On November 11, 2018, an event generating long-lasting, monotonic long-period surface waves was observed by seismographs around the world. This event occurred at around 09:28 UTC east of the Mayotte Island, in the Indian Ocean off the coast of East Africa. This event is unusual due to the absence of body waves in the seismograms and no feeling of earth shaking by people locally. The purpose of this study is to investigate this unusual event using the waveforms recorded by 26 stations of the Iranian National Broadband Seismic Network. The stations are located at epicentral distances ranging from 4542 to 5772 km north-northeast of the event’s epicenter. The arrival of monochromatic long-period signals is visible around 10 UTC in the recordings of all the stations and the signals lasted for more than 30 min. Frequency analysis of the seismograms shows a clear peak at 0.064 Hz (15.6 s/cycle). The maximum amplitude of the transverse components is less than a half of the radial components. This is in agreement with the theoretical radiation pattern of Rayleigh and Love waves at a frequency of 0.06 Hz for a vertical compensated linear vector dipole source mechanism. The average apparent phase velocities were calculated as 3.31 and 2.97 km/s, in the transverse and radial directions, corresponding, respectively, to Love and Rayleigh waves in the frequency range of 0.05–0.07 Hz. A surface wave magnitude of Ms 5.07 ± 0.22 was estimated. Just before the monochromatic signal arrives, there is some dispersion in the surface waves. This observation may suggest a regular earthquake of Ms 4.3 ± 0.11 that triggered the November 11, 2018, event. The difference between the arrival times of the recorded surface waves of the two events is estimated to be less than 31 s, and most likely of ~ 7 s only.

2018年11月11日，全球地震仪观测到一个事件，该事件产生了持久的，单调的，长周期的表面波。该事件发生在UTC东部非洲沿岸印度洋马约特岛以东的世界标准时间09:28左右。由于地震图中没有体波，而且当地人没有晃动的感觉，因此此事件是不寻常的。这项研究的目的是使用伊朗国家宽带地震台网的26个台站记录的波形调查这一异常事件。这些台站位于震中东北偏北，距震中中心的距离为4542至5772 km。在所有电台的记录中，在10 UTC附近都可以看到单色长周期信号的到来，并且该信号持续了30分钟以上。地震图的频率分析显示在0.064 Hz（15.6 s /周期）处有一个清晰的峰值。横向分量的最大幅度小于径向分量的一半。这与用于垂直补偿线性矢量偶极子源机制的频率为0.06 Hz的瑞利波和洛夫波的理论辐射图一致。平均视在相速度在横向和径向分别为3.31 km / s和2.97 km / s，分别对应于0.05-0.07 Hz频率范围内的Love波和Rayleigh波。的表面波幅度为 垂直补偿线性矢量偶极子源机制的频率为06 Hz。计算出的平均视在相速度在横向和径向分别为3.31和2.97 km / s，分别对应于0.05-0.07 Hz频率范围内的Love波和Rayleigh波。的表面波幅度为 垂直补偿线性矢量偶极子源机制的频率为06 Hz。计算出的平均视在相速度在横向和径向分别为3.31 km / s和2.97 km / s，分别对应于0.05-0.07 Hz频率范围内的Love波和Rayleigh波。的表面波幅度为MS 5.07±0.22估计。在单色信号到达之前，表面波中存在一些色散。该观察结果可能表明触发了2018年11月11日事件的Ms 4.3±0.11定期地震。估计两个事件的记录面波的到达时间之间的差异小于31 s，最有可能仅为7 s。