Preliminary performance report of the RHUM-­RUM ocean bottom seismometer network around La Réunion, western Indian Ocean

Abstract

RHUM-­RUM is a German-­French seismological experiment based on the sea floor surrounding the island of La Réunion, western Indian Ocean. Its primary objective is to clarify the presence or absence of a mantle plume beneath the Reunion hotspot. RHUM-­RUM's central component is a 13-­month deployment (Oct 2012 to Nov 2013) of 57 broadband ocean bottom seismometers (OBS) and hydrophones over an area of 2000x2000 km2 surrounding the hotspot. The array contained 48 broadband OBS from the German DEPAS pool and 9 stations from the French INSU pool. It has been the largest deployment of DEPAS and INSU OBS so far, and the first large joint experiment. We give an overview of station performance and issues encountered, touching on instrument responses, recorder and battery performance, noise characteristics, and data yield. Of the 57 stations, 46 had proper seismometer and 53 proper hydrophone recordings. Out of a installation time of 13x57=741 station-­months, 412 months of data were actually realized for the seismometers, and 710 for the hydrophones. At long periods (>10 s), the DEPAS stations are affected by significantly more noise than the INSU stations, a difference that is most pronounced on the horizontal components and can probably be explained by tilting of the instrument assemblage. The DEPAS sensors are integrated into the OBS frame and buoy assemblage, and would therefore record its motions, caused for example by the action of deep sea currents. However, this integrated setup also makes the DEPAS OBS easier to deploy and recover, especially in large deployments such as this one