The ANSS event ID is ak0159h0d1de and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0159h0d1de/executive.
2015/07/25 19:57:43 61.949 -152.052 125.6 5.1 Alaska
USGS/SLU Moment Tensor Solution
ENS 2015/07/25 19:57:43:0 61.95 -152.05 125.6 5.1 Alaska
Stations used:
AK.BMR AK.BPAW AK.BRLK AK.CAPN AK.CCB AK.CNP AK.EYAK AK.FID
AK.FIRE AK.GLB AK.GLI AK.HDA AK.HIN AK.HOM AK.KLU AK.KNK
AK.KTH AK.MCK AK.MDM AK.MLY AK.NEA2 AK.PAX AK.PPLA AK.PWL
AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCM AK.SCRK AK.SKN AK.SSN
AK.SUCK AK.SWD AK.TRF AK.VRDI AK.WRH AT.PMR IM.IL31 IU.COLA
TA.I23K TA.L27K TA.M24K TA.N25K TA.O22K TA.POKR
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 5.43e+23 dyne-cm
Mw = 5.09
Z = 124 km
Plane Strike Dip Rake
NP1 339 67 153
NP2 80 65 25
Principal Axes:
Axis Value Plunge Azimuth
T 5.43e+23 35 299
N 0.00e+00 55 122
P -5.43e+23 2 30
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.23e+23
Mxy -3.89e+23
Mxz 1.09e+23
Myy 1.47e+23
Myz -2.31e+23
Mzz 1.76e+23
--------------
######-------------- P
###########------------ --
##############----------------
#################-----------------
###################-----------------
###### ############-----------------
####### T #############-----------------
####### ##############----------------
##########################---------------#
###########################------------###
###########################---------######
############################-----#########
-##########################-############
-------#############--------############
---------------------------###########
--------------------------##########
-------------------------#########
-----------------------#######
----------------------######
-------------------###
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Global CMT Convention Moment Tensor:
R T P
1.76e+23 1.09e+23 2.31e+23
1.09e+23 -3.23e+23 3.89e+23
2.31e+23 3.89e+23 1.47e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150725195743/index.html
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STK = 80
DIP = 65
RAKE = 25
MW = 5.09
HS = 124.0
The NDK file is 20150725195743.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/3.3 -30 o DIST/3.3 +70 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 2.0 150 65 -30 4.15 0.1099
WVFGRD96 4.0 250 70 25 4.22 0.1297
WVFGRD96 6.0 250 75 15 4.26 0.1411
WVFGRD96 8.0 250 75 20 4.33 0.1530
WVFGRD96 10.0 250 80 -20 4.36 0.1666
WVFGRD96 12.0 250 75 -20 4.39 0.1803
WVFGRD96 14.0 250 75 -15 4.42 0.1924
WVFGRD96 16.0 250 80 -10 4.45 0.2019
WVFGRD96 18.0 250 80 -10 4.48 0.2088
WVFGRD96 20.0 250 80 -5 4.50 0.2136
WVFGRD96 22.0 250 80 -5 4.52 0.2162
WVFGRD96 24.0 250 80 5 4.55 0.2168
WVFGRD96 26.0 250 80 5 4.56 0.2162
WVFGRD96 28.0 250 80 5 4.58 0.2141
WVFGRD96 30.0 250 80 10 4.60 0.2121
WVFGRD96 32.0 250 80 10 4.62 0.2094
WVFGRD96 34.0 250 80 10 4.64 0.2065
WVFGRD96 36.0 250 85 10 4.67 0.2067
WVFGRD96 38.0 70 90 -10 4.71 0.2099
WVFGRD96 40.0 250 85 15 4.77 0.2242
WVFGRD96 42.0 250 85 15 4.79 0.2264
WVFGRD96 44.0 250 90 20 4.81 0.2305
WVFGRD96 46.0 250 90 15 4.83 0.2365
WVFGRD96 48.0 70 90 -15 4.85 0.2431
WVFGRD96 50.0 250 90 15 4.87 0.2502
WVFGRD96 52.0 250 90 15 4.89 0.2584
WVFGRD96 54.0 70 90 -15 4.90 0.2667
WVFGRD96 56.0 250 85 15 4.92 0.2801
WVFGRD96 58.0 250 85 15 4.93 0.2929
WVFGRD96 60.0 250 85 15 4.95 0.3055
WVFGRD96 62.0 250 90 10 4.96 0.3183
WVFGRD96 64.0 250 90 10 4.97 0.3313
WVFGRD96 66.0 70 90 -10 4.98 0.3437
WVFGRD96 68.0 70 85 -5 4.99 0.3557
WVFGRD96 70.0 75 75 5 4.99 0.3695
WVFGRD96 72.0 75 75 5 5.00 0.3820
WVFGRD96 74.0 75 70 10 5.00 0.3914
WVFGRD96 76.0 75 70 10 5.01 0.4012
WVFGRD96 78.0 75 70 10 5.01 0.4092
WVFGRD96 80.0 75 70 10 5.02 0.4175
WVFGRD96 82.0 75 70 10 5.03 0.4244
WVFGRD96 84.0 75 70 10 5.03 0.4318
WVFGRD96 86.0 75 70 15 5.03 0.4389
WVFGRD96 88.0 75 70 15 5.04 0.4452
WVFGRD96 90.0 75 70 15 5.05 0.4519
WVFGRD96 92.0 75 70 15 5.05 0.4574
WVFGRD96 94.0 75 70 15 5.05 0.4620
WVFGRD96 96.0 75 70 15 5.06 0.4669
WVFGRD96 98.0 75 70 15 5.06 0.4710
WVFGRD96 100.0 75 70 15 5.07 0.4747
WVFGRD96 102.0 80 65 20 5.07 0.4783
WVFGRD96 104.0 80 65 20 5.07 0.4817
WVFGRD96 106.0 80 65 20 5.07 0.4848
WVFGRD96 108.0 80 65 20 5.08 0.4879
WVFGRD96 110.0 80 65 20 5.08 0.4905
WVFGRD96 112.0 80 65 20 5.08 0.4925
WVFGRD96 114.0 80 65 20 5.09 0.4939
WVFGRD96 116.0 80 65 20 5.09 0.4948
WVFGRD96 118.0 80 65 25 5.09 0.4955
WVFGRD96 120.0 80 65 25 5.09 0.4964
WVFGRD96 122.0 80 65 25 5.09 0.4971
WVFGRD96 124.0 80 65 25 5.09 0.4971
WVFGRD96 126.0 80 65 25 5.10 0.4968
WVFGRD96 128.0 80 65 25 5.10 0.4957
WVFGRD96 130.0 80 65 25 5.10 0.4943
WVFGRD96 132.0 80 65 25 5.10 0.4926
WVFGRD96 134.0 80 65 25 5.10 0.4910
WVFGRD96 136.0 80 65 25 5.10 0.4899
WVFGRD96 138.0 80 65 25 5.10 0.4886
WVFGRD96 140.0 80 65 25 5.10 0.4866
WVFGRD96 142.0 80 65 25 5.10 0.4841
WVFGRD96 144.0 80 65 25 5.11 0.4814
WVFGRD96 146.0 80 65 25 5.11 0.4782
WVFGRD96 148.0 80 65 25 5.11 0.4743
The best solution is
WVFGRD96 124.0 80 65 25 5.09 0.4971
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/3.3 -30 o DIST/3.3 +70 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