Source parameters and scaling relations for small earthquakes in the Kachchh region of Gujarat,India     

Santosh Kumar  Dinesh Kumar  B. K. Rastogi 《Natural Hazards》2014,73(3):1269-1289

The scaling relationships for stress drop and corner frequency with respect to magnitude have been worked out using 159 accelerograms from 34 small earthquakes (M _w 3.3–4.9) in the Kachchh region of Gujarat. The 318 spectra of P and S waves have been analyzed for this purpose. The average ratio of P- to S-wave corner frequency is found to be 1.19 suggestive of higher corner frequency for P wave as compared to that for S wave. The seismic moments estimated from P waves, M ₀(P), range from 1.98 × 10¹⁴ N m to 1.60 × 10¹⁶ N m and those from S waves, M ₀(S), range from 1.02 × 10¹⁴ N m to 3.4 × 10¹⁶ N m with an average ratio, M ₀(P)/M ₀(S), of 1.11. The total seismic energy varies from 1.83 × 10¹⁰ J to 2.84 × 10¹³ J. The estimated stress drop values do not depend on earthquake size significantly and lie in the range 30–120 bars for most of the events. A linear regression analysis between the estimated seismic moment (M ₀) and corner frequency (f _c) gives the scaling relation M ₀ f _c ³  = 7.6 × 10¹⁶ N m/s³. The proposed scaling laws are found to be consistent with similar scaling relations obtained in other seismically active regions of the world. Such an investigation should prove useful in seismic hazard and risk-related studies of the region. The relations developed in this study may be useful for the seismic hazard studies in the region.  相似文献   

News and notes     

N. Purnachandra Rao  Sukanta Roy  Kusumita Arora  B. K. Rastogi  Suman Sarkar  M. Venkataswamy  Raymond A. Duraiswami 《Journal of the Geological Society of India》2013,81(5):722-730

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GIS Based Marine Platinum Exploration, Goodnews Bay Region, Southwest Alaska     

Thomas Oommen  Anupma Prakash  Debasmita Misra  Sathy Naidu  John J. Kelley  Sukumar Bandopadhyay 《Marine Georesources & Geotechnology》2008,26(1):1-18

Goodnews Bay, southwest Alaska, is known for platinum (Pt) reserve that extends offshore in the Bering Sea. To assess the nearshore placer potential we first collated marine Pt concentrations available since 1960 in a geographic information system (GIS) database. Subsequently, in 2005, we collected 23 pipe dredge sediment samples and 26 vibracores from unexplored sites and analyzed them for Pt. This sampling was supplemented by magnetic (Sea Spy) and seismic (side scan, geoacoustic and datasonic bubble pulser) surveys. Integrating results of geospatial analysis of Pt concentrations with geophysical analysis using GIS techniques led to delineate four locations encouraging for further Pt exploration. Of these, two locations fall close to paleochannels and drowned ultramafic source, while the other two coincide with high energy environments in the Goodnews Bay and close to the Carter Bay.  相似文献   

Low CodaQ_cin the Epicentral Region of the 2001 Bhuj Earthquake ofM_w7.7     

P. Mandal  Jainendra  S. Joshi  Sudesh Kumar  Rajendra Bhunia  B. K. Rastogi 《Pure and Applied Geophysics》2004,161(8):1635-1654

On 26 January, 2001 (03:46:55,UT) a devastating intraplate earthquake of M_w 7.7 occurred in a region about 5 km NW of Bhachau, Gujarat (23.42°N, 70.23°E). The epicentral distribution of aftershocks defines a marked concentration along an E-W trending and southerly dipping (45°) zone covering an area of (60 × 40) km². The presence of high seismicity including two earthquakes of magnitudes exceeding 7.7 in the 200 years is presumed to have caused a higher level of shallow crustal heterogeneity in the Kutch area; a site lying in the seismic zone V (zone of the highest seismicity for potentially M8 earthquakes) on the seismic zoning map of India. Attenuation property of the medium around the epicentral area of the Bhuj earthquake covering a circular area of 61,500 km² with a radius of 140 km is studied by estimating the coda-Q_c from 200 local earthquakes of magnitudes varying from 3.0–4.6. The estimated Q₀ values at locations in the aftershock zone (high seismicity) are found to be low in comparison to areas at a distance from it. This can be attributed to the fact that seismic waves are highly scattered for paths through the seismically active and fractured zone but they are well behaved outside the aftershock zone. Distribution of Q₀ values suggests that the local variation in Q₀ values is probably controlled by local geology. The estimated Q₀ values at different stations suggest a low value of Q=(102 ± 0.80)^*f^{(0.98 ± 0.02)} indicating an attenuative 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 attenuation associated with heterogeneities and/or intrinsic attenuation due to fluid movement in the fault zone and fluid-filled 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 heterogeneity is expected. Based on the attenuation curve estimated for Q₀=102, the ground acceleration at 240 km distance is 13% of 1 g i.e., 0.13 g agreeing well with the ground acceleration recorded by an accelerograph at Ahmedabad (0.11 g). Hence, it is inferred that the Q₀ value obtained from this study seems to be apt for prediction of ground motion for the region.  相似文献   

Fractal Dimension of the 1999 Chamoli Earthquake from Aftershock Studies in Garhwal Himalaya     

Richa?JainEmail author  B. K.?Rastogi  V. P.?Dimri 《Pure and Applied Geophysics》2003,160(12):2329-2341

The Aftershock sequence of Chamoli earthquake (M _w 6.4) of 29 March 1999 is analyzed to study the fractal structure in space, time and magnitude distribution. The b value is found to be 0.63 less than which is usually observed worldwide and in the Himalayas. This indicates that the numbers of smaller earthquakes are relatively less than the larger ones. The spatial correlation is 1.64, indicating that events are approaching a two-dimensional region meaning that the aftershocks are uniformly distributed along the trend of the aftershock zone. Temporal correlation is 0.86 for aftershocks of M 1, indicating a nearly continuous aftershock activity. However, it is 0.5 for aftershocks of M 1.75, indicating a non continuous aftershock activity. From the assessment of slip on different faults it is inferred that 70% displacement is accommodated on the primary fault and the remainder on secondary faults.  相似文献   

Damage due to the M_w 7.7 Kutch, India earthquake of 2001     

B.K. Rastogi   《Tectonophysics》2004,390(1-4):85-103

This paper presents a study of the damage due to the M_w 7.6–7.7 intraplate Kutch earthquake of 26 January 2001. It was a powerful earthquake with a high stress drop of about 20 MPa. Aftershocks (up to M 4) have continued for 2.5 years. The distribution of early aftershocks indicates a rupture plane of 20–25 km radius at depths of 10–45 km along an E–W-trending and south-dipping hidden fault situated approximately 25 km north of the Kutch Mainland Fault. The moment tensor solution determined from regional broadband data indicates reverse motion along a south-dipping (by 47°) fault. The earthquake is the largest event in India in the last 50 years and the most destructive in the recorded history in terms of socioeconomic losses with 13,819 deaths (including 14 in Pakistan), collapse/severe damage of over a million houses and US$10 billion economic loss. Surface faulting was not observed. However, intense land deformations have been observed in a 40×20-km meizoseismal area. These include lateral spreading, ground uplifts (about a meter), ground slumping and deep cracks. Liquefaction with ejection of sand and copious water was widespread in the Banni grassland, Rann areas (salt plains), along rivers and also in the coastal areas up to 200 km distance from the epicenter in areas of intensity VII to X+. Stray incidences of liquefaction have occurred up to distances of at least 300 km. For the first time in India, multistory buildings have been destroyed/damaged by an earthquake. The maximum acceleration is inferred to be 700 cm/s² and intensities are 1–3 units higher in soil-covered areas than expected from the decay rate of acceleration for hard rock.  相似文献   

Crustal structure of the peninsular shield beneath Hyderabad (India) from the spectral characteristics of long-period P-waves     

D.D. Singh  B.K. Rastogi 《Tectonophysics》1978,51(3-4)

The crustal transfer functions have been obtained from long period P-waves of thirteen teleseismic events recorded at Hyderabad (HYB), India. The crustal structure beneath this seismograph station has been obtained after comparing these functions with the theoretical crustal transfer functions which were computed using the Thomson-Haskell matrix formulation. The method is suitable and economical for determining the fine crustal structure. The crust beneath Hyderabad is found to consist of three layers with total thickness of 36 km. The thicknesses of top, middle and bottom layers are 21 km, 8 km and 7 km, respectively.  相似文献   

Integrated production and effective loss rates in the ionosphere     

K N Iyer  R G Rastogi 《Journal of Earth System Science》1978,87(7):147-153

The total electron content data obtained at Ahmedabad through the Faraday fading records of the radio beacons abroad the satellites Explorer 22 and 27 are used to determine the overhead integrated production rate (Q ⁰) and integrated loss coefficient (β′) for the epoch 1965–1968. The production rate (Q ₀) is shown to have two peaks during a year around the equinoctal months and for a particular monthQ ₀ increases linearly with the 10·7 cm solar flux. The loss coefficient β′, too, has two equinoctial peaks within a year. The semiannual variations ofQ ₀ and β′ are discussed in relation to similar variation in the [O]/[N₂] ratio.  相似文献   

Frequency dependence of equatorial ionospheric scintillations     

M R Deshpande  R G Rastogi  Hari Om Vats  K Davies 《Journal of Earth System Science》1978,87(7):173-178

Simultaneous observations of amplitude scintillations at 40 MHz, 140 MHz and 360 MHz radiated from ATS-6 satellite at 34° E longitude were made at Ootacamund near the magnetic equator in India. It has been found that the frequency variation of scintillation index (S ₄) isS ₄ ∞f ^?n , withn being about 1·2 only for weak scintillations, i.e., so long as the scintillation index does not exceed 0·6 at the lower frequency. For strong scintillations (S ₄>0·6) where multiple scattering may be present, the exponentn itself is a function of the intensity of scintillation, the scintillation indices at two frequencies are related by:S ₄(f ₁)=S ₄(f ₂) exp [1·3 log(f ₂/f ₁)(1?S ₄(f ₂)] so long asf ₂/f ₁≤3. Thus knowing scintillation index at a given frequency one can estimate the scintillation index at another frequency. This will be of significant importance for communication problems. Evidence is also shown for the reversal of the frequency law in cases of intense scintillations.  相似文献   

Intense night-time equatorial radio scintillations by sporadicE layers     

R G Rastogi 《Journal of Earth System Science》1983,92(1):37-43

Almost saturated scintillations of radio beacons from geostationary satellites received at an equatorial station during night-time have been shown to occur even during complete absence of spreadF on the vertical incidence ionograms at the same location. These scintillation events were observed when the ionograms showed blanketing type of sporadicE layers simultaneously at different heights. It is suggested that strong equatorial radio wave scintillations during night-time are caused by multiple scattering between different levels of large plasma density gradients in theF or sometimes in theE regions of the ionosphere.  相似文献