The ANSS event ID is uu60061837 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uu60061837/executive.
2014/03/30 12:34:39 44.772 -110.685 5.6 4.83 Montana
USGS/SLU Moment Tensor Solution ENS 2014/03/30 12:34:39:0 44.77 -110.68 5.6 4.8 Montana Stations used: CN.WALA IM.PD31 IU.RSSD IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.MFID IW.PHWY IW.REDW IW.RWWY IW.SNOW IW.TPAW MB.JTMT TA.H17A TA.K22A TA.N23A TA.O20A US.AHID US.BMO US.BW06 US.DUG US.EGMT US.ELK US.HWUT US.LAO US.MSO US.RLMT UU.BGU UU.BRPU UU.CTU UU.HVU UU.JLU UU.MPU UU.NLU UU.RDMU UU.SPU UU.TCU UW.BRAN WY.YHB WY.YHH WY.YHL WY.YNE WY.YPP Filtering commands used: rtr taper w 0.05 hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 2.45e+23 dyne-cm Mw = 4.86 Z = 10 km Plane Strike Dip Rake NP1 257 86 150 NP2 350 60 5 Principal Axes: Axis Value Plunge Azimuth T 2.45e+23 24 210 N 0.00e+00 60 70 P -2.45e+23 17 308 Moment Tensor: (dyne-cm) Component Value Mxx 7.19e+22 Mxy 1.96e+23 Mxz -1.22e+23 Myy -9.04e+22 Myz 1.07e+22 Mzz 1.85e+22 -----######### -----------########### ----------------############ ------------------############ -- ----------------############# --- P -----------------############# ---- ------------------############# --------------------------############## ---------------------------############# ----------------------------#------------- --------------------#########------------- ------------#################------------- ------#######################------------- ############################------------ ############################------------ ###########################----------- ##########################---------- ######## #############---------- ###### T #############-------- ##### ############-------- ################------ ###########--- Global CMT Convention Moment Tensor: R T P 1.85e+22 -1.22e+23 -1.07e+22 -1.22e+23 7.19e+22 -1.96e+23 -1.07e+22 -1.96e+23 -9.04e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140330123439/index.html |
STK = 350 DIP = 60 RAKE = 5 MW = 4.86 HS = 10.0
The NDK file is 20140330123439.ndk The waveform inversion is preferred.
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:
rtr taper w 0.05 hp c 0.02 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 160 65 -30 4.50 0.3164 WVFGRD96 1.0 160 60 -25 4.53 0.3364 WVFGRD96 2.0 160 60 -30 4.65 0.4444 WVFGRD96 3.0 345 65 -15 4.68 0.4652 WVFGRD96 4.0 345 60 -10 4.72 0.4859 WVFGRD96 5.0 350 60 0 4.74 0.5081 WVFGRD96 6.0 350 60 0 4.77 0.5276 WVFGRD96 7.0 350 65 0 4.78 0.5441 WVFGRD96 8.0 350 60 0 4.83 0.5569 WVFGRD96 9.0 350 60 0 4.84 0.5609 WVFGRD96 10.0 350 60 5 4.86 0.5630 WVFGRD96 11.0 350 65 5 4.87 0.5614 WVFGRD96 12.0 350 65 5 4.88 0.5582 WVFGRD96 13.0 350 65 5 4.89 0.5537 WVFGRD96 14.0 350 65 5 4.90 0.5481 WVFGRD96 15.0 350 65 5 4.91 0.5410 WVFGRD96 16.0 350 65 5 4.92 0.5337 WVFGRD96 17.0 350 65 0 4.92 0.5261 WVFGRD96 18.0 350 70 0 4.93 0.5194 WVFGRD96 19.0 180 70 15 4.91 0.5162 WVFGRD96 20.0 180 70 15 4.92 0.5117 WVFGRD96 21.0 180 65 15 4.93 0.5065 WVFGRD96 22.0 180 70 15 4.93 0.5021 WVFGRD96 23.0 180 65 15 4.94 0.4975 WVFGRD96 24.0 180 70 15 4.94 0.4924 WVFGRD96 25.0 180 70 15 4.95 0.4881 WVFGRD96 26.0 180 70 15 4.95 0.4838 WVFGRD96 27.0 180 70 15 4.96 0.4792 WVFGRD96 28.0 175 75 15 4.97 0.4755 WVFGRD96 29.0 175 75 15 4.97 0.4721
The best solution is
WVFGRD96 10.0 350 60 5 4.86 0.5630
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
rtr taper w 0.05 hp c 0.02 n 3 lp c 0.06 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