2011/02/26 11:08:28 61.696 -140.243 13.0 4.30 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2011/02/26 11:08:28:0 61.70 -140.24 13.0 4.3 Alaska Stations used: AK.BAL AK.BMR AK.EYAK AK.KLU AK.PIN AK.RAG AK.SCM AT.MENT AT.PMR CN.BVCY CN.DAWY CN.HYT CN.PLBC CN.YUK1 CN.YUK2 IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 1.60e+22 dyne-cm Mw = 4.07 Z = 21 km Plane Strike Dip Rake NP1 80 90 20 NP2 350 70 180 Principal Axes: Axis Value Plunge Azimuth T 1.60e+22 14 307 N 0.00e+00 70 80 P -1.60e+22 14 213 Moment Tensor: (dyne-cm) Component Value Mxx -5.15e+21 Mxy -1.42e+22 Mxz 5.40e+21 Myy 5.15e+21 Myz -9.52e+20 Mzz -4.79e+14 ####---------- ##########------------ ##############-------------- ################-------------- # ###############--------------- ## T ################--------------- ### ################---------------- ########################---------------- ########################---------------- ##########################-----------##### ########################################## ################----------################ #####----------------------############### --------------------------############## --------------------------############## -------------------------############# ------------------------############ -----------------------########### ---- -------------########## --- P -------------######### -------------###### -----------### Global CMT Convention Moment Tensor: R T P -4.79e+14 5.40e+21 9.52e+20 5.40e+21 -5.15e+21 1.42e+22 9.52e+20 1.42e+22 5.15e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110226110828/index.html |
STK = 80 DIP = 90 RAKE = 20 MW = 4.07 HS = 21.0
The NDK file is 20110226110828.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2011/02/26 11:08:26:6 61.61 -140.52 13.0 4.3 Alaska Stations used: AK.BAL AK.BMR AK.EYAK AK.KLU AK.PIN AK.RAG AK.SCM AT.MENT AT.PMR CN.BVCY CN.DAWY CN.HYT CN.PLBC CN.YUK1 CN.YUK2 IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 1.60e+22 dyne-cm Mw = 4.07 Z = 21 km Plane Strike Dip Rake NP1 80 90 20 NP2 350 70 180 Principal Axes: Axis Value Plunge Azimuth T 1.60e+22 14 307 N 0.00e+00 70 80 P -1.60e+22 14 213 Moment Tensor: (dyne-cm) Component Value Mxx -5.15e+21 Mxy -1.42e+22 Mxz 5.40e+21 Myy 5.15e+21 Myz -9.52e+20 Mzz -4.79e+14 ####---------- ##########------------ ##############-------------- ################-------------- # ###############--------------- ## T ################--------------- ### ################---------------- ########################---------------- ########################---------------- ##########################-----------##### ########################################## ################----------################ #####----------------------############### --------------------------############## --------------------------############## -------------------------############# ------------------------############ -----------------------########### ---- -------------########## --- P -------------######### -------------###### -----------### Global CMT Convention Moment Tensor: R T P -4.79e+14 5.40e+21 9.52e+20 5.40e+21 -5.15e+21 1.42e+22 9.52e+20 1.42e+22 5.15e+21 Details of the solution is found at http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20110226110826/index.html USGS/SLU Moment Tensor Solution ENS 2011/02/26 11:08:28:0 61.70 -140.24 13.0 4.3 Alaska Stations used: AK.BAL AK.BMR AK.EYAK AK.KLU AK.PIN AK.RAG AK.SCM AT.MENT AT.PMR CN.BVCY CN.DAWY CN.HYT CN.PLBC CN.YUK1 CN.YUK2 IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 1.60e+22 dyne-cm Mw = 4.07 Z = 21 km Plane Strike Dip Rake NP1 80 90 20 NP2 350 70 180 Principal Axes: Axis Value Plunge Azimuth T 1.60e+22 14 307 N 0.00e+00 70 80 P -1.60e+22 14 213 Moment Tensor: (dyne-cm) Component Value Mxx -5.15e+21 Mxy -1.42e+22 Mxz 5.40e+21 Myy 5.15e+21 Myz -9.52e+20 Mzz -4.79e+14 ####---------- ##########------------ ##############-------------- ################-------------- # ###############--------------- ## T ################--------------- ### ################---------------- ########################---------------- ########################---------------- ##########################-----------##### ########################################## ################----------################ #####----------------------############### --------------------------############## --------------------------############## -------------------------############# ------------------------############ -----------------------########### ---- -------------########## --- P -------------######### -------------###### -----------### Global CMT Convention Moment Tensor: R T P -4.79e+14 5.40e+21 9.52e+20 5.40e+21 -5.15e+21 1.42e+22 9.52e+20 1.42e+22 5.15e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110226110828/index.html |
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(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 0.5 270 55 35 3.63 0.2464 WVFGRD96 1.0 250 75 15 3.60 0.2578 WVFGRD96 2.0 265 60 30 3.76 0.3457 WVFGRD96 3.0 265 75 30 3.79 0.3822 WVFGRD96 4.0 80 90 -25 3.81 0.4156 WVFGRD96 5.0 260 90 20 3.84 0.4448 WVFGRD96 6.0 80 90 -20 3.86 0.4688 WVFGRD96 7.0 80 80 -15 3.89 0.4908 WVFGRD96 8.0 260 80 -20 3.92 0.5140 WVFGRD96 9.0 260 75 -20 3.95 0.5325 WVFGRD96 10.0 260 75 -20 3.96 0.5475 WVFGRD96 11.0 260 75 -20 3.98 0.5589 WVFGRD96 12.0 260 75 -20 3.99 0.5678 WVFGRD96 13.0 260 75 -15 4.00 0.5740 WVFGRD96 14.0 260 75 -15 4.01 0.5786 WVFGRD96 15.0 260 75 -15 4.02 0.5813 WVFGRD96 16.0 260 75 -15 4.03 0.5826 WVFGRD96 17.0 260 80 -15 4.04 0.5834 WVFGRD96 18.0 260 80 -15 4.05 0.5841 WVFGRD96 19.0 260 85 -15 4.05 0.5852 WVFGRD96 20.0 260 85 -15 4.06 0.5859 WVFGRD96 21.0 80 90 20 4.07 0.5864 WVFGRD96 22.0 80 90 20 4.08 0.5862 WVFGRD96 23.0 80 90 20 4.08 0.5856 WVFGRD96 24.0 260 90 -20 4.09 0.5845 WVFGRD96 25.0 80 90 20 4.10 0.5827 WVFGRD96 26.0 260 90 -20 4.11 0.5800 WVFGRD96 27.0 80 90 20 4.12 0.5768 WVFGRD96 28.0 260 90 -20 4.12 0.5725 WVFGRD96 29.0 260 90 -15 4.13 0.5686
The best solution is
WVFGRD96 21.0 80 90 20 4.07 0.5864
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 0.06 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: