Groundwater radon anomalies associated with earthquakes

Earthquake-related changes in groundwater radon have been detected at a sensitive observation site located right on a major active fault in Northeast Japan. A time-series analysis based on Bayesian statistics was successfully applied to remove background variations from the observed radon data, enabling us to examine the earthquake-related changes in detail.

We set a simple criterion of amplitude and duration for an anomaly observed in our radon data; we define an anomaly as a radon change that kept its level beyond 2σ (a standard deviation over the whole observation period) during a period longer than one day. We have observed 20 radon anomalies that satisfied this criterion from January 1984 to December 1988. Most of these anomalies have turned out to be related to large earthquakes that occurred in East Japan and its surrounding area; we have identified 12 post-seismic and 2-pre-seismic radon anomalies out of a total of 30 earthquakes with magnitude M 6.0 and hypocentral distance D 1000 km.

The typical pattern of the post-seismic anomalies is a radon decrease which started just after an earthquake, lasting for periods ranging from a few days to more than one week. The amplitude of the post-seismic anomalies depends on both magnitude and hypocentral distance, and can, in general, be expressed by a simple magnitude-distance relationships.

A possible pre-seismic anomaly was observed about one week before the largest earthquake that occurred in this region during the observation period (March 6, 1984; M = 7.9, D = 1000 km). Another possible pre-seismic anomaly was observed about three days before two nearby large earthquakes that occurred at almost the same place in a time interval of 53 min (February 6, 1987; M = 6.4 and M = 6.7, D = 130 km).     

Extended probit mortality model for zooplankton against transient change of PCO(2)

The direct injection of CO(2) in the deep ocean is a promising way to mitigate global warming. One of the uncertainties in this method, however, is its impact on marine organisms in the near field. Since the concentration of CO(2), which organisms experience in the ocean, changes with time, it is required to develop a biological impact model for the organisms against the unsteady change of CO(2) concentration. In general, the LC(50) concept is widely applied for testing a toxic agent for the acute mortality. Here, we regard the probit-transformed mortality as a linear function not only of the concentration of CO(2) but also of exposure time. A simple mathematical transform of the function gives a damage-accumulation mortality model for zooplankton. In this article, this model was validated by the mortality test of Metamphiascopsis hirsutus against the transient change of CO(2) concentration.     

Bioconcentration and biomagnification of polybrominated diphenyl ethers (PBDEs) through lower-trophic-level coastal marine food web

Bivalves, crabs, fishes, seawater, and sediment collected from the inner part of Tokyo Bay, Japan, were measured for 20 polybrominated diphenyl ether (PBDE) and 5 polychlorinated biphenyl (PCB) congeners. To determine the trophic levels of the organisms, carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) were also measured. Bioconcentration factors of PBDE and PCB congeners increased as the octanol-water partition coefficient (K_ow) rose to log K_ow = 7, above which they decreased again. Biomagnification of PCBs and several PBDE congeners (BDE47, 99, 100, 153 and 154) up the trophic ladder was confirmed by a positive correlation between their concentrations and δ¹⁵N. Other PBDE congeners showed a negative or no correlation, suggesting their biotransformation through metabolism. The more hydrophobic congeners of both PBDEs (Br = 2-6) and PCBs (Cl = 6-9) were biomagnified more. It thus appears that PBDEs are less biomagnified than PCBs.     

Ecology and restoration techniques for Sargassum beds in the Seto Inland Sea,Japan

Due to the reduction and degradation of coastal areas in Japan by land reclamation and anthropogenic perturbations, from the point of view of conservation of the coastal environment, the restoration of Sargassum beds is essential. Between 1978 and 1991, 6400 ha of seagrass and seaweed beds have been lost along the Japanese coast, of which Sargassum beds were 22%. New techniques for Sargassum bed restoration are summarized based on three coastal engineering techniques. (1) Construction of shallow and gentle sloping bottom substrata have been shown to be effective for the reestablishment of 'management-free seagrass and Sargassum beds' on developed coasts. (2) Seeding or transplanting using artificial substratum for extension of nursery and fishing grounds around natural Sargassum beds. (3) Periodic transplanting of Sargassum plants using artificially produced seedlings is effective to produce niches to allow faunal re-colonization in severely polluted and sparsely vegetated area. However, prior to implementation, the suitability and limitations of these three techniques requires to be ascertained for effective Sargassum bed restoration.     

OPS mélange: a new term for mélanges of convergent margins of the world

Ocean plate stratigraphy (OPS) is essential to understanding accretionary wedges and complexes along convergent plate margins. Mélanges within accretionary wedges and complexes are the products of fragmentation and mixing processes during and following OPS accretion. A new term, ‘OPS mélange’, is proposed here for mélanges composed mostly of blocks of OPS with an argillaceous matrix, and for a mixture of mélanges of multiple origins with either broken or coherent formations. An OPS mélange results from the fragmentation and disruption of OPS, without admixing of other components. Three major types of OPS mélange can be distinguished on the basis of their components: turbidite type, chert–turbidite type, and limestone–basalt type. These three types potentially form similar mélanges, but they are derived from different parts of the OPS, depending on the level of the decollement surface. The concept of ‘OPS mélange’ can be applied to most of the mélanges in accretionary prisms and complexes worldwide. In addition, this proposal recognizes a distinction between processes of fragmentation and mixing of OPS components, and mixing of ophiolite components, the latter of which results in serpentinite mélanges, not OPS mélanges. Mélanges composed of OPS sequences occur worldwide. The recognition of OPS mélanges is a key aspect of understanding tectonic processes at convergent margins, which result in mélange formation in orogenic belts globally.     

Soil Condition and Seismic Characteristics in Shiga Prefecture,Japan

The seismic observation network in Shiga prefecture iscomposed of four systems.All the observation data obtained were used to estimatethe dynamic characteristicsof the surface soils around the lake and the seismichazard for Hikone City. Since1995, 21 records have been obtained at the USP site ofwhich those for the 1999Shigaken-Hokubu Earthquake and 1999 Wakayarnaken-HokubuEarthquake wereused in this study. Transfer functions of the surfacesoil in each ward of ShigaPrefecture based on the Mt. Kojin site (KJY), whichhas relatively hard soil, werecalculated from the records of the two earthquakes.Assuming a scenario earthquakeat the Hyakusaiji fault close to Hikone City, maximumground motions were obtainedfor 15 city blocks in order to establish a damageestimation for that city. The numberof collapsed wooden houses and the damage ratiowere calculated based on the distributionof construction of wooden houses by year. Blockswith a larger ratio of old, wooden housesin Hikone showed a close correlation with blockswith a large ratio of aged persons inthem, indicative that weak persons, such as theelderly, may find themselves in a severesituation during a natural disaster.     

Influence of climate fluctuation on clay formation in the Baikal drainage basin

Sedimentary cores BDP 96 and 98 and VER 96-2 St. 3 from Academician Ridge in Lake Baikal were investigated to investigate the effect of climatic fluctuations on rock weathering and clay formation in the Baikal drainage basin. Illite, smectite, vermiculite, and kaolinite were identified as the major clay minerals in the sediments by X-ray diffraction analysis. Biotite in gravels in alluvial soils of the Baikal drainage area weathers through illite to vermiculite, smectite, and finally to kaolinite. To investigate the relationship between weathering and climate, we measured the clay content and the concentration of biogenic silica in the sediments. High surface productivity (increased biogenic silica) and high chemical weathering (decreased clay content) occurred simultaneously, showing that crustal weathering and soil formation were enhanced under warm climatic conditions.Clay formation was enhanced in the watershed from the Late Miocene to the Middle Pliocene, and mechanical weathering of rocks increased during glacial intervals after the climate began to cool in Late Pliocene time. This change in the weathering mode in the watershed reduced the nutrient flux and aquatic productivity of Lake Baikal.     

