Aswini K K, Dewangan Pawan, Kamesh Raju K A, Yatheesh V, Singha Pabitra, Arya Lalit, Ramakrushana Reddy T
CSIR-National Institute of Oceanography, Dona Paula, Goa, 403004, India.
School of Earth, Ocean and Atmospheric Sciences, Goa University, Taleigao Plateau, Goa, 403206, India.
Sci Rep. 2020 Dec 4;10(1):21219. doi: 10.1038/s41598-020-78216-2.
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.
监测通常由地下岩浆活动引发的海底火山的火山活动是一项挑战。我们展示了一组新的海底地震仪（OBS）数据，这些数据显示了地球物理证据，表明安达曼海尼科巴群岛附近海域的海底火山存在地下岩浆活动。在该区域，我们首次观测到被动OBS实验记录的混合超长周期地震。这些事件由高频（5 - 10赫兹）起始，有清晰的P波初至，随后是300 - 600秒范围内的低频（0.01 - 0.5赫兹）振荡，并伴有突出的高频（10 - 40赫兹）水声声相。2014年3月21日和22日共检测到141次高频事件，其中71次伴有低频振荡。这些事件沿海底火山弧和大苏门答腊断裂的瑟利梅乌姆地段呈西北 - 东南方向分布。自2004年12月26日苏门答腊海啸地震以来，尼科巴群岛附近海域频繁发生地震群。这些地震群分别发生在2005年1月、2014年3月和10月、2015年11月以及2019年3月。低频地震的发生和突出的水声声相表明存在地下构造和岩浆影响。我们认为，岩浆脉冲从深部岩浆库向上移动至浅部岩浆房，激活了条状断层的走滑运动，并在尼科巴群岛附近海域诱发了地震群。
