Location
Location ANSS
The ANSS event ID is ak01439k6eg1 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak01439k6eg1/executive.
2014/03/12 08:43:35 59.288 -153.169 85.9 4.6 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2014/03/12 08:43:35:0 59.29 -153.17 85.9 4.6 Alaska
Stations used:
AK.BRLK AK.CNP AK.GHO AK.HOM AK.KNK AK.KTH AK.RC01 AK.SAW
AK.SCM AK.SII AK.SWD AT.OHAK AT.PMR AT.SVW2
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 = 1.32e+23 dyne-cm
Mw = 4.68
Z = 85 km
Plane Strike Dip Rake
NP1 65 75 45
NP2 320 47 159
Principal Axes:
Axis Value Plunge Azimuth
T 1.32e+23 42 293
N 0.00e+00 43 80
P -1.32e+23 17 187
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.07e+23
Mxy -4.00e+22
Mxz 6.30e+22
Myy 6.06e+22
Myz -5.60e+22
Mzz 4.66e+22
--------------
----------------------
#########-------------------
###############---------------
####################--------------
#######################-------------
##########################-----------#
####### ###################--------###
####### T ####################-----#####
######## #####################-#########
###############################--#########
############################------########
########################-----------#######
###################---------------######
##############--------------------######
######---------------------------#####
--------------------------------####
-------------------------------###
-----------------------------#
----------- -------------#
-------- P -----------
---- -------
Global CMT Convention Moment Tensor:
R T P
4.66e+22 6.30e+22 5.60e+22
6.30e+22 -1.07e+23 4.00e+22
5.60e+22 4.00e+22 6.06e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140312084335/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 = 65
DIP = 75
RAKE = 45
MW = 4.68
HS = 85.0
The NDK file is 20140312084335.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 2014/03/12 08:43:35:0 59.29 -153.17 85.9 4.6 Alaska
Stations used:
AK.BRLK AK.CNP AK.GHO AK.HOM AK.KNK AK.KTH AK.RC01 AK.SAW
AK.SCM AK.SII AK.SWD AT.OHAK AT.PMR AT.SVW2
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 = 1.32e+23 dyne-cm
Mw = 4.68
Z = 85 km
Plane Strike Dip Rake
NP1 65 75 45
NP2 320 47 159
Principal Axes:
Axis Value Plunge Azimuth
T 1.32e+23 42 293
N 0.00e+00 43 80
P -1.32e+23 17 187
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.07e+23
Mxy -4.00e+22
Mxz 6.30e+22
Myy 6.06e+22
Myz -5.60e+22
Mzz 4.66e+22
--------------
----------------------
#########-------------------
###############---------------
####################--------------
#######################-------------
##########################-----------#
####### ###################--------###
####### T ####################-----#####
######## #####################-#########
###############################--#########
############################------########
########################-----------#######
###################---------------######
##############--------------------######
######---------------------------#####
--------------------------------####
-------------------------------###
-----------------------------#
----------- -------------#
-------- P -----------
---- -------
Global CMT Convention Moment Tensor:
R T P
4.66e+22 6.30e+22 5.60e+22
6.30e+22 -1.07e+23 4.00e+22
5.60e+22 4.00e+22 6.06e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140312084335/index.html
|
Moment 1.20e+16 N-m
Magnitude 4.7
Percent DC 89%
Depth 79.0 km
Updated 2014-03-12 15:19:47 UTC
Author us
Catalog us
Contributor us
Code us_c000n8ry_mwr
Principal Axes
Axis Value Plunge Azimuth
T 1.233 32 292
N -0.067 53 78
P -1.166 17 191
Nodal Planes
Plane Strike Dip Rake
NP1 65 80 36
NP2 327 54 168
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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 0.5 340 80 -20 3.79 0.2283
WVFGRD96 1.0 165 85 5 3.81 0.2464
WVFGRD96 2.0 345 90 -10 3.92 0.3177
WVFGRD96 3.0 160 75 -15 3.96 0.3400
WVFGRD96 4.0 345 90 -15 3.99 0.3556
WVFGRD96 5.0 165 75 10 4.02 0.3670
WVFGRD96 6.0 165 75 10 4.04 0.3760
WVFGRD96 7.0 165 75 10 4.06 0.3804
WVFGRD96 8.0 255 85 -5 4.09 0.3966
WVFGRD96 9.0 255 85 -5 4.11 0.4125
WVFGRD96 10.0 80 90 10 4.15 0.4258
WVFGRD96 11.0 80 90 0 4.17 0.4388
WVFGRD96 12.0 80 90 0 4.18 0.4506
WVFGRD96 13.0 80 90 0 4.20 0.4612
WVFGRD96 14.0 255 90 0 4.20 0.4707
WVFGRD96 15.0 75 90 5 4.21 0.4794
WVFGRD96 16.0 75 90 0 4.22 0.4878
WVFGRD96 17.0 75 80 0 4.24 0.4975
WVFGRD96 18.0 75 80 0 4.25 0.5074
WVFGRD96 19.0 75 80 0 4.26 0.5171
WVFGRD96 20.0 75 80 0 4.27 0.5267
WVFGRD96 21.0 75 80 0 4.29 0.5357
WVFGRD96 22.0 75 80 0 4.30 0.5446
WVFGRD96 23.0 75 80 0 4.31 0.5540
WVFGRD96 24.0 75 80 0 4.32 0.5632
WVFGRD96 25.0 75 80 0 4.33 0.5726
WVFGRD96 26.0 75 80 0 4.34 0.5812
WVFGRD96 27.0 75 80 0 4.35 0.5889
WVFGRD96 28.0 75 80 0 4.36 0.5959
WVFGRD96 29.0 75 80 5 4.37 0.6027
WVFGRD96 30.0 75 80 5 4.38 0.6087
WVFGRD96 31.0 70 80 0 4.38 0.6145
WVFGRD96 32.0 70 80 0 4.39 0.6206
WVFGRD96 33.0 70 80 0 4.40 0.6258
WVFGRD96 34.0 70 80 0 4.41 0.6305
WVFGRD96 35.0 70 80 0 4.42 0.6351
WVFGRD96 36.0 70 80 0 4.43 0.6398
WVFGRD96 37.0 70 80 0 4.44 0.6440
WVFGRD96 38.0 70 80 0 4.46 0.6479
WVFGRD96 39.0 65 80 0 4.47 0.6513
WVFGRD96 40.0 65 75 -5 4.49 0.6554
WVFGRD96 41.0 65 75 -5 4.50 0.6561
WVFGRD96 42.0 65 75 -5 4.51 0.6565
WVFGRD96 43.0 65 75 -5 4.52 0.6569
WVFGRD96 44.0 65 75 -5 4.53 0.6576
WVFGRD96 45.0 65 75 -5 4.54 0.6582
WVFGRD96 46.0 65 75 5 4.54 0.6592
WVFGRD96 47.0 65 75 5 4.55 0.6608
WVFGRD96 48.0 65 75 5 4.55 0.6624
WVFGRD96 49.0 65 75 5 4.56 0.6639
WVFGRD96 50.0 65 75 5 4.57 0.6654
WVFGRD96 51.0 65 75 10 4.57 0.6669
WVFGRD96 52.0 65 80 15 4.58 0.6683
WVFGRD96 53.0 65 80 20 4.58 0.6700
WVFGRD96 54.0 65 80 20 4.59 0.6727
WVFGRD96 55.0 65 80 20 4.59 0.6749
WVFGRD96 56.0 65 80 20 4.60 0.6767
WVFGRD96 57.0 65 75 20 4.60 0.6783
WVFGRD96 58.0 65 80 25 4.61 0.6809
WVFGRD96 59.0 65 75 25 4.61 0.6841
WVFGRD96 60.0 65 75 25 4.62 0.6863
WVFGRD96 61.0 65 75 25 4.62 0.6872
WVFGRD96 62.0 65 75 30 4.63 0.6902
WVFGRD96 63.0 65 75 30 4.63 0.6932
WVFGRD96 64.0 65 75 30 4.63 0.6945
WVFGRD96 65.0 65 75 30 4.63 0.6963
WVFGRD96 66.0 65 75 35 4.64 0.6983
WVFGRD96 67.0 65 75 35 4.64 0.6995
WVFGRD96 68.0 65 75 35 4.65 0.7013
WVFGRD96 69.0 65 75 35 4.65 0.7028
WVFGRD96 70.0 65 75 35 4.65 0.7028
WVFGRD96 71.0 65 75 40 4.66 0.7056
WVFGRD96 72.0 65 75 40 4.66 0.7061
WVFGRD96 73.0 65 75 40 4.66 0.7061
WVFGRD96 74.0 65 75 40 4.66 0.7082
WVFGRD96 75.0 65 75 40 4.66 0.7073
WVFGRD96 76.0 65 75 40 4.66 0.7092
WVFGRD96 77.0 65 75 40 4.66 0.7092
WVFGRD96 78.0 65 75 40 4.66 0.7094
WVFGRD96 79.0 65 75 45 4.67 0.7102
WVFGRD96 80.0 65 75 45 4.67 0.7100
WVFGRD96 81.0 65 75 45 4.67 0.7100
WVFGRD96 82.0 65 75 45 4.68 0.7098
WVFGRD96 83.0 65 75 45 4.68 0.7106
WVFGRD96 84.0 65 75 45 4.68 0.7092
WVFGRD96 85.0 65 75 45 4.68 0.7106
WVFGRD96 86.0 65 75 45 4.68 0.7086
WVFGRD96 87.0 65 75 45 4.68 0.7101
WVFGRD96 88.0 65 75 45 4.68 0.7077
WVFGRD96 89.0 65 75 45 4.68 0.7096
WVFGRD96 90.0 65 75 45 4.68 0.7072
WVFGRD96 91.0 65 75 45 4.68 0.7086
WVFGRD96 92.0 65 75 50 4.69 0.7071
WVFGRD96 93.0 65 75 50 4.69 0.7072
WVFGRD96 94.0 65 75 50 4.69 0.7066
WVFGRD96 95.0 65 75 50 4.69 0.7062
WVFGRD96 96.0 65 75 50 4.69 0.7059
WVFGRD96 97.0 65 75 50 4.69 0.7048
WVFGRD96 98.0 65 75 50 4.69 0.7048
WVFGRD96 99.0 65 75 50 4.69 0.7030
The best solution is
WVFGRD96 85.0 65 75 45 4.68 0.7106
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 03:46:36 PM CDT 2024
