2009/06/23 14:27:56 61.9310 -150.6750 55.0 4.10 Alaska
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/06/23 14:27:56:0 61.93 -150.68 55.0 4.1 Alaska
Stations used:
AK.EYAK AK.MCK AK.PAX AK.PPLA AK.SAW AK.TRF AT.PMR IU.COLA
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.06e+22 dyne-cm
Mw = 3.95
Z = 55 km
Plane Strike Dip Rake
NP1 137 83 -135
NP2 40 45 -10
Principal Axes:
Axis Value Plunge Azimuth
T 1.06e+22 24 260
N 0.00e+00 44 144
P -1.06e+22 36 9
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.50e+21
Mxy 3.75e+20
Mxz -5.65e+21
Myy 8.34e+21
Myz -4.74e+21
Mzz -1.84e+21
--------------
----------------------
--------------- ---------#
##-------------- P ----------#
#####------------- -----------##
#######--------------------------###
##########------------------------####
############-----------------------#####
##############--------------------######
################-------------------#######
##################----------------########
#### ############---------------########
#### T ##############------------#########
### ################---------#########
########################-----###########
#########################--###########
########################--##########
####################-------#######
###############------------###
##########------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-1.84e+21 -5.65e+21 4.74e+21
-5.65e+21 -6.50e+21 -3.75e+20
4.74e+21 -3.75e+20 8.34e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090623142756/index.html
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STK = 40
DIP = 45
RAKE = -10
MW = 3.95
HS = 55.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/06/23 14:27:56:0 61.93 -150.68 55.0 4.1 Alaska
Stations used:
AK.EYAK AK.MCK AK.PAX AK.PPLA AK.SAW AK.TRF AT.PMR IU.COLA
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.06e+22 dyne-cm
Mw = 3.95
Z = 55 km
Plane Strike Dip Rake
NP1 137 83 -135
NP2 40 45 -10
Principal Axes:
Axis Value Plunge Azimuth
T 1.06e+22 24 260
N 0.00e+00 44 144
P -1.06e+22 36 9
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.50e+21
Mxy 3.75e+20
Mxz -5.65e+21
Myy 8.34e+21
Myz -4.74e+21
Mzz -1.84e+21
--------------
----------------------
--------------- ---------#
##-------------- P ----------#
#####------------- -----------##
#######--------------------------###
##########------------------------####
############-----------------------#####
##############--------------------######
################-------------------#######
##################----------------########
#### ############---------------########
#### T ##############------------#########
### ################---------#########
########################-----###########
#########################--###########
########################--##########
####################-------#######
###############------------###
##########------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-1.84e+21 -5.65e+21 4.74e+21
-5.65e+21 -6.50e+21 -3.75e+20
4.74e+21 -3.75e+20 8.34e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090623142756/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 0.10 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 40.0 40 45 -10 3.93 0.5079
WVFGRD96 41.0 40 45 -10 3.94 0.5161
WVFGRD96 42.0 40 45 -10 3.96 0.5230
WVFGRD96 43.0 40 45 -10 3.97 0.5285
WVFGRD96 44.0 40 45 -10 3.98 0.5329
WVFGRD96 45.0 40 45 -10 3.98 0.5366
WVFGRD96 46.0 45 50 -5 3.99 0.5394
WVFGRD96 47.0 45 50 -5 3.99 0.5415
WVFGRD96 48.0 45 50 -5 4.00 0.5443
WVFGRD96 49.0 45 50 -10 4.01 0.5478
WVFGRD96 50.0 45 50 -5 4.01 0.5507
WVFGRD96 51.0 45 50 -10 4.02 0.5531
WVFGRD96 52.0 45 50 -10 4.02 0.5540
WVFGRD96 53.0 45 50 -10 4.02 0.5541
WVFGRD96 54.0 45 50 -10 4.03 0.5526
WVFGRD96 55.0 50 50 -5 4.04 0.5543
WVFGRD96 56.0 50 50 -5 4.04 0.5555
WVFGRD96 57.0 50 50 -5 4.04 0.5549
WVFGRD96 58.0 50 50 -5 4.05 0.5525
WVFGRD96 59.0 50 50 -5 4.05 0.5527
WVFGRD96 60.0 50 50 -5 4.05 0.5520
WVFGRD96 61.0 50 50 -5 4.05 0.5487
WVFGRD96 62.0 50 50 -5 4.05 0.5477
WVFGRD96 63.0 50 55 0 4.04 0.5469
WVFGRD96 64.0 50 55 0 4.04 0.5430
WVFGRD96 65.0 55 55 10 4.05 0.5415
WVFGRD96 66.0 55 55 10 4.05 0.5410
WVFGRD96 67.0 55 55 10 4.06 0.5370
WVFGRD96 68.0 55 55 10 4.06 0.5370
WVFGRD96 69.0 55 55 15 4.05 0.5352
The best solution is
WVFGRD96 56.0 50 50 -5 4.04 0.5555
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 0.10 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=Wed Jun 24 20:44:23 CDT 2009