trigs meeting april 7th 2009
DESCRIPTION
The Team: Jean-Robert Grasso Researcher Agnes Helmstetter Researcher David Amitrano Researcher. Pascal Lacroix Postdoc since Nov. 2008 Lucile Tatard PhD, 2007-2009. TRIGS meeting April 7th 2009. Landslides : - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/1.jpg)
TRIGS meeting April 7th 2009
The Team:
Jean-Robert Grasso
Researcher
Agnes Helmstetter
Researcher
David Amitrano
Researcher
Pascal Lacroix
Postdoc since
Nov. 2008
Lucile Tatard
PhD, 2007-2009
![Page 2: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/2.jpg)
• Landslides :
seismic monitoring, triggering mechanisms, displacement
measurement… (JR Grasso. Tatard, A. Helmstetter, D. Amitrano, P. Lacroix)
• Volcanoes :
eruptions, seismicity, and forecasting(JR Grasso, L. Tatard)
• Earthquakes :
• statistical analysis of catalogs, triggering mechanisms and
forecasting(A. Helmstetter, D. Amitrano)
• Laboratory expermients :
Fracture and friction experiments(D Amitrano, JR Grasso)
Research Topics
![Page 3: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/3.jpg)
Seismic monitoring of Séchilienne landslideWP5.1
Laffrey, 1999; 2005
Grenoble30 km
Séchilienne
Seveso plant
![Page 4: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/4.jpg)
Séchilienne landslide and geodetic network
The landslide instrumented since 1988 by CETE Lyon, with extensometers, inclinometers, strainmeters, GPS and distancemeters (laser and radar).
![Page 5: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/5.jpg)
Seismic network
• vertical seismometer∆ 3 component Seismometer
Stations THE and RUI installed may 2007GAL installed April 2008
Data, catalogs, … :Google OMIV -> Sechilienne-> seismology
![Page 6: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/6.jpg)
Séchilienne Photo taken from just above the most active zone :
![Page 7: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/7.jpg)
Seismic network : objectives
• detection and classification of seismic signals produced by the rockslide:
Micro-seismicity, distant EQs, rockfalls, natural or artificial tremors, …
• event location (work in progress)
• imaging the structure of the movement and its temporal evolution with
Seismic wave tomography with explosions or seismic noise
• site effects : amplification of ground motion due to the damaged zone
(project)
• comparison of micro-seismic activity with meteorological data,
displacement, PS, and external earthquakes
![Page 8: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/8.jpg)
Micro-earthquake? Fracture? Crevasse opening?TH
E R
UI
G
AL
(int)
(ext)
![Page 9: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/9.jpg)
Regional earthquakes
• Example of earthquake
located about 5km from the
landslide (p-s ≈ 0.7s)• Higher frequency than
local events !?
> Strong attenuation of
local events due to
damaged rocks?
![Page 10: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/10.jpg)
Rockfall seismicsignal
![Page 11: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/11.jpg)
Rockfall experiments
Rock boulder of ≈20x30x50cm pushed from the top of the ruins
![Page 12: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/12.jpg)
Characteristics of events
energy (t)
duration (t)
amplitude (t) cdf(amplitude)
cdf(energy)
cdf(duration)
30s duration of rockfall propagation from the top of the ruins
T<5 secMicro EQs?
T>5, rockfalls?
0.05m3
≈100m3?
micro EQs? rockfalls?
![Page 13: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/13.jpg)
Location of seismic signals using antenna methods
TH
E
RU
I
(in
t)
G
AL
(ext
)
• find seismic wave velocity V and
source location by maximizing the
average inter-traces correlation after
shifting the traces in time by the
travel time t=distance/V
1-40Hz
Map of average correlation
![Page 14: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/14.jpg)
Location of seismic signals using antenna methods
Problems • We assume seismic wave velocity is constant in time and
space, but there is a mixture of waves of different type and V • V is highly heterogeneous in the rock mass • The types of seismic waves is unkown : P? S? surface waves?
(work in progress of waves polarization with 3C sensor)
Advantages: • Fully automatic • Works well with emergent signals or rockfall, and for looking at
the propagation of the source • Time accuracy potentially smaller than sampling rate
![Page 15: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/15.jpg)
Propagation of rockfall avalanches
Location using a sliding time window
Location in the direction of propagation All 3 stations
Azimut relative to station THE, using only THE
![Page 16: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/16.jpg)
Location of seismic signals using antenna methods
• events location using a single station : only the azimuth is constrained
• histogramm of the direction of natural local events recorded by stations RUI (207 events) and THE (349 events) from 10/4/2008 to 7/2008.
• most events located at top of the Ruins (grey area)
![Page 17: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/17.jpg)
Influence of climate on displacement and seismicity
Displacement rate of target point #631 (CETE Lyon)
Chamrousse Weather station(Meteo France)
Natural local events recorded by station THE
![Page 18: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/18.jpg)
Influence of climate forcing on displacement and seismicity
![Page 19: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/19.jpg)
Influence of climate forcing on seismicity
Precipitation : • Peak correlation for zero time lag (<1hr)•+ rain increases on average 2 days before seismic events
Temperature: • seismic events associated with a temperature decrease (freezing?),
or just a result of the correlation between rain and temperature?
![Page 20: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/20.jpg)
Correlation between climate and displacement rate
Precipitation : • Peak correlation for a time lag of 4days
+ rain increases on average 20 days before landslide acceleration
Temperature: • no significant correlation -> look at data since 1996?
![Page 21: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/21.jpg)
Correlation between displacement and seismicity
Peak of correlation for zero time lag (<1 day),
But acceleration lasts longer than seismic crisis
![Page 22: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/22.jpg)
Displacement since 1996 (Data CETE Lyon)
![Page 23: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/23.jpg)
Influence of distant EQs on the landslide?
11/1/1999 m=3.5 1/10/2005 m=2.8
• 2 EQs occured about 4km from Séchilienne in 1999 and 2005, with m=3.5 and m=2.8• Only the 2nd smaller EQ produced an acceleration of the movement !?
![Page 24: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/24.jpg)
Super Sauze displacement
Displacement amplitude measured by correlating pictures taken at one
month interval
Pictures from EOST Strasbourg (JP Mallet), with 1 month interval
Method developped and applied by P. Lacroix
1m0 60 m
• Same results than standard method, but 100 times faster
![Page 25: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/25.jpg)
m
Displacement prior to the 2006 V>20000m3 rockfall
Displacement amplitude measured by correlating pictures taken one
day and a few hours before the rockfall, from the other side of the
valley
Pictures from CETE Lyon (Y. Kaspersky)
Method developped by P. Lacroix
0 15 m
![Page 26: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/26.jpg)
Conclusion and perpectives for Séchilienne
• A few thousands seismic events recorded of varous types
• Intermittent activity, influenced by climate and distance EQs (?)
• Better location using a 3D velocity model (work in progress by
LGIT and SAGE), and seismometers in boreholes (project 2009
INERIS and CETE)?
• Video camera (installed summer 2009 by CETE) : calibration of
seismic netwok, estimation of rockfall volume and propagation
speed from seismic signals
• Quantify rockfall hazard and the influence of rain and distant
EQs, using numerous small events to estimate the probability
of a 106m3 event?
![Page 27: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/27.jpg)
Project: seismic monitoring of snow avalanches
• P. Lacroix, A. Helmstetter, JR Grasso, and « Centre D’étude de la Neige » (Grenoble)• Col d’Ornon (~20km South of Grenoble), winter 2009-2010 • Comparison of seismic signals• Location and propagation of avalanches
![Page 28: TRIGS meeting April 7th 2009](https://reader035.vdocument.in/reader035/viewer/2022062500/5681574d550346895dc4ef9b/html5/thumbnails/28.jpg)
OMIV: Muldisciplinary Observatory of Slope Instabilities
http://www-lgit.obs.ujf-grenoble.fr/observations/omiv/
Rockslides (Mica shists and gneiss)
Clay or soft rocks