2009/06/07 23:24:39 58.9670 -136.7190 37.0 5.00 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/06/07 23:24:39:0 58.97 -136.72 37.0 5.0 Alaska
Stations used:
AK.BESE AK.DIV AK.EYAK AK.PNL AT.CRAG AT.MID AT.SKAG
CN.DAWY CN.DLBC CN.FNBB CN.MOBC CN.RUBB CN.WHY US.WRAK
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 1.68e+23 dyne-cm
Mw = 4.75
Z = 15 km
Plane Strike Dip Rake
NP1 32 57 130
NP2 155 50 45
Principal Axes:
Axis Value Plunge Azimuth
T 1.68e+23 57 359
N 0.00e+00 33 188
P -1.68e+23 4 95
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.88e+22
Mxy 1.37e+22
Mxz 7.79e+22
Myy -1.66e+23
Myz -1.36e+22
Mzz 1.17e+23
##############
-#####################
----######################--
----#######################---
-----########################-----
------########## ###########------
-------########## T ###########-------
--------########## ###########--------
--------#######################---------
----------######################----------
----------#####################-----------
-----------###################---------
-----------##################---------- P
-----------################-----------
------------##############--------------
------------###########---------------
-------------########---------------
-------------#####----------------
------------------------------
---------#####--------------
###############-------
##############
Global CMT Convention Moment Tensor:
R T P
1.17e+23 7.79e+22 1.36e+22
7.79e+22 4.88e+22 -1.37e+22
1.36e+22 -1.37e+22 -1.66e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090607232439/index.html
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STK = 155
DIP = 50
RAKE = 45
MW = 4.75
HS = 15.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/06/07 23:24:39:0 58.97 -136.72 37.0 5.0 Alaska
Stations used:
AK.BESE AK.DIV AK.EYAK AK.PNL AT.CRAG AT.MID AT.SKAG
CN.DAWY CN.DLBC CN.FNBB CN.MOBC CN.RUBB CN.WHY US.WRAK
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 1.68e+23 dyne-cm
Mw = 4.75
Z = 15 km
Plane Strike Dip Rake
NP1 32 57 130
NP2 155 50 45
Principal Axes:
Axis Value Plunge Azimuth
T 1.68e+23 57 359
N 0.00e+00 33 188
P -1.68e+23 4 95
Moment Tensor: (dyne-cm)
Component Value
Mxx 4.88e+22
Mxy 1.37e+22
Mxz 7.79e+22
Myy -1.66e+23
Myz -1.36e+22
Mzz 1.17e+23
##############
-#####################
----######################--
----#######################---
-----########################-----
------########## ###########------
-------########## T ###########-------
--------########## ###########--------
--------#######################---------
----------######################----------
----------#####################-----------
-----------###################---------
-----------##################---------- P
-----------################-----------
------------##############--------------
------------###########---------------
-------------########---------------
-------------#####----------------
------------------------------
---------#####--------------
###############-------
##############
Global CMT Convention Moment Tensor:
R T P
1.17e+23 7.79e+22 1.36e+22
7.79e+22 4.88e+22 -1.37e+22
1.36e+22 -1.37e+22 -1.66e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090607232439/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 0.5 270 45 -85 4.45 0.3224
WVFGRD96 1.0 170 90 5 4.38 0.3136
WVFGRD96 2.0 330 70 -30 4.48 0.3710
WVFGRD96 3.0 155 90 45 4.55 0.3942
WVFGRD96 4.0 320 80 -50 4.59 0.4340
WVFGRD96 5.0 320 80 -50 4.60 0.4676
WVFGRD96 6.0 320 80 -45 4.60 0.4917
WVFGRD96 7.0 320 80 -40 4.61 0.5108
WVFGRD96 8.0 320 80 -45 4.65 0.5250
WVFGRD96 9.0 315 75 -45 4.66 0.5342
WVFGRD96 10.0 160 45 50 4.73 0.5619
WVFGRD96 11.0 165 45 55 4.74 0.6043
WVFGRD96 12.0 165 45 55 4.75 0.6334
WVFGRD96 13.0 165 45 55 4.76 0.6493
WVFGRD96 14.0 165 45 55 4.76 0.6577
WVFGRD96 15.0 155 50 45 4.75 0.6593
WVFGRD96 16.0 155 50 45 4.75 0.6585
WVFGRD96 17.0 155 50 45 4.75 0.6529
WVFGRD96 18.0 155 50 40 4.76 0.6467
WVFGRD96 19.0 150 55 35 4.76 0.6403
WVFGRD96 20.0 150 55 35 4.76 0.6321
WVFGRD96 21.0 150 55 35 4.77 0.6256
WVFGRD96 22.0 150 55 30 4.77 0.6166
WVFGRD96 23.0 150 55 30 4.78 0.6062
WVFGRD96 24.0 150 55 30 4.78 0.5961
WVFGRD96 25.0 145 60 25 4.78 0.5851
WVFGRD96 26.0 320 75 25 4.79 0.5733
WVFGRD96 27.0 320 75 25 4.79 0.5667
WVFGRD96 28.0 320 75 25 4.80 0.5599
WVFGRD96 29.0 320 75 25 4.81 0.5525
WVFGRD96 30.0 320 75 25 4.81 0.5445
WVFGRD96 31.0 320 75 25 4.82 0.5363
WVFGRD96 32.0 150 75 -15 4.82 0.5271
WVFGRD96 33.0 150 75 -15 4.83 0.5197
WVFGRD96 34.0 150 75 -15 4.84 0.5128
WVFGRD96 35.0 150 75 -15 4.84 0.5056
WVFGRD96 36.0 150 80 -15 4.85 0.4980
WVFGRD96 37.0 150 80 -15 4.86 0.4908
WVFGRD96 38.0 150 80 -15 4.87 0.4834
WVFGRD96 39.0 150 80 -15 4.88 0.4752
WVFGRD96 40.0 115 50 -50 4.98 0.4886
WVFGRD96 41.0 115 55 -50 4.98 0.4832
WVFGRD96 42.0 115 55 -50 4.98 0.4777
WVFGRD96 43.0 115 55 -50 4.99 0.4724
WVFGRD96 44.0 115 55 -50 4.99 0.4669
WVFGRD96 45.0 115 55 -50 5.00 0.4613
WVFGRD96 46.0 115 55 -50 5.01 0.4557
WVFGRD96 47.0 155 70 25 4.98 0.4519
WVFGRD96 48.0 155 70 25 4.99 0.4491
WVFGRD96 49.0 155 70 25 4.99 0.4458
The best solution is
WVFGRD96 15.0 155 50 45 4.75 0.6593
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=Sun Jun 7 21:10:29 CDT 2009