Very-long-period seismicity of Mayotte's 2018-2019 seismo-volcanic crisis

On November 11, 2018, an intriguing highly energetic signal originating from Mayotte's region in the Comoros archipelago was recorded by seismic stations all over the world. This seismic event was particularly unusual because of its highly monochromatic Rayleigh wave trains with very long period (15.4 s) and long duration (~20 min). A volcanic origin of the event, associated with an ongoing seismic swarm east of Mayotte that started six months earlier in May 2018, was first postulated in the scientific literature by Lemoine et al. (2019). Bathymetry campaigns conducted in May 2019 revealed the birth of an underwater volcano located 50 km east of Mayotte island, thereby confirming the volcanic nature of this seismic swarm and enigmatic monochromatic VLP signal.

We apply a seismic network-based method to characterize this VLP event. We analyze one year of seismic data continuously recorded between mid-April 2018 and mid-May 2019 by 12 stations regionally distributed around Mayotte island. The network we consider has an aperture of ~4000 km and is composed of different sensors attached to various networks. Those seismic data are free access data hosted online by the IRIS Data Management Center. Our network-based method, based on the seismic network covariance matrix, indicates that more than 110 self-similar VLP events were triggered between May 2018 and May 2019. We first show the time-frequency features of these repeating VLP events and their relation to higher-frequency volcano-tectonic earthquakes. We then investigate the source mechanism of the main November 11, 2018 VLP event to quantify its relationship to the ongoing volcano-tectonic crisis near Mayotte.

Lemoine, A., Bertil, D., Roullé, A., & Briole, P. (2019). The volcano-tectonic crisis of 2018 east of Mayotte, Comoros islands. EarthArXiv.