Location
Location ANSS
The ANSS event ID is ak022crtctc4 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak022crtctc4/executive.
2022/10/05 03:28:15 59.965 -152.919 117.6 4.6 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2022/10/05 03:28:15:0 59.97 -152.92 117.6 4.6 Alaska
Stations used:
AK.BRLK AK.CAPN AK.CNP AK.EYAK AK.GHO AK.GLI AK.K20K AK.KNK
AK.L17K AK.L19K AK.L20K AK.N18K AK.N19K AK.O18K AK.O19K
AK.P17K AK.P23K AK.PPLA AK.PWL AK.Q19K AK.RC01 AK.SLK
AK.SSN AK.SWD AT.OHAK AT.PMR AV.ACH AV.SPCP II.KDAK
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 0.10 n 3
Best Fitting Double Couple
Mo = 1.00e+23 dyne-cm
Mw = 4.60
Z = 122 km
Plane Strike Dip Rake
NP1 70 65 45
NP2 317 50 147
Principal Axes:
Axis Value Plunge Azimuth
T 1.00e+23 49 291
N 0.00e+00 40 93
P -1.00e+23 9 190
Moment Tensor: (dyne-cm)
Component Value
Mxx -8.90e+22
Mxy -3.17e+22
Mxz 3.25e+22
Myy 3.49e+22
Myz -4.36e+22
Mzz 5.42e+22
--------------
----------------------
----------------------------
############------------------
##################----------------
######################--------------
#########################-------------
############################-----------#
######### #################---------##
########## T ###################-----#####
########## ####################--#######
#################################-########
##############################----########
#########################---------######
#####################-------------######
----#######-----------------------####
---------------------------------###
--------------------------------##
-----------------------------#
----------------------------
------ -------------
-- P ---------
Global CMT Convention Moment Tensor:
R T P
5.42e+22 3.25e+22 4.36e+22
3.25e+22 -8.90e+22 3.17e+22
4.36e+22 3.17e+22 3.49e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20221005032815/index.html
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 70
DIP = 65
RAKE = 45
MW = 4.60
HS = 122.0
The NDK file is 20221005032815.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
| SLU |
USGSMWR |
USGS/SLU Moment Tensor Solution
ENS 2022/10/05 03:28:15:0 59.97 -152.92 117.6 4.6 Alaska
Stations used:
AK.BRLK AK.CAPN AK.CNP AK.EYAK AK.GHO AK.GLI AK.K20K AK.KNK
AK.L17K AK.L19K AK.L20K AK.N18K AK.N19K AK.O18K AK.O19K
AK.P17K AK.P23K AK.PPLA AK.PWL AK.Q19K AK.RC01 AK.SLK
AK.SSN AK.SWD AT.OHAK AT.PMR AV.ACH AV.SPCP II.KDAK
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 0.10 n 3
Best Fitting Double Couple
Mo = 1.00e+23 dyne-cm
Mw = 4.60
Z = 122 km
Plane Strike Dip Rake
NP1 70 65 45
NP2 317 50 147
Principal Axes:
Axis Value Plunge Azimuth
T 1.00e+23 49 291
N 0.00e+00 40 93
P -1.00e+23 9 190
Moment Tensor: (dyne-cm)
Component Value
Mxx -8.90e+22
Mxy -3.17e+22
Mxz 3.25e+22
Myy 3.49e+22
Myz -4.36e+22
Mzz 5.42e+22
--------------
----------------------
----------------------------
############------------------
##################----------------
######################--------------
#########################-------------
############################-----------#
######### #################---------##
########## T ###################-----#####
########## ####################--#######
#################################-########
##############################----########
#########################---------######
#####################-------------######
----#######-----------------------####
---------------------------------###
--------------------------------##
-----------------------------#
----------------------------
------ -------------
-- P ---------
Global CMT Convention Moment Tensor:
R T P
5.42e+22 3.25e+22 4.36e+22
3.25e+22 -8.90e+22 3.17e+22
4.36e+22 3.17e+22 3.49e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20221005032815/index.html
|
Regional Moment Tensor (Mwr)
Moment 9.949e+15 N-m
Magnitude 4.60 Mwr
Depth 114.0 km
Percent DC 92%
Half Duration -
Catalog US
Data Source US 3
Contributor US 3
Nodal Planes
Plane Strike Dip Rake
NP1 325 52 145
NP2 78 64 44
Principal Axes
Axis Value Plunge Azimuth
T 10.134e+15 N-m 49 297
N -0.381e+15 N-m 40 103
P -9.753e+15 N-m 7 199
|
Magnitudes
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.
ML Magnitude
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.
Context
The left panel of the next figure presents the focal mechanism for this earthquake (red) in the context of other nearby events (blue) in the SLU Moment Tensor Catalog. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors). Thus context plot is useful for assessing the appropriateness of the moment tensor of this event.
Waveform Inversion using wvfgrd96
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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Location of broadband stations used for waveform inversion
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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 0.10 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 105 45 -90 3.75 0.1532
WVFGRD96 4.0 325 80 35 3.72 0.1496
WVFGRD96 6.0 325 90 -35 3.77 0.1685
WVFGRD96 8.0 145 90 40 3.86 0.1832
WVFGRD96 10.0 145 85 35 3.90 0.1899
WVFGRD96 12.0 320 90 -35 3.93 0.1881
WVFGRD96 14.0 140 90 35 3.95 0.1799
WVFGRD96 16.0 140 90 35 3.97 0.1681
WVFGRD96 18.0 50 60 -5 4.00 0.1618
WVFGRD96 20.0 260 75 55 4.03 0.1668
WVFGRD96 22.0 255 70 50 4.07 0.1750
WVFGRD96 24.0 255 70 45 4.10 0.1836
WVFGRD96 26.0 255 70 45 4.13 0.1926
WVFGRD96 28.0 250 70 40 4.15 0.2003
WVFGRD96 30.0 250 70 40 4.17 0.2055
WVFGRD96 32.0 250 70 40 4.18 0.2047
WVFGRD96 34.0 245 75 35 4.19 0.2013
WVFGRD96 36.0 250 75 40 4.21 0.1989
WVFGRD96 38.0 60 80 -10 4.22 0.1946
WVFGRD96 40.0 250 75 45 4.33 0.2044
WVFGRD96 42.0 60 75 -5 4.31 0.2018
WVFGRD96 44.0 60 75 -5 4.34 0.2038
WVFGRD96 46.0 60 75 -10 4.36 0.2047
WVFGRD96 48.0 60 75 -10 4.38 0.2048
WVFGRD96 50.0 60 75 -10 4.39 0.2049
WVFGRD96 52.0 220 55 -20 4.41 0.2097
WVFGRD96 54.0 225 60 -20 4.42 0.2165
WVFGRD96 56.0 225 60 -20 4.43 0.2240
WVFGRD96 58.0 225 60 -20 4.44 0.2302
WVFGRD96 60.0 65 75 15 4.46 0.2422
WVFGRD96 62.0 70 70 30 4.48 0.2569
WVFGRD96 64.0 75 65 45 4.50 0.2713
WVFGRD96 66.0 75 65 45 4.51 0.2866
WVFGRD96 68.0 75 65 45 4.52 0.3017
WVFGRD96 70.0 75 65 45 4.53 0.3142
WVFGRD96 72.0 75 65 45 4.54 0.3267
WVFGRD96 74.0 75 65 45 4.54 0.3377
WVFGRD96 76.0 70 65 40 4.54 0.3484
WVFGRD96 78.0 70 65 40 4.55 0.3581
WVFGRD96 80.0 70 65 40 4.55 0.3658
WVFGRD96 82.0 70 65 40 4.56 0.3743
WVFGRD96 84.0 70 65 40 4.56 0.3816
WVFGRD96 86.0 70 65 40 4.57 0.3885
WVFGRD96 88.0 70 65 40 4.57 0.3949
WVFGRD96 90.0 70 65 40 4.57 0.4012
WVFGRD96 92.0 70 65 40 4.58 0.4069
WVFGRD96 94.0 70 65 40 4.58 0.4114
WVFGRD96 96.0 70 65 40 4.58 0.4159
WVFGRD96 98.0 70 65 45 4.58 0.4208
WVFGRD96 100.0 70 65 45 4.59 0.4256
WVFGRD96 102.0 70 65 45 4.59 0.4303
WVFGRD96 104.0 70 65 45 4.59 0.4347
WVFGRD96 106.0 70 65 45 4.59 0.4388
WVFGRD96 108.0 70 65 45 4.59 0.4421
WVFGRD96 110.0 70 65 45 4.60 0.4448
WVFGRD96 112.0 70 65 45 4.60 0.4469
WVFGRD96 114.0 70 65 45 4.60 0.4485
WVFGRD96 116.0 70 65 45 4.60 0.4493
WVFGRD96 118.0 70 65 45 4.60 0.4501
WVFGRD96 120.0 70 65 45 4.60 0.4510
WVFGRD96 122.0 70 65 45 4.60 0.4514
WVFGRD96 124.0 75 65 50 4.60 0.4513
WVFGRD96 126.0 75 65 50 4.60 0.4507
WVFGRD96 128.0 75 65 50 4.60 0.4501
WVFGRD96 130.0 75 65 50 4.60 0.4492
WVFGRD96 132.0 75 65 50 4.61 0.4478
WVFGRD96 134.0 75 65 50 4.61 0.4458
WVFGRD96 136.0 75 65 50 4.61 0.4448
WVFGRD96 138.0 75 65 55 4.61 0.4431
WVFGRD96 140.0 75 65 55 4.61 0.4409
WVFGRD96 142.0 75 65 55 4.61 0.4392
WVFGRD96 144.0 75 65 55 4.61 0.4367
WVFGRD96 146.0 75 65 55 4.61 0.4358
WVFGRD96 148.0 75 65 55 4.61 0.4336
The best solution is
WVFGRD96 122.0 70 65 45 4.60 0.4514
The mechanism corresponding to the best fit is
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Figure 1. Waveform inversion focal mechanism
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The best fit as a function of depth is given in the following figure:
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Figure 2. Depth sensitivity for waveform mechanism
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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 0.10 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.
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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:
- The origin time and epicentral distance are incorrect
- The velocity model used for the inversion is incorrect
- The velocity model used to define the P-arrival time is not the
same as the velocity model used for the waveform inversion
(assuming that the initial trace alignment is based on the
P arrival time)
Assuming only a mislocation, the time shifts are fit to a functional form:
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.
Velocity Model
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
Last Changed Thu Apr 25 01:19:06 AM CDT 2024
