Location

SLU location

Location ANSS

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2019/01/16 03:34:30:0 37.05 -97.37 2.5 4.0 Kansas Stations used: AG.HHAR GS.KAN01 GS.KAN05 GS.KAN08 GS.KAN12 GS.KAN14 GS.KAN17 GS.OK029 GS.OK031 GS.OK038 GS.OK051 GS.OK052 N4.R32B N4.S39B N4.T35B N4.TUL3 N4.U38B O2.CHAN O2.DOVR O2.DRUM O2.PERK O2.PERY O2.POCA O2.SHWN OK.CHOK OK.CROK OK.DEOK OK.FNO OK.NOKA OK.W35A TX.PH01 US.CBKS US.KSU1 US.MIAR Filtering commands used: cut o DIST/3.3 -20 o DIST/3.3 +40 rtr taper w 0.1 hp c 0.04 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 1.30e+22 dyne-cm Mw = 4.01 Z = 3 km Plane Strike Dip Rake NP1 140 85 -20 NP2 232 70 -175 Principal Axes: Axis Value Plunge Azimuth T 1.30e+22 10 188 N 0.00e+00 69 307 P -1.30e+22 18 94 Moment Tensor: (dyne-cm) Component Value Mxx 1.23e+22 Mxy 2.50e+21 Mxz -2.00e+21 Myy -1.16e+22 Myz -4.05e+21 Mzz -7.74e+20 ############## ###################### -########################### ---########################### ------#######################----- --------#################----------- -----------###########---------------- -------------#######-------------------- ---------------###---------------------- ----------------#------------------------- --------------#####------------------ -- ------------########----------------- P -- -----------###########--------------- -- --------##############------------------ -------#################---------------- -----####################------------- ---######################----------- -#########################-------- ##########################---- ###########################- ####### ############ ### T ######## Global CMT Convention Moment Tensor: R T P -7.74e+20 -2.00e+21 4.05e+21 -2.00e+21 1.23e+22 -2.50e+21 4.05e+21 -2.50e+21 -1.16e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190116033430/index.html

Preferred Solution

      STK = 140
      DIP = 85
     RAKE = -20
       MW = 4.01
       HS = 3.0

The NDK file is 20190116033430.ndk It was not appropriate to use the WUS model here, The surface wave tomography indicated a dispersion that required a low velocity layer at short periods, but in the intermediate period range used for the RMT, the CUS model was better. This points out the need for a local model.

Moment Tensor Comparison

The following compares this source inversion to others

SLU	USGSMWR	SLUFM
USGS/SLU Moment Tensor Solution ENS 2019/01/16 03:34:30:0 37.05 -97.37 2.5 4.0 Kansas Stations used: AG.HHAR GS.KAN01 GS.KAN05 GS.KAN08 GS.KAN12 GS.KAN14 GS.KAN17 GS.OK029 GS.OK031 GS.OK038 GS.OK051 GS.OK052 N4.R32B N4.S39B N4.T35B N4.TUL3 N4.U38B O2.CHAN O2.DOVR O2.DRUM O2.PERK O2.PERY O2.POCA O2.SHWN OK.CHOK OK.CROK OK.DEOK OK.FNO OK.NOKA OK.W35A TX.PH01 US.CBKS US.KSU1 US.MIAR Filtering commands used: cut o DIST/3.3 -20 o DIST/3.3 +40 rtr taper w 0.1 hp c 0.04 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 1.30e+22 dyne-cm Mw = 4.01 Z = 3 km Plane Strike Dip Rake NP1 140 85 -20 NP2 232 70 -175 Principal Axes: Axis Value Plunge Azimuth T 1.30e+22 10 188 N 0.00e+00 69 307 P -1.30e+22 18 94 Moment Tensor: (dyne-cm) Component Value Mxx 1.23e+22 Mxy 2.50e+21 Mxz -2.00e+21 Myy -1.16e+22 Myz -4.05e+21 Mzz -7.74e+20 ############## ###################### -########################### ---########################### ------#######################----- --------#################----------- -----------###########---------------- -------------#######-------------------- ---------------###---------------------- ----------------#------------------------- --------------#####------------------ -- ------------########----------------- P -- -----------###########--------------- -- --------##############------------------ -------#################---------------- -----####################------------- ---######################----------- -#########################-------- ##########################---- ###########################- ####### ############ ### T ######## Global CMT Convention Moment Tensor: R T P -7.74e+20 -2.00e+21 4.05e+21 -2.00e+21 1.23e+22 -2.50e+21 4.05e+21 -2.50e+21 -1.16e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190116033430/index.html	Regional Moment Tensor (Mwr) Moment 1.411e+15 N-m Magnitude 4.03 Mwr Depth 3.0 km Percent DC 95% Half Duration - Catalog US Data Source US 1 Contributor US 1 Nodal Planes Plane Strike Dip Rake NP1 232 52 -166 NP2 134 79 -38 Principal Axes Axis Value Plunge Azimuth T 1.392e+15 N-m 17 188 N 0.036e+15 N-m 50 300 P -1.429e+15 N-m 34 86	First motions and takeoff angles from an elocate run.

Magnitudes

mLg Magnitude

(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.

ML Magnitude

(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.

(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.

Context

Waveform Inversion using wvfgrd96

The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for the waveform inversion are shown in the next figure.

Location of broadband stations used for waveform inversion

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 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 -20 o DIST/3.3 +40
rtr
taper w 0.1
hp c 0.04 n 3 
lp c 0.08 n 3 

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    1.0   140    80   -20   3.94 0.5201
WVFGRD96    2.0   140    80   -15   3.98 0.5453
WVFGRD96    3.0   140    85   -20   4.01 0.5467
WVFGRD96    4.0   320    90    25   4.03 0.5386
WVFGRD96    5.0   320    70     0   4.03 0.5315
WVFGRD96    6.0   320    70     0   4.03 0.5271
WVFGRD96    7.0   320    70     0   4.04 0.5235
WVFGRD96    8.0   320    70     0   4.05 0.5202
WVFGRD96    9.0   320    70     0   4.06 0.5158
WVFGRD96   10.0   320    70     0   4.07 0.5111
WVFGRD96   11.0   320    70     5   4.08 0.5052
WVFGRD96   12.0   320    70     0   4.08 0.4990
WVFGRD96   13.0   320    70     0   4.09 0.4922
WVFGRD96   14.0   140    90    20   4.10 0.4863
WVFGRD96   15.0   140    90    20   4.11 0.4806
WVFGRD96   16.0   320    90   -20   4.11 0.4739
WVFGRD96   17.0   320    90   -20   4.12 0.4664
WVFGRD96   18.0   320    85   -15   4.12 0.4590
WVFGRD96   19.0   320    85   -15   4.13 0.4512
WVFGRD96   20.0   320    85   -20   4.14 0.4436
WVFGRD96   21.0   320    85   -20   4.14 0.4362
WVFGRD96   22.0   320    70   -10   4.14 0.4296
WVFGRD96   23.0   320    70   -10   4.15 0.4234
WVFGRD96   24.0   320    70   -10   4.15 0.4174
WVFGRD96   25.0   320    70   -10   4.16 0.4114
WVFGRD96   26.0   320    70   -10   4.16 0.4058
WVFGRD96   27.0   320    70   -10   4.17 0.4008
WVFGRD96   28.0   320    70   -10   4.18 0.3967
WVFGRD96   29.0   320    70   -15   4.19 0.3933

The best solution is

WVFGRD96    3.0   140    85   -20   4.01 0.5467

The mechanism correspond to the best fit is

Figure 1. Waveform inversion focal mechanism

The best fit as a function of depth is given in the following figure:

Figure 2. Depth sensitivity for waveform mechanism

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 and because the velocity model used in the predictions may not be perfect. 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 -20 o DIST/3.3 +40
rtr
taper w 0.1
hp c 0.04 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.

Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms. 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:

• 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)

 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.

Discussion

Acknowledgements

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.

Velocity Model

The CUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

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 

Quality Control

Here we tabulate the reasons for not using certain digital data sets

The following stations did not have a valid response files: