2010/12/10 05:42:34 59.357 -135.165 1.0 4.60 Alaska
The event was relocation using arrival times from nearby ANSS and NRCAN stations. This solution provided a better fit than the initial solution in that the nearby waveforms were correctly rotated into certical, raidla and transverse components of gorund motion. The detailed relocation is in elocate.txt.
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/12/10 05:42:34:0 59.36 -135.16 1.0 4.6 Alaska Stations used: AK.BAL AK.BMR AK.CRQ AK.CTG AK.DCPH AT.CRAG AT.SKAG CN.BVCY CN.DAWY CN.DLBC CN.HYT CN.PLBC CN.WHY CN.YUK1 CN.YUK2 CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 US.WRAK Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.68e+22 dyne-cm Mw = 4.38 Z = 1 km Plane Strike Dip Rake NP1 7 50 94 NP2 180 40 85 Principal Axes: Axis Value Plunge Azimuth T 4.68e+22 84 306 N 0.00e+00 3 184 P -4.68e+22 5 94 Moment Tensor: (dyne-cm) Component Value Mxx -4.58e+14 Mxy 2.62e+21 Mxz 3.12e+21 Myy -4.59e+22 Myz -8.09e+21 Mzz 4.59e+22 ----#######--- ------##########------ -------##############------- -------################------- --------#################--------- --------###################--------- --------#####################--------- --------######################---------- --------######################---------- ---------######### ##########----------- ---------######### T ##########-------- ---------######### ##########-------- P ---------######################-------- --------#####################----------- --------#####################----------- --------###################----------- --------#################----------- --------################---------- -------#############---------- -------###########---------- ------#######--------- ----###------- Global CMT Convention Moment Tensor: R T P 4.59e+22 3.12e+21 8.09e+21 3.12e+21 -4.58e+14 -2.62e+21 8.09e+21 -2.62e+21 -4.59e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101210054234/index.html |
STK = 180 DIP = 40 RAKE = 85 MW = 4.38 HS = 1.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/12/10 05:42:34:0 59.36 -135.16 1.0 4.6 Alaska Stations used: AK.BAL AK.BMR AK.CRQ AK.CTG AK.DCPH AT.CRAG AT.SKAG CN.BVCY CN.DAWY CN.DLBC CN.HYT CN.PLBC CN.WHY CN.YUK1 CN.YUK2 CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 US.WRAK Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.68e+22 dyne-cm Mw = 4.38 Z = 1 km Plane Strike Dip Rake NP1 7 50 94 NP2 180 40 85 Principal Axes: Axis Value Plunge Azimuth T 4.68e+22 84 306 N 0.00e+00 3 184 P -4.68e+22 5 94 Moment Tensor: (dyne-cm) Component Value Mxx -4.58e+14 Mxy 2.62e+21 Mxz 3.12e+21 Myy -4.59e+22 Myz -8.09e+21 Mzz 4.59e+22 ----#######--- ------##########------ -------##############------- -------################------- --------#################--------- --------###################--------- --------#####################--------- --------######################---------- --------######################---------- ---------######### ##########----------- ---------######### T ##########-------- ---------######### ##########-------- P ---------######################-------- --------#####################----------- --------#####################----------- --------###################----------- --------#################----------- --------################---------- -------#############---------- -------###########---------- ------#######--------- ----###------- Global CMT Convention Moment Tensor: R T P 4.59e+22 3.12e+21 8.09e+21 3.12e+21 -4.58e+14 -2.62e+21 8.09e+21 -2.62e+21 -4.59e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101210054234/index.html |
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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 5 50 95 4.34 0.7073 WVFGRD96 1.0 180 40 85 4.38 0.7074 WVFGRD96 2.0 180 25 80 4.48 0.6234 WVFGRD96 3.0 0 70 85 4.46 0.5599 WVFGRD96 4.0 175 70 85 4.44 0.5449 WVFGRD96 5.0 15 20 110 4.42 0.5442 WVFGRD96 6.0 175 75 85 4.40 0.5530 WVFGRD96 7.0 175 80 80 4.39 0.5594 WVFGRD96 8.0 315 10 55 4.39 0.5652 WVFGRD96 9.0 305 10 45 4.39 0.5681 WVFGRD96 10.0 300 10 40 4.43 0.5674 WVFGRD96 11.0 175 85 80 4.43 0.5647 WVFGRD96 12.0 355 90 -80 4.43 0.5572 WVFGRD96 13.0 355 90 -80 4.44 0.5491 WVFGRD96 14.0 210 30 -70 4.46 0.5502 WVFGRD96 15.0 210 30 -70 4.47 0.5496 WVFGRD96 16.0 215 30 -65 4.47 0.5468 WVFGRD96 17.0 215 30 -65 4.48 0.5401 WVFGRD96 18.0 215 30 -65 4.49 0.5315 WVFGRD96 19.0 225 30 -55 4.49 0.5204 WVFGRD96 20.0 215 25 -65 4.52 0.5067 WVFGRD96 21.0 215 25 -65 4.53 0.4942 WVFGRD96 22.0 220 25 -60 4.53 0.4808 WVFGRD96 23.0 220 25 -60 4.54 0.4653 WVFGRD96 24.0 220 25 -60 4.54 0.4492 WVFGRD96 25.0 225 25 -55 4.55 0.4328 WVFGRD96 26.0 230 25 -50 4.55 0.4150 WVFGRD96 27.0 160 80 -85 4.60 0.4064 WVFGRD96 28.0 160 80 -85 4.60 0.4013 WVFGRD96 29.0 160 80 -85 4.61 0.3950
The best solution is
WVFGRD96 1.0 180 40 85 4.38 0.7074
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 CUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 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=Fri Dec 10 11:38:21 CST 2010