Location
Location ANSS
The ANSS event ID is ak022cs4ljsx and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak022cs4ljsx/executive.
2022/10/05 22:16:48 62.972 -150.444 98.8 4.8 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2022/10/05 22:16:48:0 62.97 -150.44 98.8 4.8 Alaska
Stations used:
AK.BPAW AK.CAST AK.CCB AK.CUT AK.DHY AK.FID AK.GHO AK.H21K
AK.H22K AK.H23K AK.H24K AK.HDA AK.I21K AK.I23K AK.J19K
AK.J20K AK.J25K AK.K20K AK.K24K AK.KLU AK.KNK AK.L20K
AK.L22K AK.L26K AK.MCK AK.MLY AK.NEA2 AK.PAX AK.POKR
AK.PPLA AK.RC01 AK.RIDG AK.SAW AK.SCM AK.SKN AK.SSN AK.WRH
AT.PMR AV.SPCP AV.STLK IM.IL31 IU.COLA
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 0.10 n 3
Best Fitting Double Couple
Mo = 1.93e+23 dyne-cm
Mw = 4.79
Z = 114 km
Plane Strike Dip Rake
NP1 11 86 135
NP2 105 45 5
Principal Axes:
Axis Value Plunge Azimuth
T 1.93e+23 33 318
N 0.00e+00 45 188
P -1.93e+23 27 67
Moment Tensor: (dyne-cm)
Component Value
Mxx 5.22e+22
Mxy -1.22e+23
Mxz 3.51e+22
Myy -6.90e+22
Myz -1.31e+23
Mzz 1.68e+22
###########---
###############-------
##################----------
##################------------
###### ###########--------------
####### T ###########---------------
######## ##########----------- ---
######################----------- P ----
######################----------- ----
--####################--------------------
---###################--------------------
----##################--------------------
-----################---------------------
------##############--------------------
--------############-------------------#
----------########------------------##
-------------####--------------#####
---------------###################
-------------#################
-----------#################
--------##############
---###########
Global CMT Convention Moment Tensor:
R T P
1.68e+22 3.51e+22 1.31e+23
3.51e+22 5.22e+22 1.22e+23
1.31e+23 1.22e+23 -6.90e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20221005221648/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 = 105
DIP = 45
RAKE = 5
MW = 4.79
HS = 114.0
The NDK file is 20221005221648.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 22:16:48:0 62.97 -150.44 98.8 4.8 Alaska
Stations used:
AK.BPAW AK.CAST AK.CCB AK.CUT AK.DHY AK.FID AK.GHO AK.H21K
AK.H22K AK.H23K AK.H24K AK.HDA AK.I21K AK.I23K AK.J19K
AK.J20K AK.J25K AK.K20K AK.K24K AK.KLU AK.KNK AK.L20K
AK.L22K AK.L26K AK.MCK AK.MLY AK.NEA2 AK.PAX AK.POKR
AK.PPLA AK.RC01 AK.RIDG AK.SAW AK.SCM AK.SKN AK.SSN AK.WRH
AT.PMR AV.SPCP AV.STLK IM.IL31 IU.COLA
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 0.10 n 3
Best Fitting Double Couple
Mo = 1.93e+23 dyne-cm
Mw = 4.79
Z = 114 km
Plane Strike Dip Rake
NP1 11 86 135
NP2 105 45 5
Principal Axes:
Axis Value Plunge Azimuth
T 1.93e+23 33 318
N 0.00e+00 45 188
P -1.93e+23 27 67
Moment Tensor: (dyne-cm)
Component Value
Mxx 5.22e+22
Mxy -1.22e+23
Mxz 3.51e+22
Myy -6.90e+22
Myz -1.31e+23
Mzz 1.68e+22
###########---
###############-------
##################----------
##################------------
###### ###########--------------
####### T ###########---------------
######## ##########----------- ---
######################----------- P ----
######################----------- ----
--####################--------------------
---###################--------------------
----##################--------------------
-----################---------------------
------##############--------------------
--------############-------------------#
----------########------------------##
-------------####--------------#####
---------------###################
-------------#################
-----------#################
--------##############
---###########
Global CMT Convention Moment Tensor:
R T P
1.68e+22 3.51e+22 1.31e+23
3.51e+22 5.22e+22 1.22e+23
1.31e+23 1.22e+23 -6.90e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20221005221648/index.html
|
Regional Moment Tensor (Mwr)
Moment 2.149e+16 N-m
Magnitude 4.82 Mwr
Depth 106.0 km
Percent DC 95%
Half Duration -
Catalog US
Data Source US 2
Contributor US 2
Nodal Planes
Plane Strike Dip Rake
NP1 11 85 139
NP2 106 49 6
Principal Axes
Axis Value Plunge Azimuth
T 2.124e+16 N-m 32 320
N 0.051e+16 N-m 48 186
P -2.175e+16 N-m 24 66
|
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.
