Sub-surface magma movement inferred from low-frequency seismic events in the off-Nicobar region, Andaman Sea

K K Aswini,T Ramakrushana Reddy,Pawan Dewangan,Pabitra Singha,V Yatheesh,K A Kamesh Raju,Lalit Arya

doi:10.1038/s41598-020-78216-2

K K Aswini, T Ramakrushana Reddy + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-78216-2

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Abstract

Monitoring volcanic activity along the submarine volcanoes that are usually induced by subsurface magmatism is a challenge. We present fresh set of Ocean Bottom Seismometer (OBS) data that shows geophysical evidence indicative of subsurface magmatism along the submarine volcanoes in the off Nicobar region, Andaman Sea. In this region, we observed for the first time, hybrid very long-period earthquakes documented by passive OBS experiment. These events were initiated by high-frequency (5–10 Hz) with a clear onset of P-phase followed by low-frequency (0.01–0.5 Hz) oscillations in the range of 300–600 s with a prominent high-frequency (10–40 Hz) hydro-acoustic phase. A total of 141 high-frequency events were detected on 21st and 22nd March 2014 out of which 71 were of low-frequency oscillations. These events are distributed in the northwest–southeast direction along the submarine volcanic arc and Seulimeum strand of Great Sumatra fault. Off Nicobar region has been witnessing frequent earthquake swarms since 26th December 2004 tsunamigenic Sumatra earthquake. These swarms occurred in January 2005, March and October 2014, November 2015 and March 2019. The occurrence of low-frequency earthquakes and prominent hydro-acoustic phase are suggestive of sub-surface tectonic and magmatic influence. We propose that upward movement of magma pulses from deeper magma reservoir to the shallow magma chamber activated the strike-slip movement of sliver faults and induced earthquake swarms in the off Nicobar region.

Highlights

Monitoring volcanic activity along the submarine volcanoes that are usually induced by subsurface magmatism is a challenge
Bathymetry data show the presence of cratered submarine v olcanoes[23] in the off Nicobar region; no other geophysical evidence of recent magma movement has been reported from this region
We report for the first time the occurrence of low-frequency earthquakes on 21st and 22nd March 2014, a suggestive of subsurface magma movement in the off-Nicobar region

Summary

Introduction

Monitoring volcanic activity along the submarine volcanoes that are usually induced by subsurface magmatism is a challenge. We observed for the first time, hybrid very long-period earthquakes documented by passive OBS experiment These events were initiated by high-frequency (5–10 Hz) with a clear onset of P-phase followed by low-frequency (0.01–0.5 Hz) oscillations in the range of 300–600 s with a prominent high-frequency (10–40 Hz) hydro-acoustic phase. Volcanotectonic events that occur underwater often generate hydro-acoustic waves (observed as T-waves in continental stations) that propagate through the SOFAR (Sound Fixing and Ranging) channel in deep-ocean, and can be detected by broadband hydrophones. Such phases are commonly used to monitor submarine volcanic a ctivity[6,7,8,9,10]. Bathymetry data show the presence of cratered submarine v olcanoes[23] in the off Nicobar region; no other geophysical evidence of recent magma movement has been reported from this region

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