Where and why do large shallow intraslab earthquakes occur?

We try to find how often, and in what regions large earthquakes (M≥7.0) occur within the shallow portion (20-60 km depth) of a subducting slab. Searching for events in published individual studies and the Harvard University centroid moment tensor catalogue, we find twenty such events in E. Hokkaido, Kyushu-SW, Japan, S. Mariana, Manila, Sumatra, Vanuatu, N. Chile, C. Peru, El Salvador, Mexico, N. Cascadia and Alaska. Slab stresses revealed from the mechanism solutions of these large intraslab events and nearby smaller events are almost always down-dip tensional. Except for E. Hokkaido, Manila, and Sumatra, the upper plate shows horizontal stress gradient in the arc-perpendicular direction. We infer that shear tractions are operating at the base of the upper plate in this direction to produce the observed gradient and compression in the outer fore-arc, balancing the down-dip tensional stress of the slab. This tectonic situation in the subduction zone might be realized as part of the convection system with some conditions, as shown by previous numerical simulations.     

The Dependence of Constitutive Properties on Temperature and Effective Normal Stress in Seismogenic Environments

— We have evaluated how the parameters prescribing the slip-dependent constitutive law are affected by temperature and effective normal stress, by conducting the triaxial fracture experiments on Tsukuba-granite samples in seismogenic environments, which correspond to a depth range to 15 km. The normalized critical slip displacement D _c almost remains constant below 300^oC (insensitive to both temperature and effective normal stress σ _n ^eff); D _c increases with increasing temperature above 300 °C, and the rate of D _c increase with temperature tends to be largest at higher σ _n ^eff. The breakdown stress drop Δτ _b for the granite at constant σ _n ^eff is roughly 80 MPa below 300 °C, and does not depend on σ _n ^eff. Above 300 °C, Δτ _b decreases gradually with increasing temperature, and the rate of Δτ _b reduction with temperature increases at higher σ _n ^eff. The peak shear strength τ _p increases nearly linearly with increasing σ _n ^eff below 300 °C. However, τ _p becomes lower above 300 °C, deviating from the linear relation extrapolated from below 300 °C. This is consistent with the onset of crystal plastic deformation mechanisms of Tsukuba granite.     

Adsorption of tributyltin by tributyltin resistant marine Pseudoalteromonas sp. cells

The isolate, Pesudoalteromonas sp. TBT1, could grow to overcome the toxicity of tributyltin chloride (TBTCl) up to 30 μM in the absence of Cl⁻ in the medium until the cells reached an exponential phase of growth. The viability, however, was reduced after the cells reached a stationary phase. The degradation products, such as dibutyltin (DBT) and monobutyltin (MBT), were not detected in the growth medium, indicating that the isolate has no ability to degrade TBT into less toxic DBT and MBT. Up to about 10^7.5 TBT molecules were adsorbed by a single cell. The observation of morphological changes with an electron microscope showed that the cell surface became wrinkled after exposure to the lethal concentration of 10 mM TBTCl. These results indicate that the resistance of the isolate toward the toxicity of TBTCl is not related to the unique cell surface, which seems to play an important role in preventing the diffusion of TBTCl into the cytoplasm.     

Adsorption of tributyltin by tributyltin resistant marine Pseudoalteromonas sp. cells

The isolate, Pesudoalteromonas sp. TBT1, could grow to overcome the toxicity of tributyltin chloride (TBTCl) up to 30 microM in the absence of Cl(-) in the medium until the cells reached an exponential phase of growth. The viability, however, was reduced after the cells reached a stationary phase. The degradation products, such as dibutyltin (DBT) and monobutyltin (MBT), were not detected in the growth medium, indicating that the isolate has no ability to degrade TBT into less toxic DBT and MBT. Up to about 10(7.5) TBT molecules were adsorbed by a single cell. The observation of morphological changes with an electron microscope showed that the cell surface became wrinkled after exposure to the lethal concentration of 10 mM TBTCl. These results indicate that the resistance of the isolate toward the toxicity of TBTCl is not related to the unique cell surface, which seems to play an important role in preventing the diffusion of TBTCl into the cytoplasm.     

Ion upflow and downflow at the topside ionosphere observed by the EISCAT VHF radar

We have determined the MLT distribution and KpK_P dependence of the ion upflow and downflow of the thermal bulk oxygen ion population based on a data analysis using the EISCAT VHF radar CP-7 data obtained at Tromsø during the period between 1990 and 1996: (1) both ion upflow and downflow events can be observed at any local time (MLT), irrespective of dayside and nightside, and under any magnetic disturbance level, irrespective of quiet and disturbed levels; (2) these upflow and downflow events are more frequently observed in the nightside than in the dayside; (3) the upflow events are more frequently observed than the downflow events at any local time except midnight and at any K_P level and the difference of the occurrence frequencies between the upflow and downflow events is smaller around midnight; and (4) the occurrence frequencies of both the ion upflow and downflow events appear to increase with increasing KP level, while the occurrence frequency of the downflow appears to stop increasing at some KP level     

A new regime of volcanic eruption due to the relative motion between liquid and gas

