Transcript Deschamps_Paris2016

Seismology at Antares Site.
Anne Deschamps, Diane Rivet, Géoazur,
UCA,CNRS,IRD,OCA
Seismologists question : earthquakes
understanding
Location from land based
instrumentation
• Not very precise
THALES WAS RIGHT EU project
Offshore EQs located by
5 OBS and ~10 land-stations
(6 months)
LOC WITHOUT OBS
(Permanent network,
NOA catalogues)
 Shift in location to the SW
reaching ~100 km !
LOC WITH OBS
Previously located
“Aegean Sea events”
are in fact :
“Ionian Sea subduction events”
In Mediterannean
area
Last 14 days of seismicity
Seismicity is mainly moderate
But, for a large part, just offshore along coasts.
Installing permanent seismological
observations is important for some
specific studies
At Antares Site in 2005/2006:
Current speed influence on seismic noise.
•
•
Burying the sensor improve
the signal/noise ratio at
low frequency
Noise is lower during
summer
* DSP = density power spectra
Variation of the DSP of the EW acceleration of sea
bottom (12 hours periods)
At Antares site 2010/2016 ASEAF station.
Velocimeter,
Accelerometer
Absolute Pressure
Sensor
Interlink Cable
Velocimeter
sensors response
Protection bell
function of frequency
Differential
Pressure Gauge
Electronic Container
Velocimeter sensors
response as function
of frequency
Large earthquakes observations
Earth normal modes observed
at ASEAF (Antares) and SSB
(Massif Central, less than
300km away) after the M=8.5
Sumatra event April 2012:
-the very good agreement
shows the quality of the
instrument.
-Detail on each pick contribue to
the knowledge of earth internal
properties.
0S3
period 36 mn
frequency
0S3
period 26 mn
frequency
0S5
period 20 mn
frequency
0S0
period 21 mn
frequency
Pressure measurement
Absolute pressure : tides
and high frequency signal
are present.
Ground acceleration (black), pressure gauge (red) and
absolute pressure (green) signal during Tohoku-Oki
march 2011 event. In the frequency range 0.01 and 0.1
signals are equivalent. Absolute pressure is more noisy.
Tsunami observation : a pressure gauge
Pressure 2010
Real time observation needed
At Antares site 2010/2016 ASEAF station:
Data send continously to EPOS eida nodes to be integrated in European
seismological data base where the quality control is performed.
winter
ASEAF
CALF
summer
Regional sismicity
• Contribue to 20% of evnts detected by
Géoazur network
Regional sismicity
• Contribue to 20% of evnts detected by
Géoazur network
Regional seismicity
Waveform modeling allows to determine location, magnitude and focal mechanism of the
regional seismicity.
After a period of extension during which Corsica went away from the continent, the present
deformation of the Earth crust shows a shortening of the distance. How is distributed this
deformation, what are the largest potentialy seismic faults?
Structure of the Earth at different scales
Regional scale: P and S waves velocities beneath North American plate
Farrallon plate beneath
North America
USARRAY data
Contribution to AlpArray program
European effort 2012-2018
French participation :
on land : 80 stations
on seafloor 40 OBS
But we did not suceed to
synchronize with Antares
recording period.
EMSO- Ligure East
EMSO- Ligure East
Thanks you