Simultaneous inversion of the aftershock data of the
1993 Killari earthquake in Peninsular India and its seismotectonic implicationsS Mukhopadhyay
1 , J R Kayal 2 , K N Khattri 3 and B K Pradhan 11
Department of Earth Sciences, Indian Institute of Technology (formerly University of Roorkee), Roorkee, Uttaranchal 247 667, India2
Geological Survey of India, Central Geophysics Division, 27 J.L.N. Road, Kolkata 700 016, India3
100 Rajendra Nagar, Dehra Dun, Uttaranchal 248 001, India e-mail: sagarfes@iitr.ernet.in The aftershock sequence of the September 30th, 1993 Killari earthquake in the Latur district of Maharashtra state, India, recorded by 41 temporary seismograph stations are used for estimating 3-D velocity structure in the epicentral area. The local earthquake tomography (LET) method of Thurber (1983) is used. About 1500 P and 1200 S wave travel-times are inverted. The P and S wave velocities as well as VP :VS ratio vary more rapidly in the vertical as well as in the horizontal directions in the source region compared to the adjacent areas. The main shock hypocentre is located at the junction of a high velocity and a low velocity zone, representing a fault zone at 6 - 7 km depth. The estimated average errors of P velocity and VP =VS ratio are ± 0.07 km/s and ± 0:016, respectively. The best resolution of P and S-wave velocities is obtained in the aftershock zone. The 3-D velocity structure and precise locations of the aftershocks suggest a `stationary concept' of the Killari earthquake sequence.K S Krishna
*, D Gopala Rao and Yu P NeprochnovyNational Institute of Oceanography, Dona Paula, Goa 403 004, India.
y
P.P. Shirshov Institute of Oceanology, 36 Nakhimovsky Prospect, Moscow 117851, Russia.*
e-mail: krishna@csnio.ren.nic.inAnalyses of bathymetry, gravity and seismic reflection data of the diffusive plate boundary in the central Indian Ocean reveal a new kind of deformed structure besides the well-reported structures of long-wavelength anticlinal basement rises and high-angle reverse faults. The structure (basement trough) has a length of about 150 km and deepens by up to 1 km from its regional trend (northward dipping). The basement trough includes a rise at its center with a height of about 1.5 km. The rise is about 10 km wide with rounded upper surface and bounded by vertical faults. A broad free-air gravity low of about 20 mGal and a local high of 8 mGal in its center are associated with the identified basement trough and rise structure respectively. Seismic results reveal that the horizontal crustal compression prevailing in the diffusive plate boundary might have formed the basement trough possibly in early Pliocene time. Differential loading stresses have been generated from unequal crust/sediment thickness on lower crustal and upper mantle rocks. A thin semi-ductile serpentinite layer existing near the base of the crust that is interpreted to have been formed at mid-ocean ridge and become part of the lithosphere, may have responded to the downward loading stresses generated by the sediments and crustal rocks to inject the serpentinites into the overlying strata to form a classic diapiric structure.
Reflection of plane waves from free surface of a microstretch elastic solid
Baljeet Singh
Department of Mathematics, Jat College, Rohtak 124 001, Haryana, India.
e-mail: baljeet_gill@hotmail.com
In the present investigation, it is shown that there exists five basic waves in a microstretch elastic solid half-space. The problem of reflection of plane waves from free surface of a microstretch elastic solid half-space is studied. The energy ratios for various reflected waves are obtained for aluminium- epoxy composite as a microstretch elastic solid half-space. The variations of the energy ratios with the angle of incidence are shown graphically. The microstretch effect is shown on various reflected waves.
V N Nijampurkar
1 , D K Rao 1 , H B Clausen 2 , M K Kaul 3 and A Chaturvedi 31
Physical Research Laboratory, Ahmedabad, India2
Department of Geophysics, Niels Bohr Institute of Astronomy, Physics and Geophysics, DK 2200 Copenhagen O, Denmark3
Geological Survey of India, Antarctica Division, Faridabad, IndiaThe depth profiles of electrical conductance,
1 O, 21 Pb and cosmogenic radio isotopes 1 Be and 3 Cl have been measured in a 30 m ice core from east Antarctica near the Indian station, Dakshin Gangotri. Using 21 Pb and 1 O, the mean annual accumulation rates have been calculated to be 20 and 21 cm of ice equivalent per year during the past ~ 150 years. Using these acumulation rates, the volcanic event that occurred in 1815 AD, has been identified based on electrical conductance measurements. Based on 1 O measurements, the mean annual surface air temperatures (MASAT) data observed during the last 150 years indicates that the beginning of the 19th century was cooler by about 20 C than the recent past and the middle of 18th century. The fallout of cosmogenic radio isotope 1 Be compares reasonably well with those obtained on other stations (730 S to 900 S) from Antarctica and higher latitudes beyond 770N. The fallout of 3 Cl calculated based on the present work agrees well with the mean global production rate estimated earlier by Lal and Peters (1967) The bomb pulse of 3 Cl observed in Greenland is not observed in the present studies { a result which is puzzling and needs to be studied on neighbouring ice cores from the same region.
Velocity of small-scale auroral ionospheric current systems over Indian Antarctic station Maitri
Girija Rajaram, A N Hanchinal, R Kalra, K Unnikrishnan, K Jeeva, M Sridharan and A Dhar
Indian Institute of Geomagnetism, Colaba, Mumbai 400 005, India
The Indian Antarctic station Maitri (geog. 70
045/S; 11045/E, geom. 660:03S; 530:21E) occupies a sub-auroral location during magnetically quiet conditions (sigmaKp < 10), but attains an auroral position when the auroral oval shifts equatorwards with increasing strength of magnetic disturbance. At the latter times, triangulation with 3 uxgate magnetometers located at the vertices of a suitable triangle provides a means of monitoring mobile auroral ionospheric current systems over Maitri. The spacing between the magnetometers is typically kept at 75-200 km, keeping in mind the scale-sizes of ~ 100 km for these mobile current systems. This work reports the results of two triangulation experiments carried out around Maitri in January 1992 and January 1995, both during Antarctic summer. The velocities estimated for pulsations of the Pc4 and Pc5 type were about 0.59 km/sec in the direction 1020:7 east of due north, in the first case, and about 1-3 km/sec in the second case in the east-west direction. While several magnetometer arrays exist in the northern auroral regions (e.g., the Alberta array in Canada, the Alaskan array in the U.S. and the IMS Scandinavian array), there is no report in literature of triangulation through arrays in Antarctica, except for a one-day study by Neudegg et al 1995 for ULF pulsations of the Pc1 and Pc2 type. The velocities obtained for the Pi3 type of irregular pulsations over Antarctica in the present study tally well with those obtained for northern auroral locations.
Thermal Internal Boundary Layer characteristics at a
tropical coastal site as observed by a mini-SODAR under varying synoptic conditionsThara V Prabha
1 , R Venkatesan 2 Erich Mursch-Radlgruber 3 , G Rengarajan 3 N Jayanthi 41
Crop and Soil Sciences, University of Georgia, GA, USA .2 Health and Safety Division, SHINE Group, IGCAR, Kalpakkam, India 603 102.
e-mail: rv@igcar.ernet.in
3
Boundary Layer Meteorology Division, Institut fuer Meteorologie und Physik (IMP-BOKU), Wien, Austria.4
India Meteorological Department, Chennai, India. Atmospheric boundary layer observations are conducted at a coastal site during a transition phase from winter to summer season over the Indian peninsula. Thermal Internal Boundary Layer (TIBL) characteristics in presence of an off-shore and a weakly in uenced on-shore synoptic wind are examined with the help of measurements carried out with a mini-SODAR (SOund Detection And Ranging), tethered balloon, and tower-based micrometeorological measurements. In uence of the changing synoptic scale conditions on turbulent characteristics of TIBL is discussed. Mini-SODAR data showed the development and decay of sea and land breeze. It is seen that the characteristics of TIBL over the coastal land after sea breeze onset are similar to that of a shallow convective boundary layer (CBL) commonly found over plain land. Inside the TIBL, a maximum wind speed was noted close to the surface due to the penetration of sea breeze. In the off-shore case, a distinct sea breeze circulation was observed unlike in the case of on-shore ow. In the presence of weak on-shore case, a `minor sea' breeze is noted before the establishment of sea breeze and a reduction in the momentum uxes gives rise to decrease in the turbulence intensity. Updraft in the sea breeze front was stronger during weak synoptic conditions. In uence of synoptic changes on the sea breeze-land breeze circulation such as onset, strength and duration of the sea-land breeze are also examined.
Temperature mapping, thermal diffusivity and subsoil
heat ux at Kariavattom of KeralaTessy Chacko P and G Renuka
Department of Physics, University of Kerala, Kariavattom, Thiruvananthapuram, 695 581, India.
We have studied the soil and air temperature characteristics over a period of one year at Kariavattom of Kerala. Thermal diffusivity (ks) of the soil has been calculated by range and lag methods and also from amplitudes and phase angles of first and second harmonics. The two methods lead to similar results. Diurnal soil heat ux and soil temperatures at different depths are modelled and found to be comparable with observations.