Focal M echanisms of M icro-earthquakes in the Little Carpathians - the Influence
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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.
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Outline
Introduction
Moment Tensor Inversion Using Isola Program
Source Time Function
Influence of the Model
Results
Q&A
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Area Under Investigation
Model by Geofyzika Brno, 1985
- events out of seismic network (including the strongest one)
- complicated geological situation
- insufficiently accurate model
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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
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Time Function
displacement velocity
1Hz 5Hz 1Hz 5Hz
1Hz 5Hz1Hz 5Hz
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Time Function
gabor_function (delta-like) 1 Hz
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Time Function
gabor_function (delta-like) 3 Hz
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Time Function
gabor_function (delta-like) 5 Hz
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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
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Velocity Models
low -speed model
high -velocity
model
medium - speed model
2.1
4.0
4.2
JABO SPAC
DVODHRADKATALANCMODSPVESSMOL
PLAVBUKOLAKS
A
B
C
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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
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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:
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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
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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
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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:
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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