either that subducted sediments are an unlikely source for heavy nitrogen in plume‐related rocks or secular variation in the isotopic composition of subducted sediments. Better constraints on nitrogen recycling at other arcs are required to test these conclusions.

Manifestation of renal disease in obesity: pathophysiology of obesity-related dysfunction of the kidney.

Albuminuria in individuals whose body mass index exceeds 40 kg/m(2) is associated with the presence of large glomeruli, thickened basement membrane and epithelial cellular (podocyte) distortion. Obstructive sleep apnea magnifies glomerular injury as well, probably through a vasoconstrictive mechanism. Insulin resistance from excess fatty acids is exacerbated by decreased secretion of high molecular weight adiponectin from adipose cells in the obese state. Adiponectin potentiates insulin in its post-receptor signaling resulting in glucose oxidation in mitochondria. Recent studies of podocyte physiology have concentrated on the structural and functional requirements that prevent glomerular albumin leakage. The architecture of the podocyte involves nephrin and podocin, proteins that cooperate to keep slit pores between foot processes competent to retain albumin. Insulin and adiponectin are necessary for high-energy phosphate generation. When fatty acids bind to albumin, the toxicity to proximal renal tubules is magnified. Albumin and fatty acids are elevated in urine of individuals with obesity related nephrotic syndrome. Fatty acid accumulation and resistin inhibit insulin and adiponectin. Study of cytokines produced by adipose tissue (adiponectin and leptin) and macrophages (resistin) has led to a better understanding of the relationship between weight and hypertension. Leptin, is presumably secreted after food intake to inhibit the midbrain/hypothalamic appetite centers. Resistance to leptin results in excess signaling to hypothalamic sympathetics leading to hypertension. Demonstration of the existence of a cerebral receptor mutation provide evidence for a role in hypertension of a central nervous reflex arc in humans. Further understanding of obesity-related renal dysfunction has been accomplished recently using experimental models. Rapid weight loss following bariatric surgery may reverse renal pathology of obesity with restoration of normal blood pressure.

The 2006–2007 Kuril Islands great earthquake sequence

The southwestern half of a ∼500 km long seismic gap in the central Kuril Island arc subduction zone experienced two great earthquakes with extensive preshock and aftershock sequences in late 2006 to early 2007. The nature of seismic coupling in the gap had been uncertain due to the limited historical record of prior large events and the presence of distinctive upper plate, trench and outer rise structures relative to adjacent regions along the arc that have experienced repeated great interplate earthquakes in the last few centuries. The intraplate region seaward of the seismic gap had several shallow compressional events during the preceding decades (notably an MS 7.2 event on 16 March 1963), leading to speculation that the interplate fault was seismically coupled. This issue was partly resolved by failure of the shallow portion of the interplate megathrust in an MW = 8.3 thrust event on 15 November 2006. This event ruptured ∼250 km along the seismic gap, just northeast of the great 1963 Kuril Island (Mw = 8.5) earthquake rupture zone. Within minutes of the thrust event, intense earthquake activity commenced beneath the outer wall of the trench seaward of the interplate rupture, with the larger events having normal‐faulting mechanisms. An unusual double band of interplate and intraplate aftershocks developed. On 13 January 2007, an MW = 8.1 extensional earthquake ruptured within the Pacific plate beneath the seaward edge of the Kuril trench. This event is the third largest normal‐faulting earthquake seaward of a subduction zone on record, and its rupture zone extended to at least 33 km depth and paralleled most of the length of the 2006 rupture. The 13 January 2007 event produced stronger shaking in Japan than the larger thrust event, as a consequence of higher short‐period energy radiation from the source. The great event aftershock sequences were dominated by the expected faulting geometries; thrust faulting for the 2006 rupture zone, and normal faulting for the 2007 rupture zone. A large intraplate compressional event occurred on 15 January 2009 (Mw = 7.4) near 45 km depth, below the rupture zone of the 2007 event and in the vicinity of the 16 March 1963 compressional event. The fault geometry, rupture process and slip distributions of the two great events are estimated using very broadband teleseismic body and surface wave observations. The occurrence of the thrust event in the shallowest portion of the interplate fault in a region with a paucity of large thrust events at greater depths suggests that the event removed most of the slip deficit on this portion of the interplate fault. This great earthquake doublet demonstrates the heightened seismic hazard posed by induced intraplate faulting following large interplate thrust events. Future seismic failure of the remainder of the seismic gap appears viable, with the northeastern region that has also experienced compressional activity seaward of the megathrust warranting particular attention.

Shear-wave anisotropy beneath the Ryukyu arc

Abstract We have investigated regional shear-wave splitting beneath the Ryukyu arc in order to clarify the mantle flow beneath the Ryukyu arc and compare it with the extension of the Okinawa Trough. The splitting of regional shear waves (direct S) in the central and southern Ryukyu arc regions was analyzed in terms of fast-polarization direction and delay time using data from 11 short-period stations and two broadband seismic stations. The events occurred at depths ranging between 45 and 217 km, and the magnitude of the events ranged from 2.8 to 5.2. In general, the orientations of fast polarization were found to parallel to the strike of the Ryukyu Trench, with average delay times of 0.25–0.56 s. Specifically, the orientation of fast polarization was parallel to the direction of the extension in the south Ryukyu arc, suggesting that the direction of mantle flow is parallel to the extension in the south Okinawa Trough. However, the orientation of fast polarization was oblique to the direction of extension in the central Ryukyu arc, indicating that the mantle flow beneath the central Ryukyu arc is not parallel to the extension of the central Okinawa Trough. Based on these results, we suggest that the difference between the direction of the mantle flow and that of the lithosphere extension induces extensional strain with a simple shear component, which in turn causes oblique rifting in the central Okinawa Trough.

