Location
2015/07/20 20:19:04 36.807 -98.127 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 2015/07/20 20:19:04:0 36.81 -98.13 5.0 4.4 Oklahoma
Stations used:
AG.HHAR GS.KAN05 GS.KAN08 GS.KAN09 GS.KAN10 GS.KAN11
GS.KAN12 GS.KAN13 GS.KS20 GS.OK025 GS.OK029 GS.OK031
N4.N33B N4.P38B N4.R32B N4.T35B N4.U38B N4.Z35B N4.Z38B
NM.MGMO OK.BCOK OK.BLOK OK.CCOK OK.CHOK OK.CROK OK.FNO
OK.QUOK OK.U32A OK.X37A TA.ABTX TA.BGNE TA.KSCO TA.W39A
US.AMTX US.CBKS US.KSU1 US.MIAR US.WMOK
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 = 2.99e+22 dyne-cm
Mw = 4.25
Z = 4 km
Plane Strike Dip Rake
NP1 270 55 -70
NP2 58 40 -116
Principal Axes:
Axis Value Plunge Azimuth
T 2.99e+22 8 346
N 0.00e+00 16 78
P -2.99e+22 72 231
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.64e+22
Mxy -8.36e+21
Mxz 9.59e+21
Myy -1.99e+14
Myz 5.86e+21
Mzz -2.64e+22
# T ##########
##### ##############
############################
##############################
##################################
####################################
#############------------############-
########------------------------######--
####--------------------------------#---
###-----------------------------------#---
#------------------------------------####-
---------------- ------------------#####
---------------- P -----------------######
--------------- ---------------#######
--------------------------------########
-----------------------------#########
-------------------------###########
#--------------------#############
####----------################
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-2.64e+22 9.59e+21 -5.86e+21
9.59e+21 2.64e+22 8.36e+21
-5.86e+21 8.36e+21 -1.99e+14
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150720201904/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 = 270
DIP = 55
RAKE = -70
MW = 4.25
HS = 4.0
The NDK file is 20150720201904.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
USGSMT |
USGS/SLU Moment Tensor Solution
ENS 2015/07/20 20:19:04:0 36.81 -98.13 5.0 4.4 Oklahoma
Stations used:
AG.HHAR GS.KAN05 GS.KAN08 GS.KAN09 GS.KAN10 GS.KAN11
GS.KAN12 GS.KAN13 GS.KS20 GS.OK025 GS.OK029 GS.OK031
N4.N33B N4.P38B N4.R32B N4.T35B N4.U38B N4.Z35B N4.Z38B
NM.MGMO OK.BCOK OK.BLOK OK.CCOK OK.CHOK OK.CROK OK.FNO
OK.QUOK OK.U32A OK.X37A TA.ABTX TA.BGNE TA.KSCO TA.W39A
US.AMTX US.CBKS US.KSU1 US.MIAR US.WMOK
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 = 2.99e+22 dyne-cm
Mw = 4.25
Z = 4 km
Plane Strike Dip Rake
NP1 270 55 -70
NP2 58 40 -116
Principal Axes:
Axis Value Plunge Azimuth
T 2.99e+22 8 346
N 0.00e+00 16 78
P -2.99e+22 72 231
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.64e+22
Mxy -8.36e+21
Mxz 9.59e+21
Myy -1.99e+14
Myz 5.86e+21
Mzz -2.64e+22
# T ##########
##### ##############
############################
##############################
##################################
####################################
#############------------############-
########------------------------######--
####--------------------------------#---
###-----------------------------------#---
#------------------------------------####-
---------------- ------------------#####
---------------- P -----------------######
--------------- ---------------#######
--------------------------------########
-----------------------------#########
-------------------------###########
#--------------------#############
####----------################
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-2.64e+22 9.59e+21 -5.86e+21
9.59e+21 2.64e+22 8.36e+21
-5.86e+21 8.36e+21 -1.99e+14
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150720201904/index.html
|
Regional Moment Tensor (Mwr)
Moment 4.866e+15 N-m
Magnitude 4.39
Depth 4.0 km
Percent DC 71%
Half Duration –
Catalog US (us20002yq7)
Data Source US1
Contributor US1
Nodal Planes
Plane Strike Dip Rake
NP1 48 46 -125
NP2 273 54 -59
Principal Axes
Axis Value Plunge Azimuth
T 4.450 4 341
N 0.746 24 73
P -5.196 65 242
|
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.
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.
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Location of broadband stations used for waveform inversion
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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 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 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 1.0 110 45 -35 4.03 0.3699
WVFGRD96 2.0 105 40 -40 4.16 0.4408
WVFGRD96 3.0 275 65 -70 4.22 0.4900
WVFGRD96 4.0 270 55 -70 4.25 0.5239
WVFGRD96 5.0 280 60 -60 4.24 0.4801
WVFGRD96 6.0 280 60 -60 4.22 0.4161
WVFGRD96 7.0 125 80 20 4.23 0.3715
WVFGRD96 8.0 275 60 -70 4.27 0.3619
WVFGRD96 9.0 310 55 25 4.29 0.3654
WVFGRD96 10.0 310 55 25 4.30 0.3748
WVFGRD96 11.0 310 60 25 4.31 0.3808
WVFGRD96 12.0 310 60 25 4.32 0.3835
WVFGRD96 13.0 310 60 25 4.32 0.3837
WVFGRD96 14.0 310 60 25 4.33 0.3831
WVFGRD96 15.0 310 60 25 4.34 0.3814
WVFGRD96 16.0 310 60 25 4.35 0.3788
WVFGRD96 17.0 310 60 25 4.35 0.3759
WVFGRD96 18.0 310 60 25 4.36 0.3728
WVFGRD96 19.0 305 60 25 4.37 0.3701
WVFGRD96 20.0 85 90 -50 4.29 0.3648
WVFGRD96 21.0 75 85 -55 4.30 0.3646
WVFGRD96 22.0 75 85 -55 4.31 0.3643
WVFGRD96 23.0 75 85 -55 4.32 0.3636
WVFGRD96 24.0 80 90 -50 4.33 0.3625
WVFGRD96 25.0 75 85 -55 4.34 0.3611
WVFGRD96 26.0 75 85 -55 4.36 0.3591
WVFGRD96 27.0 260 90 50 4.36 0.3561
WVFGRD96 28.0 75 85 -55 4.38 0.3532
WVFGRD96 29.0 75 85 -55 4.39 0.3501
The best solution is
WVFGRD96 4.0 270 55 -70 4.25 0.5239
The mechanism correspond to the best fit is
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Figure 1. Waveform inversion focal mechanism
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The best fit as a function of depth is given in the following figure:
|
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Figure 2. Depth sensitivity for waveform mechanism
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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 -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.
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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.
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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 was 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 Jul 20 17:52:11 CDT 2015