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991.
The Aluto-Langano geothermal field is located in the central southern portion of Ethiopia within the Ethiopian Rift Valley.
The gravity of the area was surveyed in an attempt to delineate the subsurface structure and to better understand the relationship
between the geothermal systems and the subsurface structure. The gravity data were analyzed using integrated gradient interpretation
techniques, such as the Horizontal Gradient (HG), Source Edge Detection (SED), and Euler Deconvolution (ED) methods. These
techniques detected many faults that were compared with the mapped faults in the surface geology. The results of the present
study will lead to an improved understanding of the geothermal system in the study area and aid the future geothermal exploration
of the area. 相似文献
992.
通过对六安地区BBVS-60与KS-2000地震计系统记录台基噪声功率谱密度计算,和正弦标定数据处理,尤其通过对仪器系统记录地震震相分析,比较两种类型宽频带地震计系统的性能差异,为台站地震记录震相分析与仪器维护提供技术支持. 相似文献
993.
对拟建设的新疆且末地磁台进行场址勘选,采取十字剖面测量和密跨度测量方法进行地磁场总强度F测量,对测量结果进行初步分析.分析结果表明,且末地磁台的地质条件、磁场梯度分布和背景噪声环境等地磁观测环境条件,符合国家地磁台建设规范的要求,适宜地磁基准台站建设. 相似文献
994.
The effect exerted by the seabed morphology on the flow is commonly expressed by the hydraulic roughness, a fundamental parameter
in the understanding and simulation of hydro- and sediment dynamics in coastal areas. This study quantifies the hydraulic
roughness of large compound bedforms throughout a tidal cycle and investigates its relationship to averaged bedform dimensions.
Consecutive measurements with an acoustic Doppler current profiler and a multibeam echosounder were carried out in the Jade
tidal channel (North Sea, Germany) along large compound bedforms comprising ebb-oriented primary bedforms with superimposed
smaller secondary bedforms. Spatially averaged velocity profiles produced log-linear relationships which were used to calculate
roughness lengths. During the flood phase, the velocity profiles were best described by a single log-linear fit related to
the roughness created by the secondary bedforms. During the ebb phase, the velocity profiles were segmented, showing the existence
of at least two boundary layers: a lower one scaling with the superimposed secondary bedforms and an upper one scaling with
the ebb-oriented primary bedforms. The drag induced by the primary bedform during the ebb phase is suggested to be related
to flow expansion, separation, and recirculation on the downstream side of the bedform. Three existing formulas were tested
to predict roughness lengths from the local bedform dimensions. All three predicted the right order of magnitude for the average
roughness length but failed to predict its variation over the tidal cycle. 相似文献
995.
In this paper we present a model for the growth of a maar-diatreme complex in a shallow marine environment. The Miocene-age
Costa Giardini diatreme near Sortino, in the region of the Iblei Mountains of southern Sicily, has an outer tuff ring formed
by the accumulation of debris flows and surge deposits during hydromagmatic eruptions. Vesicular lava clasts, accretionary
lapilli and bombs in the older ejecta indicate that initial eruptions were of gas-rich magma. Abundant xenoliths in the upper,
late-deposited beds of the ring suggest rapid magma ascent, and deepening of the eruptive vent is shown by the change in slope
of the country rock. The interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts
of variable size and amount. The occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle-lower part
of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity. Intrusions of nonvesicular
magma, forming plugs and dikes, occur on the western side of the diatreme, and at the margins, close to the contact between
breccia deposits and country rock; they indicate involvement of volatile-poor magma, possibly during late stages of activity.
We propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a
rampart that isolated for a short time the inner crater from the surrounding marine environment. This allowed explosive activity
to draw down the water table in the vicinity of the vent and caused deepening of the explosive center. A subsequent decrease
in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water, at which time the hyaloclastite
was deposited. Emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and
unconsolidated, locally forming peperites. The sheltered, low-energy lagoon filled with marine limestones mixed with volcaniclastic
material eroded from the surrounding ramparts. Ultimately, lagoonal sediments accumulated in the crater until subsidence or
erosion of the tuff ring caused a return to normal shallow marine conditions. 相似文献
996.
