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71.
The aim of this work was to study the forest fire potential and frequency of forest fires under the projected climate change in Finland (N 60°–N 70°). Forest fire index, generally utilized in Finland, was used as an indicator for forest fire potential due to climatological parameters. Climatic scenarios were based on the A2 emission scenario. According to the results, the forest fire potential will have increased by the end of this century; as a result of increased evaporative demand, which will increase more than the rise in precipitation and especially in southern Finland. The annual number of forest fire alarm days is expected to increase in southern Finland to 96–160 days by the end of this century, compared to the current 60–100 days. In the north, the corresponding increase was from 30 to 36 days. The expected increase in the annual frequency of forest fires over the whole country was about 20% by the end of this century compared to the present day. The greatest increase in the frequency of fires, per 1,000 km2, was in the southernmost part of the country, with six to nine fires expected annually per 1,000 km2 at the end of this century, meaning a 24–29% increase compared to the present day frequencies.  相似文献   
72.
73.
The DACIA-PLAN (Danube and Carpathian Integrated Action on Processes in the Lithosphere and Neotectonics) deep seismic reflection survey was performed in August–September 2001, with the objective of obtaining new information on the deep structure of the external Carpathians nappe system and the architecture of the Tertiary/Quaternary basins developed within and adjacent to the Vrancea zone, including the rapidly subsiding Focsani Basin. The DACIA-PLAN profile is about 140 km long, having a roughly WNW–ESE direction, from near the southeast Transylvanian Basin, across the mountainous south-eastern Carpathians and their foreland to near the Danube River. A high resolution 2.5D velocity model of the upper crust along the seismic profile has been determined from a tomographic inversion of the DACIA-PLAN first arrival data. The results show that the data fairly accurately resolve the transition from sediment to crystalline basement beneath the Focsani Basin, where industry seismic data are available for correlation, at depths up to about 10 km. Beneath the external Carpathians nappes, apparent basement (material with velocities above 5.8 km/s) lies at depths as shallow as 3–4 km, which is less than previously surmised on the basis of geological observations. The first arrival travel-time data suggest that there is significant lateral structural heterogeneity on the apparent basement surface in this area, suggesting that the high velocity material may be involved in Carpathian thrusting.  相似文献   
74.
75.
The influence of the predicted climate warming on soil frost conditions in Finland was studied using a climate scenario based on a Hadley Centre (U.K.) global ocean-atmosphere general circulation model (HadCM2) run. HadCM2 results were dynamically downscaled to the regional level using the regional climate model at the Rossby Centre (Sweden). The future period this study focuses on is the end of the 21st century. The study was limited to ground surface conditions in which snow has been removed. The predicted air temperature rise was interpreted in terms of changes in soil frost conditions using an empirical dependence that was found between measured soil frost depths and the sum of daily mean air temperatures calculated from the beginning of the freezing period. On average the annual maximum soil frost depth will decrease in southern and central Finland from the present approx. 100–150 cm by about 50 cm. In northern Finland the change will be from depths of about 200–300 cm to about 100–200 cm depending on station. The annual maximum soil frost depth in the future would thus be about the same in northern Finland as it is in the current climate in southern Finland. In southern Finland after about 100 years the ground will seldom be frozen in December and even in January there will be no soil frost in about half of the years. In Central and northern Finland the probability of completely unfrozen ground in December–March is very small, even in the future.  相似文献   
76.
A project implemented to study the effects of space weather on the Finnish natural gas pipeline was started in August 1998. The aims of the project were (1) to derive a model for calculating geomagnetically induced currents (GIC) and pipe-to-soil (P/S) voltages in the Finnish natural gas pipeline, (2) to perform measurements of GIC and P/S voltages in the pipeline and (3) to derive statistical predictions for the occurrences of GIC and P/S voltages at different locations in the pipeline network.GIC and P/S voltage were recorded at a compressor station. The GIC measurement was made with two magnetometers, one right above the pipe, and another at the Nurmijärvi Geophysical Observatory about 30 km southwest. The largest GIC since November 1998 has been 30 A. The P/S voltage recording was stopped in May 1999, but GIC is still measured.GIC statistics were derived based on the recordings of the geomagnetic field at Nurmijärvi. The geoelectric field was calculated by using the plane wave model. This field was input to the general pipeline model resulting in the distribution of currents and P/S voltages at selected points in the pipeline. As could be expected, the largest P/S voltage variations occur at the ends of the pipeline network, while the largest GIC flow in the middle parts.  相似文献   
77.
Summary Earthquake shear waves with period around 12.2 min have been lately reported byM. Båth (1958), who suggests that these might be due to torsional vibrations of the whole mantle on some axis through the centre of the earth. An attempt has been made here to put forward a theory which accounts for such vibrations. The general elastokinetic equation for a heterogeneous isotropic medium is solved for a free spherical shell overlying a liquid core, and the solution is investigated for the first two modes. The frequency equation is solved for a shell and the limiting cases of a full sphere and an infinitely thin shell. Application is then made for various approximate mantle models, and periods are found which are in fair agreement with the observed. It is then shown that if the rigidity of the core is taken into consideration a closer agreement with the observed might be attained.
Zusammenfassung Seismische Transversalwellen mit einer Periode von rund 12.2 min sind neulich vonM. Båth (1958) beobachtet worden, der vermutet, dass sie Torsionsschwingungen des ganzen Erdmantels um eine Achse durch das Erdzentrum sind. Ein Versuch wird hier gemacht eine Theorie für solche Schwingungen zu entwickeln. Die allgemeine elastokinetische Gleichung für ein heterogenes, isotropisches Medium wird für eine freie, sphärische Schale über einem flüssigen Kern gelöst, und die Lösung wird für die zwei ersten Schwingungsformen untersucht. Die Frequenzgleichung wird für eine Schale und für die Grenzfälle einer ganzen Sphäre und einer unendlich dünnen Schale gelöst. Die Lösungen werden dann auf verschiedene, approximative Mantel-Modellen angewendet, und Perioden werden gefunden, die ziemlich gute Übereinstimmung mit der beobachteten Periode zeigen. Es wird danach gezeigt, dass, falls die Righeit des Erdkerns in Betracht gezogen wird, eine noch bessere Übereinstimmung mit der beobachteten Periode erreicht wird.


This research was supported by Eng.Herbert E. Linden of Beverly Hills, California.  相似文献   
78.
Summary An explicit solution is obtained for the system of equations describing the spheroidal motion in a homogeneous, isotropic, gravitating, elastic medium possessing spherical symmetry. This solution is used to derive the Green's dyad for a homogeneous gravitating sphere. The Green's dyad is then employed to obtain the displacement field induced by tangential and tensile dislocations of arbitrary orientation and depth within the sphere.Notation G Gravitational constant - a Radius of the earth - A o =4/3 G - Perturbation of the gravitational potential - Circular frequency - V p ,V s Compressional and shear wave velocities - k p =/V p - k s =/V s - k p [(2.8)] - , [(2.17)] - f l + Spherical Bessel function of the first kind - f l Spherical Hankel function of the second kind - x =r - y =r - x o =r o - y o =ro - x =r k s - y =r k p - x o =r o k s - y o =r o k p - =a - =a - [(5.17)] - m, l   相似文献   
79.
The seismicity of Israel has been evaluated from documented earthquake records of the present century and two years of routine monitoring of microearthquake activity by means of eleven stations spreading from the Gulf of Elat to northern Galilee.

The Dead Sea rift asserts itself as the tectonic feature that accounts for the seismicity of our region. The activity peaks at zones where the fault branches sideways or at a junction with other fault systems. In particular, the crescent fault of Wadi Faria seems to be a zone of high strain accumulation. This is probably the site of many historical earthquakes which caused inland and coastal damage. It is thus found that the most active fault today which constitutes the greatest seismic risk to Israeli metropolitan areas extends along the Dead Sea rift from 31.2°N to 33.4°N.

The seismicity around the Dead Sea conforms with the proposed movement along en-echelon faults. While the southwest segment is presently inactive, most of the seismic activity there is limited to the neighbourhood of its eastern shore with extreme seismicity at its southern tip near the prehistorical site of Bab-a-Dara'a. The seismicity of the Arava is much lower than the Jordan-Dead Sea section. The seismicity of the Israeli coast was found to be somewhat higher than that of the Arava.  相似文献   

80.
In this study we estimated the amount of carbon (C) stored in the forest growing stock and in wood-based products, and the C-sequestration capacity of the forest sector in Finland. Comparison of different management and utilization options for forest resources over the period 1990-2039 indicates that C is stored more efficiently in standing timber than in wood-based products. This implies that an appropriate increase in the length of the rotation in forestry could be optimal for balancing the needs of forest resources for C sequestration and timber production. Increased use of wood, based on sustainable use of forest resources, to substitute for fossil fuels and materials, could decrease the overall C emissions. Release of sequestered C back to the atmosphere can be delayed by prolonging product lifespans, by increasing recycling, or by disposing of discarded products in landfills. To delay C release, and affect the C balance, however, these changes should be substantial.In 1990, the net C balance of the growing stemwood stock was 5.5 Tg C/a, which increased to 16.3 Tg C/a by 2039 if in the future the use of wood would be at the level of the late 1980s. Increased use of wood resulted in a balance of 6.6 Tg C/a or -0.2 Tg C/a, depending on the extent of the use of wood. The average C balance in wood products for the whole period was 3.9, 5.6 or 6.6 Tg C/a, respectively. Changes in production capacity, and consideration of timber and product import and export decreased the average balance from 6.6 Tg C/a to 0.9–1.3 Tg C/a. By comparison, emission from the use of fossil fuels in 1990 C was 14.5 Tg C/a.  相似文献   
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