2008/09/06 19:48:03 45.8560 26.4780 31.0 4.70 ROMANIA
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
2008/09/06 19:48:03 45.8560 26.4780 31.0 4.70 ROMANIA
Best Fitting Double Couple
Mo = 2.09e+22 dyne-cm
Mw = 4.18
Z = 14 km
Plane Strike Dip Rake
NP1 337 80 107
NP2 95 20 30
Principal Axes:
Axis Value Plunge Azimuth
T 2.09e+22 52 267
N 0.00e+00 17 153
P -2.09e+22 33 52
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.59e+21
Mxy -6.68e+21
Mxz -6.49e+21
Myy -1.13e+21
Myz -1.76e+22
Mzz 6.71e+21
--------------
####------------------
########--------------------
###########-------------------
##############--------------------
################------------ -----
##################----------- P ------
####################---------- -------
#####################-------------------
#######################-------------------
########## ##########-------------------
-######### T ###########------------------
-######### ############----------------#
-########################---------------
--#######################--------------#
--#######################------------#
---#####################----------##
----####################-------###
----##################----####
-------##############-######
-------------------###
--------------
Harvard Convention
Moment Tensor:
R T F
6.71e+21 -6.49e+21 1.76e+22
-6.49e+21 -5.59e+21 6.68e+21
1.76e+22 6.68e+21 -1.13e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20080906194803/index.html
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STK = 95
DIP = 20
RAKE = 30
MW = 4.18
HS = 14.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
2008/09/06 19:48:03 45.8560 26.4780 31.0 4.70 ROMANIA
Best Fitting Double Couple
Mo = 2.09e+22 dyne-cm
Mw = 4.18
Z = 14 km
Plane Strike Dip Rake
NP1 337 80 107
NP2 95 20 30
Principal Axes:
Axis Value Plunge Azimuth
T 2.09e+22 52 267
N 0.00e+00 17 153
P -2.09e+22 33 52
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.59e+21
Mxy -6.68e+21
Mxz -6.49e+21
Myy -1.13e+21
Myz -1.76e+22
Mzz 6.71e+21
--------------
####------------------
########--------------------
###########-------------------
##############--------------------
################------------ -----
##################----------- P ------
####################---------- -------
#####################-------------------
#######################-------------------
########## ##########-------------------
-######### T ###########------------------
-######### ############----------------#
-########################---------------
--#######################--------------#
--#######################------------#
---#####################----------##
----####################-------###
----##################----####
-------##############-######
-------------------###
--------------
Harvard Convention
Moment Tensor:
R T F
6.71e+21 -6.49e+21 1.76e+22
-6.49e+21 -5.59e+21 6.68e+21
1.76e+22 6.68e+21 -1.13e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20080906194803/index.html
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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.
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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 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:
hp c 0.02 n 3 lp c 0.05 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 95 60 30 3.88 0.3367
WVFGRD96 1.0 90 75 15 3.91 0.3360
WVFGRD96 2.0 95 65 30 3.99 0.3693
WVFGRD96 3.0 90 65 -15 4.07 0.3649
WVFGRD96 4.0 80 5 15 4.16 0.4298
WVFGRD96 5.0 75 10 5 4.16 0.5424
WVFGRD96 6.0 80 10 15 4.15 0.6199
WVFGRD96 7.0 85 10 20 4.14 0.6736
WVFGRD96 8.0 85 10 20 4.21 0.7088
WVFGRD96 9.0 85 10 20 4.20 0.7424
WVFGRD96 10.0 95 15 30 4.19 0.7649
WVFGRD96 11.0 95 15 30 4.19 0.7808
WVFGRD96 12.0 95 15 30 4.18 0.7880
WVFGRD96 13.0 95 20 30 4.18 0.7913
WVFGRD96 14.0 95 20 30 4.18 0.7914
WVFGRD96 15.0 105 20 50 4.17 0.7885
WVFGRD96 16.0 105 20 50 4.17 0.7840
WVFGRD96 17.0 295 75 85 4.18 0.7785
WVFGRD96 18.0 125 20 95 4.18 0.7700
WVFGRD96 19.0 125 20 95 4.18 0.7619
WVFGRD96 20.0 300 70 90 4.18 0.7508
WVFGRD96 21.0 120 15 95 4.19 0.7412
WVFGRD96 22.0 120 15 95 4.19 0.7292
WVFGRD96 23.0 120 15 95 4.19 0.7168
WVFGRD96 24.0 115 15 90 4.20 0.7047
WVFGRD96 25.0 110 15 85 4.20 0.6919
WVFGRD96 26.0 110 15 85 4.20 0.6794
WVFGRD96 27.0 110 15 85 4.20 0.6668
WVFGRD96 28.0 110 15 85 4.20 0.6538
WVFGRD96 29.0 110 15 80 4.20 0.6407
WVFGRD96 30.0 100 15 70 4.20 0.6281
WVFGRD96 31.0 105 15 75 4.20 0.6162
WVFGRD96 32.0 105 15 75 4.21 0.6038
WVFGRD96 33.0 110 15 80 4.21 0.5913
WVFGRD96 34.0 100 15 70 4.21 0.5802
WVFGRD96 35.0 85 70 25 4.37 0.5701
WVFGRD96 36.0 85 70 20 4.37 0.5691
WVFGRD96 37.0 85 70 20 4.39 0.5674
WVFGRD96 38.0 85 75 15 4.41 0.5637
WVFGRD96 39.0 85 75 15 4.43 0.5589
WVFGRD96 40.0 90 60 30 4.46 0.5623
WVFGRD96 41.0 90 60 30 4.47 0.5560
WVFGRD96 42.0 90 60 25 4.47 0.5501
WVFGRD96 43.0 85 70 20 4.49 0.5442
WVFGRD96 44.0 85 65 20 4.48 0.5379
WVFGRD96 45.0 85 65 20 4.49 0.5321
WVFGRD96 46.0 85 65 20 4.50 0.5272
WVFGRD96 47.0 85 65 20 4.50 0.5212
WVFGRD96 48.0 85 65 20 4.51 0.5152
WVFGRD96 49.0 85 65 20 4.52 0.5092
WVFGRD96 50.0 85 65 20 4.52 0.5027
The best solution is
WVFGRD96 14.0 95 20 30 4.18 0.7914
The mechanism correspond 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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was
hp c 0.02 n 3 lp c 0.05 n 3
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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. |
Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
The WUS 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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Sat Sep 6 16:14:45 MDT 2008