Fracture risk estimation for Swedish earthquakes

For Swedish earthquakes, the average magnitude increases gently with the focal depth, whereas the seismic wave energy exhibits significant maxima at 15, 23 and 28 km depth. The earthquake fracture risk is estimated to be about 10^?6 for an underground storage facility in a carefully selected site.     

Low temperature spectral studies of Mn3+-bearing andalusite and epidote type minerals in the range 30000–5000 cm−1

Polarized absorption spectra of natural piemontite (Ca_1.802Mn ²⁺_0.178 Mg_0.025) (Mn ³⁺_0.829 Fe ³⁺_0.346 Al_1.825) [(Si_2.992Al_0.008) O₁₂OH], viridine (Al_1.945Mn ³⁺_0.033 Fe ³⁺_0.063 Mg_0.003) [O|Si_0.970 O₄], and kanonaite (Al_1.291Mn ³⁺_0.682 Fe ³⁺_0.019 ) [O|Si_1.006 O₄] were measured at 295 and ca. 100 K. For piemontite, lowering the temperature resulted in a sharpening of broad bands in the 10 000–25 000 cm⁻¹ region supporting their assignment to single ion Mn³⁺ in M3 non-centrosymmetric sites.

Alternatively, in kanonaite, temperature behaviour pointed to a slightly stronger influence of vibronic coupling on strong bands near 16 000 and 22 000 cm⁻¹, which supported an interpretation of Mn³⁺ in nearly centrosymmetric M1 sites. Measurements at ca. 100 K show pronounced fine structure in the viridine spectra which is attributed to Fe³⁺. The ɛ values for Mn³⁺ spin-allowed bands in the three minerals lie in the range 18 to 227 [1·g-atom⁻¹·cm⁻¹].

For the same band and polarisation, ɛ values in Mn³⁺-bearing andalusite-type minerals viridine and kanonaite are the same, which indicates an absence of strong magnetic coupling effects between Mn³⁺ ions in the andalusite type structure down to ca. 100 K.

In silicates, the high ɛ values for Mn³⁺ spin-allowed bands, in comparison to those obtained for Fe²⁺ spin-allowed bands from sites of “similar distortion”, is attributed to a higher degree of covalency in the Mn³⁺-O bonds compared to the Fe²⁺-O bonds, as a result of the higher valence state of manganese.

     

Experimental determination of the temperature and pressure dependence of the Fe-Mg partition coefficient for coexisting garnet and clinopyroxene

An experimental study initiated to calibrate the distribution coefficient \(K_D = \frac{{({\text{FeO}}/{\text{MgO}})_{{\text{ga}}} }}{{{\text{(FeO}}/{\text{MgO)}}_{{\text{cpx}}} }}\) in eclogites as a geothermometer has been done on (a) a mineral mis, (b) a glass of the typical tholeiite composition and (c) a series of glasses of tholeiite compositions with \(6.2 < \frac{{100{\text{Mg}}}}{{{\text{Mg}} + {\text{Fe}}^{ + + } }} < 93.\) The mineral mix was found to be unsuitable as reactant due to incomplete equilibration but the minimum K _D of the mineral mix and the K _D from glass of tholeiite composition are identical within experimental uncertainty. These data constitute a reversal of the garnet/clinopyroxene partition relationship and provide justification of the use of glass as a reactant for the project. To eliminate any uncertainty in interpretation of mineral analyses due to possible variation in Fe⁺⁺⁺/Fe⁺⁺ between runs, experiments were carried out in iron capsules on the nine tholeiite glasses, thus maintaining iron as Fe⁺⁺. Microprobe analytical techniques yielded mineral analyses of comparable accuracy to analyses of natural phases for experiments within the temperature range from 600° C to 1500° C and a pressure range from 20 kb to 40 kb. It has been shown that for \(6.2 < \frac{{100{\text{Mg}}}}{{{\text{Mg}} + {\text{Fe}}^{ + + } }} < 85\) , the bulk chemical composition does not perceptibly affect the K _D value. At 30 kb the K _D value ranges from 18.0 at 600° C to 1.45 at 1400° C, defining the linear relationship in a ln K _D vs 1/T(°K) plot. The pressure dependence of the K _D -value has been shown to be greater than previously predicted. There is a straight line relationship in ln K _D vs Pressure (Kb) between 20 and 40 kb at constant temperature (1100°C). This enables us to determine K _D =fn (T, P) and \(T(^\circ {\text{K}}) = \frac{{3686 + 28.35 \times P({\text{Kb}})}}{{\ln K_D + 2.33}}\) . This expression uniquely determines the temperature of equilibration of natural eclogites of basaltic bulk composition when the K _D ^ga,cpx is known and a pressure estimate can be given.     

Sm-Nd dating of Seve eclogites,Norrbotten, Sweden — Evidence for early Caledonian (505 Ma) subduction

The Seve Nappes consist of long-transported thrust sheets belonging to the Upper Allochthon within the Scandinavian Caledonides. Eclogites from two different megalenses within the Seve Nappe Complex in Norrbotten (northern Sweden) have been dated with the Sm-Nd method. The two eclogite-bearing megalenses have been subjected to different pressure and temperature conditions during the high-pressure metamorphism. Garnet + omphacite + whole-rock from TS2 within the Tsäkkok Lens give an age of 505±18 Ma (2), I=0.512231±0.000024, MSWD=0.10. Garnet and whole-rock from TS5 and whole-rock TS3 also fall on the above isochron. The composite isochron gives an age of 503±18 Ma (2). These results are interpreted to date the peak of the high-pressure metamorphism (500–630° C and 12–15 kbars) for the Tsäkkok Lens. The eclogites in the Vaimok Lens (at Grapesvarre) were subjected to higher pressure and temperature conditions and more extensive reequilibration during the early cooling stages. Retrograde breakdown-reactions accompanied by retrograde zoning of relict garnet seems to be associated with disturbance of the Sm-Nd isotopic systems. In contrast, a sample with unzoned garnet and well preserved high-pressure mineralogy from Grapesvarre gives a Sm-Nd garnet + omphacite age of 503±14 Ma (2), I = 0.512010±0.000038 (2). The ages for the Seve eclogites are significantly older than the Sm-Nd eclogite dates from the Western Gneiss Region of Norway (WGR), suggesting the existence of at least two eclogite-forming events in the Caledonide Orogen. The younger event has been related to the main continent-continent collision stage of the Caledonian Orogeny, while the older event that led to the production of the Norrbotten eclogites must have taken place several hundred kilometres to the north and in a different tectonic setting more oceanward to the WGR. It appears that the older event (ca. 505 Ma) was restricted to the subduction of dyke-intruded sedimentary cover rocks which are thought to represent the rifted edge of the Baltic continent.     

Models to predict water chemical cluster variables

This study is an attempt to quantify and rank variables of significance to predict mean values of lake pH and related variables (alkalinity, conductivity, hardness, etc.) in small glacial lakes. The work is based on a new and extensive set of data from 95 Swedish lakes and their catchment areas. Several empirical models based on catchment and lake morphometric parameters have been presented. These empirical models can only be used to predict mean values of these variables for lakes of the same type, and these models based on geological map parameters can evidently not be used for highly time-dependent and site-typical predictions. Various hypotheses concerning the factors regulating the mean values of the cluster variables were formulated and tested. Different statistical tests were used to separate random influences from causal. The most important map parameters were: the percent of rocks and open (=cultivated) land in the so-called near area to the lake [as determined with the drainage area zonation (DAZ) method], mean depth, linked to resuspension and the form and size of lakes, relief of the drainage area and lake area. Each of these variables only provides a limited degree of (statistical) explanation of the variability in mean annual values of pH and the water chemical cluster variables among the lakes. The predictability of some of the models can be markedly improved by accounting for the distribution of the characteristics in the drainage area. The variability in mean annual values of pH (and related variables) from other parameters, such as specific anthropogenic load, etc., may then be quantitatively differentiated from the impact of these geological parameters. This paper also gives a simple method to estimate natural, preindustrial reference values of these water chemical variables from the presented models.     

Slow Crack Propagation and Slip Correlations

— The propagation of an interfacial crack through a weak plane of a transparent Plexiglas block is studied experimentally. The toughness is controlled artificially by a sand blasting procedure, and fluctuates locally in space like uncorrelated random noise. The block is fractured in mode I at low speed (10^?7?10^?4 m/s). The crack front is observed optically with a microscope and a high resolution digital camera. During the propagation, the front is pinned by micro-regions of high toughness and becomes rough. Roughness of the crack front is analyzed in terms of self-affinity. The in-plane roughness exponent is shown to be 0.63±0.05. Experimental results are compared to a numerical model. The model reproduces the self-affine behavior of the crack front, i.e., long-range correlations of the roughness. Analogies between mode I and mode III are presented in order to discuss implications of the experimental results for creeping faults. Accordingly, correlations of the slip pattern are shown to exist over scales substantially larger than the asperity sizes.     

浅层土（溶）洞的地震探测问题探讨

对埋深≤30m的土(溶)洞做了理论模型,并对其进行研究(高斯射线束法),再依据三维地震勘探方法,根据我院在工作中的实测成果,指出了土(溶)洞异常的解释理论要点和解释依据,说明了土(溶)洞在实际工作中的复杂多变性。     

The influence of a heavily polluted urban river on the adjacent aquifer systems

 Ankara Creek is often subjected to overflowing of sewage caused by rainfall or direct discharge of raw sewage. Alluvial aquifers adjacent to Ankara Creek and its tributaries have considerable groundwater potential. The present status of groundwater quality is far from drinking water standards. Groundwater contamination in Ankara is suspected to be caused by Ankara Creek which is heavily polluted by raw sewage discharge, surface runoff and other common sources. In order to investigate the influence of heavily polluted Ankara Creek on the groundwater contamination in the adjacent alluvial aquifers, five sampling stations on Ankara Creek and 25 water wells were monitored during 1996. At five different sampling periods, water samples were collected from both surface water and groundwater. Chemical analyses of basic ions, pollution parameters and heavy metals in natural waters were carried out. The organic pollution prevails in Ankara Creek whereas total dissolved solids (TDS) and heavy metal concentrations are considerably low. Starting from the idea that Ankara Creek somewhat influences the groundwater quality and the contaminants in groundwater should attenuate with respect to distance, a series of water wells in a certain area, each having different distance from the creek, were examined using four pollution parameters. It is concluded that Ankara Creek barely influences the aquifer systems in connection. This is attributed to two reasons: rapid attenuation of contaminants due to dilution in groundwater and a blanket of very fine sized materials covering the bottom of Ankara Creek. Received: 28. April 1997 · Accepted: 23. February 1998     

Hekla 1947, 1845, 1510 and 1158 tephra in Finland: challenges of tracing tephra from moderate eruptions

Several cryptotephra layers that originate from Icelandic volcanic eruptions with a volcanic explosivity index (VEI) of ≤ 4 and tephra volumes of < 1 km³ have previously been identified in Northern Europe, albeit within a restricted geographical area. One of these is the Hekla 1947 tephra that formed a visible fall-out in southern Finland. We searched for the Hekla 1947 tephra from peat archives within the previously inferred fall-out zone but found no evidence of its presence. Instead, we report the first identification of Hekla 1845 and Hekla 1510 cryptotephra layers outside of Iceland, the Faroe Islands, Ireland and the UK. Additionally, Hekla 1158 tephra was found in Finland for the first time. Our results confirm that Icelandic eruptions of moderate size can form cryptotephra deposits that are extensive enough to be used in inter-regional correlations of environmental archives and carry a great potential for refining regional tephrochronological frameworks. Our results also reveal that Icelandic tephra has been dispersed into Finnish airspace at least seven times during the past millennium and in addition to a direct eastward route the ash clouds can travel either via a northerly or a southerly transport pathway.