Special care was taken in the processing of this event because it was shallow an thus had significant short-period surface waves. Because of this an incorrect model would improperly model the surface waves to the detriment of the solution. A comparison of the observed SLU/USGS dispersion at the coordinates near the epicentral coordinates of (38N, 98W) shows (comparison ) that the local structure must be intermediate between the CUS and WUS models. On the other hand CRUST1.0 fits the dispersion well. The CRUST1.0 model was changed in that the S-velocity in the first layer was changed from 1.070 km/s to 1.250 km/s which gives a Poisson ratio more typical of rock.
Surprisingly, This improved model provides excellent fits, especially to the P wave over a wide range if diatances.
By being able to fit the short period dispersion ebtter, higher freuqencies could be used and the results believed.
USGS/SLU Moment Tensor Solution ENS 2020/01/19 19:08:41:0 38.02 -97.97 4.6 4.4 Kansas Stations used: AG.HHAR C0.LAMA GS.OK029 GS.OK038 GS.OK048 GS.OK051 GS.OK052 N4.BGNE N4.KSCO N4.N35B N4.P38B N4.R32B N4.T35B N4.TUL3 N4.U38B O2.ARC2 O2.CALT O2.CHAN O2.CRES O2.DOVR O2.DRUM O2.DUST O2.ERNS O2.FREE O2.FW03 O2.FW06 O2.KS01 O2.MRSH O2.PERK O2.PERY O2.PW05 O2.PW09 O2.PW18 O2.SC04 O2.SC07 O2.SC11 O2.SC12 O2.SC13 O2.SC14 O2.SC15 O2.SC17 O2.SC19 O2.SC20 O2.SMNL OK.AMES OK.CHOK OK.CROK OK.DEOK OK.ELIS OK.FNO OK.HTCH OK.MOOR OK.NOKA OK.QUOK OK.RLOK OK.SWND OK.W35A OK.X34A TX.DRZT TX.SMWD US.CBKS US.KSU1 US.WMOK 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 0.10 n 3 Best Fitting Double Couple Mo = 5.96e+22 dyne-cm Mw = 4.45 Z = 4 km Plane Strike Dip Rake NP1 300 85 -10 NP2 31 80 -175 Principal Axes: Axis Value Plunge Azimuth T 5.96e+22 3 346 N 0.00e+00 79 94 P -5.96e+22 11 255 Moment Tensor: (dyne-cm) Component Value Mxx 5.20e+22 Mxy -2.84e+22 Mxz 6.27e+21 Myy -5.02e+22 Myz 9.52e+21 Mzz -1.80e+21 T ########### #### ############### ########################---- #########################----- ##########################-------- -#########################---------- ------####################------------ -----------###############-------------- --------------###########--------------- -------------------#######---------------- ----------------------##------------------ -----------------------##----------------- - ------------------######-------------- P -----------------##########---------- ----------------##############------- -----------------#################---- --------------###################### ------------###################### --------###################### ------###################### -##################### ############## Global CMT Convention Moment Tensor: R T P -1.80e+21 6.27e+21 -9.52e+21 6.27e+21 5.20e+22 2.84e+22 -9.52e+21 2.84e+22 -5.02e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200119190841/index.html |
STK = 300 DIP = 85 RAKE = -10 MW = 4.45 HS = 4.0
The NDK file is 20200119190841.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2020/01/19 19:08:41:0 38.02 -97.97 4.6 4.4 Kansas Stations used: AG.HHAR C0.LAMA GS.OK029 GS.OK038 GS.OK048 GS.OK051 GS.OK052 N4.BGNE N4.KSCO N4.N35B N4.P38B N4.R32B N4.T35B N4.TUL3 N4.U38B O2.ARC2 O2.CALT O2.CHAN O2.CRES O2.DOVR O2.DRUM O2.DUST O2.ERNS O2.FREE O2.FW03 O2.FW06 O2.KS01 O2.MRSH O2.PERK O2.PERY O2.PW05 O2.PW09 O2.PW18 O2.SC04 O2.SC07 O2.SC11 O2.SC12 O2.SC13 O2.SC14 O2.SC15 O2.SC17 O2.SC19 O2.SC20 O2.SMNL OK.AMES OK.CHOK OK.CROK OK.DEOK OK.ELIS OK.FNO OK.HTCH OK.MOOR OK.NOKA OK.QUOK OK.RLOK OK.SWND OK.W35A OK.X34A TX.DRZT TX.SMWD US.CBKS US.KSU1 US.WMOK 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 0.10 n 3 Best Fitting Double Couple Mo = 5.96e+22 dyne-cm Mw = 4.45 Z = 4 km Plane Strike Dip Rake NP1 300 85 -10 NP2 31 80 -175 Principal Axes: Axis Value Plunge Azimuth T 5.96e+22 3 346 N 0.00e+00 79 94 P -5.96e+22 11 255 Moment Tensor: (dyne-cm) Component Value Mxx 5.20e+22 Mxy -2.84e+22 Mxz 6.27e+21 Myy -5.02e+22 Myz 9.52e+21 Mzz -1.80e+21 T ########### #### ############### ########################---- #########################----- ##########################-------- -#########################---------- ------####################------------ -----------###############-------------- --------------###########--------------- -------------------#######---------------- ----------------------##------------------ -----------------------##----------------- - ------------------######-------------- P -----------------##########---------- ----------------##############------- -----------------#################---- --------------###################### ------------###################### --------###################### ------###################### -##################### ############## Global CMT Convention Moment Tensor: R T P -1.80e+21 6.27e+21 -9.52e+21 6.27e+21 5.20e+22 2.84e+22 -9.52e+21 2.84e+22 -5.02e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200119190841/index.html |
Regional Moment Tensor (Mwr) Moment 7.218e+15 N-m Magnitude 4.51 Mwr Depth 3.0 km Percent DC 100% Half Duration - Catalog US Data Source US 1 Contributor US 1 Nodal Planes Plane Strike Dip Rake NP1 299 65 -19 NP2 38 73 -153 Principal Axes Axis Value Plunge Azimuth T 7.222e+15 N-m 5 167 N -0.008e+15 N-m 59 69 P -7.215e+15 N-m 31 260 |
(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.
(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.
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.
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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 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 0.10 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 305 70 15 4.31 0.4778 WVFGRD96 2.0 120 90 5 4.36 0.5666 WVFGRD96 3.0 300 85 -10 4.42 0.6068 WVFGRD96 4.0 300 85 -10 4.45 0.6084 WVFGRD96 5.0 120 85 15 4.47 0.5976 WVFGRD96 6.0 120 85 15 4.49 0.5923 WVFGRD96 7.0 305 75 15 4.50 0.5889 WVFGRD96 8.0 300 80 10 4.52 0.5840 WVFGRD96 9.0 300 80 10 4.53 0.5767 WVFGRD96 10.0 300 80 10 4.55 0.5672 WVFGRD96 11.0 300 80 10 4.56 0.5554 WVFGRD96 12.0 300 80 10 4.57 0.5408 WVFGRD96 13.0 300 80 10 4.59 0.5240
The best solution is
WVFGRD96 4.0 300 85 -10 4.45 0.6084
The mechanism correspond 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 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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3
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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:
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.
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 Bureau of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Oklahoma Geological Survey, TexNet, the Iris stations, the Transportable Array of EarthScope and other networks.
The HutchKS model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 CRUST1.0 at (38.01, -98.01) with top layer adjusted 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 0.500 2.500 1.250 2.110 225.0 100.0 0.0 0.0 1.0 1.0 1.200 4.600 2.590 2.460 225.0 100.0 0.0 0.0 1.0 1.0 12.020 6.100 3.530 2.740 0.0 0.0 0.0 0.0 1.0 1.0 13.530 6.500 3.710 2.830 0.0 0.0 0.0 0.0 1.0 1.0 12.020 6.900 3.930 2.920 0.0 0.0 0.0 0.0 1.0 1.0 0.000 8.160 4.530 3.360 0.0 0.0 0.0 0.0 1.0 1.0
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files: