Aftershock sequences

in the Little Carpatian region

following two earthquakes in 2006

AIM Third Annual Meeting

October, 10.-12., 2012 Smolenice

Jiří Málek and Lucia Fojtíková

Institute of Rock Structure and Mechanics, v.v.i.

Juraj Sekereš

Progseis, Ltd., Trnava, Slovakia

Motivation

Seismic activity 1987-2010

source.: Progseis, Ltd, GPI SAS, EQUIS, Ltd.

Tectonic situation

2006, Ml=2.2

2006, Ml=3.4

Focal mechanism

ID

Date

Time

Mw

Latitude

Longitude

Depth

Focal mechanism

V03

13.3.2006 08:28:38.39

3.4

48.550

17.694

10.2

V14

5.8.2006 09:00:08.63

2.2

48,516

17,468

5.2

Aftershocks

New Stations

Method

Master-event relative location

• The shape of an aftershock cluster is determined.

• Time differences between aftershock and the main shock (master event) are used.

• The seismograms are compared only at the same station (not between stations).

• Similarity of the seismograms enables to read time differences more accurately.

• Relative locations are less sensitive to the velocity model.

• Linear inverse problem, which can be easily solved.

Method

earthquakejstationiP

jiS

konstv

vk

s

p 1jiu

jx

jir

Mi

ji

ji rrr

ji

Mi

jip

ji xuDDkvr

)(

jmi

Mm

jm

Mi

jip

jm

ji xuuPPPPvrr

)(

Index M means master-event (normaly the main shock) Index m means master-station (normaly the nearest station)

unit vector of the ray leaving j-th event to i-th station

space vector from master-event to j-th event - unknown

travel distance of j-th event and i-th station

ji

ji

ji PSD

iMi

ji uuu

Linear inverse problem

Velocity model

Data

Application at WEBNET

46000 47000 48000 49000

7000

8000

9000

10000

dR

Master event

15000 20000 25000 30000 35000 40000 45000Y (m )

40000

45000

50000

55000

60000

65000

70000

X (

m)

NKC

KOC

KRC

SKC

STC

VAC

LBC

SNE

KVE

Z(m)

X(m)

Málek and Horálek, 2008

Master-event

Master-event

Master-event

Master-event

Master-event

Master-event

Master-event

Data

SMOL

SMOL

KATA

KATA

P

S

Z Z

N E

Result and Model sensitivity

-2 -1 0 1 2

X (km) East

-2

-1

0

1

2

Y (

km)

Nor

th

Grad. model vp=5.5 km/s Hom. model vp=6.0 km/s

Grad. model vp=6.0 km/s

Result and Model sensitivity

-2 -1 0 1 2

X (km) East

-2

-1

0

1

2

Z (

km)

Up

Grad. model vp=5.5 km/s Hom. model vp=6.0 km/s Grad. model vp=6.0 km/s

Results

Dep

th

Y

X

Conclusions

J. Hók, modified after Fusán et. al 1987

Conclusions

J. Hók, modified after Fusán et. al 1987

Conclusions

• Master-event method is a useful tool for determination of aftershock cluster shape

• It can be applied even to small magnitudes (ML=2.2)

• One of the nodal plane was selected as fault plane, with azimuth of about 300°

• This fault was identified on tectonic map

• Faults of NW-SE azimuths are active in the Little Carpathian region

and they are important for seismic hazard assesment