Temporal changes in electrical resistivity at Sakurajima volcano from continuous magnetotelluric observations

Continuous magnetotelluric (MT) measurements were conducted from May 2008 to July 2009 at Sakurajima, one of the most active volcanoes in Japan. Two observation sites were established at locations 3.3 km east and 3 km west–northwest of the summit crater. At both observation sites, the high-quality component of the impedance tensor (Zyx) showed variations in apparent resistivity of approximately ± 20% and phase change of ± 2°, which continued for 20–180 days in the frequency range between 320 and 4 Hz. The start of the period of changes in apparent resistivity approximately coincided with the start of uplift in the direction of the summit crater, as observed by a tiltmeter, which is one of the most reliable pieces of equipment with which to detect magma intrusion beneath a volcano. A 2D inversion of MT impedance suggests that the resistivity change occurred at a depth around sea level. One of the possible implications of the present finding is that the degassed volatiles migrated not only vertically through the conduit but also laterally through a fracture network, mixing with shallow groundwater beneath sea level and thereby causing the observed resistivity change.     

Future changes in tropical cyclone activity in the North Indian Ocean projected by high-resolution MRI-AGCMs

New and previous versions of the high-resolution 20- and 60-km-mesh Meteorological Research Institute atmospheric general circulation models are used to investigate potential future changes in tropical cyclone (TC) activity in the North Indian Ocean (NIO). Fifteen ensemble experiments are performed under the International Panel on Climate Change A1B scenario. Most of the ensemble future (2075–2099) experiments do not project significant future changes in the basin-scale TC genesis number; however, they commonly show a substantial increase (by 46 %) in TC frequency over the Arabian Sea and a decrease (by 31 %) in the Bay of Bengal. Projected future changes in TC genesis frequency show a marked seasonal variation in the NIO: a significant and robust reduction during the pre-monsoon season, an increase during the peak-monsoon season, and a westward shift during the post-monsoon season. Several large-scale thermodynamic and dynamical parameters are analysed to elucidate the physical mechanism responsible for the future changes in TC activity; this analysis reveals a seasonal dependence of the relative contribution of these parameters to the projected future changes in TC genesis frequency.     

Landslide influence on turbidity and total solids in Cubat?o do Norte River, Santa Catarina, Brazil

The rainfall events that occurred in the Cubat?o do Norte River watershed, Santa Catarina State, Brazil, in 2008, were characterized by both high intensities and amounts and triggered landslides in this watershed. The objective of the present study was to analyze the influence of landslides on the turbidity and the total solid concentration (TS) in this river using turbidity, TS, and river discharge data obtained from March 23, 2008, to June 11, 2010. The comparison between turbidity and discharge patterns implies that the landslide process was not continuous and increased the turbidity intermittently and irregularly. The sediment yield during the landslide occurrence was approximately five times higher than without the landslide, even though the discharges were similar. The turbidity/discharge relationship during the landslide occurrence was markedly different from that before and after the occurrence. The correlation coefficients between turbidity and TS showed that the landslide significantly changed the sediment yield in this watershed. The result indicates that sediment yield estimations at the watershed level should be treated more carefully when landslides occur.     

Model tests and numerical analyses on horizontal impedance functions of inclined single piles embedded in cohesionless soil

Horizontal impedance functions of inclined single piles are measured experimentally for model soil-pile systems with both the effects of local soil nonlinearity and resonant characteristics.Two practical pile inclinations of 5° and 10° in addition to a vertical pile embedded in cohesionless soil and subjected to lateral harmonic pile head loadings for a wide range of frequencies are considered.Results obtained with low-to-high amplitude of lateral loadings on model soil-pile systems encased in a laminar shear box show that the local nonlinearities have a profound impact on the horizontal impedance functions of piles.Horizontal impedance functions of inclined piles are found to be smaller than the vertical pile and the values decrease as the angle of pile inclination increases.Distinct values of horizontal impedance functions are obtained for the ’positive’ and ’negative’ cycles of harmonic loadings,leading to asymmetric force-displacement relationships for the inclined piles.Validation of these experimental results is carried out through three-dimensional nonlinear finite element analyses,and the results from the numerical models are in good agreement with the experimental data.Sensitivity analyses conducted on the numerical models suggest that the consideration of local nonlinearity at the vicinity of the soil-pile interface influence the response of the soil-pile systems.     

Horizontal structure of planetary-scale waves at the cloud top of Venus deduced from Galileo SSI images with an improved cloud-tracking technique

An improved cloud tracking method for deriving wind velocities from successive planetary images was developed. The new method incorporates into the traditional cross-correlation method an algorithm that corrects for erroneous cloud motion vectors by re-determining the most plausible correlation peak among all of the local maxima on the correlation surface by comparing each vector with its neighboring vectors. The newly developed method was applied to the Venusian violet images obtained by the Solid State Imaging system (SSI) onboard the Galileo spacecraft during its Venus flyby. Although the results may be biased by the choice of spatial scale of atmospheric features, the cloud tracking is the most practical mean of estimating the wind velocities with extensive spatial and temporal coverage. The two-dimensional distribution of the horizontal wind vector field over 5 days was obtained. It was found from these wind maps that the solar-fixed component in 1990 was similar to that in 1982 obtained by the Pioneer Venus orbiter. The deviation of the instantaneous zonal wind field from the solar-fixed component shows a distinct wavenumber-1 structure in the equatorial region. On the assumption that this structure is a manifestation of an equatorial Kelvin wave, the phase relationship between the zonal wind and the cloud brightness suggests a short photochemical lifetime of the violet absorber. The momentum deposition by this Kelvin wave, which is subject to radiative damping, would induce a westward mean-wind acceleration of ～0.3 m s^?1 per Earth day.     