|
|
Location of broadband stations used for waveform inversion
|
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 0.10 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 5 65 -25 3.82 0.1721
WVFGRD96 4.0 10 75 15 3.89 0.1932
WVFGRD96 6.0 195 75 20 3.96 0.2118
WVFGRD96 8.0 190 75 20 4.04 0.2239
WVFGRD96 10.0 190 75 15 4.08 0.2257
WVFGRD96 12.0 190 80 15 4.12 0.2226
WVFGRD96 14.0 190 80 15 4.15 0.2165
WVFGRD96 16.0 190 85 15 4.17 0.2075
WVFGRD96 18.0 190 85 15 4.19 0.1958
WVFGRD96 20.0 275 75 -10 4.22 0.2009
WVFGRD96 22.0 275 70 -10 4.26 0.2176
WVFGRD96 24.0 275 75 -10 4.28 0.2346
WVFGRD96 26.0 275 75 -5 4.31 0.2512
WVFGRD96 28.0 275 75 -5 4.33 0.2674
WVFGRD96 30.0 275 75 -5 4.36 0.2839
WVFGRD96 32.0 100 90 0 4.36 0.3022
WVFGRD96 34.0 100 90 0 4.39 0.3240
WVFGRD96 36.0 100 85 0 4.41 0.3441
WVFGRD96 38.0 100 80 0 4.45 0.3636
WVFGRD96 40.0 100 75 0 4.50 0.3841
WVFGRD96 42.0 100 80 0 4.53 0.3886
WVFGRD96 44.0 100 75 5 4.55 0.3911
WVFGRD96 46.0 100 75 5 4.57 0.3923
WVFGRD96 48.0 100 75 0 4.58 0.3986
WVFGRD96 50.0 100 70 5 4.60 0.4049
WVFGRD96 52.0 100 70 0 4.61 0.4104
WVFGRD96 54.0 100 65 0 4.62 0.4185
WVFGRD96 56.0 100 65 0 4.63 0.4269
WVFGRD96 58.0 100 60 0 4.64 0.4365
WVFGRD96 60.0 100 60 0 4.65 0.4461
WVFGRD96 62.0 100 55 0 4.66 0.4561
WVFGRD96 64.0 100 55 0 4.67 0.4662
WVFGRD96 66.0 100 55 0 4.67 0.4756
WVFGRD96 68.0 100 55 0 4.68 0.4854
WVFGRD96 70.0 105 50 10 4.70 0.4945
WVFGRD96 72.0 105 50 10 4.70 0.5031
WVFGRD96 74.0 105 50 10 4.71 0.5097
WVFGRD96 76.0 105 50 10 4.72 0.5176
WVFGRD96 78.0 105 55 10 4.72 0.5256
WVFGRD96 80.0 105 55 10 4.73 0.5317
WVFGRD96 82.0 105 55 10 4.73 0.5389
WVFGRD96 84.0 105 55 10 4.74 0.5444
WVFGRD96 86.0 105 55 10 4.74 0.5510
WVFGRD96 88.0 105 55 10 4.75 0.5570
WVFGRD96 90.0 105 55 10 4.75 0.5604
WVFGRD96 92.0 105 55 10 4.75 0.5655
WVFGRD96 94.0 105 50 10 4.76 0.5696
WVFGRD96 96.0 105 50 10 4.76 0.5724
WVFGRD96 98.0 105 50 10 4.77 0.5767
WVFGRD96 100.0 105 50 10 4.77 0.5782
WVFGRD96 102.0 105 50 10 4.77 0.5804
WVFGRD96 104.0 105 45 10 4.78 0.5821
WVFGRD96 106.0 105 45 10 4.78 0.5828
WVFGRD96 108.0 105 45 5 4.78 0.5835
WVFGRD96 110.0 105 45 5 4.79 0.5853
WVFGRD96 112.0 105 45 5 4.79 0.5850
WVFGRD96 114.0 105 45 5 4.79 0.5862
WVFGRD96 116.0 105 45 5 4.79 0.5846
WVFGRD96 118.0 105 45 5 4.80 0.5856
WVFGRD96 120.0 105 45 5 4.80 0.5838
WVFGRD96 122.0 105 45 5 4.80 0.5836
WVFGRD96 124.0 105 45 5 4.80 0.5820
WVFGRD96 126.0 105 45 5 4.81 0.5810
WVFGRD96 128.0 105 45 5 4.81 0.5775
WVFGRD96 130.0 100 45 0 4.81 0.5750
WVFGRD96 132.0 100 45 0 4.81 0.5718
WVFGRD96 134.0 100 45 0 4.81 0.5691
WVFGRD96 136.0 100 45 0 4.81 0.5660
WVFGRD96 138.0 100 45 0 4.81 0.5643
WVFGRD96 140.0 100 45 0 4.82 0.5597
WVFGRD96 142.0 100 45 0 4.82 0.5576
WVFGRD96 144.0 100 45 0 4.82 0.5547
WVFGRD96 146.0 100 45 0 4.82 0.5522
WVFGRD96 148.0 100 45 0 4.82 0.5508
The best solution is
WVFGRD96 114.0 105 45 5 4.79 0.5862
The mechanism corresponding to the best fit is
|
|
Figure 1. Waveform inversion focal mechanism
|
The best fit as a function of depth is given in the following figure:
|
|
Figure 2. Depth sensitivity for waveform mechanism
|
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 0.10 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:
- 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 01:40:58 AM CDT 2024
