2013/05/24 05:44:24 35.305 -92.725 6.8 3.5 Arkansas
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2013/05/24 05:44:24:0 35.31 -92.72 6.8 3.5 Arkansas Stations used: AG.CCAR AG.FCAR AG.HHAR AG.WLAR IU.CCM NM.CLTN NM.HALT NM.MGMO NM.PLAL NM.UALR TA.TUL1 TA.U40A TA.V48A TA.W39A TA.W41B TA.X40A TA.X48A TA.Z41A US.LRAL US.MIAR Filtering commands used: hp c 0.03 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 1.76e+21 dyne-cm Mw = 3.43 Z = 2 km Plane Strike Dip Rake NP1 187 71 -159 NP2 90 70 -20 Principal Axes: Axis Value Plunge Azimuth T 1.76e+21 1 318 N 0.00e+00 62 227 P -1.76e+21 28 49 Moment Tensor: (dyne-cm) Component Value Mxx 3.86e+20 Mxy -1.55e+21 Mxz -4.61e+20 Myy -1.36e+14 Myz -5.65e+20 Mzz -3.86e+20 #########----- ###########----------- T ###########--------------- ###########---------------- ###############------------ ---- ###############------------- P ----- ################------------- ------ ################------------------------ ################------------------------ #################------------------------- ################-------------------------- --##############------------------------## ------##########--------------------###### -------------##------------############# ---------------######################### --------------######################## -------------####################### ------------###################### ----------#################### ----------################## -------############### ----########## Global CMT Convention Moment Tensor: R T P -3.86e+20 -4.61e+20 5.65e+20 -4.61e+20 3.86e+20 1.55e+21 5.65e+20 1.55e+21 -1.36e+14 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130524054424/index.html |
STK = 90 DIP = 70 RAKE = -20 MW = 3.43 HS = 2.0
The NDK file is 20130524054424.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2013/05/24 05:44:24:0 35.31 -92.72 6.8 3.5 Arkansas Stations used: AG.CCAR AG.FCAR AG.HHAR AG.WLAR IU.CCM NM.CLTN NM.HALT NM.MGMO NM.PLAL NM.UALR TA.TUL1 TA.U40A TA.V48A TA.W39A TA.W41B TA.X40A TA.X48A TA.Z41A US.LRAL US.MIAR Filtering commands used: hp c 0.03 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 1.76e+21 dyne-cm Mw = 3.43 Z = 2 km Plane Strike Dip Rake NP1 187 71 -159 NP2 90 70 -20 Principal Axes: Axis Value Plunge Azimuth T 1.76e+21 1 318 N 0.00e+00 62 227 P -1.76e+21 28 49 Moment Tensor: (dyne-cm) Component Value Mxx 3.86e+20 Mxy -1.55e+21 Mxz -4.61e+20 Myy -1.36e+14 Myz -5.65e+20 Mzz -3.86e+20 #########----- ###########----------- T ###########--------------- ###########---------------- ###############------------ ---- ###############------------- P ----- ################------------- ------ ################------------------------ ################------------------------ #################------------------------- ################-------------------------- --##############------------------------## ------##########--------------------###### -------------##------------############# ---------------######################### --------------######################## -------------####################### ------------###################### ----------#################### ----------################## -------############### ----########## Global CMT Convention Moment Tensor: R T P -3.86e+20 -4.61e+20 5.65e+20 -4.61e+20 3.86e+20 1.55e+21 5.65e+20 1.55e+21 -1.36e+14 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130524054424/index.html |
(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.
(a) ML computed using the IASPEI formula for Horizontal components; (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
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 0.03 n 3 lp c 0.08 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 -10 3.37 0.4182 WVFGRD96 1.0 90 70 -15 3.39 0.4355 WVFGRD96 2.0 90 70 -20 3.43 0.4528 WVFGRD96 3.0 90 70 -20 3.45 0.4518 WVFGRD96 4.0 90 70 -15 3.45 0.4432 WVFGRD96 5.0 95 90 -25 3.47 0.4331 WVFGRD96 6.0 95 90 -25 3.47 0.4305 WVFGRD96 7.0 90 90 -30 3.49 0.4311 WVFGRD96 8.0 90 90 -30 3.50 0.4336 WVFGRD96 9.0 90 90 -30 3.51 0.4368 WVFGRD96 10.0 275 85 30 3.52 0.4425 WVFGRD96 11.0 275 85 30 3.53 0.4431 WVFGRD96 12.0 275 80 30 3.54 0.4448 WVFGRD96 13.0 275 85 30 3.55 0.4446 WVFGRD96 14.0 275 80 30 3.56 0.4440 WVFGRD96 15.0 275 80 30 3.56 0.4418 WVFGRD96 16.0 275 80 30 3.57 0.4397 WVFGRD96 17.0 275 80 30 3.58 0.4369 WVFGRD96 18.0 275 80 30 3.59 0.4333 WVFGRD96 19.0 275 80 30 3.59 0.4290 WVFGRD96 20.0 275 80 30 3.61 0.4248 WVFGRD96 21.0 275 80 30 3.61 0.4190 WVFGRD96 22.0 275 80 30 3.62 0.4133 WVFGRD96 23.0 275 80 30 3.62 0.4075 WVFGRD96 24.0 275 60 10 3.62 0.4039 WVFGRD96 25.0 275 60 10 3.63 0.4026 WVFGRD96 26.0 275 60 10 3.63 0.4018 WVFGRD96 27.0 275 60 5 3.64 0.4001 WVFGRD96 28.0 275 60 5 3.64 0.3988 WVFGRD96 29.0 275 60 5 3.65 0.3959
The best solution is
WVFGRD96 2.0 90 70 -20 3.43 0.4528
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 0.03 n 3 lp c 0.08 n 3
The plots below start 30 seconds before the theoretical S arrival and continue until 60 seconds after the theoretical S arrival.
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:
The time shifts for this inversion lead to the next figure:
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.
The CUS model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
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.
Assuming only a mislocation, the time shifts are fit to a functional form:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.
Discussion
Acknowledgements
Velocity Model
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
Quality Control