The effect of a vertical temperature gradient in the lithosphere on seismic and tectonic waves     

B. I. Birger 《Izvestiya Physics of the Solid Earth》2008,44(9):738-747

A linear analysis of the stability of the lithosphere considered as a viscoelastic layer with an equilibrium vertical gradient of temperature is carried out. The problem is solved with a complete system of linearized equations of a continuous medium represented in the dimensionless form and containing a set of dimensionless parameters that determine thermomechanical properties of the lithosphere. As a result of the stability analysis, decrements are found that give the time dependence of perturbations and correspond to high-frequency seismic waves and low-frequency tectonic waves. The frequency and velocity of seismic waves are determined by the elasticity and inertial properties of the lithosphere, and their attenuation, by viscous properties of the lithosphere. The temperature gradient existing in the lithosphere influences seismic waves very weakly. On the contrary, the pattern of tectonic waves is controlled by the temperature gradient and viscous properties, while the effect of elastic and inertial properties on these waves is negligibly small. The stability of a viscoelastic lithosphere is examined using such rheological models as the Maxwell, standard linear, and Andrade media (the frequency of tectonic waves is zero in the Maxwell medium).  相似文献   

Structure and U–Pb zircon geochronology in the Variscan foreland of SW Sardinia,Italy     

P. Pavanetto  A. Funedda  C. J. Northrup  M. Schmitz  J. Crowley  A. Loi 《Geological Journal》2012,47(4):426-445

New field mapping, U–Pb zircon geochronology and structural analysis of the southernmost Sardinia metamorphic basement, considered a branch of the Variscan foreland, indicate that it is, in part, allochthonous and was structurally emplaced within the foreland area, rather than being older depositional basement beneath the foreland succession. The Bithia Formation, classically considered part of the ‘Southern Sulcis metamorphic Complex’ (and here termed the Bithia tectonic unit, or BTU), is a greenschist facies metamorphic unit commonly interpreted as Precambrian in age. New geochronology of felsic volcanic rocks in the BTU, however, yield a U–Pb zircon age of 457.01 ± 0.17 Ma (Upper Ordovician). Thus, the depositional age of the unit is younger than the weakly metamorphosed Lower Cambrian rocks of the adjacent foreland succession. New detailed mapping and analysis of the field relationships between the BTU and foreland succession indicates that their contact is a mylonitic shear zone. The metamorphic character, general lithology, and deformational history of the BTU are similar to those of units in the Variscan Nappe Zone located northeast of the foreland area. We reinterpret the BTU as a synformal klippe of material related tectonically to the Variscan Nappe Zone. We infer that it was thrust over and became infolded into the foreland during late stages of the Variscan contractional deformation. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Towards an integrated arid zone water management using simulation-based optimisation   总被引：5，自引：3，他引：2  

Jens Grundmann  Niels Schütze  Gerd H. Schmitz  Saif Al-Shaqsi 《Environmental Earth Sciences》2012,65(5):1381-1394

For ensuring both optimal sustainable water resources management and long-term planning in a changing arid environment, we propose an integrated Assessment-, Prognoses-, Planning- and Management tool (APPM). The new APPM integrates the complex interactions of the strongly nonlinear meteorological, hydrological and agricultural phenomena, considering the socio-economic aspects. It aims at achieving best possible solutions for water allocation, groundwater storage and withdrawals including saline water management together with a substantial increase of the water use efficiency employing novel optimisation strategies for irrigation control and scheduling. To obtain a robust and fast operation of the water management system, it unites process modeling with artificial intelligence tools and evolutionary optimisation techniques for managing both water quality and quantity. We demonstrate some key components of our methodology by an exemplary application to the south Al-Batinah region in the Sultanate of Oman which is affected by saltwater intrusion into a coastal aquifer due to excessive groundwater withdrawal for irrigated agriculture. We show the effectiveness and functionality of a new simulation-based water management system for the optimisation and evaluation of different irrigation practices, crop pattern and resulting abstraction scenarios. The results of several optimisation runs indicate that due to contradicting objectives, such as profit-oriented agriculture versus aquifer sustainability only a multi-objective optimisation can provide sustainable solutions for the management of the water resources in respect of the environment as well as the socio-economic development.  相似文献   

