Focal Mechanisms of Micro-earthquakes in the Little Carpathians

-the Influence

of the Model and of the Source Time Function Used

AIM Second Annual Meeting

September, 29.-30., 2011 Prague

Lucia Fojtíková, Martin Gális a Jiří Zahradník

Geophysical Institute SAS, Bratislava, Slovakia

in cooperation with

industrial partner:

Juraj Sekereš Dagmar Sekerešová

Progseis, Ltd., Trnava, Slovakia

Progseis, Ltd.

Outline

Introduction

Moment Tensor Inversion Using Isola Program

Source Time Function

Influence of the Model

Results

Q&A

Area Under Investigation

Model by Geofyzika Brno, 1985

- events out of seismic network (including the strongest one)

- complicated geological situation

- insufficiently accurate model

Isola

Sokos and Zahradník (2009)

- waveform inversion

- the Green functions were calculated using the discrete-wave-number method (1D model)

orfinal differences method (3D model)

- low frequency content of seismic signal

- the match between the observed and best-fitting synthetic data is characterized by the overall variance reduction (VR)

pq.

pqM M x S t

6

( )

1

1, 2, 3, * , ,j

i j pq i p qj

iu t a M G

x

Time Function

displacement velocity

1Hz 5Hz 1Hz 5Hz

1Hz 5Hz1Hz 5Hz

Time Function

gabor_function (delta-like) 1 Hz

Time Function

gabor_function (delta-like) 3 Hz

Time Function

gabor_function (delta-like) 5 Hz

gabor_function(delta-like) 1 Hz

Time Function

V14, Ml=2.2, h=5.2km

gabor_function(delta-like) 3 Hz

gabor_function(delta-like) 5 Hz

VR = 5.64E-1VR = 2.204E-1VR = 4.954E-2

Velocity Models

low -speed model

high -velocity

model

medium - speed model

2.1

4.0

4.2

JABO SPAC

DVODHRADKATALANCMODSPVESSMOL

PLAVBUKOLAKS

A

B

C

V14, Ml=2.2, h=5.2km

A

C

A+B+C

C–>VR = 2.76E-1 A+B+C–>VR=2.99E-01A–>VR = 2.68E-1

V14, Ml=2.2, h=5.2km

stationazimuth

[°]distance

[km]

SMO 265 2.6

BUK 305 5.3

KAT 59.0 7.2

SPA 128 14.5

A+B+C

A+B+C–>VR=2.68E-01

3D

3D–>VR=1.81E-01

Reference focal mechanism from

inversion of amplitudes:

V14, Ml=2.2, h=5.2km -> 4.2km

3D 2Hz–>VR=2.12E-01

Reference focal mechanism from

inversion of amplitudes:

stationazimuth

[°]distance

[km]

SMO 265 2.6

BUK 305 5.3

KAT 59.0 7.2

SPA 128 14.5

3D 1-2Hz

V14, Ml=2.2, h=5.2km -> 4.2km

3D 3Hz–>VR=2.45E-01

Reference focal mechanism from

inversion of amplitudes:

stationazimuth

[°]distance

[km]

SMO 265 2.6

BUK 305 5.3

KAT 59.0 7.2

SPA 128 14.5

3D 1-3Hz

V03, Ml=3.4, h=10.2km

stationazimuth

[°]distance

[km]

JAB 177 5.7

LAN 328 6.3

PVE 336 10.2

SPA 202 13.9

A+B+C

A+B+C–>VR=5.31E-01

3D

3D–>VR=4.17E-01

Reference focal mechanism from

inversion of amplitudes:

CONCLUSIONS

We have analyzed an influence of the time function on the wave form inversion

It is important to check corner frequency of the earthquake and choose the appropriate time function

Velocity model has a high influence on the inversion

Using suitable 1D models individually for each station produced better results than 3D model

This is caused by the 3D model not being accurate enough for this area, therefore it is needed to improve the 3D model for Little Carpathians region