2012/08/24 21:58:09 63.931 -148.416 12.7 3.70 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2012/08/24 21:58:09:0 63.93 -148.42 12.7 3.7 Alaska Stations used: AK.BAL AK.BPAW AK.BRLK AK.BWN AK.CCB AK.COLD AK.CTG AK.DHY AK.FID AK.FYU AK.GHO AK.GLI AK.GLM AK.HDA AK.HIN AK.HMT AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.NEA AK.PAX AK.PPD AK.PPLA AK.RAG AK.RIDG AK.RND AK.SAW AK.SCM AK.SGA AK.SKN AK.SSN AK.TGL AK.WAX AK.WRH AK.YAH AT.MID AT.SVW2 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 = 6.53e+21 dyne-cm Mw = 3.81 Z = 17 km Plane Strike Dip Rake NP1 82 67 101 NP2 235 25 65 Principal Axes: Axis Value Plunge Azimuth T 6.53e+21 66 12 N 0.00e+00 10 258 P -6.53e+21 22 164 Moment Tensor: (dyne-cm) Component Value Mxx -4.14e+21 Mxy 1.73e+21 Mxz 4.55e+21 Myy -3.96e+20 Myz -1.33e+20 Mzz 4.53e+21 -------------- ---------------------- ----------###############--- -------######################- -------########################### ------############################## -----############## ################ -----############### T ################# ----################ ################# ----###################################### ---#####################################-- ---##################################----- ---##############################--------- ##-#######################-------------- ##-------------------------------------- #------------------------------------- ------------------------------------ ---------------------------------- ------------------ --------- ----------------- P -------- -------------- ----- -------------- Global CMT Convention Moment Tensor: R T P 4.53e+21 4.55e+21 1.33e+20 4.55e+21 -4.14e+21 -1.73e+21 1.33e+20 -1.73e+21 -3.96e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120824215809/index.html |
STK = 235 DIP = 25 RAKE = 65 MW = 3.81 HS = 17.0
The NDK file is 20120824215809.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2012/08/24 21:58:09:0 63.93 -148.42 12.7 3.7 Alaska Stations used: AK.BAL AK.BPAW AK.BRLK AK.BWN AK.CCB AK.COLD AK.CTG AK.DHY AK.FID AK.FYU AK.GHO AK.GLI AK.GLM AK.HDA AK.HIN AK.HMT AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.NEA AK.PAX AK.PPD AK.PPLA AK.RAG AK.RIDG AK.RND AK.SAW AK.SCM AK.SGA AK.SKN AK.SSN AK.TGL AK.WAX AK.WRH AK.YAH AT.MID AT.SVW2 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 = 6.53e+21 dyne-cm Mw = 3.81 Z = 17 km Plane Strike Dip Rake NP1 82 67 101 NP2 235 25 65 Principal Axes: Axis Value Plunge Azimuth T 6.53e+21 66 12 N 0.00e+00 10 258 P -6.53e+21 22 164 Moment Tensor: (dyne-cm) Component Value Mxx -4.14e+21 Mxy 1.73e+21 Mxz 4.55e+21 Myy -3.96e+20 Myz -1.33e+20 Mzz 4.53e+21 -------------- ---------------------- ----------###############--- -------######################- -------########################### ------############################## -----############## ################ -----############### T ################# ----################ ################# ----###################################### ---#####################################-- ---##################################----- ---##############################--------- ##-#######################-------------- ##-------------------------------------- #------------------------------------- ------------------------------------ ---------------------------------- ------------------ --------- ----------------- P -------- -------------- ----- -------------- Global CMT Convention Moment Tensor: R T P 4.53e+21 4.55e+21 1.33e+20 4.55e+21 -4.14e+21 -1.73e+21 1.33e+20 -1.73e+21 -3.96e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120824215809/index.html |
NEIC Mwr Moment 6.34e+14 N-m Magnitude 3.8 Percent DC 89% Depth 14.0 km Principal Axes Axis Value Plunge Azimuth T 6.506 62 11 N -0.336 15 249 P -6.170 22 153 Nodal Planes Plane Strike Dip Rake NP1 225 34 61 NP2 78 64 118 |
(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 0.5 275 40 -90 3.48 0.3567 WVFGRD96 1.0 275 40 -90 3.51 0.3353 WVFGRD96 2.0 115 50 -95 3.60 0.3929 WVFGRD96 3.0 330 55 -30 3.68 0.3513 WVFGRD96 4.0 335 60 -15 3.71 0.3298 WVFGRD96 5.0 175 20 -5 3.68 0.3725 WVFGRD96 6.0 180 20 0 3.68 0.4237 WVFGRD96 7.0 180 25 0 3.68 0.4595 WVFGRD96 8.0 185 20 5 3.75 0.4849 WVFGRD96 9.0 190 20 15 3.75 0.5144 WVFGRD96 10.0 200 20 25 3.75 0.5382 WVFGRD96 11.0 210 20 35 3.76 0.5579 WVFGRD96 12.0 210 25 40 3.77 0.5725 WVFGRD96 13.0 220 25 50 3.78 0.5847 WVFGRD96 14.0 220 25 50 3.79 0.5931 WVFGRD96 15.0 230 25 60 3.80 0.5975 WVFGRD96 16.0 230 25 60 3.80 0.5994 WVFGRD96 17.0 235 25 65 3.81 0.5994 WVFGRD96 18.0 230 25 60 3.81 0.5966 WVFGRD96 19.0 230 25 60 3.81 0.5918 WVFGRD96 20.0 230 25 60 3.81 0.5860 WVFGRD96 21.0 235 25 65 3.83 0.5799 WVFGRD96 22.0 235 25 65 3.83 0.5716 WVFGRD96 23.0 230 25 60 3.83 0.5624 WVFGRD96 24.0 230 25 60 3.84 0.5529 WVFGRD96 25.0 230 25 60 3.84 0.5427 WVFGRD96 26.0 230 25 60 3.84 0.5320 WVFGRD96 27.0 230 25 60 3.85 0.5211 WVFGRD96 28.0 225 25 55 3.85 0.5096 WVFGRD96 29.0 225 25 55 3.85 0.4975
The best solution is
WVFGRD96 17.0 235 25 65 3.81 0.5994
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: