Location
Location ANSS
The ANSS event ID is ak019gjee93 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak019gjee93/executive.
2019/01/10 00:04:31 61.449 -149.883 32.3 4 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2019/01/10 00:04:31:0 61.45 -149.88 32.3 4.0 Alaska
Stations used:
AK.FID AK.FIRE AK.GHO AK.KLU AK.KNK AK.KTH AK.PPLA AK.PWL
AK.RC01 AK.RND AK.SAW AK.SKN AK.SLK AK.SWD AT.PMR AV.STLK
TA.M20K TA.M22K TA.N25K
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 0.08 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 1.35e+22 dyne-cm
Mw = 4.02
Z = 47 km
Plane Strike Dip Rake
NP1 165 55 -70
NP2 313 40 -116
Principal Axes:
Axis Value Plunge Azimuth
T 1.35e+22 8 241
N 0.00e+00 16 333
P -1.35e+22 72 126
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.69e+21
Mxy 6.25e+21
Mxz 1.43e+21
Myy 9.22e+21
Myz -4.87e+21
Mzz -1.19e+22
-#############
----##################
-------#####################
######----------##############
########--------------############
#########----------------###########
#########-------------------##########
##########---------------------#########
##########----------------------########
############-----------------------#######
############-----------------------#######
############----------- ----------######
#############---------- P -----------#####
############---------- -----------####
#############-----------------------####
# #########----------------------###
T ##########---------------------##
###########--------------------#
############------------------
#############---------------
############----------
###########---
Global CMT Convention Moment Tensor:
R T P
-1.19e+22 1.43e+21 4.87e+21
1.43e+21 2.69e+21 -6.25e+21
4.87e+21 -6.25e+21 9.22e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190110000431/index.html
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Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 165
DIP = 55
RAKE = -70
MW = 4.02
HS = 47.0
The NDK file is 20190110000431.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 2019/01/10 00:04:31:0 61.45 -149.88 32.3 4.0 Alaska
Stations used:
AK.FID AK.FIRE AK.GHO AK.KLU AK.KNK AK.KTH AK.PPLA AK.PWL
AK.RC01 AK.RND AK.SAW AK.SKN AK.SLK AK.SWD AT.PMR AV.STLK
TA.M20K TA.M22K TA.N25K
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 0.08 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 1.35e+22 dyne-cm
Mw = 4.02
Z = 47 km
Plane Strike Dip Rake
NP1 165 55 -70
NP2 313 40 -116
Principal Axes:
Axis Value Plunge Azimuth
T 1.35e+22 8 241
N 0.00e+00 16 333
P -1.35e+22 72 126
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.69e+21
Mxy 6.25e+21
Mxz 1.43e+21
Myy 9.22e+21
Myz -4.87e+21
Mzz -1.19e+22
-#############
----##################
-------#####################
######----------##############
########--------------############
#########----------------###########
#########-------------------##########
##########---------------------#########
##########----------------------########
############-----------------------#######
############-----------------------#######
############----------- ----------######
#############---------- P -----------#####
############---------- -----------####
#############-----------------------####
# #########----------------------###
T ##########---------------------##
