32 research outputs found
Modelling of the hydro-acoustic signal and tsunami wave generated by sea floor motion including a porous seabed
Within the framework of a 2-D compressible tsunami generation model with a flat porous seabed, acoustic waves are generated and travel outwards from the source area.
The effects of the porous seabed during tsunami generation and propagation processes
include wave amplitude attenuation and low pass filtering of both the hydro-acoustic
signal and tsunami wave. The period of the acoustic wave generated by the seafloor
motion depends on water depth over the source area and is given by four times the period of time required for sound to travel from the sea bed to the surface: these waves carry information about seafloor motion.
The semi-analytical solution of the 2-D compressible water layer model overlying a
porous seabed is presented and discussed.
Furthermore, to include the effects generated by the coupling between
compressible porous sedimentary and water layers, a simplified two layer model with the
sediment modelled as a compressible viscous fluid is presented
Modelling of the hydro-acoustic signal as a Tsunami Precursor
In the frame of a 2-D compressible tsunami generation model with flat
porous seabed, we show that acoustic waves are generated and travel
outside the source area at sound speed. These waves carry information
as to sea floor motion. The acoustic wave period depends on water
height at the source area and is given by four times the travel time
the sound takes to reach the sea surface from the sea bottom.
The fundamental frequency ranges from 1 to 0.05 Hz, at 400 m and 8000
m water depth, respectively. The sound waves produced by seafloor
motion can propagate far from the source, with a small attenuation in
amplitude. Moreover, the typical wavelengths of the acoustic waves
produced by the water layer oscillation
allows the waves to overcome most of the seafloor reliefs. The
semi-analytical solution of the 2-D compressible water layer model
overlying a porous seabed is presente
A new real time tsunami detection algorithm for bottom pressure measurements in open ocean: characterization and benchmarks
In the last decades the use of the Bottom Pressure Recorder (BPR) in a deep ocean environment for tsunami
detection has had a relevant development. A key role for an early warning system based on BPRs is played by
the tsunami detection algorithms running in real time on the BPR itself or at installation site. We present a new
algorithm for tsunami detection that is based on real time pressure data analysis, consisting in tide removing, spike
removing, low pass filtering and linear prediction: the output is then matched against a given pressure threshold
allowing the detection of anomalous events. Different configurations of the algorithm, consisting for instance in a
real time band pass filtering of the pressure signal in place of linear prediction, are also tested for comparison. The
algorithm is designed to be used in an autonomous early warning system, with a finite set of input parameters that
can be reconfigured in real time.
A realistic benchmark scheme is developed in order to characterize the algorithm features with particular regards
to false alarm probability, sensitivity to the amplitude and wavelength of the tsunami and detection earliness. The
algorithm behaviour in real operation is numerically estimated performing statistical simulations where a large
number of synthetic tsunami waves with various amplitude, period, shape and phase is generated and superimposed
to time series of real pressure data recorded in different environmental conditions and locations
The tsumani detector prototype deployed in the Gulf of Cadiz: data collection and functionality evaluation
A new tsunami detector prototype designed to operate in tsunami generation areas has been tested offshore SW Iberia, in the Gulf of Cadiz. The prototype, hosted on board of GEOSTAR has been deployed, at to 3200 meters
depth, in August 2007 and recovered one year later by R/V Urania. After refurbishment and a partial upgrade, the tsunameter has been re-deployed in the same location on November 2009 by R/V Sarmiento de Gamboa.We report
samples of the data collected by the pressure sensors and the critical analysis of the achievements and problems faced during these test periods
The tsumani detector prototype installed on board of SN1-cabled abyssal station.
The new stand-alone tsunami detector prototype designed to operate in tsunami generation areas, already tested in the Gulf of Cadiz (SW Iberia) on board of GEOSTAR abyssal station, has been re-designed to be hosted on the cabled SN1 abyssal station. A new control software has been implemented to manage, in real time, from the land-based control room the basic component of the tsunameter. The tsunami detection software which perform the real time analysis of the parent tsunami signals, differently form the Gulf of Cadiz stand-alone prototype, runs
on a land-based PC.
Moreover, the cabled tsunameter is equipped with a new low-frequency hydrophone to detect the hydro-acoustic noise and signals that may be related to tsunami generation
Tsunami Early Warning System: Deep Sea Measurements in the Source Area
In the framework of the EU project NEAREST, a new Tsunami Early Warning System (TEWS), able to operate in tsunami generation areas, was developed and installed in the Gulf of Cadiz. The TEWS is based on the abyssal station GEOSTAR, placed above a major tsunamigenic structure, and on three seismic centres of Portugal, Spain and Morocco. The core of the system is a tsunami detector installed onboard of GEOSTAR. The tsunami detector communicates with a surface buoy
through a dual acoustic link. The buoy is connected to land stations via satellite link.
The system was designed for near-field conditions and successfully operated from
August 2007 to August 2008, 100 km SW of Cabo de Sao Vincente (Portugal). A
new mission started on November 11th, 2009 in the same location. The tsunami detection is based either on pressure events either on seismic events. The bottom pressure data are analysed in real-time at the seafloor by a new tsunami detection algorithm, which can recognize tsunami waves as small as one centimetre. At the same time it was developed a new theoretical approach to account for tsunami generation in compressible water and in presence of a porous sediment. This model showed that hydro-acoustic waves, travelling much faster than the tsunami, are caused by the seafloor motion. These waves can propagate outside the generation area and are characterised by a modulation carrying valuable information on the seafloor motion, which can be recovered from their first arrival
An innovative tsunami detector operating in tsunami generation environment
On August 25th 2007 a tsunami detector installed onboard the multi-parameter observatory GEOSTAR was successfully deployed at 3200 b. s. l. in the Gulf of Cadiz, Portugal. This activity is within the NEAREST EC Project (http://nearest.bo.ismar.cnr.it/ ). Among other deliverables, the NEAREST project will produce and test the basic parts of an operational prototype of a near field tsunami warning system. This system includes an onshore warning centre, based on the geophysical monitoring networks which are already operating, and a tsunami detector deployed on board GEOSTAR at the sea bottom. On land the warning centre is in charge of collecting, integrating, and evaluating data recorded at sea. At the sea bottom data is recorded and processed by an advanced type of tsunami detector which includes: a pressure sensor, a seismometer and two accelerometers. The detector communicates acoustically with a surface buoy in two-way mode. The buoy is equipped with meteo station, GPS and tiltmeter and is connected to a shore station via satellite link. The prototype is designed to operate in tsunami generation areas for detection-warning purpose as well as for scientific measurements. The tsunami detector sends a near real time automatic alert message when a seismic or pressure threshold are exceeded. Pressure signals are processed by the tsunami detection algorithm and the water pressure perturbation caused by the seafloor motion is taken into account. The algorithm is designed to detect small tsunami waves, less than one centimetre, in a very noisy environment. Our objective is to combine a novel approach to the tsunami warning problem, with a study of the coupling between the water column perturbations and sea floor motion, together with the long term monitoring of geophysical, geochemical and oceanographic parameters
NEMO-SN1 (Western Ionian Sea, off Eastern Sicily): A Cabled Abyssal Observatory with Tsunami Early Warning Capability
The NEMO-SN1 (NEutrino Mediterranean Observatory - Submarine
Network 1) seafloor observatory is located in the central
Mediterranean, Western Ionian Sea, off Eastern Sicily Island (Southern
Italy) at 2100 m water depth, 25 km from the harbour of the city of
Catania. It is a prototype of cabled deep-sea multiparameter
observatory, and the first operating with real-time data transmission in
Europe since 2005. NEMO-SN1 is also the first-established node of
EMSO (European Multidisciplinary Seafloor Observatory,
http://emso-eu.org), one of the European large-scale research
infrastructures. EMSO will address long-term monitoring of
environmental processes related to marine ecosystems, climate change
and geo-hazards. NEMO-SN1 will perform geophysical and
environmental long-term monitoring by acquiring seismological,
geomagnetic, gravimetric, accelerometric, physico-oceanographic,
hydro-acoustic, bio-acoustic measurements to study earthquake and
tsunami generation, and to characterize ambient noise which includes
marine mammal sounds, and environmental and anthropogenic sources.
NEMO-SN1 is also equipped with a prototype tsunami detector, based
on the simultaneous measurement of the seismic and bottom pressure
signals and a new high performance tsunami detection algorithm.
NEMO-SN1 will be a permanent tsunami early warning node in
Western Ionian Sea, an area where very destructive earthquakes have
occurred in the past, some of them tsunamigenic (e.g., 1693, M=7.5;
1908, M=7.4).
Another important feature of NEMO-SN1 is the installation of a low
frequency-high sensibility hydrophone and two (scalar and vector,
respectively) magnetometers. The objective is to improve the tsunami
detection capability of SN1 through the recognition of tsunami-induced
hydro-acoustic and electro-magnetic precursors.SubmittedRhodes, Greece3A. Ambiente Marinorestricte
Tsunami Warning prototype in the frame of the EC NEAREST project.
Nell' ambito del progetto NEAREST finanziato dalla EC sono stati
sviluppati alcuni elementi di un sistema di allerta per tsunami, fra i quali un
prototipo di detector di onde anomale istallato a bordo dell' osservatorio
abissale GEOSTAR: l' osservatorio con il detector di onde anomale ha operato
per un anno nel Golfo di Cadice, a 3200m di profonditĂ PublishedSassari1.8. Osservazioni di geofisica ambientaleope