Grain-size dependence of two-dimensional micromagnetic structures for pseudo-single-domain magnetite (0.2–2.5 μm)

Micromagnetic modelling with a Monte Carlo method was performed to obtain 2-D micromagnetic structures of pseudo-single-domain (PSD) magnetite (0.2–2.5  μm). Cubic model grains were subdivided into a 2-D array with a maximum of 100×100 cells. In order to find an appropriate cell size, the variation of the self-consistency parameter ( S ) with cell size was examined. We regard solutions with S >0.95, which corresponds to cell sizes ≤0.03  μm, as representing realistic micromagnetic structures. For saturation remanence states, we found vortex structures for small PSD grains (≤0.25  μm) and closure domain structures for larger PSD grains (0.6–2.5  μm). Between 0.25 and 0.6  μm, structures remained chaotic even after a very large number of Monte Carlo steps. In grains with a closure domain structure, domain walls were usually subdivided into several segments with opposite polarities of magnetization rotation.     

Biological organic carbon export estimated from the annual carbon budget observed in the surface waters of the western subarctic and subtropical North Pacific Ocean from 2004 to 2013

The annual flux of biologically produced organic carbon from surface waters is equivalent to annual net community production (NCP) at a steady state and equals the export of particulate and dissolved organic carbon (POC and DOC, respectively) to the ocean interior. NCP was estimated from carbon budgets of salinity-normalized dissolved inorganic carbon (nDIC) inventories at two time-series stations in the western subarctic (K2) and subtropical (S1) North Pacific Ocean. By using quasi-monthly biogeochemical observations from 2004 to 2013, monthly mean nDIC inventories were integrated from the surface to the annual maximum mixed layer depth and corrected for changes due to net air–sea CO₂ exchange, net CaCO₃ production, vertical diffusion from the upper thermocline, and horizontal advection. The annual organic carbon flux at K2 (1.49 ± 0.42 mol m^?2 year^?1) was lower than S1 (2.81 ± 0.53 mol m^?2 year^?1) (p < 0.001 based on t test). These fluxes consist of three components: vertically exported POC fluxes (K2: 1.43 mol m^?2 year^?1; S1: 2.49 mol m^?2 year^?1), vertical diffusive DOC fluxes (K2: 0.03 mol m^?2 year^?1; S1: 0.25 mol m^?2 year^?1), and suspended POC fluxes (K2: 0.03 mol m^?2 year^?1; S1: 0.07 mol m^?2 year^?1). The estimated POC export flux at K2 was comparable to the sum of the POC flux observed with drifting sediment traps and active carbon flux exported by migrating zooplankton. The export fluxes at both stations were higher than those reported at other time-series sites (ALOHA, the Bermuda Atlantic Time-series Study, and Ocean Station Papa).     

Early Cretaceous tectonic events implied in the time-lag between the age of radiolarian chert and its metamorphic basement in the Bantimala area, South Sulawesi, Indonesia

Abstract The Bantimala Complex of South Sulawesi consists mainly of mélange, chert, basalt, ultramafic rocks and high pressure type metamorphic rocks. Well-preserved radiolarians were extracted from 10 samples of chert, and K-Ar age dating was done for muscovite from five samples of schist of the Bantimala Complex. The radiolarian assemblage from chert is assigned middle Cretaceous (late Albian-early Cenomanian) age, while the K-Ar age data from schist range from 132 Ma to 114 Ma except for one sample with rare muscovite. The radiolarian chert is unconformably underlain by schist in the Bantimala Complex. The stratigraphie relationship and the time lag of these two kinds of age data from chert and underlying schist suggest short-time tectonic events immediately followed by a quick waning tectonism in this region during the Albian-Cenomanian transgression.