Effect of solar flare on the equatorial electrojet in eastern Brazil region     

R G Rastogi  P Janardhan  H Chandra  N B Trivedi  Vidal Erick 《Journal of Earth System Science》2017,126(4):51

The effect of solar flare, sudden commencement of magnetic storm and of the disturbances ring current on the equatorial electrojet in the Eastern Brazil region, where the ground magnetic declination is as large as \(20^{^{\circ }}\hbox {W}\) is studied based on geomagnetic data with one minute resolution from Bacabal during November–December 1990. It is shown that the mean diurnal vector of the horizontal field was aligned along \(2{^{\circ }}\hbox {E}\) of north at Huancayo and \(30{^{\circ }}\hbox {W}\) of north at Bacabal during the month of December 1990. Number of solar flares that occurred on 30 December 1990 indicated the direction of solar flare related \(\Delta H\) vector to be aligned along \(5{^{\circ }}\hbox {E}\) of north at Huancayo and \(28{^{\circ }}\hbox {W}\) of north at Bacabal. This is expected as the solar flare effects are due to the enhanced conductivity in the ionosphere. The SC at 2230 UT on 26 November 1990 produced a positive impulse in \(\Delta X\) and negative impulse in \(\Delta Y\) at Bacabal with \(\Delta H\) vector aligned along \(27{^{\circ }}\hbox {W}\) of north. At Huancayo the \(\Delta H\) vector associated with SC is aligned along \(8{^{\circ }}\hbox {E}\) of north, few degrees east to the alignment of the diurnal vector of H. The magnetic storm that followed the SC had a minimum Dst index of –150 nT. The corresponding storm time disturbance in \(\Delta X\) at Huancayo as well as at Bacabal were about –250 nT but \(\Delta Y\) at Bacabal was about +70 nT and very small at Huancayo, that give the alignment of the H vector due to ring current about \(16{^{\circ }}\hbox {W}\) of north at Bacabal and almost along N–S at Huancayo. Thus alignment of the \(\Delta H\) vector due to ring current at Bacabal is \(14{^{\circ }}\hbox {E}\) of the mean direction of \(\Delta H\) vector during December 1990. This is consistent with the direction of ring current dependent on the dipole declination at the ring current altitude which is about \(5{^{\circ }}\hbox {W}\) of north over Bacabal and the deviation of declination due to the ring current during disturbed period given by the angle (\(\psi \)-D).  相似文献   

Earthquake m_b vs M_s Relations and Source Multiplicity     

Harsh K. Gupta  B. K. Rastogi 《Geophysical Journal International》1972,28(1):65-89

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The deadliest stable continental region earthquake occurred near Bhuj on 26 January 2001     

B.K. Rastogi  H.K. Gupta  Prantik Mandal  H.V.S. Satyanarayana  M. Kousalya  R. Raghavan  Richa Jain  A.N.S. Sarma  N. Kumar  C. Satyamurty 《Journal of Seismology》2001,5(4):609-615

A large destructive earthquake occurred on 26 January 2001 in the region of Kutch, Gujarat, in Western India, with magnitude Mw 7.7. The earthquake caused very heavy damage and a large number of casualties with more than 20,000 deaths. A preliminary study of ground deformation, damage pattern and aftershock distribution is presented.  相似文献   

Aftershock Activity and Frequency-dependent Low Coda Qc in the Epicentral Region of the 1999 Chamoli Earthquake of Mw 6.4     

P. Mandal  S. Padhy  B. K. Rastogi  H. V. S. Satyanarayana  M. Kousalya  R. Vijayraghavan  A. Srinivasan 《Pure and Applied Geophysics》2001,158(9-10):1719-1735

