1

Two M5 earthquakes in Two M5 earthquakes in Corinth Gulf, January 2010Corinth Gulf, January 2010

J. Janský, O. Novotný, J. ZahradníkJ. Janský, O. Novotný, J. Zahradník - Prague - PragueE. Sokos - PatrasE. Sokos - Patras

2

Outline

• Records

• Hypocenter

• Centroid and moment tensor

• Finite source

• Faults ?

3

4

5

Stations and records

6

7

8

9

peak accel.1.7 m/s2

Intensity6 to 7

acceleration velocity

displacement

the near-field ramp

10Pre-shock

11

Possible signal from hypocenter (P)before signal from asperity (P’).

This is not the anti-alias filter effect !

12

Thisis thefiltereffect.

13

8 9 10 11 12

-0.0004

-0.0002

0

0.0002

Jan 18SER raw _Z

8 12 16 20

-0.03

-0 .02

-0 .01

0

0.01

0.02

0.03

Jan 18SER raw _Z

11 11.1 11.2 11.3 11.4

0.000108

0.000112

0.000116

0.00012

0.000124

0.000128

0.000132

Jan 18SERraw _Z

Zooming the first arrival.

14

60 62 64 66 68 70tim e (se c)

-0 .012

-0 .008

-0 .004

0

0.004

dis

pla

cem

en

t (m

)

Jan 18SER filf> 0.01 H zblack: EW

The near-field ramp. Where is S ?

S?

S?

15

60 62 64 66 68 70tim e (se c)

-0 .012

-0.008

-0.004

0

0.004

dis

pla

cem

en

t (m

)

Jan 18SER filf> 0.01 H zblue: Zblack: EW

16

Stations and records – a summary:

Clipping of CMG-3T, double P arrival (P, P’?), unclear S onset,

a clear near-field ramp at SER (thanks to CMG-5T)…

17

Location

18

19

21.8 21.9 22 22.1Lon E (deg)

38.3

38.35

38.4

38.45

38.5

Lat

N (

deg)

SEREFP

U PR

plus: 11circ le : 14square: 16cross: 17

One event located by many methods.

21

-100000 0 100000

EW re lative d isp lacem ent

-100000

0

100000

NS

rel

ativ

e di

spla

cem

ent

10.43 sec

9.96 sec

Jan 18, 2010EFP

clip 10.60 sec

-100 0 100

EW re lative d isp lacem ent

-100

0

100

NS

rel

ativ

e di

spla

cem

ent

12.90 sec 11.41 sec

Jan 18, 2010SER 5T

(clip on 3T at 13.1 sec)

-100000 0 100000

EW re la tive d isp lacem ent

-100000

0

100000

NS

rel

ativ

e di

spla

cem

ent

12.95 sec

11.41 sec

Jan 18, 2010SER 3T

(clip at 13.1sec)

-10000 0 10000

EW re la tive d isp lacem ent

-10000

0

10000

NS

rel

ativ

e d

isp

lace

me

nt 13.40 sec

12.61 sec

Jan 18, 2010UPR

22

21.8 21.9 22 22.1Lon E (deg)

38.3

38.35

38.4

38.45

38.5

Lat

N (

deg)

SEREFP

U PR

23

24

4 6 8 1 0 1 2 1 4

z ( k m )

0

1 0

2 0

3 0

4 0

Grid-search location.

25

38.38 38.4 38.42 38.44 38.46 38.48

0

10

20

30

Jan 18depth 8.1 km

21.84 21.88 21.92 21.96 22 22.04

0

5

10

15

20

25

Jan 18depth 8.1 km

26

Grid search combined with station-differences; trade off between depth and origin time is eliminated.

27

21.8 21.9 22 22.1Lon E (deg)

38.3

38.35

38.4

38.45

38.5

Lat

N (

deg)

SEREFP

U PR

plus: 11circ le : 14square: 16cross: 17

EM SC (5 km )

TH E (0.8 km )N O A (20.38 km )

U PSL (9.24 km )G SnoSD (10.5 km )

ATH (7.15 km )

Jan 18

One event located by many methods,agencies included.

