The ANSS event ID is ak024gb66mji and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak024gb66mji/executive.
2024/12/20 04:03:22 60.357 -152.294 84.7 4.5 Alaska
USGS/SLU Moment Tensor Solution
ENS 2024/12/20 04:03:22:0 60.36 -152.29 84.7 4.5 Alaska
Stations used:
AK.BRLK AK.CAPN AK.CUT AK.FIRE AK.GHO AK.HOM AK.L19K
AK.L22K AK.M20K AK.N18K AK.N19K AK.O18K AK.O19K AK.P17K
AK.RC01 AK.SAW AK.SLK AK.SSN AK.SWD AT.PMR AV.ACH AV.RED
AV.STLK II.KDAK
Filtering commands used:
cut o DIST/3.3 -50 o DIST/3.3 +40
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 = 1.19e+23 dyne-cm
Mw = 4.65
Z = 112 km
Plane Strike Dip Rake
NP1 50 70 35
NP2 307 57 156
Principal Axes:
Axis Value Plunge Azimuth
T 1.19e+23 39 272
N 0.00e+00 50 76
P -1.19e+23 8 176
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.16e+23
Mxy 5.69e+21
Mxz 1.86e+22
Myy 7.20e+22
Myz -5.91e+22
Mzz 4.38e+22
--------------
----------------------
----------------------------
------------------------------
###########----------------------#
#################----------------###
#####################------------#####
#########################--------#######
###########################----#########
####### ####################-###########
####### T ###################---##########
####### ##################-----#########
##########################---------#######
######################-------------#####
####################---------------#####
################-------------------###
############----------------------##
#######---------------------------
------------------------------
----------------------------
----------- --------
------- P ----
Global CMT Convention Moment Tensor:
R T P
4.38e+22 1.86e+22 5.91e+22
1.86e+22 -1.16e+23 -5.69e+21
5.91e+22 -5.69e+21 7.20e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20241220040322/index.html
|
STK = 50
DIP = 70
RAKE = 35
MW = 4.65
HS = 112.0
The NDK file is 20241220040322.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.
 |
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.
|
|
|
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 -50 o DIST/3.3 +40 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 55 65 30 3.94 0.4263
WVFGRD96 4.0 235 65 25 4.00 0.4775
WVFGRD96 6.0 230 75 15 4.02 0.4990
WVFGRD96 8.0 225 65 -20 4.07 0.5176
WVFGRD96 10.0 225 70 -15 4.09 0.5273
WVFGRD96 12.0 225 75 -10 4.11 0.5255
WVFGRD96 14.0 225 80 5 4.12 0.5214
WVFGRD96 16.0 225 80 5 4.14 0.5170
WVFGRD96 18.0 225 80 5 4.16 0.5116
WVFGRD96 20.0 45 80 5 4.18 0.5084
WVFGRD96 22.0 45 80 5 4.20 0.5069
WVFGRD96 24.0 45 80 10 4.22 0.5066
WVFGRD96 26.0 45 80 10 4.23 0.5075
WVFGRD96 28.0 45 80 10 4.25 0.5102
WVFGRD96 30.0 45 80 10 4.27 0.5137
WVFGRD96 32.0 45 80 10 4.29 0.5178
WVFGRD96 34.0 45 85 10 4.31 0.5216
WVFGRD96 36.0 45 85 10 4.34 0.5256
WVFGRD96 38.0 45 85 10 4.37 0.5313
WVFGRD96 40.0 45 80 10 4.41 0.5438
WVFGRD96 42.0 45 80 10 4.43 0.5458
WVFGRD96 44.0 45 80 15 4.45 0.5471
WVFGRD96 46.0 45 80 15 4.46 0.5494
WVFGRD96 48.0 45 80 15 4.48 0.5523
WVFGRD96 50.0 45 80 15 4.49 0.5556
WVFGRD96 52.0 45 80 15 4.50 0.5586
WVFGRD96 54.0 45 80 15 4.51 0.5639
WVFGRD96 56.0 45 80 15 4.52 0.5692
WVFGRD96 58.0 45 80 20 4.53 0.5764
WVFGRD96 60.0 45 80 20 4.54 0.5837
WVFGRD96 62.0 45 80 20 4.54 0.5908
WVFGRD96 64.0 45 75 20 4.55 0.5968
WVFGRD96 66.0 45 75 20 4.56 0.6036
WVFGRD96 68.0 45 75 25 4.56 0.6099
WVFGRD96 70.0 45 75 25 4.57 0.6167
WVFGRD96 72.0 45 75 25 4.57 0.6227
WVFGRD96 74.0 50 70 30 4.58 0.6276
WVFGRD96 76.0 50 70 30 4.58 0.6331
WVFGRD96 78.0 50 70 30 4.59 0.6380
WVFGRD96 80.0 50 70 30 4.59 0.6423
WVFGRD96 82.0 50 70 30 4.59 0.6459
WVFGRD96 84.0 50 70 30 4.60 0.6491
WVFGRD96 86.0 50 70 30 4.60 0.6516
WVFGRD96 88.0 50 70 30 4.61 0.6545
WVFGRD96 90.0 50 70 30 4.61 0.6564
WVFGRD96 92.0 50 70 35 4.62 0.6587
WVFGRD96 94.0 50 75 35 4.62 0.6613
WVFGRD96 96.0 50 75 35 4.62 0.6629
WVFGRD96 98.0 50 75 35 4.62 0.6636
WVFGRD96 100.0 50 75 35 4.63 0.6642
WVFGRD96 102.0 50 75 35 4.63 0.6654
WVFGRD96 104.0 50 75 35 4.63 0.6661
WVFGRD96 106.0 50 75 35 4.64 0.6658
WVFGRD96 108.0 50 70 35 4.64 0.6656
WVFGRD96 110.0 50 70 35 4.64 0.6661
WVFGRD96 112.0 50 70 35 4.65 0.6661
WVFGRD96 114.0 50 70 35 4.65 0.6652
WVFGRD96 116.0 50 70 35 4.65 0.6646
WVFGRD96 118.0 50 70 35 4.65 0.6640
WVFGRD96 120.0 50 70 35 4.66 0.6629
WVFGRD96 122.0 50 70 35 4.66 0.6620
WVFGRD96 124.0 50 70 35 4.66 0.6609
WVFGRD96 126.0 50 70 35 4.67 0.6596
WVFGRD96 128.0 50 70 35 4.67 0.6580
WVFGRD96 130.0 50 70 35 4.67 0.6566
WVFGRD96 132.0 50 70 35 4.67 0.6548
WVFGRD96 134.0 50 70 35 4.68 0.6517
WVFGRD96 136.0 50 70 35 4.68 0.6505
WVFGRD96 138.0 50 70 35 4.68 0.6471
WVFGRD96 140.0 50 70 35 4.68 0.6448
WVFGRD96 142.0 50 70 35 4.69 0.6418
WVFGRD96 144.0 50 70 35 4.69 0.6382
WVFGRD96 146.0 50 70 35 4.69 0.6345
WVFGRD96 148.0 50 70 35 4.69 0.6296
The best solution is
WVFGRD96 112.0 50 70 35 4.65 0.6661
The mechanism corresponding to the best fit is
|
|
|
The best fit as a function of depth is given in the following figure:
|
|
|
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 -50 o DIST/3.3 +40 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
|
| 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. |
|
| 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. |
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