2010/12/22 00:53:57 43.151 -110.799 3.8 3.40 Wyoming
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/12/22 00:53:57:3 43.15 -110.80 3.8 3.4 Wyoming Stations used: IW.FLWY IW.IMW IW.MOOW IW.REDW IW.SNOW US.AHID US.BW06 US.HWUT UU.HVU Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 3.51e+21 dyne-cm Mw = 3.63 Z = 10 km Plane Strike Dip Rake NP1 179 55 -93 NP2 5 35 -85 Principal Axes: Axis Value Plunge Azimuth T 3.51e+21 10 271 N 0.00e+00 3 181 P -3.51e+21 79 75 Moment Tensor: (dyne-cm) Component Value Mxx -5.51e+18 Mxy -1.12e+20 Mxz -1.45e+20 Myy 3.29e+21 Myz -1.21e+21 Mzz -3.28e+21 #####------### #######-----------#### #########-------------###### #########----------------##### ##########------------------###### ###########-------------------###### ###########--------------------####### ############---------------------####### ###########----------------------####### # ########----------- ---------####### # T ########----------- P ---------####### # ########----------- ---------####### ############----------------------######## ############---------------------####### ############--------------------######## ###########--------------------####### ###########------------------####### ###########----------------####### ##########--------------###### ##########-----------####### ########--------###### ######---##### Global CMT Convention Moment Tensor: R T P -3.28e+21 -1.45e+20 1.21e+21 -1.45e+20 -5.51e+18 1.12e+20 1.21e+21 1.12e+20 3.29e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101222005357/index.html |
STK = 5 DIP = 35 RAKE = -85 MW = 3.63 HS = 10.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/12/22 00:53:57:3 43.15 -110.80 3.8 3.4 Wyoming Stations used: IW.FLWY IW.IMW IW.MOOW IW.REDW IW.SNOW US.AHID US.BW06 US.HWUT UU.HVU Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 3.51e+21 dyne-cm Mw = 3.63 Z = 10 km Plane Strike Dip Rake NP1 179 55 -93 NP2 5 35 -85 Principal Axes: Axis Value Plunge Azimuth T 3.51e+21 10 271 N 0.00e+00 3 181 P -3.51e+21 79 75 Moment Tensor: (dyne-cm) Component Value Mxx -5.51e+18 Mxy -1.12e+20 Mxz -1.45e+20 Myy 3.29e+21 Myz -1.21e+21 Mzz -3.28e+21 #####------### #######-----------#### #########-------------###### #########----------------##### ##########------------------###### ###########-------------------###### ###########--------------------####### ############---------------------####### ###########----------------------####### # ########----------- ---------####### # T ########----------- P ---------####### # ########----------- ---------####### ############----------------------######## ############---------------------####### ############--------------------######## ###########--------------------####### ###########------------------####### ###########----------------####### ##########--------------###### ##########-----------####### ########--------###### ######---##### Global CMT Convention Moment Tensor: R T P -3.28e+21 -1.45e+20 1.21e+21 -1.45e+20 -5.51e+18 1.12e+20 1.21e+21 1.12e+20 3.29e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101222005357/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 3 br c 0.12 0.25 n 4 p 2The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 0 45 -90 3.23 0.2932 WVFGRD96 1.0 225 90 5 3.10 0.2598 WVFGRD96 2.0 220 65 -30 3.31 0.3819 WVFGRD96 3.0 225 75 -20 3.31 0.3943 WVFGRD96 4.0 20 90 60 3.41 0.4063 WVFGRD96 5.0 305 20 25 3.50 0.4879 WVFGRD96 6.0 315 20 40 3.52 0.5475 WVFGRD96 7.0 325 25 60 3.54 0.5838 WVFGRD96 8.0 180 65 -85 3.63 0.6029 WVFGRD96 9.0 180 55 -95 3.64 0.6314 WVFGRD96 10.0 5 35 -85 3.63 0.6380 WVFGRD96 11.0 5 35 -85 3.62 0.6297 WVFGRD96 12.0 175 65 -80 3.59 0.6200 WVFGRD96 13.0 15 65 -75 3.62 0.6143 WVFGRD96 14.0 20 65 -70 3.62 0.6133 WVFGRD96 15.0 20 65 -70 3.62 0.6094 WVFGRD96 16.0 20 70 -70 3.63 0.6052 WVFGRD96 17.0 15 70 -65 3.65 0.6017 WVFGRD96 18.0 15 70 -65 3.66 0.5965 WVFGRD96 19.0 15 70 -65 3.67 0.5906 WVFGRD96 20.0 15 75 -65 3.68 0.5836 WVFGRD96 21.0 20 75 -60 3.69 0.5756 WVFGRD96 22.0 20 75 -60 3.70 0.5646 WVFGRD96 23.0 20 75 -60 3.71 0.5512 WVFGRD96 24.0 20 75 -60 3.72 0.5355 WVFGRD96 25.0 20 75 -60 3.73 0.5170 WVFGRD96 26.0 25 75 -55 3.74 0.4971 WVFGRD96 27.0 35 75 -50 3.73 0.4772 WVFGRD96 28.0 100 25 -10 3.72 0.4579 WVFGRD96 29.0 100 25 -10 3.72 0.4426
The best solution is
WVFGRD96 10.0 5 35 -85 3.63 0.6380
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 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2
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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.
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=Tue Dec 21 20:42:27 CST 2010