2012/06/05 11:19:36 62.402 -152.672 7.2 4.00 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2012/06/05 11:19:36:0 62.40 -152.67 7.2 4.0 Alaska Stations used: AK.BPAW AK.BWN AK.CAST AK.CCB AK.DHY AK.DIV AK.FYU AK.GHO AK.GLM AK.HDA AK.KLU AK.KNK 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.SKN AK.SSN AK.TRF AK.WRH AT.PMR AT.SVW2 II.KDAK IU.COLA Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 7.76e+21 dyne-cm Mw = 3.86 Z = 14 km Plane Strike Dip Rake NP1 222 51 124 NP2 355 50 55 Principal Axes: Axis Value Plunge Azimuth T 7.76e+21 64 198 N 0.00e+00 26 19 P -7.76e+21 1 289 Moment Tensor: (dyne-cm) Component Value Mxx 5.45e+20 Mxy 2.82e+21 Mxz -2.95e+21 Myy -6.81e+21 Myz -8.51e+20 Mzz 6.26e+21 -------####### --------------######## ------------------########## ------------------###--------- ----------------########---------- ---------------###########---------- ------------##############----------- P -----------################----------- ---------##################----------- -----------####################----------- ----------#####################----------- ---------######################----------- --------#######################----------- ------########### ##########---------- ------########### T ##########---------- -----########### #########---------- ---########################--------- --#######################--------- -#####################-------- ####################-------- ################------ ##########---- Global CMT Convention Moment Tensor: R T P 6.26e+21 -2.95e+21 8.51e+20 -2.95e+21 5.45e+20 -2.82e+21 8.51e+20 -2.82e+21 -6.81e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120605111936/index.html |
STK = -5 DIP = 50 RAKE = 55 MW = 3.86 HS = 14.0
The NDK file is 20120605111936.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2012/06/05 11:19:36:0 62.40 -152.67 7.2 4.0 Alaska Stations used: AK.BPAW AK.BWN AK.CAST AK.CCB AK.DHY AK.DIV AK.FYU AK.GHO AK.GLM AK.HDA AK.KLU AK.KNK 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.SKN AK.SSN AK.TRF AK.WRH AT.PMR AT.SVW2 II.KDAK IU.COLA Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 7.76e+21 dyne-cm Mw = 3.86 Z = 14 km Plane Strike Dip Rake NP1 222 51 124 NP2 355 50 55 Principal Axes: Axis Value Plunge Azimuth T 7.76e+21 64 198 N 0.00e+00 26 19 P -7.76e+21 1 289 Moment Tensor: (dyne-cm) Component Value Mxx 5.45e+20 Mxy 2.82e+21 Mxz -2.95e+21 Myy -6.81e+21 Myz -8.51e+20 Mzz 6.26e+21 -------####### --------------######## ------------------########## ------------------###--------- ----------------########---------- ---------------###########---------- ------------##############----------- P -----------################----------- ---------##################----------- -----------####################----------- ----------#####################----------- ---------######################----------- --------#######################----------- ------########### ##########---------- ------########### T ##########---------- -----########### #########---------- ---########################--------- --#######################--------- -#####################-------- ####################-------- ################------ ##########---- Global CMT Convention Moment Tensor: R T P 6.26e+21 -2.95e+21 8.51e+20 -2.95e+21 5.45e+20 -2.82e+21 8.51e+20 -2.82e+21 -6.81e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120605111936/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 0.5 160 75 -20 3.47 0.3587 WVFGRD96 1.0 160 80 -15 3.50 0.3696 WVFGRD96 2.0 160 75 -20 3.59 0.4040 WVFGRD96 3.0 160 75 -20 3.63 0.3865 WVFGRD96 4.0 335 80 -55 3.71 0.3663 WVFGRD96 5.0 335 80 -55 3.72 0.3947 WVFGRD96 6.0 340 30 5 3.72 0.4253 WVFGRD96 7.0 345 35 20 3.73 0.4642 WVFGRD96 8.0 350 35 25 3.80 0.4872 WVFGRD96 9.0 0 45 50 3.84 0.5450 WVFGRD96 10.0 0 45 60 3.86 0.6019 WVFGRD96 11.0 0 45 60 3.86 0.6403 WVFGRD96 12.0 5 45 65 3.87 0.6613 WVFGRD96 13.0 0 45 60 3.87 0.6700 WVFGRD96 14.0 -5 50 55 3.86 0.6709 WVFGRD96 15.0 -5 50 55 3.86 0.6660 WVFGRD96 16.0 355 50 55 3.86 0.6563 WVFGRD96 17.0 355 50 55 3.86 0.6431 WVFGRD96 18.0 350 50 50 3.85 0.6277 WVFGRD96 19.0 350 50 50 3.85 0.6116 WVFGRD96 20.0 350 50 50 3.85 0.5942 WVFGRD96 21.0 350 50 45 3.86 0.5794 WVFGRD96 22.0 345 55 40 3.86 0.5625 WVFGRD96 23.0 345 55 40 3.86 0.5454 WVFGRD96 24.0 345 55 40 3.86 0.5278 WVFGRD96 25.0 345 55 40 3.86 0.5099 WVFGRD96 26.0 345 55 35 3.86 0.4928 WVFGRD96 27.0 345 55 35 3.87 0.4757 WVFGRD96 28.0 345 55 35 3.87 0.4589 WVFGRD96 29.0 340 60 30 3.87 0.4430
The best solution is
WVFGRD96 14.0 -5 50 55 3.86 0.6709
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: