A tentative model for the explanation of Båth law using the order parameter of seismicity in natural time

Using the order parameter of seismicity defined in natural time, we suggest a simple model for the explanation of Båth law, according to which a mainshock differs in magnitude from its largest aftershock by approximately 1.2 regardless of the mainshock magnitude. In addition, the validity of Båth law is studied in the Global Centroid Moment Tensor catalogue by using two different aftershock definitions. It is found that the mean of this difference, when considering all the pairs mainshock-largest aftershock, does not markedly differ from 1.2 and the corresponding distributions do not depend on the mainshock’s magnitude threshold in a statistically significant manner. Finally, the analysis of the cumulative distribution functions provides evidence in favour of the proposed model.     

Statistical Significance of Minimum of the Order Parameter Fluctuations of Seismicity Before Major Earthquakes in Japan

In a previous publication, the seismicity of Japan from 1 January 1984 to 11 March 2011 (the time of the \(M9\) Tohoku earthquake occurrence) has been analyzed in a time domain called natural time \(\chi.\) The order parameter of seismicity in this time domain is the variance of \(\chi\) weighted for normalized energy of each earthquake. It was found that the fluctuations of the order parameter of seismicity exhibit 15 distinct minima—deeper than a certain threshold—1 to around 3 months before the occurrence of large earthquakes that occurred in Japan during 1984–2011. Six (out of 15) of these minima were followed by all the shallow earthquakes of magnitude 7.6 or larger during the whole period studied. Here, we show that the probability to achieve the latter result by chance is of the order of \(10^{-5}\). This conclusion is strengthened by employing also the receiver operating characteristics technique.     

Modified capacity design rule for columns in tall steel MRFs with linear viscous dampers within the framework of Eurocode 8

Seismic design codes enforce a set of capacity design rules for steel moment-resisting frames (MRFs) to promote a ductile sway plastic mechanism that involves plastic hinges in beams and column bases. Previous research showed that these capacity design rules may not be effective for tall steel MRFs with viscous dampers under strong earthquakes due to high axial forces in columns. To address this issue, steel MRFs with linear viscous dampers of different stories are designed according to Eurocode 8 along with using a slightly modified conservative capacity design rule. According to this rule, the axial force for the capacity design of a column in the force path of viscous dampers is calculated as the envelope of the axial force from the peak drift state, and, the axial force from the peak velocity state times a scale factor. This envelope axial force value along with the bending moment and shear force from the peak drift state are used to carry out the capacity design of the column by using the formulae of Eurocode 8, i.e. in the same way with a column of a steel MRF without dampers. Incremental dynamic analyses for 44 earthquake ground motions show that the modified conservative capacity design rule results in steel MRFs with viscous dampers that have plastic mechanisms similar to those of steel MRFs without dampers. Moreover, the proposed capacity design rule becomes stricter for buildings with more than 10 stories to address that available analysis methods for structures with dampers underestimate the peak damper forces in the lower stories of yielding tall steel MRFs. More work is needed to extend the findings of this work to the case of steel MRFs with nonlinear viscous dampers.     

On‐line hybrid test method for evaluating the performance of structural details to failure

A test environment to evaluate the seismic performance of gusset plate connections intended for steel braced frames is proposed. The developed test method combines the substructuring techniques with finite element analysis methods in an on‐line hybrid scheme. Numerical substructure analysis is conducted on bracing members, while bracing connections are treated as experimental substructures. A force‐displacement combined control imposed with the aid of 2 jacks ensures physical continuity between the analysis and test. The rotational behavior of gusset plate connections subjected to large inelasticity and varying axial loading until fracture is investigated. Two gusset plate details were designed and tested to verify the efficiency of the proposed method. The test method is rational, and smooth operation is achieved. The test results revealed the advantage of the developed on‐line hybrid test method in exploring the ultimate capacity of bracing connections.     

Geochemical and Sr-Nd isotopic evidence for petrogenesis and geodynamic setting of Lower-Middle Triassic volcanogenic rocks from central Greece: Implications for the Neotethyan Pindos ocean

Mineralogy and Petrology - Geochemistry and Sr-Nd isotopes were determined in Triassic calcalkaline metalava and metapyroclastic rocks from Attica and Argolida, central Greece, to ascertain their...     

Morphological and molecular analysis of bloom-forming Cyanobacteria in two eutrophic, shallow Mediterranean lakes

We investigated the diversity of Cyanobacteria by microscopic observation and sequencing of cyanobacterial-specific amplified 16S rRNA genes in the water column of two shallow, eutrophic lakes (Doirani and Kastoria, northern Greece) during summer blooms. Previous phytoplankton studies in these lakes have shown that prolonged cyanobacterial blooms can occur, which are dominated by known toxic species, as well as other less known, co-occurring species. A total of 118 clones were sequenced which were grouped in 23 Cyanobacteria and 11 chloroplast-like phylotypes. Phylogenetic analysis revealed that each library included several unique phylotypes, as well as members of all common bloom-forming Cyanobacteria. Most of the phylotypes belonged to the genera Microcystis, Anabaena, Aphanizomenon, Cylindrospermopsis-Raphidiopsis group, Limnothrix and Planktothrix, comprising most of the diversity previously recognized by morphological observations in cyanobacterial morphospecies in these lakes. In addition, novel phylotypes belonging to the Chroococcales were recognized in both lakes. The structure of the cyanobacterial communities of the lakes were very similar, as revealed by the diversity index H (2.06 and 2.01 for L. Doirani and Kastoria, respectively) and LIBSHUFF analysis (XY₁₂P-value = 0.122 and YX₁₂P-value = 0.536), due to occurrence of groups of common phylotypes. This study gives an example for successful cyanobacterial bloom analysis by the combination of morphological and phylogenetic methods useful for monitoring cyanobacteria and water quality in freshwaters.     

Electrical resistivity tomography mapping of beachrocks: application to the island of Thassos (N. Greece)

Electrical resistivity tomography (ERT) technique is widely used in mapping subsurface electrical properties. In this study, ERT was used to map a beachrock outcrop, extended both inland, under beach sediments, and seawards, on and under seafloor sediments. Mapping of beachrock is considered important because it can help evaluate the lateral and vertical extend of the formation. Fast and reliable mapping of beachrocks may contribute in several applications like engineering and construction, coastal management, recreational reformation as well as scientific approaches like coastal evolution research, and palaeo-environmental studies. The outcome of the survey was the mapping of the formation with centimeter precision, especially towards the sea. Special processing was applied to the data in order to constrain the inversion procedure to include the known sea water layer.     

New magnetic mineralogy and archaeointensity results from greek kilns and baked clays

Seven archaeological sites in Northern Greece and a pottery assemblage from Ithaki Island (Ionian Sea) have provided material from kilns and a collection of baked clays. The whole dataset consists of 69 samples and covers a period of almost 4000 years. Although the majority of the samples was oriented, only few directions could be obtained, mostly due to small sample size and fragility. Detailed rock magnetic experiments identified magnetite/titano-magnetite and substituted magnetite as the main magnetic minerals. Variable amounts of haematite were detected in some cases. In three out of eight sites, multi-domain grains prevail, whereas single-, pseudo-single domain or mixtures are detected in the remaining five. The classical Thellier-Thellier palaeointensity method was applied to 94 specimens. Following stringent acceptance criteria, 66 results from the 8 sites were considered successful and retained. These new results show a convergence with regional and global compilations and improve the knowledge of the past geomagnetic field behaviour in Greece.     

Maximum Likelihood Estimation of Seismic Hazard for Sweden

The maximum magnitude, the activity rate, and the Gutenberg-Richterb parameter as earthquake hazard parameters, have been evaluated for Sweden. The maximum likelihood method permits the combination of historical and instrumental data. The catalog used consists of 1100 earthquakes in the time interval 1375–1989. The extreme part of the catalog contains only the strongest historical earthquakes, whereas the complete part is divided into several subcatalogs, each assumed complete above a specified threshold magnitude. The uncertainty in magnitude determination was taken into account. For southern Sweden, the calculations giveb-values of 1.04 (0.05) for the whole area south of 60° N and 0.98 (0.06) for a subregion of enhanced seismicity in the Lake Vänern area. For the whole area north of 60° N, theb-value is 1.35 (0.06) and for the seismicity zone along the Gulf of Bothnia 1.26 (0.06). The number of annually expected earthquakes with magnitude equal to or larger than 2.4 [M_L(UPP) or M_M(UPP)] is 1.8 for the whole southern Sweden, 1.3 for the Lake Vänern region, 3.7 for northern Sweden, and 2.4 for the region along the Gulf of Bothnia. The maximum expected regional magnitude is calculated to 4.9 (0.5) for a time span of 615 years for southern Sweden and the Lake Vänern subregion, and 4.3 (0.5) for a time span of 331 years for northern Sweden and the Gulf of Bothnia subregion. However, several historical earthquakes with magnitude above 5 in nearby areas of Norway indicate that the seismic potential may be higher.     

Possible implications of climatic variability on the presence of capelin (Mallotus villosus) off the Norwegian coast

The distribution of capelin in the southern Barents Sea shifts in the east-west direction in response to warming or cooling trends. The capelin arrives at the spawning grounds earlier and spawning takes place in deeper water in cold years as compared to warm years. Although the ultimate regulators of capelin distribution/abundance in the Barents Sea may involve complex interactions/responses between capelin and abiotic and biotic variables, water temperature was found to be a successful predictor and proximate regulator of capelin distribution/ abundance in that area.It has been maintained that capelin did not visit the Norwegian coastal waters during the turn of the 18th century and in 1830–1840. Yet, meteorological, oceanographic and ecological data hitherto presented provide cumulative evidence that capelin migrated to the Norwegian spawning grounds during both periods. Nevertheless, capelin arrived early in the year and remained and spawned further offshore in deeper waters. Since capelin in earlier fisheries were fished by means of land-fixed nets, the size of the catch depended on access by the capelin to the immediate coastal fishing areas. Thus, capelin were not accessible to Norwegian fishermen.