2008/08/03 00:39:17 39.6390 23.8370 10.0 4.90 GREECE
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
2008/08/03 00:39:17 39.6390 23.8370 10.0 4.90 GREECE
Best Fitting Double Couple
Mo = 5.01e+23 dyne-cm
Mw = 5.10
Z = 20 km
Plane Strike Dip Rake
NP1 248 80 -165
NP2 155 75 -10
Principal Axes:
Axis Value Plunge Azimuth
T 5.01e+23 4 21
N 0.00e+00 72 279
P -5.01e+23 18 112
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.73e+23
Mxy 3.23e+23
Mxz 8.39e+22
Myy -3.29e+23
Myz -1.22e+23
Mzz -4.35e+22
############ T
--############## ###
-----#######################
-------#######################
---------#########################
----------##########################
------------##########################
-------------##################---------
--------------###########---------------
----------------#####---------------------
----------------#-------------------------
-------------####-------------------------
---------#########------------------------
-----#############----------------- --
---################---------------- P --
###################--------------- -
###################-----------------
####################--------------
###################-----------
###################---------
##################----
##############
Harvard Convention
Moment Tensor:
R T F
-4.35e+22 8.39e+22 1.22e+23
8.39e+22 3.73e+23 -3.23e+23
1.22e+23 -3.23e+23 -3.29e+23
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20080803003917/index.html
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STK = 155
DIP = 75
RAKE = -10
MW = 5.10
HS = 20.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
2008/08/03 00:39:17 39.6390 23.8370 10.0 4.90 GREECE
Best Fitting Double Couple
Mo = 5.01e+23 dyne-cm
Mw = 5.10
Z = 20 km
Plane Strike Dip Rake
NP1 248 80 -165
NP2 155 75 -10
Principal Axes:
Axis Value Plunge Azimuth
T 5.01e+23 4 21
N 0.00e+00 72 279
P -5.01e+23 18 112
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.73e+23
Mxy 3.23e+23
Mxz 8.39e+22
Myy -3.29e+23
Myz -1.22e+23
Mzz -4.35e+22
############ T
--############## ###
-----#######################
-------#######################
---------#########################
----------##########################
------------##########################
-------------##################---------
--------------###########---------------
----------------#####---------------------
----------------#-------------------------
-------------####-------------------------
---------#########------------------------
-----#############----------------- --
---################---------------- P --
###################--------------- -
###################-----------------
####################--------------
###################-----------
###################---------
##################----
##############
Harvard Convention
Moment Tensor:
R T F
-4.35e+22 8.39e+22 1.22e+23
8.39e+22 3.73e+23 -3.23e+23
1.22e+23 -3.23e+23 -3.29e+23
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20080803003917/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 0.04 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 145 30 -20 5.04 0.3754
WVFGRD96 1.0 145 45 -25 4.96 0.3896
WVFGRD96 2.0 145 35 -20 5.06 0.4317
WVFGRD96 3.0 145 40 -20 5.04 0.4544
WVFGRD96 4.0 150 55 -20 4.99 0.4721
WVFGRD96 5.0 150 60 -20 4.99 0.4843
WVFGRD96 6.0 155 70 5 4.98 0.5014
WVFGRD96 7.0 155 70 15 5.01 0.5197
WVFGRD96 8.0 155 70 15 5.02 0.5298
WVFGRD96 9.0 155 70 20 5.04 0.5376
WVFGRD96 10.0 155 70 20 5.06 0.5444
WVFGRD96 11.0 155 75 20 5.06 0.5461
WVFGRD96 12.0 155 75 20 5.07 0.5506
WVFGRD96 13.0 155 75 20 5.07 0.5498
WVFGRD96 14.0 155 70 0 5.06 0.5501
WVFGRD96 15.0 155 70 -10 5.07 0.5569
WVFGRD96 16.0 155 70 -10 5.07 0.5582
WVFGRD96 17.0 155 70 -10 5.08 0.5612
WVFGRD96 18.0 155 75 -10 5.09 0.5605
WVFGRD96 19.0 155 75 -10 5.09 0.5603
WVFGRD96 20.0 155 75 -10 5.10 0.5617
WVFGRD96 21.0 155 75 -10 5.11 0.5602
WVFGRD96 22.0 155 75 -10 5.12 0.5576
WVFGRD96 23.0 155 75 -10 5.12 0.5568
WVFGRD96 24.0 155 75 -10 5.13 0.5533
WVFGRD96 25.0 155 75 -10 5.14 0.5511
WVFGRD96 26.0 155 80 -10 5.14 0.5470
WVFGRD96 27.0 155 80 -10 5.15 0.5428
WVFGRD96 28.0 155 80 -10 5.16 0.5398
WVFGRD96 29.0 155 80 -10 5.17 0.5350
The best solution is
WVFGRD96 20.0 155 75 -10 5.10 0.5617
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 0.04 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=Sun Aug 3 12:23:06 MDT 2008