28

21.8 21.9 22 22.1Lon E (deg)

38.3

38.35

38.4

38.45

38.5

Lat

N (

deg)

SEREFP

U PR

square: 13triangle: 15plus: 18circ le : 19

Jan 22

One event located by many methods

29

21.8 21.9 22 22.1Lon E (deg)

38.3

38.35

38.4

38.45

38.5La

t N

(de

g)

SEREFP

U PR

30

21.8 21.9 22 22.1Lon E (deg)

38.3

38.35

38.4

38.45

38.5

Lat

N (

deg)

SEREFP

U PR

black: Jan 18blue: Jan 22

The two eventsslightly shiftedone to another.

Independently supportedby a relative location of Jan 22 with respect to Jan 18.

31

Location - summary:

Conjugate gradients, grid search, relative location, all providing a

stable epicenter location. Two events close to each other. Depth ~10 km.

32

Centroid and moment tensor

33

Distances < 100 km

34

Even date-time: 20100122 15:56:00Displacement (m). Inversion band (Hz) 0.05 0.06 0.10 0.2

ObservedSynthetic

Gray waveforms weren't used in inversion.

Blue numbers are variance reduction

-101

x 10-3 NS

SE

R

-0.00-10-505

x 10-4 EW

0.64-4-202

x 10-4 Z

0.45

-2-101

x 10-4

MA

M

0.68-4-2024

x 10-4

0.87 -2

0

2x 10

-4

0.77

-1

0

1x 10

-4

DS

F

0.48 -505

x 10-5

0.28-1

0

1x 10

-4

0.44

-202

x 10-4

DR

O

0.53-2

0

2x 10

-4

0.48 -1012

x 10-4

0.69

-2

0

2x 10

-4

GU

R

0.82 -202

x 10-4

0.60 -505

10x 10

-5

0.55

-1

0

1x 10

-4

PD

O

-0.02 -101

x 10-4

0.46 -505

x 10-5

0.55

50 100 150-2

02

x 10-4

Time (sec)

LT

K

0.92

50 100 150

-505

10x 10

-5

Time (sec)

0.60

50 100 150

-202

x 10-5

Time (sec)

0.12

Specific role of thenearest station.Excluded from inversion.

Jan 18

Frequency < 0.2 Hz

35

Even date-time: 20100122 15:56:00Displacement (m). Inversion band (Hz) 0.05 0.06 0.10 0.2

ObservedSynthetic

Gray waveforms weren't used in inversion.

Blue numbers are variance reduction

-505

x 10-4 NS

SE

R

0.17 -101

x 10-3 EW

0.77 -505

x 10-4 Z

0.45

-101

x 10-4

MA

M

0.70 -202

x 10-4

0.70 -101

x 10-4

0.80

-505

x 10-5

DS

F

0.04-1

0

1x 10

-4

0.65-10-505

x 10-5

0.65

-202

x 10-4

DR

O

0.75 -1012

x 10-4

0.68-2-101

x 10-4

0.72

-2-101

x 10-4

GU

R

0.90 -101

x 10-4

0.41 -505

x 10-5

0.66

-101

x 10-4

PD

O

0.58 -505

x 10-5

0.47-505

x 10-5

0.63

50 100 150-2

0

2x 10

-4

Time (sec)

LT

K

0.88

50 100 150-1

01

x 10-4

Time (sec)

0.81

50 100 150-6-4-2024

x 10-5

Time (sec)

0.33

strike, dip, rake Jan 18: Plane 1: 108 57 -74 Plane 2: 260 37 -113Jan 22: Plane 1: 76 38 -108 Plane 2: 279 54 -76

Jan 22

36

(Lat 38.4250, Lon 21.9187, model ON)

Centroidal depth ~ 3-5 km,independent of crustal models.

37

Uncertainty ofthe centroid position

38

Centroid and moment tensor - summary

Two normal events, slightly different positions and mechanisms, small

centroid depths (~ 4 km).

39

Fault plane

40

-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

Jan 18: H-C consistency; fault dipping to South

4121.92 21.94 21.96 21.98 22 22.02

38.38

38.4

38.42

38.44

38.46

38.48

No

Yes !

Jan 18

4221.92 21.94 21.96 21.98 22 22.02

38.38

38.4

38.42

38.44

38.46

38.48

21.92 21.94 21.96 21.98 22 22.02

38.38

38.4

38.42

38.44

38.46

38.48

No

Yes !

Jan 18 Jan 18, Jan 22

??

44

-20

0

20

-20 -15 -10 -5 0 5 10 15 20

-20

-15

-10

-5

0

5

10 jan22

North-South (km)

Dep

th

East-West (km)

Jan 22: H-C consistency achieved when C shifted by 0.02° to North.

46

-200

20-20 -15 -10 -5 0 5 10 15 20

-20

-15

-10

-5

0

5

10

East-West (km)

North-South (km)

jan18 green, jan22 red (same C)

Dep

th

If the H depths are 8 km, both H’s are in the same planedetermined by the strike and dip of Jan 22.

47

-20

-10

0

10

20 -20

-10

0

10

20

-20

-15

-10

-5

0

5

10

North-South (km)

jan18 green, jan22 red (same C)

East-West (km)

Dep

th

Caution: These are the two likely fault planes, not the conjugate nodal planes !

48

49

Fault plane - summary

Jan 18 fault plane dipping to South,

Jan 22 a bit more problematic

(a Northward 0.02° shift of C would be needed, but allowed within the

uncertainty limits).

Relation to surface faults is unclear.

50

Fault plane – additional data ?

51

Preliminary location of the sequence (Patras Univ.)

5250 60 70 80 90 100

tim e (s)

-0 .008

-0 .004

0

0.004

0.008

0.012

dis

pla

cem

en

t (m

)

SER _EWblack: dataco lor: synt

blue: fin ite_25pink: fin ite_43green: 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

2543

Finite-fault modeling(forward simulation for SER)

Finite-source effectsare evident, but no simple preferencecan be made.

53

-1.5 -1 -0.5 0 0.5 1 1.5

-1

-0.5

0

0.5

1

50 60 70 80 90 100tim e (s)

-0 .008

-0 .004

0

0.004

0.008

0.012

dis

pla

cem

en

t (m

)

SER _EWblack: datacolor: synt

blue: fin ite_25pink: fin ite_49green: fin ite_hypred: po in t source

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

55

Finite fault (additional data) – summary

Relocation of the sequence by relative methods would be useful.

Finite-source effects were found but their interpretation is non-unique.

The near stations are few, only forward simulation is possible.

56

Interesting observation

Fast long-period waves were observed at many stations for these events, perhaps leaking modes PL. How to use them in the source and

crustal structure studies?

57

58

Even date-time: 20100122 15:56:00Displacement (m). Inversion band (Hz) 0.05 0.06 0.9 1.0

ObservedSynthetic

Gray waveforms weren't used in inversion.

Blue numbers are variance reduction

-5

0

5x 10

-3 NS

SE

R

-1.92 -4-20

x 10-3 EW

0.61-4-20

x 10-3 Z

-0.76

-505

x 10-4

MA

M-1.90 -10

-505

x 10-4

-1.68 -505

10x 10

-4

-4.58

-202

x 10-4

DS

F

-0.60-4-2024

x 10-4

-0.07-5

0

5x 10

-4

-0.51

-505

x 10-4

DR

O

0.07-4-2024

x 10-4

0.03 -505

x 10-4

-1.18

-4-20246

x 10-4

GU

R

-0.71 -505

x 10-4

-2.04 -50

5x 10

-4

-2.26

-4-202

x 10-4

PD

O

-0.46-2

0

2x 10

-4

0.10 -202

x 10-4

-1.00

60 80 100

-2024

x 10-4

Time (sec)

LT

K

-0.31

60 80 100-202

x 10-4

Time (sec)

-0.25

60 80 100-202

x 10-4

Time (sec)

-1.99

Source depth 5.5 km, source duration 1 sec: ableto simulate the 5-sec waves. It is a structural effect.

59

Concluding remarks

• Routine epicenter location is surprisingly good.• Details needed for local tectonic interpretation are ‘on the

edge’ of the available data. • It seems possible to formulate an H-C consistent model of

both events. • How to produce the whole class of possible (non-unique)

models automatically?• Combining the geometry constrains and finite-source

effects is a good strategy. • The near-filed effects and the long-period waves (PL?)

provide interesting additional data.

60

Thanks for your attention !