The monthly, seasonal, and annual precipitation trends in the Yangtze river catchment have been detected through analysis of 51 meteorological stations‘ data between 1950-2002 provided by National Meteorological Administration. Results reveal that: 1) Summer precipitation in the Yangtze river catchment shows significant increasing tendency. The Poyanghu lake basin, Dongtinghu lake basin and Taihu lake basin in the middle and lower reaches are the places showing significant positive trends. Summer precipitation in the middle and lower reaches experienced an abrupt change in the year 1992; 2) The monthly precipitation in months just adjoining to summer shows decreasing tendency in the Yangtze river catchment. The upper and middle reaches in Jialingjiang river basin and Hanshui river basin are the places showing significant negative trends; 3) Extreme precipitation events show an increasing tendency in most places, especially in the middle and lower reaches of the Yangtze river catchment. 相似文献
Combining CHAMP satellite magnetic measurements with aeromagnetic and marine magnetic data, the global geomagnetic field has now been modelled to spherical harmonic degree 720. An important tool in field modelling is the geomagnetic power spectrum. It allows the comparison of field models estimated from different data sets and can be used to identify noise levels and systematic errors. A correctly defined geomagnetic power spectrum is flat (white) for an uncorrelated field, such as the Earth's crustal magnetic field at long wavelengths. It can be inferred from global spherical harmonic models as well as from regional grids. Marine and aeromagnetic grids usually represent the anomaly of the total intensity of the magnetic field. Appropriate corrections have to be applied in estimating the geomagnetic power spectrum from such data. The comparison of global and regional spectra using a consistently defined azimuthally averaged geomagnetic power spectrum facilitates quality control in field modelling and should provide new insights in magnetic anomaly interpretation. 相似文献
Wind speed, friction velocity and significant wave height data from the FINO1 platform in the southern German Bight 45 km
off the coast for the years 2004 to 2006 have been evaluated and related to each other. The data show a clear dependence of
the hourly mean wave height to the hourly mean friction velocity and wind speed. Wave heights increase with decreasing stratification
and increasing fetch. Synoptic weather patterns for the highest wave heights in the southern German Bight are determined.
The analysis is made separately for four wind direction sectors. The two strongest storms in the evaluated period, “Britta”
and “Erwin”, are analysed in more detail. Finally, the 50-year extreme significant wave height has been estimated to be about
11 m most probably coming from northerly directions. 相似文献
We present the results of a new genera tion of probabilistic seismic hazard assessment for Switzerland. This study replaces
the previous intensity-based generation of national hazard maps of 1978. Based on a revised moment-magnitude earthquake catalog
for Switzerland and the surrounding regions, covering the period 1300–2003, sets of recurrence parameters (a and b values, M max ) are estimated. Information on active faulting in Switzerland is too sparse to be used as source model. We develop instead
two models of areal sources. The first oriented towards capturing historical and instrumental seismicity, the second guided
largely by tectonic principles and express ing the alterative view that seismicity is less stationary and thus future activity
may occur in previously quiet regions. To estimate three alterna tive a and b value sets and their relative weighting, we introduce a novel approach based on the modified Akaike information criterion,
which allows us to decide when the data in a zone deserves to be fitted with a zone-specific b value. From these input parameters, we simulate synthetic earthquake catalogs of one-million-year duration down to magnitude
4.0, which also reflect the difference in depth distribution between the Alpine Foreland and the Alps. Using a specific predictive
spectral ground motion model for Switzerland, we estimate expected ground motions in units of the 5% damped acceleration response
spectrum at frequencies of 0.5–10 Hz for all of Switzerland, referenced to rock sites with an estimated shear wave velocity
of 1,500 m/s2 in the upper 30 m. The highest hazard is found in the Wallis, in the Basel region, in Graubünden and along the Alpine front,
with maximum spectral accelerations at 5 Hz frequency reaching 150 cm/s2 for a return period of 475 years and 720 cm/s2 for 10,000 years.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
Transient hydrogeochemical anomalies were detected in a granite-hosted aquifer, which is located at a depth of 110 m, north
of the Shillong Plateau, Assam, India, where groundwater chemistry is mainly buffered by feldspar alteration to kaolinite.
Their onsets preceded moderate earthquakes on December 9, 2004 (MW = 5.3) and February 15, 2005 (MW = 5.0), respectively, 206 and 213 km from the aquifer. The ratios [Na+K]/Si, Na/K and [Na+K]/Ca, conductivity, alkalinity
and chloride concentration began increasing 3–5 weeks before the MW = 5.3 earthquake. By comparison with field, experimental and theoretical studies, we interpret a transient switchover between
source aquifers, which induced an influx of groundwater from a second aquifer, where groundwater chemistry was dominantly
buffered by the alteration of feldspar to smectite. This could have occurred in response to fracturing of a hydrological barrier.
