Repeating earthquakes : identification, quantification and

Report
Repeating Earthquakes
Olivier Lengliné - IPGS Strasbourg
Cargese school
Please interrupt
Questions / remarks
1 – Review of Repeating earthquake observations &
interpretations
2 – Two examples of application
Observations - Waveforms
Nadeau & Johnson, 1998
Parkfield, California – Mw6.0
USGS
De Bilt, The Netherlands
Bakun et al., 2005
Off Kamaishi, Japan – M4.9
Uchida et al., 2012
Time (s)
Chihshang fault,
Taiwan
Chen et al., 2008
Soultz-Sous-Forêts geothermal reservoir, France
9 events
9 events
13 events
BRGM
19 events
0.0
0.5
1.0
1.5
2.0
Time (s)
2.5
3.0
3.5
San-Andreas Fault
Rubinstein et al., 2012
Schaff & Beroza, 1998
u(t) = Source * Path * Station
u(t) = Source * Path * Station
u(t) = Source * Path * Station
Station is the same
Change in medium property, [e.g Poupinet et al., 1984]
Change in source properties, [e.g. Lengliné & Got, 2011]
Lengliné and Got, 2011
Directivity
Velocity variations
Poupinet et al., 1984
u(t) = Source * Path * Station
!
Homogeneous medium
 waveform similarity
Station the same
Change in medium property, [e.g Poupinet et al., 1984]
Change in source properties, [e.g. Lengliné & Got, 2011]
Observations - Locations
Waldhauser et al., 2004
Parkfield
Murray & Langbein, 2006
Off Kamaishi
Moment release
distribution
Relative moment
released normalized
by each maximum
value
Okada et al., 2002
Earthquake relative relocation
 Uncertainties P-wave picks
 Uncertainties of the velocity model
Earthquake relative relocation
 Uncertainties P-wave picks
 Uncertainties of the velocity model
 More precise data: time delays estimated from cross-correlation
 Ray geometry – rotation
 Do not correct absolute position
Earthquake relative relocation
 Uncertainties P-wave picks
 Uncertainties of the velocity model
 More precise data: time delays estimated from cross-correlation
 Ray geometry – rotation
 Do not correct absolute position
From cross-correlation  centroid location
Got et al., 1994
Waldhauser & Ellsworth, 2000
Earthquake relative relocation
 Uncertainties P-wave picks
 Uncertainties of the velocity model
 More precise data: time delays estimated from cross-correlation
 Ray geometry – rotation
 Do not correct absolute position
From cross-correlation  centroid location
Got et al., 1994
Waldhauser & Ellsworth, 2000
See Tutorial this afternoon for Methods
Lengliné & Marsan, 2008
Size = Assumed stress drop + circular crack + moment – magnitude relation
Taiwan
Soultz-sous-Forêts
Bourouis & Bernard, 2007
Chen et al., 2008
Radius estimated from corner frequency
Murray & Langbein, 2006
Clusters of co-located,
similar
waveforms
earthquakes, appears at
the transition between
fully locked and fully
creeping areas
Rau et al., 2007
Example from Northern-California
Parkfield
Waldhauser & Schaff, 2008
Is it related to fault slip velocity ?
San Andreas Fault
Rubin et al., 1999
Streaks of microearthquakes – along slip direction
Rheological / frictional / geological / geometrical transition ?
Observations - Timing
Parkfield
8
Earthquake number
7
6
5
4
3
2
Year
Number
1857
1
1
1881
2
1901
3
0
1800
1922
4
1934
5
1966
6
2004
7
1850
μΔt = 24.5 yr
σΔt = 9.5 yr
COV = 0.37
1900
1950
Time (years)
2000
2050
Repeaters off Kamaishi
Repeating interval = 5.35 +/- 0.5 yrs
Time (years)
Year
San-Andreas fault at Parkfield
Distance along strike (km)
Waldhauser et al., 2004
Year
Periodic repeating ruptures
Distance along strike (km)
Waldhauser et al., 2004
Rubinstein et al., 2012
Quasi-periodic behavior of the slip activity
The simplest model
No interacting asperity
A locked seismic patch embedded in a fully creeping zone
Aseismic slip
Slip on the creeping part
Slip
Slip on the seismic asperity
Time
dseis
Slip
 Aseismic slip on the fault = seismic slip
Time
 Aseismic slip on the fault = seismic slip
 Elastic solution for a circular crack
 Aseismic slip on the fault = seismic slip
 Elastic solution for a circular crack
 Aseismic slip on the fault = seismic slip
 Elastic solution for a circular crack
 Constant stress drop
Chen et al., 2007
1st Hypothesis
The constant stress drop hypothesis is not correct
Empirical fit to the data then suggests in order to have Tr ~ M01/6
Implies that the stress-drop is higher for small events.
Stress levels reach 2 GPa for the smallest events (more than 10 times laboratory strength)
This result is at odds with estimates based on seismic spectra
Relation not consistent with established scaling relations for large earthquakes.
Imanishi & Ellsworth, 2006
Chen & Lapusta, 2009
Chen & Lapusta, 2009
But not the estimated plate velocity – streaks close to locked section  reduced velocity ?
Slip on the creeping part
Slip
Slip on the seismic asperity
Time
Seismic slip
Off Kamaishi repeating sequence following Tohoku, 2011, Mw9 earthquake
Uchida, 2014
Lengliné & Marsan 2008
Schaff & Beroza, 1998
30
25
Number of earthquakes
20
15
10
5
0
1985
1990
1995
Following Parkfield, 2004, Mw6 event
2000
Time( years)
2005
2010
2015
Response of a velocity strengthening area to a stress-step
Marone, 1991
The Omori like decay of RES is well rendered by the slip evolution of the
creeping area following a stress step
Nadeau & McEvilly, 1999
Nadeau & McEvilly, 1999
Bourouis & Bernard, 2007
29˚00'
41˚00'
29˚30'
30˚00'
30˚30'
31˚00'
41˚00'
UCG
40˚30'
29˚00'
29˚30'
30˚00'
30˚30'
Bouchon et al., 2011
40˚30'
31˚00'
Kato & Nakagawa, 2014
Kato et al., 2012
Repeating earthquake are local (sparse) creep-meter at depth
Difficult to quantify if the seismic slip reflects the surrounding
aseismic loading
Complications to the idealized picture
8
Number of earthquakes
7
6
5
4
3
2
1
0
0
5
10
15
Time after 01/01/1984 (years)
Repeating sequence of small micro-earthquakes at Parkfield
20
Complications to the idealized picture
8
Number of earthquakes
7
6
5
4
3
2
1
0
0
5
10
15
Time after 01/01/1984 (years)
Repeating sequence of small micro-earthquakes at Parkfield
20
Interactions from nearby small events
More isolated events = more periodic
Chen et al., 2013
Chen et al., 2013
How can strength of the interface build up so quickly between 2 events ?
Healing of the interface
Vidale et al., 1994
Questions
What is an asperity ? (geometrical/frictional/geological …)
What is the lifetime of an asperity ?
In which case do we observe periodicity ? (density of asperity)
Are repeating LFE earthquakes obeying a similar mechanism ?
2 examples of use of repeating earthquake sequences
- Earthquake detection and time activity (with P. Ampuero)
- Variation of source properties
Cuenot, J. Schmittbuhl)
(with L. Lamourette, L. Vivin, N.
Parkfield
Landweber deconvolution
Example for one pair at one station
Landweber deconvolution
All pairs at all stations
Sparse deconvolution
54 new detected events
in the first 20s following a
repeating earthquakes
Typical rupture duration
Stack aftershock sequence
Wang et al., 2014
Omori’s law extended almost up to the rupture duration
No flatenning of the earthquake rate at early times
Is this particular to the repeating earthquakes ?
Seismicity rate
Implies a very low c-value and thus a very
large stress changes in the R&S Dieterich
framework
Time (t/ta)
2010
11 months long circulation test
411 earthquakes recorded
Largest magnitude event M2.3
Station surface sites
150 Hz sampling frequency
•
•
•
•
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4 groups of similar events
Relocation suggest a similar location
Each group have at least one event larger than 1.4
4/6 of the largest events of the circulation are
included in these groups
SVD analysis
(Rubinstein & Ellsworth, 2010 )
Up to a factor x 300 of
moment ratio
SVD analysis
(Rubinstein & Ellsworth, 2010 )
Up to a factor x 300 of
moment ratio
For the largest event of each group
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0
0.5
1.0
1.5
2.0
2.5
Corner frequency of the
largest event of each group
fc ~ [10-20] Hz
3.0
3.5
Wiener filter (equivalent to spectral ratio)
Same rupture area
The difference of seismic moment reflects
a difference of seismic slip/ stress drop
Increase of pore pressure lowers the
normal stress on the fault plane
Bourouis & Bernard, 2007
2 effects:
• Shear failure promoted (reach the Coulomb enveloppe)
• Stabilizes the slip
Several instances of aseismic movements have been suggested in the Soultz reservoir
We are observing a transition from unstable to stable slip on the interface
Thank you

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