A hypothesis of the Senoumi submarine megaslide in Suruga Bay in Japan—based on the undrained dynamic-loading ring shear tests and computer simulation

The distinctive bathymetric feature exists in the Suruga Bay, Japan. It has been called as Senoumi (Stone flower sea) from old times. Senoumi is a 30?km wide and 20?km long concave feature. Its origin has not been explained yet; however, the feature might be a combined consequence of intensive tectonic activity in the plate border, landslides, and a submarine flow coming from the Oi River. If the Senoumi was caused by a landslide, the latter would be larger than any on-land landslide in Japan. The downshelf “exit” from this feature is much narrower than its central part. This is not usual shape of landslides, but it is similar to the liquefied landslides such as those in quick clays which mobilize great strength reduction after failure. To study Senoumi as a landslide, the shear behaviors of the following three soil samples were investigated by the cyclic and seismic undrained stress control ring shear tests. One sample is volcanic ash taken from the base of landslide deposits (mass transport deposits), from 130 to 190?m deep layer below the submarine floor which was drilled and cored by the Integrated Ocean Drilling Program Expedition 333. Another two samples are the Neogene silty–sand and silt taken from the Omaezaki hill adjacent to the Senoumi, because the shear zone might have been formed in Neogene layers extending from on-land to the continental shelf. The largest strength reduction from peak to steady-state shear resistance in the undrained cyclic loading test was found in volcanic ash. The strength reduction in Neogene silty–sand was smaller than volcanic ash, while the Neogene silt mobilized the least post-failure strength reduction. An integrated model simulating the initiation and motion of earthquake-induced rapid landslides (landslide simulation (LS)-RAPID, Sassa et al. Landslides 7–3:219–236, 2010) was applied to this study. The steady-state shear resistance and other geotechnical parameters measured by the undrained ring shear tests and the greatest strong motion record in the 2011 off-the-Pacific Coast of Tohoku earthquake (M _w 9.0), also known as “2011 Tohoku Earthquake” at the observation point MYG004 (2,933?gal) were input to this model. As the result, it was found that landslides would be triggered by 0.30–1.0 times of MYG004 in volcanic ash, 0.4–1.0 times of MYG004 in Neogene silty–sand and Neogene silt, though the depth and area of triggered landslides were different in soils and intensity of shaking. Feature, created by LS-RAPID using the parameters of volcanic ash, was most similar to the Senoumi in depth and extent. The result obtained from this study includes a hypothesis to be proved, but presents the strong need to investigate the risk of the large-scale submarine landslides which could enhance tsunami wave and possibly enlarge the submarine landslide retrogressively into the adjacent coastal plain by the upcoming mega earthquake in the Nankai Trough.     

Rocky desertification and its causes in karst areas: a case study in Yongshun County,Hunan Province,China

Rocky desertification, a process of land degradation characterized by soil erosion and bedrock exposure, is one of the most serious land degradation problems in karst areas, and is regarded as an obstacle to local sustainable development. It is well known that human activities can accelerate rocky desertification; however, the effects of climate change on rocky desertification in karst areas are still unclear. This study focused on the effects of temperature and precipitation changes and human activities on rocky desertification in karst areas to determine the impacts of climate change and human disturbances on rocky desertification. Areas of different level of rocky desertification were obtained from Landsat TM (1987) and Landsat ETM+ (2000) images. The results show that, although the total desertification area increased by only 1.27% between 1987 and 2000, 17.73% of the slightly desertified land had degraded to a moderate or intense level, 2.01 and 15.71%, respectively. Meanwhile, between 1987 and 2000, the air temperature increased by 0.7°C, and precipitation increased by 170 mm. Statistical results indicate that the increase in precipitation was caused by heavy rainfall. In addition, under the interactive influences of heavy rainfall and temperature, the average karst dissolution rate was about 87 m³ km⁻² a⁻¹ during the 14 years in the study area. Further analysis indicated that rocky desertification was positively related with the increase in temperature and precipitation and especially with the heavy rainfall events. Climate change accelerated rocky desertification in the karst areas. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Maximum-likelihood ambiguity resolution based on Bayesian principle

