Kiyoshi Baba

Upper mantle electrical resistivity structure beneath the central Mariana subduction system

This paper reports on a magnetotelluric (MT) survey across the central Mariana subduction system, providing a comprehensive electrical resistivity image of the upper mantle to address issues of mantle dynamics in the mantle wedge and beneath the slow back-arc spreading ridge. After calculation of MT response functions and their correction for topographic distortion, two-dimensional electrical resistivity structures were generated using an inversion algorithm with a smoothness constraint and with additional restrictions imposed by the subducting slab. The resultant isotropic electrical resistivity structure contains several key features. There is an uppermost resistive layer with a thickness of up to 150 km beneath the Pacific Ocean Basin, 80–100 km beneath the Mariana Trough, and 60 km beneath the Parece Vela Basin along with a conductive mantle beneath the resistive layer. A resistive region down to 60 km depth and a conductive region at greater depth are inferred beneath the volcanic arc in the mantle wedge. There is no evidence for a conductive feature beneath the back-arc spreading center. Sensitivity tests were applied to these features through inversion of synthetic data. The uppermost resistive layer is the cool, dry residual from the plate accretion process. Its thickness beneath the Pacific Ocean Basin is controlled mainly by temperature, whereas the roughly constant thickness beneath the Mariana Trough and beneath the Parece Vela Basin regardless of seafloor age is controlled by composition. The conductive mantle beneath the uppermost resistive layer requires hydration of olivine and/or melting of the mantle. The resistive region beneath the volcanic arc down to 60 km suggests that fluids such as melt or free water are not well connected or are highly three-dimensional and of limited size. In contrast, the conductive region beneath the volcanic arc below 60 km depth reflects melting and hydration driven by water release from the subducting slab. The resistive region beneath the back-arc spreading center can be explained by dry mantle with typical temperatures, suggesting that any melt present is either poorly connected or distributed discontinuously along the strike of the ridge. Evidence for electrical anisotropy in the central Mariana upper mantle is weak.

Guidelines for diagnosis and management of cardiovascular sequelae in Kawasaki disease

Over 35 years have elapsed since the first case of Kawasaki disease was described in 1967. 1 As they grow older, many patients with a history of Kawasaki disease are treated in departments of internal medicine rather than in pediatric departments. This disease has been extensively studied throughout the world, and many reports have been published on its etiology and cardiovascular sequelae. While the causes of Kawasaki disease unfortunately remain unknown, its cardiovascular sequelae have been intensively studied, contributing to the establishment of their pathology, natural history, diagnosis, and treatment. This provided the impetus for the Japanese Circulation Society to prepare a set of guidelines. The latest guidelines for the diagnosis of Kawasaki disease, as revised in 2002, are shown in Table 1. These are used to diagnose the disease in its acute phase. The diagnostic guidelines may be useful in adults with an unknown history of Kawasaki disease when the illness is suspected from the morphology of any coronary artery aneurysms. In preparing the present guidelines for the cardiovascular sequelae of Kawasaki disease, the first issue addressed was the classification of the size and severity of coronary artery aneurysms using standardized criteria. The consensus criteria shown in Table 2 were prepared according to the conventional classification and the opinions of specialists.

A solid-phase enzyme immunoassay for the determination of IgM and IgG antibodies against translation products of pre-S1 and pre-S2 regions of hepatitis B virus

The envelope of hepatitis B virus is coded for by pre-S1, pre-S2 regions and the S gene. A method was developed to determine antibody to the product of pre-S1 region (anti-pre-S1) and antibody to the product of pre-S2 region (anti-pre-S2), either of IgM or IgG class, by a solid-phase enzyme immunoassay. For the determination of anti-pre-S1, tubular particles containing translation products of pre-S1, pre-S2 regions and the S gene were broken into constituent envelope polypeptides and immobilized on a solid support. Serums were absorbed with spherical particles containing translation products of pre-S2 region and the S gene, obtained from plasma positive for hepatitis B e antigen (HBeAg) and deprived of particles carrying pre-S1 product by an affinity column. They were then tested for the binding with tubular polypeptides fixed on a solid support, and the bound antibody representing anti-pre-S1 was detected by monoclonal antibody to human IgM/mu or IgG/gamma labeled with horseradish peroxidase. For the determination of anti-pre-S2, test serums were absorbed with spherical particles containing the product of the S gene, obtained from plasma positive for antibody to HBeAg and deprived of particles bearing pre-S2 product by an affinity column. They were then tested for the binding with polypeptides, fixed on a solid support, composed of products of pre-S2 region and the S gene. The assay was applied to the determination of anti-pre-S1 and anti-pre-S2 of IgM or IgG class in asymptomatic carriers and in persons who had recovered from infection with hepatitis B virus.

Ocean Bottom Array Probes Stagnant Slab Beneath the Philippine Sea

Global seismic tomography has revealed the existence of a now-stagnant subducted slab (Figure 1c, inset) in the mantle transition zone (MTZ) of the western Pacific Ocean [e.g., Fukao et al., 2001], where the old Pacific plate subducts at the Kuril/Japan/Mariana Trench system. Fukao et al. [2001] showed that a stagnant slab is a common feature of many subduction systems around the world, although it is still not well understood why and how a subducted slab may or may not become stagnant. In addition to a subducted slab itself, water entrained with the slab may also accumulate in the MTZ in association with stagnation. The MTZ has been thought to play a key role in the Earths water cycle, with water transported to the MTZ possibly being released and supplied to the upper mantle to drive back-arc volcanism [e.g., Ichiki et al., 2006].

TIARES Project—Tomographic investigation by seafloor array experiment for the Society hotspot

We conducted geophysical observations on the French Polynesian seafloor in the Pacific Ocean from 2009 to 2010 to determine the mantle structure beneath the Society hotspot, which is a region of underlying volcanic activity responsible for forming the Society Islands. The network for Tomographic Investigation by seafloor ARray Experiment for the Society hotspot (TIARES, named after the most common flower in Tahiti) is composed of multi-sensor stations that include broadband ocean-bottom seismometers, ocean-bottom electro-magnetometers, and differential pressure gauges. The network is designed to obtain seismic and electrical conductivity structures of the mantle beneath the Society hotspot. In addition to providing data to study the mantle structure, the TIARES network recorded unprecedented data of pressure and electromagnetic (EM) signals by tsunamis associated with large earthquakes in the Pacific Ocean, including the 2010 Chilean earthquake (Mw 8.8).

Resistivity image of the Philippine Sea Plate around the 1944 Tonankai earthquake zone deduced by Marine and Land MT surveys

The Nankai Trough is an active convergent region in southwest Japan and mega-thrust earthquakes have repeatedly occurred in some areas of its plate-boundary interface. Generation of mega-thrust earthquakes is inferred to be related to the existence of water. The resistivity structure is very sensitive to the existence of water. For that reason, it is important to obtain the resistivity image around the rupture area of mega-thrust earthquakes. We carried out land and marine magnetotelluric surveys in the Kii Peninsula and the offshore Kii Peninsula where the 1944 Tonankai earthquake occurred. We constructed a 2D resistivity model using an inversion technique. The modeled resistivity structure portrayed the Philippine Sea Plate as a resistive region. However, its resistivity becomes more conductive as the plate subducts, showing 10 Ω-m around the down-dip limit. These characteristics are considered to relate to the water. Therefore, we infer that water might control the generation of mega-thrust earthquakes.

