Location
SLU Solution
The program elocate was used to locate this earthquake. The results are in the file elocate.txt. The reason for the relocation was that the USGS location was about 10 south of the EMSC location and the delay plot, such as at the bottom of this page, indicate the need for a change in epicenter.
2012/11/28 01:49:45 42.47 20.06 16.3 4.2 Albania
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 2012/11/28 01:49:45:0 42.47 20.06 16.3 4.2 Albania
Stations used:
HL.KEK HT.AGG HT.GRG HT.KNT HT.LIT HT.SOH HT.SRS HT.THE
HT.XOR MN.BLY MN.DIVS MN.PDG MN.TIR MN.VTS RO.BZS RO.VOIR
SJ.BBLS SJ.FRGS
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 1.26e+22 dyne-cm
Mw = 4.00
Z = 12 km
Plane Strike Dip Rake
NP1 275 65 -90
NP2 95 25 -90
Principal Axes:
Axis Value Plunge Azimuth
T 1.26e+22 20 5
N 0.00e+00 -0 95
P -1.26e+22 70 185
Moment Tensor: (dyne-cm)
Component Value
Mxx 9.57e+21
Mxy 8.37e+20
Mxz 8.06e+21
Myy 7.33e+19
Myz 7.05e+20
Mzz -9.64e+21
####### ####
########### T ########
############## ###########
##############################
##################################
####################################
######################################
###############---######################
#####-------------------------##########
##---------------------------------#######
---------------------------------------###
#----------------------------------------#
##----------------- -------------------#
#----------------- P -------------------
###--------------- -----------------##
###---------------------------------##
####-----------------------------###
#####-------------------------####
######-------------------#####
#############---############
######################
##############
Global CMT Convention Moment Tensor:
R T P
-9.64e+21 8.06e+21 -7.05e+20
8.06e+21 9.57e+21 -8.37e+20
-7.05e+20 -8.37e+20 7.33e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20121128014945/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 = 275
DIP = 65
RAKE = -90
MW = 4.00
HS = 12.0
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
SLU |
USGS/SLU Moment Tensor Solution
ENS 2012/11/28 01:49:45:0 42.47 20.06 16.3 4.2 Albania
Stations used:
HL.KEK HT.AGG HT.GRG HT.KNT HT.LIT HT.SOH HT.SRS HT.THE
HT.XOR MN.BLY MN.DIVS MN.PDG MN.TIR MN.VTS RO.BZS RO.VOIR
SJ.BBLS SJ.FRGS
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 1.26e+22 dyne-cm
Mw = 4.00
Z = 12 km
Plane Strike Dip Rake
NP1 275 65 -90
NP2 95 25 -90
Principal Axes:
Axis Value Plunge Azimuth
T 1.26e+22 20 5
N 0.00e+00 -0 95
P -1.26e+22 70 185
Moment Tensor: (dyne-cm)
Component Value
Mxx 9.57e+21
Mxy 8.37e+20
Mxz 8.06e+21
Myy 7.33e+19
Myz 7.05e+20
Mzz -9.64e+21
####### ####
########### T ########
############## ###########
##############################
##################################
####################################
######################################
###############---######################
#####-------------------------##########
##---------------------------------#######
---------------------------------------###
#----------------------------------------#
##----------------- -------------------#
#----------------- P -------------------
###--------------- -----------------##
###---------------------------------##
####-----------------------------###
#####-------------------------####
######-------------------#####
#############---############
######################
##############
Global CMT Convention Moment Tensor:
R T P
-9.64e+21 8.06e+21 -7.05e+20
8.06e+21 9.57e+21 -8.37e+20
-7.05e+20 -8.37e+20 7.33e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20121128014945/index.html
|
First motions and takeoff angles from an elocate run.
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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:
hp c 0.02 n 3
lp c 0.05 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 90 35 -95 3.71 0.4028
WVFGRD96 1.0 265 50 -100 3.74 0.4068
WVFGRD96 2.0 105 35 -70 3.83 0.4499
WVFGRD96 3.0 285 60 -75 3.88 0.4340
WVFGRD96 4.0 115 30 -50 3.91 0.3976
WVFGRD96 5.0 120 25 -45 3.91 0.4019
WVFGRD96 6.0 110 20 -65 3.92 0.4341
WVFGRD96 7.0 100 20 -80 3.93 0.4644
WVFGRD96 8.0 100 20 -80 4.00 0.5039
WVFGRD96 9.0 90 20 -95 4.00 0.5268
WVFGRD96 10.0 90 25 -95 4.01 0.5408
WVFGRD96 11.0 275 65 -90 4.01 0.5490
WVFGRD96 12.0 275 65 -90 4.00 0.5498
WVFGRD96 13.0 280 65 -85 4.00 0.5461
WVFGRD96 14.0 280 65 -85 4.00 0.5380
WVFGRD96 15.0 280 65 -85 3.99 0.5270
WVFGRD96 16.0 280 70 -85 3.98 0.5144
WVFGRD96 17.0 280 70 -85 3.98 0.5016
WVFGRD96 18.0 285 70 -80 3.98 0.4893
WVFGRD96 19.0 285 70 -80 3.98 0.4771
WVFGRD96 20.0 285 75 -80 3.97 0.4642
WVFGRD96 21.0 285 75 -80 3.98 0.4558
WVFGRD96 22.0 285 75 -80 3.98 0.4433
WVFGRD96 23.0 285 75 -80 3.98 0.4309
WVFGRD96 24.0 285 75 -80 3.98 0.4182
WVFGRD96 25.0 285 80 -75 3.98 0.4061
WVFGRD96 26.0 285 85 -75 3.98 0.3941
WVFGRD96 27.0 285 85 -75 3.99 0.3825
WVFGRD96 28.0 95 75 75 3.98 0.3749
WVFGRD96 29.0 95 75 75 3.99 0.3655
The best solution is
WVFGRD96 12.0 275 65 -90 4.00 0.5498
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
hp c 0.02 n 3
lp c 0.05 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=Wed Nov 28 09:01:45 CST 2012
Last Changed 2012/11/28