Location
Location ANSS
The ANSS event ID is tx2023vxae and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/tx2023vxae/executive.
2023/11/08 10:27:49 31.622 -103.982 7.4 5.2 Texas
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2023/11/08 10:27:49:0 31.62 -103.98 7.4 5.2 Texas
Stations used:
4O.AT01 4O.BP01 4O.CV01 4O.DB02 4O.DB03 4O.DB04 4O.GV01
4O.GV02 4O.LWM1 4O.LWM2 4O.MBBB2 4O.MBBB4 4O.MBBB5 4O.MID01
4O.MID02 4O.MID03 4O.MO01 4O.OP01 4O.SA02 4O.SA04 4O.SA06
4O.SA07 4O.SA09 4O.SM01 4O.WB06 4O.WB07 4O.WB08 4O.WB09
4O.WB10 4O.WB11 4O.WB12 4T.NM01 4T.NM02 4T.NM03 TX.435B
TX.ALPN TX.APMT TX.BRDY TX.DKNS TX.DRZT TX.FW06 TX.FW07
TX.FW11 TX.FW14 TX.FW15 TX.HNDO TX.INDO TX.MB01 TX.MB02
TX.MB03 TX.MB04 TX.MB05 TX.MB06 TX.MB07 TX.MB08 TX.MB09
TX.MB10 TX.MB11 TX.MB12 TX.MB13 TX.MB14 TX.MB15 TX.MB17
TX.MB18 TX.MB19 TX.MB22 TX.MB23 TX.MNHN TX.ODSA TX.OZNA
TX.PB01 TX.PB03 TX.PB04 TX.PB05 TX.PB07 TX.PB08 TX.PB09
TX.PB10 TX.PB11 TX.PB12 TX.PB13 TX.PB14 TX.PB16 TX.PB17
TX.PB18 TX.PB21 TX.PB22 TX.PB28 TX.PB29 TX.PB30 TX.PB35
TX.PB37 TX.PB38 TX.PB42 TX.PB43 TX.PB44 TX.PB51 TX.PCOS
TX.PECS TX.PH02 TX.PH03 TX.PLPT TX.POST TX.RTBA TX.SAND
TX.SGCY TX.SMWD TX.SN02 TX.SN03 TX.SN04 TX.SN07 TX.SN08
TX.SN09 TX.SN10 TX.VHRN TX.WTFS
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +60
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
Best Fitting Double Couple
Mo = 5.25e+23 dyne-cm
Mw = 5.08
Z = 8 km
Plane Strike Dip Rake
NP1 289 55 -93
NP2 115 35 -85
Principal Axes:
Axis Value Plunge Azimuth
T 5.25e+23 10 21
N 0.00e+00 3 291
P -5.25e+23 79 185
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.24e+23
Mxy 1.71e+23
Mxz 1.78e+23
Myy 6.76e+22
Myz 4.16e+22
Mzz -4.91e+23
############
################ T ###
################### ######
##############################
##################################
####################################
##--------------------################
#--------------------------#############
#-----------------------------##########
###-------------------------------########
###---------------------------------######
####--------------- ----------------####
#####-------------- P -----------------###
#####------------- ------------------#
######----------------------------------
#######-------------------------------
#########--------------------------#
###########---------------------##
##############-----------#####
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-4.91e+23 1.78e+23 -4.16e+22
1.78e+23 4.24e+23 -1.71e+23
-4.16e+22 -1.71e+23 6.76e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20231108102749/index.html
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 115
DIP = 35
RAKE = -85
MW = 5.08
HS = 8.0
The NDK file is 20231108102749.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
| SLU |
USGSW |
USGS/SLU Moment Tensor Solution
ENS 2023/11/08 10:27:49:0 31.62 -103.98 7.4 5.2 Texas
Stations used:
4O.AT01 4O.BP01 4O.CV01 4O.DB02 4O.DB03 4O.DB04 4O.GV01
4O.GV02 4O.LWM1 4O.LWM2 4O.MBBB2 4O.MBBB4 4O.MBBB5 4O.MID01
4O.MID02 4O.MID03 4O.MO01 4O.OP01 4O.SA02 4O.SA04 4O.SA06
4O.SA07 4O.SA09 4O.SM01 4O.WB06 4O.WB07 4O.WB08 4O.WB09
4O.WB10 4O.WB11 4O.WB12 4T.NM01 4T.NM02 4T.NM03 TX.435B
TX.ALPN TX.APMT TX.BRDY TX.DKNS TX.DRZT TX.FW06 TX.FW07
TX.FW11 TX.FW14 TX.FW15 TX.HNDO TX.INDO TX.MB01 TX.MB02
TX.MB03 TX.MB04 TX.MB05 TX.MB06 TX.MB07 TX.MB08 TX.MB09
TX.MB10 TX.MB11 TX.MB12 TX.MB13 TX.MB14 TX.MB15 TX.MB17
TX.MB18 TX.MB19 TX.MB22 TX.MB23 TX.MNHN TX.ODSA TX.OZNA
TX.PB01 TX.PB03 TX.PB04 TX.PB05 TX.PB07 TX.PB08 TX.PB09
TX.PB10 TX.PB11 TX.PB12 TX.PB13 TX.PB14 TX.PB16 TX.PB17
TX.PB18 TX.PB21 TX.PB22 TX.PB28 TX.PB29 TX.PB30 TX.PB35
TX.PB37 TX.PB38 TX.PB42 TX.PB43 TX.PB44 TX.PB51 TX.PCOS
TX.PECS TX.PH02 TX.PH03 TX.PLPT TX.POST TX.RTBA TX.SAND
TX.SGCY TX.SMWD TX.SN02 TX.SN03 TX.SN04 TX.SN07 TX.SN08
TX.SN09 TX.SN10 TX.VHRN TX.WTFS
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +60
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
Best Fitting Double Couple
Mo = 5.25e+23 dyne-cm
Mw = 5.08
Z = 8 km
Plane Strike Dip Rake
NP1 289 55 -93
NP2 115 35 -85
Principal Axes:
Axis Value Plunge Azimuth
T 5.25e+23 10 21
N 0.00e+00 3 291
P -5.25e+23 79 185
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.24e+23
Mxy 1.71e+23
Mxz 1.78e+23
Myy 6.76e+22
Myz 4.16e+22
Mzz -4.91e+23
############
################ T ###
################### ######
##############################
##################################
####################################
##--------------------################
#--------------------------#############
#-----------------------------##########
###-------------------------------########
###---------------------------------######
####--------------- ----------------####
#####-------------- P -----------------###
#####------------- ------------------#
######----------------------------------
#######-------------------------------
#########--------------------------#
###########---------------------##
##############-----------#####
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-4.91e+23 1.78e+23 -4.16e+22
1.78e+23 4.24e+23 -1.71e+23
-4.16e+22 -1.71e+23 6.76e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20231108102749/index.html
|
W-phase Moment Tensor (Mww)
Moment
7.621e+16 N-m
Magnitude
5.19 Mww
Depth
11.5 km
Percent DC
99%
Half Duration
1.03 s
Catalog
US
Data Source
US 2
Contributor
US 2
Nodal Planes
Plane Strike Dip Rake
NP1 286 45 -91
NP2 107 45 -89
Principal Axes
Axis Value Plunge Azimuth
T 7.611e+16 0 197
N 0.019e+16 0 287
P -7.631e+16 90 100
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Magnitudes
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula
for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
mLg Magnitude
Left: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated.
Right: residuals as a function of distance and azimuth.
ML Magnitude
Left: ML computed using the IASPEI formula for Horizontal components. Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
Context
The left panel of the next figure presents the focal mechanism for this earthquake (red) in the context of other nearby events (blue) in the SLU Moment Tensor Catalog. 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). Thus context plot is useful for assessing the appropriateness of the moment tensor of this event.
Waveform Inversion using wvfgrd96
The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the
stations used for (red) 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's 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 +60
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 330 65 -45 4.67 0.2491
WVFGRD96 2.0 310 55 -70 4.85 0.3268
WVFGRD96 3.0 130 25 -65 4.95 0.3853
WVFGRD96 4.0 110 25 -100 4.98 0.4547
WVFGRD96 5.0 105 30 -100 4.99 0.4982
WVFGRD96 6.0 115 35 -85 5.00 0.5182
WVFGRD96 7.0 115 35 -85 5.01 0.5268
WVFGRD96 8.0 115 35 -85 5.08 0.5461
WVFGRD96 9.0 115 35 -85 5.08 0.5308
WVFGRD96 10.0 115 40 -85 5.08 0.5065
WVFGRD96 11.0 115 40 -85 5.07 0.4797
WVFGRD96 12.0 120 50 -80 5.06 0.4551
WVFGRD96 13.0 345 65 35 5.01 0.4364
WVFGRD96 14.0 345 65 30 5.02 0.4226
WVFGRD96 15.0 345 65 30 5.02 0.4096
WVFGRD96 16.0 345 65 30 5.02 0.3969
WVFGRD96 17.0 345 65 25 5.03 0.3850
WVFGRD96 18.0 345 65 25 5.03 0.3733
WVFGRD96 19.0 345 65 25 5.04 0.3626
WVFGRD96 20.0 345 65 25 5.05 0.3529
WVFGRD96 21.0 345 65 25 5.05 0.3431
WVFGRD96 22.0 345 65 25 5.06 0.3342
WVFGRD96 23.0 345 65 25 5.06 0.3263
WVFGRD96 24.0 345 65 25 5.07 0.3188
WVFGRD96 25.0 345 65 20 5.08 0.3121
WVFGRD96 26.0 335 75 -15 5.11 0.3123
WVFGRD96 27.0 335 75 -15 5.12 0.3091
WVFGRD96 28.0 335 75 -15 5.13 0.3056
WVFGRD96 29.0 335 75 -15 5.13 0.3015
The best solution is
WVFGRD96 8.0 115 35 -85 5.08 0.5461
The mechanism corresponding 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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off.
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 +60
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 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. The time scale is relative to the first trace sample.
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms.
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.
Velocity Model
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows
(The format is in the model96 format of Computer Programs in Seismology).
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
Last Changed Tue Apr 23 05:22:32 AM CDT 2024
