2010/08/17 02:49:55 43.616 -110.498 5.0 4.3 Wyoming
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/08/17 02:49:55:0 43.62 -110.50 5.0 4.3 Wyoming Stations used: IU.RSSD IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.MFID IW.MOOW IW.PHWY IW.PLID IW.REDW IW.SNOW IW.TPAW TA.H17A US.AHID US.BW06 US.HLID UU.BGU UU.HVU UU.NLU UU.SPU UU.TCRU UU.TCU WY.YFT WY.YMR WY.YNR Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 1.97e+22 dyne-cm Mw = 4.13 Z = 8 km Plane Strike Dip Rake NP1 55 85 -20 NP2 147 70 -175 Principal Axes: Axis Value Plunge Azimuth T 1.97e+22 10 103 N 0.00e+00 69 222 P -1.97e+22 18 9 Moment Tensor: (dyne-cm) Component Value Mxx -1.66e+22 Mxy -6.87e+21 Mxz -6.37e+21 Myy 1.77e+22 Myz 2.49e+21 Mzz -1.17e+21 -------- --- ------------ P ------- ###------------ ---------- ####-------------------------- ######---------------------------- ########-------------------------### #########-----------------------###### ###########--------------------######### ############----------------############ ##############-------------############### ###############----------################# ################------#################### #################--################### # ###############--#################### T #############-----################### #########----------################### ####----------------################ --------------------############## ---------------------######### ----------------------###### ---------------------- -------------- Global CMT Convention Moment Tensor: R T P -1.17e+21 -6.37e+21 -2.49e+21 -6.37e+21 -1.66e+22 6.87e+21 -2.49e+21 6.87e+21 1.77e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100817024955/index.html |
STK = 55 DIP = 85 RAKE = -20 MW = 4.13 HS = 8.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/08/17 02:49:55:0 43.62 -110.50 5.0 4.3 Wyoming Stations used: IU.RSSD IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.MFID IW.MOOW IW.PHWY IW.PLID IW.REDW IW.SNOW IW.TPAW TA.H17A US.AHID US.BW06 US.HLID UU.BGU UU.HVU UU.NLU UU.SPU UU.TCRU UU.TCU WY.YFT WY.YMR WY.YNR Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 1.97e+22 dyne-cm Mw = 4.13 Z = 8 km Plane Strike Dip Rake NP1 55 85 -20 NP2 147 70 -175 Principal Axes: Axis Value Plunge Azimuth T 1.97e+22 10 103 N 0.00e+00 69 222 P -1.97e+22 18 9 Moment Tensor: (dyne-cm) Component Value Mxx -1.66e+22 Mxy -6.87e+21 Mxz -6.37e+21 Myy 1.77e+22 Myz 2.49e+21 Mzz -1.17e+21 -------- --- ------------ P ------- ###------------ ---------- ####-------------------------- ######---------------------------- ########-------------------------### #########-----------------------###### ###########--------------------######### ############----------------############ ##############-------------############### ###############----------################# ################------#################### #################--################### # ###############--#################### T #############-----################### #########----------################### ####----------------################ --------------------############## ---------------------######### ----------------------###### ---------------------- -------------- Global CMT Convention Moment Tensor: R T P -1.17e+21 -6.37e+21 -2.49e+21 -6.37e+21 -1.66e+22 6.87e+21 -2.49e+21 6.87e+21 1.77e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100817024955/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 0.5 240 80 15 3.67 0.3208 WVFGRD96 1.0 235 90 5 3.70 0.3460 WVFGRD96 2.0 240 80 15 3.86 0.4689 WVFGRD96 3.0 240 80 25 3.94 0.5109 WVFGRD96 4.0 55 90 -30 3.99 0.5460 WVFGRD96 5.0 55 85 -25 4.02 0.5708 WVFGRD96 6.0 55 85 -20 4.05 0.5928 WVFGRD96 7.0 55 85 -20 4.08 0.6095 WVFGRD96 8.0 55 85 -20 4.13 0.6194 WVFGRD96 9.0 55 85 -20 4.15 0.6180 WVFGRD96 10.0 55 85 -15 4.17 0.6141 WVFGRD96 11.0 55 85 -15 4.19 0.6071 WVFGRD96 12.0 55 80 -10 4.20 0.5991 WVFGRD96 13.0 55 80 -10 4.22 0.5895 WVFGRD96 14.0 55 75 -5 4.24 0.5805 WVFGRD96 15.0 55 75 -5 4.25 0.5704 WVFGRD96 16.0 55 80 -5 4.26 0.5599 WVFGRD96 17.0 55 80 -5 4.27 0.5509 WVFGRD96 18.0 55 80 -5 4.27 0.5403 WVFGRD96 19.0 55 80 -5 4.28 0.5296 WVFGRD96 20.0 55 80 -5 4.29 0.5205 WVFGRD96 21.0 55 80 -5 4.30 0.5105 WVFGRD96 22.0 55 80 -5 4.30 0.5029 WVFGRD96 23.0 55 80 -5 4.31 0.4943 WVFGRD96 24.0 55 80 -5 4.31 0.4875 WVFGRD96 25.0 55 80 -5 4.32 0.4802 WVFGRD96 26.0 55 80 -5 4.32 0.4740 WVFGRD96 27.0 55 80 -5 4.32 0.4679 WVFGRD96 28.0 55 80 -5 4.33 0.4637 WVFGRD96 29.0 55 80 -5 4.33 0.4592
The best solution is
WVFGRD96 8.0 55 85 -20 4.13 0.6194
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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 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. |
Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
The WUS 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:
DATE=Mon Aug 16 22:37:59 CDT 2010