The ANSS event ID is ak0128mxrejd and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0128mxrejd/executive.
2012/07/06 01:22:04 61.677 -151.274 84.8 4.7 Alaska
USGS/SLU Moment Tensor Solution ENS 2012/07/06 01:22:04:0 61.68 -151.27 84.8 4.7 Alaska Stations used: AK.BRLK AK.CNP AK.FIB AK.GHO AK.HOM AK.PPLA AK.RC01 AK.SAW AK.SCM AK.SKN AK.SSN AT.PMR Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 1.19e+23 dyne-cm Mw = 4.65 Z = 87 km Plane Strike Dip Rake NP1 65 65 40 NP2 315 54 149 Principal Axes: Axis Value Plunge Azimuth T 1.19e+23 45 285 N 0.00e+00 44 92 P -1.19e+23 6 188 Moment Tensor: (dyne-cm) Component Value Mxx -1.11e+23 Mxy -3.06e+22 Mxz 2.82e+22 Myy 5.28e+22 Myz -5.56e+22 Mzz 5.85e+22 -------------- ---------------------- ---------------------------- ##########-------------------- ################------------------ ####################---------------- #######################--------------- ##########################------------## ######## #################--------#### ######### T ##################------###### ######### ####################--######## ################################-######### #############################-----######## #########################--------####### #####################-------------###### ###############-------------------#### ---------------------------------### --------------------------------## ------------------------------ ---------------------------- ------- ------------ --- P -------- Global CMT Convention Moment Tensor: R T P 5.85e+22 2.82e+22 5.56e+22 2.82e+22 -1.11e+23 3.06e+22 5.56e+22 3.06e+22 5.28e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120706012204/index.html |
STK = 65 DIP = 65 RAKE = 40 MW = 4.65 HS = 87.0
The NDK file is 20120706012204.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:
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 85 40 65 3.82 0.1913 WVFGRD96 1.0 60 80 15 3.75 0.1967 WVFGRD96 2.0 55 90 20 3.87 0.2726 WVFGRD96 3.0 35 70 25 3.93 0.3091 WVFGRD96 4.0 35 75 20 3.95 0.3325 WVFGRD96 5.0 40 90 25 3.98 0.3553 WVFGRD96 6.0 45 85 25 4.01 0.3774 WVFGRD96 7.0 45 85 25 4.03 0.3961 WVFGRD96 8.0 45 85 25 4.07 0.4113 WVFGRD96 9.0 225 90 -25 4.08 0.4211 WVFGRD96 10.0 235 90 -25 4.12 0.4338 WVFGRD96 11.0 55 85 25 4.13 0.4481 WVFGRD96 12.0 55 85 25 4.14 0.4584 WVFGRD96 13.0 55 90 25 4.15 0.4666 WVFGRD96 14.0 55 90 25 4.16 0.4732 WVFGRD96 15.0 55 90 20 4.18 0.4796 WVFGRD96 16.0 55 90 20 4.19 0.4847 WVFGRD96 17.0 55 90 20 4.19 0.4889 WVFGRD96 18.0 55 90 20 4.20 0.4935 WVFGRD96 19.0 60 85 20 4.22 0.4971 WVFGRD96 20.0 60 85 20 4.23 0.5011 WVFGRD96 21.0 240 90 -20 4.24 0.5025 WVFGRD96 22.0 60 85 20 4.25 0.5068 WVFGRD96 23.0 240 90 -20 4.26 0.5083 WVFGRD96 24.0 240 90 -20 4.27 0.5105 WVFGRD96 25.0 60 85 20 4.27 0.5145 WVFGRD96 26.0 240 90 -20 4.28 0.5151 WVFGRD96 27.0 60 85 20 4.28 0.5181 WVFGRD96 28.0 60 85 20 4.29 0.5196 WVFGRD96 29.0 60 85 20 4.30 0.5210 WVFGRD96 30.0 240 90 -20 4.31 0.5220 WVFGRD96 31.0 240 90 -20 4.32 0.5228 WVFGRD96 32.0 240 90 -20 4.33 0.5236 WVFGRD96 33.0 240 90 -20 4.34 0.5246 WVFGRD96 34.0 60 90 20 4.34 0.5250 WVFGRD96 35.0 60 90 20 4.35 0.5250 WVFGRD96 36.0 60 90 20 4.36 0.5245 WVFGRD96 37.0 240 90 -20 4.38 0.5240 WVFGRD96 38.0 240 90 -20 4.39 0.5231 WVFGRD96 39.0 60 90 20 4.40 0.5222 WVFGRD96 40.0 60 90 30 4.45 0.5226 WVFGRD96 41.0 240 90 -25 4.46 0.5189 WVFGRD96 42.0 60 90 25 4.46 0.5159 WVFGRD96 43.0 60 90 25 4.47 0.5132 WVFGRD96 44.0 60 85 30 4.47 0.5106 WVFGRD96 45.0 60 85 30 4.48 0.5084 WVFGRD96 46.0 60 85 30 4.48 0.5066 WVFGRD96 47.0 60 85 30 4.49 0.5057 WVFGRD96 48.0 60 85 30 4.50 0.5054 WVFGRD96 49.0 60 85 30 4.50 0.5049 WVFGRD96 50.0 65 65 35 4.50 0.5079 WVFGRD96 51.0 65 65 35 4.51 0.5120 WVFGRD96 52.0 65 65 35 4.51 0.5158 WVFGRD96 53.0 65 65 35 4.52 0.5199 WVFGRD96 54.0 65 65 35 4.53 0.5251 WVFGRD96 55.0 65 65 35 4.53 0.5308 WVFGRD96 56.0 65 65 35 4.54 0.5360 WVFGRD96 57.0 65 65 35 4.54 0.5408 WVFGRD96 58.0 65 65 35 4.55 0.5466 WVFGRD96 59.0 65 65 35 4.55 0.5515 WVFGRD96 60.0 65 65 35 4.56 0.5558 WVFGRD96 61.0 65 65 35 4.56 0.5607 WVFGRD96 62.0 65 65 35 4.57 0.5652 WVFGRD96 63.0 65 65 35 4.57 0.5689 WVFGRD96 64.0 65 65 35 4.58 0.5733 WVFGRD96 65.0 70 60 40 4.58 0.5764 WVFGRD96 66.0 65 65 35 4.58 0.5804 WVFGRD96 67.0 65 65 40 4.59 0.5838 WVFGRD96 68.0 65 65 40 4.59 0.5861 WVFGRD96 69.0 65 65 40 4.60 0.5897 WVFGRD96 70.0 65 65 40 4.60 0.5922 WVFGRD96 71.0 65 65 40 4.60 0.5951 WVFGRD96 72.0 65 65 40 4.61 0.5970 WVFGRD96 73.0 65 65 40 4.61 0.5993 WVFGRD96 74.0 65 65 40 4.61 0.6011 WVFGRD96 75.0 65 65 40 4.62 0.6031 WVFGRD96 76.0 65 65 40 4.62 0.6044 WVFGRD96 77.0 65 65 40 4.62 0.6057 WVFGRD96 78.0 65 65 40 4.63 0.6073 WVFGRD96 79.0 65 65 40 4.63 0.6081 WVFGRD96 80.0 65 65 40 4.63 0.6088 WVFGRD96 81.0 65 65 40 4.64 0.6097 WVFGRD96 82.0 65 65 40 4.64 0.6104 WVFGRD96 83.0 65 65 40 4.64 0.6113 WVFGRD96 84.0 65 65 40 4.65 0.6110 WVFGRD96 85.0 65 65 40 4.65 0.6122 WVFGRD96 86.0 65 65 40 4.65 0.6117 WVFGRD96 87.0 65 65 40 4.65 0.6127 WVFGRD96 88.0 65 65 40 4.66 0.6120 WVFGRD96 89.0 65 65 40 4.66 0.6124 WVFGRD96 90.0 65 65 40 4.66 0.6124 WVFGRD96 91.0 65 65 40 4.67 0.6121 WVFGRD96 92.0 65 65 40 4.67 0.6117 WVFGRD96 93.0 65 65 40 4.67 0.6104 WVFGRD96 94.0 65 65 40 4.67 0.6109 WVFGRD96 95.0 65 65 40 4.68 0.6098 WVFGRD96 96.0 65 65 40 4.68 0.6093 WVFGRD96 97.0 65 65 40 4.68 0.6081 WVFGRD96 98.0 65 65 40 4.68 0.6070 WVFGRD96 99.0 65 65 40 4.69 0.6067 WVFGRD96 100.0 65 65 40 4.69 0.6053 WVFGRD96 101.0 65 65 40 4.69 0.6039 WVFGRD96 102.0 65 65 40 4.69 0.6029 WVFGRD96 103.0 65 65 40 4.70 0.6013 WVFGRD96 104.0 65 65 40 4.70 0.6001 WVFGRD96 105.0 65 65 40 4.70 0.5989 WVFGRD96 106.0 65 65 40 4.70 0.5961 WVFGRD96 107.0 65 65 40 4.70 0.5956 WVFGRD96 108.0 65 65 40 4.71 0.5939 WVFGRD96 109.0 65 65 40 4.71 0.5917 WVFGRD96 110.0 65 65 40 4.71 0.5904 WVFGRD96 111.0 65 65 40 4.71 0.5878 WVFGRD96 112.0 65 65 40 4.71 0.5861 WVFGRD96 113.0 65 65 40 4.72 0.5843 WVFGRD96 114.0 65 65 40 4.72 0.5821 WVFGRD96 115.0 65 65 40 4.72 0.5795 WVFGRD96 116.0 65 65 40 4.72 0.5777 WVFGRD96 117.0 65 65 40 4.72 0.5754 WVFGRD96 118.0 65 60 40 4.71 0.5733 WVFGRD96 119.0 65 60 40 4.72 0.5722 WVFGRD96 120.0 65 60 40 4.72 0.5697 WVFGRD96 121.0 65 60 40 4.72 0.5673 WVFGRD96 122.0 65 60 40 4.72 0.5660 WVFGRD96 123.0 65 60 40 4.72 0.5637 WVFGRD96 124.0 65 60 40 4.73 0.5611 WVFGRD96 125.0 65 60 40 4.73 0.5595 WVFGRD96 126.0 65 60 40 4.73 0.5568 WVFGRD96 127.0 65 60 40 4.73 0.5544 WVFGRD96 128.0 65 60 40 4.73 0.5520 WVFGRD96 129.0 65 60 40 4.73 0.5503
The best solution is
WVFGRD96 87.0 65 65 40 4.65 0.6127
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
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