Strong ground motions from the 2011 off-the Pacific-Coast-of-Tohoku, Japan (Mw?=?9.0) earthquake obtained from a dense nationwide seismic network

The dense recordings of the K-NET and KiK-net nationwide strong motion network of 1,189 accelerometers show clearly the radiation and propagation properties of the strong ground motions associated with the 2011 off-the-Pacific Coast-of-Tohoku, Japan (Mw = 9.0) earthquake. The snapshots of seismic wave propagation reveal strong ground motions from this earthquake that originate from three large slips; the first two slips occurred over the plate interface of off-Miyagi at the southwest and the east of the hypocenter, and the third one just beneath the northern end of Ibaraki over the plate interface or in the crust. Such multiple shocks of this event caused large accelerations (maximum 1–2 G) and prolonged ground shaking lasting several minutes with dominant high-frequency (T < 1 s) signals over the entire area of northern Japan. On the other hand, ground motions of relatively longer–period band (T = 1–2 s), which caused significant damage to wooden-frame houses, were about 1/2–1/3 of those observed near the source area of the destructive 1995 Kobe, Japan (M = 7.3) earthquake. Also, the long-period (T = 6–8 s) ground motion in the Kanto (Tokyo) sedimentary basin was at an almost comparable level of those observed during the recent Mw = 7 inland earthquakes, but not as large as that from the former M = 8 earthquakes. Therefore, the impact of the strong ground motion from the present M = 9 earthquake was not as large as expected from the previously M = 7–8 earthquakes and caused strong motion damage only to short-scale construction and according to instruments inside the buildings, both have a shorter (T < 1 s) natural period.     

Putting a spin on palaeotsunami deposits

Palaeotsunami research is a relatively young discipline and while considerable progress has been made in identifying the evidence of past events there are still difficulties on occasion in differentiating between palaeotsunami and palaeostorm deposits. This has tended to focus debate on the similarities and differences between deposits laid down by the two differing processes at the expense of alternative hypotheses. Although coastal research in New Zealand a decade ago drew attention to high elevation coarse sediment deposits laid down by waterspouts, it was largely ignored by the research community. Re‐analysis of a possible palaeotsunami deposit on a nearshore island in New Zealand, however, highlights the likelihood that this deposit, and perhaps many similar coastal ones, may have been laid down by waterspouts. In essence, the palaeotsunami–palaeostorm debate can no longer ignore waterspouts as an alternative hypothesis, but only time will tell how significant a contribution waterspouts have made to catastrophic coastal sedimentation. Copyright © 2016 John Wiley & Sons, Ltd.     

Could tsunami risk be underestimated using core‐based reconstructions? Lessons from ground penetrating radar

Where should we take cores for palaeotsunami research? It is generally considered that local depressions with low energy environments such as wetlands are one of the best places. However, it is also recognized that the presence or absence of palaeotsunami deposits (and their relative thickness) is highly dependent upon subsoil microtopography. In the beach ridge system of Ishinomaki Plain, Japan, several palaeotsunami deposits linked to past Japan Trench earthquakes have been reported. However, the number of palaeotsunami deposits reported at individual sites varies considerably. This study used ground penetrating radar (GPR) combined with geological evidence to better understand the relationship between palaeotopography and palaeotsunami deposit characteristics. The subsurface topography of the ~3000–4000 bp beach ridge was reconstructed using GPR data coupled with core surveys of the underlying sediments. We noted that the number (and thickness) of the palaeotsunami deposits inferred from the cores was controlled by the palaeotopography. Namely, a larger number of events and thicker palaeotsunami deposits were observed in depressions in the subsurface microtopography. We noted a total of three palaeotsunami deposits dated to between 1700 and 3000 cal bp , but they were only observed together in 11% of the core sites. This result is important for tsunami risk assessments that use the sedimentary evidence of past events because we may well be underestimating the number of tsunamis that have occurred. We suggest that GPR is an efficient and invaluable tool to help researchers identify the most appropriate places to carry out geological fieldwork in order to provide a more comprehensive understanding of past tsunami activity. Copyright © 2017 John Wiley & Sons, Ltd.     

Depositional processes of impactites from the YAX-1 drill core in the Chicxulub impact structure inferred from vertical profiles of PDF orientations and grain size distributions of shocked quartz

Core samples from the Chicxulub impact structure provide insights into the formation processes of a shallow-marine-target, complex crater. Although previous studies investigated the impactites (generally suevitic and polymict breccias) of the Yaxcopoil-1 (YAX-1) drill core in the Chicxulub impact structure, the interpretation of its deposition remains controversial. Here, we analyze planar deformation features (PDFs), grain size, and abundance of shocked quartz throughout the YAX-1 impactite sequence (794–895 m in depth). PDF orientations of most quartz grains in YAX-1 impactites show a distribution of both low angles ({104}, {103}, {102}) and high angles (orientations higher than 55° to c-axis), while the lower part of the impactite sequence contains quartz showing only PDF orientations of low angles. High-abundance, coarse-grained shocked quartz is found from the lower to middle parts of the impactites, whereas it abruptly changes to low-abundance, fine-grained shocked quartz within the upper part. In the uppermost part of the impactites, repeated oscillations in contents of these two components are observed. PDF orientation pattern suggests most of the shocked quartz grains experienced a range of shock pressure, except two samples in the lower part of impactites, which experienced only a high level of shock. We suggest that the base and lower part of the impactite sequence were formed by ejecta curtain and melt surge deposits, respectively. Our results are also consistent with the interpretation that the middle part of the impactite sequence is fallback ejecta from the impact plume. Additionally, we support the contention that massive seawater resurges into the crater occurred during the deposition of the upper and uppermost part of the impactites.     

Simple coprecipitation method combined with low-background γ-spectrometry: Determination of 7Be, 137Cs, 210Pb, and radium and thorium isotopes in small-volume coastal water samples

Application of a coprecipitation method combined with low-background γ-spectrometry allowed the isolation of ⁷Be, ¹³⁷Cs, ²¹⁰Pb, and radium and thorium isotopes together with BaSO₄, Fe(OH)₃, or AMP/Cs in 18 L of coastal water. This simple method showed high chemical yields of 77–91% (mean, 85%) for ²¹⁰Pb and radium isotopes, 87–92% (mean, 91%) for 7Be and thorium isotopes, and 98% for ¹³⁷Cs. The activity of the nuclides showed good reproducibility with standard deviations of 1–8%, while the deviation of activity in particle-reactive ²¹⁰Pb (32%) and ⁷Be (21%) in filtered water samples was exceptionally large.     

应用压力感知胶片测定岩石连通空隙的分布

应用砂岩微观孔隙模型驱替实验技术,首次研究了张天渠油田长2油层在注水开发过程中的水驱油微观机理、孔隙结构与水驱油效率的关系.通过不同驱替压力、注入水倍数下的水驱油效率驱替实验证明油层孔隙结构的非均质性直接影响水驱油效果.分析了不同渗透率砂岩模型的驱替压力、注入倍数与驱油效率之间的相互关系以及残余水、残余油的分布特征,认为非活塞式驱油、绕流、卡断是残余油形成的主要原因.该实验研究为科学、合理地制定油田注采方案、提高水驱油效率提供了可借鉴的理论依据.     

Cretaceous high-temperature rapid loading and unloading in the Abukuma metamorphic terrane, Japan

The Cretaceous Abukuma metamorphic terrane consists of the oceanic Gosaisyo Series overthrust onto the terrigenous Takanuki Series. Although the dominant mineralogy defines one of the classic areas of andalusite–sillimanite type progressive metamorphism, there are several lines of evidence suggesting an earlier higher-pressure (up to c . 12  kbar) history of the Takanuki Series and the nearby Gosaisyo Series. These are: (1) the occurrence of rare although widespread relic kyanite in sillimanite+K-feldspar zone-grade pelitic rocks; (2) the high grossular content of garnet interiors (up to c . 30  mol %) overgrown by Ca-poor rims ( c . 2  mol % grossular) in pelitic rocks containing Al₂SiO₅ minerals (sillimanite±relic kyanite±retrograde andalusite), plagioclase and quartz; (3) the occurrence of rutile as inclusions in garnet in pelitic rocks; and (4) the occurrence of relic corundum+almandine association in silica-poor and Al–Fe-rich rocks. Garnet in the Takanuki Series pelitic rocks commonly shows textural sector zoning and preserves growth zoning despite the high metamorphic grade, suggesting rapid changes in P–T  conditions and a relatively short duration of high-temperature conditions. Combined with radiometric dating, these observations suggest that the Abukuma sillimanite+K-feldspar zone-grade rocks underwent a clockwise P–T  path with very fast (>4  mm  y⁻¹) average burial and exhumation rates.     

