2010/12/14 02:22:36 62.251 -150.177 0.0 4.00 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/12/14 02:22:36:0 62.25 -150.18 0.0 4.0 Alaska Stations used: AK.BPAW AK.DHY AK.EYAK AK.FID AK.MCK AK.RAG AK.RC01 AK.RND AK.SAW AK.SCM AK.TRF AK.WRH AT.PMR AT.TTA Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.47e+21 dyne-cm Mw = 3.70 Z = 19 km Plane Strike Dip Rake NP1 245 70 142 NP2 350 55 25 Principal Axes: Axis Value Plunge Azimuth T 4.47e+21 41 202 N 0.00e+00 48 41 P -4.47e+21 9 300 Moment Tensor: (dyne-cm) Component Value Mxx 1.08e+21 Mxy 2.81e+21 Mxz -2.40e+21 Myy -2.85e+21 Myz -2.33e+20 Mzz 1.77e+21 -----######### ------------########## ----------------############ -------------------########### --------------------############ P ---------------------############ - ----------------------#----------- ----------------------#####------------- ------------------##########------------ ---------------##############------------- ------------##################------------ ---------#####################------------ -------#######################------------ ----#########################----------- ---##########################----------- ############################---------- ############ ############--------- ########### T ###########--------- ######### ###########------- #####################------- #################----- ############-- Global CMT Convention Moment Tensor: R T P 1.77e+21 -2.40e+21 2.33e+20 -2.40e+21 1.08e+21 -2.81e+21 2.33e+20 -2.81e+21 -2.85e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101214022236/index.html |
STK = 350 DIP = 55 RAKE = 25 MW = 3.70 HS = 19.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/12/14 02:22:36:0 62.25 -150.18 0.0 4.0 Alaska Stations used: AK.BPAW AK.DHY AK.EYAK AK.FID AK.MCK AK.RAG AK.RC01 AK.RND AK.SAW AK.SCM AK.TRF AK.WRH AT.PMR AT.TTA Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.47e+21 dyne-cm Mw = 3.70 Z = 19 km Plane Strike Dip Rake NP1 245 70 142 NP2 350 55 25 Principal Axes: Axis Value Plunge Azimuth T 4.47e+21 41 202 N 0.00e+00 48 41 P -4.47e+21 9 300 Moment Tensor: (dyne-cm) Component Value Mxx 1.08e+21 Mxy 2.81e+21 Mxz -2.40e+21 Myy -2.85e+21 Myz -2.33e+20 Mzz 1.77e+21 -----######### ------------########## ----------------############ -------------------########### --------------------############ P ---------------------############ - ----------------------#----------- ----------------------#####------------- ------------------##########------------ ---------------##############------------- ------------##################------------ ---------#####################------------ -------#######################------------ ----#########################----------- ---##########################----------- ############################---------- ############ ############--------- ########### T ###########--------- ######### ###########------- #####################------- #################----- ############-- Global CMT Convention Moment Tensor: R T P 1.77e+21 -2.40e+21 2.33e+20 -2.40e+21 1.08e+21 -2.81e+21 2.33e+20 -2.81e+21 -2.85e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101214022236/index.html |
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 0.10 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 215 45 90 3.13 0.1602 WVFGRD96 1.0 165 85 0 3.09 0.1485 WVFGRD96 2.0 215 45 90 3.32 0.1986 WVFGRD96 3.0 170 55 10 3.31 0.1856 WVFGRD96 4.0 165 45 0 3.35 0.2008 WVFGRD96 5.0 160 45 -10 3.38 0.2254 WVFGRD96 6.0 160 45 -10 3.40 0.2496 WVFGRD96 7.0 160 50 -10 3.43 0.2704 WVFGRD96 8.0 330 45 -20 3.50 0.2874 WVFGRD96 9.0 325 45 -25 3.52 0.3085 WVFGRD96 10.0 330 50 -25 3.55 0.3268 WVFGRD96 11.0 330 50 -25 3.57 0.3417 WVFGRD96 12.0 330 50 -20 3.59 0.3523 WVFGRD96 13.0 330 50 -20 3.60 0.3604 WVFGRD96 14.0 345 50 25 3.61 0.3695 WVFGRD96 15.0 350 55 25 3.64 0.3805 WVFGRD96 16.0 350 55 25 3.66 0.3892 WVFGRD96 17.0 350 55 25 3.67 0.3948 WVFGRD96 18.0 350 55 25 3.69 0.3976 WVFGRD96 19.0 350 55 25 3.70 0.3990 WVFGRD96 20.0 350 55 25 3.71 0.3975 WVFGRD96 21.0 350 55 25 3.73 0.3920 WVFGRD96 22.0 350 50 25 3.73 0.3862 WVFGRD96 23.0 350 50 25 3.74 0.3793 WVFGRD96 24.0 350 50 25 3.75 0.3699 WVFGRD96 25.0 350 50 25 3.75 0.3591 WVFGRD96 26.0 345 50 25 3.76 0.3467 WVFGRD96 27.0 345 50 25 3.76 0.3336 WVFGRD96 28.0 345 50 25 3.76 0.3195 WVFGRD96 29.0 345 50 25 3.76 0.3046
The best solution is
WVFGRD96 19.0 350 55 25 3.70 0.3990
The mechanism correspond 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 0.10 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.
Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
The WUS 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:
DATE=Tue Dec 14 00:03:15 MST 2010