2012/08/09 16:43:25 60.341 -147.518 10.7 4.90 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2012/08/09 16:43:25:0 60.34 -147.52 10.7 4.9 Alaska Stations used: AK.BMR AK.BPAW AK.BRLK AK.BWN AK.CAST AK.CCB AK.CHUM AK.CNP AK.CTG AK.DHY AK.DIV AK.EYAK AK.FIB AK.GHO AK.GLI AK.GLM AK.HDA AK.HIN AK.HOM AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.NEA AK.PAX AK.PPD AK.PPLA AK.RAG AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCM AK.SCRK AK.SKN AK.SSN AK.TGL AK.TRF AK.WAX AK.WRH AT.MID AT.OHAK CN.DAWY II.KDAK IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 9.33e+22 dyne-cm Mw = 4.58 Z = 27 km Plane Strike Dip Rake NP1 182 61 -118 NP2 50 40 -50 Principal Axes: Axis Value Plunge Azimuth T 9.33e+22 11 292 N 0.00e+00 24 197 P -9.33e+22 63 45 Moment Tensor: (dyne-cm) Component Value Mxx 3.34e+21 Mxy -4.14e+22 Mxz -2.00e+22 Myy 6.71e+22 Myz -4.32e+22 Mzz -7.04e+22 ######-------- #########------------- ###########----------------- ###########------------------- ############---------------------# ############-----------------------# ##########-----------------------## # T #########---------- -----------### # #########---------- P ----------#### ##############---------- ----------##### ##############----------------------###### #############-----------------------###### ##############---------------------####### #############-------------------######## #############------------------######### ############----------------########## ############-------------########### ###########----------############# ##########------############## ----------################## --------############## -----######### Global CMT Convention Moment Tensor: R T P -7.04e+22 -2.00e+22 4.32e+22 -2.00e+22 3.34e+21 4.14e+22 4.32e+22 4.14e+22 6.71e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120809164325/index.html |
STK = 50 DIP = 40 RAKE = -50 MW = 4.58 HS = 27.0
The NDK file is 20120809164325.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2012/08/09 16:43:25:0 60.34 -147.52 10.7 4.9 Alaska Stations used: AK.BMR AK.BPAW AK.BRLK AK.BWN AK.CAST AK.CCB AK.CHUM AK.CNP AK.CTG AK.DHY AK.DIV AK.EYAK AK.FIB AK.GHO AK.GLI AK.GLM AK.HDA AK.HIN AK.HOM AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.NEA AK.PAX AK.PPD AK.PPLA AK.RAG AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCM AK.SCRK AK.SKN AK.SSN AK.TGL AK.TRF AK.WAX AK.WRH AT.MID AT.OHAK CN.DAWY II.KDAK IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 9.33e+22 dyne-cm Mw = 4.58 Z = 27 km Plane Strike Dip Rake NP1 182 61 -118 NP2 50 40 -50 Principal Axes: Axis Value Plunge Azimuth T 9.33e+22 11 292 N 0.00e+00 24 197 P -9.33e+22 63 45 Moment Tensor: (dyne-cm) Component Value Mxx 3.34e+21 Mxy -4.14e+22 Mxz -2.00e+22 Myy 6.71e+22 Myz -4.32e+22 Mzz -7.04e+22 ######-------- #########------------- ###########----------------- ###########------------------- ############---------------------# ############-----------------------# ##########-----------------------## # T #########---------- -----------### # #########---------- P ----------#### ##############---------- ----------##### ##############----------------------###### #############-----------------------###### ##############---------------------####### #############-------------------######## #############------------------######### ############----------------########## ############-------------########### ###########----------############# ##########------############## ----------################## --------############## -----######### Global CMT Convention Moment Tensor: R T P -7.04e+22 -2.00e+22 4.32e+22 -2.00e+22 3.34e+21 4.14e+22 4.32e+22 4.14e+22 6.71e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120809164325/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 20 45 90 4.11 0.2628 WVFGRD96 1.0 20 45 90 4.16 0.2634 WVFGRD96 2.0 200 45 90 4.25 0.3250 WVFGRD96 3.0 20 45 -90 4.30 0.3073 WVFGRD96 4.0 210 45 -75 4.31 0.2745 WVFGRD96 5.0 95 60 -5 4.27 0.2538 WVFGRD96 6.0 270 45 10 4.29 0.2678 WVFGRD96 7.0 270 45 20 4.30 0.2915 WVFGRD96 8.0 275 35 10 4.37 0.3090 WVFGRD96 9.0 275 35 10 4.39 0.3330 WVFGRD96 10.0 275 35 5 4.40 0.3540 WVFGRD96 11.0 275 35 5 4.41 0.3736 WVFGRD96 12.0 265 30 -15 4.42 0.3939 WVFGRD96 13.0 50 35 -50 4.45 0.4196 WVFGRD96 14.0 45 35 -60 4.47 0.4511 WVFGRD96 15.0 40 35 -65 4.48 0.4798 WVFGRD96 16.0 40 35 -65 4.49 0.5045 WVFGRD96 17.0 45 40 -55 4.50 0.5261 WVFGRD96 18.0 45 40 -55 4.51 0.5450 WVFGRD96 19.0 45 40 -55 4.52 0.5611 WVFGRD96 20.0 45 40 -55 4.53 0.5747 WVFGRD96 21.0 45 40 -55 4.54 0.5858 WVFGRD96 22.0 50 40 -50 4.55 0.5952 WVFGRD96 23.0 50 40 -50 4.56 0.6028 WVFGRD96 24.0 50 40 -50 4.56 0.6084 WVFGRD96 25.0 50 40 -50 4.57 0.6120 WVFGRD96 26.0 50 40 -50 4.58 0.6139 WVFGRD96 27.0 50 40 -50 4.58 0.6141 WVFGRD96 28.0 55 40 -45 4.59 0.6128 WVFGRD96 29.0 55 40 -45 4.60 0.6099 WVFGRD96 30.0 55 40 -45 4.61 0.6053 WVFGRD96 31.0 55 40 -45 4.61 0.5991 WVFGRD96 32.0 55 40 -45 4.62 0.5914 WVFGRD96 33.0 55 40 -45 4.62 0.5824 WVFGRD96 34.0 55 40 -45 4.63 0.5722 WVFGRD96 35.0 55 40 -45 4.64 0.5613 WVFGRD96 36.0 55 40 -45 4.64 0.5499 WVFGRD96 37.0 60 45 -40 4.65 0.5382 WVFGRD96 38.0 60 45 -40 4.66 0.5262 WVFGRD96 39.0 60 40 -45 4.67 0.5145
The best solution is
WVFGRD96 27.0 50 40 -50 4.58 0.6141
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: