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Source of Unusual Monochromatic Wave Packets Recorded Globally in the Seismograms of 11 November 2018


Affiliations
1 National Center for Seismology, New Delhi 110 003, India
 

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.
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  • Source of Unusual Monochromatic Wave Packets Recorded Globally in the Seismograms of 11 November 2018

Abstract Views: 393  |  PDF Views: 129

Authors

S. N. Bhattacharya
National Center for Seismology, New Delhi 110 003, India
V. K. Gahalaut
National Center for Seismology, New Delhi 110 003, India
Narendra Pandey
National Center for Seismology, New Delhi 110 003, India
Shankar Pal
National Center for Seismology, New Delhi 110 003, India
Rajeev Manhas
National Center for Seismology, New Delhi 110 003, India
G. Suresh
National Center for Seismology, New Delhi 110 003, India

Abstract


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.

References





DOI: https://doi.org/10.18520/cs%2Fv118%2Fi7%2F1069-1076