The ANSS event ID is ak015e0i0jm1 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak015e0i0jm1/executive.
2015/11/01 05:21:12 62.209 -152.000 106.0 4.4 Alaska
USGS/SLU Moment Tensor Solution
ENS 2015/11/01 05:21:12:0 62.21 -152.00 106.0 4.4 Alaska
Stations used:
AK.CAST AK.DIV AK.FIRE AK.GHO AK.HDA AK.HIN AK.KLU AK.KNK
AK.KTH AK.MCK AK.MDM AK.PAX AK.PPLA AK.PWL AK.RC01 AK.SAW
AK.SCM AK.SKN AK.TRF AK.WRH AT.PMR AT.SVW2 AT.TTA TA.J20K
TA.K20K TA.L19K TA.M19K TA.N19K TA.O19K
Filtering commands used:
cut o DIST/3.6 -30 o DIST/3.6 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
Best Fitting Double Couple
Mo = 4.84e+22 dyne-cm
Mw = 4.39
Z = 106 km
Plane Strike Dip Rake
NP1 195 88 -100
NP2 95 10 -10
Principal Axes:
Axis Value Plunge Azimuth
T 4.84e+22 42 294
N 0.00e+00 10 195
P -4.84e+22 46 95
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.29e+21
Mxy -7.90e+21
Mxz 1.20e+22
Myy -1.42e+21
Myz -4.61e+22
Mzz -2.88e+21
############--
################------
##################----------
##################------------
####################--------------
####################----------------
#####################-----------------
######## ##########-------------------
######## T ##########-------------------
######### #########---------------------
#####################--------- ---------
####################---------- P ---------
-###################---------- --------#
##################----------------------
-#################---------------------#
-###############---------------------#
-##############--------------------#
--###########--------------------#
--#########------------------#
---#######---------------###
----##------------####
--############
Global CMT Convention Moment Tensor:
R T P
-2.88e+21 1.20e+22 4.61e+22
1.20e+22 4.29e+21 7.90e+21
4.61e+22 7.90e+21 -1.42e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20151101052112/index.html
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STK = 95
DIP = 10
RAKE = -10
MW = 4.39
HS = 106.0
The NDK file is 20151101052112.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 o DIST/3.6 -30 o DIST/3.6 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 190 45 85 3.43 0.1558
WVFGRD96 4.0 190 35 80 3.52 0.1434
WVFGRD96 6.0 130 40 40 3.51 0.1502
WVFGRD96 8.0 135 35 50 3.60 0.1690
WVFGRD96 10.0 135 35 45 3.60 0.1823
WVFGRD96 12.0 320 50 -55 3.65 0.1974
WVFGRD96 14.0 155 60 -45 3.70 0.2112
WVFGRD96 16.0 155 60 -45 3.72 0.2199
WVFGRD96 18.0 155 60 -45 3.74 0.2252
WVFGRD96 20.0 155 65 -45 3.76 0.2285
WVFGRD96 22.0 350 55 35 3.74 0.2411
WVFGRD96 24.0 350 55 35 3.76 0.2500
WVFGRD96 26.0 350 55 30 3.78 0.2530
WVFGRD96 28.0 350 55 30 3.80 0.2506
WVFGRD96 30.0 350 50 30 3.81 0.2419
WVFGRD96 32.0 10 55 25 3.84 0.2342
WVFGRD96 34.0 185 80 -50 3.88 0.2429
WVFGRD96 36.0 185 80 -50 3.90 0.2566
WVFGRD96 38.0 180 75 -55 3.92 0.2709
WVFGRD96 40.0 190 75 -55 4.05 0.2878
WVFGRD96 42.0 30 35 -60 4.03 0.3097
WVFGRD96 44.0 10 30 -80 4.07 0.3369
WVFGRD96 46.0 45 35 -55 4.08 0.3597
WVFGRD96 48.0 45 35 -55 4.10 0.3706
WVFGRD96 50.0 55 35 -50 4.11 0.3747
WVFGRD96 52.0 55 35 -50 4.13 0.3784
WVFGRD96 54.0 60 30 -40 4.14 0.3867
WVFGRD96 56.0 65 30 -35 4.16 0.3963
WVFGRD96 58.0 195 85 -65 4.19 0.4152
WVFGRD96 60.0 15 90 70 4.20 0.4407
WVFGRD96 62.0 15 90 70 4.22 0.4684
WVFGRD96 64.0 190 80 -70 4.23 0.4885
WVFGRD96 66.0 190 80 -75 4.24 0.5109
WVFGRD96 68.0 190 80 -75 4.25 0.5335
WVFGRD96 70.0 190 80 -75 4.26 0.5533
WVFGRD96 72.0 190 80 -80 4.27 0.5725
WVFGRD96 74.0 190 85 -85 4.28 0.5942
WVFGRD96 76.0 190 85 -85 4.29 0.6172
WVFGRD96 78.0 25 5 -80 4.30 0.6340
WVFGRD96 80.0 15 90 90 4.31 0.6499
WVFGRD96 82.0 70 5 -35 4.32 0.6739
WVFGRD96 84.0 40 5 -65 4.33 0.6889
WVFGRD96 86.0 75 5 -30 4.34 0.7070
WVFGRD96 88.0 75 5 -30 4.34 0.7200
WVFGRD96 90.0 80 5 -25 4.35 0.7321
WVFGRD96 92.0 80 5 -25 4.36 0.7417
WVFGRD96 94.0 80 5 -25 4.36 0.7497
WVFGRD96 96.0 80 5 -25 4.36 0.7568
WVFGRD96 98.0 95 10 -10 4.38 0.7600
WVFGRD96 100.0 95 10 -10 4.38 0.7660
WVFGRD96 102.0 95 10 -10 4.38 0.7683
WVFGRD96 104.0 95 10 -10 4.39 0.7692
WVFGRD96 106.0 95 10 -10 4.39 0.7701
WVFGRD96 108.0 90 10 -15 4.39 0.7677
WVFGRD96 110.0 90 10 -15 4.39 0.7657
WVFGRD96 112.0 90 10 -10 4.40 0.7622
WVFGRD96 114.0 90 10 -10 4.40 0.7572
WVFGRD96 116.0 90 10 -10 4.40 0.7528
WVFGRD96 118.0 90 10 -10 4.40 0.7462
The best solution is
WVFGRD96 106.0 95 10 -10 4.39 0.7701
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 o DIST/3.6 -30 o DIST/3.6 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 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