Mean slope-angle frequency distribution and size frequency distribution of landslide masses in Higashikubiki area, Japan

Landslide mass size frequency distributions and mean slope-angle frequency distributions were calculated for slump, slide, and creep type landslides in the Higashikubiki area. Mean slope-angle frequency distributions closely approximated Weibull distributions. Size frequency distributions show power-law dependencies. Both can be explained by modeling landslides as linked uniform blocks in tensile force. Power coefficients for size frequency distributions were 2.01–2.32 (approximation to power functions) or 2.10–2.24 (approximation to Pareto distributions).     

Transpiration and plant water relations of evergreen woody vegetation on a recently constructed artificial ecosystem under seasonally dry conditions in Western Australia

Understanding transpiration and plant physiological responses to environmental conditions is crucial for the design and management of vegetated engineered covers. Engineered covers rely on sustained transpiration to reduce the risk of deep drainage into potentially hazardous wastes, thereby minimizing contamination of water resources. This study quantified temporal trends of plant water potential (ψ_p), stomatal conductance (g_s), and transpiration in a 4‐year‐old evergreen woody vegetation growing on an artificial sandy substrate at a mine waste disposal facility. Transpiration averaged 0.7 mm day^?1 in winter, when rainfall was frequent, but declined to 0.2 mm day^?1 in the dry summer, when the plants were quite stressed. In winter, the mean ψ_p was ?0.6 MPa at predawn and ?1.5 MPa at midday, which were much higher than the corresponding summer values of ?2.0 MPa and ?4.8 MPa, respectively. The g_s was also higher in winter (72.1–95.0 mmol m^?2 s^?1) than in summer (<30 mmol m^?2 s^?1), and negatively correlated with ψ_p (p < 0.05, r² = 0.71–0.75), indicating strong stomatal control of transpiration in response to moisture stress. Total annual transpiration (147.2 mm) accounted for only 22% of the annual rainfall (673 mm), compared with 77% to 99% for woody vegetation in Western Australia. The low annual transpiration was attributed to the collective effects of a sparse and young vegetation, low moisture retention of the sandy substrate, and a superficial root system constrained by high subsoil pH. Amending the substrate with fine‐textured materials should improve water storage of the substrate and enhance canopy growth and deep rooting, while further reducing the risk of deep drainage during the early stages of vegetation establishment and in the long term. Overall, this study highlights the need to understand substrate properties, vegetation characteristics, and rainfall patterns when designing artificial ecosystems to achieve specific hydrological functions. Copyright © 2011 John Wiley & Sons, Ltd.     

Pn velocities beneath Iran

In active tectonic areas like Iran, where the coverage of seismograph stations is inadequate but earthquakes occur frequently, uppermost mantle body wave velocities are conventionally determined by using a single station and an array of earthquake sources. This method fails when earthquakes are mislocated or source areas have varied structures. An extension of the traditional surface wave two-station method is developed for body waves and shown to be independent of mislocation errors. It thus gives accurate estimates of body wave velocities along two station paths with greatly reduced errors.Uppermost mantle P wave (P_n) velocities are determined along several paths in Iran using this method and show zones of low-velocity corresponding to zones of high attenuation and Quaternary volcanic activity in the country. A remarkably high P_n velocity of 8.30 km/s is found for the Zagros area of western Iran more typical of shield like structures than that of tectonic areas.     

Overview of Holocene Tsunami Deposits along the Nankai,Suruga, and Sagami Troughs,Southwest Japan

Tsunami deposits provide a basis for reconstructing Holocene histories of great earthquakes and tsunamis on the Pacific Coast of southwest Japan. The deposits have been found in the past 15 years at lakes, lagoons, outcrops, and archaeological excavations. The inferred tsunami histories span 3000 years for the Nankai and Suruga Troughs and nearly 10,000 years for the Sagami Trough. The inferred histories contain recurrence intervals of variable length. The shortest of these —100–200 years for the Nankai Trough, 150–300 years for the Sagami Trough — resemble those known from written history of the past 1000–1500 years. Longer intervals inferred from the tsunami deposits probably reflect variability in rupture mode, incompleteness of geologic records, and insufficient research. The region's tsunami history could be clarified by improving the geologic distinction between tsunami and storm, dating the inferred tsunamis more accurately and precisely, and using the deposits to help quantify the source areas and sizes of the parent earthquakes.     

The Effect of Tidal Interaction with a Gas Disk on Formation of Terrestrial Planets

We have performed N-body simulation on final accretion stage of terrestrial planets, including the effect of damping of eccentricity and inclination caused by tidal interaction with a remnant gas disk. As a result of runway and oligarchic accretion, about 20 Mars-sized protoplanets would be formed in nearly circular orbits with orbital separation of several to ten Hill radius. The orbits of the protoplanets would be eventually destabilized by long-term mutual gravity and/or secular resonance of giant gaseous planets. The protoplanets would coalesce with each other to form terrestrial planets through the orbital crossing. Previous N-body simulations, however, showed that the final eccentricities of planets are around 0.1, which are about 10 times higher than the present eccentricities of Earth and Venus. The obtained high eccentricities are the remnant of orbital crossing. We included the effect of eccentricity damping caused by gravitational interaction with disk gas as a drag force (“gravitational drag”) and carried out N-body simulation of accretion of protoplanets. We start with 15 protoplanets with 0.2M⊕ and integrate the orbits for 10⁷ years, which is consistent with the observationally inferred disk lifetime (in some runs, we start with 30 protoplanets with 0.1M⊕). In most runs, the damping time scale, which is equivalent to the strength of the drag force, is kept constant throughout each run in order to clarify the effects of the damping. We found that the planets' final mass, spatial distribution, and eccentricities depend on the damping time scale. If the damping time scale for a 0.2M⊕ mass planet at 1 AU is longer than 10⁸ years, planets grow to Earth's size, but the final eccentricities are too high as in gas-free cases. If it is shorter than 10⁶ years, the eccentricities of the protoplanets cannot be pumped up, resulting in not enough orbital crossing to make Earth-sized planets. Small planets with low eccentricities are formed with small orbital separation. On the other hand, if it is between 10⁶ and 10⁸ years, which may correspond to a mostly depleted disk (0.01-0.1% of surface density of the minimum mass model), some protoplanets can grow to about the size of Earth and Venus, and the eccentricities of such surviving planets can be diminished within the disk lifetime. Furthermore, in innermost and outermost regions in the same system, we often find planets with smaller size and larger eccentricities too, which could be analogous to Mars and Mercury. This is partly because the gravitational drag is less effective for smaller mass planets, and partly due to the “edge effect,” which means the innermost and outermost planets tend to remain without collision. We also carried out several runs with time-dependent drag force according to depletion of a gas disk. In these runs, we used exponential decay model with e-folding time of 3×10⁶ years. The orbits of protoplanets are stablized by the eccentricity damping in the early time. When disk surface density decays to ?1% of the minimum mass disk model, the damping force is no longer strong enough to inhibit the increase of the eccentricity by distant perturbations among protoplanets so that the orbital crossing starts. In this disk decay model, a gas disk with 10⁻⁴-10⁻³ times the minimum mass model still remains after the orbital crossing and accretional events, which is enough to damp the eccentricities of the Earth-sized planets to the order of 0.01. Using these results, we discuss a possible scenario for the last stage of terrestrial planet formation.     

Records of environmental and ecological changes related to excavation in varve sediment from Lake Hiruga in central Japan

Journal of Paleolimnology - Sub-annual-scale environmental and ecosystem changes since the mid-18th century were reconstructed in a semi-closed lagoon, Lake Hiruga, located along the Sea of Japan...     

Secondary‐volatiles linked metallic iron in eucrites: The dual‐origin metals of Camel Donga

