Microearthquake seismicity and active tectonics of northwestern Greece

We carried out a microearthquake survey lasting for six weeks in northwest Greece using 18 portable seismograph stations to examine a region in which normal and thrust faulting have been reported in close proximity to one another. With this array we located 148 events and determined fault plane solutions for eight events using only rays radiated upwards. The seismicity of the region is diffuse with events extending to depths of nearly 30 km, and there is a minimum in activity near a depth of 15 km. The fault plane solutions exhibit a wide spectrum of fault types and orientations and are not consistent with simple zones of shortening or extension. Neither tractions applied to the edges or bottom of the region nor deviatoric stresses that compensate for lateral variations in crustal thickness can account for the variety of fault plane solutions. We think that the complicated behavior is a manifestation of inhomogeneous deformation due, at least in part, to a pre-existing complicated juxtaposition of structures and formations.     

Relations between surface deformation,fault geometry,seismicity, and rupture characteristics during the El Asnam (Algeria) earthquake of 10 October 1980

The El Asnam earthquake of October 10, 1980 (M_s=7.3) produced surface faulting on a northeast-trending thrust fault of 30 km length with displacements of up to 6.5 m, though average displacements were about 3 m. In addition, widespread tensional features were formed, some in clear association with folding above the thrust, and others, in an area beyond the exposure of the thrust at the surface, which may be related to buried reverse faults.The observed thrust fault is split into southern, central and northern segments. Local and teleseismic data are examined to show that the main shock nucleated at the southwest end of the fault, and propagated 12 km northeast where a second rupture of approximately equal moment occurred, continuing the faulting a further 12 km northeast along the central segment. Both ruptures nucleated at about 8–10 km depth. Displacements were largest on the central segment, where they were probably enlarged by aftershocks, including one of m_b=6.1 three hours after the main shock. The northern segment was much shorter than the other two, and showed smaller displacement.The junctions between fault segments are marked by distinct geomorphological characteristics and a change in strike of the faulting, as well as a sudden drop in the observed displacement. It appears that the rupture development is influenced by the changes in fault geometry between segments, and that such junctions or barriers have persisted through much of the late Quaternary.     

Coda wave attenuation characteristics for Kumaon and Garhwal Himalaya,India

Natural Hazards - Uttarakhand Himalayas are among one of the most seismically active continental regions of the world. The Himalayan belt in this region is divided into Kumaon and Garhwal Himalaya....     

Period-mass ratio relations for eclipsing binaries with periods not exceeding 5 days

The dependence of mass ratio of eclipsing binary systems on period has been studied. It has been found that semi-detached systems obey the relationm ₂/m ₁=0.64–0.079P orm ₂/m ₁=0.29–0.028P depending upon whether the mass ratio is >0.3 or <0.3. The mass ratio of deteched systems generally appears to be independent of the period.     

Identification of seismically susceptible areas in western Himalaya using pattern recognition

Seismicity in the western Himalayas is highly variable. Several historical and instrumentally recorded devastating earthquakes originated in the western Himalayas which are part of the Alpine–Himalayan belt. Earthquakes cause tremendous loss of life and to the built environment. The amount of loss in terms of life and infrastructure has been rising continuously due to significant increase in population and infrastructure. This study is an attempt to identify seismically susceptible areas in western Himalaya, using pattern recognition technique. An area between latitude 29^°–36^°N and longitude 73^°–80^°E was considered for this study. Pattern recognition starts with identification, selection and extraction of features from seismotectonic data. These features are then subjected to discriminant analysis and the study area was classified into three categories, viz., Area A: most susceptible area, Area B: moderately susceptible area, and Area C: least susceptible area. Results show that almost the entire states of Himachal Pradesh and Uttarakhand and a portion of Jammu & Kashmir are classified as Area A, while most of Jammu & Kashmir is classified as Area B and the Indo-Gangetic plains are classified as Area C.     

Seismicity and the state of stress from investigations of local earthquakes in the Kumaon Himalaya

Results of investigations of local earthquakes in the region of the Main Central Thrust (MCT) in the Kumaon Himalaya, between and adjacent to the valleys of the Bhagirathi and Yamuna rivers, are presented. Records of over 250 earthquakes were analysed and the following facts emerged:

1. (1) Earthquakes in the Himalayas occur in specific areas and belts. One such belt has been identified in the region under investigation, hypocentral estimates being more reliable for earthquakes occurring in the middle segment approximately 70 km long of this belt, crossing the Yamuna river between the villages of Barkot and Syanachatti.

2. (2) All but a few epicentres in this middle segment, lie to the southwest of the surface trace of the MCT in a zone with a width of 10–30 km.

3. (3) Most of the earthquakes in this segment occur at depths of less than 10 km below the ground surface, the maximum estimated depth being 32 km.

Using observations of first motion for a composite focal mechanism solution, the nodal planes were observed to be near vertical and the compression axis near horizontal and normal to the local strike of the seismic belt and of the MCT.We conclude that although the Main Central Thrust itself is not seismically active in this region, there is considerable activity immediately to the southwest of it. Furthermore, the mode of faulting as inferred from the records of these earthquakes, is strike slip.     

Energy distribution in early K-stars

The spectral distribution of energy for 21 early K-stars in the wavelength region 450 nm to 750 nm at a definition of 5 nm have been obtained. A two dimensional photometric spectral classification index-system for these stars has been devised and discussed.     

Isoseismals for the Kutch earthquake of 26th January 2001

Damage observed during the Kutch earthquake of 26th January 2001 is classified according to the type of structure. This damage pattern has been used to draw the isoseismal map on the basis of the intensity scale given in IS 1893-2002 which covers only traditional one to two storey houses. Having thus estimated intensities, and observed damage to other types of structures, a new criterion was adopted which is included in this paper. Areas that showed maximum damage to structures have been assigned maximum intensity X.     

The effect of metallicity on the empirical relations for RR Lyrae stars

It has empirically been shown that, for a given value of the effective temperature, the correction in (B-V) due to line blanketing varies linearly with the metallicity parameter S. Next, on the basis of considerations different from those used to obtain a similar result by Sturch (1966), a relation between reciprocal effective temperature _e (=5040/T _e ) and intrinsic line-free colour index(B-V) _o,c has been obtained based on the _e and (B-V) values for five RR Lyr variables. Relations between _e and intrinsic colour(B-V) _o for different groups of stars having a S parameter in the range 0S11 have also been obtained.