The ANSS event ID is ak01972zidym and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak01972zidym/executive.
2019/06/03 18:05:25 63.092 -150.819 127.0 3.6 Alaska
USGS/SLU Moment Tensor Solution
ENS 2019/06/03 18:05:25:0 63.09 -150.82 127.0 3.6 Alaska
Stations used:
AK.BPAW AK.CAST AK.DHY AK.FID AK.GHO AK.GLI AK.KNK AK.MCK
AK.MLY AK.PAX AK.PPLA AK.PWL AK.RC01 AK.RND AK.SAW AK.SCM
AK.SCRK AK.SKN AK.SSN AK.TRF AT.PMR AT.TTA TA.K24K TA.L19K
TA.M19K TA.M22K
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
Best Fitting Double Couple
Mo = 6.53e+21 dyne-cm
Mw = 3.81
Z = 118 km
Plane Strike Dip Rake
NP1 47 69 103
NP2 195 25 60
Principal Axes:
Axis Value Plunge Azimuth
T 6.53e+21 64 339
N 0.00e+00 12 223
P -6.53e+21 22 127
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.80e+20
Mxy 2.28e+21
Mxz 3.80e+21
Myy -3.35e+21
Myz -2.75e+21
Mzz 4.33e+21
-------#######
------################
------######################
-----#########################
------##########################--
-----###########################----
-----########## ##############------
------########## T #############--------
-----########### ############---------
-----##########################-----------
-----########################-------------
-----#######################--------------
-----#####################----------------
----###################-----------------
-----################-------------------
----#############------------- -----
----#########---------------- P ----
----#####------------------- ---
-##---------------------------
###-------------------------
##--------------------
#-------------
Global CMT Convention Moment Tensor:
R T P
4.33e+21 3.80e+21 2.75e+21
3.80e+21 -9.80e+20 -2.28e+21
2.75e+21 -2.28e+21 -3.35e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190603180525/index.html
|
STK = 195
DIP = 25
RAKE = 60
MW = 3.81
HS = 118.0
The NDK file is 20190603180525.ndk The waveform inversion is preferred.
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.
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.
 |
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.
|
|
|
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 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 30 45 -85 3.02 0.2025
WVFGRD96 4.0 205 60 -95 3.09 0.1753
WVFGRD96 6.0 260 60 35 3.07 0.1877
WVFGRD96 8.0 265 55 40 3.14 0.2044
WVFGRD96 10.0 265 60 45 3.17 0.2182
WVFGRD96 12.0 205 75 75 3.17 0.2318
WVFGRD96 14.0 205 75 70 3.19 0.2428
WVFGRD96 16.0 205 75 70 3.22 0.2486
WVFGRD96 18.0 205 75 65 3.24 0.2510
WVFGRD96 20.0 205 75 65 3.26 0.2495
WVFGRD96 22.0 205 75 70 3.29 0.2450
WVFGRD96 24.0 205 75 70 3.31 0.2383
WVFGRD96 26.0 200 75 65 3.33 0.2294
WVFGRD96 28.0 200 75 65 3.34 0.2193
WVFGRD96 30.0 205 70 70 3.35 0.2087
WVFGRD96 32.0 200 60 70 3.35 0.1988
WVFGRD96 34.0 200 65 70 3.37 0.1891
WVFGRD96 36.0 210 40 -85 3.37 0.1924
WVFGRD96 38.0 25 50 -90 3.40 0.1961
WVFGRD96 40.0 210 40 -85 3.51 0.2080
WVFGRD96 42.0 25 50 -90 3.53 0.2032
WVFGRD96 44.0 30 50 -80 3.56 0.1968
WVFGRD96 46.0 25 55 -75 3.58 0.1916
WVFGRD96 48.0 25 55 -75 3.59 0.1875
WVFGRD96 50.0 30 55 -70 3.59 0.1832
WVFGRD96 52.0 30 55 -70 3.60 0.1790
WVFGRD96 54.0 200 70 50 3.61 0.1812
WVFGRD96 56.0 200 65 55 3.63 0.2025
WVFGRD96 58.0 190 60 55 3.64 0.2302
WVFGRD96 60.0 190 60 55 3.66 0.2652
WVFGRD96 62.0 185 55 55 3.68 0.3009
WVFGRD96 64.0 180 55 50 3.70 0.3368
WVFGRD96 66.0 180 55 50 3.71 0.3701
WVFGRD96 68.0 175 55 45 3.73 0.4032
WVFGRD96 70.0 185 45 50 3.73 0.4359
WVFGRD96 72.0 190 40 55 3.74 0.4697
WVFGRD96 74.0 185 40 50 3.75 0.4993
WVFGRD96 76.0 195 35 60 3.75 0.5239
WVFGRD96 78.0 190 35 55 3.76 0.5475
WVFGRD96 80.0 200 30 65 3.76 0.5684
WVFGRD96 82.0 200 30 65 3.76 0.5819
WVFGRD96 84.0 200 30 65 3.77 0.5925
WVFGRD96 86.0 200 30 65 3.77 0.6029
WVFGRD96 88.0 185 30 55 3.78 0.6127
WVFGRD96 90.0 185 30 55 3.78 0.6212
WVFGRD96 92.0 185 30 55 3.78 0.6282
WVFGRD96 94.0 195 25 65 3.78 0.6353
WVFGRD96 96.0 195 25 65 3.79 0.6415
WVFGRD96 98.0 195 25 65 3.79 0.6471
WVFGRD96 100.0 195 25 65 3.79 0.6507
WVFGRD96 102.0 195 25 65 3.79 0.6550
WVFGRD96 104.0 195 25 65 3.79 0.6571
WVFGRD96 106.0 195 25 65 3.79 0.6593
WVFGRD96 108.0 195 25 60 3.80 0.6616
WVFGRD96 110.0 195 25 60 3.80 0.6630
WVFGRD96 112.0 195 25 60 3.80 0.6635
WVFGRD96 114.0 195 25 60 3.80 0.6642
WVFGRD96 116.0 195 25 60 3.80 0.6636
WVFGRD96 118.0 195 25 60 3.81 0.6644
WVFGRD96 120.0 195 25 60 3.81 0.6641
WVFGRD96 122.0 195 25 60 3.81 0.6628
WVFGRD96 124.0 190 25 55 3.81 0.6624
WVFGRD96 126.0 190 25 55 3.82 0.6611
WVFGRD96 128.0 190 25 55 3.82 0.6599
WVFGRD96 130.0 190 25 55 3.82 0.6585
WVFGRD96 132.0 190 25 55 3.82 0.6575
WVFGRD96 134.0 190 25 55 3.82 0.6552
WVFGRD96 136.0 190 25 55 3.83 0.6537
WVFGRD96 138.0 195 25 60 3.83 0.6509
WVFGRD96 140.0 205 20 70 3.83 0.6501
WVFGRD96 142.0 195 25 60 3.83 0.6470
WVFGRD96 144.0 210 20 70 3.83 0.6458
WVFGRD96 146.0 195 25 60 3.83 0.6425
WVFGRD96 148.0 215 20 75 3.84 0.6417
The best solution is
WVFGRD96 118.0 195 25 60 3.81 0.6644
The mechanism corresponding to the best fit is
|
|
|
The best fit as a function of depth is given in the following figure:
|
|
|
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
|
| 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:
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.
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