Location
Location ANSS
The ANSS event ID is ak01434q4y01 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak01434q4y01/executive.
2014/03/09 16:11:23 61.030 -150.686 55.3 3.7 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2014/03/09 16:11:23:0 61.03 -150.69 55.3 3.7 Alaska
Stations used:
AK.CRQ AK.DHY AK.GLB AK.GLI AK.KNK AK.MCK AK.RC01 AK.SAW
AK.SCM AK.SKN AK.SSN AK.TGL AT.MENT 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 = 1.02e+22 dyne-cm
Mw = 3.94
Z = 58 km
Plane Strike Dip Rake
NP1 190 75 -80
NP2 336 18 -123
Principal Axes:
Axis Value Plunge Azimuth
T 1.02e+22 29 272
N 0.00e+00 10 7
P -1.02e+22 59 114
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.35e+20
Mxy 7.51e+20
Mxz 1.97e+21
Myy 5.47e+21
Myz -8.51e+21
Mzz -5.04e+21
-#####----####
#############----#####
###############--------#####
###############-----------####
################--------------####
#################---------------####
#################-----------------####
#################-------------------####
#################--------------------###
##### ##########--------------------####
##### T #########---------------------####
##### #########---------- ---------###
#################---------- P ---------###
###############----------- --------###
###############----------------------###
##############----------------------##
#############---------------------##
############--------------------##
##########-------------------#
#########-----------------##
#######--------------#
###-----------
Global CMT Convention Moment Tensor:
R T P
-5.04e+21 1.97e+21 8.51e+21
1.97e+21 -4.35e+20 -7.51e+20
8.51e+21 -7.51e+20 5.47e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140309161123/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 = 190
DIP = 75
RAKE = -80
MW = 3.94
HS = 58.0
The NDK file is 20140309161123.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 2014/03/09 16:11:23:0 61.03 -150.69 55.3 3.7 Alaska
Stations used:
AK.CRQ AK.DHY AK.GLB AK.GLI AK.KNK AK.MCK AK.RC01 AK.SAW
AK.SCM AK.SKN AK.SSN AK.TGL AT.MENT 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 = 1.02e+22 dyne-cm
Mw = 3.94
Z = 58 km
Plane Strike Dip Rake
NP1 190 75 -80
NP2 336 18 -123
Principal Axes:
Axis Value Plunge Azimuth
T 1.02e+22 29 272
N 0.00e+00 10 7
P -1.02e+22 59 114
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.35e+20
Mxy 7.51e+20
Mxz 1.97e+21
Myy 5.47e+21
Myz -8.51e+21
Mzz -5.04e+21
-#####----####
#############----#####
###############--------#####
###############-----------####
################--------------####
#################---------------####
#################-----------------####
#################-------------------####
#################--------------------###
##### ##########--------------------####
##### T #########---------------------####
##### #########---------- ---------###
#################---------- P ---------###
###############----------- --------###
###############----------------------###
##############----------------------##
#############---------------------##
############--------------------##
##########-------------------#
#########-----------------##
#######--------------#
###-----------
Global CMT Convention Moment Tensor:
R T P
-5.04e+21 1.97e+21 8.51e+21
1.97e+21 -4.35e+20 -7.51e+20
8.51e+21 -7.51e+20 5.47e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140309161123/index.html
|
Moment
1.06e+15 N-m
Magnitude
4.0
Percent DC
71%
Depth
58.0 km
Updated
2014-03-09 17:31:46 UTC
Author
us
Catalog
ak
Contributor
us
Code
us_c000n5yj_mwr
Principal Axes
Axis Value Plunge Azimuth
T 0.987 33° 277°
N 0.139 7° 12°
P -1.126 56° 113°
Nodal Planes
Plane Strike Dip Rake
NP1 194° 78° -82°
NP2 341° 14° -122°
|
|
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 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 0.5 200 80 -10 3.10 0.1446
WVFGRD96 1.0 200 80 -10 3.14 0.1586
WVFGRD96 2.0 200 80 -15 3.25 0.2018
WVFGRD96 3.0 195 65 -20 3.34 0.2339
WVFGRD96 4.0 200 75 -15 3.37 0.2537
WVFGRD96 5.0 200 75 -5 3.41 0.2663
WVFGRD96 6.0 200 80 0 3.44 0.2745
WVFGRD96 7.0 200 80 0 3.46 0.2808
WVFGRD96 8.0 200 75 10 3.50 0.2899
WVFGRD96 9.0 200 75 10 3.51 0.2952
WVFGRD96 10.0 200 75 10 3.53 0.2960
WVFGRD96 11.0 200 80 10 3.54 0.2943
WVFGRD96 12.0 200 80 10 3.55 0.2925
WVFGRD96 13.0 200 80 20 3.56 0.2931
WVFGRD96 14.0 200 80 20 3.57 0.2970
WVFGRD96 15.0 20 85 35 3.55 0.3023
WVFGRD96 16.0 20 85 35 3.55 0.3098
WVFGRD96 17.0 20 90 35 3.56 0.3171
WVFGRD96 18.0 20 90 35 3.57 0.3244
WVFGRD96 19.0 20 90 35 3.57 0.3316
WVFGRD96 20.0 195 85 -35 3.59 0.3404
WVFGRD96 21.0 20 90 40 3.59 0.3447
WVFGRD96 22.0 20 90 40 3.60 0.3518
WVFGRD96 23.0 20 90 40 3.60 0.3589
WVFGRD96 24.0 20 90 40 3.61 0.3656
WVFGRD96 25.0 195 85 -40 3.62 0.3730
WVFGRD96 26.0 20 90 45 3.62 0.3785
WVFGRD96 27.0 20 90 45 3.63 0.3853
WVFGRD96 28.0 20 90 45 3.64 0.3917
WVFGRD96 29.0 20 90 50 3.65 0.3985
WVFGRD96 30.0 195 85 -50 3.65 0.4079
WVFGRD96 31.0 20 90 50 3.66 0.4116
WVFGRD96 32.0 195 85 -50 3.67 0.4210
WVFGRD96 33.0 195 85 -55 3.68 0.4271
WVFGRD96 34.0 195 85 -55 3.68 0.4328
WVFGRD96 35.0 195 85 -55 3.69 0.4380
WVFGRD96 36.0 195 80 -55 3.69 0.4426
WVFGRD96 37.0 195 80 -55 3.70 0.4480
WVFGRD96 38.0 195 80 -60 3.70 0.4519
WVFGRD96 39.0 195 80 -55 3.71 0.4558
WVFGRD96 40.0 195 80 -65 3.84 0.4557
WVFGRD96 41.0 195 80 -65 3.84 0.4600
WVFGRD96 42.0 195 80 -65 3.85 0.4635
WVFGRD96 43.0 195 80 -70 3.86 0.4672
WVFGRD96 44.0 195 80 -70 3.86 0.4702
WVFGRD96 45.0 195 80 -70 3.87 0.4728
WVFGRD96 46.0 195 80 -70 3.87 0.4760
WVFGRD96 47.0 195 80 -70 3.88 0.4778
WVFGRD96 48.0 190 75 -70 3.88 0.4805
WVFGRD96 49.0 190 75 -70 3.89 0.4828
WVFGRD96 50.0 190 75 -70 3.89 0.4849
WVFGRD96 51.0 190 75 -75 3.90 0.4872
WVFGRD96 52.0 190 75 -75 3.91 0.4888
WVFGRD96 53.0 190 75 -75 3.91 0.4907
WVFGRD96 54.0 190 75 -75 3.92 0.4916
WVFGRD96 55.0 190 75 -75 3.92 0.4925
WVFGRD96 56.0 190 75 -80 3.93 0.4930
WVFGRD96 57.0 190 75 -80 3.93 0.4935
WVFGRD96 58.0 190 75 -80 3.94 0.4937
WVFGRD96 59.0 190 75 -80 3.94 0.4929
WVFGRD96 60.0 0 15 -100 3.95 0.4920
WVFGRD96 61.0 190 75 -85 3.95 0.4914
WVFGRD96 62.0 0 15 -100 3.96 0.4907
WVFGRD96 63.0 10 15 -90 3.97 0.4888
WVFGRD96 64.0 10 15 -90 3.97 0.4874
WVFGRD96 65.0 10 15 -90 3.97 0.4860
WVFGRD96 66.0 45 15 -60 3.99 0.4841
WVFGRD96 67.0 45 15 -60 3.99 0.4829
WVFGRD96 68.0 45 15 -60 3.99 0.4817
WVFGRD96 69.0 60 15 -50 4.00 0.4794
WVFGRD96 70.0 50 15 -55 4.00 0.4784
WVFGRD96 71.0 65 15 -45 4.01 0.4767
WVFGRD96 72.0 65 15 -45 4.01 0.4743
WVFGRD96 73.0 65 15 -45 4.01 0.4727
WVFGRD96 74.0 75 20 -35 4.03 0.4700
WVFGRD96 75.0 75 20 -35 4.03 0.4680
WVFGRD96 76.0 75 20 -35 4.03 0.4662
WVFGRD96 77.0 75 20 -35 4.03 0.4634
WVFGRD96 78.0 85 20 -30 4.04 0.4611
WVFGRD96 79.0 85 20 -30 4.04 0.4591
WVFGRD96 80.0 90 25 -25 4.06 0.4564
WVFGRD96 81.0 90 25 -25 4.06 0.4545
WVFGRD96 82.0 90 25 -25 4.06 0.4527
WVFGRD96 83.0 90 25 -25 4.07 0.4502
WVFGRD96 84.0 90 25 -25 4.07 0.4472
WVFGRD96 85.0 90 25 -25 4.07 0.4450
WVFGRD96 86.0 90 25 -25 4.07 0.4422
WVFGRD96 87.0 95 30 -20 4.09 0.4387
WVFGRD96 88.0 95 30 -20 4.09 0.4370
WVFGRD96 89.0 95 30 -20 4.09 0.4345
WVFGRD96 90.0 95 30 -20 4.09 0.4320
WVFGRD96 91.0 95 30 -20 4.09 0.4291
WVFGRD96 92.0 95 30 -20 4.10 0.4268
WVFGRD96 93.0 95 30 -20 4.10 0.4238
WVFGRD96 94.0 95 30 -20 4.10 0.4206
WVFGRD96 95.0 100 30 -20 4.11 0.4177
WVFGRD96 96.0 100 35 -20 4.12 0.4151
WVFGRD96 97.0 100 35 -20 4.12 0.4126
WVFGRD96 98.0 105 35 -15 4.13 0.4099
WVFGRD96 99.0 105 35 -15 4.13 0.4079
The best solution is
WVFGRD96 58.0 190 75 -80 3.94 0.4937
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 a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 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 Fri Apr 26 03:37:39 PM CDT 2024