A knowledge of seismic wave velocities in the sedimentary cover is of great importance for interpreting reflection and refraction
seismic data, deep seismic soundings and regional and global seismic tomography. This is particularly true for regions characterized
by significant thicknesses and a complex sedimentary cover structure. This paper presents the results of an analysis of seismic
P-wave velocities in the sedimentary cover of Poland, a complex area of juxtaposition of major tectonic units: the Precambrian
East European Craton, the Palaeozoic Platform of Central and Western Europe, and the Alpine orogen represented by the Carpathian
Mountains. Based on vertical seismic profiling data from 1188 boreholes, the dependence of velocity versus depth was determined for regional geological units and for successions from the Tertiary and Quaternary to the Cambrian.
The data have been approximated by polynomials, and velocity-depth formulas are given down to 6000 m depth. The velocities
in the sedimentary cover have been compared with those from other areas in Europe. 相似文献
997.
Leszek Czechowski 《Acta Geophysica》2012,60(4):1192-1212
Thermal history of Rhea from the beginning of accretion is investigated. We developed a numerical model of convection combined with the parameterized theory. Large scale melting of the satellite’s matter and gravitational differentiation of silicates from ices are included. The results are confronted with observational data from Cassini spacecraft that indicate minor differentiation of the satellite’s interior. We suggest that partial differentiation of the satellite’s interior is accompanied (or followed) by the process of light fraction uprising to the surface. The calculation indicates that the partial differentiation of the matter of the satellite’s interior is possible only for narrow range of parameters. In particular, we found that the time from the formation of CAI (calciumaluminum rich inclusions in chondrites) to the end of accretion of Rhea is in the range of 3–4 My. 相似文献
998.
Sebastian Sobek Roland Zurbrügg Ilia Ostrovsky 《Aquatic Sciences - Research Across Boundaries》2011,73(3):355-364
Even though lake sediments constitute a significant long-term carbon sink, studies on the regulation of carbon burial in lakes
sediments have, to date, been surprisingly few. We investigated to what degree the organic carbon (OC) being deposited onto
the bottom of Lake Kinneret (Israel) is buried in the sediment at four different sites with varying degrees of oxygenation
and varying supply of allochthonous particles from the River Jordan. For estimation of the OC burial efficiency (OC BE), i.e.,
the ratio between buried and deposited OC, we calculated OC burial from dated sediment cores, and calculated OC deposition
using three different approaches. Calculation of OC deposition from sediment trap-derived mass deposition rates multiplied
with the OC content of surface sediment yielded OC BE values that were at odds with published values for sediments dominated
by autochthonous OC sources. Calculation via sediment trap data on organic matter flux collected within the Lake Kinneret
monitoring program, as well as calculation of OC deposition as the sum of OC burial plus OC mineralization, returned fairly
congruent estimates of OC BE (range 10–41%), but only if the sediment trap data were corrected for the proportion of resuspended
particles in the traps. Differences in OC BE between sites were small, indicating that OC source (common to all sites) was
a more important regulator of OC BE in Lake Kinneret than oxygen exposure or mineral particles characteristics. 相似文献
999.
1000.
Despite vigorous tidal and wind mixing, observations in an estuarine tidal inlet in the Wadden Sea show that during part of
the tidal cycle, vertical stratification and internal waves may still develop. Acoustic Doppler current profiler (ADCP) and
conductivity, temperature, depth observations, collected over the past 6 years at 13 h anchor stations (ASs), reveal that
these occur especially during slack tide, when there is little wind and large freshwater discharge from nearby Lake IJssel.
Measurements with a moored ADCP show that in the same tidal phase, strong cross-channel circulation develops, which may suddenly
reverse circulation sense due to passing density fronts. In the vertically stratified phase that follows after the front passage,
propagating mode-one solitary internal waves are observed. These are resonantly generated during decelerating tidal ebb currents
when the (shear) flow passes a transcritical regime (Froude number equal to 1). A combination of photographs (including one
from the International Space Station), bathymetric data, and ASs data leads to the discovery of yet another source of internal
waves in this area, produced during slackening tide by propagating lee waves that develop over a deep trench. We suggest that
both the cross-channel circulation as well as the (solitary) internal waves may locally be of importance for the (re)distribution
and transport of sediments and nutrients and may influence tidally averaged transports. 相似文献