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1.
We infer the groundwater-level anomalies associated with a hypothetical preslip prior to the anticipated M 8 Tokai earthquake,
and evaluate the detectability of the anomalies using data from seven groundwater wells. We evaluate the detectability of
the anomalies under the following assumptions: (1) an Mw 5.5–6.5 aseismic preslip event occurs at the plate boundary in and
around the hypothetical focal zone of the Tokai earthquake; (2) the total amount of the strain step at each observation associated
with the preslip can be calculated by tensile and shear faulting based on the dislocation model; (3) a normalized strain history
associated with the preslip is defined from the results of numerical simulations based on rate- and state-dependent friction
laws; and (4) the groundwater-level anomaly prior to the earthquake is proportional to the estimated history of the strain
change associated with the preslip. We investigate the detection time of the anomaly at seven wells given an Mw 5.5, 6.0,
or 6.5 aseismic preslip at one of the 272 grid points in and around the area of the hypothetical focal zone of the Tokai earthquake.
As a result, over the time interval between 1 and 48 hours prior to the hypothetical Tokai earthquake, we are able to detect
at each of the seven wells a hypothetical Mw 6.5 preslip at 10–86 of the 272 grid points, an Mw 6 preslip at 0–19 grid points,
and an Mw 5.5 preslip at 0–5 grid points. 相似文献
2.
Correlated accretion ages and ε54Cr of meteorite parent bodies and the evolution of the solar nebula
We look at the relationship between the value of ε54Cr in bulk meteorites and the time (after calcium‐aluminum‐rich inclusion, CAI) when their parent bodies accreted. To obtain accretion ages of chondrite parent bodies, we estimated the maximum temperature reached in the insulated interior of each parent body, and estimated the initial 26Al/27Al for this temperature to be achieved. This initial 26Al/27Al corresponds to the time (after CAI formation) when cold accretion of the parent body would have occurred, assuming 26Al/27Al throughout the solar system began with the canonical value of 5.2 × 10?5. In cases of iron meteorite parent bodies, achondrite parent bodies, and carbonaceous chondrite parent bodies, we use published isotopic ages of events (such as core formation, magma crystallization, and growth of secondary minerals) in each body's history to obtain the probable time of accretion. We find that ε54Cr correlates with accretion age: the oldest accretion ages (1 ± 0.5 Ma) are for iron and certain other differentiated meteorites with ε54Cr of ?0.75 ± 0.5, and the youngest ages (3.5 ± 0.5 Ma) are for hydrated carbonaceous chondrites with ε54Cr values of 1.5 ± 0.5. Despite some outliers (notably Northwest Africa [NWA] 011 and Tafassasset), we feel that the correlation is significant and we suggest that it resulted from late, localized injection of dust with extremely high ε54Cr. 相似文献
3.
Hydrological and geochemical studies for earthquake prediction in Japan during the last two decades are reviewed. Following the 1995 Hyogo-ken Nanbu (Kobe) earthquake, the central approach to research on earthquake prediction was modified. Instead of precursory detection, emphasis was placed on understanding the entire earthquake cycle. Moreover, the prediction program for the anticipated Tokai earthquake was revised in 2003 to include the detection of preslip-related precursors. These changes included the promotion of the following hydrological and geochemical studies for earthquake prediction: (1) development and/or application of statistical methods to extract small fluctuations from hydrological/geochemical data, (2) evaluation of the detectability of preslip-related anomalies in terms of groundwater levels in wells in the Tokai region, and (3) establishment of a new groundwater and borehole strain observation network for Nankai and Tonankai earthquake prediction research. The following basic geochemical studies were carried out: (1) development of a new monitoring system using a quadrupole mass spectrometer, (2) experimental studies on hydrogen generation by the grinding of rock and crystal powders, (3) comprehensive monitoring of groundwater gas and precise crustal deformation, and (4) mantle-derivative helium observation to compare with seismic velocity structures and the distribution of non-volcanic tremors. Moreover, hydrological and geochemical investigations related to the evolution of fault zones were introduced within the framework of fault zone drilling projects. 相似文献
4.
Takayuki Ushikubo Yunbin Guan Hajime Hiyagon Naoji Sugiura Laurie A. Leshin 《Meteoritics & planetary science》2007,42(7-8):1267-1279
Abstract— We measured 36Cl‐36S and 26Al‐26Mg systematics and O isotopes of secondary phases in a moderately altered type B2 CAI (CAI#2) from the Allende CV3 chondrite. CAI#2 has two distinct alteration domains: the anorthite‐grossular (An‐Grs) domain that mostly consists of anorthite and grossular, and the Na‐rich domain that mostly consists of sodalite, anorthite, and Fe‐bearing phases. Large 36S excesses (up to ～400‰) corresponding to an initial 36Cl/35Cl ratio of (1.4 ± 0.3) × 10?6 were observed in sodalite of the Na‐rich domain, but no resolvable 26Mg excesses were observed in anorthite and sodalite of the Na‐rich domain (the initial 26Al/27Al ratio < 4.4 × 10?7). If we assume that the 36Cl‐36S and the 26Al‐26Mg systematics were closed simultaneously, the 36Cl/35Cl ratio would have to be on the order of ～10?2 when CAIs were formed. In contrast to sodalite in Na‐rich domain, significant 26Mg excesses (up to ～35‰) corresponding to an initial 26Al/27Al ratio of (1.2 ± 0.2) × 10?5 were identified in anorthite of the An‐Grs domain. The 26Al‐26Mg systematics of secondary phases in CAI#2 suggest that CAIs experienced multiple alteration events. Some of the alteration processes occurred while 36Cl (half‐life is 0.3 Myr) and 26Al (half‐life is 0.72 Myr) were still alive, whereas others took place much later. Assuming that 26Al was homogeneously distributed in the solar nebula, our study implies that alteration of CAIs occurred as early as within 1.5 Myr of CAI formation and as late as 5.7 Myr after. 相似文献
5.
The paleomagnetic field intensity is estimated with the aid of the Koenigsberger-Thellier method for four ordinary chondrites and one carbonaceous chondrite by assuming that the stable NRM component of these meteorites is attributable to the TRM acquired in a low-temperature range (lower than about 400°C) during their extremely-slow cooling process. The results are summarized in Table IV, where the paleomagnetic field intensity ranges from 0.10 to 0.97 Oe.Possible effects of the extremely-slow cooling rate of meteorites and the secondary TRM acquisition of the surface fusion crust upon the original NRM of the meteorite interior are discussed. 相似文献
6.
Abstract— Nitrogen abundances and isotopic compositions of four CK chondrites (ALH85002, EET92002, Yamato6903 and Karoonda) were measured by a stepped-combustion method. Neon and Ar were also measured for the same samples. Two types of isotopically light N were observed. One of them is labile N released at low temperatures (～300 °C). This N is observed only in ALH85002. The other N is extracted at high temperatures (900?1200 °C) from all CK chondrites; although, the isotopic compositions are somewhat variable. There is a fair correlation between the excess 15N values and the abundance of trapped 36Ar for the high-temperature component, suggesting presolar origin of these species. The light N (δ15N = ?106.8‰) observed in Karoonda is one of the lightest N components ever reported for bulk chondrites. 相似文献
7.
NAOJI SUGIURA 《Meteoritics & planetary science》1998,33(3):393-409
Abstract— Carbon and nitrogen distributions in iron meteorites, their concentrations in various phases, and their isotopic compositions in certain phases were measured by secondary ion mass spectrometry (SIMS). Taenite (and its decomposition products) is the main carrier of C, except for IAB iron meteorites, where graphite and/or carbide (cohenite) may be the main carrier. Taenite is also the main carrier of N in most iron meteorites unless nitrides (carlsbergite CrN or roaldite (Fe, Ni)4N) are present. Carbon and N distributions in taenite are well correlated unless carbides and/or nitrides are exsolved. There seem to be three types of C and N distributions within taenite. (1) These elements are enriched at the center of taenite (convex type). (2) They are enriched at the edge of taenite (concave type). (3) They are enriched near but some distance away from the edge of taenite (complex type). The first case (1) is explained as equilibrium distribution of C and N in Fe-Ni alloy with M-shape Ni concentration profile. The second case (2) seems to be best explained as diffusion controlled C and N distributions. In the third case (3), the interior of taenite has been transformed to the α phase (kamacite or martensite). Carbon and N were expelled from the α phase and enriched near the inner border of the remaining γ phase. Such differences in the C and N distributions in taenite may reflect different cooling rates of iron meteorites. Nitrogen concentrations in taenite are quite high approaching 1 wt% in some iron meteorites. Nitride (carlsbergite and roaldite) is present in meteorites with high N concentrations in taenite, which suggests that the nitride was formed due to supersaturation of the metallic phases with N. The same tendency is generally observed for C (i.e., high C concentrations in taenite correlate with the presence of carbide and/or graphite). Concentrations of C and N in kamacite are generally below detection limits. Isotopic compositions of C and N in taenite can be measured with a precision of several permil. Isotopic analysis in kamacite in most iron meteorites is not possible because of the low concentrations. The C isotopic compositions seem to be somewhat fractionated among various phases, reflecting closure of C transport at low temperatures. A remarkable isotopic anomaly was observed for the Mundrabilla (IIICD anomalous) meteorite. Nitrogen isotopic compositions of taenite measured by SIMS agree very well with those of the bulk samples measured by conventional mass spectrometry. 相似文献
8.
Abstract— Nitrogen and Ar in more than 20 primitive ordinary chondrites were studied by a stepped combustion method. Several N carriers that are characterized by N isotopic composition, N release pattern and trapped Ar release pattern are recognized in the primitive ordinary chondrites. Large fractions of anomalous N and associated Ar are removed by acid treatment in most cases. The N isotopic anomalies cannot be explained by known presolar grains (with a possible exception of graphite), and some of the N isotopic anomalies may be due to unknown presolar grains. There is no specific relationship between the type of N carriers contained in an ordinary chondrite and the chemical type (H, L, or LL) of the chondrite. It is likely that as a result of impacts, the carriers of isotopically anomalous N were mixed in various parent bodies as rock fragments rather than as individual fine particles. The presence of distinctive N isotopic anomalies in primitive meteorites indicates that the primitive solar nebula may have been heterogeneous either spatially or temporally. 相似文献
9.
Kazutoshi SATO Jun INOUE Akira YAMAZAKI Naohiko HIRASAWA Konosuke SUGIURA Kyohei YAMADA 《大气科学进展》2020,37(5):431-440
Cyclones with strong winds can make the Southern Ocean and the Antarctic a dangerous environment.Accurate weather forecasts are essential for safe shipping in the Southern Ocean and observational and logistical operations at Antarctic research stations.This study investigated the impact of additional radiosonde observations from Research Vessel"Shirase"over the Southern Ocean and Dome Fuji Station in Antarctica on reanalysis data and forecast experiments using an ensemble data assimilation system comprising the Atmospheric General Circulation Model for the Earth Simulator and the Local Ensemble Transform Kalman Filter Experimental Ensemble Reanalysis,version 2.A 63-member ensemble forecast experiment was conducted focusing on an unusually strong Antarctic cyclonic event.Reanalysis data with(observing system experiment)and without(control)additional radiosonde data were used as initial values.The observing system experiment correctly captured the central pressure of the cyclone,which led to the reliable prediction of the strong winds and moisture transport near the coast.Conversely,the control experiment predicted lower wind speeds because it failed to forecast the central pressure of the cyclone adequately.Differences were found in cyclone predictions of operational forecast systems with and without assimilation of radiosonde observations from Dome Fuji Station. 相似文献
10.
Abstract— We report in situ magnesium isotope measurements of 7 porphyritic magnesium‐rich (type I) chondrules, 1 aluminum‐rich chondrule, and 16 refractory inclusions (14 Ca‐Al‐rich inclusions [CAIs] and 2 amoeboid olivine aggregates [AOAs]) from the ungrouped carbonaceous chondrite Acfer 094 using a Cameca IMS 6f ion microprobe. Both AOAs and 9 CAIs show radiogenic 26Mg excesses corresponding to initial 26Al/27Al ratios between ～5 × 10?5 ～7 × 10?5 suggesting that formation of the Acfer 094 CAIs may have lasted for ～300,000 years. Four CAIs show no evidence for radiogenic 26Mg; three of these inclusions (a corundum‐rich, a grossite‐rich, and a pyroxene‐hibonite spherule CAI) are very refractory objects and show deficits in 26Mg, suggesting that they probably never contained 26Al. The fourth object without evidence for radiogenic 26Mg is an anorthite‐rich, igneous (type C) CAI that could have experienced late‐stage melting that reset its Al‐Mg systematics. Significant excesses in 26Mg were observed in two chondrules. The inferred 26Al/27Al ratios in these two chondrules are (10.3 ± 7.4) × 10?6 (6.0 ± 3.8) × 10?6 (errors are 2σ), suggesting formation 1.6+1.2‐0.6 and 2.2+0.4‐0.3 Myr after CAIs with the canonical 26Al/27Al ratio of 5 × 10?5. These age differences are consistent with the inferred age differences between CAIs and chondrules in primitive ordinary (LL3.0–LL3.1) and carbonaceous (CO3.0) chondrites. 相似文献