Transcript Double-difference location method: principles and application to microseimic data Fateh Bouchaala 29.09.2011 AIM project, Prague Algorithm (F.

Double-difference location
method: principles and
application to microseimic data
Fateh Bouchaala
29.09.2011
AIM project, Prague
1
Algorithm (F. Waldhauser & W L. Ellsworth)
t ik
i
k

m

r
i
 x i , y i , z i , i


Standard approach
tik : Travel time from hypocenter i to seismic station k
x, y, z  :
Spatial coordinates of hypocenter i.
 : Origin time of event.
ri  t
k
observed
t

calculated i
k
: Residual time
m i  x i , y i , z i ,  i  : Perturbation
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AIM project, Prague
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Algorithm (F. Waldhauser & W L. Ellsworth)
t ik
t kj
i
m 
m j  drkij
m
m
t ik
t ik
t ik
t kj
t kj
t kj
i
i
i
i
j
j
x 
y 
z   
x 
y 
z j   j  drkij
x
y
z
x
y
z
Double difference
t
i
k
 t kj

observed

 t ik  t kj

calculated
 drkij
Gm  d
G : Matrix containing the partial derivaties; size Mx4N (M number of pairs; N
number of hypocenters)
m : Vector containing the changes in hypocentral parameters, size, 4xN.
d : Vector containing double difference , size M.
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AIM project, Prague
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Algorithm (F. Waldhauser & W L. Ellsworth)
y
Station k
Station l
dtkij
dtlij
x
depth
m j
event j
uik
u jl
u jk
event i
uil
u
t
m
mi
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AIM project, Prague
AIM Project
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Advantages of the method
-The travel time differences can be related with high accuracy to the offsets between
hypocenters
- It allows the use of difference time computed from cross correlation
- The common mode errors can be neglected, as those related to the receiver-side
structure
- Can be used for high number of events
- Free software (hypoDD).
Application examples of the method
- Northern Hayward Fault, North California earthquakes, 1984-1998 (F.
Waldhauser & W L. Ellsworth. 2000).
- Southern California earthquakes, 1984-2002 (E.Hauksson and P.Shearer. 2005)
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AIM project, Prague
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Method application (West Bohemia)
50.4°-
- West Bohemia Seismic
Network (WEBNET) :
-13 permanent and 10
mobile stations
- Swarm 2008
- Magnitude < 3.8
50°-
- Dense distribution
http://www.ig.cas.cz
12°
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12.8°
AIM project, Prague
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HYPODD software (F. Waldhauser & W L. Ellsworth)
Initial location + Structure Model
Pair events is cancelled
N
Pair events selection
Some conditions
Y
Pair events is saved
Initial location
+
P or/and S wave
+
Catalog or/and correlated data
Events relocation
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AIM project, Prague
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Computation Time
M (number of events) : 478
Data
Number of station : 23
N (number of pair-events) : more than 500000 pairs
RAM : 2.0 GB
Computer
characteristics
Processor : intel(R) Corel(TM)2.40 GHZ
System : Linux
Time consuming : less than 1 hour
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AIM project, Prague
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Results (478 events are relocated)
N
Cross correlation data, P and S waves are used.
MAP VIEW
2.5
E
W
A`
2
1.5
S
1
distance [km]
0.5
B`
0
B
-0.5
-1
-1.5
-2
A
-2.5
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
distance [km]
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AIM project, Prague
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Results (478 events are relocated)
Cross correlation data, P and S waves are used.
Cross Section: B-B`
-5
-6
depth [km]
-7
-8
East
-9
-10
-11
-12
-2
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-1
0
distance [km]
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2
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Results (478 events are relocated)
Cross correlation data, P and S waves are used.
Cross Section: B-B`
-8
-8.2
depth [km]
-8.4
-8.6
East
-8.8
-9
-0.4
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-0.3
-0.2
-0.1
0
distance [km]
0.1
0.2
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Results (478 events are relocated)
Cross correlation data, P and S waves are used.
Cross Section: B-B`
-5
-6
depth [km]
-7
-8
East
-9
-10
-11
-12
-2
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-1
0
distance [km]
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1
2
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Results (478 events are relocated)
Cross correlation data, P and S waves are used.
Cross Section: B-B`
-10.2
-10.3
-10.4
depth [km]
-10.5
-10.6
East
-10.7
-10.8
-10.9
-11
-0.7
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-0.6
-0.5
-0.4
distance [km]
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-0.3
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Results (478 events are relocated)
N
Comparison relocated and initial location :
MAP VIEW
2.5
E
W
A`
2
1.5
S
1
distance [km]
0.5
B`
0
B
-0.5
-1
-1.5
relocation
location
data3
data4
-2
-2.5
-2.5
-2
-1.5
-1
A
-0.5
0
0.5
1
1.5
2
2.5
distance [km]
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AIM project, Prague
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Results (478 events are relocated)
Comparison relocated and initial location :
Cross Section: B-B`
-5
-6
depth [km]
-7
-8
-9
East
-10
-11
relocation
initial location
-12
-2
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-1
0
1
distance [km]
2
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-7
-7.5
-8
-8.5
-9
-9.5
-10
-10.5
-2
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-1.5
-1
-0.5
0
0.5
1
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2
2.5
-1
0
1
2
17
-7
-7.5
-8
-8.5
-9
-9.5
-10
-10.5
2
1
0
-2
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-1
-1
-0.5
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2
2.5
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-7
-7.5
-8
-8.5
-9
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1
0
-1
-2
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1.5
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2.5
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1
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-1
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2
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2.5
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-7
-7.5
-8
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-9.5
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-10.5
2.5
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-1.5
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-1
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Conclusion
- DD method improves the event location accuracy
- The use of this method has resulted in a reduced
dispersion of hypocenters, which leads to a better
identification of fault segments
- Fault plane activated in West Bohemia in 2008 is complex
with several segments
- The fault complexity is proved by focal mechanisms
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AIM project, Prague
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Perspective
- To relocate the West Bohemia earthquakes recorded in
2009 to study the deeper part of the fault
- To relocate microseismic data in other regions (e.g., the
Dobra Voda area)
- To relocate data recorded at laboratory experiments
provided by project partners
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AIM project, Prague
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Acknowledgements
I thank Josef Horálek, Alena Boušková and other colleagues
from the WEBNET group for providing me with the data
from the 2008 swarm activity and for kind help with their
preprocessing.
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