On the deformation cycle of a strongly coupled plate interface: The triple earthquakes of 16 March 1963, 15 November 2006, and 13 January 2007 along the Kurile subduction zone

The great plate interface Kurile earthquake of 15 November 2006 (Mw = 8.3) was immediately followed by normal aftershocks in the outer rise of the central Kurile subduction zone. Two months later at a distance &lt;50 km from this event the 13 January 2007 (Mw = 8.1) earthquake with a pure normal mechanism occurred in the outer rise of the central Kurile. The 15 November 2006 earthquake ruptured an area of 280 × 150 km2 with maximum slip of almost 7 m, while the 13 January 2007 earthquake ruptured an area of 240 × 40 km2 with a maximum slip of almost 14 m. These two significant events were preceded by a major reverse earthquake on 16 March 1963 (Mw = 7.7) that took place close to the location of the 13 January 2007 earthquake. These very different earthquakes demonstrate the different stages of the deformation cycle along strongly coupled plates at the central Kurile arc and present a rare case of stress regime reversal over a short time span. In order to understand the details of these three earthquakes, we inverted for the source rupture processes of the earthquakes and delineated the location and dimension of asperities. The role of gravity and topography anomalies and their correlation to the asperity distribution as well as the long‐term seismicity is studied in detail. Using trench‐parallel Bouguer anomaly, we have identified the differences in the asperities and the location of larger normal outer rise aftershocks as well as the location of 13 January 2007 earthquake. We also show that the long‐term seismicity of the central Kurile arc is confined to the intraslab and not the plate interface. The static stress transfer for these earthquakes showed that the stress on optimally oriented thrust faults is increased in the northeastern part of the rupture area of the 15 November 2006 earthquake. Absence of major and great earthquakes to the northeastern immediate vicinity of the rupture area of the 15 November 2006 earthquake supports the hypothesis that this area is mature for the next strong earthquake along the Kurile arc.

Wave forecasting and longshore sediment transport gradients along a transgressive barrier island: Chandeleur Islands, Louisiana

Louisiana barrier islands, such as the chain surrounding the southeast region of the state, are experiencing rapid loss of land area, shoreline erosion, and landward migration due to transgression and in-place drowning, and the landfall of several major hurricanes in the last decade. Observations of migration rates and overall impacts to these barrier islands are poorly understood since they do not respond in a traditional way, such as barrier rollover. This paper aims to verify how wave energy and potential longshore sediment transport trends have influenced the recent evolution of the Chandeleur Islands, by direct comparison with recent observations of migration and erosion trends. The Chandeleur Islands are characterized by a bidirectional transport system, with material moving from the central arc to the flanks. The longshore sediment transport along the barrier islands was calculated after propagation and transformation of waves to breaking (generated using observed winds), and through the use of a common longshore sediment transport formula. Seasonal variations in wind climate produced changes in the transport trends and gradients that agree with migration and rotation patterns observed for this barrier island system. Results suggest that wind dominance produces seasonal oscillations that cause an imbalance in the resulting transport gradients that over time are responsible for higher rates of transport in the northward direction. These results and data from other works verify the evolutionary model previously suggested, and qualitatively confirm the recent observations in asymmetric shoreline erosion.

An experimental determination of chlorine isotope fractionation in acid systems and applications to volcanic fumaroles

The δ 37Cl values of volcanic fumarole gases and bubbling springs were measured from the Central American and the Kurile arcs. Low temperature gas samples from the Central American arc have δ 37Cl values generally between −2 and 2‰, whereas high-temperature fumaroles (>100 °C) range from 4 to 12‰, with several outliers. This is in contrast to the high-temperature fumaroles from the Kurile island Kudryavy which have slightly positive δ 37Cl values, averaging 0.8‰ (±0.6, 1σ), and from our previous work on Izu and Mariana arc samples in which the δ 37Cl values of fumarole and ash samples are similar to each other and negative. Assuming that the source for the high-T Central American fumaroles has typical subduction δ 37Cl values (−2.5 to 1‰), then there must be a large Cl isotope fractionation in the near-surface fumarolic system. The most likely fractionation mechanism for the high δ 37Cl values is between Cl − aq − HCl( g), but published theoretical fractionation for this pair is only ∼1.5‰, insufficient to explain the large range of values observed in the fumaroles. Three experiments were undertaken in order to identify a process that could cause the wide range of δ 37Cl values observed in the high-temperature fumaroles. Results are the following: (1) A sub-boiling equilibration experiment between aqueous chloride and HCl gas had 1000 ln α HCl ( g ) - Cl - = 1.4 to 1.8 ‰ , in agreement with the theoretical calculations. (2) Evaporation of HCl( g) from hydrochloric acid at room temperature had fractionation in the opposite sense, with a 1000 ln α HCl ( g ) - Cl - = - 3.92 ‰ . (3) A ‘synthetic fumarole’ gave large positive fractionations up to 9‰, with 37Cl strongly partitioned into the vapor phase. The ‘fumarole’ experiments were made by bubbling dry air through boiling hydrochloric acid in an Erlenmeyer flask, and collecting the evolved HCl( g) in a second ‘downstream’ flask filled with distilled water. This extreme enrichment is likely due to a distillation process in which 37Cl-enriched HCl( g) is stripped from the hydrochloric acid followed by a significant fraction of the light HCl( g) redissolving into the constantly condensing water vapor on the walls of the first flask. This distillation experiment creates a Cl isotope fractionation that is the same order of magnitude as observed in the high-temperature fumaroles in Central America. These results suggest that there must be a H 2O liquid–vapor region in the sub-surface fumarole conduit where light Cl is stripped from the HCl gas as it passes through the fumarole. Similar 37Cl enrichments are expected in fossil epithermal boiling systems.