2010/01/13 11:17:55 47.431 -113.174 20.8 3.90
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/01/13 11:17:55:0 47.43 -113.17 20.8 3.9 Stations used: TA.A19A TA.C19A TA.C20A TA.D19A TA.D20A TA.E19A US.BOZ US.MSO UW.BRAN 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 = 5.13e+21 dyne-cm Mw = 3.74 Z = 20 km Plane Strike Dip Rake NP1 342 50 -113 NP2 195 45 -65 Principal Axes: Axis Value Plunge Azimuth T 5.13e+21 3 88 N 0.00e+00 17 357 P -5.13e+21 72 186 Moment Tensor: (dyne-cm) Component Value Mxx -4.55e+20 Mxy 1.65e+20 Mxz 1.48e+21 Myy 5.10e+21 Myz 3.97e+20 Mzz -4.65e+21 ##--------#### ###################### ###########----############# ##########--------############ ##########------------############ ##########--------------############ ##########----------------############ ##########------------------############ ##########-------------------########### ##########---------------------######### ##########---------------------######### T #########-----------------------######## #########---------- ----------########## ########---------- P ----------######### ########---------- ----------######### ########----------------------######## #######----------------------####### ######---------------------####### #####--------------------##### #####------------------##### ###----------------### #------------- Global CMT Convention Moment Tensor: R T P -4.65e+21 1.48e+21 -3.97e+20 1.48e+21 -4.55e+20 -1.65e+20 -3.97e+20 -1.65e+20 5.10e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100113111755/index.html |
STK = 195 DIP = 45 RAKE = -65 MW = 3.74 HS = 20.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/01/13 11:17:55:0 47.43 -113.17 20.8 3.9 Stations used: TA.A19A TA.C19A TA.C20A TA.D19A TA.D20A TA.E19A US.BOZ US.MSO UW.BRAN 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 = 5.13e+21 dyne-cm Mw = 3.74 Z = 20 km Plane Strike Dip Rake NP1 342 50 -113 NP2 195 45 -65 Principal Axes: Axis Value Plunge Azimuth T 5.13e+21 3 88 N 0.00e+00 17 357 P -5.13e+21 72 186 Moment Tensor: (dyne-cm) Component Value Mxx -4.55e+20 Mxy 1.65e+20 Mxz 1.48e+21 Myy 5.10e+21 Myz 3.97e+20 Mzz -4.65e+21 ##--------#### ###################### ###########----############# ##########--------############ ##########------------############ ##########--------------############ ##########----------------############ ##########------------------############ ##########-------------------########### ##########---------------------######### ##########---------------------######### T #########-----------------------######## #########---------- ----------########## ########---------- P ----------######### ########---------- ----------######### ########----------------------######## #######----------------------####### ######---------------------####### #####--------------------##### #####------------------##### ###----------------### #------------- Global CMT Convention Moment Tensor: R T P -4.65e+21 1.48e+21 -3.97e+20 1.48e+21 -4.55e+20 -1.65e+20 -3.97e+20 -1.65e+20 5.10e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100113111755/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 0.5 330 45 -90 3.30 0.2336 WVFGRD96 1.0 80 90 0 3.38 0.2108 WVFGRD96 2.0 160 45 -90 3.46 0.3016 WVFGRD96 3.0 5 60 -40 3.51 0.2703 WVFGRD96 4.0 190 90 -45 3.60 0.2726 WVFGRD96 5.0 200 80 65 3.66 0.3074 WVFGRD96 6.0 205 75 65 3.68 0.3444 WVFGRD96 7.0 210 70 65 3.68 0.3629 WVFGRD96 8.0 205 75 65 3.74 0.3691 WVFGRD96 9.0 210 70 65 3.74 0.3781 WVFGRD96 10.0 210 70 60 3.73 0.3833 WVFGRD96 11.0 10 70 -80 3.69 0.3865 WVFGRD96 12.0 10 70 -75 3.70 0.3947 WVFGRD96 13.0 10 70 -70 3.70 0.4015 WVFGRD96 14.0 10 70 -70 3.71 0.4045 WVFGRD96 15.0 10 70 -70 3.72 0.4083 WVFGRD96 16.0 10 70 -65 3.72 0.4074 WVFGRD96 17.0 10 70 -65 3.73 0.4099 WVFGRD96 18.0 10 70 -65 3.74 0.4110 WVFGRD96 19.0 190 45 -70 3.73 0.4121 WVFGRD96 20.0 195 45 -65 3.74 0.4130 WVFGRD96 21.0 185 45 -70 3.74 0.4120 WVFGRD96 22.0 185 45 -70 3.75 0.4110 WVFGRD96 23.0 190 45 -65 3.76 0.4087 WVFGRD96 24.0 195 45 -65 3.78 0.4054 WVFGRD96 25.0 200 40 -60 3.78 0.4022 WVFGRD96 26.0 200 40 -60 3.79 0.3982 WVFGRD96 27.0 205 40 -60 3.81 0.3938 WVFGRD96 28.0 210 40 -60 3.83 0.3887 WVFGRD96 29.0 220 45 -55 3.87 0.3836
The best solution is
WVFGRD96 20.0 195 45 -65 3.74 0.4130
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 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. |
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=Wed Jan 13 05:56:46 MST 2010