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  • 1
    Electronic Resource
    Electronic Resource
    CrustalP-wave velocity and velocity-ratio study in northeast India by a microearthquake survey (1990)
    Springer
    Pure and applied geophysics 134 (1990), S. 93-108 
    Details
    ISSN: 1420-9136
    Keywords: Microearthquake ; Wadati plot ; station-by-station method ; velocity-ratio ; upper crust ; lower crust ; precursor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The upper crustal (≤20 km)P-wave velocity beneath the Shillong Plateau and Nowgong area has been studied by the time-distance plot method. TheP-arrival data of the shallow (≤20 km) microearthquakes from three temporary networks are used, and the average velocity is found to be 5.55 km/s. The velocity ratio (V p /V s ) for the upper crust (0–20 km) as well as for the lower crust (21–40 km) are determined by the Wadati-plot method and station-by-station method. The average value obtained by the two methods is compatible; theV p /V s ranges between 1.74 to 1.76. A generalized seismic velocity model of the area is suggested by this study, which has been very useful for microearthquake location.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878082
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Correlation of T-log with E-log in coal-bearing formations (1980)
    Springer
    Pure and applied geophysics 119 (1980), S. 349-355 
    Details
    ISSN: 1420-9136
    Keywords: Borehole logs ; Coal bearing formations ; Gondwana Basin (India)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The profile of temperature gradient versus depth (T-log) has been found to be very useful for correlation with electrical resistivity log (E-log) in coal-bearing formations. A positive correlation between electrical resistivity and thermal resistivity is observed in coal sections whereas a negative correlation is found in sandstone/shale beds, thus helping in coal prospect evaluation. T logs have been used to correct the location of coal bed which had apparently been misinterpreted by the E-log. Hole to hole correlation of T-log and E-log is found to be excellent and it is observed that thermal resistivity characteristics of given formations remain fairly uniform. A rough estimation of coal grade is possible from the detailed study of the T-logs. Abrupt changes of temperature gradient as also its reversals have been observed in burnt coal sections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00877770
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  • 3
    Electronic Resource
    Electronic Resource
    Seismic velocity-ratio in the crust and uppermost mantle in southeast Wellington province, New Zealand (1982)
    Springer
    Pure and applied geophysics 120 (1982), S. 809-819 
    Details
    ISSN: 1420-9136
    Keywords: Microearthquakes ; Velocity-ratio ; Wadati plot ; Poisson's ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The regional variation of the seismic velocity-ratio (γ) over a 200 km long traverse has been studied by means of microearthquake surveys. The Wadati-plot method is used with a minimum of four P and S arrivals for each of 49 earthquakes. The area as a whole is found to be characterized by a γ value of 1.74–1.76 for earthquakes of depth 12–40 km, except in a 50 km long section near Wellington, where γ is low at 1.60. This low γ has been attributed to the fault zones in the region. A small change of γ is observed between the upper crust (≤5 km) and lower crust (≥12 km), but there is no change of γ between the lower crust and uppermost mantle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876663
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  • 4
    Electronic Resource
    Electronic Resource
    Earthquake prediction in northeast India—A review (1991)
    Springer
    Pure and applied geophysics 136 (1991), S. 297-313 
    Details
    ISSN: 1420-9136
    Keywords: Precursor ; resistivity ; magnetic ; gravity ; earthquake swarm ; microseismicity-rate ; velocity-ratio ; radon gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A multidimensional geophysical approach is made to study earthquake precursors in northeast India. Resistivity, gravity and seismological precursor anomalies for the two recent damaging earthquakes, one on December 30, 1984, magnitude 5.8, and the other on August 6, 1988, magnitude 7.5, are very encouraging to intensify these studies in the region. Improved methods of magnetic and geohydrological precursor studies are suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876379
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  • 5
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    The attenuation mechanism of S-waves in the source zone of the 1999 Chamoli earthquake (2013)
    Elsevier Science Limited
    Details
    Publication Date: 2017-04-04
    Description: In the present study the attenuation mechanism of seismic wave energy in and around the source area of the Chamoli earthquake of 29th March 1999 is estimated using the aftershock data. Most of the analyzed events are from the vicinity of the Main Central Thrust (MCT), which is a well-defined tectonic discontinuity in the Himalayas. Separation of intrinsic (Q 1 i ) and scattering (Q 1 s ) attenuation coefficient is done over the frequencies 1, 2, 4, 8 and 16 Hz using Multiple Lapse Time Window Analysis (MLTWA) method. It is observed that S-waves and their coda are primarily attenuated due to scattering attenuation and seismic albedo is very high at all the frequencies. A comparison of attenuation characteristics obtained using these aftershock data with those obtained using data of general seismicity of this region reveal that at lower frequencies both intrinsic and scattering attenuation for Chamoli was much higher compared to those for Garwhal-Kumaun region using general seismicity data. At higher frequencies intrinsic attenuation for Chamoli is lower than and scattering attenuation is comparable to those obtained using general seismicity data of Garwhal-Kumaun region.
    Description: A partial support has been given by Italy INGV-DPC (Istituto Nazionale di Geofisica e Vulcanologia and Dipartimento di Protezione Civile) Projects UNREST and SPEED, and by Italy’s Ministry of Education PRIN project (Seismic Hazard in Central Apennines, UR Del Pezzo).
    Description: Published
    Description: 446-454
    Description: 1T. Geodinamica e interno della Terra
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: restricted
    Keywords: MLTWA ; Intrinsic attenuation ; Scattering attenuation ; Chamoli Himalayas ; Himalayas ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Crustal seismic anisotropy beneath Shillong plateau - Assam valley in North East India: Shear-wave splitting analysis using local earthquakes (2018)
    Details
    Publication Date: 2022-06-09
    Description: We present crustal anisotropy estimates constrained by shear wave splitting (SWS) analysis using local earthquakes in the Shillong plateau and Assam valley area, North East India (NE India) region. Splitting parameters are determined using an automated cross-correlation (CC) method. We located 330 earthquakes recorded by 17 broadband seismic stations during 2001–2014 in the study area. Out of these 330 events, seismograms of 163 events are selected for the SWS analysis. Relatively small average delay times (0.039–0.084 s) indicate existence of moderate crack density in the crust below the study area. It is found that fast polarization directions vary from station to station depending on the regional stress system as well as geological conditions. The spatial pattern of crustal anisotropy in the area is controlled mostly by tectonic movement of the Indian plate towards NE. Presence of several E-W and N-S trending active faults in the area also play an important role on the observed pattern of crustal anisotropy.
    Description: Published
    Description: 425-432
    Description: 7T. Struttura della Terra e geodinamica
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Acceleration Attenuation Regularities in the Western Himalayas (2020)
    Springer
    Details
    Publication Date: 2020-01-01
    Print ISSN: 0747-9239
    Electronic ISSN: 1934-7871
    Topics: Geosciences
    Published by Springer
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  • 8
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    Source parameters and focal mechanisms of local earthquakes: Single broadband observatory at ISM Dhanbad (2009)
    Springer
    Details
    Publication Date: 2009-09-01
    Print ISSN: 0016-7622
    Electronic ISSN: 0974-6889
    Topics: Geosciences
    Published by Springer
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  • 9
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    Anomalous behaviour of precursor resistivity in Shillong area, NE India (1988)
    Oxford University Press
    Details
    Publication Date: 1988-07-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 10
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    Fault Geometry of the Mw 7.7 Western India Intraplate Earthquake: Constrained from Double-Difference Tomography and Fault-Plane Solutions (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-07-26
    Description: Globally, one of the largest intraplate earthquakes of M w  7.7 occurred on 26 January 2001 in the Kachchh rift basin (KRB), western India. The continuing long aftershock sequence over decades has generated much debate on the seismogenic fault(s). We have analyzed more than 10,000 aftershocks ( M w 〉1.0) recorded by a 50-station broadband network in the region during 2006–2014. A total of 834 aftershocks ( M w 〉2.4), each recorded by at least eight broadband seismic stations with a minimum of eight P and six S phases, are relocated in this study by double-difference tomography (tomoDD) method. The relocated aftershocks and velocity images reveal a near-vertical or steeply south-dipping deeper structure as the source zone of the mainshock and aftershocks; the structure correlates well with the geologically mapped South Wagad fault (SWF). Among the other geologically known faults, the Kachchh Mainland fault (KMF) and the Gedi fault (GF) are also well identified in the seismic sections. Further, fault-plane solutions of 109 aftershocks having M w ≥3.5 corroborate well with the known faults. The geological model and seismological observations suggest that the SWF overstepped the KMF and intersects it at depth. The intersecting fault zone is the source area for the deeper (10–35 km) reverse faulting earthquakes in the KRB. At the fault end of the SWF, a heterogeneous velocity structure is imaged, which is attributed to a fluid-filled rock matrix that triggered the mainshock. On the other hand, the GF is reported to be a later-activated fault to the north of SWF; it generated some shallower aftershocks (0–20 km) mostly by strike-slip mechanisms.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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