Ground motion directionality inferred from a survey of minaret damage during the 1999 Kocaeli and Düzce, Turkey earthquakes

Directionality of ground motions has been discussed in near-source groundmotion study. This is interesting from the point of structural response.Dominance of the fault normal (FN) component has been reported inrelation to fault rupture direction based on the observation recordsobtained in the source area (e.g.. Somerville et al., 1996). The authorsperformed the damage survey of the two Turkey earthquakes in 1999, theKocaeli and the Düzce earthquake, and realized that minaret is a goodtarget to investigate the ground motion directionality, because a minaret isa simple cantilever structure without structural directionality. This paperdescribes the ground motion directionality based on the survey of minaretdamages during the two earthquakes in Turkey. From the damage survey,it is found that the fault normal direction was dominant with a certaindistance from the fault, say, less than 1km. While, at the region withshorter distances, the damage direction was not fault normal but about40^° from the fault strike. Discussion is addressed for the specificdamage direction inferred from the minaret damage near the fault.     

川滇菱形地块白垩纪古地磁学特征

在位于川滇菱形地块的西昌西南大德里向斜两翼的白恶系红和岩内采集古地磁学定向样品９６个,进行了古地学研究,研究结果表明,西昌晚白垩世末期的古地磁偏角为５．９°,古地磁倾角为４５．８°,地磁极位置为北纬８４．７°,东径１９３．３°,将该数据与作前期研究结果对比,则可见自楚雄至无谋,进而至西昌,其古地磁偏角逐渐靠近正北,而古地磁极纬度渐次升高,这反映了川滇菱形地块内的断块呈自西南至东北逐渐减弱的顺时针     

Numerical studies on the influence of the variations of the Kuroshio Path on the transport of fish eggs and larvae

Main spawning and nursery grounds of the Pacific Sardine are formed in the coastal boundary regions of the Kuroshio S of Kyushu and S of Honshu, respectively. Numerical experiments on the transport and dispersion of particles in and neighbouring areas of the Kuroshio were done to investigate the transport process of the fish eggs and larvae from the spawning ground to the downstream nursery ground. Surface currents measured with GEK in the past were averaged for both paths with and without large meanders of the Kuroshio in the S of Honshu and used as the data basis. Particles were released in the Kuroshio SE of Kyushu. The results show that the transport rate of them into the S coastal waters of Honshu during large meandered path is larger than the rate during the straight path period. However, recruitment rates of the Pacific Sardine in the S coastal waters of Honshu decreases during the large meander periods of the Kuroshio path. This inverse correlation is considered to be caused by the poorer food environment strongly influenced by the intrusion of the Kuroshio water.     

Recursive evaluation of interaction forces of unbounded soil in the time domain

The interaction forces representing the contribution of the linear unbounded soil to the equations of motion of a nonlinear soil-structure-interaction analysis are specified in the form of convolution integrals. They can be evaluated recursively in the time domain. In this procedure, the forces at a specific time are computed from the displacements at the same time and from the most recent forces and most recent past displacements. It is, in principle, only approximate. When the dynamic-stiffness coefficients can be expressed as the ratios of two polynomials in frequency, the appropriately chosen recursive equations are exact. Two possibilities of choosing a recursive equation are discussed.

• (i) The impulse-invariant method, where the unknown recursive coefficients are calculated by solving a system of equations which are established by equating the rigorous and recursive formulations for a discretized unit impulse displacement.
• (ii) In the segment approach, the dynamic-stiffness coefficients in the time domain are interpolated piecewise. Applying the z-transformation analytically then results in an explicit recursive equation without solving a system of equations.

The recursive evaluation of the convolution integrals in the time domain leads to a dramatic reduction in the computational effort up to two and three orders of magnitude and in the storage requirement. This makes the time-domain analysis using the substructure method computationally competitive with the corresponding direct (non-recursive) frequency-domain procedure of determining the complex response which is, however, applicable only to a linear (total) system.     

Mongolian herders’ vulnerability to <Emphasis Type="Italic">dzud</Emphasis>: a study of record livestock mortality levels during the severe 2009/2010 winter

The livelihoods of people inhabiting inland Eurasia have long been jeopardized by repeated natural hazards associated with a harsh environment and a cold, arid climate. Dzud is a Mongolian word indicating harsh winter conditions. In the present study, we considered dzud damage (e.g., livestock loss) to result from a combination of climate hazard (e.g., cold surges) and herders’ socioeconomic vulnerability. For this study, we integrated crucial socioeconomic factors accounting for major spatiotemporal variations in Mongolia by applying principal component analysis (PCA) to a comprehensive province-level, multiyear dataset. We subsequently characterized the regionality of herders’ vulnerability to the dzud event that occurred during the 2009/2010 winter by conducting a cluster analysis of the provincial principal component (PC) scores for the pre-dzud year (2009). Our results revealed a distinct geographical pattern of vulnerability. Herding households in the northern and northeastern (relatively wet and plain) areas were found to be well prepared for harsh winters, with shelters against wind and availability of forage, including hay, as well as easy access to major urban markets. By contrast, herding households in the southern and southwestern (arid and mountainous) areas were poorly prepared, with inadequate circumstances that facilitate pursuing of otor (movement of nomadic herders in search of better pastures) and lack of access to markets and dzud relief support because of their remote locations. The time coefficients of PC 2, related to winter preparedness, indicated that vulnerability increased between 2003 and 2009 (the pre-dzud year). This was partly responsible for the record-level mortality observed in 2010 across the southern and southwestern rural region, in conjunction with harsh winter weathers.