1

Cythera M6.7 earthquake Cythera M6.7 earthquake (January 8, 2006) in southern (January 8, 2006) in southern

Aegean: uneasy retrieval of the Aegean: uneasy retrieval of the upward rupture propagationupward rupture propagation

    

J. Zahradnik, J. Jansky, V. Plicka, E. Sokos J. Zahradnik, J. Jansky, V. Plicka, E. Sokos   

Charles University in Prague Charles University in Prague University of Patras University of Patras

4

EMSC

• Diverse centroid position• Unclear aftershock pattern • Unclear fault

• Low DC%: ETH 60%, Mednet 56%

5

Inconsistent hypocenter and centroid moment solution

Lon E[km] Lat N[km]

-130-120-110-100-90-80-70-60-50-40-30

Depth[km] Mednet nod.IMednet nod.II

EMSC hypocenterMednet centroid

-40 -20 0 20 40 60 80

-100-80-60-40-20 0 20

Depth[km]

nodal planes, and centroid in the middle

6

Teleseismic records

Kikuchi-Kanamori method

• pP: depth

• P: complexity

PpP

7

Bottom trace = synthetics (K & K)simple event and complex event

8

Regional records and EGF methodapparent source time functions prove complexity

-60 -40 -20 0 20 40 60Size in km along the strike

-40

-20

0

20

40

Siz

e in

km

alo

ng

the

dip

-60 -40 -20 0 20 40 60Size in km along the strike

-40

-20

0

20

40

Siz

e in

km

alo

ng

the

dip

plane 2strike ~70°

plane 1strike ~200°

... Neighborhood Algorithm provides two slip patches

(similar to M. Vallée)

9

Lower misfit identifies

the fault plane:

strike ~70°

10

Relocation

• 30 teleseismic stations, pP-P: depth 90 km• 21 regional stations (Greece + Italy), P and S • Wadati diagram: Vp/Vs=1.75• Optimization of RMS: Vp/Vs=1.75• Relocation of regional data with first

approximation of depth = 90 km and Vp/Vs=1.75 with various azimuthal and epic.distance weighting schemes

11

Free depth:

-4 -2 0 2 4 6 8 10 12 14 16 18-25

-20-15

-10-5

0

-100-95-90-85-80-75-70-65-60-55

Depth[km]EMSC

free depth

Lon E[km]

Lat N[km]

Depth[km]

This is uncertaintyof mainshock location,not the aftershocks !

12

First approximation of depth 90 km:

-4 -2 0 2 4 6 8 10 12 14 16 18-25

-20-15

-10-5

0

-105-100-95-90-85-80-75-70-65-60-55

Depth[km]EMSC

free deptharound 90km

Lon E[km]

Lat N[km]

Depth[km]

13

Optimized Vp/Vs ratio:

-4 -2 0 2 4 6 8 10 12 14 16 18-25

-20-15

-10-5

0

-105-100-95-90-85-80-75-70-65-60-55

Depth[km]EMSC

free depthopt. Vp/Vs

around 90km

Lon E[km]

Lat N[km]

Depth[km]

14

hypo1

-4 -2 0 2 4 6 8 10 12 14 16 18-25

-20-15

-10-5

0

-105-100-95-90-85-80-75-70-65-60-55

Depth[km]EMSC

free depthopt. Vp/Vs

around 90km

Lon E[km]

Lat N[km]

Depth[km]

We relocated hypocenter 15 km South, 10 km Eastand 25 km below EMSC.

EMSC

this study

15

ISOLA code (Fortran & Matlab) multiple point-source moment tensors

Free on web:

Full waveform modeling of regional records

16

Iterative deconvolution (Kikuchi and Kanamori) modified for regional records

Moment tensor (deviatoric, or DC-constrained)at each trial space-time position by minimization of the L2 waveform misfit (least squares)

Optimum space-time positionof subevents by maximization of the waveform correlation (grid search)

17

Free BB waveform

data(Internet)

Our LTKstation soon onOrfeus, too.

19

Waveform modeling for f<0.1 Hz enables the source study

EW

0 100 200 300 400time (sec)

3.2E-003

2.3E-003

2.0E-003

1.2E-003

1.0E-003

1.6E-003

1.1E-003

5.7E-004

1.4E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

3.5E-003

1.5E-003

1.2E-003

6.1E-004

5.8E-004

2.3E-003

1.3E-003

3.5E-004

9.3E-004

3.0E-003

1.6E-003

1.1E-003

6.4E-004

9.2E-004

1.9E-003

1.1E-003

3.1E-004

7.8E-004

6stations (varred=54%)9 stations (varred=56%)

20

Hierarchic grid search of centroid f < 0.1 Hz

search 1 search 2, etc.

EMSC EMSC epic.is just thecoordinateorigin

21

Accurate centroid location needed for usable DC%

0 0.2 0.4 0.6 0.8 1

CO RRELATIO N

0

20

40

60

80

100

DC

%

search 2

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60

EASTING (KM)

-40

-36

-32

-28

-24

-20

-16

-12

-8

-4

0

4

8

12

16

20

NO

RT

HIN

G (

KM

)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

search 1 search 2

230 0.2 0.4 0.6 0.8 1

CO RRELATIO N

0

20

40

60

80

100

DC

%

search 4opt. position

Getting more accurate centroid makes DC% to converge

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60

EASTING (KM)

-40

-36

-32

-28

-24

-20

-16

-12

-8

-4

0

4

8

12

16

20

NO

RT

HIN

G (

KM

)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

search 2 search 3…DC%10-30 only !

24

0 0.2 0.4 0.6 0.8 1

CO RRELATIO N

0

20

40

60

80

100

DC

%

search 4

0 0.2 0.4 0.6 0.8 1

CO RRELATIO N

0

20

40

60

80

100

DC

%

search 2

25

We found centroid 25 km East of

EMSC epicenterand the DC% has converged

to 10-30%.

Does it imply that the source is

actually strongly non-DC ?Not !

26

EW

0 100 200 300 400time (sec)

3.2E-003

2.3E-003

2.0E-003

1.2E-003

1.0E-003

1.6E-003

1.1E-003

5.7E-004

1.4E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

2.7E-003

1.3E-003

1.0E-003

6.7E-004

2.4E-004

2.1E-003

1.4E-003

3.2E-004

6.7E-004

2.2E-003

9.6E-004

8.5E-004

1.2E-003

6.5E-004

1.8E-003

1.1E-003

4.6E-004

6.8E-004

deviatoric DC-constrained NS

0 100 200 300 400time (sec)

3.4E-003

4.2E-003

2.1E-003

2.6E-003

1.1E-003

1.0E-003

1.4E-003

1.7E-003

1.6E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

1.7E-003

3.4E-003

1.9E-003

2.3E-003

5.1E-004

1.0E-003

1.2E-003

1.1E-003

5.3E-004

1.2E -003

2.8E -003

1.8E -003

1.7E -003

6.6E -004

6.9E -004

7.6E -004

7.9E -004

4.4E -004

deviatoric DC-constrained Z

0 100 200 300 400time (sec)

3.3E-003

2.8E-003

2.4E-003

1.4E-003

1.0E-003

8.8E-004

1.1E-003

5.6E-004

2.1E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

1.5E-003

1.7E-003

1.9E-003

5.5E-004

3.5E-004

1.5E-003

1.2E-003

3.8E-004

8.0E-004

1.4E -003

1.7E -003

1.9E -003

8.4E -004

9.2E -004

1.4E -003

1.2E -003

5.1E -004

7.6E -004

deviatoric DC-constrained

27

DC-constrained solution is an equivalent model

Note different optimal source position.

deviatoric

DC-constrained

M

EMSC and Mednet M

28

Can we better justify our centroid position and MT ?

Remember the inconsistency for Mednet centroid and EMSC hypocenter:

Lon E[km] Lat N[km]

-130-120-110-100-90-80-70-60-50-40-30

Depth[km] Mednet nod.IMednet nod.II

EMSC hypocenterMednet centroid

-40 -20 0 20 40 60 80

-100-80-60-40-20 0 20

Depth[km]

29

Our CMT is fully consistent with our relocation.

Far from being trivial!5

Lon E [km]

Lat N [km]

-110-100-90-80-70-60-50-40-30-20-10

Depth [km]nodal plane Inodal plane II

hypoc. uncert.subevent 1

-40-20

0 20

40 60

80 100

-80-60-40-20 0 20 40 60 80

Depth [km]

… and it identifies the fault plane

as the “red” nodal plane,strike ~ 80°

30

The EMSC hypocenter is also in the fault plane o5

Lon E [km]

Lat N [km]

-110-100-90-80-70-60-50-40-30-20-10

Depth [km]nodal plane Inodal plane II

hypoc. uncert.subevent 1

EMSC hypoc.

-40-20

0 20

40 60

80 100

-80-60-40-20 0 20 40 60 80

Depth [km]

31

The BB first-motion polarities are consistent with the CMT

solutiono5

Red: this studyBlack: others

32

Where’s complexity found in EGF analysis and teleseismic modeling ?

For f < 0.1 Hz,in addition to stable subevent 1(1.1e19 Nm)the waveformsclearly indicatesubevent 2,6-sec later,comparable size !

(1.1e19 Nm)

? Sub 2 ?

Solution for sub2 is not unique.

Sub 1

M

33

-50 -40 -30 -20 -10 0 10 20 30 40 50

EASTING (KM )

-50

-40

-30

-20

-10

0

10

20N

OR

TH

ING

(K

M)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

26 27 28 29 30

31 32 33 34 35

36 37 38 39 40

41 42 43 44 45

46 47 48 49 50

1

2

Seeking sub 2 in the fault plane of sub 1: DC-constrainedpo5

X depth 85 km

X

X…EMSCX…this study

depth 72 km

depth 60 km

35

A double-event interpretation:• Subevent 1: 1.10e19 Nm

strike, dip, rake: (84, 64, 121)=(209 40 43)• Subevent 2 (6 sec later): 0.87e19 Nm

strike, dip, rake: (61, 86, 52)=(326, 38, 174)

12

EMSC

this study

DepthsSub 1: 60 kmSub 2: 76 kmHyp.: 85 km

36

Possible explanation of the apparently large non-DC:

Summing up MT of these two 100% DC events provides a non-DC solution

strike, dip, rake: (82, 70, 94) 1.6e19 Nm, DC%=57

near to long-period Mednet CMT

strike, dip, rake: (81, 67, 139) 1.4e19 Nm, DC%=56

But Mednet centroid is too far…

12

M

38

Can we identify fault plane of subevent 2 ?

-40 -20 0 20 40 60 80 100

-30-20

-10 0

10 20

30

-110-100-90-80-70-60-50-40-30-20-10

Depth [km]nodal plane I

subevent 1hypoc. uncert.

subevent 2

Lon E [km]

Lat N [km]

Depth [km]

x+1

2

39

Can we identify fault plane of subevent 2 ? 5

-80 -60 -40 -20 0 20 40 60 80 100

-40-30-20-10 0 10 20 30

-140-120-100-80-60-40-20

0

Depth [km]nodal plane I

subevent 1hypoc. uncert.

subevent 2fault plane 2 ?

Lon E [km]

Lat N [km]

Depth [km]

-80 -60 -40 -20 0 20 40 60 80 100

-80-60-40-20 0 20 40 60

-110-100-90-80-70-60-50-40-30-20-10

Depth [km]nodal plane I

subevent 1hypoc. uncert.

subevent 2fault plane 2

Lon E [km]

Lat N [km]

Depth [km]

strike 61° strike 326°

112 2

Nodal plane with strike 326° passesthrough the hypoc. !

40

hypo5

-80 -60 -40 -20 0 20 40 60 80 100-80-60-40-20 0 20 40 60-110-100-90-80-70-60-50-40-30-20-10

Depth [km]nodal plane I

subevent 1hypoc. uncert.

subevent 2fault plane 2

Lon E [km]

Lat N [km]

Depth [km]

Nodal plane with strike 326° passesthrough the hypoc. !

41

hypo5

-80 -60 -40 -20 0 20 40 60 80 100-80-60

-40-20

0 20

40 60

-110-100-90-80-70-60-50-40-30-20-10

Depth [km]

nodal plane Isubevent 1

hypoc. uncert.subevent 2

fault plane 2

Lon E [km]

Lat N [km]

Depth [km]

Hypothesis: both patches (on different fault planes)nucleated close to the same point, andruptured upward, sub 2 being delayed with respect to sub 1.

DepthsSub 1: 60 kmSub 2: 76 kmHyp.: 85 km

1

12

2

common hypoc.

42-50 -40 -30 -20 -10 0 10 20 30 40 50

EASTING (KM )

-50

-40

-30

-20

-10

0

10

20

NO

RT

HIN

G (

KM

)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

26 27 28 29 30

31 32 33 34 35

36 37 38 39 40

41 42 43 44 45

46 47 48 49 50

12

X

X

X…EMSCX…this study

Another possibility:fixed DC focal mechanism (that of sub 1).

It moves sub 2 close to sub 1.

