Location
2013/07/27 04:38:32 40.14 21.84 10.0 4.00 Greece
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports archive
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2013/07/27 04:38:32:4 40.14 21.84 10.0 4.0 Greece
Stations used:
HL.KEK HT.AGG HT.HORT HT.KNT HT.LIT HT.LKD2 HT.SRS HT.THE
HT.XOR MN.VTS SJ.BBLS
Filtering commands used:
cut a -20 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 8.32e+21 dyne-cm
Mw = 3.88
Z = 14 km
Plane Strike Dip Rake
NP1 250 60 -70
NP2 34 36 -121
Principal Axes:
Axis Value Plunge Azimuth
T 8.32e+21 13 326
N 0.00e+00 17 60
P -8.32e+21 68 201
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.39e+21
Mxy -4.06e+21
Mxz 4.16e+21
Myy 2.38e+21
Myz 2.48e+14
Mzz -6.77e+21
##############
###################
### T #####################-
#### ######################-
###############################---
#################################---
####################--------------##--
################-------------------#####
############-----------------------#####
##########--------------------------######
#######-----------------------------######
######-----------------------------#######
####-------------- --------------#######
##--------------- P -------------#######
#---------------- ------------########
------------------------------########
---------------------------#########
------------------------##########
--------------------##########
----------------############
#------###############
##############
Global CMT Convention Moment Tensor:
R T P
-6.77e+21 4.16e+21 -2.48e+14
4.16e+21 4.39e+21 4.06e+21
-2.48e+14 4.06e+21 2.38e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20130727043832/index.html
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is
STK = 250
DIP = 60
RAKE = -70
MW = 3.88
HS = 14.0
The NDK file is 20130727043832.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
NOA |
USGS/SLU Moment Tensor Solution
ENS 2013/07/27 04:38:32:4 40.14 21.84 10.0 4.0 Greece
Stations used:
HL.KEK HT.AGG HT.HORT HT.KNT HT.LIT HT.LKD2 HT.SRS HT.THE
HT.XOR MN.VTS SJ.BBLS
Filtering commands used:
cut a -20 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 8.32e+21 dyne-cm
Mw = 3.88
Z = 14 km
Plane Strike Dip Rake
NP1 250 60 -70
NP2 34 36 -121
Principal Axes:
Axis Value Plunge Azimuth
T 8.32e+21 13 326
N 0.00e+00 17 60
P -8.32e+21 68 201
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.39e+21
Mxy -4.06e+21
Mxz 4.16e+21
Myy 2.38e+21
Myz 2.48e+14
Mzz -6.77e+21
##############
###################
### T #####################-
#### ######################-
###############################---
#################################---
####################--------------##--
################-------------------#####
############-----------------------#####
##########--------------------------######
#######-----------------------------######
######-----------------------------#######
####-------------- --------------#######
##--------------- P -------------#######
#---------------- ------------########
------------------------------########
---------------------------#########
------------------------##########
--------------------##########
----------------############
#------###############
##############
Global CMT Convention Moment Tensor:
R T P
-6.77e+21 4.16e+21 -2.48e+14
4.16e+21 4.39e+21 4.06e+21
-2.48e+14 4.06e+21 2.38e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20130727043832/index.html
|
|
|
Waveform Inversion
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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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 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 a -20 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 60 45 -85 3.49 0.2587
WVFGRD96 1.0 285 85 -5 3.42 0.2688
WVFGRD96 2.0 285 80 -10 3.53 0.3372
WVFGRD96 3.0 285 65 -5 3.60 0.3561
WVFGRD96 4.0 280 55 -15 3.66 0.3785
WVFGRD96 5.0 280 55 -15 3.68 0.3986
WVFGRD96 6.0 275 75 -45 3.72 0.4240
WVFGRD96 7.0 280 85 -45 3.74 0.4584
WVFGRD96 8.0 260 70 -65 3.83 0.4922
WVFGRD96 9.0 255 65 -70 3.86 0.5386
WVFGRD96 10.0 255 65 -70 3.87 0.5727
WVFGRD96 11.0 250 60 -75 3.88 0.5972
WVFGRD96 12.0 250 60 -70 3.88 0.6120
WVFGRD96 13.0 250 60 -70 3.88 0.6191
WVFGRD96 14.0 250 60 -70 3.88 0.6210
WVFGRD96 15.0 255 65 -65 3.88 0.6201
WVFGRD96 16.0 255 65 -65 3.88 0.6163
WVFGRD96 17.0 255 65 -65 3.89 0.6104
WVFGRD96 18.0 255 65 -60 3.88 0.6033
WVFGRD96 19.0 260 65 -55 3.89 0.5972
WVFGRD96 20.0 265 65 -45 3.88 0.5905
WVFGRD96 21.0 265 65 -50 3.90 0.5874
WVFGRD96 22.0 265 70 -50 3.90 0.5796
WVFGRD96 23.0 265 70 -50 3.91 0.5711
WVFGRD96 24.0 265 70 -50 3.91 0.5626
WVFGRD96 25.0 265 70 -50 3.91 0.5532
WVFGRD96 26.0 265 70 -50 3.92 0.5429
WVFGRD96 27.0 260 65 -50 3.92 0.5315
WVFGRD96 28.0 260 65 -50 3.92 0.5197
WVFGRD96 29.0 275 75 -35 3.92 0.5087
The best solution is
WVFGRD96 14.0 250 60 -70 3.88 0.6210
The mechanism correspond 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 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 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 a -20 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
|
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Figure 3. Waveform comparison for selected depth
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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.
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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.
Discussion
The Future
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.
Acknowledgements
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.
Velocity Model
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
Quality Control
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Sat Jul 27 19:00:55 CDT 2013
Last Changed 2013/07/27