The ANSS event ID is usp000a8dr and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000a8dr/executive.
2001/01/26 03:03:19 41.942 -80.802 5 3.9 Ohio
USGS/SLU Moment Tensor Solution
ENS 2001/01/26 03:03:19:0 41.94 -80.80 5.0 3.9 Ohio
Stations used:
IU.SSPA NM.BLO US.ACSO US.BINY US.BLA US.LSCT US.MCWV
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 = 7.00e+21 dyne-cm
Mw = 3.83
Z = 5 km
Plane Strike Dip Rake
NP1 185 90 -150
NP2 95 60 0
Principal Axes:
Axis Value Plunge Azimuth
T 7.00e+21 21 316
N 0.00e+00 60 185
P -7.00e+21 21 54
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.05e+21
Mxy -5.97e+21
Mxz 3.05e+20
Myy -1.05e+21
Myz -3.49e+21
Mzz 0.00e+00
#########-----
#############---------
###############-------------
## ###########--------------
#### T ###########----------- --
##### ###########----------- P ---
####################----------- ----
#####################-------------------
####################--------------------
#####################---------------------
-####################---------------------
---##################---------------------
-----################--------------------#
--------############-----------------###
-------------######-------------########
------------------####################
-----------------###################
----------------##################
--------------################
-------------###############
---------#############
-----#########
Global CMT Convention Moment Tensor:
R T P
0.00e+00 3.05e+20 3.49e+21
3.05e+20 1.05e+21 5.97e+21
3.49e+21 5.97e+21 -1.05e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20010126030319/index.html
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STK = 95
DIP = 60
RAKE = 0
MW = 3.83
HS = 5.0
The NDK file is 20010126030319.ndk The waveform inversion is preferred.
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.
USGS/SLU Moment Tensor Solution
ENS 2001/01/26 03:03:19:0 41.94 -80.80 5.0 3.9 Ohio
Stations used:
IU.SSPA NM.BLO US.ACSO US.BINY US.BLA US.LSCT US.MCWV
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 = 7.00e+21 dyne-cm
Mw = 3.83
Z = 5 km
Plane Strike Dip Rake
NP1 185 90 -150
NP2 95 60 0
Principal Axes:
Axis Value Plunge Azimuth
T 7.00e+21 21 316
N 0.00e+00 60 185
P -7.00e+21 21 54
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.05e+21
Mxy -5.97e+21
Mxz 3.05e+20
Myy -1.05e+21
Myz -3.49e+21
Mzz 0.00e+00
#########-----
#############---------
###############-------------
## ###########--------------
#### T ###########----------- --
##### ###########----------- P ---
####################----------- ----
#####################-------------------
####################--------------------
#####################---------------------
-####################---------------------
---##################---------------------
-----################--------------------#
--------############-----------------###
-------------######-------------########
------------------####################
-----------------###################
----------------##################
--------------################
-------------###############
---------#############
-----#########
Global CMT Convention Moment Tensor:
R T P
0.00e+00 3.05e+20 3.49e+21
3.05e+20 1.05e+21 5.97e+21
3.49e+21 5.97e+21 -1.05e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20010126030319/index.html
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Du et al (2003) 2001/01/26 03:03:19:0 41.942 -80.802 5.0 3.8 Ohio
Stations used:
Filtering commands used:
Best Fitting Double Couple
Mo = 7.50e+21 dyne-cm
Mw = 3.85
Z = 2 km
Plane Strike Dip Rake
NP1 5 79 159
NP2 99 69 12
Principal Axes:
Axis Value Plunge Azimuth
T 7.50e+21 23 321
N 0.00e+00 66 159
P -7.50e+21 7 53
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.19e+21
Mxy -6.68e+21
Mxz 1.55e+21
Myy -2.19e+21
Myz -2.37e+21
Mzz 1.01e+21
#########-----
##############--------
#################-----------
### ############-----------
##### T ############----------- P
###### ############----------- -
######################----------------
#######################-----------------
#######################-----------------
-#######################------------------
---#####################------------------
------##################------------------
-----------#############------------------
----------------######---------------###
----------------------##################
---------------------#################
-------------------#################
------------------################
----------------##############
--------------##############
----------############
------########
Global CMT Convention Moment Tensor:
R T P
1.01e+21 1.55e+21 2.37e+21
1.55e+21 1.19e+21 6.68e+21
2.37e+21 6.68e+21 -2.19e+21
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For this earthquake the source reference is the following:
Du, Wen-xuan; Kim, Won-Young; Sykes, Lynn R. (2003). Earthquake Source Parameters and State of Stress for the Northeastern United States and Southeastern Canada from Analysis of Regional Seismograms, Bull. Seism. Soc. Am. 93, 1633 - 164
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.
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.
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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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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 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 50 20 85 4.08 0.4276
WVFGRD96 2.0 95 60 0 3.80 0.4275
WVFGRD96 3.0 100 55 20 3.84 0.4390
WVFGRD96 4.0 95 60 5 3.82 0.4407
WVFGRD96 5.0 95 60 0 3.83 0.4407
WVFGRD96 6.0 270 65 -15 3.83 0.4394
WVFGRD96 7.0 270 70 -20 3.84 0.4398
WVFGRD96 8.0 270 70 -20 3.84 0.4385
WVFGRD96 9.0 270 70 -15 3.85 0.4345
WVFGRD96 10.0 270 70 -20 3.87 0.4305
WVFGRD96 11.0 270 70 -20 3.88 0.4236
WVFGRD96 12.0 270 70 -20 3.89 0.4148
WVFGRD96 13.0 270 75 -25 3.89 0.4050
WVFGRD96 14.0 270 75 -25 3.90 0.3941
WVFGRD96 15.0 270 75 -25 3.91 0.3828
WVFGRD96 16.0 265 70 -35 3.93 0.3729
WVFGRD96 17.0 250 65 -60 4.00 0.3646
WVFGRD96 18.0 245 70 -75 4.06 0.3583
WVFGRD96 19.0 245 75 -75 4.08 0.3521
WVFGRD96 20.0 245 75 -75 4.11 0.3515
WVFGRD96 21.0 245 75 -75 4.12 0.3453
WVFGRD96 22.0 245 75 -75 4.13 0.3386
WVFGRD96 23.0 245 75 -75 4.13 0.3320
WVFGRD96 24.0 245 75 -75 4.14 0.3253
WVFGRD96 25.0 245 75 -75 4.15 0.3187
WVFGRD96 26.0 245 80 -75 4.17 0.3121
WVFGRD96 27.0 245 80 -75 4.18 0.3059
WVFGRD96 28.0 5 80 -30 4.00 0.3046
WVFGRD96 29.0 5 80 -30 4.02 0.3080
The best solution is
WVFGRD96 5.0 95 60 0 3.83 0.4407
The mechanism corresponding to the best fit is
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The best fit as a function of depth is given in the following figure:
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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. |
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:
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.
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