2009/01/02 14:17:13 58.5260 -152.2540 60.0 5.20 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/01/02 14:17:13:0 58.53 -152.25 60.0 5.2 Alaska
Stations used:
AK.CAST AK.PPLA AK.RAG AK.SWD AT.OHAK AT.PMR II.KDAK
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 7.41e+23 dyne-cm
Mw = 5.18
Z = 62 km
Plane Strike Dip Rake
NP1 235 80 35
NP2 138 56 168
Principal Axes:
Axis Value Plunge Azimuth
T 7.41e+23 31 102
N 0.00e+00 54 249
P -7.41e+23 16 2
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.60e+23
Mxy -1.36e+23
Mxz -2.67e+23
Myy 5.14e+23
Myz 3.16e+23
Mzz 1.45e+23
------ -----
---------- P ---------
------------- ------------
#-----------------------------
###-------------------------------
####--------------------------######
#####-----------------------##########
#######------------------###############
#######---------------##################
#########------------#####################
##########--------########################
###########----################## ######
############-#################### T ######
##########---################### #####
########------##########################
#####----------#######################
##--------------####################
------------------################
--------------------##########
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T F
1.45e+23 -2.67e+23 -3.16e+23
-2.67e+23 -6.60e+23 1.36e+23
-3.16e+23 1.36e+23 5.14e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090102141713/index.html
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STK = 235
DIP = 80
RAKE = 35
MW = 5.18
HS = 62.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/01/02 14:17:13:0 58.53 -152.25 60.0 5.2 Alaska
Stations used:
AK.CAST AK.PPLA AK.RAG AK.SWD AT.OHAK AT.PMR II.KDAK
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 7.41e+23 dyne-cm
Mw = 5.18
Z = 62 km
Plane Strike Dip Rake
NP1 235 80 35
NP2 138 56 168
Principal Axes:
Axis Value Plunge Azimuth
T 7.41e+23 31 102
N 0.00e+00 54 249
P -7.41e+23 16 2
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.60e+23
Mxy -1.36e+23
Mxz -2.67e+23
Myy 5.14e+23
Myz 3.16e+23
Mzz 1.45e+23
------ -----
---------- P ---------
------------- ------------
#-----------------------------
###-------------------------------
####--------------------------######
#####-----------------------##########
#######------------------###############
#######---------------##################
#########------------#####################
##########--------########################
###########----################## ######
############-#################### T ######
##########---################### #####
########------##########################
#####----------#######################
##--------------####################
------------------################
--------------------##########
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T F
1.45e+23 -2.67e+23 -3.16e+23
-2.67e+23 -6.60e+23 1.36e+23
-3.16e+23 1.36e+23 5.14e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090102141713/index.html
|
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 40 50 -70 4.64 0.2158
WVFGRD96 1.0 35 45 -85 4.58 0.2043
WVFGRD96 2.0 35 45 -80 4.74 0.3029
WVFGRD96 3.0 205 45 -95 4.76 0.2949
WVFGRD96 4.0 255 90 20 4.57 0.2925
WVFGRD96 5.0 255 90 20 4.60 0.3138
WVFGRD96 6.0 75 90 -15 4.63 0.3313
WVFGRD96 7.0 75 90 -15 4.65 0.3485
WVFGRD96 8.0 75 90 -20 4.69 0.3698
WVFGRD96 9.0 75 90 -15 4.71 0.3874
WVFGRD96 10.0 75 90 -15 4.72 0.4008
WVFGRD96 11.0 75 90 -15 4.73 0.4110
WVFGRD96 12.0 75 85 -10 4.74 0.4192
WVFGRD96 13.0 75 85 -10 4.75 0.4253
WVFGRD96 14.0 75 85 -15 4.74 0.4306
WVFGRD96 15.0 75 80 -10 4.75 0.4345
WVFGRD96 16.0 75 80 -10 4.76 0.4384
WVFGRD96 17.0 75 70 -35 4.71 0.4379
WVFGRD96 18.0 75 70 -35 4.72 0.4507
WVFGRD96 19.0 75 70 -35 4.73 0.4630
WVFGRD96 20.0 75 70 -35 4.74 0.4738
WVFGRD96 21.0 30 70 -50 4.81 0.4847
WVFGRD96 22.0 30 70 -50 4.82 0.5012
WVFGRD96 23.0 30 70 -50 4.83 0.5171
WVFGRD96 24.0 30 75 -55 4.87 0.5325
WVFGRD96 25.0 30 75 -55 4.88 0.5472
WVFGRD96 26.0 30 70 -50 4.86 0.5610
WVFGRD96 27.0 30 75 -55 4.89 0.5744
WVFGRD96 28.0 30 75 -55 4.90 0.5867
WVFGRD96 29.0 35 75 -50 4.89 0.5988
WVFGRD96 30.0 35 75 -50 4.90 0.6107
WVFGRD96 31.0 35 75 -50 4.90 0.6219
WVFGRD96 32.0 35 75 -50 4.91 0.6325
WVFGRD96 33.0 35 75 -50 4.92 0.6422
WVFGRD96 34.0 35 75 -50 4.93 0.6516
WVFGRD96 35.0 35 75 -45 4.92 0.6604
WVFGRD96 36.0 35 75 -45 4.93 0.6687
WVFGRD96 37.0 35 75 -45 4.94 0.6763
WVFGRD96 38.0 35 75 -45 4.94 0.6832
WVFGRD96 39.0 35 75 -45 4.95 0.6888
WVFGRD96 40.0 35 75 -60 5.08 0.6919
WVFGRD96 41.0 35 75 -55 5.07 0.6984
WVFGRD96 42.0 35 75 -55 5.08 0.7053
WVFGRD96 43.0 35 75 -55 5.09 0.7117
WVFGRD96 44.0 235 70 40 5.07 0.7172
WVFGRD96 45.0 235 70 40 5.07 0.7294
WVFGRD96 46.0 235 70 40 5.08 0.7408
WVFGRD96 47.0 235 75 35 5.09 0.7518
WVFGRD96 48.0 235 75 35 5.10 0.7626
WVFGRD96 49.0 235 75 35 5.11 0.7727
WVFGRD96 50.0 235 75 35 5.12 0.7814
WVFGRD96 51.0 235 75 35 5.12 0.7889
WVFGRD96 52.0 235 75 35 5.13 0.7963
WVFGRD96 53.0 235 75 40 5.13 0.8026
WVFGRD96 54.0 235 75 40 5.14 0.8075
WVFGRD96 55.0 235 75 40 5.14 0.8124
WVFGRD96 56.0 235 75 40 5.15 0.8158
WVFGRD96 57.0 235 75 40 5.15 0.8184
WVFGRD96 58.0 235 80 35 5.16 0.8220
WVFGRD96 59.0 235 80 35 5.17 0.8251
WVFGRD96 60.0 235 80 35 5.17 0.8280
WVFGRD96 61.0 235 80 35 5.18 0.8293
WVFGRD96 62.0 235 80 35 5.18 0.8303
WVFGRD96 63.0 235 80 35 5.19 0.8302
WVFGRD96 64.0 235 80 40 5.18 0.8301
WVFGRD96 65.0 235 80 40 5.19 0.8288
WVFGRD96 66.0 235 80 40 5.19 0.8274
WVFGRD96 67.0 235 85 35 5.20 0.8260
WVFGRD96 68.0 235 85 35 5.20 0.8250
WVFGRD96 69.0 235 85 35 5.21 0.8249
The best solution is
WVFGRD96 62.0 235 80 35 5.18 0.8303
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=Tue Jan 6 10:50:48 MST 2009