The ANSS event ID is ak0247ocufye and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0247ocufye/executive.
2024/06/15 10:24:03 63.317 -148.847 81.4 3.7 Alaska
USGS/SLU Moment Tensor Solution
ENS 2024/06/15 10:24:03:0 63.32 -148.85 81.4 3.7 Alaska
Stations used:
AK.CCB AK.CUT AK.GHO AK.H22K AK.HDA AK.I23K AK.J19K AK.K24K
AK.L22K AK.MCK AK.NEA2 AK.PAX AK.RIDG AK.SAW AK.SCM AK.WRH
AT.PMR IU.COLA
Filtering commands used:
cut o DIST/3.5 -40 o DIST/3.5 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
Best Fitting Double Couple
Mo = 4.47e+21 dyne-cm
Mw = 3.70
Z = 88 km
Plane Strike Dip Rake
NP1 90 60 50
NP2 329 48 138
Principal Axes:
Axis Value Plunge Azimuth
T 4.47e+21 55 307
N 0.00e+00 34 113
P -4.47e+21 7 207
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.96e+21
Mxy -2.49e+21
Mxz 1.71e+21
Myy -2.17e+14
Myz -1.44e+21
Mzz 2.96e+21
--------------
####------------------
############----------------
################--------------
####################--------------
#######################-------------
##########################------------
############ #############------------
############ T ##############-----------
############# ###############-----------
################################----------
-################################--------#
---##############################------###
------###########################-######
-----------##################----#######
--------------------------------######
-------------------------------#####
------------------------------####
---------------------------###
---- -------------------##
- P ------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.96e+21 1.71e+21 1.44e+21
1.71e+21 -2.96e+21 2.49e+21
1.44e+21 2.49e+21 -2.17e+14
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240615102403/index.html
|
STK = 90
DIP = 60
RAKE = 50
MW = 3.70
HS = 88.0
The NDK file is 20240615102403.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 -40 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 125 40 -85 2.86 0.1635
WVFGRD96 4.0 340 25 -25 2.92 0.1467
WVFGRD96 6.0 350 30 -10 2.93 0.1847
WVFGRD96 8.0 350 30 -10 3.01 0.2116
WVFGRD96 10.0 345 35 -20 3.04 0.2330
WVFGRD96 12.0 340 35 -25 3.06 0.2498
WVFGRD96 14.0 340 40 -30 3.10 0.2601
WVFGRD96 16.0 340 40 -25 3.11 0.2654
WVFGRD96 18.0 340 40 -25 3.13 0.2655
WVFGRD96 20.0 340 40 -25 3.15 0.2616
WVFGRD96 22.0 130 75 -45 3.21 0.2569
WVFGRD96 24.0 125 75 -50 3.21 0.2564
WVFGRD96 26.0 125 80 -45 3.24 0.2537
WVFGRD96 28.0 100 70 -45 3.27 0.2499
WVFGRD96 30.0 95 70 -45 3.29 0.2471
WVFGRD96 32.0 100 70 -40 3.32 0.2408
WVFGRD96 34.0 100 70 -40 3.34 0.2337
WVFGRD96 36.0 100 70 -35 3.37 0.2273
WVFGRD96 38.0 100 70 -35 3.39 0.2203
WVFGRD96 40.0 295 50 85 3.41 0.2346
WVFGRD96 42.0 115 40 85 3.45 0.2464
WVFGRD96 44.0 115 40 85 3.47 0.2555
WVFGRD96 46.0 100 45 55 3.53 0.2705
WVFGRD96 48.0 100 45 55 3.55 0.2885
WVFGRD96 50.0 100 45 55 3.57 0.3051
WVFGRD96 52.0 100 45 55 3.59 0.3215
WVFGRD96 54.0 95 55 55 3.60 0.3393
WVFGRD96 56.0 95 55 55 3.61 0.3620
WVFGRD96 58.0 95 55 55 3.63 0.3838
WVFGRD96 60.0 95 55 55 3.64 0.4038
WVFGRD96 62.0 90 60 50 3.65 0.4211
WVFGRD96 64.0 90 60 50 3.66 0.4373
WVFGRD96 66.0 90 60 50 3.67 0.4502
WVFGRD96 68.0 90 60 50 3.67 0.4626
WVFGRD96 70.0 95 60 50 3.68 0.4713
WVFGRD96 72.0 90 60 50 3.68 0.4797
WVFGRD96 74.0 90 60 50 3.69 0.4874
WVFGRD96 76.0 90 60 50 3.69 0.4919
WVFGRD96 78.0 90 60 45 3.70 0.4972
WVFGRD96 80.0 90 60 50 3.70 0.5005
WVFGRD96 82.0 90 60 45 3.71 0.5030
WVFGRD96 84.0 90 60 50 3.70 0.5052
WVFGRD96 86.0 90 60 50 3.70 0.5054
WVFGRD96 88.0 90 60 50 3.70 0.5070
WVFGRD96 90.0 90 60 50 3.70 0.5062
WVFGRD96 92.0 90 60 50 3.71 0.5067
WVFGRD96 94.0 90 60 50 3.71 0.5056
WVFGRD96 96.0 90 60 50 3.71 0.5046
WVFGRD96 98.0 90 60 50 3.71 0.5037
WVFGRD96 100.0 90 60 50 3.71 0.5027
WVFGRD96 102.0 90 60 50 3.71 0.4997
WVFGRD96 104.0 90 60 50 3.71 0.4990
WVFGRD96 106.0 90 60 50 3.71 0.4961
WVFGRD96 108.0 90 60 50 3.71 0.4947
WVFGRD96 110.0 100 60 50 3.72 0.4920
WVFGRD96 112.0 100 60 50 3.72 0.4903
WVFGRD96 114.0 100 60 50 3.72 0.4882
WVFGRD96 116.0 100 60 50 3.72 0.4860
WVFGRD96 118.0 100 60 50 3.72 0.4842
The best solution is
WVFGRD96 88.0 90 60 50 3.70 0.5070
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 -40 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 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