The ANSS event ID is ak013eaf6wll and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak013eaf6wll/executive.
2013/11/07 05:13:09 62.032 -150.488 53.1 4.4 Alaska
USGS/SLU Moment Tensor Solution
ENS 2013/11/07 05:13:09:0 62.03 -150.49 53.1 4.4 Alaska
Stations used:
AK.BAL AK.BARN AK.BPAW AK.BWN AK.CCB AK.CNP AK.CRQ AK.DHY
AK.DOT AK.GHO AK.GLB AK.GLI AK.GOAT AK.GRNC AK.HDA AK.HIN
AK.KHIT AK.KIAG AK.KNK AK.MCAR AK.MESA AK.PPD AK.PWL AK.RAG
AK.RIDG AK.RND AK.SAMH AK.SAW AK.SCM AK.SGA AK.SKN AK.SSN
AK.SUCK AK.SWD AK.TGL AK.VRDI AK.WAT1 AK.WAT2 AK.WAT3
AK.WAT4 AK.WAT5 AK.WAT6 AK.WAT7 AK.WAX AK.YAH AT.PMR
AT.SVW2 IM.IL31 IU.COLA TA.POKR US.EGAK YE.PIC2 YE.PIC4
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 4.37e+22 dyne-cm
Mw = 4.36
Z = 64 km
Plane Strike Dip Rake
NP1 160 81 -94
NP2 5 10 -65
Principal Axes:
Axis Value Plunge Azimuth
T 4.37e+22 36 253
N 0.00e+00 4 160
P -4.37e+22 54 65
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.53e+20
Mxy 1.98e+21
Mxz -1.49e+22
Myy 1.40e+22
Myz -3.86e+22
Mzz -1.35e+22
-------------#
####-----------------#
#######-------------------##
#########--------------------#
###########---------------------##
############----------------------##
##############----------------------##
###############------------ --------##
################----------- P --------##
##################---------- ---------##
##################----------------------##
###################---------------------##
####### ##########--------------------##
###### T ##########-------------------##
###### ###########------------------##
####################----------------##
####################--------------##
####################------------##
###################---------##
###################-------##
#################---##
############--
Global CMT Convention Moment Tensor:
R T P
-1.35e+22 -1.49e+22 3.86e+22
-1.49e+22 -4.53e+20 -1.98e+21
3.86e+22 -1.98e+21 1.40e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20131107051309/index.html
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STK = 5
DIP = 10
RAKE = -65
MW = 4.36
HS = 64.0
The NDK file is 20131107051309.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 180 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 165 40 -90 3.68 0.2153
WVFGRD96 4.0 165 45 -90 3.77 0.2064
WVFGRD96 6.0 15 60 -45 3.74 0.1766
WVFGRD96 8.0 155 50 85 3.85 0.1923
WVFGRD96 10.0 100 40 -35 3.83 0.2112
WVFGRD96 12.0 90 40 -35 3.84 0.2353
WVFGRD96 14.0 230 55 55 3.89 0.2644
WVFGRD96 16.0 230 50 55 3.91 0.2914
WVFGRD96 18.0 230 50 55 3.93 0.3130
WVFGRD96 20.0 130 30 60 3.91 0.3299
WVFGRD96 22.0 130 30 60 3.94 0.3491
WVFGRD96 24.0 130 30 60 3.96 0.3657
WVFGRD96 26.0 140 25 75 3.97 0.3790
WVFGRD96 28.0 55 25 -15 3.99 0.3937
WVFGRD96 30.0 50 20 -20 4.01 0.4149
WVFGRD96 32.0 45 20 -25 4.03 0.4358
WVFGRD96 34.0 45 20 -25 4.04 0.4551
WVFGRD96 36.0 45 20 -25 4.06 0.4725
WVFGRD96 38.0 40 20 -30 4.07 0.4864
WVFGRD96 40.0 30 15 -40 4.22 0.4983
WVFGRD96 42.0 30 15 -40 4.23 0.5078
WVFGRD96 44.0 30 15 -40 4.24 0.5179
WVFGRD96 46.0 30 15 -40 4.26 0.5284
WVFGRD96 48.0 30 15 -40 4.27 0.5386
WVFGRD96 50.0 30 15 -40 4.28 0.5474
WVFGRD96 52.0 30 15 -40 4.29 0.5557
WVFGRD96 54.0 30 15 -40 4.30 0.5622
WVFGRD96 56.0 30 15 -40 4.32 0.5673
WVFGRD96 58.0 10 10 -60 4.33 0.5715
WVFGRD96 60.0 10 10 -60 4.34 0.5748
WVFGRD96 62.0 5 10 -65 4.35 0.5768
WVFGRD96 64.0 5 10 -65 4.36 0.5773
WVFGRD96 66.0 0 10 -70 4.37 0.5763
WVFGRD96 68.0 355 10 -75 4.38 0.5739
WVFGRD96 70.0 345 10 -85 4.39 0.5704
WVFGRD96 72.0 160 80 -90 4.39 0.5656
WVFGRD96 74.0 165 80 -80 4.41 0.5603
WVFGRD96 76.0 165 80 -80 4.42 0.5538
WVFGRD96 78.0 165 80 -80 4.43 0.5459
WVFGRD96 80.0 165 80 -80 4.43 0.5367
WVFGRD96 82.0 160 85 -80 4.43 0.5274
WVFGRD96 84.0 160 85 -80 4.44 0.5185
WVFGRD96 86.0 165 85 -75 4.45 0.5085
WVFGRD96 88.0 165 85 -75 4.45 0.4981
WVFGRD96 90.0 160 85 -70 4.46 0.4881
WVFGRD96 92.0 335 90 70 4.46 0.4787
WVFGRD96 94.0 155 90 -70 4.46 0.4718
WVFGRD96 96.0 335 90 70 4.46 0.4646
WVFGRD96 98.0 155 90 -70 4.47 0.4567
The best solution is
WVFGRD96 64.0 5 10 -65 4.36 0.5773
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 180 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 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