Barium, SiO₂ (excess), and P₂O₅ as proxies of biological productivity in the Middle East during the Palaeocene and the latest Palaeocene benthic extinction event     

Birger Schmitz  Stella D. Charisi  Elisabet I. Thompson  Robert P. Speijer 《地学学报》1997,9(2):95-99

The distribution of barium and other elements related to biological productivity has been studied in two Palaeocene sections from the Middle East. In the bathyal Ben Gurion section, Israel, Ba* (= Ba/Al₂O₃× 15%) concentrations are low, in the range 0.04% to 0.3% in the lower Palaeocene, and very high, 1% to 2%, throughout most of the upper Palaeocene. In the neritic Gebel Aweina section in Egypt Ba* values are low, < 0.1%, throughout the entire Palaeocene. The Ba* enrichments at Ben Gurion and their correlations with increases in P₂O₅ and opaline silica, and local and global δ¹³C maxima, indicate that upwelling and high productivity were important in this region during the late Palaeocene. The absence of Ba* enrichments in the shallower Gebel Aweina section probably reflects the strong depth dependence of biobarium deposition. In the uppermost Palaeocene, at the level where the global benthic extinction event is registered, Ba* concentrations in the Ben Gurion section increase to anomalous 6%. which suggests that upwelling and possibly wind strengths intensified during this event. The results speak against deep-water formation in this region since downwelling and not upwelling is required.  相似文献   

Application of the Lorenz equations for studying thermal convection in the lithosphere     

B. I. Birger 《Izvestiya Physics of the Solid Earth》2011,47(6):541-554

Stationary solutions including wave solutions with constant amplitudes are found for nonlinear equations of thermal convection in a layer with nonlinear rheology. The solution is based on the Fourier expansion of unknown velocities and temperatures with only the first and first two terms retained in the velocity and temperature series, respectively. This method, which can be regarded as the Lorenz method, yields the Lorenz equations that fairly well describe the thermal convection in a layer with Newtonian rheology if the Rayleigh number is not very large. The obtained generalization of the Lorenz equations to the case of an integral (having a memory) nonlinear rheology implies that only the first term is retained in the Fourier series for the stress components, i.e., the nonlinear rheological equation is harmonically linearized. However, in the Fourier series of temperature, it is essential to keep the second term: this term, which is independent of the horizontal coordinate, models the thermal boundary layer that characterizes the developed convection. We constructed the bifurcation curves that describe the stationary convection in the nonlinear integral medium simulating the rheology of the mantle, and analyzed the stability of stationary convective flows. The Lorenz method is applied to study small-scale thermal convection in the lithosphere of the Earth.  相似文献   

The Main Ostrava Whetstone: composition, sedimentary processes, palaeogeography and geochronology of a major Mississippian volcaniclastic unit of the Upper Silesian Basin (Poland and Czech Republic)     

Jakub Jirásek  Lada Hýlová  Martin Sivek  Janusz Jureczka  Karel Martínek  Ivana Sýkorová  Mark Schmitz 《International Journal of Earth Sciences》2013,102(4):989-1006

The Main Ostrava Whetstone (MOW) is an important lithostratigraphic horizon of the Late Carboniferous sedimentary fill of the late Palaeozoic foreland Upper Silesian Basin. It is the largest and best-identified volcanogenic horizon in the basin, reaching thicknesses of 15.3 m and occupying an area of ca 2,973 km² and a volume after lithification of 9.24 km³. It consists of volcanic materials transported to the basin probably by an aeolian process. Just after sedimentation, these materials were redeposited a short distance away in a shallow water environment. Granularity corresponds to a range from argillaceous siltstones to fine-grained sandstones. The components are dominated by glass shards replaced by clay minerals (mixed illite–smectite structures) in addition to quartz of volcanogenic and terrigenous origins. Sanidine and a plagioclase close to albite are also present. The sedimentary structures, micro-structures and composition of the MOW indicate variable and dynamic hydrodynamic conditions. The MOW represents a series of flooding events, which could be connected with unusual rainfall. Such major flooding events were most likely induced by volcanic eruptions. The available drill-core log data were used to construct a digital model of the whetstone, which showed an east–west zonality in the thicknesses, with the majority being synsedimentary. CA-TIMS U–Pb dating the volcanogenic zircons yields an age of 327.35 ± 0.15 Ma. The source location of the volcanogenic material is not clear; however, it is presumed to have been located in the west of the Upper Silesian Basin.  相似文献   

