Location
Location ANSS
The ANSS event ID is us7000krer and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/us7000krer/executive.
2023/08/28 02:43:26 41.731 -80.972 5.0 3.6 Ohio
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2023/08/28 02:43:26:0 41.73 -80.97 5.0 3.6 Ohio
Stations used:
CN.CHRO CN.EFO CN.GAC CN.KGNO CN.SADO IU.SSPA IU.WCI LD.FOR
LD.GCMD LD.GEDE LD.KSCT LD.KSPA LD.MMNY LD.SDMD LD.WVNY
LM.NHBP MU.EARS MU.MUG1 N4.E46A N4.I45A N4.I49A N4.J47A
N4.J55A N4.J57A N4.J59A N4.K50A N4.K57A N4.L46A N4.L56A
N4.L59A N4.M44A N4.M50A N4.M57A N4.N47A N4.N49A N4.N51A
N4.N53A N4.N58A N4.N62A N4.O48B N4.O49A N4.O52A N4.O54A
N4.P46A N4.P48A N4.P53A N4.Q51A N4.Q52A N4.Q54A N4.R49A
N4.R50A N4.R55A N4.S51A N4.S54A N4.SFIN N4.T50A N4.T57A
N4.T59A N4.V55A NE.TRY NE.WSPT NM.BLO NW.L44A OH.CPOH
OH.KLOH OH.MFOH US.AAM US.ACSO US.BINY US.CBN US.ERPA
US.GLMI US.LONY US.MCWV US.TZTN WU.BASO
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 = 3.76e+21 dyne-cm
Mw = 3.65
Z = 4 km
Plane Strike Dip Rake
NP1 5 90 -150
NP2 275 60 0
Principal Axes:
Axis Value Plunge Azimuth
T 3.76e+21 21 136
N 0.00e+00 60 5
P -3.76e+21 21 234
Moment Tensor: (dyne-cm)
Component Value
Mxx 5.65e+20
Mxy -3.21e+21
Mxz -1.64e+20
Myy -5.65e+20
Myz 1.87e+21
Mzz 0.00e+00
#########-----
#############---------
###############-------------
################--------------
##################----------------
###################-----------------
####################------------------
########-------------######-------------
###-----------------############--------
#--------------------################-----
---------------------##################---
---------------------####################-
---------------------#####################
--------------------####################
-------------------#####################
---- -----------####################
--- P -----------########### #####
-- -----------########### T ####
--------------########### ##
-------------###############
---------#############
-----#########
Global CMT Convention Moment Tensor:
R T P
0.00e+00 -1.64e+20 -1.87e+21
-1.64e+20 5.65e+20 3.21e+21
-1.87e+21 3.21e+21 -5.65e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20230828024326/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 = 275
DIP = 60
RAKE = 0
MW = 3.65
HS = 4.0
The NDK file is 20230828024326.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 |
USGS/SLU Moment Tensor Solution
ENS 2023/08/28 02:43:26:0 41.73 -80.97 5.0 3.6 Ohio
Stations used:
CN.CHRO CN.EFO CN.GAC CN.KGNO CN.SADO IU.SSPA IU.WCI LD.FOR
LD.GCMD LD.GEDE LD.KSCT LD.KSPA LD.MMNY LD.SDMD LD.WVNY
LM.NHBP MU.EARS MU.MUG1 N4.E46A N4.I45A N4.I49A N4.J47A
N4.J55A N4.J57A N4.J59A N4.K50A N4.K57A N4.L46A N4.L56A
N4.L59A N4.M44A N4.M50A N4.M57A N4.N47A N4.N49A N4.N51A
N4.N53A N4.N58A N4.N62A N4.O48B N4.O49A N4.O52A N4.O54A
N4.P46A N4.P48A N4.P53A N4.Q51A N4.Q52A N4.Q54A N4.R49A
N4.R50A N4.R55A N4.S51A N4.S54A N4.SFIN N4.T50A N4.T57A
N4.T59A N4.V55A NE.TRY NE.WSPT NM.BLO NW.L44A OH.CPOH
OH.KLOH OH.MFOH US.AAM US.ACSO US.BINY US.CBN US.ERPA
US.GLMI US.LONY US.MCWV US.TZTN WU.BASO
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 = 3.76e+21 dyne-cm
Mw = 3.65
Z = 4 km
Plane Strike Dip Rake
NP1 5 90 -150
NP2 275 60 0
Principal Axes:
Axis Value Plunge Azimuth
T 3.76e+21 21 136
N 0.00e+00 60 5
P -3.76e+21 21 234
Moment Tensor: (dyne-cm)
Component Value
Mxx 5.65e+20
Mxy -3.21e+21
Mxz -1.64e+20
Myy -5.65e+20
Myz 1.87e+21
Mzz 0.00e+00
#########-----
#############---------
###############-------------
################--------------
##################----------------
###################-----------------
####################------------------
########-------------######-------------
###-----------------############--------
#--------------------################-----
---------------------##################---
---------------------####################-
---------------------#####################
--------------------####################
-------------------#####################
---- -----------####################
--- P -----------########### #####
-- -----------########### T ####
--------------########### ##
-------------###############
---------#############
-----#########
Global CMT Convention Moment Tensor:
R T P
0.00e+00 -1.64e+20 -1.87e+21
-1.64e+20 5.65e+20 3.21e+21
-1.87e+21 3.21e+21 -5.65e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20230828024326/index.html
|
egional Moment Tensor (Mwr)
Moment 3.229e+14 N-m
Magnitude 3.61 Mwr
Depth 3.0 km
Percent DC 61%
Half Duration -
Catalog US
Data Source US 1
Contributor US 1
Nodal Planes
Plane Strike Dip Rake
NP1 278 49 13
NP2 180 81 138
Principal Axes
Axis Value Plunge Azimuth
T 3.519e+14 N-m 35 130
N -0.691e+14 N-m 48 349
P -2.828e+14 N-m 20
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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 +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 1.0 275 55 0 3.60 0.4410
WVFGRD96 2.0 275 50 0 3.65 0.4569
WVFGRD96 3.0 275 55 0 3.65 0.4660
WVFGRD96 4.0 275 60 0 3.65 0.4680
WVFGRD96 5.0 275 60 0 3.66 0.4660
WVFGRD96 6.0 275 65 -5 3.66 0.4601
WVFGRD96 7.0 275 65 -5 3.67 0.4518
WVFGRD96 8.0 275 65 0 3.67 0.4408
WVFGRD96 9.0 275 70 -5 3.68 0.4278
WVFGRD96 10.0 275 65 -5 3.69 0.4132
WVFGRD96 11.0 275 70 -5 3.70 0.3980
WVFGRD96 12.0 275 70 -5 3.71 0.3820
WVFGRD96 13.0 275 70 -5 3.71 0.3657
WVFGRD96 14.0 90 65 -15 3.71 0.3513
WVFGRD96 15.0 95 65 -5 3.72 0.3370
WVFGRD96 16.0 95 65 -5 3.73 0.3229
WVFGRD96 17.0 95 65 -5 3.74 0.3089
WVFGRD96 18.0 95 60 -5 3.74 0.2949
WVFGRD96 19.0 95 60 -5 3.74 0.2813
WVFGRD96 20.0 95 55 -5 3.76 0.2680
WVFGRD96 21.0 95 55 0 3.76 0.2559
WVFGRD96 22.0 95 55 0 3.76 0.2442
WVFGRD96 23.0 270 70 -15 3.75 0.2348
WVFGRD96 24.0 270 70 -15 3.76 0.2279
WVFGRD96 25.0 270 70 -15 3.76 0.2212
WVFGRD96 26.0 270 70 -20 3.77 0.2149
WVFGRD96 27.0 270 70 -20 3.77 0.2089
WVFGRD96 28.0 270 65 -15 3.78 0.2040
WVFGRD96 29.0 270 65 -20 3.79 0.2006
The best solution is
WVFGRD96 4.0 275 60 0 3.65 0.4680
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 CUS.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
CUS Model with Q from simple gamma values
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
1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00
9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00
10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00
20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00
0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00
Last Changed Tue Apr 23 03:22:23 AM CDT 2024