Transcatheter polytetrafluoroethylene-covered stent implantation in a giant coronary artery aneurysm of a child with Kawasaki disease—A potential novel treatment

We report a case of an eight‐year‐old boy with Kawasaki disease (KD) who had a giant aneurysm with stenotic lesions located in the right coronary artery, and was treated by transcatheter implantation of a polytetrafluoroethylene(PTFE)‐covered stent. Follow‐up coronary angiography showed good coronary blood flow. To the best of our knowledge, this is the first child with KD who underwent covered‐stent implantation in a coronary aneurysm. Although close follow‐up is mandatory, because the long‐term outcome is unclear, implantation of a covered stent in a giant aneurysm appears to be a promising treatment option.

Tsunami: Ocean dynamo generator

Secondary magnetic fields are induced by the flow of electrically conducting seawater through the Earths primary magnetic field (‘ocean dynamo effect’), and hence it has long been speculated that tsunami flows should produce measurable magnetic field perturbations, although the signal-to-noise ratio would be small because of the influence of the solar magnetic fields. Here, we report on the detection of deep-seafloor electromagnetic perturbations of 10-micron-order induced by a tsunami, which propagated through a seafloor electromagnetometer array network. The observed data extracted tsunami characteristics, including the direction and velocity of propagation as well as sea-level change, first to verify the induction theory. Presently, offshore observation systems for the early forecasting of tsunami are based on the sea-level measurement by seafloor pressure gauges. In terms of tsunami forecasting accuracy, the integration of vectored electromagnetic measurements into existing scalar observation systems would represent a substantial improvement in the performance of tsunami early-warning systems.

Analysis of Kawasaki disease showing elevated antibody titres of Yersinia pseudotuberculosis

Aim: To elucidate a clinical difference between patients with Kawasaki disease documented with Yersinia pseudotuberculosis infection and patients with Kawasaki disease without Yersinia pseudotuberculosis infection. Patients and methods: From January 1985 to July 2004, 452 patients were diagnosed with Kawasaki disease. Forty‐two patients had elevated antibody titres of Yersinia pseudotuberculosis and/or positive stool culture (Yersinia‐positive group). Three hundred and thirty patients had no elevated antibody titres (Yersinia‐negative group). We compared the clinical characteristics retrospectively. Results: The age of onset in the Yersinia‐positive group (3.05±2.20 y) was significantly higher than that in the Yersinia‐negative group (2.31±2.05 y) (p=0.03). The age‐adjusted statistical analysis demonstrated that the incidence of coronary artery lesions (dilatations plus aneurysms) in the Yersinia‐positive group (22/42, 52.4%) was significantly higher than in the Yersinia‐negative group (105/330, 31.8%) (p=0.001), and the incidence of additional administration of immunoglobulin in the Yersinia‐positive group (13/36, 36.1%) was significantly higher than in the Yersinia‐negative group (41/256, 16.0%) (p=0.004).

Approximate treatment of seafloor topographic effects in three-dimensional marine magnetotelluric inversion

Seafloor magnetotelluric (MT) observations using ocean bottom electromagnetometers (OBEMs) provide information on the electrical conductivity structure of the oceanic mantle. A three-dimensional (3-D) analysis is particularly important for marine MT data because the electric and magnetic fields observed on the seafloor are distorted by the rugged seafloor topography and the distribution of land and ocean. Incorporating topography into 3-D models is crucial to making accurate estimates of the oceanic mantle’s conductivity structure. Here we propose an approximate treatment of seafloor topography to accurately incorporate the effect of topography without significantly increasing the computational burden. First, the topography (lateral variation in water depth) is converted to lateral variation in effective conductivity by volumetric averaging. Second, we compute the electric and magnetic field components used to calculate the MT responses at arbitrary points from the electric field components on staggered grids, using a modified interpolation and extrapolation scheme. To verify the performance of this approximate treatment of seafloor topography in 3-D inversions, we tested the method using synthetic seafloor datasets and both 3-D forward modeling and inversion. The results of the synthetic inversions show that a given conductivity anomaly in the oceanic upper mantle can be recovered with sufficient accuracy after several iterations.