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Bhattacharya, S. N.
- Source Parameters and Focal Mechanisms of Local Earthquakes: Single Broadband Observatory at ISM Dhanbad
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Authors
Affiliations
1 Department of Applied Geophysics, Indian School of Mines, Dhanbad - 826 004, IN
2 Department Geology and Geophysics, IIT Kharagpur, Kharagpur - 721 302, IN
1 Department of Applied Geophysics, Indian School of Mines, Dhanbad - 826 004, IN
2 Department Geology and Geophysics, IIT Kharagpur, Kharagpur - 721 302, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 74, No 3 (2009), Pagination: 413-419Abstract
A three-component broadband seismograph is in operation since January 2007 at the Indian School of Mines (ISM) campus. We have used the broadband seismograms of two local earthquakes M <3 recorded by this single station to illustrate its efficacy in understanding the source processes and tectonics in Dhanbad area. Source parameters and fault plane solutions are obtained through waveform inversion. It is observed that these two earthquakes occurred in the lower crust at a depth of 26 km by strike slip faulting. North-south compressional and east-west tensional stresses are dominant in the area, and the lower crust is the source area for the local earthquakes.Keywords
Earthquake, Broadband, Seismograph, Dhanbad.
References
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- Source of Unusual Monochromatic Wave Packets Recorded Globally in the Seismograms of 11 November 2018
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Authors
S. N. Bhattacharya
1,
V. K. Gahalaut
1,
Narendra Pandey
1,
Shankar Pal
1,
Rajeev Manhas
1,
G. Suresh
1
Affiliations
1 National Center for Seismology, New Delhi 110 003, IN
1 National Center for Seismology, New Delhi 110 003, IN
Source
Current Science, Vol 118, No 7 (2020), Pagination: 1069-1076Abstract
On 11 November 2018, all global seismic stations recorded unusual long-period wave packets without any discernible body waves. Our analyses show that the wave packets are monochromatic with period 15.6 sec and are fundamental-mode non-dispersive Rayleigh waves. Using the arrival times of wave packets, the source is approximately located at the northeastern edge of the recent earthquake swarm zone, off the east coast of Mayotte, a volcanic island between North Madagascar and East Africa. Synthetic seismograms for an isotropic source at 15 km depth with a transient oscillation of the same periodas that observed in the wave packets, are consistent with the recorded seismograms. We estimate an equivalent magnitude (Mw) of ~4.8 for this source and suggest that a volcanic fluid sphere of radius ~5 km might have generated such radial oscillations. Interestingly, similar monochromatic waves with lesser amplitude were also recorded on many occasions from the same source during 21 June 2018 to 10 September 2019. The period of waves increased from 15.2 sec in June to 15.6 sec in October– November 2018 and then decreased to 15.0 sec in September 2019, which implies an increase and then decrease in radius of the fluid sphere at the source.Keywords
Monochromatic Wave Packets, Seismograms, Seismic Stations, Source Characterization.Full Text
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