Location
Location ANSS
The ANSS event ID is ak014gluxf3 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak014gluxf3/executive.
2014/01/10 04:17:37 62.236 -149.337 42.7 3.8 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2014/01/10 04:17:37:0 62.24 -149.34 42.7 3.8 Alaska
Stations used:
AK.DHY AK.FIRE AK.KNK AK.KTH AK.PAX AK.PPLA AK.RND AK.SAW
AK.SKN AK.SSN AK.WAT1 AK.WAT4 AK.WAT6 AK.WAT7 AT.PMR
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.40e+22 dyne-cm
Mw = 4.03
Z = 60 km
Plane Strike Dip Rake
NP1 210 60 -75
NP2 2 33 -114
Principal Axes:
Axis Value Plunge Azimuth
T 1.40e+22 14 289
N 0.00e+00 13 22
P -1.40e+22 71 154
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.10e+20
Mxy -3.49e+21
Mxz 4.94e+21
Myy 1.15e+22
Myz -4.94e+21
Mzz -1.17e+22
###########---
#################---##
###################---######
#################--------#####
#################-----------######
################--------------######
############-----------------######
# T ###########------------------#######
# ##########--------------------######
##############---------------------#######
#############----------------------#######
############-----------------------#######
###########----------- ----------#######
##########----------- P ---------#######
#########------------ ---------#######
########-----------------------#######
#######-----------------------######
######----------------------######
####--------------------######
###-------------------######
-----------------#####
----------####
Global CMT Convention Moment Tensor:
R T P
-1.17e+22 4.94e+21 4.94e+21
4.94e+21 2.10e+20 3.49e+21
4.94e+21 3.49e+21 1.15e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140110041737/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 = 210
DIP = 60
RAKE = -75
MW = 4.03
HS = 60.0
The NDK file is 20140110041737.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 |
USGSMT |
USGS/SLU Moment Tensor Solution
ENS 2014/01/10 04:17:37:0 62.24 -149.34 42.7 3.8 Alaska
Stations used:
AK.DHY AK.FIRE AK.KNK AK.KTH AK.PAX AK.PPLA AK.RND AK.SAW
AK.SKN AK.SSN AK.WAT1 AK.WAT4 AK.WAT6 AK.WAT7 AT.PMR
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.40e+22 dyne-cm
Mw = 4.03
Z = 60 km
Plane Strike Dip Rake
NP1 210 60 -75
NP2 2 33 -114
Principal Axes:
Axis Value Plunge Azimuth
T 1.40e+22 14 289
N 0.00e+00 13 22
P -1.40e+22 71 154
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.10e+20
Mxy -3.49e+21
Mxz 4.94e+21
Myy 1.15e+22
Myz -4.94e+21
Mzz -1.17e+22
###########---
#################---##
###################---######
#################--------#####
#################-----------######
################--------------######
############-----------------######
# T ###########------------------#######
# ##########--------------------######
##############---------------------#######
#############----------------------#######
############-----------------------#######
###########----------- ----------#######
##########----------- P ---------#######
#########------------ ---------#######
########-----------------------#######
#######-----------------------######
######----------------------######
####--------------------######
###-------------------######
-----------------#####
----------####
Global CMT Convention Moment Tensor:
R T P
-1.17e+22 4.94e+21 4.94e+21
4.94e+21 2.10e+20 3.49e+21
4.94e+21 3.49e+21 1.15e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140110041737/index.html
|
Moment
1.51e+15 N-m
Magnitude
4.1
Percent DC
80%
Depth
59.0 km
Updated
2014-01-10 15:02:47 UTC
Author
us
Catalog
ak
Contributor
us
Code
us_c000lztg_mwr
Principal Axes
Axis Value Plunge Azimuth
T 1.437 14 289
N 0.137 13 23
P -1.573 70 155
Nodal Planes
Plane Strike Dip Rake
NP1 210 60 -75
NP2 1 33 -115
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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 a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 5 45 90 3.23 0.1844
