Location
Location ANSS
The ANSS event ID is tx2025iqwk and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/tx2025iqwk/executive.
2025/05/04 01:47:05 31.647 -104.458 7.5 5.4 Texas
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2025/05/04 01:47:05:0 31.65 -104.46 7.5 5.4 Texas
Stations used:
4O.BB01 4O.BP01 4O.CT01 4O.CT02 4O.CV01 4O.DB02 4O.DB03
4O.DB04 4O.LWM1 4O.LWM2 4O.LWM3 4O.MBBB2 4O.MID01 4O.MID02
4O.MID03 4O.NGL01 4O.NGL02 4O.PL01 4O.PR01 4O.PRS01 4O.SA04
4O.SA06 4O.SA07 4O.SA09 4O.SE01 4O.SM02 4O.SM05 4O.VW01
4O.WB02 4O.WB03 4O.WB04 4O.WB05 4O.WB06 4O.WB07 4O.WB08
4O.WB09 4O.WB10 4O.WB11 4O.WB12 4O.WW01 4T.NM01 4T.NM02
4T.NM03 TX.MB01 TX.MB04 TX.MB08 TX.MB15 TX.MB18 TX.MB25
TX.MNHN TX.ODSA TX.PB01 TX.PB03 TX.PB04 TX.PB05 TX.PB06
TX.PB07 TX.PB08 TX.PB09 TX.PB10 TX.PB11 TX.PB12 TX.PB13
TX.PB14 TX.PB16 TX.PB17 TX.PB18 TX.PB20 TX.PB21 TX.PB22
TX.PB23 TX.PB24 TX.PB25 TX.PB26 TX.PB30 TX.PB31 TX.PB33
TX.PB34 TX.PB39 TX.PB40 TX.PB43 TX.PB44 TX.PB46 TX.PB47
TX.PB51 TX.PB54 TX.PECS TX.VHRN
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 0.10 n 3
Best Fitting Double Couple
Mo = 5.82e+23 dyne-cm
Mw = 5.11
Z = 9 km
Plane Strike Dip Rake
NP1 246 55 -87
NP2 60 35 -95
Principal Axes:
Axis Value Plunge Azimuth
T 5.82e+23 10 334
N 0.00e+00 3 64
P -5.82e+23 80 170
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.34e+23
Mxy -2.21e+23
Mxz 1.93e+23
Myy 1.11e+23
Myz -6.32e+22
Mzz -5.45e+23
##############
# T ##################
#### #####################
##############################
##################################
#####################------------###
################---------------------#
#############-------------------------##
##########----------------------------##
#########------------------------------###
#######-------------------------------####
######-------------- ---------------####
####---------------- P --------------#####
##----------------- -------------#####
##-------------------------------#######
------------------------------########
---------------------------#########
#----------------------###########
###--------------#############
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-5.45e+23 1.93e+23 6.32e+22
1.93e+23 4.34e+23 2.21e+23
6.32e+22 2.21e+23 1.11e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250504014705/index.html
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Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 60
DIP = 35
RAKE = -95
MW = 5.11
HS = 9.0
The NDK file is 20250504014705.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 |
USGSMWR |
USGSW |
USGS/SLU Moment Tensor Solution
ENS 2025/05/04 01:47:05:0 31.65 -104.46 7.5 5.4 Texas
Stations used:
4O.BB01 4O.BP01 4O.CT01 4O.CT02 4O.CV01 4O.DB02 4O.DB03
4O.DB04 4O.LWM1 4O.LWM2 4O.LWM3 4O.MBBB2 4O.MID01 4O.MID02
4O.MID03 4O.NGL01 4O.NGL02 4O.PL01 4O.PR01 4O.PRS01 4O.SA04
4O.SA06 4O.SA07 4O.SA09 4O.SE01 4O.SM02 4O.SM05 4O.VW01
4O.WB02 4O.WB03 4O.WB04 4O.WB05 4O.WB06 4O.WB07 4O.WB08
4O.WB09 4O.WB10 4O.WB11 4O.WB12 4O.WW01 4T.NM01 4T.NM02
4T.NM03 TX.MB01 TX.MB04 TX.MB08 TX.MB15 TX.MB18 TX.MB25
TX.MNHN TX.ODSA TX.PB01 TX.PB03 TX.PB04 TX.PB05 TX.PB06
TX.PB07 TX.PB08 TX.PB09 TX.PB10 TX.PB11 TX.PB12 TX.PB13
TX.PB14 TX.PB16 TX.PB17 TX.PB18 TX.PB20 TX.PB21 TX.PB22
TX.PB23 TX.PB24 TX.PB25 TX.PB26 TX.PB30 TX.PB31 TX.PB33
TX.PB34 TX.PB39 TX.PB40 TX.PB43 TX.PB44 TX.PB46 TX.PB47
TX.PB51 TX.PB54 TX.PECS TX.VHRN
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 0.10 n 3
Best Fitting Double Couple
Mo = 5.82e+23 dyne-cm
Mw = 5.11
Z = 9 km
Plane Strike Dip Rake
NP1 246 55 -87
NP2 60 35 -95
Principal Axes:
Axis Value Plunge Azimuth
T 5.82e+23 10 334
N 0.00e+00 3 64
P -5.82e+23 80 170
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.34e+23
Mxy -2.21e+23
Mxz 1.93e+23
Myy 1.11e+23
Myz -6.32e+22
Mzz -5.45e+23
##############
# T ##################
#### #####################
##############################
##################################
#####################------------###
################---------------------#
#############-------------------------##
##########----------------------------##
#########------------------------------###
#######-------------------------------####
######-------------- ---------------####
####---------------- P --------------#####
##----------------- -------------#####
##-------------------------------#######
------------------------------########
---------------------------#########
#----------------------###########
###--------------#############
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-5.45e+23 1.93e+23 6.32e+22
1.93e+23 4.34e+23 2.21e+23
6.32e+22 2.21e+23 1.11e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250504014705/index.html
|
Regional Moment Tensor (Mwr)
Moment 5.077e+16 N-m
Magnitude 5.07 Mwr
Depth 9.0 km
Percent DC 85%
Half Duration -
Catalog US
Data Source US
Contributor US
Nodal Planes
Plane Strike Dip Rake
NP1 57 39 -104
NP2 255 52 -79
Principal Axes
Axis Value Plunge Azimuth
T 4.870e+16 6 337
N 0.390e+16 8 68
P -5.260e+16 79 210
|
W-phase Moment Tensor (Mww)
Moment 6.968e+16 N-m
Magnitude 5.16 Mww
Depth 11.5 km
Percent DC 34%
Half Duration 0.50 s
Catalog US
Data Source US
Contributor US
Nodal Planes
Plane Strike Dip Rake
NP1 273 48 -58
NP2 51 51 -120
Principal Axes
Axis Value Plunge Azimuth
T 5.300e+16 2 161
N 2.593e+16 23 71
P -7.893e+16 67 256
|
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 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 150 40 65 4.58 0.1925
WVFGRD96 2.0 135 35 50 4.75 0.2422
WVFGRD96 3.0 270 25 -20 4.85 0.3228
WVFGRD96 4.0 270 30 -40 4.89 0.4071
WVFGRD96 5.0 250 60 -85 4.97 0.4804
WVFGRD96 6.0 250 60 -85 5.00 0.5427
WVFGRD96 7.0 60 35 -95 5.01 0.5761
WVFGRD96 8.0 245 55 -85 5.09 0.5869
WVFGRD96 9.0 60 35 -95 5.11 0.5981
WVFGRD96 10.0 60 35 -95 5.11 0.5898
WVFGRD96 11.0 60 35 -95 5.12 0.5697
WVFGRD96 12.0 65 40 -85 5.12 0.5430
WVFGRD96 13.0 70 45 -80 5.13 0.5132
WVFGRD96 14.0 70 45 -80 5.13 0.4820
WVFGRD96 15.0 75 50 -70 5.13 0.4526
WVFGRD96 16.0 80 55 -65 5.14 0.4251
WVFGRD96 17.0 85 60 -55 5.14 0.4006
WVFGRD96 18.0 90 60 -50 5.14 0.3804
WVFGRD96 19.0 90 60 -50 5.15 0.3619
WVFGRD96 20.0 90 65 -50 5.16 0.3450
WVFGRD96 21.0 90 65 -50 5.18 0.3318
WVFGRD96 22.0 90 65 -50 5.18 0.3188
WVFGRD96 23.0 90 65 -50 5.19 0.3065
WVFGRD96 24.0 90 65 -50 5.19 0.2949
WVFGRD96 25.0 90 70 -50 5.20 0.2856
WVFGRD96 26.0 95 70 -45 5.20 0.2783
WVFGRD96 27.0 95 70 -45 5.21 0.2714
WVFGRD96 28.0 95 70 -45 5.21 0.2641
WVFGRD96 29.0 95 75 -45 5.22 0.2576
The best solution is
WVFGRD96 9.0 60 35 -95 5.11 0.5981
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 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 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. 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
Inversions at higher frequencies
For a large event, it is interesting to see how well the Green's functions can fit the filtered waveforms at
higher frequencies. These computations are not meant to provide the moment tensor. The pupose is to determine the upper frequencies at which simple Earth models suffice. Even if the fits are not good, it is interesting to see how well peak amplitudes agree.
In the figures that follow, the red traces are the filtered observed ground velocities (m/s) and the blue are the model predictions.
It is interesting that the surface wave is so strong, event ar higher frequencies.
0.03 - 0.25 Hz
Here the inversion is run at higher frequencies. A good fit is not surprising since the 0.05 - 0.15 Hz band is used successfully for smaller events in this region. The best fitting solution is
WVFGRD96 9.0 70 50 -80 5.10 0.4721
snd the waveform comaparison is
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0.03 - 0.50 Hz
Here the inversion is run at higher frequencies. A good fit is not surprising since the 0.05 - 0.15 Hz band is used successfully for smaller events in this region. The best fitting solution is
WVFGRD96 8.0 60 45 -90 4.97 0.1741
snd the waveform comaparison is
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Last Changed Sun May 4 15:53:18 CDT 2025