 Based on the Bayesian principle and the fact that GPS carrier-phase ambiguities are integers, the posterior distribution of the ambiguities and the position parameters is derived. This is then used to derive the maximum posterior likelihood solution of the ambiguities. The accuracy of the integer ambiguity solution and the position parameters is also studied according to the posterior distribution. It is found that the accuracy of the integer solution depends not only on the variance of the corresponding float ambiguity solution but also on its values. Received: 27 July 1999 / Accepted: 22 November 2000     

Variation of mineral composition,fabric and oxygen fugacity from massive to foliated eclogites during exhumation of subducted ocean crust in the North Qilian suture zone,NW China

Eclogites from the North Qilian suture zone are high‐pressure low‐temperature metamorphic rocks of ocean crust protolith, and occur in both massive and foliated varieties as individual blocks of tens to hundreds of metres in size. The massive type is weakly deformed and shows granoblastic texture characterized by a coarse‐grained peak mineral assemblage of Grt¹ + Omp¹ + Ph + Rt ± Lws (or retrograde Cz). In contrast, the foliated type is strongly deformed and shows a fine‐grained retrograde mineral assemblage of Grt² + Omp² + Cz + Gln + Ph. Both total FeO and aegirine contents in omphacite, as well as X_Fe[=Fe³⁺/(Fe³⁺ + Al^VI)] in clinozoisite/epidote, increase significantly from massive to foliated eclogites. Lattice preferred orientation (LPO) of omphacite, determined by electron back‐scatter diffraction analysis, is characterized by weak and strong SL‐type fabrics for massive and foliated eclogites, respectively. Clinozoisite/epidote also developed SL‐type fabric, but different from the LPOs of omphacite in <010> and <001> axes, owing to their opposite crystallographic long and short axis definitions. The transition of deformation mechanism from dislocation creep to diffusive mass transfer (DMT) creep in omphacite and the concomitant retrograde metamorphism both are efficiently facilitated when the original coarse‐grained Omp¹ + Grt¹ + Lws assemblage is dynamically recrystallized and retrogressed into the fine‐grained Fe³⁺‐rich assemblage of Omp² + Grt² + Cz + Gln. The DMT process with concomitant anisotropic growth assisted by fluids is considered to be an important deformation mechanism for most minerals in the foliated eclogite. P–T estimates yielded 2.3–2.6 GPa and 485?510 °C for the massive eclogite and 1.8–2.2 GPa and 450?480 °C for the foliated eclogite. The significant increase in total Fe and Fe³⁺ contents in omphacite and clinozoisite/epidote from massive to foliated eclogite suggests changes in mineral compositions accompanied by an increase in oxygen fugacity during ductile deformation associated with exhumation. The LPO transition of omphacite, clinozoisite and rutile from weak SL‐type in massive eclogites to strong SL‐type in foliated eclogites is interpreted to represent the increment of shear strain during exhumation along the ‘subduction channel’.     

High-resolution profiles of iron, manganese, cobalt, cadmium, copper and zinc in the pore water of estuarine sediment

The remobilization of iron, manganese, cobalt, cadmium, copper and zinc in the pore water of estuarine sediment cores at Yingkou was assessed using diffusive equilibrium in thin films and diffusive gradients in thin films techniques. A relatively anoxic system (+33.7 to ?224.1 mV) in the sediment cores might cause the reductive release of iron, manganese and cobalt into pore water from the estuarine sediment. High-average concentrations of iron (47.85 μg ml^?1) and manganese (3.81 μg ml^?1) were observed using diffusive equilibrium in thin films on the sediment core, but the concentration of cobalt (18.02 ng ml^?1) was relatively low. A strong correlation between iron and cobalt was observed based on the vertical profiles of the metals. Manganese and iron were more readily released from the solid phase to the solution. The peak cobalt, copper and zinc concentrations were observed in the upper layer (2–4 cm) measured using diffusive gradients in thin films. However, the peak iron, manganese and cobalt concentrations were located in the deeper layer (≥7 cm). In addition, the concentration profiles measured using diffusive gradients in thin films of cobalt, copper and zinc were independent of the iron, manganese and cobalt distribution with respect to depth.     

Exhumation rates and age of metamorphism in the Sanbagawa belt: new constraints from zircon fission track analysis

Zircon fission track dating and track length analysis in the high‐grade part of the Asemigawa region of the Sanbagawa belt demonstrates a simple cooling history passing through the partial annealing zone at 63.2 ± 5.8 (2 σ) Ma. Combining this age with previous results of phengite and amphibole K–Ar and ⁴⁰Ar/³⁹Ar dating gives a cooling rate of between 6 and 13 °C Myr^?1, which can be converted to a maximum exhumation rate of 0.7 mm year^?1 using the known shape of the P–T path. This is an order of magnitude lower than the early part of the exhumation history. In contrast, zircon fission track analyses in the low‐grade Oboke region show that this area has undergone a complex thermal history probably related to post‐orogenic secondary reheating younger than c. 30 Ma. This event may correlate with the widespread igneous activity in south‐west Japan around 15 Ma. The age of subduction‐related metamorphism in the Oboke area is probably considerably older than the generally accepted range of 77–70 Ma.     

Calibration of JASON-1 Altimeter over Lake Erie

This article describes absolute calibration results for both JASON-1 and TOPEX Side B (TSB) altimeters obtained at the Lake Erie calibration site, Marblehead, Ohio, USA. Using 15 overflights, the estimated JASON altimeter bias at Marblehead is 58 ± 38 mm, with an uncertainty of 19 mm based on detailed error analysis. Assuming that the TSB bias is negligible, relative bias estimates using both data from the TSB-JASON formation flight period and data from 48 water level gauges around the entire Great Lakes confirmed the Marblehead results. Global analyses using both the formation flight data and dual-satellite (TSB and JASON) crossovers yield a similar relative bias estimate of 146 ± 59 mm, which agrees well with open ocean absolute calibration results obtained at Harvest, Corsica, and Bass Strait (e.g., Watson et al. 2003). We find that there is a strong dependence of bias estimates on the choice of sea state bias (SSB) models. Results indicate that the invariant JASON instrument bias estimated oceanwide is 71 mm, with additional biases of 76 mm or 28 mm contributed by the choice of Collecte Localisation Satellites (CLS) SSB or Center for Space Research (CSR) SSB model, respectively. Similar analysis in the Great Lakes yields the invariant JASON instrument bias at 19 mm, with the SSB contributed biases at 58 mm or 13 mm, respectively. The reason for the discrepancy is currently unknown and warrants further investigation. Finally, comparison of the TOPEX/POSEIDON mission (1992-2002) data with the Great Lakes water level gauge measurements yields a negligible TOPEX altimeter drift of 0.1 mm/yr.     

Dynamical effects of environmental vertical wind shear on tropical cyclone motion, structure, and intensity

Summary A series of numerical experiments on an f plane are conducted using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model, version 3 (MM5) to investigate how environmental vertical wind shear affects the motion, structure, and intensity of a tropical cyclone. The results show that a tropical cyclone has a motion component perpendicular to the vertical shear vector, first to the right of the shear and then to the left. An initially axisymmetric, upright tropical cyclone vortex develops a downshear tilt and wavenumber-one asymmetry when embedded in environmental vertical wind shear. In both small-moderate shears, a storm weakens slightly compared to that in a quiescent environment. The circulation centers between 300 hPa and the surface varies from 20 km to over 80 km. The secondary circulation becomes quite asymmetric about the surface cyclone center. As a result, convection on the upshear-right quadrant diminishes, limiting the upward heat transport in the eyewall and thus lowering the warm core and leading to a weakening of the storm. In strong vertical shear (above 12 m s⁻¹), the vertical tilt exceeds 160 km in 48 h of simulation and the secondary circulation on the upshear side is completely destroyed with low-level outflow. The axisymmetric component of eyewall convection weakens remarkably and becomes much less penetrative. As a result, the warm core becomes weak and appears at lower levels and the storm weakens rapidly accordingly. This up-down weakening mechanism discussed in this study is different from those previously discussed. It emphasizes the penetrative role of eyewall convection in transporting heat from the ocean to the mid-upper troposphere, maintaining the warm core structure of the tropical cyclone. The vertical shear is found negative to eyewall penetrative convection.