Observation of the long-period monotonic seismic waves of the November 11, 2018, Mayotte event by Iranian broadband seismic stations

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