The ANSS event ID is hv74103036 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/hv74103036/executive.
2024/02/09 20:06:31 19.187 -155.493 37.0 5.7 Hawaii
USGS/SLU Moment Tensor Solution
ENS 2024/02/09 20:06:31:0 19.19 -155.49 37.0 5.7 Hawaii
Stations used:
HV.DEVL HV.HAT HV.RSDD HV.STCD IU.POHA PT.HPAH PT.MLOA
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 = 2.57e+24 dyne-cm
Mw = 5.54
Z = 33 km
Plane Strike Dip Rake
NP1 285 90 -115
NP2 195 25 0
Principal Axes:
Axis Value Plunge Azimuth
T 2.57e+24 40 38
N 0.00e+00 25 285
P -2.57e+24 40 172
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.43e+23
Mxy 9.41e+23
Mxz 2.25e+24
Myy 5.43e+23
Myz 6.03e+23
Mzz 0.00e+00
-------#######
------################
------######################
-----#########################
------################# ########
-----################### T #########
-----#################### ##########
------##################################
###--###################################
#####------###############################
#####-------------########################
#####-------------------##################
#####--------------------------###########
####---------------------------------###
#####-----------------------------------
####----------------------------------
####-------------- ---------------
####------------- P --------------
###------------ ------------
###-------------------------
##--------------------
#-------------
Global CMT Convention Moment Tensor:
R T P
0.00e+00 2.25e+24 -6.03e+23
2.25e+24 -5.43e+23 -9.41e+23
-6.03e+23 -9.41e+23 5.43e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240209200631/index.html
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STK = 195
DIP = 25
RAKE = 0
MW = 5.54
HS = 33.0
The NDK file is 20240209200631.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.
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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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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 1.0 100 45 90 4.91 0.1725
WVFGRD96 2.0 95 50 90 5.07 0.2434
WVFGRD96 3.0 290 75 -10 5.10 0.2418
WVFGRD96 4.0 290 75 -10 5.15 0.2658
WVFGRD96 5.0 290 80 -5 5.18 0.2787
WVFGRD96 6.0 290 80 -5 5.22 0.2988
WVFGRD96 7.0 220 45 -10 5.19 0.3238
WVFGRD96 8.0 230 40 20 5.26 0.3618
WVFGRD96 9.0 225 45 10 5.28 0.3951
WVFGRD96 10.0 225 45 5 5.29 0.4279
WVFGRD96 11.0 220 45 -10 5.31 0.4581
WVFGRD96 12.0 220 45 -15 5.33 0.4871
WVFGRD96 13.0 220 45 -5 5.34 0.5145
WVFGRD96 14.0 220 45 -5 5.36 0.5392
WVFGRD96 15.0 220 45 -5 5.37 0.5609
WVFGRD96 16.0 215 45 -15 5.39 0.5811
WVFGRD96 17.0 215 45 -10 5.40 0.5996
WVFGRD96 18.0 215 45 -10 5.41 0.6156
WVFGRD96 19.0 215 45 -5 5.42 0.6294
WVFGRD96 20.0 215 45 -5 5.43 0.6417
WVFGRD96 21.0 215 40 0 5.44 0.6517
WVFGRD96 22.0 210 40 -5 5.45 0.6612
WVFGRD96 23.0 210 40 0 5.46 0.6706
WVFGRD96 24.0 210 35 0 5.46 0.6785
WVFGRD96 25.0 210 35 5 5.47 0.6861
WVFGRD96 26.0 205 35 0 5.49 0.6924
WVFGRD96 27.0 205 30 5 5.49 0.6992
WVFGRD96 28.0 205 30 5 5.50 0.7052
WVFGRD96 29.0 200 30 0 5.51 0.7111
WVFGRD96 30.0 200 30 0 5.52 0.7156
WVFGRD96 31.0 200 30 0 5.53 0.7190
WVFGRD96 32.0 195 25 0 5.54 0.7211
WVFGRD96 33.0 195 25 0 5.54 0.7224
WVFGRD96 34.0 190 25 -5 5.55 0.7221
WVFGRD96 35.0 190 25 -5 5.55 0.7199
WVFGRD96 36.0 190 25 -5 5.56 0.7172
WVFGRD96 37.0 190 25 -5 5.56 0.7116
WVFGRD96 38.0 190 30 -5 5.57 0.7055
WVFGRD96 39.0 190 30 -5 5.57 0.6995
WVFGRD96 40.0 190 20 -5 5.71 0.6931
WVFGRD96 41.0 185 20 -10 5.71 0.6883
WVFGRD96 42.0 185 20 -10 5.72 0.6826
WVFGRD96 43.0 190 25 -10 5.72 0.6775
WVFGRD96 44.0 190 25 -15 5.72 0.6725
WVFGRD96 45.0 190 25 -15 5.73 0.6677
WVFGRD96 46.0 185 25 -20 5.73 0.6620
WVFGRD96 47.0 185 25 -20 5.74 0.6574
WVFGRD96 48.0 185 25 -20 5.74 0.6518
WVFGRD96 49.0 185 25 -20 5.75 0.6462
WVFGRD96 50.0 185 25 -20 5.76 0.6404
WVFGRD96 51.0 185 30 -25 5.76 0.6352
WVFGRD96 52.0 185 30 -25 5.76 0.6298
WVFGRD96 53.0 185 30 -25 5.77 0.6237
WVFGRD96 54.0 185 30 -25 5.77 0.6185
WVFGRD96 55.0 185 30 -25 5.78 0.6126
WVFGRD96 56.0 185 30 -25 5.79 0.6059
WVFGRD96 57.0 185 30 -25 5.79 0.6001
WVFGRD96 58.0 180 30 -30 5.79 0.5944
WVFGRD96 59.0 180 30 -30 5.80 0.5885
The best solution is
WVFGRD96 33.0 195 25 0 5.54 0.7224
The mechanism corresponding to the best fit is
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The best fit as a function of depth is given in the following figure:
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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 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
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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. |
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