WVFGRD96 1.0 185 45 90 3.26 0.1807
WVFGRD96 2.0 5 45 90 3.38 0.2391
WVFGRD96 3.0 5 45 90 3.43 0.2365
WVFGRD96 4.0 100 80 25 3.39 0.2221
WVFGRD96 5.0 95 90 30 3.42 0.2309
WVFGRD96 6.0 95 90 30 3.44 0.2406
WVFGRD96 7.0 275 85 -30 3.46 0.2522
WVFGRD96 8.0 260 80 -30 3.49 0.2604
WVFGRD96 9.0 255 70 -30 3.51 0.2711
WVFGRD96 10.0 225 75 -45 3.50 0.2811
WVFGRD96 11.0 225 75 -45 3.51 0.2943
WVFGRD96 12.0 225 70 -45 3.53 0.3066
WVFGRD96 13.0 225 70 -45 3.54 0.3177
WVFGRD96 14.0 225 70 -40 3.55 0.3289
WVFGRD96 15.0 225 70 -40 3.56 0.3395
WVFGRD96 16.0 225 70 -40 3.57 0.3490
WVFGRD96 17.0 225 70 -40 3.58 0.3587
WVFGRD96 18.0 225 70 -40 3.59 0.3679
WVFGRD96 19.0 225 70 -40 3.60 0.3766
WVFGRD96 20.0 225 70 -40 3.61 0.3848
WVFGRD96 21.0 225 70 -40 3.62 0.3914
WVFGRD96 22.0 225 70 -45 3.64 0.3987
WVFGRD96 23.0 225 70 -45 3.64 0.4057
WVFGRD96 24.0 225 70 -45 3.65 0.4120
WVFGRD96 25.0 225 70 -45 3.66 0.4180
WVFGRD96 26.0 225 70 -45 3.67 0.4234
WVFGRD96 27.0 225 70 -45 3.68 0.4281
WVFGRD96 28.0 225 70 -45 3.69 0.4320
WVFGRD96 29.0 225 70 -45 3.69 0.4355
WVFGRD96 30.0 225 70 -45 3.70 0.4384
WVFGRD96 31.0 225 70 -45 3.71 0.4405
WVFGRD96 32.0 225 70 -45 3.72 0.4418
WVFGRD96 33.0 225 70 -45 3.72 0.4427
WVFGRD96 34.0 220 70 -50 3.73 0.4441
WVFGRD96 35.0 220 70 -50 3.74 0.4455
WVFGRD96 36.0 220 70 -50 3.75 0.4471
WVFGRD96 37.0 220 70 -50 3.75 0.4489
WVFGRD96 38.0 220 70 -50 3.76 0.4502
WVFGRD96 39.0 220 65 -50 3.78 0.4517
WVFGRD96 40.0 220 70 -60 3.87 0.4504
WVFGRD96 41.0 220 70 -60 3.88 0.4545
WVFGRD96 42.0 215 65 -65 3.90 0.4595
WVFGRD96 43.0 220 65 -60 3.90 0.4651
WVFGRD96 44.0 215 60 -65 3.92 0.4710
WVFGRD96 45.0 215 60 -65 3.93 0.4776
WVFGRD96 46.0 215 60 -65 3.94 0.4840
WVFGRD96 47.0 215 60 -65 3.95 0.4896
WVFGRD96 48.0 215 60 -65 3.95 0.4945
WVFGRD96 49.0 210 60 -70 3.97 0.5007
WVFGRD96 50.0 210 60 -70 3.97 0.5068
WVFGRD96 51.0 210 60 -70 3.98 0.5125
WVFGRD96 52.0 210 60 -70 3.99 0.5173
WVFGRD96 53.0 210 60 -75 4.00 0.5219
WVFGRD96 54.0 210 60 -75 4.01 0.5260
WVFGRD96 55.0 210 60 -75 4.01 0.5290
WVFGRD96 56.0 210 60 -75 4.02 0.5315
WVFGRD96 57.0 210 60 -75 4.02 0.5334
WVFGRD96 58.0 210 60 -75 4.02 0.5346
WVFGRD96 59.0 210 60 -75 4.03 0.5350
WVFGRD96 60.0 210 60 -75 4.03 0.5351
WVFGRD96 61.0 210 60 -75 4.03 0.5345
WVFGRD96 62.0 210 60 -75 4.03 0.5330
WVFGRD96 63.0 210 60 -75 4.04 0.5312
WVFGRD96 64.0 210 60 -75 4.04 0.5288
WVFGRD96 65.0 210 60 -75 4.04 0.5255
WVFGRD96 66.0 210 60 -75 4.04 0.5222
WVFGRD96 67.0 210 60 -75 4.04 0.5185
WVFGRD96 68.0 210 60 -75 4.04 0.5136
WVFGRD96 69.0 210 60 -75 4.04 0.5095
WVFGRD96 70.0 215 65 -75 4.04 0.5045
WVFGRD96 71.0 215 65 -75 4.04 0.5002
WVFGRD96 72.0 215 65 -70 4.03 0.4961
WVFGRD96 73.0 215 65 -70 4.03 0.4916
WVFGRD96 74.0 215 65 -70 4.03 0.4867
WVFGRD96 75.0 210 65 -75 4.04 0.4821
WVFGRD96 76.0 210 65 -75 4.03 0.4780
WVFGRD96 77.0 210 65 -75 4.03 0.4740
WVFGRD96 78.0 210 65 -75 4.03 0.4695
WVFGRD96 79.0 215 70 -80 4.04 0.4655
WVFGRD96 80.0 215 70 -80 4.04 0.4621
WVFGRD96 81.0 215 70 -80 4.04 0.4586
WVFGRD96 82.0 215 70 -80 4.04 0.4550
WVFGRD96 83.0 215 70 -80 4.04 0.4511
WVFGRD96 84.0 215 70 -80 4.04 0.4474
WVFGRD96 85.0 215 70 -80 4.04 0.4432
WVFGRD96 86.0 215 70 -80 4.04 0.4394
WVFGRD96 87.0 215 70 -80 4.04 0.4350
WVFGRD96 88.0 215 70 -80 4.03 0.4311
WVFGRD96 89.0 215 70 -80 4.03 0.4268
WVFGRD96 90.0 215 70 -80 4.03 0.4227
WVFGRD96 91.0 215 70 -80 4.03 0.4184
WVFGRD96 92.0 220 70 -75 4.03 0.4146
WVFGRD96 93.0 220 70 -75 4.03 0.4106
WVFGRD96 94.0 210 65 -80 4.03 0.4076
WVFGRD96 95.0 210 65 -80 4.03 0.4044
WVFGRD96 96.0 210 65 -80 4.02 0.4018
WVFGRD96 97.0 210 65 -80 4.02 0.3987
WVFGRD96 98.0 210 65 -80 4.02 0.3959
WVFGRD96 99.0 210 65 -80 4.02 0.3929
The best solution is
WVFGRD96 60.0 210 60 -75 4.03 0.5351
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 a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 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 Fri Apr 26 02:39:18 PM CDT 2024
