2013/05/22 17:19:39 35.299 -92.715 2.0 3.50
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 3.5
Stations used:
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.40e+21 dyne-cm
Mw = 3.52
Z = 2 km
Plane Strike Dip Rake
NP1 85 70 -25
NP2 184 67 -158
Principal Axes:
Axis Value Plunge Azimuth
T 2.40e+21 2 135
N 0.00e+00 58 229
P -2.40e+21 32 44
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.92e+20
Mxy -2.07e+21
Mxz -8.38e+20
Myy 3.60e+20
Myz -6.73e+20
Mzz -6.52e+20
#######-------
##########------------
############----------------
############------------------
#############------------ ------
##############------------ P -------
##############------------- --------
###############-------------------------
###############-------------------------
###############---------------------------
###############--------------------------#
###############-----------------------####
--#############------------------#########
-------#######----------################
--------------##########################
-------------#########################
------------########################
------------################## #
----------################## T
----------#################
--------##############
-----#########
Global CMT Convention Moment Tensor:
R T P
-6.52e+20 -8.38e+20 6.73e+20
-8.38e+20 2.92e+20 2.07e+21
6.73e+20 2.07e+21 3.60e+20
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 = -25
MW = 3.52
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 3.5
Stations used:
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.40e+21 dyne-cm
Mw = 3.52
Z = 2 km
Plane Strike Dip Rake
NP1 85 70 -25
NP2 184 67 -158
Principal Axes:
Axis Value Plunge Azimuth
T 2.40e+21 2 135
N 0.00e+00 58 229
P -2.40e+21 32 44
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.92e+20
Mxy -2.07e+21
Mxz -8.38e+20
Myy 3.60e+20
Myz -6.73e+20
Mzz -6.52e+20
#######-------
##########------------
############----------------
############------------------
#############------------ ------
##############------------ P -------
##############------------- --------
###############-------------------------
###############-------------------------
###############---------------------------
###############--------------------------#
###############-----------------------####
--#############------------------#########
-------#######----------################
--------------##########################
-------------#########################
------------########################
------------################## #
----------################## T
----------#################
--------##############
-----#########
Global CMT Convention Moment Tensor:
R T P
-6.52e+20 -8.38e+20 6.73e+20
-8.38e+20 2.92e+20 2.07e+21
6.73e+20 2.07e+21 3.60e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130522171939/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:
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 75 -5 3.44 0.3185
WVFGRD96 1.0 85 60 -10 3.50 0.3308
WVFGRD96 2.0 85 70 -25 3.52 0.3465
WVFGRD96 3.0 85 70 -20 3.53 0.3373
WVFGRD96 4.0 90 80 -15 3.52 0.3230
WVFGRD96 5.0 270 85 20 3.53 0.3116
WVFGRD96 6.0 270 85 20 3.53 0.3061
WVFGRD96 7.0 270 80 20 3.54 0.3019
WVFGRD96 8.0 270 80 15 3.55 0.2978
WVFGRD96 9.0 270 80 15 3.56 0.2942
WVFGRD96 10.0 275 75 20 3.57 0.2911
WVFGRD96 11.0 275 75 20 3.58 0.2858
WVFGRD96 12.0 275 70 15 3.58 0.2811
WVFGRD96 13.0 275 75 15 3.59 0.2775
WVFGRD96 14.0 275 70 15 3.60 0.2744
WVFGRD96 15.0 275 70 15 3.60 0.2721
WVFGRD96 16.0 275 75 15 3.61 0.2698
WVFGRD96 17.0 275 70 15 3.62 0.2671
WVFGRD96 18.0 275 70 15 3.63 0.2640
WVFGRD96 19.0 275 70 15 3.63 0.2619
WVFGRD96 20.0 275 70 15 3.65 0.2596
WVFGRD96 21.0 275 70 15 3.65 0.2561
WVFGRD96 22.0 275 70 15 3.66 0.2537
WVFGRD96 23.0 275 65 15 3.67 0.2517
WVFGRD96 24.0 275 65 15 3.67 0.2498
WVFGRD96 25.0 90 90 -20 3.67 0.2478
WVFGRD96 26.0 270 85 -20 3.65 0.2481
WVFGRD96 27.0 270 80 -10 3.66 0.2481
WVFGRD96 28.0 270 80 -15 3.66 0.2485
WVFGRD96 29.0 90 90 -15 3.68 0.2495
WVFGRD96 30.0 90 90 -15 3.69 0.2509
WVFGRD96 31.0 90 90 -15 3.70 0.2515
WVFGRD96 32.0 90 85 -15 3.70 0.2518
WVFGRD96 33.0 90 85 -15 3.71 0.2521
WVFGRD96 34.0 90 85 -10 3.71 0.2525
WVFGRD96 35.0 90 85 -10 3.72 0.2523
WVFGRD96 36.0 90 85 -10 3.73 0.2511
WVFGRD96 37.0 90 85 -10 3.74 0.2502
WVFGRD96 38.0 90 85 -10 3.75 0.2484
WVFGRD96 39.0 90 85 -10 3.77 0.2475
WVFGRD96 40.0 90 80 -10 3.79 0.2480
WVFGRD96 41.0 90 80 -10 3.81 0.2472
WVFGRD96 42.0 90 80 -10 3.82 0.2456
WVFGRD96 43.0 90 80 -10 3.83 0.2443
WVFGRD96 44.0 90 80 -10 3.84 0.2422
WVFGRD96 45.0 90 80 -10 3.84 0.2405
WVFGRD96 46.0 90 80 -10 3.85 0.2385
WVFGRD96 47.0 90 80 -10 3.86 0.2368
WVFGRD96 48.0 90 80 -10 3.86 0.2346
WVFGRD96 49.0 90 85 -10 3.87 0.2330
The best solution is
WVFGRD96 2.0 85 70 -25 3.52 0.3465
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: