2013/05/22 17:19:39 35.299 -92.715 2.0 4.00
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2013/05/22 17:19:39:0 35.30 -92.71 2.0 4.0
Stations used:
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.26e+22 dyne-cm
Mw = 4.00
Z = 2 km
Plane Strike Dip Rake
NP1 182 71 -159
NP2 85 70 -20
Principal Axes:
Axis Value Plunge Azimuth
T 1.26e+22 1 313
N 0.00e+00 62 222
P -1.26e+22 28 44
Moment Tensor: (dyne-cm)
Component Value
Mxx 8.16e+20
Mxy -1.12e+22
Mxz -3.64e+21
Myy 1.95e+21
Myz -3.74e+21
Mzz -2.77e+21
#######-------
##########------------
###########----------------
T ##########------------------
# ##########------------ -----
##############------------- P ------
###############------------- -------
################------------------------
################------------------------
################--------------------------
################-------------------------#
################----------------------####
--##############-----------------#########
-------########---------################
---------------#########################
---------------#######################
--------------######################
-------------#####################
-----------###################
-----------#################
---------#############
-----#########
Global CMT Convention Moment Tensor:
R T P
-2.77e+21 -3.64e+21 3.74e+21
-3.64e+21 8.16e+20 1.12e+22
3.74e+21 1.12e+22 1.95e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130522171939/index.html
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STK = 85
DIP = 70
RAKE = -20
MW = 4.00
HS = 2.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2013/05/22 17:19:39:0 35.30 -92.71 2.0 4.0
Stations used:
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.26e+22 dyne-cm
Mw = 4.00
Z = 2 km
Plane Strike Dip Rake
NP1 182 71 -159
NP2 85 70 -20
Principal Axes:
Axis Value Plunge Azimuth
T 1.26e+22 1 313
N 0.00e+00 62 222
P -1.26e+22 28 44
Moment Tensor: (dyne-cm)
Component Value
Mxx 8.16e+20
Mxy -1.12e+22
Mxz -3.64e+21
Myy 1.95e+21
Myz -3.74e+21
Mzz -2.77e+21
#######-------
##########------------
###########----------------
T ##########------------------
# ##########------------ -----
##############------------- P ------
###############------------- -------
################------------------------
################------------------------
################--------------------------
################-------------------------#
################----------------------####
--##############-----------------#########
-------########---------################
---------------#########################
---------------#######################
--------------######################
-------------#####################
-----------###################
-----------#################
---------#############
-----#########
Global CMT Convention Moment Tensor:
R T P
-2.77e+21 -3.64e+21 3.74e+21
-3.64e+21 8.16e+20 1.12e+22
3.74e+21 1.12e+22 1.95e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130522171939/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 0.10 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 90 65 0 3.94 0.8718
WVFGRD96 1.0 85 60 -10 3.98 0.9027
WVFGRD96 2.0 85 70 -20 4.00 0.9430
WVFGRD96 3.0 85 70 -20 4.01 0.9180
WVFGRD96 4.0 85 75 -15 4.01 0.8774
WVFGRD96 5.0 90 80 -15 4.01 0.8362
WVFGRD96 6.0 270 85 20 4.01 0.8081
WVFGRD96 7.0 270 80 15 4.02 0.7921
WVFGRD96 8.0 270 80 15 4.03 0.7795
WVFGRD96 9.0 270 80 15 4.03 0.7678
WVFGRD96 10.0 270 75 15 4.05 0.7571
WVFGRD96 11.0 270 75 15 4.05 0.7439
WVFGRD96 12.0 270 75 15 4.06 0.7316
WVFGRD96 13.0 270 75 15 4.07 0.7199
WVFGRD96 14.0 270 75 10 4.07 0.7097
WVFGRD96 15.0 270 75 10 4.08 0.7004
WVFGRD96 16.0 270 75 10 4.09 0.6925
WVFGRD96 17.0 270 75 10 4.09 0.6839
WVFGRD96 18.0 270 75 10 4.10 0.6763
WVFGRD96 19.0 270 75 10 4.11 0.6692
WVFGRD96 20.0 270 70 10 4.12 0.6616
WVFGRD96 21.0 270 70 10 4.12 0.6540
WVFGRD96 22.0 270 70 10 4.13 0.6488
WVFGRD96 23.0 270 70 10 4.13 0.6453
WVFGRD96 24.0 270 70 10 4.14 0.6420
WVFGRD96 25.0 270 80 15 4.14 0.6441
WVFGRD96 26.0 270 80 15 4.15 0.6484
WVFGRD96 27.0 270 80 15 4.16 0.6516
WVFGRD96 28.0 270 80 15 4.16 0.6559
WVFGRD96 29.0 270 80 15 4.17 0.6596
WVFGRD96 30.0 270 80 10 4.17 0.6643
WVFGRD96 31.0 270 80 10 4.17 0.6679
WVFGRD96 32.0 270 80 10 4.18 0.6698
WVFGRD96 33.0 270 80 10 4.19 0.6708
WVFGRD96 34.0 270 80 10 4.19 0.6692
WVFGRD96 35.0 270 75 10 4.21 0.6695
WVFGRD96 36.0 270 75 10 4.22 0.6672
WVFGRD96 37.0 270 75 10 4.23 0.6655
WVFGRD96 38.0 270 75 10 4.24 0.6611
WVFGRD96 39.0 270 75 5 4.25 0.6582
WVFGRD96 40.0 265 65 -10 4.29 0.6563
WVFGRD96 41.0 265 65 -10 4.30 0.6504
WVFGRD96 42.0 265 65 -10 4.31 0.6439
WVFGRD96 43.0 265 65 -10 4.32 0.6381
WVFGRD96 44.0 265 65 -10 4.33 0.6313
WVFGRD96 45.0 265 65 -10 4.33 0.6256
WVFGRD96 46.0 265 65 -10 4.34 0.6192
WVFGRD96 47.0 265 65 -10 4.35 0.6140
WVFGRD96 48.0 265 65 -10 4.35 0.6082
WVFGRD96 49.0 265 65 -10 4.36 0.6047
The best solution is
WVFGRD96 2.0 85 70 -20 4.00 0.9430
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 0.10 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. |
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.
The CUS model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 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: