Location
Location ANSS
The ANSS event ID is ak0145z8amwh and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak0145z8amwh/executive.
2014/05/10 14:16:10 60.010 -152.126 89.1 5.8 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2014/05/10 14:16:10:0 60.01 -152.13 89.1 5.8 Alaska
Stations used:
AK.BAL AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.DHY AK.DOT
AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.HARP AK.HDA AK.HIN
AK.KNK AK.KTH AK.MCAR AK.MCK AK.MDM AK.MLY AK.NEA AK.PAX
AK.PPLA AK.RAG AK.RC01 AK.RND AK.SAW AK.SCM AK.TRF AK.VRDI
AK.WRH AK.YAH AT.CHGN AT.MENT AT.MID AT.OHAK AV.RDWB AV.RED
IM.IL31 IU.COLA
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 3.63e+24 dyne-cm
Mw = 5.64
Z = 88 km
Plane Strike Dip Rake
NP1 102 48 109
NP2 255 45 70
Principal Axes:
Axis Value Plunge Azimuth
T 3.63e+24 76 82
N 0.00e+00 14 269
P -3.63e+24 2 179
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.62e+24
Mxy 9.25e+22
Mxz 2.27e+23
Myy 2.10e+23
Myz 8.48e+23
Mzz 3.41e+24
--------------
----------------------
----------------------------
------------------------------
----------------------------------
-------------##################-----
----------##########################--
--------###############################-
------##################################
#----################## ################
##--################### T ################
####################### ################
##---#####################################
------##################################
---------#############################--
-----------#######################----
----------------############--------
----------------------------------
------------------------------
----------------------------
---------- ---------
------ P -----
Global CMT Convention Moment Tensor:
R T P
3.41e+24 2.27e+23 -8.48e+23
2.27e+23 -3.62e+24 -9.25e+22
-8.48e+23 -9.25e+22 2.10e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140510141610/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 = 255
DIP = 45
RAKE = 70
MW = 5.64
HS = 88.0
The NDK file is 20140510141610.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 |
GCMT |
USGS/SLU Moment Tensor Solution
ENS 2014/05/10 14:16:10:0 60.01 -152.13 89.1 5.8 Alaska
Stations used:
AK.BAL AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.DHY AK.DOT
AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.HARP AK.HDA AK.HIN
AK.KNK AK.KTH AK.MCAR AK.MCK AK.MDM AK.MLY AK.NEA AK.PAX
AK.PPLA AK.RAG AK.RC01 AK.RND AK.SAW AK.SCM AK.TRF AK.VRDI
AK.WRH AK.YAH AT.CHGN AT.MENT AT.MID AT.OHAK AV.RDWB AV.RED
IM.IL31 IU.COLA
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 3.63e+24 dyne-cm
Mw = 5.64
Z = 88 km
Plane Strike Dip Rake
NP1 102 48 109
NP2 255 45 70
Principal Axes:
Axis Value Plunge Azimuth
T 3.63e+24 76 82
N 0.00e+00 14 269
P -3.63e+24 2 179
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.62e+24
Mxy 9.25e+22
Mxz 2.27e+23
Myy 2.10e+23
Myz 8.48e+23
Mzz 3.41e+24
--------------
----------------------
----------------------------
------------------------------
----------------------------------
-------------##################-----
----------##########################--
--------###############################-
------##################################
#----################## ################
##--################### T ################
####################### ################
##---#####################################
------##################################
---------#############################--
-----------#######################----
----------------############--------
----------------------------------
------------------------------
----------------------------
---------- ---------
------ P -----
Global CMT Convention Moment Tensor:
R T P
3.41e+24 2.27e+23 -8.48e+23
2.27e+23 -3.62e+24 -9.25e+22
-8.48e+23 -9.25e+22 2.10e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140510141610/index.html
|
Body-wave Moment Tensor (Mwb)
Moment magnitude derived from a moment
tensor inversion of long-period (~10 - 100 s)
body-waves (P-, SH- ) at teleseismic distances
(~30 to ~90 degrees).
Moment
4.62e+17 N-m
Magnitude
5.7
Percent DC
58%
Depth
93.0 km
Updated
2014-05-10 15:25:09 UTC
Author
us
Catalog
us
Contributor
us
Code
us_b000qgyt_mwb
Principal Axes
Axis Value Plunge Azimuth
T 4.129 70 101
N 0.858 19 264
P -4.988 5 356
Nodal Planes
Plane Strike Dip Rake
NP1 249 53 66
NP2 106 43 118
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|
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May 10, 2014, SOUTHERN ALASKA, MW=5.8
Meredith Nettles
Goran Ekstrom
CENTROID-MOMENT-TENSOR SOLUTION
GCMT EVENT: C201405101416A
DATA: II IU CU MN G IC LD GE DK
KP
L.P.BODY WAVES:107S, 202C, T= 40
SURFACE WAVES: 111S, 241C, T= 50
TIMESTAMP: Q-20140510174259
CENTROID LOCATION:
ORIGIN TIME: 14:16:12.0 0.1
LAT:59.98N 0.01;LON:152.07W 0.02
DEP:104.9 0.7;TRIANG HDUR: 1.9
MOMENT TENSOR: SCALE 10**24 D-CM
RR= 4.160 0.053; TT=-6.300 0.061
PP= 2.140 0.063; RT=-0.375 0.054
RP=-1.210 0.045; TP= 0.260 0.057
PRINCIPAL AXES:
1.(T) VAL= 4.744;PLG=65;AZM= 95
2.(N) 1.575; 25; 271
3.(P) -6.319; 2; 1
BEST DBLE.COUPLE:M0= 5.53*10**24
NP1: STRIKE=115;DIP=48;SLIP= 125
NP2: STRIKE=249;DIP=52;SLIP= 57
---- P ----
-------- --------
-----------------------
---------------------------
----------------#########----
#----------###################-
#-------#######################
###---###########################
####-############### ##########
###--############### T ##########
##----############## ##########
-------########################
----------#####################
-------------##############--
---------------------------
-----------------------
-------------------
-----------
|
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 0.05 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 5 40 -85 4.87 0.2141
WVFGRD96 4.0 350 85 5 4.92 0.2189
WVFGRD96 6.0 170 90 0 4.97 0.2282
WVFGRD96 8.0 170 90 0 5.02 0.2319
WVFGRD96 10.0 35 65 -40 5.03 0.2476
WVFGRD96 12.0 40 70 -35 5.04 0.2613
WVFGRD96 14.0 40 70 -35 5.06 0.2727
WVFGRD96 16.0 40 70 -30 5.07 0.2813
WVFGRD96 18.0 40 70 -30 5.09 0.2878
WVFGRD96 20.0 50 65 50 5.08 0.2990
WVFGRD96 22.0 50 65 50 5.10 0.3125
WVFGRD96 24.0 50 65 50 5.12 0.3242
WVFGRD96 26.0 50 65 50 5.13 0.3333
WVFGRD96 28.0 50 65 50 5.15 0.3396
WVFGRD96 30.0 50 65 50 5.16 0.3443
WVFGRD96 32.0 50 65 50 5.18 0.3469
WVFGRD96 34.0 50 65 45 5.19 0.3473
WVFGRD96 36.0 50 65 45 5.20 0.3475
WVFGRD96 38.0 50 65 45 5.22 0.3491
WVFGRD96 40.0 60 65 60 5.35 0.3592
WVFGRD96 42.0 60 60 55 5.36 0.3693
WVFGRD96 44.0 65 45 50 5.37 0.3833
WVFGRD96 46.0 65 45 50 5.39 0.3980
WVFGRD96 48.0 65 45 50 5.40 0.4124
WVFGRD96 50.0 70 45 55 5.42 0.4266
WVFGRD96 52.0 70 45 60 5.43 0.4422
WVFGRD96 54.0 70 45 60 5.45 0.4578
WVFGRD96 56.0 75 45 65 5.47 0.4734
WVFGRD96 58.0 75 45 65 5.48 0.4887
WVFGRD96 60.0 75 45 65 5.49 0.5022
WVFGRD96 62.0 80 45 75 5.50 0.5160
WVFGRD96 64.0 80 45 75 5.51 0.5292
WVFGRD96 66.0 85 45 80 5.53 0.5414
WVFGRD96 68.0 85 45 80 5.54 0.5523
WVFGRD96 70.0 85 45 80 5.55 0.5616
WVFGRD96 72.0 270 45 90 5.56 0.5709
WVFGRD96 74.0 90 45 90 5.57 0.5789
WVFGRD96 76.0 95 45 95 5.59 0.5853
WVFGRD96 78.0 95 45 95 5.59 0.5909
WVFGRD96 80.0 265 45 85 5.60 0.5951
WVFGRD96 82.0 260 45 80 5.61 0.5984
WVFGRD96 84.0 260 45 80 5.61 0.6003
WVFGRD96 86.0 255 45 70 5.64 0.6021
WVFGRD96 88.0 255 45 70 5.64 0.6024
WVFGRD96 90.0 250 45 65 5.65 0.6018
WVFGRD96 92.0 250 45 65 5.66 0.6000
WVFGRD96 94.0 240 50 55 5.69 0.5999
WVFGRD96 96.0 240 50 55 5.69 0.5981
WVFGRD96 98.0 240 50 55 5.69 0.5951
WVFGRD96 100.0 240 50 55 5.70 0.5905
WVFGRD96 102.0 240 50 55 5.70 0.5851
WVFGRD96 104.0 240 50 55 5.70 0.5787
WVFGRD96 106.0 235 50 50 5.72 0.5718
WVFGRD96 108.0 235 50 50 5.72 0.5644
The best solution is
WVFGRD96 88.0 255 45 70 5.64 0.6024
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 0.05 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 06:44:30 PM CDT 2024
