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 Slovakia

National 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 velocity [km /s]

30

20

10

0

Dep

th [k

m]

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 22

tim e [s]

N

E

Z

P

S

JABO

12 14 16 18 20 22

tim e [s]

N

E

Z

P

S

SPAC

Data

An example of simple waveforms – displacement

V14

12 14 16 18 20 22

tim e [s]

N

E

Z

P

S

JABO

12 14 16 18 20 22

tim e [s]

N

E

Z

P

S

SPAC

Data

S03

An example of complicate waveforms – velocity

20 22 24 26 28

tim e [s]

N

E

Z

P

S

DVO D

20 22 24 26 28

tim e [s]

N

E

Z

P

HRAD

Data

An example of complicate waveforms – displacement

S03

20 22 24 26 28

tim e [s]

N

E

Z

P

S

D VO D

20 22 24 26 28

tim e [s]

N

E

Z

P

H RAD

Data

48.5 48.6 48.7 48.8 48.9 49

tim e [s]

N

E

Z

P+

H O ST

velocity displacement

48.5 48.6 48.7 48.8 48.9 49

tim e [s]

N

E

Z

P+

H O ST

40.9 41 41.1 41.2 41.3 41.4

tim e [s]

N

E

Z

P+

PVES

velocity displacement

40.9 41 41.1 41.2 41.3 41.4

tim e [s]

N

E

Z

P+

PVES

Clear polarity identification

Datavelocity displacement

42.3 42.4 42.5 42.6 42.7 42.8

tim e [s]

N

E

Z

P- ?

SM O L

42.3 42.4 42.5 42.6 42.7 42.8

tim e [s]

N

E

Z

P - ?

SM O L

velocity displacement

48 48.1 48.2 48.3 48.4 48.5

tim e [s]

N

E

ZP+ ?

KO LL

48 48.1 48.2 48.3 48.4 48.5

tim e [s]

N

E

Z

P + ?

KO LL

Problematic polarity identification

Direct versus head waves

Data

54.4 54.8 55.2 55.6 56

tim e [s]

N

E

Z

Ph+

BO R Y

P-

57 .2 57.6 58 58.4 58.8

tim e [s]

N

E

Z

Ph-

M IC H

P+

Locations: Epicentres

Locations: Hypocentres

V03

Latitude [°

]Longitude [°]

De

pth

of h

yp

oc

en

tre [k

m]

• 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 ISOLA

events 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

of e

vent

s

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

ISO [% ]

0

4

8

12

Num

ber

of e

vent

s

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

CLVD [% ]

0

2

4

6

8

Num

ber

of e

vent

s

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

ISO [% ]

0

4

8

12

16

Nu

mb

er

of

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