THE EMSC location for this event is 2010/09/15 02:21:17 45.62 14.26 2.0 3.80 Slovenia
We read arrival times from waveforms downloaded from EIDA and picked first motions. We used both the nnCIA and WUS velocity models. The nnCIA model gave a shallow depth than the WUS model. However we prefer the use of the WUS model because of the waveforms fits. The output of the elocate computations is in the file elocate.txt.
As a test on the EMSC solution, we examined the azimuthal distribution of time shifts required for the waveform match. These were fit to an equaiton of the form
TimeShift = A + B sin Az + C cos Az
The B and C terms are related to a spatial shift of the epicenter DR through the assumed group velocity of the Love and Rayleigh waves, which we take to be 3.1/0.92 and 3.1 km/s respectively. The next figure shows the pattern of inferred residuals in distance to each station.
The simplified analysis calls for the origin time to be 0.8 sec earlier than the EMSC soltuion and for the EMSC epicenter to move about 1.9 km in the southwest. These are not significant shifts. The EMSC solution is accepted.
USGS/SLU Moment Tensor Solution
ENS 2010/09/15 02:21:17:0 45.62 14.26 2.0 3.8 Slovenia
Best Fitting Double Couple
Mo = 8.32e+21 dyne-cm
Mw = 3.88
Z = 27 km
Plane Strike Dip Rake
NP1 342 85 -160
NP2 250 70 -5
Principal Axes:
Axis Value Plunge Azimuth
T 8.32e+21 11 114
N 0.00e+00 69 354
P -8.32e+21 17 208
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.59e+21
Mxy -6.11e+21
Mxz 1.49e+21
Myy 5.06e+21
Myz 2.47e+21
Mzz -4.66e+20
#-------------
######----------------
#########-------------------
###########-------------------
##############--------------------
################--------------------
#################---------------------
###################-----################
##################--####################
##############-------#####################
###########-----------####################
########---------------###################
######-----------------###################
###--------------------#################
#----------------------############ ##
-----------------------########### T #
----------------------###########
----------------------############
------ -----------##########
----- P ------------########
-- ------------#####
-------------#
Global CMT Convention Moment Tensor:
R T P
-4.66e+20 1.49e+21 -2.47e+21
1.49e+21 -4.59e+21 6.11e+21
-2.47e+21 6.11e+21 5.06e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20100915022117/index.html
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STK = 250
DIP = 70
RAKE = -5
MW = 3.88
HS = 27.0
The waveform inversion is preferred. The apparent lack of depth control may be do to the fact that the Rayleigh wave spectral holes for a strike slip source preclude such resolution. There is a second event on the seismograms at the same location at 2010 09 15 02 23 13 806.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2010/09/15 02:21:17:0 45.62 14.26 2.0 3.8 Slovenia
Best Fitting Double Couple
Mo = 8.32e+21 dyne-cm
Mw = 3.88
Z = 27 km
Plane Strike Dip Rake
NP1 342 85 -160
NP2 250 70 -5
Principal Axes:
Axis Value Plunge Azimuth
T 8.32e+21 11 114
N 0.00e+00 69 354
P -8.32e+21 17 208
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.59e+21
Mxy -6.11e+21
Mxz 1.49e+21
Myy 5.06e+21
Myz 2.47e+21
Mzz -4.66e+20
#-------------
######----------------
#########-------------------
###########-------------------
##############--------------------
################--------------------
#################---------------------
###################-----################
##################--####################
##############-------#####################
###########-----------####################
########---------------###################
######-----------------###################
###--------------------#################
#----------------------############ ##
-----------------------########### T #
----------------------###########
----------------------############
------ -----------##########
----- P ------------########
-- ------------#####
-------------#
Global CMT Convention Moment Tensor:
R T P
-4.66e+20 1.49e+21 -2.47e+21
1.49e+21 -4.59e+21 6.11e+21
-2.47e+21 6.11e+21 5.06e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20100915022117/index.html
|
First motion solution using the polarity picks, azimuths and takeoff angles indicated in the elocate.txt output. The nodal planes plotted are those of the preferred solution. |
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for the waveform inversion are shown in the next figure.
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The program wvfgrd96 was used with good traces observed at short distance to determine the focal mechanism, depth and seismic moment. This technique requires a high quality signal and well determined velocity model for the Green functions. To the extent that these are the quality data, this type of mechanism should be preferred over the radiation pattern technique which requires the separate step of defining the pressure and tension quadrants and the correct strike.
The observed and predicted traces are filtered using the following gsac commands:
hp c 0.02 n 3 lp c 0.10 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 150 60 -40 3.23 0.2389
WVFGRD96 1.0 165 85 -10 3.20 0.2535
WVFGRD96 2.0 160 75 -20 3.37 0.3399
WVFGRD96 3.0 165 90 -10 3.42 0.3661
WVFGRD96 4.0 165 75 20 3.48 0.3806
WVFGRD96 5.0 165 75 20 3.51 0.3928
WVFGRD96 6.0 160 75 20 3.54 0.4010
WVFGRD96 7.0 160 90 25 3.57 0.4095
WVFGRD96 8.0 335 80 -30 3.62 0.4197
WVFGRD96 9.0 335 75 -30 3.65 0.4241
WVFGRD96 10.0 255 70 15 3.67 0.4456
WVFGRD96 11.0 255 70 10 3.70 0.4672
WVFGRD96 12.0 250 70 10 3.71 0.4859
WVFGRD96 13.0 250 70 10 3.73 0.5013
WVFGRD96 14.0 250 70 10 3.75 0.5142
WVFGRD96 15.0 250 70 10 3.76 0.5242
WVFGRD96 16.0 250 70 10 3.77 0.5310
WVFGRD96 17.0 250 70 10 3.79 0.5367
WVFGRD96 18.0 250 70 10 3.80 0.5432
WVFGRD96 19.0 250 70 10 3.81 0.5471
WVFGRD96 20.0 250 75 -5 3.82 0.5503
WVFGRD96 21.0 250 75 -5 3.84 0.5546
WVFGRD96 22.0 250 70 0 3.84 0.5563
WVFGRD96 23.0 250 70 0 3.85 0.5594
WVFGRD96 24.0 250 75 -5 3.86 0.5615
WVFGRD96 25.0 250 75 -5 3.87 0.5638
WVFGRD96 26.0 250 75 -5 3.87 0.5625
WVFGRD96 27.0 250 70 -5 3.88 0.5639
WVFGRD96 28.0 250 70 -5 3.88 0.5618
WVFGRD96 29.0 250 70 -5 3.89 0.5610
WVFGRD96 30.0 250 65 -5 3.90 0.5585
WVFGRD96 31.0 250 65 -5 3.90 0.5551
WVFGRD96 32.0 250 65 -5 3.91 0.5500
WVFGRD96 33.0 250 65 -5 3.91 0.5439
WVFGRD96 34.0 250 65 -5 3.92 0.5393
WVFGRD96 35.0 250 65 -5 3.92 0.5335
WVFGRD96 36.0 250 65 -5 3.93 0.5268
WVFGRD96 37.0 250 65 -5 3.94 0.5215
WVFGRD96 38.0 250 65 -5 3.95 0.5165
WVFGRD96 39.0 245 65 -10 3.96 0.5142
The best solution is
WVFGRD96 27.0 250 70 -5 3.88 0.5639
The mechanism correspond to the best fit is
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The best fit as a function of depth is given in the following figure:
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The comparison of the observed and predicted waveforms is given in the next figure. The red traces are the observed and the blue are the predicted. Each observed-predicted componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces it the time shift required for maximum correlation between the observed and predicted traces. This time shift is required because the synthetics are not computed at exactly the same distance as the observed and because the velocity model used in the predictions may not be perfect. A positive time shift indicates that the prediction is too fast and should be delayed to match the observed trace (shift to the right in this figure). A negative value indicates that the prediction is too slow. The bandpass filter used in the processing and for the display was
hp c 0.02 n 3 lp c 0.10 n 3
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| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms. Each solution is plotted as a vector at a given value of strike and dip with the angle of the vector representing the rake angle, measured, with respect to the upward vertical (N) in the figure. |
The WUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01
Model after 8 iterations
ISOTROPIC
KGS
FLAT EARTH
1-D
CONSTANT VELOCITY
LINE08
LINE09
LINE10
LINE11
H(KM) VP(KM/S) VS(KM/S) RHO(GM/CC) QP QS ETAP ETAS FREFP FREFS
1.9000 3.4065 2.0089 2.2150 0.302E-02 0.679E-02 0.00 0.00 1.00 1.00
6.1000 5.5445 3.2953 2.6089 0.349E-02 0.784E-02 0.00 0.00 1.00 1.00
13.0000 6.2708 3.7396 2.7812 0.212E-02 0.476E-02 0.00 0.00 1.00 1.00
19.0000 6.4075 3.7680 2.8223 0.111E-02 0.249E-02 0.00 0.00 1.00 1.00
0.0000 7.9000 4.6200 3.2760 0.164E-10 0.370E-10 0.00 0.00 1.00 1.00
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Wed Sep 15 18:07:08 CDT 2010