The ratio Ba/Sr began decreasing 3–6 days before the MW = 5.0 earthquake. We interpret a transient switchover to anorthite dissolution caused by exposure of fresh plagioclase to
groundwater interaction. This could have been induced by microfracturing, locally within the main aquifer. By comparison with
experimental studies of feldspar dissolution, we interpret that hydrogeochemical recovery was facilitated by groundwater interaction
and clay mineralization, which could have been coupled with fracture sealing. The coincidence in timing of these two hydrogeochemical
events with the only two MW ≥ 5 earthquakes in the study area argues in favor of cause-and-effect seismic-hydrogeochemical coupling. However, reasons
for ambiguity include the lack of similar hydrogeochemical anomalies coupled with smaller seismic events near the monitoring
station, the >200 km length scale of inferred seismic-hydrogeochemical coupling, and the potential for far-field effects related
to the Great Sumatra–Andaman Islands Earthquake of December 26, 2004. 相似文献
Segmentation along convergent margins controls earthquake magnitude and location, but the physical causes of segment boundaries, and their impact on earthquake rupture dynamics, are still poorly understood. One aspect of the 2004 and 2005 great Sumatra–Andaman earthquakes is their abrupt termination along a common boundary. This has led to speculation on the nature of the boundary, its origin and why it was not breached.
For the first time the boundary has been imaged and, with newly acquired marine geophysical data, we demonstrate that a ridge on the subducting Indo-Australian oceanic crust may exert a control on margin segmentation. This suggests a lower plate influence on margin structure, particularly its segmentation. The ridge is masked by the sedimentary cover in the trench. Its most likely trend is NNE–SSW. It is interpreted as a fracture zone on the subducting oceanic plate. A ramp or tear along the eastern flank of the subducting fracture zone beneath Simeulue Island may be considered as an intensification factor in terms of rupture propagation barrier. 相似文献
Software Global Navigation Satellite Systems (GNSS) receivers are those that implement signal correlation processing not in
hardware, but in their software. The main problem for the development of real-time software (SW) multichannel GNSS receivers
is the tremendous amount of calculations to perform signal correlation.
The article reviews recent developments of SW GNSS receivers. The emphasis is made on the computationally effective correlation
processing algorithms and the optimization of processing allocation to the receiver's hardware (HW) and SW.
An architecture is suggested that implements the PRN signals despreading in a special HW preprocessor while all the other
correlation processing functions are still kept in SW. The combination of the most time-consuming processing in HW, and all
signal structure-dependent processing in SW, enables unique flexibility of sophisticated GNSS receiver design based on inexpensive
digital signal processors. ? 2000 John Wiley & Sons, Inc. 相似文献
This work questions, starting from dimensional considerations, the generality of the belief that the marine drag coefficient levels off with increasing wind speed. Dimensional analysis shows that the drag coefficient scales with the wave steepness as opposed to a wave-age scaling. A correlation equation is employed here that uses wave steepness scaling at low aspect ratios (inverse wave steepnesses) and a constant drag coefficient at high aspect ratios. Invoked in support of the correlation are measurements sourced from the literature and at the FINO1 platform in the North Sea. The correlation equation is then applied to measurements recorded from buoys during the passage of hurricanes Rita, Katrina (2005) and Ike (2008). Results show that the correlation equation anticipates the expected levelling off in deeper water, but a drag coefficient more consistent with a Charnock type relation is also possible in more shallower water. Some suggestions are made for proceeding with a higher-order analysis than that conducted here. 相似文献
More than 50 000 tons of CO2 have been injected at Ketzin into the Stuttgart Formation, a saline aquifer, at approximately 620 m depth, as of summer 2011. We present here results from the 1st repeat 3D seismic survey that was performed at the site in autumn 2009, after about 22 000 tons of CO2 had been injected. We show here that rather complex time‐lapse signatures of this CO2 can be clearly observed within a radius of about 300 m from the injection well. The highly irregular amplitude response within this radius is attributed to the heterogeneity of the injection reservoir. Time delays to a reflection below the injection level are also observed. Petrophysical measurements on core samples and geophysical logging of CO2 saturation levels allow an estimate of the total amount of CO2 visible in the seismic data to be made. These estimates are somewhat lower than the actual amount of CO2 injected at the time of the survey and they are dependent upon the choice of a number of parameters. In spite of some uncertainty, the close agreement between the amount injected and the amount observed is encouraging for quantitative monitoring of a CO2 storage site using seismic methods. 相似文献