Paleoearthquakes in the Uimon basin (Gorny Altai)

Paleoseismological studies confirm that the Uimon basin is thrust by its northern mountain border along the active South Terekta fault. The latest motion along the fault in the 7-8th centuries AD induced an earthquake with a magnitude of M_w= 7.4-7.7 and a shaking intensity of I = 9-11 on the MSK-64 scale. The same fault generated another event (M > 7, I = 9-10), possibly, about 16 kyr ago, which triggered gravity sliding. The rockslide dammed the Uimon valley and produced a lake, where lacustrine deposition began about 14 ± 1 kyr ago, and a later M > 7 (I = 9-10) earthquake at ~ 6 ka caused the dam collapse and the lake drainage. Traces of much older earthquakes that occurred within the Uimon basin are detectable from secondary deformation structures (seismites) in soft sediments deposited during the drainage of a Late Pleistocene ice-dammed lake between 100 and 90 ka and in ~ 77 ka alluvium. The magnitude and intensity of these paleoearthquakes were at least M > 5.0-5.5 and I > 6-7.     

Center-to-Limb Variations of the Ca II H and K Lines in Sunspot Umbrae

A comparison of theoretical and observed Caii H and K line profiles in sunspot umbrae has been made for different sunspot positions on the solar disk. Four semi-empirical static umbral models were used in calculations: the SUNSPOT model of Avrett (1981), and the models of Staude (1982), Maltby et al. (1986), and Severino, Gomez, and Caccin (1994). The models suggested by Avrett, Maltby et al., and Severino, Gomez, and Caccin reproduce the center-to-limb evolution of the shape of observed profiles. The best agreement with profile parameters obtained from observations is given by the Severino, Gomez, and Caccin model.     

On umbral flashes in different sunspot groups

The results of a statistical investigation of the occurrence of umbral flashes for 40 sunspot groups are reported for the period 1966–1983. The following characteristics were chosen for the analysis: (a) position on the solar disk; (b) group area; (c) sunspot area; (d) maximum magnetic field strength of a sunspot; (e) modified Zürich class; (f) sunspot age; (g) magnetic structure; and (h) flare activity of a group. The dependence of umbral flashes on magnetic structure of a sunspot is the most essential feature. The absence of umbral flashes in the umbrae of main sunspots perhaps may be used as one of the predictors of flare activity.     

Unknown large ancient earthquakes along the Kurai fault zone (Gorny Altai): new results of palaeoseismological and archaeoseismological studies

Palaeoseismological and archaeoseismological studies in the Kurai fault zone, along which the Kurai Range is thrust onto Cenozoic deposits of the Chuya intramontane basin, led to the identification of a long reverse fault scarp 8.0 m high. The scarp segments are primary seismic deformations of large ancient earthquakes. The scarp’s morphology, results of trenching investigations, and deformations of Neogene deposits indicate a thrusting of the piedmont plain onto the Kurai Range, which is unique for the Gorny Altai. Similarly for Northern Tien Shan, we explain this by the formation of both a thrust transporting the mountain range onto the depression and a branching thrust dislocation that forms the detected fault scarp. In a trench made in one of the scarp segments, we identified the parameters of the seismogenic fault – a thrust with a 30° dipping plane. The reconstructed displacement along the fault plane is 4.8 m and the vertical displacement is 2.4 m, which indicates a 7.2–7.6 magnitude of the ancient earthquake. The ¹⁴C age of the humus-rich loamy sand from the lower part of the colluvial wedge constrains the age of the earthquake at 3403–3059 years BP. Younger than 2500 years seismogenic displacements along the fault scarp are indicated by deformations of cairn structures of the Turalu–Dzhyurt-III burial mound, which was previously dated as iron age between the second half of I BC and I AD.     

Chromospheric oscillations in CaII lines

The dynamic regime of eight regions in the quiet solar chromosphere was analyzed. Observations in CaII lines were performed with a moderate spatial resolution of around 2″. The purpose of this study was to compare the diagnostic capabilities of these observations with high-precision measurements conducted in recent years by different authors with new-generation instruments. Being probably of importance in the chromospheric heating, the recently revealed structural formations (magnetoacoustic portals, magnetic aureoles, and magnetic shadows) were found to manifest themselves at moderate resolutions too. These findings are important in the context of investigations of coronal hole bases conducted by the authors with the same observational data.     

The ratios I(K1)/I(H1) and I(K3)/I(H3) of ca II as diagnostics of the chromosphere above sunspots

The ratios I(K ₁)/I(H ₁) and I(K ₃)/I(H ₃) were calculated from four semi-empirical models of sunspot umbra. We determined the dependencies of both ratios of such parameters as temperature gradient and atmospheric opacity. A certain influence on the expected ratios I(K ₁)/I(H ₁) and I(K ₃)/I(H ₃) can also come from the FIP effect provided it exists in the chromosphere above sunspot umbra. Theoretical and observed values of I(K ₁)/I(H ₁) and I(K ₃)/I(H ₃) are compared. It is shown that for one of the sunspots we observed, the values obtained for the ratio I(K ₁)/I(H ₁) cannot be explained in terms of existing umbra models.     

Some Peculiarities of Intensity Oscillations in Ca <Emphasis Type="SmallCaps">ii</Emphasis> Lines under Coronal Holes

Observations of the central intensity of the Ca ii K and 849.8 nm lines are used to derive the ratios of the oscillation power in the frequency ranges of the “five-minute” (W ₅) and “three-minute” (W ₃) oscillations. It is shown that at high significance level ratios, (W ₅/W ₃) >1 at coronal hole bases, and W ₅/W ₃ ≈1 in quiet chromospheric areas far from holes.     

On traces of a strong earthquake in walls of the Sary-Bulun medieval sites along the great silk route (western Issyk-Kul Lake region,Northern Tien Shan)

The Sary-Bulun archeological sites located along the Great Silk Route of medieval times are studied. The study revealed a number of the deformations of seismogenic origin: tilts, shifts, and collapse and lateral bends of walls as well as long fissures in corner parts of the rooms. Judging by archeological artifacts, the seismic event occurred at the end of the 12th–beginning of the 13th century AD. Judging by degree of damage, the intensity of this ancient earthquake was I ≥ VIII on the MSK-64. The source of the seismic oscillations was apparently located in the faults cutting the active Boz-Barmak anticline. The studied archeological sites are located on the western limb of this anticline structure. In the medieval period, the Sary-Bulun settlements were the largest metallurgic centers of the Issyk-Kul depression and, thus, they are of a great significance for studying industrial processes of that time.     

On the unusual H∈ emission in a sunspot umbra spectrum

A study is made of characteristics of the oscillatory process in a sunspot where, in addition to the high brightness in the cores of the H and K Caii lines, the H∈ line was also in emission. A bright H∈ emission persisted during six days at least. An analog of the behaviour of the Caii and H∈ lines can be seen, presumably, on dwarf stars dKe and dMe.     

Brightness distribution at the base of a coronal hole

A coronal hole was observed for three days of its passage near the central meridian of the Sun. Spectrograms containing strong lines of ionized calcium were obtained. The central intensities of the Ca II H, K, and λ849.8 nm lines in the region of the coronal hole and in the quiet-Sun region outside its boundaries were measured. Only the line profiles that were confidently identified as being undisturbed even by weak flocculi were selected. All profiles were averaged in each of the two chromospheric network components (network and cell), and the average profiles were calculated using all of the available data (network+cell). Small differences were found between the central intensities of the Ca II H and K lines inside and outside the coronal hole, with the hole being brighter than the quiet region. A detailed statistical analysis shows that these small differences are real at high confidence levels owing to the large sample sizes. A difference of the same sign is slightly noticeable in the infrared line, but its confidence level is less than 90%. The chromosphere in the coronal hole is brightened by the cell alone; in the network, the chromospheric foot of the coronal hole does not differ from the quiet region. Comparison with the results of other authors obtained from observations in higher atmospheric layers suggests that the network also contains a brightness peak that subsequently gives way to a characteristic depression, but it lies higher than that in the cell.