Location
The SLU location is used here. This differs from the USGS solution by about 2 km. The
output is in elocate.txt.
2015/11/23 21:17:46 36.829 -98.293 5.0 4.4 Oklahoma
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports main page
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2015/11/23 21:17:46:0 36.83 -98.29 5.0 4.4 Oklahoma
Stations used:
AG.HHAR GS.KAN01 GS.KAN05 GS.KAN06 GS.KAN08 GS.KAN10
GS.KAN11 GS.KAN12 GS.KAN14 GS.KAN16 GS.OK025 GS.OK029
GS.OK030 N4.N35B N4.P38B N4.R32B N4.S39B N4.U38B N4.Z35B
N4.Z38B OK.BCOK OK.CHOK OK.CROK OK.FNO OK.LOOK OK.OKCFA
OK.U32A OK.W35A OK.X34A OK.X37A TA.BGNE TA.KSCO TA.U40A
TA.W39A US.CBKS US.KSU1 US.MIAR US.WMOK
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +60
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 3.43e+22 dyne-cm
Mw = 4.29
Z = 3 km
Plane Strike Dip Rake
NP1 255 50 -75
NP2 52 42 -107
Principal Axes:
Axis Value Plunge Azimuth
T 3.43e+22 4 334
N 0.00e+00 11 65
P -3.43e+22 78 226
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.70e+22
Mxy -1.40e+22
Mxz 7.03e+21
Myy 5.58e+21
Myz 4.02e+21
Mzz -3.26e+22
##############
# T ##################
#### #####################
##############################
##################################
#################------------######-
############-----------------------#--
##########---------------------------##-
#######-----------------------------####
######-------------------------------#####
####--------------------------------######
###-------------- ---------------#######
##--------------- P --------------########
---------------- -------------########
------------------------------##########
----------------------------##########
------------------------############
--------------------##############
#------------#################
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-3.26e+22 7.03e+21 -4.02e+21
7.03e+21 2.70e+22 1.40e+22
-4.02e+21 1.40e+22 5.58e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20151123211746/index.html
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is
STK = 255
DIP = 50
RAKE = -75
MW = 4.29
HS = 3.0
The NDK file is 20151123211746.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
USGSMT |
SLUFM |
USGS/SLU Moment Tensor Solution
ENS 2015/11/23 21:17:46:0 36.83 -98.29 5.0 4.4 Oklahoma
Stations used:
AG.HHAR GS.KAN01 GS.KAN05 GS.KAN06 GS.KAN08 GS.KAN10
GS.KAN11 GS.KAN12 GS.KAN14 GS.KAN16 GS.OK025 GS.OK029
GS.OK030 N4.N35B N4.P38B N4.R32B N4.S39B N4.U38B N4.Z35B
N4.Z38B OK.BCOK OK.CHOK OK.CROK OK.FNO OK.LOOK OK.OKCFA
OK.U32A OK.W35A OK.X34A OK.X37A TA.BGNE TA.KSCO TA.U40A
TA.W39A US.CBKS US.KSU1 US.MIAR US.WMOK
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +60
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 3.43e+22 dyne-cm
Mw = 4.29
Z = 3 km
Plane Strike Dip Rake
NP1 255 50 -75
NP2 52 42 -107
Principal Axes:
Axis Value Plunge Azimuth
T 3.43e+22 4 334
N 0.00e+00 11 65
P -3.43e+22 78 226
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.70e+22
Mxy -1.40e+22
Mxz 7.03e+21
Myy 5.58e+21
Myz 4.02e+21
Mzz -3.26e+22
##############
# T ##################
#### #####################
##############################
##################################
#################------------######-
############-----------------------#--
##########---------------------------##-
#######-----------------------------####
######-------------------------------#####
####--------------------------------######
###-------------- ---------------#######
##--------------- P --------------########
---------------- -------------########
------------------------------##########
----------------------------##########
------------------------############
--------------------##############
#------------#################
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-3.26e+22 7.03e+21 -4.02e+21
7.03e+21 2.70e+22 1.40e+22
-4.02e+21 1.40e+22 5.58e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20151123211746/index.html
|
Regional Moment Tensor (Mwr)
Moment 4.362e+15 N-m
Magnitude 4.36
Depth 3.0 km
Percent DC 56%
Half Duration –
Catalog US (us100040je)
Data Source US1
Contributor US1
Nodal Planes
Plane Strike Dip Rake
NP1 220 62 -112
NP2 81 35 -55
Principal Axes
Axis Value Plunge Azimuth
T 3.745 14 326
N 1.045 20 231
P -4.790 66 90
|
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; (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
The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).
Waveform Inversion
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 -30 o DIST/3.3 +60
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 n 3
The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 70 40 -80 4.13 0.4991
WVFGRD96 2.0 65 35 -85 4.23 0.5867
WVFGRD96 3.0 255 50 -75 4.29 0.6164
WVFGRD96 4.0 255 50 -75 4.32 0.5819
WVFGRD96 5.0 255 50 -80 4.31 0.4780
WVFGRD96 6.0 105 90 5 4.27 0.3983
WVFGRD96 7.0 280 90 -10 4.28 0.3733
WVFGRD96 8.0 90 25 -65 4.32 0.3751
WVFGRD96 9.0 285 65 15 4.34 0.3621
WVFGRD96 10.0 285 65 15 4.35 0.3573
WVFGRD96 11.0 110 20 -30 4.29 0.3596
WVFGRD96 12.0 115 20 -25 4.28 0.3683
WVFGRD96 13.0 120 20 -20 4.28 0.3769
WVFGRD96 14.0 135 20 -15 4.28 0.3855
WVFGRD96 15.0 145 20 -5 4.28 0.3936
WVFGRD96 16.0 155 20 10 4.29 0.4016
WVFGRD96 17.0 160 20 15 4.30 0.4100
WVFGRD96 18.0 165 20 20 4.31 0.4176
WVFGRD96 19.0 170 20 25 4.31 0.4243
WVFGRD96 20.0 60 70 75 4.34 0.4326
WVFGRD96 21.0 60 70 75 4.35 0.4381
WVFGRD96 22.0 60 70 75 4.36 0.4465
WVFGRD96 23.0 60 70 75 4.36 0.4529
WVFGRD96 24.0 60 70 75 4.37 0.4575
WVFGRD96 25.0 60 65 80 4.37 0.4609
WVFGRD96 26.0 60 65 80 4.38 0.4643
WVFGRD96 27.0 60 65 80 4.38 0.4661
WVFGRD96 28.0 60 65 85 4.39 0.4662
WVFGRD96 29.0 60 65 85 4.39 0.4653
The best solution is
WVFGRD96 3.0 255 50 -75 4.29 0.6164
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 -30 o DIST/3.3 +60
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.05 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)
Assuming only a mislocation, the time shifts are fit to a functional form:
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 WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
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
Quality Control
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
Last Changed Mon Nov 23 19:58:34 CST 2015