Depth 60 kmdepth 69 km

depth 72 km

43

EW

0 100 200 300 400time (sec)

3.2E-003

2.3E-003

2.0E-003

1.2E-003

1.0E-003

1.6E-003

1.1E-003

5.7E-004

1.4E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

3.1E-003

7.4E-004

7.0E-004

6.4E-004

4.9E-004

1.3E-003

9.8E-004

3.0E-004

1.0E-003

3.7E-003

1.8E-003

1.5E-003

9.3E-004

9.9E-004

1.7E-003

8.6E-004

4.2E-004

9.6E-004

fixed (varred=52%) DC-constrained (varred=64%) NS

0 100 200 300 400time (sec)

3.4E-003

4.2E-003

2.1E-003

2.6E-003

1.1E-003

1.0E-003

1.4E-003

1.7E-003

1.6E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

1.2E-003

2.7E-003

1.9E-003

1.1E-003

3.0E-004

4.0E-004

7.0E-004

5.8E-004

6.3E-004

2.0E -003

3.6E -003

1.8E -003

1.8E -003

9.8E -004

7.9E -004

8.2E -004

7.7E -004

8.1E -004

fixed (varred=52%) DC-constrained (varred=64%) Z

0 100 200 300 400time (sec)

3.3E-003

2.8E-003

2.4E-003

1.4E-003

1.0E-003

8.8E-004

1.1E-003

5.6E-004

2.1E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

1.7E-003

2.1E-003

2.1E-003

5.6E-004

7.0E-004

1.2E-003

9.5E-004

3.7E-004

1.1E-003

3.0E -003

2.4E -003

2.1E -003

6.0E -004

7.8E -004

1.4E -003

1.3E -003

3.7E -004

1.0E -003

fixed (varred=52%) DC-constrained (varred=64%)

44-50 -40 -30 -20 -10 0 10 20 30 40 50

EASTING (KM )

-50

-40

-30

-20

-10

0

10

20

NO

RT

HIN

G (

KM

)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

26 27 28 29 30

31 32 33 34 35

36 37 38 39 40

41 42 43 44 45

46 47 48 49 50

12

Another possibility:fixed DC focal mechanism (that of sub 1)

moves sub 2 close to sub 1

now we do notneed the left

segment… but how to explain low DC %

and why the 6-sec delay ?

depth 60 kmdepth 69 km

45-50 -40 -30 -20 -10 0 10 20 30 40 50

EASTING (KM )

-50

-40

-30

-20

-10

0

10

20

NO

RT

HIN

G (

KM

)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

26 27 28 29 30

31 32 33 34 35

36 37 38 39 40

41 42 43 44 45

46 47 48 49 50

-50 -40 -30 -20 -10 0 10 20 30 40 50

EASTING (KM )

-50

-40

-30

-20

-10

0

10

20

NO

RT

HIN

G (

KM

)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

26 27 28 29 30

31 32 33 34 35

36 37 38 39 40

41 42 43 44 45

46 47 48 49 50

Interpretation I:Fixed mechanismVarred= 52%

Interpretation II:DC-constrainedVarred=64% !!

strike, dip, rake:84° 64°, 121°(for both)

84°, 64°, 121°

329°, 36°, 179°

x

x

hypocenterdepth 85 km(this study)

72 km

60 km

85 km

69 and 60 km

46

Methodical lesson and Cythera model• Relocation and CMT inversion in same model enabled identification of the fault

plane (strike ~80°) of the main patch.

• Hierarchic space-time grid search lead to convergence of the DC% to a low value.

• 100% DC-constrained solution provided a double-event model and explained the low DC% as only apparent non-DC.

• Rupture started at depth 85 km. Most stable slip patch was centered 35 km apart, at depth 60 km.

• Second large patch was delayed by 6 sec. Position and mechanism not unique. Possibly on a different fault plane.

http://geo.mff.cuni.cz

47

48

The most important essence is visions and dreams

http://geo.mff.cuni.cz

49

„Blind“ experiment on slip inversion from synthetic data (EC projekt SPICE)

Data = synthetics for a „secret“ slip distribution

53

54

56

New BB satellite

network Patras

Univ.

= statusMay 21

green=Trilliumand CMG

57

ITSAK-GR 2006-2009 starts right these days

= a new EC Marie CurieRTN

accelerographsnear Cythera available !

Ch. Papaioannou

58

59

60

The fault plane is needed for correct identification of the slip patches

apparent source time functionsfrom EGF method ... and slip patches by NA algorithm

61

The fault plane is needed for correct identification of the slip patches

apparent source time functionsfrom EGF method ... and slip patches by NA algorithm

63

66

-50 -40 -30 -20 -10 0 10 20 30 40 50

EASTING (KM )

-50

-40

-30

-20

-10

0

10

20N

OR

TH

ING

(K

M)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

fixed mechanism: blue crosses 13 and 21 (varred 52%)

DC-constrained:blue cross 12 and green square 8 (varred 64%) !

67

-50 -40 -30 -20 -10 0 10 20 30 40 50

EASTING (KM )

-50

-40

-30

-20

-10

0

10

20N

OR

TH

ING

(K

M)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

68

70

71

72-50 -40 -30 -20 -10 0 10 20 30 40 50

EASTING (KM )

-50

-40

-30

-20

-10

0

10

20

NO

RT

HIN

G (

KM

)

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23 24 25

26 27 28 29 30

31 32 33 34 35

36 37 38 39 40

41 42 43 44 45

46 47 48 49 50

73

EW

0 100 200 300 400time (sec)

3.2E-003

2.3E-003

2.0E-003

1.2E-003

1.0E-003

1.6E-003

1.1E-003

5.7E-004

1.4E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

2.0E-003

1.1E-003

8.4E-004

9.4E-004

6.9E-004

1.8E-003

1.1E-003

4.1E-004

7.0E-004

3.6E -003

1.5E -003

1.3E -003

9.4E -004

7.9E -004

1.8E -003

9.4E -004

5.8E -004

9.2E -004

sub 1 (varred=38%) sub 1+2 (varred=55%)

NS

0 100 200 300 400time (sec)

3.4E-003

4.2E-003

2.1E-003

2.6E-003

1.1E-003

1.0E-003

1.4E-003

1.7E-003

1.6E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

1.2E-003

2.7E-003

1.7E-003

1.8E-003

5.0E-004

7.9E-004

8.9E-004

8.3E-004

4.0E-004

2.3E -003

3.2E -003

1.6E -003

1.8E -003

1.1E -003

8.7E -004

8.6E -004

7.8E -004

7.3E -004

sub 1 (varred=38%) sub 1+2 (varred=55%)

Z

0 100 200 300 400time (sec)

3.3E-003

2.8E-003

2.4E-003

1.4E-003

1.0E-003

8.8E-004

1.1E-003

5.6E-004

2.1E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

1.3E-003

1.7E-003

1.9E-003

8.1E-004

9.7E-004

1.3E-003

1.1E-003

4.6E-004

7.1E-004

2.4E -003

2.1E -003

2.1E -003

1.0E -003

1.1E -003

2.1E -003

1.7E -003

4.8E -004

9.6E -004

sub 1 (varred=38%) sub 1+2 (varred=55%)

74

hypo5

-40 -20 0 20 40 60 80 100

-80-60-40-20 0 20 40 60 80

-110-100-90-80-70-60-50-40-30-20-10

Depth [km] nodal plane Inodal plane II

hypoc. uncert.subevent 1

Lon E [km]Lat N [km]

Depth [km]

75

Incorrect timing strongly biases DC% even for correct position

0 0.2 0.4 0.6 0.8 1

CO RRELATIO N

0

20

40

60

80

100

DC

%

search 2

0 0.2 0.4 0.6 0.8 1

CO RRELATIO N

0

20

40

60

80

100

DC

%

search 4opt. position

76

==> Identification of fault plane ispossible using CMT + hypocenter

centroidhypocenter(with uncertainty)

two nodal planes

77

A double-event interpretation:• Subevent 1: 1.10e19 Nm

strike, dip, rake: (84, 64, 121)=(209 40 43)• Subevent 2 (6 sec later): 0.87e19 Nm

strike, dip, rake: (61, 86, 52)=(326, 38, 174)

12

EMSC

this study

Sub 1:x=0, y=30, z=60Sub 2:x=-14, y=-20, z=76Hyp:x=-15, y=10, z=85

78

Waveform fit for f < 0.1 Hz enables detailed source analysis.

EW

0 100 200 300 400time (sec)

3.2E-003

2.3E-003

2.0E-003

1.2E-003

1.0E-003

1.6E-003

1.1E-003

5.7E-004

1.4E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

3.5E-003

1.5E-003

1.2E-003

6.1E-004

5.8E-004

2.3E-003

1.3E-003

3.5E-004

9.3E-004

3.0E-003

1.6E-003

1.1E-003

6.4E-004

9.2E-004

1.9E-003

1.1E-003

3.1E-004

7.8E-004

6stations (varred=54%)9 stations (varred=56%) NS

0 100 200 300 400time (sec)

3.4E-003

4.2E-003

2.1E-003

2.6E-003

1.1E-003

1.0E-003

1.4E-003

1.7E-003

1.6E-003

ITM

GVD

LTR

SAN

APE

LAS

ZKR

ARG

KEK

2.2E-003

3.1E-003

2.0E-003

2.7E-003

8.4E-004

9.9E-004

1.2E-003

1.1E-003

6.7E-004

2.2E-003

2.8E-003

1.3E-003

2.2E-003

4.9E-004

5.9E-004

1.1E-003

8.6E-004

5.7E-004

6stations (varred=54%)9 stations (varred=56%)