The ANSS event ID is ak0119lvnlpb and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0119lvnlpb/executive.
2011/07/28 14:00:00 62.048 -151.303 86.5 5.3 Alaska
USGS/SLU Moment Tensor Solution
ENS 2011/07/28 14:00:00:0 62.05 -151.30 86.5 5.3 Alaska
Stations used:
AK.BAL AK.BMR AK.BRLK AK.CAST AK.CCB AK.CHUM AK.CNP AK.COLD
AK.CRQ AK.CTG AK.DHY AK.DIV AK.EYAK AK.FIB AK.FID AK.FYU
AK.GHO AK.HOM AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY
AK.PAX AK.PPLA AK.RAG AK.RC01 AK.RND AK.SAW AK.SCM AK.SSN
AK.SWD AK.TGL AK.TRF AK.WRH AT.MENT AT.OHAK AT.PMR AT.SVW2
IU.COLA US.EGAK
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 8.81e+23 dyne-cm
Mw = 5.23
Z = 84 km
Plane Strike Dip Rake
NP1 348 70 105
NP2 130 25 55
Principal Axes:
Axis Value Plunge Azimuth
T 8.81e+23 62 281
N 0.00e+00 14 162
P -8.81e+23 23 66
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.14e+23
Mxy -3.09e+23
Mxz -6.10e+22
Myy -4.39e+23
Myz -6.49e+23
Mzz 5.53e+23
###-----------
#########-------------
#############---------------
###############---------------
##################----------------
-###################----------------
-#####################---------- ---
--######################--------- P ----
--######################--------- ----
---########## ##########----------------
---########## T ##########----------------
----######### ##########----------------
----#######################---------------
----######################--------------
-----#####################--------------
-----####################-------------
------##################------------
-------################-----------
-------##############---------
----------##########------##
----------------######
------------##
Global CMT Convention Moment Tensor:
R T P
5.53e+23 -6.10e+22 6.49e+23
-6.10e+22 -1.14e+23 3.09e+23
6.49e+23 3.09e+23 -4.39e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110728140000/index.html
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STK = 130
DIP = 25
RAKE = 55
MW = 5.23
HS = 84.0
The NDK file is 20110728140000.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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 40 45 -70 4.34 0.2072
WVFGRD96 3.0 40 50 -60 4.50 0.2543
WVFGRD96 4.0 235 70 -45 4.49 0.2417
WVFGRD96 7.0 70 80 30 4.53 0.2689
WVFGRD96 9.0 70 75 35 4.58 0.2782
WVFGRD96 11.0 70 75 35 4.60 0.2832
WVFGRD96 13.0 75 70 35 4.61 0.2824
WVFGRD96 15.0 75 70 35 4.63 0.2798
WVFGRD96 17.0 80 70 30 4.64 0.2770
WVFGRD96 19.0 250 60 40 4.66 0.2759
WVFGRD96 21.0 250 65 35 4.68 0.2769
WVFGRD96 23.0 250 65 40 4.69 0.2777
WVFGRD96 25.0 250 65 35 4.71 0.2781
WVFGRD96 27.0 250 65 40 4.72 0.2777
WVFGRD96 29.0 250 65 40 4.74 0.2769
WVFGRD96 31.0 80 85 25 4.76 0.2787
WVFGRD96 33.0 80 80 20 4.78 0.2828
WVFGRD96 35.0 80 85 20 4.81 0.2901
WVFGRD96 37.0 80 85 20 4.83 0.2970
WVFGRD96 39.0 80 80 15 4.87 0.3051
WVFGRD96 41.0 75 40 -20 4.94 0.3044
WVFGRD96 43.0 80 45 -10 4.96 0.3084
WVFGRD96 45.0 85 40 0 4.98 0.3197
WVFGRD96 47.0 85 40 0 5.00 0.3327
WVFGRD96 49.0 90 40 5 5.02 0.3456
WVFGRD96 51.0 90 40 10 5.04 0.3597
WVFGRD96 53.0 90 35 10 5.06 0.3737
WVFGRD96 55.0 90 35 10 5.07 0.3875
WVFGRD96 57.0 95 35 20 5.09 0.4005
WVFGRD96 59.0 100 35 30 5.11 0.4147
WVFGRD96 61.0 100 35 30 5.12 0.4332
WVFGRD96 63.0 120 20 40 5.15 0.4511
WVFGRD96 65.0 125 20 50 5.17 0.4728
WVFGRD96 67.0 125 20 50 5.18 0.4924
WVFGRD96 69.0 125 20 50 5.19 0.5088
WVFGRD96 70.0 130 20 55 5.19 0.5161
WVFGRD96 71.0 130 20 55 5.20 0.5230
WVFGRD96 72.0 130 20 55 5.20 0.5288
WVFGRD96 73.0 130 20 55 5.20 0.5348
WVFGRD96 74.0 130 20 55 5.21 0.5391
WVFGRD96 75.0 130 20 55 5.21 0.5436
WVFGRD96 76.0 130 20 55 5.21 0.5469
WVFGRD96 77.0 125 25 50 5.21 0.5504
WVFGRD96 78.0 125 25 50 5.21 0.5534
WVFGRD96 79.0 125 25 50 5.22 0.5560
WVFGRD96 80.0 125 25 50 5.22 0.5578
WVFGRD96 81.0 130 25 55 5.22 0.5597
WVFGRD96 82.0 130 25 55 5.22 0.5609
WVFGRD96 83.0 130 25 55 5.22 0.5613
WVFGRD96 84.0 130 25 55 5.23 0.5619
WVFGRD96 85.0 130 25 55 5.23 0.5618
WVFGRD96 86.0 130 25 55 5.23 0.5616
WVFGRD96 87.0 130 25 55 5.23 0.5609
WVFGRD96 88.0 130 25 55 5.23 0.5598
WVFGRD96 89.0 130 25 55 5.23 0.5587
WVFGRD96 90.0 130 25 55 5.23 0.5566
WVFGRD96 91.0 130 25 55 5.23 0.5550
WVFGRD96 92.0 130 25 55 5.23 0.5530
WVFGRD96 93.0 130 25 55 5.23 0.5502
WVFGRD96 94.0 130 25 55 5.23 0.5482
WVFGRD96 95.0 130 25 55 5.23 0.5451
WVFGRD96 96.0 130 25 55 5.23 0.5423
WVFGRD96 97.0 130 25 55 5.23 0.5395
WVFGRD96 98.0 130 25 55 5.23 0.5360
WVFGRD96 99.0 130 25 55 5.23 0.5327
WVFGRD96 100.0 130 25 55 5.23 0.5296
WVFGRD96 101.0 130 25 55 5.23 0.5256
WVFGRD96 102.0 130 25 55 5.23 0.5226
WVFGRD96 103.0 135 25 60 5.23 0.5187
WVFGRD96 104.0 135 25 60 5.23 0.5152
WVFGRD96 105.0 135 25 60 5.23 0.5114
WVFGRD96 106.0 135 25 60 5.23 0.5085
WVFGRD96 107.0 135 25 60 5.23 0.5042
WVFGRD96 108.0 135 25 60 5.23 0.5017
WVFGRD96 109.0 135 25 60 5.23 0.4977
WVFGRD96 111.0 135 25 60 5.23 0.4906
WVFGRD96 113.0 135 25 60 5.23 0.4836
WVFGRD96 115.0 135 25 60 5.23 0.4769
WVFGRD96 117.0 125 30 55 5.23 0.4696
WVFGRD96 119.0 125 30 55 5.23 0.4631
WVFGRD96 121.0 135 25 65 5.23 0.4564
WVFGRD96 123.0 135 25 65 5.23 0.4497
WVFGRD96 125.0 135 25 65 5.22 0.4429
WVFGRD96 127.0 140 25 70 5.22 0.4361
WVFGRD96 129.0 140 25 70 5.22 0.4297
The best solution is
WVFGRD96 84.0 130 25 55 5.23 0.5619
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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 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