2011/09/25 13:17:10 42.53 18.57 2.0 4.40 Montenegro
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2011/09/25 13:17:10:0 42.53 18.57 2.0 4.4 Montenegro
Stations used:
HT.GRG HT.HORT HT.SRS HT.THE MN.DIVS MN.PDG MN.TIR MN.VTS
OE.ABTA OE.ARSA OE.MOA OE.MYKA OE.OBKA OE.SOKA RO.BZS
SL.BOJS SL.CRES SL.GBAS SL.GCIS SL.KOGS SL.LJU SL.MOZS
SL.PERS SL.ROBS SL.SKDS SL.VISS
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 9.55e+21 dyne-cm
Mw = 3.92
Z = 12 km
Plane Strike Dip Rake
NP1 142 69 103
NP2 290 25 60
Principal Axes:
Axis Value Plunge Azimuth
T 9.55e+21 64 74
N 0.00e+00 12 318
P -9.55e+21 22 222
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.30e+21
Mxy -3.58e+21
Mxz 3.52e+21
Myy -2.04e+21
Myz 5.88e+21
Mzz 6.34e+21
--------------
----------------------
#------#########------------
#######################-------
##---#######################------
#-----#########################-----
--------##########################----
----------##########################----
-----------##########################---
-------------############# ##########---
--------------############ T ###########--
---------------########### ###########--
----------------#########################-
-----------------#######################
------------------######################
-------------------###################
----- ------------################
---- P --------------#############
-- -----------------########
------------------------####
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
6.34e+21 3.52e+21 -5.88e+21
3.52e+21 -4.30e+21 3.58e+21
-5.88e+21 3.58e+21 -2.04e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20110925131710/index.html
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STK = 290
DIP = 25
RAKE = 60
MW = 3.92
HS = 12.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2011/09/25 13:17:10:0 42.53 18.57 2.0 4.4 Montenegro
Stations used:
HT.GRG HT.HORT HT.SRS HT.THE MN.DIVS MN.PDG MN.TIR MN.VTS
OE.ABTA OE.ARSA OE.MOA OE.MYKA OE.OBKA OE.SOKA RO.BZS
SL.BOJS SL.CRES SL.GBAS SL.GCIS SL.KOGS SL.LJU SL.MOZS
SL.PERS SL.ROBS SL.SKDS SL.VISS
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 9.55e+21 dyne-cm
Mw = 3.92
Z = 12 km
Plane Strike Dip Rake
NP1 142 69 103
NP2 290 25 60
Principal Axes:
Axis Value Plunge Azimuth
T 9.55e+21 64 74
N 0.00e+00 12 318
P -9.55e+21 22 222
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.30e+21
Mxy -3.58e+21
Mxz 3.52e+21
Myy -2.04e+21
Myz 5.88e+21
Mzz 6.34e+21
--------------
----------------------
#------#########------------
#######################-------
##---#######################------
#-----#########################-----
--------##########################----
----------##########################----
-----------##########################---
-------------############# ##########---
--------------############ T ###########--
---------------########### ###########--
----------------#########################-
-----------------#######################
------------------######################
-------------------###################
----- ------------################
---- P --------------#############
-- -----------------########
------------------------####
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
6.34e+21 3.52e+21 -5.88e+21
3.52e+21 -4.30e+21 3.58e+21
-5.88e+21 3.58e+21 -2.04e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20110925131710/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 0.5 350 40 100 3.62 0.3932
WVFGRD96 1.0 160 75 10 3.59 0.3675
WVFGRD96 2.0 160 50 85 3.71 0.3805
WVFGRD96 3.0 165 90 -45 3.75 0.3467
WVFGRD96 4.0 280 35 35 3.84 0.3764
WVFGRD96 5.0 285 25 45 3.86 0.4105
WVFGRD96 6.0 285 25 45 3.85 0.4457
WVFGRD96 7.0 290 25 55 3.86 0.4717
WVFGRD96 8.0 290 25 55 3.93 0.5008
WVFGRD96 9.0 290 25 55 3.92 0.5208
WVFGRD96 10.0 295 25 65 3.94 0.5346
WVFGRD96 11.0 290 25 60 3.93 0.5419
WVFGRD96 12.0 290 25 60 3.92 0.5437
WVFGRD96 13.0 290 25 60 3.92 0.5420
WVFGRD96 14.0 280 30 50 3.91 0.5379
WVFGRD96 15.0 280 30 50 3.91 0.5318
WVFGRD96 16.0 280 30 50 3.91 0.5244
WVFGRD96 17.0 275 30 45 3.91 0.5163
WVFGRD96 18.0 275 30 45 3.91 0.5068
WVFGRD96 19.0 270 30 40 3.90 0.4971
WVFGRD96 20.0 270 30 40 3.91 0.4869
WVFGRD96 21.0 270 30 40 3.92 0.4795
WVFGRD96 22.0 265 35 35 3.92 0.4692
WVFGRD96 23.0 265 35 30 3.92 0.4589
WVFGRD96 24.0 265 35 30 3.92 0.4487
WVFGRD96 25.0 265 35 30 3.92 0.4382
WVFGRD96 26.0 265 35 30 3.92 0.4273
WVFGRD96 27.0 260 40 25 3.93 0.4172
WVFGRD96 28.0 260 40 25 3.93 0.4070
WVFGRD96 29.0 260 40 25 3.93 0.3965
The best solution is
WVFGRD96 12.0 290 25 60 3.92 0.5437
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 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
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. |
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.
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=Thu Nov 3 20:27:49 CDT 2011