— On 28 March, 1999 (19:05:10.09, UT) a significant earthquake of M _w 6.4 occurred in the Garhwal Himalaya (30.555°N, 79.424°E). One hundred and ten well-recorded aftershocks show a WNW-ESE trending northeasterly dipping seismic zone extending from a depth of 2 to 20?km. As the main shock hypocenter occurred at the northern end of this seismic zone and aftershocks extended updip, it is inferred that the main-shock rupture nucleated on the detachment plane at a depth of 15?km and then propagated updip along a NE-dipping thrust plane. Further, the epicentral distribution of aftershocks defines a marked concentration near a zone where main central thrust (MCT) takes a significant turn towards the north, which might be acting as an asperity in response to the NNE compression due to the underthrusting of Himalayan orogenic process prevalent in the entire region. Presence of high seismicity including five earthquakes of magnitude exceeding 6 and twelve earthquakes of magnitude exceeding 5 in the 20th century is presumed to have caused a higher level of shallow crustal heterogeneity in the Garhwal Himalaya, a site lying in the central gap zone of the Himalayan frontal arc. Attenuation property of the medium around the epicentral area of the 1999 Chamoli earthquake, covering a circular area of 61,500?km² with a radius of 140?km, is studied by estimating the coda Q _c from 48 local earthquakes of magnitudes varying from 2.5–4.8. These earthquakes were recorded at nine 24-bit REFTEK digital stations; two of which were equipped with three-component CMG40T broadband seismometers and others with three-component L4-3D short-period seismometers. The estimated Q _o values at different stations suggest on average a low value of the order of (30?±?0.8), indicating an attenuating crust beneath the entire region. The frequency-dependent relation indicates a relatively low Q _c at lower frequencies (1–3?Hz) that can be attributed to the loss of energy due to scattering on heterogeneities and/or the presence of faults and cracks. The large Q _c at higher frequencies may be related to the propagation of backscattered body waves through deeper parts of the lithosphere where less heterogeneities are expected. An important observation is that the region north of MCT (more rigid highly metamorphosed crystalline rocks) is less attenuative in comparison to the region south of MCT (less rigid slightly metamorphosed rocks (sedimentary wedge)). The acceleration decays to 50% at 20?km distance and to 7% at 100?km. Hence, even 1g acceleration at the source may not cause significant damage beyond 100?km in this region.  相似文献   

Spectral analysis of body waves for earthquakes and their source parameters in the Himalaya and nearby regions     

D.D. Singh  B.K. Rastogi  Harsh K. Gupta 《Physics of the Earth and Planetary Interiors》1979,18(2):143-152

The source characteristics of 33 earthquakes with magnitude m_b between 4.4 and 6.0, which occurred in the Himalayan and nearby regions, are investigated using the records of the Hyderabad seismograph station. The P- and S-wave spectra of these events are interpreted in terms of Brune's seismic source model for estimating the source parameters, i.e., seismic moment, source dimension, stress drop, average dislocation, apparent stress and the radiated energy. Seismic moments, M₀, vary between 0.3 × 10²⁴ and 9.0 × 10²⁶ dyne cm; source dimensions, r, between 4.3 and 18.6 km; stress-drops, Δσ between 0.3 and 151.6 bar; average dislocations, $\text{u}$ between 0.6 and 381 cm; apparent stresses, $\text{η}\text{σ}$ between 0.1 and 73.2 bar. The radiated energy, E_R is estimated by the spectrum integration method and is found to vary between 0.2 × 10¹⁸ and 9.3 × 10²² erg. In general, the stress drop and apparent stress are found to be high, indicating high stresses in these regions.  相似文献   

Earthquake mechanisms and tectonics in the Assam-Burma region     

B.K. Rastogi  J. Singh  R.K. Verma 《Tectonophysics》1973,18(3-4)

Eleven new focal mechanisms from earthquakes in the Assam-Burma region have been determined using P-wave first-motion directions reported in the Bulletins of the International Seismological Centre (Edinburgh). Out of them, eight mechanisms indicate thrust faulting, two normal faultings and one strike-slip faulting. In the thrust type of mechanism solutions, sense of motion on the shallow dipping of the two nodal planes is consistent with underthrusting beneath the arc-like mountain ranges. Seismic slip vectors strike in almost northerly direction along the eastern Himalayas and in almost easterly direction along the Burmese arc. A predominance of thrust faulting is consistent with geological evidences of thrusting and uplift in the Himalayas and the Assam-Burma region.  相似文献   

Ionospheric effects of transient celestial X-ray and gamma-ray events     

K. Kasturirangan  U. R. Rao  D. P. Sharma  R. G. Rastogi  S. C. Chakravarty 《Astrophysics and Space Science》1976,42(1):57-62

The paper presents the results on investigations of the ionospheric effects arising out of the transient celestial events at X-ray and gamma-ray energies such as that from X-ray novae and cosmic gamma-ray bursts. The VLF data recorded at Ahmedabad corresponding to the 164 kHz transmission from Tashkent are examined to see whether there are any observable effects time coincident with the transit of the X-ray novae Cen X-4 and Cet X-2 around their intensity maxima. Besides, the VLF data have also been examined in relation to the cosmic gamma-ray bursts detected by Vela, IMP-6 and OSO-7 satellites.Theoretical computations are carried out for estimating electron density enhancements using the available data on intensities and energy spectra for these events. Further, the observational resutls are explained in terms of these theoretical calculations.Presently at Indian Space Research Organization, Bangalore, India.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.  相似文献   

On the occurrence of SSC (− +) at Kodaikanal     

R.G. Rastogi 《Planetary and Space Science》1971

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Sensitivity analysis of seismic hazard for the northwestern portion of the state of Gujarat, India   总被引：1，自引：0，他引：1  

Mark D. Petersen  B.K. Rastogi  Eugene S. Schweig  Stephen C. Harmsen  Joan S. Gomberg 《Tectonophysics》2004,390(1-4):105-115

We test the sensitivity of seismic hazard to three fault source models for the northwestern portion of Gujarat, India. The models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years. These recurrence intervals imply that large earthquakes occur on one of these faults every 266–533 years, similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the New Madrid region in the central United States. If one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults, the peak ground accelerations (PGA; horizontal) and 1-Hz spectral acceleration ground motions (5% damping) are greater than 1 g over a broad region for a 2% probability of exceedance in 50 years' hazard level. These probabilistic PGAs at this hazard level are similar to median deterministic ground motions. The PGAs for 10% in 50 years' hazard level are considerably lower, generally ranging between 0.2 g and 0.7 g across northwestern Gujarat. Ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals. These higher ground motions are mainly caused by the application of intraplate attenuation relations, which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies. For sites in Bhuj and Ahmedabad, magnitude (M) 7 3/4 earthquakes contribute most to the PGA and the 0.2- and 1-s spectral acceleration ground motion maps at the two considered hazard levels.  相似文献   

An intense SFE and SSC event in geomagnetic H, Y and Z fields at the Indian chain of observatories     

R. G. Rastogi  D. R. K. Rao  S. Alex  B. M. Pathan  T. S. Sastry 《Annales Geophysicae》1997,15(10):1301-1308

Changes in the three components of geomagnetic field are reported at the chain of ten geomagnetic observatories in India during an intense solar crochet that occurred at 1311 h 75° EMT on 15 June 1991 and the subsequent sudden commencement (SSC) of geomagnetic storm at 1518h on 17 June 1991. The solar flare effects (SFE) registered on the magnetograms appear to be an augmentation of the ionospheric current system existing at the start time of the flare. An equatorial enhancement in AH due to SFE is observed to be similar in nature to the latitudinal variation of SQ (H) at low latitude. AF registered the largest effect at 3.6° dip latitude at the fringe region of the electrojet. AZ had positive amplitudes at the equatorial stations and negative at stations north of Hyderabad. The SSC amplitude in the H component is fairly constant with latitude, whereas the Z component again showed larger positive excursions at stations within the electrojet belt. These results are discussed in terms of possible currents of internal and external origin. The changes in the Y field strongly support the idea that meridional current at an equatorial electrojet station flows in the ionospheric dynamo, E.Presently at: School of Physics, University of New South Wales, Sydney, Australia  相似文献