From statistics of avalanches to microscopic dynamics parameters in a toy model of earthquakes

A toy model of earthquakes — Random Domino Automaton — is investigated in its finite version. A procedure of reconstruction of intrinsic dynamical parameters of the model from produced statistics of avalanches is presented. Examples of exponential, inverse-power and M-shape distributions of avalanches illustrate remarkable flexibility of the model as well as the efficiency of proposed reconstruction procedure.     

Analysis of spatial distribution of mining tremors occurring in Rudna copper mine (Poland)

The distribution of mining tremors is strictly related to the exploitation progress of mining works and, consequently, to the local stress field. In case the distribution is known, it is possible to determine future area of intensive seismicity in exploited mining panel. In the paper, an analysis of working face-to-tremor distance for Rudna copper mine in Poland is presented. In order to develop a spatial model of tremors’ occurrence in the exploited mine, the seismicity of four mining sections in the five-month period was investigated and the tremors’ distribution was obtained. It was compared with the spatial distribution of tremors in coal mines found in the literature. The results show that the places where tremors mostly occur — the vicinity of the face, in front of it — coincide with the high-stress area predicted by literature models. The obtained results help to predict the future seismic zone connected with planned mining section, which can be used in seismic hazard analysis.     

Modelling of Shape Changes of the Nuclei of Comets C/1995 O1 Hale–Bopp and 46P/Wirtanen Caused by Water Ice Sublimation

The aim of this modelling work is to assess shape changes of cometary nuclei caused by sublimation of ices. The simplest possible model is assumed with the nucleus being initially spherical and its thermal conductivity being neglected. We have calculated the time-dependent sublimation flux versus cometographic latitude. If the rotation axis of the comet is inclined to the orbital plane, then sublimation leads to non-symmetrical changes of the nucleus shape. Calculations were performed for the nuclei of comets Hale–Bopp and Wirtanen.     

A Study of Non-Gravitational Effects of Comet C/1995 O1 HALE–BOPP

The role of non-gravitational forces in the evolution of orbitalmotion of C/1995 O1 (Hale–Bopp) has been investigated. Inorbital calculations the observational material covering theperiod from April 1993 up to August 2001 was used. To model thenon-gravitational acceleration, observed and theoretical profilesof the H₂O production rates were employed. A set of forcedprecession models of a rotating cometary nucleus consistent withthe observed spin axis orientation was fitted to positionalobservations. The non-gravitational models allowed us to constrainthe mass and radius of the comet. The orbitalevolution of Comet Hale–Bopp was investigated over ±400 k yusing two sets of randomly varied orbital elements wellrepresenting all positional observations in the pure gravitationalcase, as well as in the non-gravitational case. The calculationsshowed that the comet's motion is predictable only over an interval ofa few orbital periods. The statistical conclusions changesignificantly when non-gravitational effects are included in the analysis.     

Rapid migration of heavy metals and <Superscript>137</Superscript>Cs in alluvial sediments,Upper Odra River valley,Poland

The studies presented explore post-depositional changes of zinc, cadmium, lead, manganese and ¹³⁷Cs distribution in alluvial sediments accumulated in the upper Odra River valley in southern Poland. The rate of these changes was estimated by comparing metal and ¹³⁷Cs distributions in four vertical alluvial profiles with a history of river pollution and sediment deposition. The untypical ¹³⁷Cs distribution with peaks in the surface 40–60 cm and lower down, even at a depth of 2.5 m in strata deposited before the beginning of nuclear tests in 1954, indicates rapid post-depositional migration of this isotope from the surface and its retention in lower, less permeable layers. Moreover, the highest concentrations of lead, zinc and cadmium were found at a depth of 4 m in sediments accumulated in the mid-nineteenth century in spite of the growth of industrialization and the pollution of the Odra River with heavy metals until the end of the twentieth century. The post-depositional changes in heavy metals and ¹³⁷Cs are rapid in comparison with the slow element migration usually observed in uninundated soils. This difference is explained by the frequent and easy infiltration of polluted river water into the gravelly and sandy sediments present in the profiles.     

Unusual reaction of diatom assemblage on climate changes during the last millennium: a record from Spitsbergen lake

A sediment core from the Arctic Revvatnet (Hornsund area, SW Spitsbergen, Svalbard) provided data on environmental changes over the last 3100 years. Diatom analysis showing the domination of planktonic Cyclotella forms suggested good edaphic conditions until the middle of the nineteenth century, even during the Little Ice Age. A thermally stratified and relatively stable water column with good mixing allowed small, less heavily silicified Cyclotella sensu lato to develop during this time. The climate warming at the beginning of the twentieth century induced intensification of erosion processes in the catchment of the lake and caused an increase in the sedimentation rate. These processes have caused a lack of thermal stratification by disturbances in the water column and an increase of nutrients, consequently driving changes in the diatom species composition, which became dominated by benthic forms. In this period, almost all planktonic taxa disappeared or abruptly decreased in frequency. Higher temperatures accelerated the melting of nearby glaciers, which caused an increase in the activity of diatoms typical of running waters. Also a few Cladocera species appeared at the first time in the youngest samples.