In explosive magma eruptions, magma ascends through a conduit as a Poiseuille flow at depth, and gas exsolves gradually and expands as the pressure decreases (bubbly flow regime). When the volume fraction of gas becomes sufficiently large, liquid or solid parts of magma fragment into droplets or ashes, and the flow dynamics becomes governed by the gas phase (gas–ash flow regime). We propose a new flow regime, which we call fractured-turbulent flow regime, between the bubbly flow regime and the gas–ash flow regime. In the new regime, both liquid magma and gas are continuous phases. The high connectivity of the two phases allows the relative velocity between them to increase significantly. We present one sample calculation, which displays basically explosive characteristics, but has three features distinct from previous models. The explosive characteristics are manifested as the fragmentation of the magma and the high speed jet that issues from the vent. The first distinct feature is a nearly lithostatic pressure distribution, which results from the increase of the height of the fragmentation surface. The second one is the atmospheric pressure at the vent; the flow is not choked. The third one is that the relative velocity between the gas and the ash is large at the vent despite the large interaction force between the two phases. The large relative velocity is established in the fractured-turbulent regime, and is maintained in the subsequent gas–ash flow regime.     

Modulation of tropical cyclogenesis in the western North Pacific by the quasi-biweekly oscillation

The quasi-biweekly oscillation(QBWO) is the second most dominant intraseasonal mode over the western North Pacific(WNP) during boreal summer. In this study, the modulation of WNP tropical cyclogenesis(TCG) by the QBWO and its association with large-scale patterns are investigated. A strong modulation of WNP TCG events by the QBWO is found.More TCG events occur during the QBWO's convectively active phase. Based on the genesis potential index(GPI), we further evaluate the role of environmental factors in affecting WNP TCG. The positive GPI anomalies associated with the QBWO correspond well with TCG counts and locations. A large positive GPI anomaly is spatially correlated with WNP TCG events during a life cycle of the QBWO. The low-level relative vorticity and mid-level relative humidity appear to be two dominant contributors to the QBWO-composited GPI anomalies during the QBWO's active phase, followed by the nonlinear and potential intensity terms. These positive contributions to the GPI anomalies are partly offset by the negative contribution from the vertical wind shear. During the QBWO's inactive phase, the mid-level relative humidity appears to be the largest contributor, while weak contributions are also made by the nonlinear and low-level relative vorticity terms.Meanwhile, these positive contributions are partly cancelled out by the negative contribution from the potential intensity.The contributions of these environmental factors to the GPI anomalies associated with the QBWO are similar in all five flow patterns—the monsoon shear line, monsoon confluence region, monsoon gyre, easterly wave, and Rossby wave energy dispersion associated with a preexisting TC. Further analyses show that the QBWO strongly modulates the synoptic-scale wave trains(SSWs) over the WNP, with larger amplitude SSWs during the QBWO's active phase. This implies a possible enhanced(weakened) relationship between TCG and SSWs during the active(inactive) phase. This study improves our understanding of the modulation of WNP TCG by the QBWO and thus helps with efforts to improve the intraseasonal prediction of WNP TCG.     

Characterization of water quality variation in the Mekong River at Vientiane by frequent observations

To better understand the variation of water quality in the Mekong River, sampling and measurement were scheduled twice a week for about 3 years at Vientiane, followed by basic statistical analysis of the observed data. The frequent measurement revealed detailed characteristics of the water quality variation, which had not been detected by monthly observation in the previous studies. The variation in total ionic content was considered to be governed by dilution of the amount of water. Increases in turbidity could be attributed to physical effects including surface soil erosion and bed material resuspension at the time of discharge increase. Nitrogen concentrations were stably low during the low flow period and abruptly increased in May. After the annual maximum in late May, the nitrate concentration steadily decreased regardless of the remarkable rise in the discharge from mid‐July, whereas the ammonium concentration remained at a similar level until October. It was considered that the first small discernable runoff after the long dry season flushed the accumulated nitrogen in the surface soil and mobilized the nitrogen in the riverbed. The variation in phosphorus concentrations was different from that in nitrogen concentrations. During the high flow period, continual dilutions at discharge peaks and occasional large additions of phosphorus by surface runoff were suggested. Copyright © 2011 John Wiley & Sons, Ltd.     

Three-body problem

In the first part of this paper [Marchal, Yoshida, Sun Yi-Sui 1985] we have analyzed three-body systems satisfying the condition rkR where k is a suitable constant, r the mutual distance of the two masses of the binary and R the distance between the center of mass of the binary and the third mass.That condition rkR puts limits on the acceleration of the third mass and these limits allow us to determine the corresponding escape velocities.In this second part we look for initial conditions under which the inequality rkR will remain forever satisfied and we develop the corresponding tests of escape and their applications.This leads to a major improvement of the knowledge of the nature of three-body motions especially in the vicinity of triple close approaches.The region of bounded motions is much smaller than was generally expected and numerical computations of particular solutions show that we approach very near to the true limit.     

Recent progress in the theory and application of symplectic integrators

In this paper various aspect of symplectic integrators are reviewed. Symplectic integrators are numerical integration methods for Hamiltonian systems which are designed to conserve the symplectic structure exactly as the original flow. There are explicit symplectic schemes for systems of the formH=T(p)+V(q), and implicit schemes for general Hamiltonian systems. As a general property, symplectic integrators conserve the energy quite well and therefore an artificial damping (excitation) caused by the accumulation of the local truncation error cannot occur. Symplectic integrators have been applied to the Kepler problem, the motion of minor bodies in the solar system and the long-term evolution of outer planets.