Location
2015/09/18 12:35:17 36.010 -96.844 3.7 4.1 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 2015/09/18 12:35:17:0 36.01 -96.84 3.7 4.1 Oklahoma
Stations used:
AG.HHAR GS.KAN05 GS.KAN10 GS.KAN12 GS.KAN13 GS.KAN14
GS.KAN16 GS.KAN17 GS.KS20 GS.KS21 GS.OK025 GS.OK029
GS.OK032 N4.R32B N4.T35B N4.U38B N4.Z35B OK.BCOK OK.BLOK
OK.CCOK OK.CHOK OK.CROK OK.FNO OK.LOOK OK.OKCFA OK.QUOK
OK.U32A OK.X34A OK.X37A TA.W39A US.KSU1 US.MIAR US.WMOK
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 0.08 n 3
Best Fitting Double Couple
Mo = 1.22e+22 dyne-cm
Mw = 3.99
Z = 4 km
Plane Strike Dip Rake
NP1 240 90 -175
NP2 150 85 0
Principal Axes:
Axis Value Plunge Azimuth
T 1.22e+22 4 15
N 0.00e+00 85 240
P -1.22e+22 4 105
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.05e+22
Mxy 6.06e+21
Mxz 9.18e+20
Myy -1.05e+22
Myz -5.30e+20
Mzz 0.00e+00
########### T
-############## ####
-----#######################
------########################
---------#########################
-----------#########################
-------------####################-----
---------------################---------
----------------############------------
------------------########----------------
-------------------####-------------------
-------------------#----------------------
----------------#####------------------
------------#########----------------- P
---------#############----------------
-----##################---------------
#######################-------------
#######################-----------
######################--------
#######################-----
#####################-
##############
Global CMT Convention Moment Tensor:
R T P
0.00e+00 9.18e+20 5.30e+20
9.18e+20 1.05e+22 -6.06e+21
5.30e+20 -6.06e+21 -1.05e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150918123517/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 = 150
DIP = 85
RAKE = 0
MW = 3.99
HS = 4.0
The NDK file is 20150918123517.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 2015/09/18 12:35:17:0 36.01 -96.84 3.7 4.1 Oklahoma
Stations used:
AG.HHAR GS.KAN05 GS.KAN10 GS.KAN12 GS.KAN13 GS.KAN14
GS.KAN16 GS.KAN17 GS.KS20 GS.KS21 GS.OK025 GS.OK029
GS.OK032 N4.R32B N4.T35B N4.U38B N4.Z35B OK.BCOK OK.BLOK
OK.CCOK OK.CHOK OK.CROK OK.FNO OK.LOOK OK.OKCFA OK.QUOK
OK.U32A OK.X34A OK.X37A TA.W39A US.KSU1 US.MIAR US.WMOK
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 0.08 n 3
Best Fitting Double Couple
Mo = 1.22e+22 dyne-cm
Mw = 3.99
Z = 4 km
Plane Strike Dip Rake
NP1 240 90 -175
NP2 150 85 0
Principal Axes:
Axis Value Plunge Azimuth
T 1.22e+22 4 15
N 0.00e+00 85 240
P -1.22e+22 4 105
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.05e+22
Mxy 6.06e+21
Mxz 9.18e+20
Myy -1.05e+22
Myz -5.30e+20
Mzz 0.00e+00
########### T
-############## ####
-----#######################
------########################
---------#########################
-----------#########################
-------------####################-----
---------------################---------
----------------############------------
------------------########----------------
-------------------####-------------------
-------------------#----------------------
----------------#####------------------
------------#########----------------- P
---------#############----------------
-----##################---------------
#######################-------------
#######################-----------
######################--------
#######################-----
#####################-
##############
Global CMT Convention Moment Tensor:
R T P
0.00e+00 9.18e+20 5.30e+20
9.18e+20 1.05e+22 -6.06e+21
5.30e+20 -6.06e+21 -1.05e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150918123517/index.html
|
egional Moment Tensor (Mwr)
Moment 1.795e+15 N-m
Magnitude 4.10
Depth 5.0 km
Percent DC 86%
Half Duration –
Catalog US (us20003l6t)
Data Source US1
Contributor US1
Nodal Planes
Plane Strike Dip Rake
NP1 149 70 -3
NP2 240 87 -160
Principal Axes
Axis Value Plunge Azimuth
T 1.858 12 13
N -0.133 70 247
P -1.725 16 106
|
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
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.
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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 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 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 1.0 330 75 0 3.79 0.3764
WVFGRD96 2.0 145 75 -15 3.91 0.4700
WVFGRD96 3.0 330 90 0 3.96 0.4973
WVFGRD96 4.0 150 85 0 3.99 0.5005
WVFGRD96 5.0 150 85 5 4.02 0.4918
WVFGRD96 6.0 150 80 5 4.05 0.4811
WVFGRD96 7.0 150 80 10 4.07 0.4717
WVFGRD96 8.0 330 70 10 4.10 0.4649
WVFGRD96 9.0 325 75 10 4.10 0.4547
WVFGRD96 10.0 325 75 10 4.12 0.4448
WVFGRD96 11.0 325 75 10 4.13 0.4344
WVFGRD96 12.0 325 75 10 4.14 0.4238
WVFGRD96 13.0 325 75 10 4.15 0.4134
WVFGRD96 14.0 325 80 10 4.16 0.4033
WVFGRD96 15.0 325 80 10 4.17 0.3932
WVFGRD96 16.0 325 80 10 4.18 0.3836
WVFGRD96 17.0 330 80 10 4.19 0.3751
WVFGRD96 18.0 330 80 10 4.20 0.3668
WVFGRD96 19.0 330 80 10 4.21 0.3590
WVFGRD96 20.0 330 80 10 4.22 0.3517
WVFGRD96 21.0 330 80 10 4.22 0.3447
WVFGRD96 22.0 330 80 10 4.23 0.3383
WVFGRD96 23.0 330 75 10 4.24 0.3320
WVFGRD96 24.0 330 75 10 4.24 0.3266
WVFGRD96 25.0 330 75 10 4.25 0.3214
WVFGRD96 26.0 330 75 10 4.26 0.3168
WVFGRD96 27.0 330 75 10 4.26 0.3124
WVFGRD96 28.0 330 75 10 4.27 0.3086
WVFGRD96 29.0 330 75 10 4.27 0.3047
The best solution is
WVFGRD96 4.0 150 85 0 3.99 0.5005
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 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 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 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 Dec 7 00:07:39 CST 2015
