The ANSS event ID is ak0243eh222y and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0243eh222y/executive.
2024/03/14 05:52:30 62.838 -150.510 100.5 3.8 Alaska
USGS/SLU Moment Tensor Solution
ENS 2024/03/14 05:52:30:0 62.84 -150.51 100.5 3.8 Alaska
Stations used:
AK.BPAW AK.BRLK AK.H22K AK.M20K AK.MCK AK.NEA2 AK.PAX
AK.POKR AK.RND AK.SCM AK.TRF AK.WRH IU.COLA
Filtering commands used:
cut o DIST/3.4 -40 o DIST/3.4 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 1.35e+22 dyne-cm
Mw = 4.02
Z = 122 km
Plane Strike Dip Rake
NP1 105 85 35
NP2 12 55 174
Principal Axes:
Axis Value Plunge Azimuth
T 1.35e+22 28 334
N 0.00e+00 55 112
P -1.35e+22 20 233
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.25e+21
Mxy -9.87e+21
Mxz 7.61e+21
Myy -5.59e+21
Myz 1.04e+21
Mzz 1.34e+21
############--
#################-----
###### ############-------
####### T #############-------
######### #############---------
###########################---------
############################----------
#############################-----------
--###########################-----------
-------#######################------------
-------------#################------------
--------------------##########------------
---------------------------##-------------
----------------------------#######-----
---------------------------#############
---- -------------------############
--- P ------------------############
-- -----------------############
------------------############
----------------############
-----------###########
-----#########
Global CMT Convention Moment Tensor:
R T P
1.34e+21 7.61e+21 -1.04e+21
7.61e+21 4.25e+21 9.87e+21
-1.04e+21 9.87e+21 -5.59e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240314055230/index.html
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STK = 105
DIP = 85
RAKE = 35
MW = 4.02
HS = 122.0
The NDK file is 20240314055230.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/3.4 -40 o DIST/3.4 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 270 80 -40 3.23 0.3660
WVFGRD96 4.0 265 80 -60 3.39 0.4086
WVFGRD96 6.0 270 85 -50 3.36 0.4319
WVFGRD96 8.0 120 60 70 3.47 0.4505
WVFGRD96 10.0 110 60 55 3.45 0.4634
WVFGRD96 12.0 105 65 50 3.45 0.4646
WVFGRD96 14.0 100 70 40 3.44 0.4628
WVFGRD96 16.0 95 75 35 3.45 0.4597
WVFGRD96 18.0 95 75 35 3.46 0.4567
WVFGRD96 20.0 95 75 35 3.48 0.4531
WVFGRD96 22.0 85 35 -25 3.56 0.4548
WVFGRD96 24.0 85 35 -25 3.58 0.4564
WVFGRD96 26.0 90 35 -15 3.60 0.4574
WVFGRD96 28.0 90 35 -15 3.62 0.4563
WVFGRD96 30.0 90 40 -15 3.62 0.4536
WVFGRD96 32.0 85 40 -25 3.65 0.4501
WVFGRD96 34.0 100 50 25 3.65 0.4476
WVFGRD96 36.0 100 50 25 3.68 0.4506
WVFGRD96 38.0 100 60 30 3.69 0.4584
WVFGRD96 40.0 105 55 40 3.77 0.4685
WVFGRD96 42.0 75 35 -45 3.86 0.4711
WVFGRD96 44.0 75 40 -45 3.87 0.4743
WVFGRD96 46.0 75 40 -45 3.89 0.4773
WVFGRD96 48.0 75 40 -45 3.92 0.4815
WVFGRD96 50.0 75 45 -45 3.92 0.4860
WVFGRD96 52.0 75 45 -45 3.94 0.4912
WVFGRD96 54.0 75 45 -45 3.96 0.4953
WVFGRD96 56.0 75 45 -45 3.98 0.4985
WVFGRD96 58.0 75 45 -45 4.00 0.5020
WVFGRD96 60.0 80 50 -40 3.98 0.5054
WVFGRD96 62.0 80 50 -40 3.99 0.5092
WVFGRD96 64.0 80 50 -40 4.01 0.5122
WVFGRD96 66.0 80 50 -40 4.02 0.5143
WVFGRD96 68.0 80 55 -40 4.01 0.5168
WVFGRD96 70.0 80 55 -40 4.02 0.5203
WVFGRD96 72.0 80 55 -40 4.03 0.5229
WVFGRD96 74.0 105 60 15 3.97 0.5235
WVFGRD96 76.0 105 65 20 3.96 0.5294
WVFGRD96 78.0 105 65 20 3.97 0.5353
WVFGRD96 80.0 105 65 20 3.98 0.5403
WVFGRD96 82.0 105 65 20 3.99 0.5450
WVFGRD96 84.0 105 70 20 3.97 0.5486
WVFGRD96 86.0 105 70 25 3.98 0.5533
WVFGRD96 88.0 105 70 25 3.99 0.5572
WVFGRD96 90.0 105 70 25 4.00 0.5613
WVFGRD96 92.0 105 70 25 4.00 0.5645
WVFGRD96 94.0 105 75 25 3.98 0.5675
WVFGRD96 96.0 105 75 25 3.99 0.5705
WVFGRD96 98.0 105 75 25 4.00 0.5743
WVFGRD96 100.0 105 75 25 4.00 0.5770
WVFGRD96 102.0 105 75 25 4.00 0.5783
WVFGRD96 104.0 105 80 30 3.99 0.5802
WVFGRD96 106.0 105 80 30 4.00 0.5829
WVFGRD96 108.0 105 80 30 4.00 0.5843
WVFGRD96 110.0 105 80 30 4.01 0.5866
WVFGRD96 112.0 105 80 30 4.01 0.5873
WVFGRD96 114.0 105 80 30 4.01 0.5880
WVFGRD96 116.0 105 80 30 4.02 0.5885
WVFGRD96 118.0 105 85 35 4.01 0.5878
WVFGRD96 120.0 105 85 35 4.01 0.5889
WVFGRD96 122.0 105 85 35 4.02 0.5889
WVFGRD96 124.0 105 85 35 4.02 0.5884
WVFGRD96 126.0 105 85 30 4.01 0.5881
WVFGRD96 128.0 285 90 -35 4.00 0.5849
WVFGRD96 130.0 105 85 30 4.02 0.5867
WVFGRD96 132.0 105 85 30 4.02 0.5853
WVFGRD96 134.0 105 85 30 4.02 0.5843
WVFGRD96 136.0 285 90 -35 4.01 0.5825
WVFGRD96 138.0 285 90 -35 4.02 0.5818
WVFGRD96 140.0 105 90 35 4.02 0.5799
WVFGRD96 142.0 105 90 30 4.01 0.5794
WVFGRD96 144.0 105 90 30 4.01 0.5776
WVFGRD96 146.0 105 90 30 4.02 0.5767
WVFGRD96 148.0 285 90 -30 4.02 0.5746
The best solution is
WVFGRD96 122.0 105 85 35 4.02 0.5889
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/3.4 -40 o DIST/3.4 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3 br c 0.12 0.25 n 4 p 2
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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