USGS/SLU Moment Tensor Solution ENS 2020/03/26 15:16:28:0 31.70 -104.06 5.0 4.7 Texas Stations used: EP.KIDD GM.NMP01 GM.NMP02 GS.VEA1 IM.TX31 IU.ANMO N4.ABTX N4.MSTX SC.121A SC.Y22A TX.ALPN TX.APMT TX.DKNS TX.DRIO TX.MB06 TX.MNHN TX.ODSA TX.OZNA TX.PB01 TX.PB05 TX.PB11 TX.PB28 TX.PB29 TX.PECS TX.POST TX.SAND TX.SGCY TX.SN07 TX.SN08 TX.VHRN US.AMTX US.JCT US.MNTX Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 2.00e+23 dyne-cm Mw = 4.80 Z = 8 km Plane Strike Dip Rake NP1 95 45 -90 NP2 275 45 -90 Principal Axes: Axis Value Plunge Azimuth T 2.00e+23 -0 185 N 0.00e+00 -0 95 P -2.00e+23 90 310 Moment Tensor: (dyne-cm) Component Value Mxx 1.98e+23 Mxy 1.73e+22 Mxz 9.23e+15 Myy 1.52e+21 Myz -5.38e+15 Mzz -2.00e+23 ############## ###################### ############################ ############################## ################################## #########---------------############ #####-------------------------######## ####------------------------------###### #-----------------------------------#### #----------------- ------------------### #----------------- P -------------------## ##---------------- --------------------# ###--------------------------------------# ####-----------------------------------# ######------------------------------#### ########-------------------------##### ############---------------######### ################################## ############################## ############################ ######## ########### #### T ####### Global CMT Convention Moment Tensor: R T P -2.00e+23 9.23e+15 5.38e+15 9.23e+15 1.98e+23 -1.73e+22 5.38e+15 -1.73e+22 1.52e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200326151628/index.html |
STK = 275 DIP = 45 RAKE = -90 MW = 4.80 HS = 8.0
The NDK file is 20200326151628.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2020/03/26 15:16:28:0 31.70 -104.06 5.0 4.7 Texas Stations used: EP.KIDD GM.NMP01 GM.NMP02 GS.VEA1 IM.TX31 IU.ANMO N4.ABTX N4.MSTX SC.121A SC.Y22A TX.ALPN TX.APMT TX.DKNS TX.DRIO TX.MB06 TX.MNHN TX.ODSA TX.OZNA TX.PB01 TX.PB05 TX.PB11 TX.PB28 TX.PB29 TX.PECS TX.POST TX.SAND TX.SGCY TX.SN07 TX.SN08 TX.VHRN US.AMTX US.JCT US.MNTX Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 2.00e+23 dyne-cm Mw = 4.80 Z = 8 km Plane Strike Dip Rake NP1 95 45 -90 NP2 275 45 -90 Principal Axes: Axis Value Plunge Azimuth T 2.00e+23 -0 185 N 0.00e+00 -0 95 P -2.00e+23 90 310 Moment Tensor: (dyne-cm) Component Value Mxx 1.98e+23 Mxy 1.73e+22 Mxz 9.23e+15 Myy 1.52e+21 Myz -5.38e+15 Mzz -2.00e+23 ############## ###################### ############################ ############################## ################################## #########---------------############ #####-------------------------######## ####------------------------------###### #-----------------------------------#### #----------------- ------------------### #----------------- P -------------------## ##---------------- --------------------# ###--------------------------------------# ####-----------------------------------# ######------------------------------#### ########-------------------------##### ############---------------######### ################################## ############################## ############################ ######## ########### #### T ####### Global CMT Convention Moment Tensor: R T P -2.00e+23 9.23e+15 5.38e+15 9.23e+15 1.98e+23 -1.73e+22 5.38e+15 -1.73e+22 1.52e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200326151628/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:
cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 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 1.0 315 70 -20 4.29 0.2173 WVFGRD96 2.0 130 70 -40 4.46 0.2671 WVFGRD96 3.0 115 80 -75 4.61 0.3725 WVFGRD96 4.0 280 50 -85 4.67 0.5048 WVFGRD96 5.0 280 50 -80 4.70 0.6083 WVFGRD96 6.0 280 45 -80 4.71 0.6435 WVFGRD96 7.0 280 45 -80 4.73 0.6447 WVFGRD96 8.0 275 45 -90 4.80 0.6627 WVFGRD96 9.0 275 45 -90 4.80 0.6315 WVFGRD96 10.0 95 45 -90 4.80 0.5867 WVFGRD96 11.0 110 50 -70 4.78 0.5390 WVFGRD96 12.0 125 55 -50 4.78 0.4989 WVFGRD96 13.0 130 60 -40 4.78 0.4677 WVFGRD96 14.0 130 60 -40 4.78 0.4396 WVFGRD96 15.0 335 55 30 4.78 0.4233 WVFGRD96 16.0 330 55 25 4.79 0.4120 WVFGRD96 17.0 330 55 25 4.79 0.4006 WVFGRD96 18.0 330 55 25 4.80 0.3885 WVFGRD96 19.0 330 55 25 4.81 0.3768 WVFGRD96 20.0 325 55 10 4.82 0.3664 WVFGRD96 21.0 325 55 10 4.83 0.3582 WVFGRD96 22.0 325 55 10 4.84 0.3493 WVFGRD96 23.0 325 55 10 4.84 0.3409 WVFGRD96 24.0 330 50 15 4.85 0.3327 WVFGRD96 25.0 330 50 15 4.85 0.3260 WVFGRD96 26.0 330 50 15 4.86 0.3197 WVFGRD96 27.0 330 50 15 4.87 0.3129 WVFGRD96 28.0 330 50 15 4.87 0.3060 WVFGRD96 29.0 330 50 15 4.88 0.2983
The best solution is
WVFGRD96 8.0 275 45 -90 4.80 0.6627
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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 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.
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 Bureau of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Oklahoma Geological Survey, TexNet, the Iris stations, the Transportable Array of EarthScope and other networks.
The WUS.model 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: