On the effect of the partial solar eclipse of 29 April 1976 on electron content

Faraday rotation measurements made at a chain of stations and group delay measurements made at Ootacamund from ATS-6 are examined for the partial solar eclipse event of 29 April 1976. There is no evidence of eclipse-induced gravity waves in these measurements extending from Ootacamund near dip equator to Patiala (dip 45° N). Eclipse-induced fluctuations were however reported at Trivandrum, about 300 km south of Ootacamund.     

On the interpretation of velocities derived from spaced fading records

A number of spaced fading records obtained at Buckland Park, South Australia, using partial reflection technique (at 80–100 km) have been subjected to different methods of analysis, viz., time delay methods, the full correlation method and the cross-spectrum method. True drift velocities derived from the full correlation method appear to be the most correct. The variation of velocity with fading frequency obtained from cross-spectrum method is most likely to be due to the variation of velocity with time within the record itself.     

Fault-plane solution and tectonic implications of the Pattan, Pakistan earthquake of December 28, 1974

A large destructive earthquake occurred on December 28, 1974 on the western bank of the Indus River near the village of Pattan. The earthquake reportedly killed 5,300 persons, injured 17,000 and left 60,000 people homeless. A seismicity map of the region is presented for the period January, 1963, to March, 1974 on a Mercator projection. Two main linear trends are recognized on the epicenter map. The northwest trend, beginning at 32.3°N, 76.6°E terminates at the southwest alignment of epicenters beginning at 36.0°N, 73.5°E and ending at 33.0°N, 71.0°E. The Pattan earthquake occurred near the junction of the two linear trends. A fault-plane solution for this earthquake has been determined from an analysis of teleseismic P-wave first-motion and S-wave polarization data. The strike and dip of the two nodal planes are N65°E, 68°SE and N50°E, 23°NW, respectively. The solution is compatible with and indicates underthrusting of the Indian plate in this region in the NNW direction along a thrust zone striking northeast.     

Seismic waves due to storm over the sea: I

Summary Elastic wave propagation problem has been studied in the composite medium — a gravitating liquid layer overlying an elastic half-space. Assuming moving normal pressure load on the free surface, an attempt has been made to study the order of disturbance on the earth's surface. In the discussion asymptotic values of the displacement, components have been considered for small values of the parameter.     

Propagation of anSH-torque pulse in a three layered solid half-space

Summary The potential functions caused due to anSH-torque pulse from a point source in any of the layers of a three-layered solid half-space have been evaluated in terms of definite integrals, usingCagniard's method. The solution is given as a double infinite series, of which only a finite number of terms contribute to the disturbance at a definite time, and the number of such terms increases with time.     

Strength enhancement in particulate solids under high loading rates

The so-called ‘strain-rate effect’ in any material has been investigated here from a structural dynamics point of view. Starting with lumped-mass models (SDOF and 2-DOF) and assuming a rate-independent failure criterion, it is shown here how a high loading rate produces an effect of strength enhancement in any massive elastic material and how failure takes place in a stronger component of a system as the loading rate increases. Extrapolating the concept of an equivalent elastic modulus as introduced in lumped-mass models and extending the analysis to a semi-infinite elastic continuum, an algorithm has been schematized to evaluate an overall equivalent elastic modulus of a concrete body under the influence of high loading rate treating the concrete as a two-component solid mixture consisting of cement paste matrix and aggregates.     

Study on penetration depth and its dependence on frequency,soil moisture,texture and temperature in the context of microwave remote sensing

A theoretical study has been made to see the influence of microwave frequency, soil moisture, soil texture and soil temperature on penetration depth in the context of microwave remote sensing. The results are presented in the form of figures and also coefficients of least square fitting. The study reveals that there is a definite dependence of penetration depth on the above parameters. The range of penetration depth has been found to be 0 to 10 cms and varies as a function of several parameters. These results are in agreement with experimental observations.     

Focal mechanism solutions and nature of plate movements in Pakistan

From the seismic point of view, the territory of Pakistan which lies between latitude 23°–37° N and longitude 61°–75° E is one of the most active zones in the world. The importance of this area lies in terms of movements of the Indian plate with respect to Eurasia on the west. Seismicity, as well as focal mechanism- solutions, throws a considerable light on the nature of forces acting in the area. All the available solutions, along with 12 new ones, have been considered for the present study. Their relationship to major faults in the area is discussed. The majority of the solutions in the central and northern parts show strike-slip faulting with a left-lateral sense of motion, followed by thrust faulting; few show normal faulting. This suggests that the Indian plate is moving with respect to the Eurasian plate along the Chaman fault, Quetta transverse zone, Sulaiman Ranges and the Hazara thrusts region joining the Hazara/Kashmir syntaxis. The orientations of P and T axes have been studied. It is seen that in a large number of cases compressive stress is acting nearly in NNW-SSE to N-S directions. The Hazara thrust region appears to be the most complex. Here, the influence of the Himalayan thrust front is evident to a large extent.The nature of faulting along the Chaman fault and Quetta transverse zone is to some extent similar to that of the San Andreas fault system of California. So far as the energy release is concerned, the maximum energy is being released in the form of strike-slip movements close to the Chaman fault and Quetta transverse ranges.