The unique occurrence of abundant (~1 vol%) near‐pure‐Fe metal in the Camel Donga eucrite is more complicated than previously believed. In addition to that component of groundmass metal, scattered within the meteorite are discrete nodules of much higher kamacite abundance. We have studied the petrology and composition of two of these nodules in the form of samples we call CD2 and CD3. The nodules are ovoids 11 (CD2) to 15 (CD3) mm across, with metal, or inferred preweathering metal, abundances of 12–17 vol% (CD2 is unfortunately quite weathered). The CD3 nodule also includes at its center a 5 mm ovoid clumping (6 vol%) of F‐apatite. Both nodules are fine‐grained, so the high Fe metal and apatite contents are clearly not flukes of inadequate sampling. The metals within the nodules are distinctly Ni‐rich (0.3–0.6 wt%) compared to the pure‐Fe (Ni generally 0.01 wt%) groundmass metals. Bulk analyses of three pieces of the CD2 nodule show that trace siderophile elements Ir, Os, and Co are commensurately enriched; Au is enriched to a lesser degree. The siderophile evidence shows the nodules did not form by in situ reduction of pyroxene FeO. Moreover, the nodules do not show features such as silica‐phase enrichment or pyroxene with reduced FeO (as constrained by FeO/MgO and especially FeO/MnO) predicted by the in situ reduction model. The oxide minerals, even in groundmass samples well away from the nodules, also show little evidence of reduction. Although the nodule boundaries are generally sharp, groundmass‐metal Ni content is anti‐correlated with distance from the CD3 nodule. We infer that the nodules represent materials that originated within impactors into the Camel Donga portion of the eucrite crust, but probably were profoundly altered during later metamorphism/metasomatism. Origin of the pure‐Fe groundmass metal remains enigmatic. In situ reduction probably played an important role, and association in the same meteorite of the Fe‐nodules is probably significant. But the fluid during alteration was probably not (as previously modeled) purely S and O, of simple heat‐driven internal derivation. We conjecture a two‐stage metasomatism, as fluids passed through Camel Donga after impact heating of volatile‐rich chondritic masses (survivors of gentle accretionary impacts) within the nearby crust. First, reduction to form troilite may have been triggered by fluids rich in S₂ and CO (derived from the protonodules?), and then in a distinct later stage, fluids were (comparatively) H₂O‐rich, and thus reacted with troilite to form pure‐Fe metal along with H₂S and SO₂. The early eucrite crust was in places a dynamic fluid‐bearing environment that hosted complex chemical processes, including some that engendered significant diversity among metal+sulfide alterations.     

Orbital evolution and accretion of protoplanets tidally interacting with a gas disk: I. Effects of interaction with planetesimals and other protoplanets

We have performed N-body simulations on the stage of protoplanet formation from planetesimals, taking into account so-called “type-I migration,” and damping of orbital eccentricities and inclinations, as a result of tidal interaction with a gas disk without gap formation. One of the most serious problems in formation of terrestrial planets and jovian planet cores is that the migration time scale predicted by the linear theory is shorter than the disk lifetime (10⁶-10⁷ years). In this paper, we investigate retardation of type-I migration of a protoplanet due to a torque from a planetesimal disk in which a gap is opened up by the protoplanet, and torques from other protoplanets which are formed in inner and outer regions. In the first series of runs, we carried out N-body simulations of the planetesimal disk, which ranges from 0.9 to 1.1 AU, with a protoplanet seed in order to clarify how much retardation can be induced by the planetesimal disk and how long such retardation can last. We simulated six cases with different migration speeds. We found that in all of our simulations, a clear gap is not maintained for more than 10⁵ years in the planetesimal disk. For very fast migration, a gap cannot be created in the planetesimal disk. For migration slower than some critical speed, a gap does form. However, because of the growth of the surrounding planetesimals, gravitational perturbation of the planetesimals eventually becomes so strong that the planetesimals diffuse into the vicinity of the protoplanets, resulting in destruction of the gap. After the gap is destroyed, close encounters with the planetesimals rather accelerate the protoplanet migration. In this way, the migration cannot be retarded by the torque from the planetesimal disk, regardless of the migration speed. In the second series of runs, we simulated accretion of planetesimals in wide range of semimajor axis, 0.5 to 2-5 AU, starting with equal mass planetesimals without a protoplanet seed. Since formation of comparable-mass multiple protoplanets (“oligarchic growth”) is expected, the interactions with other protoplanets have a potential to alter the migration speed. However, inner protoplanets migrate before outer ones are formed, so that the migration and the accretion process of a runaway protoplanet are not affected by the other protoplanets placed inner and outer regions of its orbit. From the results of these two series of simulations, we conclude that the existence of planetesimals and multiple protoplanets do not affect type-I migration and therefore the migration shall proceed as the linear theory has suggested.