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The 2011 Tohoku-oki earthquake (Mw 9.0) was characterized by a huge fault slip on the shallowest part of the plate interface, where fault behavior had been believed to be aseismic. In this study, we modeled the two-dimensional resistivity distribution across the slip area based on ocean-bottom electromagnetic measurements to understand the physical properties around the plate interface controlling fault rupture processes. The optimal 2D resistivity model showed a conductive area around the shallowest plate interface where the huge coseismic slip was observed, whereas the deeper plate interface where the fault rupture was nucleated was relatively more resistive. The shallowest plate interface was interpreted to have a high pore seawater fraction, whereas the deeper interface was interpreted as a dry area. These findings are consistent with the hypothesis that aseismic frictional conditions changed to conditions enhancing fault rupture when the rupture propagated to the wet, clay-rich shallowest plate area. The optimal resistivity model also revealed a conductive area under the outer-rise area of the Pacific Plate. This finding supports the existence of a hydrated oceanic crust that supplied aqueous water to the subduction zone, including to the huge fault slip area. [ABSTRACT FROM AUTHOR]

The 2011 Tohoku-oki earthquake (Mw 9.0) was characterized by a huge fault slip on the shallowest part of the plate interface, where fault behavior had been believed to be aseismic. In this study, we modeled the two-dimensional resistivity distribution across the slip area based on ocean-bottom electromagnetic measurements to understand the physical properties around the plate interface controlling fault rupture processes. The optimal 2D resistivity model showed a conductive area around the shallowest plate interface where the huge coseismic slip was observed, whereas the deeper plate interface where the fault rupture was nucleated was relatively more resistive. The shallowest plate interface was interpreted to have a high pore seawater fraction, whereas the deeper interface was interpreted as a dry area. These findings are consistent with the hypothesis that aseismic frictional conditions changed to conditions enhancing fault rupture when the rupture propagated to the wet, clay-rich shallowest plate area. The optimal resistivity model also revealed a conductive area under the outer-rise area of the Pacific Plate. This finding supports the existence of a hydrated oceanic crust that supplied aqueous water to the subduction zone, including to the huge fault slip area. [ABSTRACT FROM AUTHOR]

The forward calculation of magnetotelluric (MT) responses is generally assumed to be sufficiently accurate compared with typical observational errors in practical modeling and inversion studies. Although the uncertainty of the forward calculation may be examined by comparison with analytical or other numerical solutions for some simple models, such an examination does not guarantee that the uncertainty is similar for more realistic complex structures. In this study, I propose a simple method to evaluate the uncertainty of MT forward modeling for practical three-dimensional (3D) conductivity structure models in a Cartesian coordinate system. The method is based on the idea that the horizontal coordinate system can be selected arbitrarily for a general 3D structure. The synthesized MT responses are ideally identical irrespective of the selection but are different because of the difference in discretization angles, boundary values, and numerical errors. By synthesizing MT responses to the model in several different coordinate systems, the mean, standard deviation, and coefficient of variation can be calculated. These statistics provide quantitative information on how stably the forward calculations synthesize MT responses under the given conditions of the structure model, observation array, periods, numerical algorithm for the forward modeling, and mesh design. The proposed method was applied to two practical situations of seafloor MT arrays in the northwestern Pacific and southern Atlantic and a land MT array in Hokkaido, Japan. The results show that the uncertainty is comparable to real observation errors and is significantly dependent on the MT impedance element, period, site, structure model, and horizontal coordinate system. The uncertainty of the forward calculation should be considered for each element, period, and site to quantitatively evaluate how well a given model explains the data. I propose a new root-mean-square in which the residuals are normalized by both the standard errors of the MT responses observed and synthesized. This would help avoid overfitting data in the inversion analysis by ignoring the uncertainty of the forward calculation. This method is also useful for testing the appropriate selection of the coordinate system and mesh design. [ABSTRACT FROM AUTHOR]

Electrical anisotropy in the oceanic upper mantle can only be imaged by seafloor magnetotelluric (MT) data, and arguably provides important clues regarding the mantle structure and dynamics by observational determinations. Here, we attempt to probe the electrical (azimuthal) anisotropy in the oceanic mantle by analysing recent seafloor MT array data from the northwestern Pacific acquired atop 125–145 Ma seafloor. We propose a method in which an isotropic 1-D model is first obtained from seafloor MT data through an iterative correction for topographic distortions; then, the anisotropic properties are inferred as deviations from the isotropic 1-D model. We investigate the performance of this method through synthetic forward modelling and inversion using plausible anisotropic 1-D models and the actual 3-D bathymetry and topography of the target region. Synthetic tests reveal that the proposed method will detect electrical anisotropy in the conductive upper mantle or electrical asthenosphere. We also compare the performance of the proposed scheme by using two rotational invariant impedances and two topographic correction equations. The comparison reveals that using different rotational invariants and correction equations provides relatively consistent results, but among the rotational invariants, the sum of squared elements (ssq) impedance yields better recovered results for topographically distorted data than the determinant impedance. An application of the method to seafloor MT array data sets from two areas in the northwestern Pacific reveals the possible presence of two layers of electrical anisotropy in the conductive mantle (<100 Ω-m) at depths of ∼60–200 km. The anisotropy is estimated to be more intense in the shallower layer for both areas. On the other hand, the estimated anisotropic azimuth (defined as the most conductive direction) and the depth to the interface between the two layers are different between the two array areas separated by a small horizontal distance of ∼1000 km in spite of their similar seafloor ages. The most conductive directions are aligned neither with the current absolute plate motion direction nor with the fastest direction of seismic azimuthal anisotropy. The inferred electrical anisotropy features may result from array-scale (∼1000 km) mantle dynamics, such as small-scale convection, which might affect the electrical and seismic properties differently, although there remains the possibility that some portions of these features are explained by laterally heterogeneous mantle structures. [ABSTRACT FROM AUTHOR]

Nishinoshima is an active oceanic island arc volcano situated approximately 1000 km south of Tokyo, Japan. Since 2016, marine electromagnetic observations using ocean bottom electromagnetometers have been conducted around the island to investigate the electrical structure beneath the volcano for the first time. In contrast to the original purpose of the experiment, the data collected at five sites deployed in 2016–2017 showed distinct time variations in the magnetic field and the tilt of the volcano's slope. These time variations occurred coincidentally in mid-November 2016; this was during a quiet period between eruptions in 2015 and in 2017. The independence between the observed total magnetic force and tilt data was verified, highlighting that these variations were not artificial rather, associated with volcanic activity that did not invoke an eruption. Sources for demagnetization and deflation were estimated beneath the volcanic slope in the northeast of Nishinoshima Island, assuming a magnetic dipole and a spherical volume change, respectively. The resultant dipole moment and the volume change were too large to maintain simple source assumptions. However, the limited available data only enabled quantitative discussion under simple model settings, suggesting that the source mechanisms were more complex. The observations from this study demonstrate that if deployed strategically, ocean bottom electromagnetometers are useful to monitor island volcano activities. [ABSTRACT FROM AUTHOR]

Division VI of the International Association of Geomagnetism and Aeronomy (IAGA) on "Electromagnetic Induction in the Earth and Planetary Bodies" (https://www.emiw.org/) has long played an active role in the field of geophysics. Recent studies on electrical conductivity structure can treat three-dimensional (3D) heterogeneity as well as two-dimensional (2D) and one-dimensional (1D) heterogeneities by inversion analyses thanks to advances in computers and to the development of new numerical methods. Lastly, the main findings of published model analysis studies are summarized, with the positive expectation for further development of these studies as well as for optimal survey design and inversion grid design in the future. [Extracted from the article]

