Mission results from the first GEOSTAR observatory (Adriatic Sea, 1998)

Abstract

We assess the first mission of the GEOSTAR (GEophysical and Oceanographic STation for Abyssal Research) deep-sea multidisciplinary observatory for its technical capacity, performance and quality of recorded data. The functioning of the system was verified by analyzing oceanographic, seismological and geomagnetic measurements. Despite the mission's short duration (21 days), its data demonstrated the observatory's technological reliability and scientific value. After analyzing the oceanographic data, we found two different regimes of seawater circulation and a sharp and deepening pycnocline, linked to a down-welling phenomenon. The reliability of the magnetic and seismological measurements was evaluated by comparison with those made using on-land sensors. Such comparison of magnetic signals recorded by permanent land geomagnetic stations and GEOSTAR during a "quiet" day and one with a magnetic storm confirmed the correct functioning of the sensor and allowed us to estimate the seafloor observatory's orientation. The magnitudes of regional seismic events recorded by our GEOSTAR seismometer agreed with those computed from land stations. GEOSTAR has thus proven itself reliable for integrating other deep-sea observation systems, such as modular observatories, arrays, and instrumented submarine cables.

Seafloor Seismic Noise at Central Eastern Mediterranean Sites

“…4). After the observatory is deployed, the seismometer is separated from the observatory, via an electrical or acoustic command sent from the ship, and drops from a distance of ∼50 cm to the sea bottom (Beranzoli et al, 2003). The titanium vessel is linked to the Bottom Station (aluminum frame hosting the monitoring system) by a slack rope.…”

Long-term Seafloor Experiment with the CUMAS Module: Performance, Noise Analysis of Geophysical Signals, and Suggestions about the Design of a Permanent Network

“…A definite improvement in the coupling can be obtained by adopting a similar installation as for the GEOSTAR type of seafloor observatory (Beranzoli et al 1998;Monna et al 2005), where there was complete decoupling of the seismometer from the observatory frame. Alternatively, improvements in signal-to-noise ratio can be obtained installing the seismometers in boreholes (Suyehiro et al1995;Beauduin and Montagner 1996) or burying the sensors at shallow depths in the sediments of seafloor (Duennebier et al 1991;Yamamoto and Torii 1986).…”

New observations of local seismicity by the SN-1 seafloor observatory in the Ionian Sea, off-shore Eastern Sicily (Italy)

“…Amplitude saturation, overlapping of events, normal deviations in the instrument calibration or changes in seismic equipment may easily lead to systematic errors in the magnitude estimate. To quantify the size of local seismicity recorded from SN‐1 in the area of Eastern Sicily, we determined the local magnitude ( M L ), as it was possible to obtain the ground displacement waveform from the deconvolution of the well‐known SN‐1 instrumental response (Beranzoli et al 2003). Due to the flat response of the SN‐1 broad‐band seismometer we computed the M L of the 213 events by the convolution of the event waveforms with the Wood‐Anderson response curve, following the original definition by Richter (1935).…”