The ANSS event ID is ak0249ly3xrw and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0249ly3xrw/executive.
2024/07/27 18:12:14 60.312 -152.300 85.8 4.3 Alaska
USGS/SLU Moment Tensor Solution
ENS 2024/07/27 18:12:14:0 60.31 -152.30 85.8 4.3 Alaska
Stations used:
AK.BRLK AK.CUT AK.FIRE AK.GHO AK.HOM AK.KNK AK.L19K AK.L22K
AK.M20K AK.N18K AK.O18K AK.O19K AK.P23K AK.RC01 AK.SAW
AK.SLK AK.SWD AV.PLBL II.KDAK
Filtering commands used:
cut o DIST/3.5 -50 o DIST/3.5 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 5.75e+22 dyne-cm
Mw = 4.44
Z = 102 km
Plane Strike Dip Rake
NP1 304 64 146
NP2 50 60 30
Principal Axes:
Axis Value Plunge Azimuth
T 5.75e+22 41 265
N 0.00e+00 49 91
P -5.75e+22 3 358
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.71e+22
Mxy 4.78e+21
Mxz -5.00e+21
Myy 3.22e+22
Myz -2.83e+22
Mzz 2.49e+22
----- P ------
--------- ----------
----------------------------
------------------------------
---------------------------------#
############----------------------##
##################----------------####
######################------------######
#########################--------#######
############################-----#########
####### ####################--##########
####### T #####################-##########
####### ###################-----########
##########################--------######
########################-----------#####
#####################--------------###
#################------------------#
###########-----------------------
------------------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.49e+22 -5.00e+21 2.83e+22
-5.00e+21 -5.71e+22 -4.78e+21
2.83e+22 -4.78e+21 3.22e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240727181214/index.html
|
STK = 50
DIP = 60
RAKE = 30
MW = 4.44
HS = 102.0
The NDK file is 20240727181214.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/3.5 -50 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 300 60 -45 3.63 0.2457
WVFGRD96 4.0 315 65 5 3.65 0.2728
WVFGRD96 6.0 315 70 5 3.72 0.2932
WVFGRD96 8.0 315 70 10 3.80 0.2992
WVFGRD96 10.0 315 70 10 3.84 0.2978
WVFGRD96 12.0 315 70 5 3.87 0.2872
WVFGRD96 14.0 315 70 0 3.89 0.2690
WVFGRD96 16.0 315 70 -5 3.90 0.2454
WVFGRD96 18.0 225 90 20 3.92 0.2331
WVFGRD96 20.0 225 85 20 3.95 0.2347
WVFGRD96 22.0 225 85 20 3.97 0.2437
WVFGRD96 24.0 225 75 15 4.01 0.2693
WVFGRD96 26.0 225 75 15 4.04 0.2985
WVFGRD96 28.0 225 75 15 4.07 0.3272
WVFGRD96 30.0 225 75 15 4.09 0.3542
WVFGRD96 32.0 225 75 20 4.12 0.3766
WVFGRD96 34.0 225 75 20 4.14 0.3936
WVFGRD96 36.0 225 80 15 4.15 0.4021
WVFGRD96 38.0 225 85 10 4.18 0.4063
WVFGRD96 40.0 230 70 30 4.26 0.4209
WVFGRD96 42.0 45 90 -15 4.25 0.4131
WVFGRD96 44.0 45 90 -15 4.27 0.4087
WVFGRD96 46.0 45 90 -15 4.28 0.4030
WVFGRD96 48.0 45 75 15 4.30 0.4082
WVFGRD96 50.0 45 75 20 4.32 0.4139
WVFGRD96 52.0 45 75 20 4.33 0.4239
WVFGRD96 54.0 45 70 20 4.34 0.4318
WVFGRD96 56.0 45 70 25 4.35 0.4436
WVFGRD96 58.0 45 70 25 4.36 0.4515
WVFGRD96 60.0 45 70 25 4.36 0.4619
WVFGRD96 62.0 45 70 25 4.37 0.4713
WVFGRD96 64.0 45 70 25 4.37 0.4790
WVFGRD96 66.0 45 70 25 4.38 0.4842
WVFGRD96 68.0 45 70 25 4.38 0.4932
WVFGRD96 70.0 45 65 25 4.39 0.4998
WVFGRD96 72.0 45 65 25 4.39 0.5044
WVFGRD96 74.0 45 65 25 4.40 0.5102
WVFGRD96 76.0 45 65 25 4.40 0.5150
WVFGRD96 78.0 45 65 25 4.40 0.5193
WVFGRD96 80.0 45 65 25 4.41 0.5226
WVFGRD96 82.0 45 65 25 4.41 0.5254
WVFGRD96 84.0 45 65 25 4.41 0.5280
WVFGRD96 86.0 45 65 25 4.42 0.5292
WVFGRD96 88.0 45 65 25 4.42 0.5309
WVFGRD96 90.0 50 60 30 4.42 0.5341
WVFGRD96 92.0 50 60 30 4.43 0.5368
WVFGRD96 94.0 50 60 30 4.43 0.5382
WVFGRD96 96.0 50 60 30 4.43 0.5393
WVFGRD96 98.0 50 60 30 4.43 0.5386
WVFGRD96 100.0 50 60 30 4.44 0.5403
WVFGRD96 102.0 50 60 30 4.44 0.5415
WVFGRD96 104.0 50 60 30 4.44 0.5409
WVFGRD96 106.0 50 60 30 4.45 0.5381
WVFGRD96 108.0 50 60 30 4.45 0.5394
WVFGRD96 110.0 50 60 30 4.45 0.5404
WVFGRD96 112.0 50 60 30 4.46 0.5388
WVFGRD96 114.0 50 60 30 4.46 0.5389
WVFGRD96 116.0 50 60 30 4.46 0.5382
WVFGRD96 118.0 50 60 30 4.47 0.5349
WVFGRD96 120.0 50 60 30 4.47 0.5360
WVFGRD96 122.0 50 55 30 4.47 0.5353
WVFGRD96 124.0 50 55 30 4.47 0.5319
WVFGRD96 126.0 50 55 30 4.47 0.5323
WVFGRD96 128.0 50 55 30 4.48 0.5304
WVFGRD96 130.0 50 55 30 4.48 0.5286
WVFGRD96 132.0 50 55 30 4.48 0.5269
WVFGRD96 134.0 50 55 30 4.48 0.5247
WVFGRD96 136.0 50 55 30 4.49 0.5246
WVFGRD96 138.0 50 55 30 4.49 0.5207
WVFGRD96 140.0 50 55 30 4.49 0.5222
WVFGRD96 142.0 50 55 30 4.50 0.5193
WVFGRD96 144.0 50 55 30 4.50 0.5186
WVFGRD96 146.0 50 55 30 4.50 0.5177
WVFGRD96 148.0 50 55 30 4.50 0.5148
The best solution is
WVFGRD96 102.0 50 60 30 4.44 0.5415
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/3.5 -50 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3
|
| 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. |
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