Meteorological Observations in 1999 at the Arctic Station,Qeqertarsuaq (Godhavn), Central West Greenland/Evidence of a warmer climate around AD 600, Mittivakkat Glacier,South East Greenland     

Birger Ulf Hansen  Niels Nielsen  Ole Humlum  Bent Hasholt 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):85-90

In october 1990 an automatic weather station was established at the Arctic Station (65° 15', 53°31'W), Qeqertarsuaq (Godhavn), Central West Greenland. The Station register parameters each 20 minutes, and the paramters have been described in an earlier paper in this journal by Nielsen et al.(1995). The present paper summarizes meteorological parameters during 1999.

During a field campaign in 1999, woody remains from Salix glauca were found on a nunatak, 515 m. a.s.l. on the Mittivakkat Glacier, South East Greenland. Radio carbon dating determined the age of a wood sample to AD 640. Together with analyses of macroscopic botanical remains and insect rests in peaty material found nearby, these results indicate, that a warmer climate prevailed near the glacier around AD 600. These findings are in accordance with temperature records based on studies of ice cores from the Greenland Ice sheet.  相似文献   

Meteorological observations 2006 and ground temperature variations over 12-year at the Sermilik Station,Ammassalik Island,Southeast Greenland     

Sebastian H. Mernild  Bent Hasholt  Bjarne H. Jakobsen  Birger U. Hansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):153-161

Geografisk Tidsskrift, Danish Journal of Geography 108(1):153–161, 2008

Meteorological stations have been in operation since 1993 at the Sermilik Research Station (65°40′N, 38°10′W), Ammassalik Island, Southeast Greenland. This note presents meteorological observations for the calendar year 2006 from the two meteorological stations: Station Nunatak (515 m a.s.l.) and Station Coast (25 m a.s.l.). The year 2006 record is not complete due to a temporal break down of Station Coast (from end-of June through beginning of August). Special focus is given to ground temperature measurements at the meteorological Station Nunatak (1994–2006) 0.1 and 0.3 m below the surface. Data are presented to illustrate the intra- and inter-annual temperature variability and possible trends in the upper part of the soil.  相似文献   

Accumulation of elastic strains in the upper crust on the locked transform faults and the tectonomagnetic effect     

B. I. Birger 《Izvestiya Physics of the Solid Earth》2016,52(6):928-935

Plate tectonics only allows small deformations in the lithospheric plates. The laboratory experiments with the rock specimens show that the creep is transient when the creep strain is at most 1%. Hence, if we assume that the creep strain in the lithospheric plates is below this threshold, the creep is transient. The present paper addresses the role of the elastic, brittle (pseudo-plastic), and creep rheology of the lithosphere during the accumulation of elastic shear strains on the locked faults in the Earth’s crust, i.e., during the process of preparation of the earthquakes. The effective viscosity characterizing the transient creep is lower than that under the steady-state creep and it depends on the characteristic time of a given process. The characteristic duration of the stress and strain accumulation process in the vicinity of the locked faults is a few dozen years. On these time intervals, the thin upper crustal layer behaves as brittle; the underlying layer behaves as elastic (it is just this layer which accommodates stress accumulation leading to the earthquake), whereas the transient creep is predominant in the lower crust and mantle lithosphere. Transient creep entails nonlinear time dependence of the strains arising in the vicinity of the locked fault in the elastic crust. The perturbations in the magnetic field induced by these strains can be treated as the magnetic precursor of the earthquake.  相似文献   

Erratum to: Monazite trumps zircon: applying SHRIMP U–Pb geochronology to systematically evaluate emplacement ages of leucocratic,low-temperature granites in a complex Precambrian orogen     

Agnieszka?M.?PiechockaEmail authorView author&#;s OrcID profile  Courtney?J.?Gregory  Jian-Wei?Zi  Stephen?Sheppard  Michael?T.?D.?Wingate  Birger?Rasmussen 《Contributions to Mineralogy and Petrology》2017,172(9):73

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