The ANSS event ID is uu60363602 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uu60363602/executive.
2020/03/18 13:09:31 40.751 -112.078 11.9 5.7 Utah
USGS/SLU Moment Tensor Solution ENS 2020/03/18 13:09:31:0 40.75 -112.08 11.9 5.7 Utah Stations used: IW.FLWY IW.FXWY IW.LOHW IW.MFID IW.MOOW IW.SNOW N4.O20A NN.PIO US.AHID US.BW06 US.DUG US.ELK US.HLID US.HWUT UU.BGU UU.BRPU UU.BRWY UU.BSUT UU.CCUT UU.CTU UU.CVRU UU.ECUT UU.HMU UU.HVU UU.KNB UU.LCMT UU.LIUT UU.MPU UU.MTPU UU.NLU UU.PKCU UU.PNSU UU.PSUT UU.RDMU UU.SPU UU.SRU UU.SVWY UU.SZCU UU.TCRU UU.TCU UU.VRUT WY.YFT WY.YMR WY.YPP 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 = 2.02e+24 dyne-cm Mw = 5.47 Z = 12 km Plane Strike Dip Rake NP1 325 60 -109 NP2 180 35 -60 Principal Axes: Axis Value Plunge Azimuth T 2.02e+24 13 69 N 0.00e+00 17 335 P -2.02e+24 69 195 Moment Tensor: (dyne-cm) Component Value Mxx -1.01e+17 Mxy 5.79e+23 Mxz 8.27e+23 Myy 1.64e+24 Myz 5.98e+23 Mzz -1.64e+24 ----########## -----################# ######-##################### ######-----################### #######---------################## #######------------################# #######---------------############ # #######------------------########## T ## #######-------------------######### ## ########--------------------############## #######----------------------############# #######-----------------------############ ########---------- ----------########### #######---------- P -----------######### #######---------- -----------######### #######------------------------####### #######-----------------------###### #######----------------------##### ######---------------------### ######--------------------## #####----------------- ####---------- Global CMT Convention Moment Tensor: R T P -1.64e+24 8.27e+23 -5.98e+23 8.27e+23 -1.01e+17 -5.79e+23 -5.98e+23 -5.79e+23 1.64e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200318130931/index.html |
STK = 180 DIP = 35 RAKE = -60 MW = 5.47 HS = 12.0
The NDK file is 20200318130931.ndk The waveform inversion is preferred.
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
USGS/SLU Moment Tensor Solution ENS 2020/03/18 13:09:31:0 40.75 -112.08 11.9 5.7 Utah Stations used: IW.FLWY IW.FXWY IW.LOHW IW.MFID IW.MOOW IW.SNOW N4.O20A NN.PIO US.AHID US.BW06 US.DUG US.ELK US.HLID US.HWUT UU.BGU UU.BRPU UU.BRWY UU.BSUT UU.CCUT UU.CTU UU.CVRU UU.ECUT UU.HMU UU.HVU UU.KNB UU.LCMT UU.LIUT UU.MPU UU.MTPU UU.NLU UU.PKCU UU.PNSU UU.PSUT UU.RDMU UU.SPU UU.SRU UU.SVWY UU.SZCU UU.TCRU UU.TCU UU.VRUT WY.YFT WY.YMR WY.YPP 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 = 2.02e+24 dyne-cm Mw = 5.47 Z = 12 km Plane Strike Dip Rake NP1 325 60 -109 NP2 180 35 -60 Principal Axes: Axis Value Plunge Azimuth T 2.02e+24 13 69 N 0.00e+00 17 335 P -2.02e+24 69 195 Moment Tensor: (dyne-cm) Component Value Mxx -1.01e+17 Mxy 5.79e+23 Mxz 8.27e+23 Myy 1.64e+24 Myz 5.98e+23 Mzz -1.64e+24 ----########## -----################# ######-##################### ######-----################### #######---------################## #######------------################# #######---------------############ # #######------------------########## T ## #######-------------------######### ## ########--------------------############## #######----------------------############# #######-----------------------############ ########---------- ----------########### #######---------- P -----------######### #######---------- -----------######### #######------------------------####### #######-----------------------###### #######----------------------##### ######---------------------### ######--------------------## #####----------------- ####---------- Global CMT Convention Moment Tensor: R T P -1.64e+24 8.27e+23 -5.98e+23 8.27e+23 -1.01e+17 -5.79e+23 -5.98e+23 -5.79e+23 1.64e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200318130931/index.html |
