2011/12/09 01:25:41 62.255 -145.693 23 4.40 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2011/12/09 01:25:41:0 62.26 -145.69 23.0 4.4 Alaska Stations used: AK.BMR AK.BPAW AK.BRLK AK.CAST AK.CCB AK.CHUM AK.CNP AK.COLD AK.DHY AK.DIV AK.EYAK AK.FID AK.FYU AK.GHO AK.HDA AK.HIN AK.HMT AK.HOM AK.KAI AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.PAX AK.PPLA AK.RAG AK.RC01 AK.RND AK.SAW AK.SCM AK.SGA AK.SKN AK.SSN AK.SWD AK.TRF AK.WAX AT.MENT AT.MID AT.PMR AT.SVW2 CN.DAWY IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.07 n 3 Best Fitting Double Couple Mo = 4.68e+22 dyne-cm Mw = 4.38 Z = 19 km Plane Strike Dip Rake NP1 324 69 112 NP2 95 30 45 Principal Axes: Axis Value Plunge Azimuth T 4.68e+22 60 266 N 0.00e+00 21 136 P -4.68e+22 21 37 Moment Tensor: (dyne-cm) Component Value Mxx -2.56e+22 Mxy -1.88e+22 Mxz -1.40e+22 Myy -3.09e+21 Myz -3.00e+22 Mzz 2.86e+22 -------------- ---------------------- #####----------------- --- #########-------------- P ---- #############------------ ------ ################-------------------- ###################------------------- ######################------------------ #######################----------------- ##########################---------------- -########### ############--------------- -########### T #############-------------- --########## ##############------------# --###########################----------# ---###########################--------## ----##########################-----### -----########################---#### -------########################### ----------############-----### --------------------------## ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 2.86e+22 -1.40e+22 3.00e+22 -1.40e+22 -2.56e+22 1.88e+22 3.00e+22 1.88e+22 -3.09e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20111209012541/index.html |
STK = 95 DIP = 30 RAKE = 45 MW = 4.38 HS = 19.0
The NDK file is 20111209012541.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2011/12/09 01:25:41:0 62.26 -145.69 23.0 4.4 Alaska Stations used: AK.BMR AK.BPAW AK.BRLK AK.CAST AK.CCB AK.CHUM AK.CNP AK.COLD AK.DHY AK.DIV AK.EYAK AK.FID AK.FYU AK.GHO AK.HDA AK.HIN AK.HMT AK.HOM AK.KAI AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.PAX AK.PPLA AK.RAG AK.RC01 AK.RND AK.SAW AK.SCM AK.SGA AK.SKN AK.SSN AK.SWD AK.TRF AK.WAX AT.MENT AT.MID AT.PMR AT.SVW2 CN.DAWY IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.07 n 3 Best Fitting Double Couple Mo = 4.68e+22 dyne-cm Mw = 4.38 Z = 19 km Plane Strike Dip Rake NP1 324 69 112 NP2 95 30 45 Principal Axes: Axis Value Plunge Azimuth T 4.68e+22 60 266 N 0.00e+00 21 136 P -4.68e+22 21 37 Moment Tensor: (dyne-cm) Component Value Mxx -2.56e+22 Mxy -1.88e+22 Mxz -1.40e+22 Myy -3.09e+21 Myz -3.00e+22 Mzz 2.86e+22 -------------- ---------------------- #####----------------- --- #########-------------- P ---- #############------------ ------ ################-------------------- ###################------------------- ######################------------------ #######################----------------- ##########################---------------- -########### ############--------------- -########### T #############-------------- --########## ##############------------# --###########################----------# ---###########################--------## ----##########################-----### -----########################---#### -------########################### ----------############-----### --------------------------## ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 2.86e+22 -1.40e+22 3.00e+22 -1.40e+22 -2.56e+22 1.88e+22 3.00e+22 1.88e+22 -3.09e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20111209012541/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.
|
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 0.07 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 130 45 -90 3.93 0.3029 WVFGRD96 1.0 305 45 -90 3.97 0.2866 WVFGRD96 2.0 310 40 90 4.08 0.3565 WVFGRD96 3.0 130 50 90 4.13 0.3083 WVFGRD96 4.0 130 75 45 4.10 0.2632 WVFGRD96 5.0 55 20 -10 4.16 0.3137 WVFGRD96 6.0 60 20 0 4.16 0.3700 WVFGRD96 7.0 65 20 5 4.17 0.4175 WVFGRD96 8.0 70 20 10 4.25 0.4541 WVFGRD96 9.0 85 20 30 4.27 0.5038 WVFGRD96 10.0 95 20 40 4.28 0.5481 WVFGRD96 11.0 95 25 40 4.30 0.5879 WVFGRD96 12.0 100 25 50 4.31 0.6239 WVFGRD96 13.0 100 25 50 4.32 0.6533 WVFGRD96 14.0 100 30 50 4.34 0.6775 WVFGRD96 15.0 100 30 50 4.35 0.6972 WVFGRD96 16.0 100 30 50 4.36 0.7117 WVFGRD96 17.0 100 30 50 4.37 0.7215 WVFGRD96 18.0 100 30 50 4.37 0.7273 WVFGRD96 19.0 95 30 45 4.38 0.7297 WVFGRD96 20.0 95 30 40 4.39 0.7295 WVFGRD96 21.0 95 30 40 4.41 0.7274 WVFGRD96 22.0 95 30 40 4.42 0.7225 WVFGRD96 23.0 90 30 35 4.42 0.7155 WVFGRD96 24.0 90 30 35 4.43 0.7068 WVFGRD96 25.0 90 30 35 4.44 0.6962 WVFGRD96 26.0 90 30 35 4.44 0.6842 WVFGRD96 27.0 90 30 35 4.45 0.6708 WVFGRD96 28.0 90 30 35 4.46 0.6560 WVFGRD96 29.0 90 30 35 4.46 0.6399
The best solution is
WVFGRD96 19.0 95 30 45 4.38 0.7297
The mechanism correspond to the best fit is
|
The best fit as a function of depth is given in the following figure:
|
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 0.07 n 3
|
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: