Location
Location SLU
When processed in the 0.03 - 0.10 Hz band the SLU RMT solution was opposite that of the NEIC solution, e.g., thrust vs normal. First motions were read and the event located using elocate (results are in elocate.txt). The first motions were compatible with a normal faulting solution. As a result the RMT was resun using hte 0.03 - 0.07 Hz passband, and the retulsting solution, indicated on the first motion plot below, agrees with the NEIC solution.
The regional surface wave tomography (http://www.eas.slu.edu/eqc/eqc_research/CUSTOMO/CUSTOMO2/NADSP/36.-107.png support the use of the WUS model but in the lower frequency band.
Location ANSS
2021/07/12 15:33:35 36.225 -106.744 16.6 4.1 New Mexico
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2021/07/12 15:33:35:0 36.22 -106.74 16.6 4.1 New Mexico
Stations used:
AE.HANNA AE.X18A C0.LAMA C0.Q24A C0.T25A IU.ANMO N4.MSTX
SC.Y22A TX.PH02 TX.RTBA US.ISCO US.MVCO US.SDCO US.WUAZ
UU.HMU YX.UNM3 YX.UNM5
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 0.07 n 3
Best Fitting Double Couple
Mo = 2.19e+22 dyne-cm
Mw = 4.16
Z = 15 km
Plane Strike Dip Rake
NP1 145 73 -148
NP2 45 60 -20
Principal Axes:
Axis Value Plunge Azimuth
T 2.19e+22 8 273
N 0.00e+00 54 171
P -2.19e+22 34 9
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.46e+22
Mxy -3.24e+21
Mxz -9.91e+21
Myy 2.10e+22
Myz -4.62e+21
Mzz -6.48e+21
--------------
----------------------
##------------- ----------
####------------ P -----------
######------------ -----------##
########------------------------####
#########------------------------#####
###########----------------------#######
############---------------------#######
###########-------------------#########
T ############----------------###########
#############--------------############
##################-----------#############
##################--------##############
###################-----################
####################-#################
##################---###############
#############---------############
#######---------------########
-----------------------#####
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-6.48e+21 -9.91e+21 4.62e+21
-9.91e+21 -1.46e+22 3.24e+21
4.62e+21 3.24e+21 2.10e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20210712153335/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 = 45
DIP = 60
RAKE = -20
MW = 4.16
HS = 15.0
The NDK file is 20210712153335.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
USGSMWR |
SLUFM |
USGS/SLU Moment Tensor Solution
ENS 2021/07/12 15:33:35:0 36.22 -106.74 16.6 4.1 New Mexico
Stations used:
AE.HANNA AE.X18A C0.LAMA C0.Q24A C0.T25A IU.ANMO N4.MSTX
SC.Y22A TX.PH02 TX.RTBA US.ISCO US.MVCO US.SDCO US.WUAZ
UU.HMU YX.UNM3 YX.UNM5
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 0.07 n 3
Best Fitting Double Couple
Mo = 2.19e+22 dyne-cm
Mw = 4.16
Z = 15 km
Plane Strike Dip Rake
NP1 145 73 -148
NP2 45 60 -20
Principal Axes:
Axis Value Plunge Azimuth
T 2.19e+22 8 273
N 0.00e+00 54 171
P -2.19e+22 34 9
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.46e+22
Mxy -3.24e+21
Mxz -9.91e+21
Myy 2.10e+22
Myz -4.62e+21
Mzz -6.48e+21
--------------
----------------------
##------------- ----------
####------------ P -----------
######------------ -----------##
########------------------------####
#########------------------------#####
###########----------------------#######
############---------------------#######
###########-------------------#########
T ############----------------###########
#############--------------############
##################-----------#############
##################--------##############
###################-----################
####################-#################
##################---###############
#############---------############
#######---------------########
-----------------------#####
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-6.48e+21 -9.91e+21 4.62e+21
-9.91e+21 -1.46e+22 3.24e+21
4.62e+21 3.24e+21 2.10e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20210712153335/index.html
|
Regional Moment Tensor (Mwr)
Moment 2.681e+15 N-m
Magnitude 4.22 Mwr
Depth 14.0 km
Percent DC 83%
Half Duration -
Catalog US
Data Source US 1
Contributor US 1
Nodal Planes
Plane Strike Dip Rake
NP1 41° 59° -37°
NP2 152° 59° -143°
Principal Axes
Axis Value Plunge Azimuth
T 2.789e+15 N-m 0° 97°
N -0.232e+15 N-m 43° 187°
P -2.557e+15 N-m 47° 7°
|
First motions and takeoff angles from an elocate run.
|
Magnitudes
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 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 -40 o DIST/3.3 +50
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 1.0 105 45 -85 3.86 0.3784
WVFGRD96 2.0 280 45 -90 3.95 0.4469
WVFGRD96 3.0 310 70 -50 3.97 0.4449
WVFGRD96 4.0 310 70 -50 4.00 0.4749
WVFGRD96 5.0 230 50 10 3.99 0.4948
WVFGRD96 6.0 230 50 10 4.00 0.5216
WVFGRD96 7.0 230 55 10 4.02 0.5430
WVFGRD96 8.0 225 45 -10 4.07 0.5622
WVFGRD96 9.0 225 50 -15 4.08 0.5791
WVFGRD96 10.0 150 70 45 4.11 0.5942
WVFGRD96 11.0 150 70 40 4.11 0.6096
WVFGRD96 12.0 150 70 40 4.13 0.6189
WVFGRD96 13.0 150 65 40 4.14 0.6234
WVFGRD96 14.0 45 60 -20 4.15 0.6300
WVFGRD96 15.0 45 60 -20 4.16 0.6311
WVFGRD96 16.0 45 60 -15 4.17 0.6283
WVFGRD96 17.0 45 60 -15 4.18 0.6230
WVFGRD96 18.0 45 60 -15 4.19 0.6149
WVFGRD96 19.0 50 60 -10 4.19 0.6059
WVFGRD96 20.0 50 60 -10 4.20 0.5947
WVFGRD96 21.0 55 60 15 4.22 0.5839
WVFGRD96 22.0 60 60 25 4.22 0.5732
WVFGRD96 23.0 60 60 25 4.23 0.5621
WVFGRD96 24.0 60 60 25 4.24 0.5499
WVFGRD96 25.0 60 60 25 4.25 0.5368
WVFGRD96 26.0 60 60 20 4.25 0.5236
WVFGRD96 27.0 60 60 20 4.26 0.5120
WVFGRD96 28.0 60 60 20 4.27 0.5007
WVFGRD96 29.0 60 60 20 4.28 0.4890
The best solution is
WVFGRD96 15.0 45 60 -20 4.16 0.6311
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 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.07 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.
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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:
- 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 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.
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 12 Jul 2021 01:57:21 PM CDT