Regional Moment Tensor (Mwr) Moment 2.742e+17 N-m Magnitude 5.56 Mwr Depth 9.0 km Percent DC 89% Half Duration - Catalog US Data Source US 2 Contributor US 2 Nodal Planes Plane Strike Dip Rake NP1 178 38 -63 NP2 326 56 -110 Principal Axes Axis Value Plunge Azimuth T 2.659e+17 N-m 9 70 N 0.159e+17 N-m 16 337 P -2.818e+17 N-m 71 189 |
W-phase Moment Tensor (Mww) Moment 3.949e+17 N-m Magnitude 5.66 Mww Depth 15.5 km Percent DC 93% Half Duration 1.67 s Catalog US Data Source US 1 Contributor US 1 Nodal Planes Plane Strike Dip Rake NP1 324 37 -115 NP2 174 57 -73 Principal Axes Axis Value Plunge Azimuth T 3.878e+17 N-m 11 252 N 0.138e+17 N-m 15 345 P -4.017e+17 N-m 72 127 |
Moment Tensor (TDMT) Moment 2.288e+17 N-m Magnitude 5.51 Depth 9.0 km Percent DC 95% Half Duration - Catalog UU Data Source UU 3 Contributor UU 3 Nodal Planes Plane Strike Dip Rake NP1 182 34 -52 NP2 319 64 -112 Principal Axes Axis Value Plunge Azimuth T 2.316e+17 N-m 16 65 N -0.056e+17 N-m 20 329 P -2.260e+17 N-m 64 191 |
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
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The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) 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's 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 are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 75 45 85 4.99 0.1951 WVFGRD96 2.0 145 45 -90 5.16 0.2713 WVFGRD96 3.0 35 40 0 5.16 0.2513 WVFGRD96 4.0 190 25 -40 5.24 0.3186 WVFGRD96 5.0 180 25 -55 5.27 0.3989 WVFGRD96 6.0 185 30 -55 5.30 0.4658 WVFGRD96 7.0 180 30 -60 5.32 0.5226 WVFGRD96 8.0 175 30 -65 5.41 0.5695 WVFGRD96 9.0 170 30 -70 5.43 0.6116 WVFGRD96 10.0 180 35 -60 5.45 0.6409 WVFGRD96 11.0 175 35 -70 5.46 0.6582 WVFGRD96 12.0 180 35 -60 5.47 0.6650 WVFGRD96 13.0 180 35 -60 5.49 0.6640 WVFGRD96 14.0 185 40 -55 5.50 0.6574 WVFGRD96 15.0 185 40 -55 5.51 0.6449 WVFGRD96 16.0 185 40 -50 5.52 0.6281 WVFGRD96 17.0 190 45 -45 5.53 0.6089 WVFGRD96 18.0 190 45 -45 5.53 0.5879 WVFGRD96 19.0 190 45 -45 5.54 0.5639 WVFGRD96 20.0 195 50 -35 5.55 0.5383 WVFGRD96 21.0 185 30 -50 5.56 0.5160 WVFGRD96 22.0 180 30 -55 5.56 0.4921 WVFGRD96 23.0 190 35 -40 5.57 0.4686 WVFGRD96 24.0 190 35 -40 5.57 0.4450 WVFGRD96 25.0 195 35 -30 5.58 0.4225 WVFGRD96 26.0 195 35 -30 5.58 0.4004 WVFGRD96 27.0 195 40 -30 5.58 0.3799 WVFGRD96 28.0 200 35 -25 5.59 0.3648 WVFGRD96 29.0 200 35 -25 5.59 0.3519
The best solution is
WVFGRD96 12.0 180 35 -60 5.47 0.6650
The mechanism corresponding 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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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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Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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 WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
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