the january 2010 efpalio earthquake sequence in western corinth gulf: epicenter relocations, focal...
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The January 2010 Efpalio earthquake sequence
in Western Corinth Gulf: epicenter relocations, focal mechanisms,
slip models
Sokos E. 1, Kiratzi A.2, Serpetsidaki A.1, Tselentis G.1, Novotny O.3, Jansky J.3, Zahradnik J.3
1 Department of Geology, Seismological Laboratory, University of Patras, Greece 2 Department of Geophysics, Aristotle University of Thessaloniki, Greece 3 Charles University in Prague, Czech Republic
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THESS catalog, using HUSN stations(Hellenic Unified Seismic Network)
CORINTH GULF Dec 2009 to Aug 2010
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Very active extensional region
Both large and small events
Cooperative efforts
Bernard et al.Tectonophysics 426 (2006), 7–30.
REGIONAL FRAMEWORK
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A lot is known aboutthe faults on thesouthern coast,
much less for the northern coast.
Hence importance ofthe Efpalio study.
REGIONAL FRAMEWORK
Bernard et al., Tectonophysics 426 (2006) 7–30.
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HYPOINVERSE code, stations up to 120 kmtemporary UPSL network included (starting Jan 19)
SEQUENCE Jan 18 - Jan 23LOCATION
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HYPOINVERSE code, stations up to 120 kmtemporary UPSL network included (starting Jan 19)
SEQUENCE Jan 18 - Jan 23LOCATION
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Two mainshocks Jan 18 (Mw~5.3), Jan 22 (Mw~5.2), both normal mechanisms
TWO M5 MAINSHOCKS
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single global minimumof the L2 misfit, depth 8-10 km
similar results in two 1D crustal models
MAINSHOCK HYPOCENTERS RELOCATED BY 3D GRID SEARCH
6 8 10 12 14 16
depth (km )
mis
fit
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Even date-time: 20100118 1:32:39Displacement (m). Inversion band (Hz) 0.05 0.06 0.08 0.1
ObservedSynthetic
Gray waveforms weren't used in inversion.
Blue numbers are variance reduction
-101
x 10-3 NS
SE
R -0.05
-101
x 10-3 EW
0.96
-101
x 10-3 Z
0.78
-101
x 10-4
TR
Z 0.89
-101
x 10-4
0.95
-101
x 10-4
0.55
-101
x 10-4
MA
M 0.68
-101
x 10-4
0.97
-101
x 10-4
0.89
-4-2024
x 10-5
DS
F 0.74
-4-2024
x 10-5
0.62
-4-2024
x 10-5
0.39
-101
x 10-4
DR
O 0.82
-101
x 10-4
0.78
-101
x 10-4
0.88
-101
x 10-4
EV
R 0.06
-101
x 10-4
0.93
-101
x 10-4
0.80
-101
x 10-4
GU
R 0.65
-101
x 10-4
0.93
-101
x 10-4
0.83
-4-2024
x 10-5
PD
O 0.49
-4-2024
x 10-5
0.74
-4-2024
x 10-5
-2.68
0 100 200 300
-505
x 10-5
Time (sec)
LT
K 0.93
0 100 200 300
-505
x 10-5
Time (sec)
0.89
0 100 200 300
-505
x 10-5
Time (sec)
0.40
WAVEFORM INVERSION - CENTROID MOMENT TENSOR
9 near-regional stationsf < 0.1 Hz2 crustal modelsvaried station sets
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CENTROID POSITION
Stable preference of C depthshallower (~5 km) than H (~ 9km)
C-H distance of about4 km, consistent withthe assumed M5 size
HC
Centroid depth
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TWO MAINSHOCKS - SMALL BUT STABLEDIFFERENCE IN THE NODAL PLANES
North-dipping plane
South-dippingplane
Jan 18 Jan 22
Two events= two faults !
Which arethe fault planes?
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FINITE-EXTENT SOURCE (forward modeling the nearest-station
record, f<1 Hz)
54
50 60 70 80 90 100tim e (s)
-0 .004
-0 .002
0
0.002
0.004
dis
pla
cem
en
t (m
)
SER _Zblack: datacolor: synt
blue: fin ite_25pink: fin ite_43green: fin ite_hypred: po in t source
50 60 70 80 90 100tim e (s)
-0 .004
-0 .002
0
0.002
0.004
dis
pla
cem
en
t (m
)
SER _Zblack: datacolor: synt
blue: fin ite_25pink: fin ite_49green: fin ite_hypred: po in t source
-1 .5 -1 -0 .5 0 0.5 1 1.5
-1
-0 .5
0
0.5
1
-1.5 -1 -0.5 0 0.5 1 1.5
-1
-0.5
0
0.5
1
No preference of thesouth- or north-dippingplane.
Radial rupturingpossible.
Higher freq. needed, but synthetic Green f.then not reliable.
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SLIP DISTRIBUTION BY EMPIRICAL GREEN FUNCTIONS
North-dipping plane
South-dippingplane
Jan 18 Jan 22
However, horizontal position of main slip patchis stable, well resolved.
(no preference)
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HYPOCENTER AND CENTROID INDICATE THE FAUL PLANE
Hypocenter of Jan 18by different methods
-20
0
20-15 -10 -5 0 5 10 15
-20
-15
-10
-5
0
5
10
North-South (km)
jan18
East-West (km)
Dep
th
Centroid
Green: strike 102°, dip 55°(south-dipping plane; preferred)
Red: strike 270°, dip 36°north-dipping plane
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RELOCATION (HYPODD)
before relocation
after relocation
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RELOCATION (HYPODD) – MAIN FINDINGS
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RELOCATION (HYPODD) – MAIN FINDINGS
Gap around the Jan18mainshock
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RELOCATION (HYPODD) – MAIN FINDINGS
Gap between the ‘northern’and ‘southern’ clusters
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RELOCATION (HYPODD) – MAIN FINDINGS
Part of Jan18 aftershocksclustered in place of Jan22(= ‘preshocks’ of Jan22)
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RELOCATION (HYPODD) – MAIN FINDINGS
Part of Jan18 aftershocksclustered in place of Jan22(= ‘preshocks’ of Jan22)
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RELOCATION (HYPODD) – MAIN FINDINGS
Gap around the Jan18mainshock
Gap between the ‘northern’and ‘southern’ clusters
Part of Jan18 aftershocksclustered in place of Jan22(= ‘preshocks’ of Jan22)
Almost simultaneous activation
of several faults.
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FOCAL MECHANISMS OF AFTERSHOCKS
ISOLA software
Normal mechanismsare prevailing.
Other mechanismsare also present,confirming activationof several faults.
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SYNTHESIS – Jan 18
Jan 18 event rupturedthe south-dipping plane.
Aftershocks outsidemain slip patch,activation ofanother fault to the NE(place of Jan 22).
Methodical problemto be improved:
Solve the shift betweenmain slip patch (color isolines)and centroid (red).
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SYNTHESIS – Jan 22
Jan22 also on south-dippingplane (slightly differentgeometry than Jan18).
Similarly to Jan18:• no aftershocks in the main slip patch.• no aftershocks towards west.
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SYNTHESIS – Jan 18, Jan 22
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HypocenterJan 18: 21.91277 38.41260 8.9 kmJan 22: 21.94719 38.43420 9.5 km
CentroidJan 18: 21.9416000000 38.4220173190 5.0 kmstrike, dip, rake: 270. 36. -100. strike, dip, rake: 102. 55. -83.
Jan22: 21.9645110296 38.4490409549 5.0 kmstrike, dip, rake: 282. 42. -67. strike, dip, rake: 72. 52. -109.
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CONCLUSION
Accurate relocation, combined with the near-regional, low-frequencycentroid moment-tensor preferred the south-dipping planes for theJan18 and 22 mainshocks of M5.
The mainshocks ruptured from a depth ~9km upwards (centroid depth ~ 5km)and eastward.
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CONCLUSION
Accurate relocation, combined with the near-regional, low-frequencycentroid moment-tensor preferred the south-dipping planes for theJan18 and 22 mainshocks of M5.
The mainshocks ruptured from a depth ~9km upwards (centroid depth ~ 5km)and eastward.
Slip inversion by means of empirical Green functions provided stable positionsof the main slip patches (a single patch for each event).
The two mainshocks had almost no aftershocks in the main slip region.
Jan18 event activated aftershock cluster (preshocks) at place of Jan22 event.
Sequence occurred on a complex system of faults of different strike and dip.
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