2012/06/08 18:27:36 62.217 -147.879 39.4 4.30 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2012/06/08 18:27:36:0 62.22 -147.88 39.4 4.3 Alaska Stations used: AK.BAL AK.BMR AK.BWN AK.CCB AK.COLD AK.CRQ AK.CTG AK.DHY AK.DIV AK.FYU AK.GHO AK.GLM AK.HDA AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.PAX AK.PPD AK.PPLA AK.RAG AK.RIDG AK.RND AK.SAW AK.SCM AK.SCRK AK.TGL AK.TRF AK.WRH AT.PMR CN.DAWY IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 2.69e+22 dyne-cm Mw = 4.22 Z = 51 km Plane Strike Dip Rake NP1 255 60 -40 NP2 8 56 -143 Principal Axes: Axis Value Plunge Azimuth T 2.69e+22 2 312 N 0.00e+00 42 44 P -2.69e+22 48 220 Moment Tensor: (dyne-cm) Component Value Mxx 5.05e+21 Mxy -1.92e+22 Mxz 1.10e+22 Myy 9.93e+21 Myz 7.72e+21 Mzz -1.50e+22 ###########--- ################------ ###################-------- T ####################-------- # #####################--------- ##########################---------- ######################-----####------- ###############--------------#########-- ###########------------------########### #########---------------------############ ######------------------------############ ####-------------------------############# ###--------------------------############# ----------------------------############ ------------ ------------############# ----------- P ------------############ ---------- -----------############ ----------------------############ -------------------########### -----------------########### ------------########## ------######## Global CMT Convention Moment Tensor: R T P -1.50e+22 1.10e+22 -7.72e+21 1.10e+22 5.05e+21 1.92e+22 -7.72e+21 1.92e+22 9.93e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120608182736/index.html |
STK = 255 DIP = 60 RAKE = -40 MW = 4.22 HS = 51.0
The NDK file is 20120608182736.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2012/06/08 18:27:36:0 62.22 -147.88 39.4 4.3 Alaska Stations used: AK.BAL AK.BMR AK.BWN AK.CCB AK.COLD AK.CRQ AK.CTG AK.DHY AK.DIV AK.FYU AK.GHO AK.GLM AK.HDA AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.PAX AK.PPD AK.PPLA AK.RAG AK.RIDG AK.RND AK.SAW AK.SCM AK.SCRK AK.TGL AK.TRF AK.WRH AT.PMR CN.DAWY IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 2.69e+22 dyne-cm Mw = 4.22 Z = 51 km Plane Strike Dip Rake NP1 255 60 -40 NP2 8 56 -143 Principal Axes: Axis Value Plunge Azimuth T 2.69e+22 2 312 N 0.00e+00 42 44 P -2.69e+22 48 220 Moment Tensor: (dyne-cm) Component Value Mxx 5.05e+21 Mxy -1.92e+22 Mxz 1.10e+22 Myy 9.93e+21 Myz 7.72e+21 Mzz -1.50e+22 ###########--- ################------ ###################-------- T ####################-------- # #####################--------- ##########################---------- ######################-----####------- ###############--------------#########-- ###########------------------########### #########---------------------############ ######------------------------############ ####-------------------------############# ###--------------------------############# ----------------------------############ ------------ ------------############# ----------- P ------------############ ---------- -----------############ ----------------------############ -------------------########### -----------------########### ------------########## ------######## Global CMT Convention Moment Tensor: R T P -1.50e+22 1.10e+22 -7.72e+21 1.10e+22 5.05e+21 1.92e+22 -7.72e+21 1.92e+22 9.93e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120608182736/index.html |
(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.
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 0.06 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 45 45 85 3.40 0.2287 WVFGRD96 1.0 50 45 90 3.45 0.2387 WVFGRD96 2.0 230 45 95 3.56 0.3000 WVFGRD96 3.0 225 45 85 3.63 0.3088 WVFGRD96 4.0 0 75 15 3.58 0.2967 WVFGRD96 5.0 0 80 15 3.60 0.2869 WVFGRD96 6.0 90 80 -10 3.62 0.2891 WVFGRD96 7.0 275 70 30 3.66 0.3029 WVFGRD96 8.0 275 70 35 3.71 0.3181 WVFGRD96 9.0 275 70 35 3.72 0.3260 WVFGRD96 10.0 275 70 35 3.73 0.3301 WVFGRD96 11.0 275 70 35 3.74 0.3322 WVFGRD96 12.0 275 70 35 3.75 0.3330 WVFGRD96 13.0 280 65 35 3.76 0.3341 WVFGRD96 14.0 180 85 -55 3.78 0.3402 WVFGRD96 15.0 105 60 50 3.75 0.3486 WVFGRD96 16.0 80 75 -45 3.75 0.3600 WVFGRD96 17.0 80 75 -45 3.76 0.3748 WVFGRD96 18.0 80 75 -45 3.77 0.3878 WVFGRD96 19.0 80 75 -45 3.78 0.3998 WVFGRD96 20.0 80 70 -45 3.79 0.4105 WVFGRD96 21.0 80 70 -45 3.81 0.4224 WVFGRD96 22.0 80 70 -40 3.83 0.4330 WVFGRD96 23.0 80 70 -40 3.84 0.4429 WVFGRD96 24.0 80 70 -40 3.85 0.4516 WVFGRD96 25.0 260 45 -30 3.88 0.4634 WVFGRD96 26.0 260 50 -30 3.89 0.4744 WVFGRD96 27.0 260 50 -30 3.90 0.4854 WVFGRD96 28.0 260 50 -30 3.92 0.4953 WVFGRD96 29.0 260 50 -30 3.93 0.5039 WVFGRD96 30.0 260 50 -30 3.94 0.5115 WVFGRD96 31.0 260 55 -30 3.95 0.5193 WVFGRD96 32.0 260 55 -25 3.97 0.5274 WVFGRD96 33.0 260 60 -30 3.97 0.5380 WVFGRD96 34.0 260 60 -30 3.98 0.5481 WVFGRD96 35.0 260 60 -30 3.99 0.5574 WVFGRD96 36.0 260 60 -30 4.00 0.5656 WVFGRD96 37.0 260 60 -30 4.02 0.5724 WVFGRD96 38.0 260 60 -30 4.03 0.5776 WVFGRD96 39.0 260 60 -30 4.04 0.5792 WVFGRD96 40.0 255 55 -35 4.14 0.6028 WVFGRD96 41.0 255 55 -35 4.15 0.6130 WVFGRD96 42.0 255 60 -35 4.15 0.6220 WVFGRD96 43.0 255 60 -40 4.16 0.6304 WVFGRD96 44.0 255 60 -40 4.16 0.6377 WVFGRD96 45.0 255 60 -40 4.17 0.6433 WVFGRD96 46.0 255 60 -40 4.18 0.6483 WVFGRD96 47.0 255 60 -40 4.19 0.6515 WVFGRD96 48.0 255 60 -40 4.20 0.6539 WVFGRD96 49.0 255 60 -40 4.20 0.6549 WVFGRD96 50.0 255 60 -40 4.21 0.6551 WVFGRD96 51.0 255 60 -40 4.22 0.6554 WVFGRD96 52.0 255 60 -40 4.22 0.6540 WVFGRD96 53.0 255 60 -40 4.23 0.6520 WVFGRD96 54.0 255 60 -35 4.24 0.6487 WVFGRD96 55.0 255 65 -35 4.24 0.6451 WVFGRD96 56.0 255 65 -35 4.24 0.6419 WVFGRD96 57.0 255 65 -35 4.25 0.6383 WVFGRD96 58.0 255 65 -35 4.25 0.6335 WVFGRD96 59.0 255 65 -35 4.26 0.6282 WVFGRD96 60.0 255 65 -35 4.26 0.6221 WVFGRD96 61.0 255 65 -35 4.26 0.6156 WVFGRD96 62.0 255 65 -35 4.26 0.6077 WVFGRD96 63.0 255 65 -35 4.27 0.6009 WVFGRD96 64.0 255 65 -35 4.27 0.5925 WVFGRD96 65.0 255 65 -35 4.27 0.5843 WVFGRD96 66.0 260 70 -30 4.26 0.5772 WVFGRD96 67.0 260 70 -30 4.27 0.5699 WVFGRD96 68.0 260 70 -30 4.27 0.5624 WVFGRD96 69.0 260 70 -30 4.27 0.5548
The best solution is
WVFGRD96 51.0 255 60 -40 4.22 0.6554
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 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 0.06 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. |
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.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.
The WUS model 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: