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Seismic gaps and intraplate seismicity around Rodrigues Ridge (Indian Ocean) from time domain array analysis

Abstract. Rodrigues Ridge connects the Réunion hotspot track with the Central Indian Ridge (CIR) and has
been suggested to represent the surface expression of a sub-lithospheric flow channel. From global
earthquake catalogues, the seismicity in the region has been associated mainly with events related
to the fracture zones at the CIR. However, some segments of the CIR appear void of seismic
events. Here, we report on the seismicity recorded at a temporary array of 10 seismic stations
operating on Rodrigues Island from September 2014 to June 2016. The array analysis was performed
in the time domain by time shifting and stacking the complete waveforms. Event distances
were estimated based on a 1-D velocity model and the travel time differences between S and
P wave arrivals. We detected and located 63 new events that were not reported by the global
networks. Most of the events (51) are located off the CIR and can be classified as intraplate
earthquakes. Local magnitudes varied between 1.6 and 3.7. Four seismic clusters were observed that occurred to the west of the spreading
segment of the CIR. The Rodrigues Ridge appeared to be
aseismic during the period of operation. The lack of seismic activity along both Rodrigues Ridge
and the sections of the CIR to the east of Rodrigues may be explained by partially molten
upper-mantle material, possibly in relation to the proposed material flow between the Réunion
plume and the CIR.
