2013/05/28 00:09:52 43.22 41.58 2.0 5.20 Georgia
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2013/05/28 00:09:52:0 43.22 41.58 2.0 5.2 Georgia
Stations used:
GE.CSS GE.ISP GO.AKH GO.BATM GO.BGD IU.GNI IU.KIEV RO.CFR
RO.IAS
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 5.07e+23 dyne-cm
Mw = 5.07
Z = 23 km
Plane Strike Dip Rake
NP1 130 73 121
NP2 245 35 30
Principal Axes:
Axis Value Plunge Azimuth
T 5.07e+23 51 76
N 0.00e+00 30 300
P -5.07e+23 22 196
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.89e+23
Mxy -7.06e+22
Mxz 2.31e+23
Myy 1.50e+23
Myz 2.89e+23
Mzz 2.38e+23
--------------
----------------------
----------------------------
--------------###########-----
##---------#####################--
###------##########################-
######-###############################
######--################################
#####----################### #########
#####-------################# T ##########
####----------############### ##########
###-------------##########################
###---------------########################
#------------------#####################
#--------------------###################
-----------------------###############
-------------------------###########
----------------------------######
--------- ------------------
-------- P -----------------
----- --------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.38e+23 2.31e+23 -2.89e+23
2.31e+23 -3.89e+23 7.06e+22
-2.89e+23 7.06e+22 1.50e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20130528000952/index.html
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STK = 245
DIP = 35
RAKE = 30
MW = 5.07
HS = 23.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2013/05/28 00:09:52:0 43.22 41.58 2.0 5.2 Georgia
Stations used:
GE.CSS GE.ISP GO.AKH GO.BATM GO.BGD IU.GNI IU.KIEV RO.CFR
RO.IAS
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 5.07e+23 dyne-cm
Mw = 5.07
Z = 23 km
Plane Strike Dip Rake
NP1 130 73 121
NP2 245 35 30
Principal Axes:
Axis Value Plunge Azimuth
T 5.07e+23 51 76
N 0.00e+00 30 300
P -5.07e+23 22 196
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.89e+23
Mxy -7.06e+22
Mxz 2.31e+23
Myy 1.50e+23
Myz 2.89e+23
Mzz 2.38e+23
--------------
----------------------
----------------------------
--------------###########-----
##---------#####################--
###------##########################-
######-###############################
######--################################
#####----################### #########
#####-------################# T ##########
####----------############### ##########
###-------------##########################
###---------------########################
#------------------#####################
#--------------------###################
-----------------------###############
-------------------------###########
----------------------------######
--------- ------------------
-------- P -----------------
----- --------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.38e+23 2.31e+23 -2.89e+23
2.31e+23 -3.89e+23 7.06e+22
-2.89e+23 7.06e+22 1.50e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20130528000952/index.html
|
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 0.05 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 310 55 -65 4.71 0.3270
WVFGRD96 1.0 300 50 -70 4.73 0.3470
WVFGRD96 2.0 305 50 -70 4.82 0.4087
WVFGRD96 3.0 290 50 -80 4.85 0.4189
WVFGRD96 4.0 55 55 45 4.83 0.4227
WVFGRD96 5.0 30 80 15 4.85 0.4276
WVFGRD96 6.0 205 85 -5 4.89 0.4300
WVFGRD96 7.0 205 85 -5 4.91 0.4308
WVFGRD96 8.0 25 90 10 4.94 0.4304
WVFGRD96 9.0 205 80 -10 4.94 0.4214
WVFGRD96 10.0 205 70 -10 4.95 0.4173
WVFGRD96 11.0 25 50 -25 4.94 0.4251
WVFGRD96 12.0 270 40 55 5.00 0.4378
WVFGRD96 13.0 265 40 55 5.00 0.4762
WVFGRD96 14.0 260 40 50 5.00 0.4982
WVFGRD96 15.0 260 40 45 5.02 0.5162
WVFGRD96 16.0 255 40 40 5.02 0.5390
WVFGRD96 17.0 255 40 40 5.02 0.5495
WVFGRD96 18.0 255 35 40 5.04 0.5661
WVFGRD96 19.0 255 35 35 5.06 0.5714
WVFGRD96 20.0 255 35 35 5.06 0.5749
WVFGRD96 21.0 250 35 35 5.06 0.5832
WVFGRD96 22.0 250 35 30 5.08 0.5845
WVFGRD96 23.0 245 35 30 5.07 0.5871
WVFGRD96 24.0 245 35 25 5.09 0.5854
WVFGRD96 25.0 245 35 25 5.09 0.5829
WVFGRD96 26.0 245 35 25 5.10 0.5795
WVFGRD96 27.0 245 35 25 5.10 0.5750
WVFGRD96 28.0 245 35 25 5.11 0.5700
WVFGRD96 29.0 245 35 25 5.11 0.5652
WVFGRD96 30.0 245 35 25 5.12 0.5594
WVFGRD96 31.0 245 35 25 5.12 0.5527
WVFGRD96 32.0 250 35 30 5.12 0.5463
WVFGRD96 33.0 250 35 30 5.13 0.5395
WVFGRD96 34.0 250 35 30 5.14 0.5321
WVFGRD96 35.0 250 35 30 5.14 0.5243
WVFGRD96 36.0 250 35 30 5.15 0.5161
WVFGRD96 37.0 250 35 30 5.16 0.5069
WVFGRD96 38.0 265 25 40 5.17 0.4973
WVFGRD96 39.0 265 25 40 5.17 0.4886
WVFGRD96 40.0 290 20 60 5.33 0.4824
WVFGRD96 41.0 290 20 60 5.33 0.4708
WVFGRD96 42.0 290 20 60 5.34 0.4586
WVFGRD96 43.0 290 20 60 5.35 0.4458
WVFGRD96 44.0 270 30 45 5.32 0.4329
WVFGRD96 45.0 270 30 45 5.33 0.4212
WVFGRD96 46.0 260 35 40 5.31 0.4105
WVFGRD96 47.0 255 40 40 5.29 0.3991
WVFGRD96 48.0 70 45 35 5.28 0.3902
WVFGRD96 49.0 70 45 35 5.29 0.3829
The best solution is
WVFGRD96 23.0 245 35 30 5.07 0.5871
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
hp c 0.02 n 3 lp c 0.05 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=Thu Jun 20 03:46:14 CDT 2013