Publication Date:
2017-04-04
Description:
In July 2006, INGV (Istituto Nazionale di Geofisica e Vulcanologia) successfully deployed
on the flat top of the submarine Marsili volcano, the first Italian OBS/H (Ocean
Bottom Seismometer with Hydrophone), entirely developed at the Gibilmanna Geophysical
Observatory within a project funded by an agreement between Italian National
Civil Protection Department (DPC) and INGV. In this short deployment the
OBS/H was equipped with a Nanometrics Trillium 40s seismometer and an OAS E-
2PD Hydrophone. A 21 bits four channel digitizer (SEND MLS) recorded data at 200
sps to exploit, as well as possible, the wide flat response of the hydrophone (0-5 KHz).
For long-term deployments, the instrument will be provided with Cox-Webb 500s-2
Hz differential pressure gauge and Nanometrics Trillium 120s or Guralp CMG40TOBS
and will record data at 50 sps, for as long as one or two years respectively,
depending on the seismic sensor. Most of the recorded events (about 800) seem to
be associated with the active nearby Marsili volcano. The instrument, during the 9
days of the test at a depth of 790 m, recorded 835 volcano-tectonic events, classifiable
in 6 different categories: 1 teleseismic event (Java 2006/07/17, Mw=7.2), 8 located
regional tectonic events, 9 not located local tectonic events, 705 low frequency volcanic
events, 84 high frequency volcanic events, 26 “Tornillo” and 2 probable rockfall
events. Spectral analysis shows, in the first 7 days of the deployment, an evident sequence
of low energy events superimposed on the continuous background volcanic
tremor, with dominant frequencies between 2 and 6 Hz, known in literature as VT-B
(Volcanic-Tectonic event, type B) and related to shallow hypocenters (above 1-2 km).
In the last two days of operation, the hydrophone recorded high frequency events,
with dominant frequencies between 40 and 90 Hz; this kind of event could be associated
with hydrothermal activity. In March 2007, three INGV OBS/H will be deployed
in the southern Ionian sea, at different distances from the Malta escarpment, within the European project NERIES (Network of Research Information Infrastructures for
European Seismology). At present, we are planning a further improvement of the instrument,
equipping it with a 24 bits digitizer and a communication system based on
an acoustic modem and a low power consumption PC with ARM processor. In this
way, it would be possible to pick up events traces from the OBS on the sea bottom,
without recovering it. Furthermore, the acoustic link with a buoy, in its turn satellite
linked with an on shore control centre, in association with triggering algorithms, could
be employed to insert the INGV OBS/H in a tsunami warning system.
Description:
Published
Description:
Vienna
Description:
2.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomarini
Description:
open
Keywords:
OBS
;
OBS/H
;
Marsili
;
Ocean Bottom Seismometer
;
04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
Oral presentation
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