The serpentinized peridotites overlying the subducted zones in the Izu-Bonin-Mariana (IBM) arc system have been interpret as the cause of the low-velocity layer identified beneath the IBM froearc, in turn few earthquakes occurred along the plate boundary. Chrysotile, which is a low temperature and highly hydrated phase of serpentine with low frictional strength, has been suggested as the low velocity material in the serpentinized peridotites, besides, brucite is inferred to be likely conducive to stable sliding. However, such idea encounters challenging in our serpentinized peridotites from the southern Mariana forearc, which absent both the above minerals. The presence of talc, which characterized by its weak, low-friction and inherently stable sliding behavior, provides new clue. Here we report the occurrence of talc in serpentinized peridotites collected from the landward trench slope of the southern Mariana forearc. We infer that talc is mainly forming as a result of the reaction of serpentine minerals with silica-saturated fluids released from the subducting slab, and talc also occurs as talc veins sometimes. Due to its unique physical properties, talc may therefore play a significant role in aseismic slip in the IBM subduction zone.
In collocation applications, the prior covariance matrices or weight matrices between the signals and the observations should
be consistent to their uncertainties; otherwise, the solution of collocation will be distorted. To balance the covariance
matrices of the signals and the observations, a new adaptive collocation estimator is thus derived in which the corresponding
adaptive factor is constructed by the ratio of the variance components of the signals and the observations. A maximum likelihood
estimator of the variance components is thus derived based on the collocation functional model and stochastic model. A simplified
Helmert type estimator of the variance components for the collocation is also introduced and compared to the derived maximum
likelihood type estimator. Reasonable and consistent covariance matrices of the signals and the observations are arrived through
the adjustment of the adaptive factor. The new adaptive collocation with related adaptive factor constructed by the derived
variance components is applied in a transformation between the geodetic height derived by GPS and orthometric height. It is
shown that the adaptive collocation is not only simple in calculation but also effective in balancing the contribution of
observations and the signals in the collocation model. 相似文献
This paper reviews and discusses the development and many problems ofSpirulina cultivation in China, points out the advantages and disadvantages of open photobioreactor system, and predicts that seawaterSpirulina cultivation will be a new trend to be strengthened and emphasized due to its special physiological characteristics, easier management, lower fertilizer cost, and higher resistance to contaminants and rare pollution of chemicals.
Environmental change in Lake Taihu and its catchment since the early to middle part of the twentieth century has left a clear
geochemical record in the lake sediments. The human activities in the lake and its catchment responsible for the change include
agriculture, fishery, urbanisation, sewage and industrial waster disposal. Sediment cores were collected from Meilian Bay
of northern Lake Taihu to investigate the record of anthropogenic impacts on the lake’s ecosystem and to assess its natural,
pre-eutrophication baseline state. Two marked stratigraphic sediment units were identified on the basis of total phosphorus
concentration (TP), pigments, total organic carbon (TOC)/total nitrogen (TN), δ13C and δ15N corresponding to stages in the lake history dominated by phytoplankton, and by aquatic macrophytes. Results show that as
TP loading increased from the early 1950s the lake produced sediments with increasing amounts of organic matter derived from
phytoplankton. In the early 1950s, the first evidence for eutrophication at the Meilian Bay site is recorded by an increase
in C/N values and in sediment accumulation rate, but there is little change in phosphorus concentrations, pigments, δ13C and δ15N at this time. After 1990 a more rapid increase in trophic status took place indicated by increased levels of phosphorus,
pigments, δ15N and by decreased δ13C and TOC/TN values in the lake sediments. The first increase in trophic status of the early 1950s results mainly from agricultural
development in the catchment. In contrast, the acceleration from ca. 1990 originates from the recent development of fisheries
and the urbanisation and industrialisation of the catchment. 相似文献
Introduction Major tectonic activities occur in collisions zones between plates or intra-plate continental blocks. Therefore, it is significant to investigate collision processes. We know that orogenic and seismic belts in plate margins are closely relate… 相似文献