Abstract: Understanding the enigmatic intraplate volcanism in the Tristan da Cunha region requires knowledge of the temperature of the lithosphere and asthenosphere beneath it. We measured phase‐velocity curves of Rayleigh waves using cross‐correlation of teleseismic seismograms from an array of ocean‐bottom seismometers around Tristan, constrained a region‐average, shear‐velocity structure, and inferred the temperature of the lithosphere and asthenosphere beneath the hotspot. The ocean‐bottom data set presented some challenges, which required data‐processing and measurement approaches different from those tuned for land‐based arrays of stations. Having derived a robust, phase‐velocity curve for the Tristan area, we inverted it for a shear wave velocity profile using a probabilistic (Markov chain Monte Carlo) approach. The model shows a pronounced low‐velocity anomaly from 70 to at least 120 km depth. V S in the low velocity zone is 4.1–4.2 km/s, not as low as reported for Hawaii (∼4.0 km/s), which probably indicates a less pronounced thermal anomaly and, possibly, less partial melting. Petrological modeling shows that the seismic and bathymetry data are consistent with a moderately hot mantle (mantle potential temperature of 1,410–1,430°C, an excess of about 50–120°C compared to the global average) and a melt fraction smaller than 1%. Both purely seismic inversions and petrological modeling indicate a lithospheric thickness of 65–70 km, consistent with recent estimates from receiver functions. The presence of warmer‐than‐average asthenosphere beneath Tristan is consistent with a hot upwelling (plume) from the deep mantle. However, the excess temperature we determine is smaller than that reported for some other major hotspots, in particular Hawaii. [ABSTRACT FROM AUTHOR]

Seafloor magnetotelluric (MT) experiments were recently conducted in two areas of the northwestern Pacific to investigate the nature of the old oceanic upper mantle. The areas are far from any tectonic activity, and 'normal' mantle structure is therefore expected. The data were carefully analyzed to reduce the effects of coastlines and seafloor topographic changes, which are significant boundaries in electrical conductivity and thus distort seafloor MT data. An isotropic, one-dimensional electrical conductivity profile was estimated for each area. The profiles were compared with those obtained from two previous study areas in the northwestern Pacific. Between the four profiles, significant differences were observed in the thickness of the resistive layer beyond expectations based on cooling of homogeneous oceanic lithosphere over time. This surprising feature is now further clarified from what was suggested in a previous study. To explain the observed spatial variation, dynamic processes must be introduced, such as influence of the plume associated with the formation of the Shatsky Rise, or spatially non-uniform, small-scale convection in the asthenosphere. There is significant room of further investigation to determine a reasonable and comprehensive interpretation of the lithosphere-asthenosphere system beneath the northwestern Pacific. The present results demonstrate that electrical conductivity provides key information for such investigation. [ABSTRACT FROM AUTHOR]

We propose a three-dimensional (3-D) inversion scheme for deep ocean magnetotelluric (MT) data that enables us to incorporate both the local small-scale topography effect and regional large-scale topography effect, whose length scale is comparable with that of the mantle structure to be resolved by the inversion. We assume that the MT impedance tensor Z is approximately equal to the MT response of the total structure Zts, expressed by the product of the local topographic distortion term Dlt and the response to the regional structure Zrs that consists of the regional topography over the mantle electrical conductivity structure Z ≈ Zts = DltZrs. We also assume that Dlt may be treated as a site correction term, which is not dependent on the conductivity structure to be solved in the inversion. Dlt is calculated before the inversion iteration is carried out through the forward modelling of Zts and Zrs using a good initial guess for the mantle structure. However, the initial Zts is separately modelled by another forward modelling program, which is more efficient in terms of computation cost. The model space of the inversion includes only the regional structure so that the modelled response is Zrs. Thus, in the inversion, Zts is calculated from Zrs and Dlt; Zrs is modelled at every iteration but Dlt is fixed throughout the inversion. The sensitivity of Zts to the conductivity is calculated considering Dlt as a constant. This scheme requires modelling only of the regional scale structure in the inversion process, saving computational resources and time, which is critical in the 3-D case. Tests using a synthetic model and data demonstrate that incorporating the local topography effect in this scheme was successful and produced an accurate reconstruction of the given mantle structure. [ABSTRACT FROM AUTHOR]

Geomagnetic induction responses such as geomagnetic depth sounding (GDS), magnetotelluric (MT), and horizontal geomagnetic transfer function (HTF) at long periods are used to estimate the electrical conductivity in the deep mantle. The responses in the period range that are shorter than 10 s (about 1 day) are in many cases considered to be local or regional induction problems in which the source field is approximated by plane waves and therefore the sphericity of Earth is not taken into account. In the period range between 10 and 10 s, the most dominant signature of the magnetic field variation is the solar quiet daily ( Sq) variation and its higher harmonics. Therefore, when we obtain the responses due to the quasi-white background spectrum composed of plane waves, we regard the Sq field variations as noises in estimating the responses, and line spectra of the variations are removed from the observed time-series before the responses are calculated. However, with this approach, the calculated responses tend to possess a discontinuity at a period of about 10 s, and the response functions show common features at longer periods irrespective of the location of the observation site. It is particularly well known that the imaginary part of the induction vector tends to have a significant westward component for periods ranging between 10 and 10 s. Such features cannot be easily explained by the effect of the electrical conductivity structure alone. Examination of the phase of the HTF implies that the responses in the same period range are affected by the signature of sources of finite wavelength moving westward. Thus, it is suggested that the response functions in this period range were under the effect of the Sq field variations, even though the line spectra of them were removed and the responses were estimated at periods separate from the harmonic periods of Sq field variation. We examined how the influences of the Sq field appear on the responses numerically by a forward modelling. Results show most of the characteristic features in observed response functions can be ascribed to Sq source effects. [ABSTRACT FROM AUTHOR]

The 1-D electrical conductivity model in the mid-mantle beneath the northern Pacific was revised in order to discuss the mean state of the mantle and to obtain a credible starting model for 3-D inversions. Semi-global geomagnetic depth sounding (GDS) responses obtained at 13 stations and submarine cable magnetotelluric (MT) responses for eight cables in a period range of 1.7–113 d were used to obtain the revised structure. It is well known that surface conductivity heterogeneity due to the ocean–land conductivity contrast has a large influence on the responses up to a period of 20 d. The effect of surface ocean–land distribution was removed by performing 3-D electromagnetic induction modelling including a surface conductivity heterogeneity distribution laid above a 1-D mantle structure. The corrected responses were averaged in the logarithmic space, and the resulting responses (quasi-1-D response) were inverted to obtain 1-D conductivity models. Correction of the surface heterogeneity effect requires a 1-D conductivity model, and the 1-D model must be similar to the resultant 1-D model for a consistent correction. We attained this by making iterations of the surface layer correction and 1-D inversion. Synthetic tests revealed that the iterative scheme could recover the supposed structure even for a 3-D heterogeneous mantle. Since electromagnetic sounding is not sensitive to the presence of a sharp discontinuity, we examined three different cases of conductivity variation with depth: (1) a model with no discontinuity, (2) a model with two jumps at 400 and 650 km depths and (3) a model with three jumps at 400, 500 and 650 km depths. The conductivity of the two-jump model in the transition zone is higher than the experimentally determined conductivity of dry wadsleyite and ringwoodite. If the difference is entirely due to the effect of water in the transition zone, then the conductivity is consistent with a water content in the region of 0.5 wt per cent. However, if an additional discontinuity of electrical conductivity is allowed at the 500 km depth, the obtained conductivity for the upper 100 km of the transition zone is lower, and can be explained by a less water content, 0.1 wt per cent, in wadsleyite. [ABSTRACT FROM AUTHOR]

Features of the geomagnetic response functions due to a 1000 km scale isolated conductivity anomaly embedded in a radially symmetric Earth with a surface heterogeneous layer were studied by three-dimensional (3-D) global forward modelling in order to understand the fundamental characteristics of the response functions for period of about 1–100 d and to examine the validity of 1-D like treatment for some of the responses. The geomagnetic deep sounding (GDS) response function has dipolar sensitivity to the lateral electrical conductivity contrast, while the D response (ratio of the eastward to northward component of geomagnetic field variation) shows the 3-D effect as a quadrupole-like distribution having peaks outside of heterogeneity. Although GDS and D responses were used in global induction studies in the past, we examined if the horizontal transfer function (HTF), the ratios of the geomagnetic north components at a station to those at other reference station, has enough sensitivity to the mantle heterogeneity and if it is worth to be included in global conductivity soundings. Modelling result shows that the spatial distribution of anomalous HTF is somewhat similar to the projection of heterogeneity on the surface so that the information different from those due to the GDS and D responses can be obtained by the HTF. The signatures of the conductivity heterogeneity in the GDS, D and HTF are detectable if the conductivity of the 1000-km-scale heterogeneous block is more than twice as conductive or five times as resistive as the surrounding medium. Both cases have an induction number of about 0.8. The anomalous parts of the response functions due to multiple heterogeneous bodies can be represented very well by the sum of those due to each isolated heterogeneity, if an induction number of each anomalous scattering body is less than about 2. Although the linearity breaks down when the induction number is larger, the difference between them is not significant compared with typical observational error of corresponding response functions. This implies that the sensitivity to an isolated block can be applied to discuss the resolution of multiple blocks, such as conductivity distribution having checkerboard pattern, and vise versa, in 3-D inversions. The distribution of 3-D GDS response implies that 1-D like treatment of the GDS response, such as compiling single station 1-D conductivity profiles to discuss regional differences of conductivity and correcting the static shift of magnetotelluric responses with converted GDS response, may cause serious problem if lateral heterogeneity is not negligible. This shows the necessity of modelling and analyses, which are compatible with 3-D structure. [ABSTRACT FROM AUTHOR]

Aim: To elucidate a clinical difference between patients with Kawasaki disease documented with Yersinia pseudotuberculosis infection and patients with Kawasaki disease without Yersiniapseudotuberculosis 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 Yersiniapseudotuberculosis 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).Conclusion: Our data suggest that Yersiniapseudotuberculosis infection might play a role in the developing mechanism of poor response to therapy and the tendency to develop coronary artery lesions in Kawasaki disease patients. [ABSTRACT FROM AUTHOR]

Magnetotelluric and seismic data, collected during the MELT experiment at the southern East Pacific Rise, constrain the distribution of melt beneath this mid-ocean-ridge spreading centre and also the evolution of the oceanic lithosphere during its early cooling history. Here we focus on structures imaged at distances ∼100 to 350 km east of the ridge crest, corresponding to seafloor ages of ∼1.3 to 4.5 million years (Myr), where the seismic and electrical conductivity structure is nearly constant and independent of age. Beginning at a depth of about 60 km, we image a large increase in electrical conductivity and a change from isotropic to transversely anisotropic electrical structure, with higher conductivity in the direction of fast propagation for seismic waves. Conductive cooling models predict structure that increases in depth with age, extending to about 30 km at 4.5 Myr ago. We infer, however, that the structure of young oceanic plates is instead controlled by a decrease in water content above a depth of 60 km induced by the melting process beneath the spreading centre. [ABSTRACT FROM AUTHOR]

Describes a technique for incorporating seafloor topography in electromagnetic modelling. Electrical conductivity; Magnetic permeability; Test of the technique's reliability and stability.

Let R be a Noetherian domain and α an anti-integral element of degree d over R. Let a and b be elements of R. In this paper, we give a condition for R[(α-a)[SUP-1]] to be coincide with R[(α - b)[SUP-1]]. Moreover, we give a sufficient condition for R[α] ∩ R[α[SUP-1]] to be R[α- a] ∩ R[(α- a) [SUP-1]]. [ABSTRACT FROM AUTHOR]

Presents a guideline on how to effectively and appropriately perform catheter intervention in coronary artery lesion in Kawasaki disease on the basis of the information regarding evaluation of the diagnosis and the therapy reported in Japan and overseas. Natural history of coronary artery lesion in Kawasaki disease; Catheter intervention for patients with Kawasaki disease.

A 13-year-old boy had recurrent ventricular tachycardia following surgical correction of tetralogy of Fallot. Pharmacological management with multiple antiarrhythmic drugs failed, and the patient underwent electrophysiological evaluation. A reentrant tachycardia involving a slowly conducting region in the left ventricular outflow tract was demonstrated. We performed radiofrequency catheter ablation after identifying the essential components of the reentrant circuit. The ventricular tachycardia could no longer be induced and did not recur spontaneously during a 13-month follow-up. [ABSTRACT FROM AUTHOR]

We present a case of a 12-year-old boy with a rare form of cardiac anomaly, isolated double-orifice mitral valve. He was referred to our hospital at 1.5 years old because of heart murmur. Two-dimensional echocardiography showed double-orifice mitral valve without any associated cardiac anomalies. He has been followed carefully without any medication for 11 years. He has had no symptoms and an excellent natural course thus far. [ABSTRACT FROM AUTHOR]

Presents the case of a boy with human herpesvirus 6 (HHV-6) fulminant hepatic failure who was treated by living donor liver transplantation. Medical history of the patient; Details of the identification of an etiologic agent for the disease; Background on the detection of HHV-6 DNA in serum samples.