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  • 1
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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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  • 2
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    A Local Magnitude Scale ( M L ) for the Kachchh Rift Basin: An Active Intraplate Region, Gujarat, India (2018)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2018
    Description: 〈span〉〈div〉Abstract〈/div〉A calibrated local magnitude scale (ML) is essential for seismic hazard assessment of seismically active regions. In this study, an ML has been developed for the Kachchh region for the first time. This scale is derived using 9167 amplitude measurements on the horizontal‐component recordings of 1456 earthquakes, with hypocentral distances ranging from 6 to 100 km. All the amplitude measurements were inverted simultaneously to determine constants of the ML and station corrections for the Kachchh region. The resulting distance correction term is given by −log(A0)=1.86log(r/17)−0.00195(r−17)+2 and −log(A0)=1.83log(r/100)−0.00236(r−100)+3 for 17 and 100 km normalizations, respectively. The distance correction term at 17 km normalization suggests that attenuation in the Kachchh region is higher than in other regions of the world, for hypocentral distances above 45 km. Also, the standard deviation of the magnitude residuals was computed to check the effect of the new attenuation terms on the magnitude estimates. Although the standard deviation without station correction is 0.26 (variance σ2=0.068), the value is 0.22 (variance σ2=0.048) with station correction. This indicates that station correction reduces the variance by 30% and brings the average residual closer to zero. The station corrections obtained in the present study varied from −0.20 to +0.27. The relationship between the local magnitude ML (this study) and the moment magnitude Mw reveals that the derived Mw is larger for earthquakes with magnitudes smaller than 3 and smaller for earthquakes of larger magnitudes.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 3
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    A Local Magnitude Scale ( M L ) for the Kachchh Rift Basin: An Active Intraplate Region, Gujarat, India (2018)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2018
    Description: 〈span〉〈div〉Abstract〈/div〉A calibrated local magnitude scale (ML) is essential for seismic hazard assessment of seismically active regions. In this study, an ML has been developed for the Kachchh region for the first time. This scale is derived using 9167 amplitude measurements on the horizontal‐component recordings of 1456 earthquakes, with hypocentral distances ranging from 6 to 100 km. All the amplitude measurements were inverted simultaneously to determine constants of the ML and station corrections for the Kachchh region. The resulting distance correction term is given by −log(A0)=1.86log(r/17)−0.00195(r−17)+2 and −log(A0)=1.83log(r/100)−0.00236(r−100)+3 for 17 and 100 km normalizations, respectively. The distance correction term at 17 km normalization suggests that attenuation in the Kachchh region is higher than in other regions of the world, for hypocentral distances above 45 km. Also, the standard deviation of the magnitude residuals was computed to check the effect of the new attenuation terms on the magnitude estimates. Although the standard deviation without station correction is 0.26 (variance σ2=0.068), the value is 0.22 (variance σ2=0.048) with station correction. This indicates that station correction reduces the variance by 30% and brings the average residual closer to zero. The station corrections obtained in the present study varied from −0.20 to +0.27. The relationship between the local magnitude ML (this study) and the moment magnitude Mw reveals that the derived Mw is larger for earthquakes with magnitudes smaller than 3 and smaller for earthquakes of larger magnitudes.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 4
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    Seismicity and Subterranean Sounds in the Northwest Deccan Volcanic Province of India (2017)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2017-05-31
    Description: The northwestern Deccan volcanic province in India is one of the most seismically active intraplate regions of the world. In addition, the region is associated with episodic swarm activity and reports of sounds, whose linkage hitherto remains elusive. During the month of January 2016, a swarm activity occurred in the Kachchh and Saurashtra regions and continued for about two months. Many of the events were accompanied by audible sounds, like blasting, that caused severe panic among local residents, prompting us to investigate the causative mechanism. The events were recorded by our seismic stations and an additional five stations that we were able to deploy at the onset of the swarm. The activity produced sounds with good energy in the audible frequency range of humans. Spectrogram analysis of the events with associated sounds revealed frequencies ≥20 Hz, in contrast to the lower frequencies for those that did not generate the sounds. In addition to the higher frequencies, we observed horizontal particle motion that was dominated by retrograde elliptical motion consistent with Rayleigh waves. These observations were not recorded from any of the events that did not generate sounds. Audible sounds generated by earthquakes are consistently reported from shallow earthquakes that generate high-frequency surface waves.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 5
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    New Empirical Earthquake Source-Scaling Laws (2017)
    Seismological Society of America
    Details
    Publication Date: 2017-09-25
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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