2015/02/05 06:16:46 42.69 26.17 10 4.6 Bulgaria
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2015/02/05 06:16:46:0 42.69 26.17 10.0 4.6 Bulgaria
Stations used:
HT.ALN HT.GRG HT.HORT HT.PAIG HT.SOH HT.SRS HT.THE HT.XOR
MN.DIVS MN.PDG MN.TIR MN.VTS RO.AMRR RO.CVD1
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.14e+22 dyne-cm
Mw = 3.97
Z = 16 km
Plane Strike Dip Rake
NP1 145 60 65
NP2 8 38 126
Principal Axes:
Axis Value Plunge Azimuth
T 1.14e+22 65 9
N 0.00e+00 21 158
P -1.14e+22 12 253
Moment Tensor: (dyne-cm)
Component Value
Mxx 9.73e+20
Mxy -2.76e+21
Mxz 4.91e+21
Myy -9.88e+21
Myz 2.84e+21
Mzz 8.91e+21
############--
##################----
--####################------
---######################-----
-----#######################------
------#######################-------
-------############ #########-------
---------########### T #########--------
---------########### ##########-------
-----------#######################--------
------------######################--------
-------------#####################--------
--------------####################--------
- ----------##################--------
- P -----------#################--------
-------------##############--------
-----------------###########--------
------------------########--------
------------------####--------
--------------------#-------
---------------#######
-------#######
Global CMT Convention Moment Tensor:
R T P
8.91e+21 4.91e+21 -2.84e+21
4.91e+21 9.73e+20 2.76e+21
-2.84e+21 2.76e+21 -9.88e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20150205061646/index.html
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STK = 145
DIP = 60
RAKE = 65
MW = 3.97
HS = 16.0
The NDK file is 20150205061646.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2015/02/05 06:16:46:0 42.69 26.17 10.0 4.6 Bulgaria
Stations used:
HT.ALN HT.GRG HT.HORT HT.PAIG HT.SOH HT.SRS HT.THE HT.XOR
MN.DIVS MN.PDG MN.TIR MN.VTS RO.AMRR RO.CVD1
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.14e+22 dyne-cm
Mw = 3.97
Z = 16 km
Plane Strike Dip Rake
NP1 145 60 65
NP2 8 38 126
Principal Axes:
Axis Value Plunge Azimuth
T 1.14e+22 65 9
N 0.00e+00 21 158
P -1.14e+22 12 253
Moment Tensor: (dyne-cm)
Component Value
Mxx 9.73e+20
Mxy -2.76e+21
Mxz 4.91e+21
Myy -9.88e+21
Myz 2.84e+21
Mzz 8.91e+21
############--
##################----
--####################------
---######################-----
-----#######################------
------#######################-------
-------############ #########-------
---------########### T #########--------
---------########### ##########-------
-----------#######################--------
------------######################--------
-------------#####################--------
--------------####################--------
- ----------##################--------
- P -----------#################--------
-------------##############--------
-----------------###########--------
------------------########--------
------------------####--------
--------------------#-------
---------------#######
-------#######
Global CMT Convention Moment Tensor:
R T P
8.91e+21 4.91e+21 -2.84e+21
4.91e+21 9.73e+20 2.76e+21
-2.84e+21 2.76e+21 -9.88e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20150205061646/index.html
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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:
cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 130 50 -90 3.71 0.4963
WVFGRD96 2.0 130 50 -90 3.77 0.5099
WVFGRD96 3.0 310 40 -90 3.83 0.4389
WVFGRD96 4.0 145 75 -75 3.89 0.4048
WVFGRD96 5.0 140 75 -75 3.88 0.4283
WVFGRD96 6.0 135 70 -75 3.87 0.4452
WVFGRD96 7.0 315 80 -70 3.84 0.4672
WVFGRD96 8.0 315 80 -75 3.91 0.4915
WVFGRD96 9.0 315 80 -70 3.90 0.5115
WVFGRD96 10.0 315 80 -70 3.90 0.5268
WVFGRD96 11.0 315 80 -70 3.90 0.5360
WVFGRD96 12.0 320 85 -65 3.90 0.5416
WVFGRD96 13.0 145 90 60 3.90 0.5448
WVFGRD96 14.0 150 60 70 3.97 0.5487
WVFGRD96 15.0 145 60 65 3.98 0.5554
WVFGRD96 16.0 145 60 65 3.97 0.5568
WVFGRD96 17.0 145 60 65 3.97 0.5542
WVFGRD96 18.0 145 60 65 3.97 0.5487
WVFGRD96 19.0 145 60 65 3.97 0.5408
WVFGRD96 20.0 140 60 60 3.98 0.5314
WVFGRD96 21.0 140 65 60 3.98 0.5214
WVFGRD96 22.0 140 65 60 3.98 0.5111
WVFGRD96 23.0 140 65 60 3.98 0.5002
WVFGRD96 24.0 140 65 60 3.98 0.4889
WVFGRD96 25.0 135 65 55 4.00 0.4772
WVFGRD96 26.0 135 65 55 4.00 0.4652
WVFGRD96 27.0 135 70 55 4.00 0.4531
WVFGRD96 28.0 135 70 55 4.00 0.4409
WVFGRD96 29.0 135 65 55 4.01 0.4284
The best solution is
WVFGRD96 16.0 145 60 65 3.97 0.5568
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 component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 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. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.
Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
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=Sat Feb 7 11:04:13 CST 2015