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 nm60096021 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nm60096021/executive.
2015/04/02 03:51:43 36.050 -89.826 10.4 3.6 Missouri
USGS/SLU Moment Tensor Solution
ENS 2015/04/02 03:51:43:0 36.05 -89.83 10.4 3.6 Missouri
Stations used:
AG.FCAR AG.WHAR ET.CPCT ET.SWET IM.TKL IU.CCM IU.WCI IU.WVT
N4.O44A N4.P43A N4.P48A N4.R49A N4.S39B N4.S44A N4.S51A
N4.T45B N4.T50A N4.U38B N4.U49A N4.V48A N4.V51A N4.V52A
N4.W45B N4.W50A N4.W52A N4.X48A N4.Y49A N4.Y52A NM.BLO
NM.CLTN NM.FVM NM.HALT NM.HENM NM.HICK NM.LPAR NM.MGMO
NM.MPH NM.PARM NM.PBMO NM.PENM NM.PLAL NM.PVMO NM.USIN
TA.P49A TA.SFIN TA.U40A TA.W39A US.LRAL
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 3.39e+21 dyne-cm
Mw = 3.62
Z = 10 km
Plane Strike Dip Rake
NP1 290 90 -10
NP2 20 80 -180
Principal Axes:
Axis Value Plunge Azimuth
T 3.39e+21 7 335
N 0.00e+00 80 110
P -3.39e+21 7 245
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.14e+21
Mxy -2.56e+21
Mxz 5.53e+20
Myy -2.14e+21
Myz 2.01e+20
Mzz 5.14e+13
##############
# T ##############----
#### ##############-------
######################--------
#######################-----------
########################------------
########################--------------
--#######################---------------
-------#################----------------
-------------############-----------------
------------------######------------------
-----------------------#------------------
-----------------------######-------------
---------------------############-------
- ----------------##################--
P ---------------####################
---------------###################
---------------###################
------------##################
----------##################
-----#################
##############
Global CMT Convention Moment Tensor:
R T P
5.14e+13 5.53e+20 -2.01e+20
5.53e+20 2.14e+21 2.56e+21
-2.01e+20 2.56e+21 -2.14e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150402035143/index.html
|
STK = 290
DIP = 90
RAKE = -10
MW = 3.62
HS = 10.0
The NDK file is 20150402035143.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.
 |
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 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 115 75 20 3.51 0.6191
WVFGRD96 2.0 295 90 -10 3.52 0.6422
WVFGRD96 3.0 115 80 10 3.54 0.6561
WVFGRD96 4.0 115 80 10 3.55 0.6640
WVFGRD96 5.0 115 80 10 3.57 0.6704
WVFGRD96 6.0 115 80 10 3.58 0.6766
WVFGRD96 7.0 295 90 -10 3.59 0.6799
WVFGRD96 8.0 115 85 10 3.60 0.6862
WVFGRD96 9.0 110 85 10 3.61 0.6901
WVFGRD96 10.0 290 90 -10 3.62 0.6922
WVFGRD96 11.0 290 90 -10 3.63 0.6919
WVFGRD96 12.0 290 90 -10 3.64 0.6903
WVFGRD96 13.0 110 85 10 3.66 0.6881
WVFGRD96 14.0 110 85 10 3.66 0.6827
WVFGRD96 15.0 110 85 10 3.67 0.6768
WVFGRD96 16.0 290 90 -10 3.68 0.6706
WVFGRD96 17.0 290 90 -10 3.68 0.6640
WVFGRD96 18.0 110 85 10 3.69 0.6561
WVFGRD96 19.0 110 85 10 3.70 0.6486
WVFGRD96 20.0 290 85 -10 3.71 0.6440
WVFGRD96 21.0 290 85 -10 3.71 0.6364
WVFGRD96 22.0 290 85 -10 3.72 0.6318
WVFGRD96 23.0 290 85 -10 3.72 0.6288
WVFGRD96 24.0 290 85 -10 3.73 0.6241
WVFGRD96 25.0 290 85 -10 3.74 0.6235
WVFGRD96 26.0 110 85 10 3.75 0.6215
WVFGRD96 27.0 110 85 10 3.75 0.6219
WVFGRD96 28.0 290 85 -10 3.75 0.6230
WVFGRD96 29.0 290 85 -10 3.76 0.6229
The best solution is
WVFGRD96 10.0 290 90 -10 3.62 0.6922
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 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 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 CUS.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 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00