###########--------------------#
############------------------
#############---------------
############----------
###########---
Global CMT Convention Moment Tensor:
R T P
-1.19e+22 1.43e+21 4.87e+21
1.43e+21 2.69e+21 -6.25e+21
4.87e+21 -6.25e+21 9.22e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190110000431/index.html
|
Regional Moment Tensor (Mwr)
Moment 8.070e+14 N-m
Magnitude 3.87 Mwr
Depth 38.0 km
Percent DC 90%
Half Duration -
Catalog US
Data Source US 3
Contributor US 3
Nodal Planes
Plane Strike Dip Rake
NP1 313 41 -129
NP2 180 60 -61
Principal Axes
Axis Value Plunge Azimuth
T 8.278e+14 N-m 10 250
N -0.435e+14 N-m 25 345
P -7.844e+14 N-m 63 139
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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 0.08 n 3
br c 0.12 0.25 n 4 p 2
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 325 45 90 3.25 0.2519
WVFGRD96 2.0 145 45 95 3.42 0.3823
WVFGRD96 3.0 325 45 90 3.47 0.3683
WVFGRD96 4.0 140 50 -90 3.51 0.3438
WVFGRD96 5.0 345 40 -50 3.52 0.3515
WVFGRD96 6.0 15 65 50 3.50 0.3621
WVFGRD96 7.0 15 60 45 3.51 0.3753
WVFGRD96 8.0 345 35 -50 3.59 0.3773
WVFGRD96 9.0 25 35 25 3.58 0.3788
WVFGRD96 10.0 25 40 30 3.58 0.3905
WVFGRD96 11.0 25 40 30 3.59 0.3999
WVFGRD96 12.0 20 45 25 3.59 0.4088
WVFGRD96 13.0 25 45 30 3.60 0.4167
WVFGRD96 14.0 25 45 30 3.61 0.4228
WVFGRD96 15.0 25 45 25 3.62 0.4277
WVFGRD96 16.0 25 45 25 3.62 0.4322
WVFGRD96 17.0 20 50 25 3.62 0.4361
WVFGRD96 18.0 20 50 25 3.63 0.4391
WVFGRD96 19.0 25 45 20 3.65 0.4415
WVFGRD96 20.0 165 35 -45 3.68 0.4497
WVFGRD96 21.0 165 35 -45 3.70 0.4584
WVFGRD96 22.0 165 35 -45 3.71 0.4668
WVFGRD96 23.0 170 40 -40 3.71 0.4757
WVFGRD96 24.0 165 40 -50 3.72 0.4844
WVFGRD96 25.0 165 40 -50 3.73 0.4934
WVFGRD96 26.0 165 40 -50 3.74 0.5019
WVFGRD96 27.0 165 40 -50 3.75 0.5097
WVFGRD96 28.0 170 45 -45 3.76 0.5189
WVFGRD96 29.0 170 45 -45 3.77 0.5289
WVFGRD96 30.0 170 45 -45 3.78 0.5384
WVFGRD96 31.0 165 45 -50 3.78 0.5474
WVFGRD96 32.0 165 45 -50 3.79 0.5553
WVFGRD96 33.0 170 50 -50 3.80 0.5631
WVFGRD96 34.0 170 50 -50 3.81 0.5710
WVFGRD96 35.0 170 50 -55 3.82 0.5780
WVFGRD96 36.0 170 50 -55 3.84 0.5841
WVFGRD96 37.0 165 50 -60 3.85 0.5895
WVFGRD96 38.0 165 50 -60 3.86 0.5928
WVFGRD96 39.0 165 50 -60 3.88 0.5953
WVFGRD96 40.0 160 50 -65 3.96 0.5973
WVFGRD96 41.0 160 50 -65 3.97 0.6055
WVFGRD96 42.0 160 50 -65 3.98 0.6112
WVFGRD96 43.0 160 50 -65 3.99 0.6160
WVFGRD96 44.0 170 55 -65 4.00 0.6193
WVFGRD96 45.0 170 55 -65 4.01 0.6218
WVFGRD96 46.0 165 55 -70 4.02 0.6233
WVFGRD96 47.0 165 55 -70 4.02 0.6238
WVFGRD96 48.0 165 55 -70 4.03 0.6236
WVFGRD96 49.0 165 55 -70 4.04 0.6223
WVFGRD96 50.0 165 55 -70 4.04 0.6202
WVFGRD96 51.0 165 55 -70 4.05 0.6171
WVFGRD96 52.0 165 55 -70 4.05 0.6136
WVFGRD96 53.0 165 55 -70 4.05 0.6090
WVFGRD96 54.0 165 55 -70 4.06 0.6043
WVFGRD96 55.0 165 55 -70 4.06 0.5985
WVFGRD96 56.0 165 55 -70 4.06 0.5920
WVFGRD96 57.0 165 55 -65 4.06 0.5863
WVFGRD96 58.0 165 55 -65 4.07 0.5789
WVFGRD96 59.0 165 55 -65 4.07 0.5720
The best solution is
WVFGRD96 47.0 165 55 -70 4.02 0.6238
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 0.08 n 3
br c 0.12 0.25 n 4 p 2
|
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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 07:46:51 AM CDT 2024
