Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy最新文献

In the context of the MAGIC project (Meteorological Applications of GPS Integrated Column Water Vapor Measurements in the Western Mediterranean), zenith tropospheric delays (ZTD) are computed from Global Positioning System (GPS) signals at permanent sites in the western Mediterranean area continuously since November 1998. These time series are compared to the equivalent values estimated by integrating the atmospheric column derived from radiosonde profiles and the HIRLAM numerical weather prediction model in order to determine the error statistics of the data. From a year and a half of data, we show that the difference between radiosonde and GPS ZTD has a standard deviation of 12 mm and a bias of less than 5 mm for most stations. The biases between the GPS ZTD and HIRLAM estimates are smaller, but the standard deviation is greater, usually on the order of 17 mm. The standard deviation of the residuals from both comparisons depends greatly on the humidity which produces an annual signal because of the much higher humidity variability in the summer months.

The early Cretaceous volcanism occurring along the Sulu orogenic belt, east Shandong Province, demonstrates a bimodal characteristic. The volcanic rocks belong to high-K alkaline series, dominated by alkali basalt, basaltic trachyandesite, latite and trachyte with LILE (e.g. K, Sr and Ba) and LREE enrichment but HFSE depletion (especially for Nb and P) in the primitive mantle-normalized spidergrams and steeply right-declined REE patterns. The enriched initial Sr-Nd isotopic ratios (⁸⁷Sr/⁸⁶Sr = 0.70724 to 0.70750 and ε_Nd(t) = −17.0 to −15.9) of the basaltic samples suggest their origin from an enriched lithospheric mantle, which might had undergone a fluid metasomatism or source mixing by the continental crust during or shortly after the Triassic continental subduction. Significantly negative Nb anomalies observed in the spidergrams and other “crustal” signatures of these rocks suggest an important role of continental material in their petrogenesis. The felsic rocks demonstrate geochemical and Sr-Nd isotopic features (initial ⁸⁷Sr/⁸⁶Sr = 0.70814 to 0.70961 and ε_Nd (t) = −18.9 to −17.0) similar to those of the post-collisional granitic plutons, probably derived from the anatexis of lower/middle crust in response to basaltic magma underplating. The widespread melting of the metasomatized mantle was probably attributed to the thermal perturbation or lithospheric extension induced by the mega-large displacement along the Tan-Lu wrench fault system when northward strike-slipping movement of the Izanagi Plate occurred during the late Mesozoic.

Compaction bands are narrow planar zones of localized purely compressive (without shear) deformation that form perpendicular to the most compressive principal stress. Such bands have been observed in high porosity rocks in the laboratory and in the field. Because compaction presumably decreases permeability, these bands can act as barriers to flow within reservoirs. Reexamination of the results of Rudnicki and Rice (J. Mech. Phys. Solids, 1975) for shear localization, with corrections by Perrin and Leblond (J. Appl. Mech., 1993), reveals that they admit solutions for compaction bands in a range of parameters that is representative of porous rock. Solutions for compaction bands are possible when the inelastic volume deformation is compactive and is associated with a “cap” on the yield surface. The expression for the critical hardening modulus (related to the slope of the shear stress vs. shear strain curve at constant mean stress) at which compaction bands are predicted to form differs from that for shear localization. For parameters representative of porous rock, axisymmetric compression is the most favorable deviatoric stress state for formation of compaction bands. Comparison of conditions for shear localization and compaction band formation suggests that either may occur depending on the stress path and magnitude of the confining stress.

The role of GPS ground station data for the CHAMP Atmospheric Profiling experiment is discussed. The profiling activities at GeoForschungZentrum Potsdam (GFZ) are briefly described and first results of the occultation processing system are presented. The atmospheric excess phase of the occultation link between the CHAMP and the GPS satellite is derived by a double difference method using ground station data. The influence of ground station data on the accuracy of the derived atmospheric profiles is discussed. A relationship between the temperature errors at several heights resulting from errors in atmospheric excess phase is given, e.g. an error of 1mm/s in the time derivative of the excess phase results in a temperature error of 1 K at 30 km. Furthermore, a study was performed to estimate the required data rate of the ground station measurements. In particular the influence of the Selective Availability (SA) termination on May 2, 2000 is emphasized. We conclude that the acquisition rate can be reduced from 1 Hz to 0.1 Hz without loss of information. Simulations of the CHAMP occultation experiment show that the joint Jet Propulsion Laboratory, Pasadena (JPL) & GFZ “high rate & low latency” network enables the processing of globally distributed occultation events with a highly redundant number of ground stations. Latency aspects are studied in view of the future task of providing atmospheric occultation data for operational weather forecast.

The local model of troposphere is constructed on the basis of 7300 individual aerological soundings performed and processed over a period of 10 years in Poznań, Poland. The values of the zenith wet delay (ZWD) calculated using this model are shown to coincide very well with the real values obtained directly from individual aerological soundings, the systematic differences between them are not greater than the error of ZWD determination. Much larger differences were obtained assuming the standard model commonly used and the values estimated from the GPS measurements. The differences are particularly large in summer. The local model of troposphere is concluded to be the optimum for determination of water vapour content from ZWD.

We present here our hourly orbit product and we compare it to other near real-time (NRT) reliable orbits. The comparisons are based on satellite position differences with respect to the final IGS orbits. Experience shows that the use of predicted precise orbits in the NRT processing mode is usually problematic due to poorly determined arcs of only a few satellites. Thus, evaluation of satellite orbits is necessary. Nevertheless, we can find a decreased quality of some arcs also in ultra-rapid products, but the magnitude is significantly lower here. Reducing the predictions to 1–2 hours only, our hourly orbits improve especially the along-track satellite positions.