MICRO-SEISMICITY AND FOCAL MECHANISMS

IN THE MALÉ KARPATY MTS.,

SLOVAKIA

Lucia Fojtíková, Václav Vavryčuk, Andrej Cipciar, Ján Madarás

Seismic Activity in the Malé Karpaty Mts.

• January 9th 1906 – the strongest earthquakes in the region in 20th century• Ms = 5.7; h=15 km, epicentral intensity Io = 8° MSK-64

Period: 1034 - 2006

Seismic Stations

Seismic stations in SlovakiaNational seismic networkLocal seismic network LSSVSLocal seismic network EBOLocal seismic network EMO

Geological Map

Tectonic Sketch

P-wave Velocity Model

JABO

BUKO KATA

LANC

PLAV

MODS

SPAC

SMOL

KATA

HOST

DVODLAKS

[km/s]

N

[km]

JABO

BUKO KATA

LANC

PLAV

MODS

SPAC

SMOL

KATA

HOST

DVODLAKS

[km/s]

NN

[km]

4.0 5.0 6.0 7.0P-w ave ve locity [km /s]

30

20

10

0

De

pth

[km

]

3D 1D

Data

• 44 micro-earthquakes

• Period 2001 - 2009

• Area: 30km x 60km

• Magnitudes of events analyzed: 1.1 – 3.2

• Hypocenter depths: 1km – 15km

• Seismometers - short-period: SM-3, Le3D, CMG-40T

- broad-band: STS-2

• Sampling frequency - 100 Hz, 20 Hz

An example of simple waveforms - velocity

Data

V14

12 14 16 18 20 22tim e [s]

N

E

Z

P

S

JABO

12 14 16 18 20 22tim e [s]

N

E

Z

P

S

SPAC

Data

An example of simple waveforms – displacement

V14

12 14 16 18 20 22tim e [s]

N

E

Z

P

S

JABO

12 14 16 18 20 22tim e [s]

N

E

Z

P

S

SPAC

Data

S03

An example of complicate waveforms – velocity

20 22 24 26 28tim e [s]

N

E

Z

P

S

DVO D

20 22 24 26 28tim e [s]

N

E

Z

P

H RAD

Data

An example of complicate waveforms – displacement

S03

20 22 24 26 28tim e [s]

N

E

Z

P

S

D VO D

20 22 24 26 28tim e [s]

N

E

Z

P

H R AD

Data

48 .5 48 .6 48 .7 48 .8 48 .9 49tim e [s]

N

E

Z

P+

H O ST

velocity displacement

48 .5 48 .6 48 .7 48 .8 48 .9 49tim e [s]

N

E

Z

P +

HO ST

40 .9 41 41 .1 41 .2 41.3 41 .4tim e [s]

N

E

Z

P+

PVES

velocity displacement

40 .9 41 41 .1 41 .2 41 .3 41 .4tim e [s]

N

E

ZP+

PVES

Clear polarity identification

Datavelocity displacement

42 .3 42 .4 42 .5 42.6 42.7 42 .8tim e [s]

N

E

Z

P - ?

SM O L

42 .3 42 .4 42 .5 42 .6 42.7 42 .8tim e [s]

N

E

Z

P - ?

SM O L

velocity displacement

48 48 .1 48 .2 48 .3 48 .4 48 .5tim e [s]

N

E

ZP + ?

K O LL

48 48 .1 48 .2 48 .3 48 .4 48 .5tim e [s]

N

E

ZP + ?

KO LL

Problematic polarity identification

Direct versus head waves

Data

54.4 54.8 55.2 55.6 56tim e [s]

N

E

Z

Ph+

BO RY

P-

57.2 57.6 58 58 .4 58.8tim e [s]

N

E

Z

P h-

M IC H

P +

Locations: Epicentres

Locations: Hypocentres

V03

Latitude [°]Longitude [°]

Depth of hypocentre [km

]

• FOCMEC (Snoke, 2003): inversion from P-wave polarities

• AMT (Vavryčuk, 2008): inversion from P-wave amplitudes

• ISOLA (Sokos & Zahradník, 2009): inversion from seismograms

Method FOCMEC AMT ISOLAevents 16 36 43

Focal Mechanisms and Moment Tensors

ISOLA - AMT – FOCMEC – All Events

N = 35 N = 16N = 41

AMT ISOLA FOCMEC

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

CLVD [% ]

0

4

8

12

Num

ber o

f eve

nts

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

ISO [% ]

0

4

8

12

Num

ber o

f eve

nts

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

CLVD [% ]

0

2

4

6

8

Num

ber o

f eve

nts

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

ISO [% ]

0

4

8

12

16

Num

ber o

f eve

nts

Non-DC Components

AMT ISOLA

Non-DC Components

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

CLVD [% ]

-60

-40

-20

0

20

40

60

ISO

[%]

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

CLVD [% ]

-60

-40

-20

0

20

40

60

ISO

[%]

a) b)AMT ISOLA

Correlation k=0.7vp/vs= 1.46

Correlation k=0.3 vp/vs= 1.57

Conclusions

• Focal mechanism determined using three different methods are statistically similar

• The majority of mechanisms have the P axes clustered in the NE direction

• The positive correlation between ISO and CLVD can be an indicator of tensile faulting

• The positive values of ISO and CLVD can be an indicator of opening of faults

• The ISO/CLVD ratio yields the vp/vs ratio in the range of 1.46 -1.57

November 25, 2009, Praha

Thank you for your attention