Left: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated. Right: residuals as a function of distance and azimuth.
The ANSS event ID is us20002a09 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us20002a09/executive.
2015/04/28 22:18:54 37.021 -97.896 7.7 3.6 Kansas
USGS/SLU Moment Tensor Solution
ENS 2015/04/28 22:18:54:0 37.02 -97.90 7.7 3.6 Kansas
Stations used:
AG.HHAR GS.KAN08 GS.KAN10 GS.KAN11 GS.KAN12 GS.KAN13
GS.KAN16 GS.KS21 GS.OK025 GS.OK029 GS.OK030 GS.OK031
GS.OK032 N4.N33B N4.R32B N4.T35B N4.U38B OK.BCOK OK.CROK
OK.FNO OK.U32A OK.X37A US.CBKS US.KSU1
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 n 3
Best Fitting Double Couple
Mo = 3.05e+21 dyne-cm
Mw = 3.59
Z = 7 km
Plane Strike Dip Rake
NP1 69 68 -118
NP2 305 35 -40
Principal Axes:
Axis Value Plunge Azimuth
T 3.05e+21 19 180
N 0.00e+00 26 81
P -3.05e+21 57 301
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.50e+21
Mxy 4.08e+20
Mxz -1.65e+21
Myy -6.54e+20
Myz 1.19e+21
Mzz -1.85e+21
##############
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#-----------------############
-----------------------###########
---------------------------#########
------------------------------########
----------- -------------------######-
----------- P --------------------###---
------------ ---------------------#-----
----------------------------------###-----
--------------------------------######----
----------------------------##########----
-----------------------###############--
------------------####################--
#####################################-
###################################-
##################################
##############################
############ #############
######### T ##########
##### ######
Global CMT Convention Moment Tensor:
R T P
-1.85e+21 -1.65e+21 -1.19e+21
-1.65e+21 2.50e+21 -4.08e+20
-1.19e+21 -4.08e+20 -6.54e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150428221854/index.html
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STK = 305
DIP = 35
RAKE = -40
MW = 3.59
HS = 7.0
The NDK file is 20150428221854.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: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated.
Right: residuals as a function of distance and azimuth.
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 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 115 70 -40 3.34 0.2654
WVFGRD96 2.0 300 35 -30 3.48 0.2927
WVFGRD96 3.0 310 20 -25 3.58 0.3501
WVFGRD96 4.0 310 25 -25 3.57 0.4025
WVFGRD96 5.0 310 30 -30 3.58 0.4385
WVFGRD96 6.0 305 30 -40 3.58 0.4538
WVFGRD96 7.0 305 35 -40 3.59 0.4577
WVFGRD96 8.0 305 30 -40 3.65 0.4570
WVFGRD96 9.0 310 35 -30 3.64 0.4451
WVFGRD96 10.0 310 35 -30 3.64 0.4273
WVFGRD96 11.0 320 40 -15 3.63 0.4111
WVFGRD96 12.0 325 45 10 3.63 0.3954
WVFGRD96 13.0 325 45 20 3.63 0.3834
WVFGRD96 14.0 330 40 30 3.64 0.3701
WVFGRD96 15.0 335 40 35 3.64 0.3580
WVFGRD96 16.0 335 40 40 3.65 0.3469
WVFGRD96 17.0 340 40 50 3.66 0.3377
WVFGRD96 18.0 340 40 50 3.66 0.3281
WVFGRD96 19.0 345 40 55 3.67 0.3180
WVFGRD96 20.0 345 40 55 3.67 0.3076
WVFGRD96 21.0 345 40 60 3.69 0.2971
WVFGRD96 22.0 355 35 70 3.69 0.2875
WVFGRD96 23.0 -5 35 70 3.69 0.2784
WVFGRD96 24.0 250 70 50 3.66 0.2721
WVFGRD96 25.0 245 70 50 3.67 0.2664
WVFGRD96 26.0 250 65 50 3.68 0.2614
WVFGRD96 27.0 250 65 50 3.68 0.2564
WVFGRD96 28.0 250 65 50 3.68 0.2506
WVFGRD96 29.0 250 65 45 3.70 0.2445
The best solution is
WVFGRD96 7.0 305 35 -40 3.59 0.4577
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 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 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