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The paper presents the current state of magnitude estimation for Koyna earthquakes exceeding magnitude 3.0. We estimate coda duration magnitude from analogue seismograms recorded on the short period vertical (SPZ) seismometer at Hyderabad seismic observatory HYB and determine moment magnitude using very broad-band (VBB) data from the Geoscope station (HYB)and short period digital data from the local seismic network of NationalGeophysical Research Institute (NGRI) around the Koyna and Warna reservoirs.Firstly, the seismograms of 97 Koyna earthquakes exceeding magnitude 4.0 havebeen used to establish a new empirical coda duration magnitude scale which includes the higher order terms of log10, where is the coda length in seconds. Four background noise levels (1, 2, 6 and 10 mm) areconsidered to estimate the coda duration. We found that the duration magnitudes for 1 mm background level are more stable than those for 2, 6 and 10 mm. The new coda duration magnitude (Mdnew) scale, for 1 mmlevel, is:Mdnew = –0.594 + 2.04 log10 – 0.0435 (log10)2The estimated Mdnew are compatible with the reported MS values of the NGRI observatory and the mb values of the United States Geological Survey (USGS). These magnitudes can be obtained within the standard deviation of ± 0.26 units of MS (NGRI). A new relatively homogeneous catalog for Koyna earthquakes of Mdnew 4.0 is obtained. The momentmagnitudes for 34 Koyna-Warna events of Mdnew ranging from 3.0 to 5.4 have been estimated using two techniques. The first utilizes amplitudes of band-pass filtered (between 15 and 30 sec) velocity traces of moderate Koyna-Warna earthquakes of MW} 4.4 to 5.4, we abbreviate the magnitude using MA. The second is based on the S-wave spectrum of short period seismograms of local earthquakes (MW < 3.8). Moment magnitudes estimated by spectral analysis mainly depend on the estimation of event's long-period spectral level and appears to saturate for moderate Koyna-Warnaearthquakes (MW > 3.8). We recommend the use of both techniques whenever possible. The estimated moment magnitudes and Mdnew show an almost linear relationship with a standard deviation of ± 0.05. 相似文献
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It is here shown that the stellar astration of deuterium in the solar neighbourhood of the Galactic Disc over 13 Gy corresponds to a factor of about 2 only in a closed model of chemical evolution. 相似文献
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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
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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
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