Analysis on Soil Degradation Resulted From Human Activities Near City Area in China By Use of DMSP/OLS and Other Data

In order to study land use and cover changes (LUCC), especially urbanization accompanied soil degradation, authors used Asia DMSP/OLS data in 1992, Land Cover Data of Asia in 1992 and Global Assessment of Human Induced Soil Degradation (GLASOD, by ISRIC) in 1992, etc. In China the major type of soil degradation is water erosion, which is widely distributed especially in Loess Plateau and in Southeast and Southwest China and happened in forestland, grassland and arable land and mainly resulted from deforestation. The secondary type is wind erosion, which is mainly distributed in Northwest China and happened in arable land and grassland and was mainly caused by overgrazing. Chemical deterioration is mainly distributed in North and Northwest China and happened in paddy, arable land and grassland. Physical deterioration only concentrated in local area in North China and happened in arable land and paddy. Chemical and physical deterioration were resulted from unreasonable agricultural activity. From city to city + 200km with different distance away from city, different types and strength of human activities resulted in different types and distributions of soil degradation. In China human activity mainly concentrated within city+ 50km, therefore, accompanied soil degradation, such as chemical and physical deterioration, mainly happened near and around city.     

LUCC and Accompanied Soil Degradation in China from 1960''s to 1990''s

This paper tries to qualitatively analyze land use and cover changes (LUCC) and accompanied soil degradation in China, the data of World Atlas of Agriculture in 1969, Land Cover Data of Asia in 1992 and Global Assessment of Human Induced Soil Degradation in 1992, etc. have been used. From 1960' s to 1990's, the area of forestland had increased, arable land and paddy as well as grassland had significantly decreased in China. The major type of soil degradation is due to water erosion, which is widely distributed especially in Loess Plateau and in Southeast and Southwest China, this happened in forestland, grassland and arable land and mainly resulted from deforestation. The secondary type is wind erosion, which is mainly distributed in Northwest China, it happened in arable land and grassland and was caused by overgrazing. Chemical deterioration is distributed in North and Northwest China, which happened in paddy, arable land and grassland. Physical deterioration only concentrated in local area in North China, it happened in arable and paddy. Chemical and physical deteriora-tion mainly resulted from unreasonable activity. Because of different human activities, different LUCC and different natural conditions, the types and strength of soil degradation can be different.     

Subglacial drainage system changes of the Gulkana Glacier,Alaska: discharge and sediment load observations and modelling

Hydrological characteristics of englacial and subglacial drainage systems in Gulkana Glacier, Alaska, were examined by analysing temporal variations of discharge and sediment load in the proglacial Phelan Creek in 2001. From data plots on semi‐log paper, it appeared appropriate to separate both discharge and sediment load into fast and slow components. The two components were possibly produced by two different drainage systems: an englacial and subglacial, ‘channellized’ system in the ablation zone, and a subglacial, ‘distributed’ system in the accumulation zone. The data indicate the occurrence of an event during which part of the ‘distributed’ drainage system changed into the ‘channellized’ drainage system. The daily time‐series of discharge and sediment load were represented using a tank model. In the model, the drainage from an additional tank was added, supposing that a subglacial reservoir full of water and sediment collapsed slowly when the subglacial drainage system changed from distributed to channellized. The simulation with the collapsed tank gave much more reasonable results than those with no collapsed tank. The contribution of the collapsed tank to total sediment load is 24%, which is much larger than 9% to total discharge. Copyright © 2006 John Wiley & Sons, Ltd.