The ANSS event ID is ak013eiwn044 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak013eiwn044/executive.
2013/11/12 18:16:48 63.066 -150.908 131.4 4.8 Alaska
USGS/SLU Moment Tensor Solution
ENS 2013/11/12 18:16:48:0 63.07 -150.91 131.4 4.8 Alaska
Stations used:
AK.BAL AK.BPAW AK.BRLK AK.BRSE AK.BWN AK.CAST AK.CCB
AK.COLD AK.DHY AK.EYAK AK.FID AK.GLB AK.GLI AK.HIN AK.KNK
AK.KTH AK.MCAR AK.MCK AK.MLY AK.NEA AK.PAX AK.PPLA AK.RC01
AK.RND AK.SAW AK.SCM AK.SGA AK.SLK AK.SSN AK.SWD AK.TRF
AK.WAT1 AK.WAT2 AK.WAT4 AK.WAT5 AK.WAT6 AK.WAT7 AK.WRH
AT.SVW2 IM.IL31 IU.COLA TA.HDA TA.TCOL TA.TOLK YE.PIC1
YE.PIC2 YE.PIC3
Filtering commands used:
cut a -30 a 120
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.23e+23 dyne-cm
Mw = 4.66
Z = 132 km
Plane Strike Dip Rake
NP1 240 82 -96
NP2 95 10 -55
Principal Axes:
Axis Value Plunge Azimuth
T 1.23e+23 37 335
N 0.00e+00 6 240
P -1.23e+23 53 143
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.63e+22
Mxy -9.07e+21
Mxz 1.00e+23
Myy -1.87e+21
Myz -6.10e+22
Mzz -3.45e+22
##############
######################
############################
######## ###################
########## T #####################
########### #####################-
###############################-------
############################------------
########################----------------
######################--------------------
##################------------------------
###############---------------------------
-############----------------------------#
#########-------------------------------
-######------------------ -----------#
-##--------------------- P ----------#
#---------------------- ---------#
##-------------------------------#
##---------------------------#
###----------------------###
####--------------####
##############
Global CMT Convention Moment Tensor:
R T P
-3.45e+22 1.00e+23 6.10e+22
1.00e+23 3.63e+22 9.07e+21
6.10e+22 9.07e+21 -1.87e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20131112181648/index.html
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STK = 95
DIP = 10
RAKE = -55
MW = 4.66
HS = 132.0
The NDK file is 20131112181648.ndk The waveform inversion is preferred.
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
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The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) 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's 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:
cut a -30 a 120 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 335 80 -15 3.65 0.2201
WVFGRD96 4.0 160 75 10 3.77 0.2696
WVFGRD96 6.0 340 70 -5 3.85 0.3048
WVFGRD96 8.0 340 70 10 3.94 0.3370
WVFGRD96 10.0 340 75 5 3.99 0.3504
WVFGRD96 12.0 340 75 -5 4.03 0.3502
WVFGRD96 14.0 340 80 -10 4.05 0.3422
WVFGRD96 16.0 340 80 -10 4.08 0.3290
WVFGRD96 18.0 340 80 -10 4.09 0.3136
WVFGRD96 20.0 185 70 10 4.09 0.3025
WVFGRD96 22.0 185 70 5 4.10 0.2936
WVFGRD96 24.0 65 80 -10 4.14 0.2908
WVFGRD96 26.0 65 80 -5 4.15 0.3024
WVFGRD96 28.0 65 80 -5 4.17 0.3126
WVFGRD96 30.0 70 80 5 4.19 0.3193
WVFGRD96 32.0 70 80 10 4.21 0.3291
WVFGRD96 34.0 70 80 10 4.22 0.3361
WVFGRD96 36.0 70 75 10 4.24 0.3374
WVFGRD96 38.0 70 80 10 4.27 0.3448
WVFGRD96 40.0 70 70 10 4.33 0.3576
WVFGRD96 42.0 70 75 10 4.35 0.3645
WVFGRD96 44.0 70 75 15 4.38 0.3716
WVFGRD96 46.0 70 75 15 4.40 0.3781
WVFGRD96 48.0 70 75 15 4.42 0.3840
WVFGRD96 50.0 75 70 25 4.44 0.3926
WVFGRD96 52.0 75 70 25 4.46 0.4029
WVFGRD96 54.0 75 70 25 4.47 0.4127
WVFGRD96 56.0 75 70 25 4.48 0.4217
WVFGRD96 58.0 75 75 30 4.49 0.4314
WVFGRD96 60.0 75 75 30 4.50 0.4418
WVFGRD96 62.0 75 75 30 4.51 0.4492
WVFGRD96 64.0 75 75 30 4.51 0.4571
WVFGRD96 66.0 75 75 30 4.52 0.4621
WVFGRD96 68.0 75 75 30 4.52 0.4668
WVFGRD96 70.0 70 90 75 4.56 0.4665
WVFGRD96 72.0 70 90 80 4.57 0.4853
WVFGRD96 74.0 65 90 80 4.57 0.5034
WVFGRD96 76.0 65 90 80 4.58 0.5212
WVFGRD96 78.0 245 90 -80 4.58 0.5370
WVFGRD96 80.0 65 90 80 4.59 0.5499
WVFGRD96 82.0 65 90 85 4.59 0.5628
WVFGRD96 84.0 65 90 85 4.60 0.5753
WVFGRD96 86.0 65 90 85 4.60 0.5855
WVFGRD96 88.0 240 85 -85 4.61 0.5983
WVFGRD96 90.0 65 90 85 4.61 0.6023
WVFGRD96 92.0 210 -5 60 4.62 0.6187
WVFGRD96 94.0 160 -5 5 4.61 0.6196
WVFGRD96 96.0 90 5 -60 4.63 0.6321
WVFGRD96 98.0 90 5 -60 4.63 0.6410
WVFGRD96 100.0 80 5 -70 4.63 0.6483
WVFGRD96 102.0 90 5 -60 4.63 0.6540
WVFGRD96 104.0 90 5 -60 4.64 0.6588
WVFGRD96 106.0 90 5 -60 4.64 0.6654
WVFGRD96 108.0 90 5 -60 4.64 0.6666
WVFGRD96 110.0 90 5 -60 4.64 0.6728
WVFGRD96 112.0 90 5 -60 4.64 0.6732
WVFGRD96 114.0 80 5 -70 4.64 0.6785
WVFGRD96 116.0 100 10 -50 4.65 0.6801
WVFGRD96 118.0 100 10 -50 4.66 0.6847
WVFGRD96 120.0 100 10 -50 4.66 0.6883
WVFGRD96 122.0 100 10 -50 4.66 0.6903
WVFGRD96 124.0 100 10 -50 4.66 0.6932
WVFGRD96 126.0 100 10 -50 4.66 0.6931
WVFGRD96 128.0 100 10 -50 4.66 0.6976
WVFGRD96 130.0 95 10 -55 4.66 0.6960
WVFGRD96 132.0 95 10 -55 4.66 0.6990
WVFGRD96 134.0 95 10 -55 4.67 0.6971
WVFGRD96 136.0 95 10 -55 4.67 0.6987
WVFGRD96 138.0 95 10 -55 4.67 0.6970
WVFGRD96 140.0 95 10 -55 4.67 0.6967
WVFGRD96 142.0 95 10 -55 4.67 0.6958
WVFGRD96 144.0 95 10 -55 4.67 0.6936
WVFGRD96 146.0 100 10 -50 4.67 0.6903
WVFGRD96 148.0 100 10 -50 4.67 0.6904
The best solution is
WVFGRD96 132.0 95 10 -55 4.66 0.6990
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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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
cut a -30 a 120 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.10 n 3
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| Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
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| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
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