2009/03/21 08:47:50 43.3270 -110.7250 5.0 3.10 Wyoming
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2009/03/21 08:47:50:0 43.33 -110.72 5.0 3.1 Wyoming Stations used: IW.DCID1 IW.FLWY IW.IMW IW.LOHW IW.MOOW IW.RRI2 IW.SNOW IW.TPAW TA.G15A TA.G16A TA.G17A TA.H16A TA.H18A TA.H20A TA.I16A TA.I18A TA.I19A TA.I20A TA.J16A TA.J19A TA.K15A TA.K16A TA.K17A TA.K18A TA.L15A US.AHID US.BW06 US.RLMT Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 1.33e+21 dyne-cm Mw = 3.35 Z = 6 km Plane Strike Dip Rake NP1 144 76 -164 NP2 50 75 -15 Principal Axes: Axis Value Plunge Azimuth T 1.33e+21 0 277 N 0.00e+00 69 186 P -1.33e+21 21 7 Moment Tensor: (dyne-cm) Component Value Mxx -1.12e+21 Mxy -3.01e+20 Mxz -4.43e+20 Myy 1.30e+21 Myz -6.33e+19 Mzz -1.73e+20 -------------- ------------ ------- ##------------- P ---------- ###------------- ----------- ######--------------------------## ########------------------------#### ##########----------------------###### ############--------------------######## ############-----------------########## T #############---------------############ ##############------------############## #################---------################ ##################------################## ###################-#################### ##################--#################### ##############-------################# ##########------------############## #####------------------########### -----------------------####### ------------------------#### ---------------------- -------------- Global CMT Convention Moment Tensor: R T P -1.73e+20 -4.43e+20 6.33e+19 -4.43e+20 -1.12e+21 3.01e+20 6.33e+19 3.01e+20 1.30e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090321084750/index.html |
STK = 50 DIP = 75 RAKE = -15 MW = 3.35 HS = 6.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2009/03/21 08:47:50:0 43.33 -110.72 5.0 3.1 Wyoming Stations used: IW.DCID1 IW.FLWY IW.IMW IW.LOHW IW.MOOW IW.RRI2 IW.SNOW IW.TPAW TA.G15A TA.G16A TA.G17A TA.H16A TA.H18A TA.H20A TA.I16A TA.I18A TA.I19A TA.I20A TA.J16A TA.J19A TA.K15A TA.K16A TA.K17A TA.K18A TA.L15A US.AHID US.BW06 US.RLMT Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 1.33e+21 dyne-cm Mw = 3.35 Z = 6 km Plane Strike Dip Rake NP1 144 76 -164 NP2 50 75 -15 Principal Axes: Axis Value Plunge Azimuth T 1.33e+21 0 277 N 0.00e+00 69 186 P -1.33e+21 21 7 Moment Tensor: (dyne-cm) Component Value Mxx -1.12e+21 Mxy -3.01e+20 Mxz -4.43e+20 Myy 1.30e+21 Myz -6.33e+19 Mzz -1.73e+20 -------------- ------------ ------- ##------------- P ---------- ###------------- ----------- ######--------------------------## ########------------------------#### ##########----------------------###### ############--------------------######## ############-----------------########## T #############---------------############ ##############------------############## #################---------################ ##################------################## ###################-#################### ##################--#################### ##############-------################# ##########------------############## #####------------------########### -----------------------####### ------------------------#### ---------------------- -------------- Global CMT Convention Moment Tensor: R T P -1.73e+20 -4.43e+20 6.33e+19 -4.43e+20 -1.12e+21 3.01e+20 6.33e+19 3.01e+20 1.30e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090321084750/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 0.5 230 90 -15 2.98 0.2944 WVFGRD96 1.0 50 90 10 3.02 0.3173 WVFGRD96 2.0 50 70 -5 3.17 0.4033 WVFGRD96 3.0 50 70 -15 3.24 0.4437 WVFGRD96 4.0 50 70 -15 3.28 0.4727 WVFGRD96 5.0 50 75 -15 3.32 0.4869 WVFGRD96 6.0 50 75 -15 3.35 0.4906 WVFGRD96 7.0 50 75 -15 3.38 0.4892 WVFGRD96 8.0 50 75 -15 3.42 0.4844 WVFGRD96 9.0 50 75 -15 3.44 0.4713 WVFGRD96 10.0 50 75 -15 3.45 0.4553 WVFGRD96 11.0 50 75 -15 3.47 0.4390 WVFGRD96 12.0 50 75 -15 3.48 0.4224 WVFGRD96 13.0 50 75 -15 3.49 0.4055 WVFGRD96 14.0 50 75 -15 3.50 0.3897 WVFGRD96 15.0 50 75 -15 3.51 0.3741 WVFGRD96 16.0 50 75 -15 3.52 0.3596 WVFGRD96 17.0 50 75 -15 3.53 0.3461 WVFGRD96 18.0 50 75 -15 3.54 0.3325 WVFGRD96 19.0 50 70 -10 3.54 0.3200 WVFGRD96 20.0 50 70 -10 3.55 0.3080 WVFGRD96 21.0 50 70 -10 3.56 0.2978 WVFGRD96 22.0 55 70 5 3.55 0.2875 WVFGRD96 23.0 55 70 10 3.55 0.2794 WVFGRD96 24.0 55 70 10 3.56 0.2721 WVFGRD96 25.0 55 70 10 3.56 0.2649 WVFGRD96 26.0 325 90 -10 3.56 0.2585 WVFGRD96 27.0 325 90 -15 3.57 0.2622 WVFGRD96 28.0 325 90 -15 3.58 0.2666 WVFGRD96 29.0 325 90 -15 3.59 0.2701
The best solution is
WVFGRD96 6.0 50 75 -15 3.35 0.4906
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=Sat Mar 21 14:19:43 CDT 2009