Location
2009/02/15 19:35:00 61.6010 -146.3080 39.4 4.30 Alaska
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports main page
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2009/02/15 19:35:00:0 61.60 -146.31 39.4 4.3 Alaska
Stations used:
AK.BMR AK.DIV AK.PAX AK.SAW AT.PMR IU.COLA
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 5.56e+22 dyne-cm
Mw = 4.43
Z = 49 km
Plane Strike Dip Rake
NP1 222 51 -98
NP2 55 40 -80
Principal Axes:
Axis Value Plunge Azimuth
T 5.56e+22 5 318
N 0.00e+00 6 227
P -5.56e+22 82 88
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.03e+22
Mxy -2.75e+22
Mxz 3.55e+21
Myy 2.36e+22
Myz -1.15e+22
Mzz -5.39e+22
##############
######################
##########################
T ###############------------
## ###########------------------
##############---------------------#
#############-----------------------##
#############------------------------###
###########--------------------------###
###########------------ ------------####
##########------------- P -----------#####
#########-------------- ----------######
########---------------------------#######
######---------------------------#######
######-------------------------#########
#####-----------------------##########
###----------------------###########
##-------------------#############
-#------------################
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-5.39e+22 3.55e+21 1.15e+22
3.55e+21 3.03e+22 2.75e+22
1.15e+22 2.75e+22 2.36e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090215193500/index.html
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Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is
STK = 55
DIP = 40
RAKE = -80
MW = 4.43
HS = 49.0
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
AEIC |
USGS/SLU Moment Tensor Solution
ENS 2009/02/15 19:35:00:0 61.60 -146.31 24.0 4.3 Alaska
Stations used:
AK.BMR AK.DIV AK.PAX AK.SAW AT.PMR IU.COLA
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 5.56e+22 dyne-cm
Mw = 4.43
Z = 49 km
Plane Strike Dip Rake
NP1 222 51 -98
NP2 55 40 -80
Principal Axes:
Axis Value Plunge Azimuth
T 5.56e+22 5 318
N 0.00e+00 6 227
P -5.56e+22 82 88
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.03e+22
Mxy -2.75e+22
Mxz 3.55e+21
Myy 2.36e+22
Myz -1.15e+22
Mzz -5.39e+22
##############
######################
##########################
T ###############------------
## ###########------------------
##############---------------------#
#############-----------------------##
#############------------------------###
###########--------------------------###
###########------------ ------------####
##########------------- P -----------#####
#########-------------- ----------######
########---------------------------#######
######---------------------------#######
######-------------------------#########
#####-----------------------##########
###----------------------###########
##-------------------#############
-#------------################
############################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-5.39e+22 3.55e+21 1.15e+22
3.55e+21 3.03e+22 2.75e+22
1.15e+22 2.75e+22 2.36e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090215193500/index.html
|
|
Moment tensor inversion summary for event 2009/02/15 19:34
This is a fully automatic solution. It has not yet been reviewed by a seismologist.2009/02/15 19:34
Date 2009/02/15
Region: Prince William Sound Region of Alaska
Mw=4.6
Centroid Location:
Time 19:34; Lat. 61.58N; Lon. 213.64W; Depth 35 km
Best Double Couple:
Plane 1: strike = 292; dip = 88; rake = 31
Plane 2: strike = 201; dip = 59; rake = 178
Moment Tensor:
Mo = 8.98501e+22 dyn-cm
Mxx = 562.036; Mxy = -539.442; Mxz = -468.063
Myy = -528.562; Myz = -87.997; Mzz = -33.474
Principal Axes:
T: value = 84.000; azimuth = 161; plunge = 23
N: value = 80.000; azimuth = 63; plunge = 20
P: value = 78.000; azimuth = 296; plunge = 59
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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 20.0 80 75 -50 4.11 0.4327
WVFGRD96 21.0 80 75 -50 4.13 0.4449
WVFGRD96 22.0 80 70 -50 4.13 0.4590
WVFGRD96 23.0 80 70 -50 4.14 0.4728
WVFGRD96 24.0 80 70 -45 4.15 0.4864
WVFGRD96 25.0 80 70 -45 4.16 0.4987
WVFGRD96 26.0 80 65 -45 4.16 0.5115
WVFGRD96 27.0 80 65 -45 4.17 0.5247
WVFGRD96 28.0 80 65 -45 4.18 0.5362
WVFGRD96 29.0 80 65 -45 4.19 0.5465
WVFGRD96 30.0 80 60 -45 4.19 0.5569
WVFGRD96 31.0 80 60 -45 4.20 0.5678
WVFGRD96 32.0 80 60 -45 4.21 0.5769
WVFGRD96 33.0 75 55 -50 4.21 0.5844
WVFGRD96 34.0 75 55 -50 4.22 0.5916
WVFGRD96 35.0 75 55 -50 4.23 0.5968
WVFGRD96 36.0 80 55 -50 4.24 0.6014
WVFGRD96 37.0 75 50 -55 4.25 0.6057
WVFGRD96 38.0 75 50 -55 4.26 0.6099
WVFGRD96 39.0 75 50 -55 4.28 0.6126
WVFGRD96 40.0 65 45 -65 4.36 0.5986
WVFGRD96 41.0 65 45 -65 4.37 0.6086
WVFGRD96 42.0 65 45 -65 4.38 0.6163
WVFGRD96 43.0 65 45 -65 4.38 0.6220
WVFGRD96 44.0 55 40 -75 4.39 0.6288
WVFGRD96 45.0 55 40 -80 4.40 0.6351
WVFGRD96 46.0 55 40 -80 4.41 0.6403
WVFGRD96 47.0 55 40 -80 4.42 0.6433
WVFGRD96 48.0 55 40 -80 4.42 0.6459
WVFGRD96 49.0 55 40 -80 4.43 0.6470
WVFGRD96 50.0 55 40 -80 4.43 0.6462
WVFGRD96 51.0 225 50 -95 4.44 0.6435
WVFGRD96 52.0 55 40 -80 4.44 0.6421
WVFGRD96 53.0 225 50 -95 4.45 0.6363
WVFGRD96 54.0 45 35 -90 4.45 0.6341
WVFGRD96 55.0 45 35 -90 4.46 0.6304
WVFGRD96 56.0 45 35 -90 4.46 0.6266
WVFGRD96 57.0 45 35 -90 4.47 0.6214
WVFGRD96 58.0 230 55 -85 4.47 0.6158
WVFGRD96 59.0 230 55 -85 4.48 0.6101
WVFGRD96 60.0 45 35 -90 4.48 0.6066
WVFGRD96 61.0 45 35 -90 4.48 0.6019
WVFGRD96 62.0 230 55 -85 4.49 0.5979
WVFGRD96 63.0 230 55 -85 4.49 0.5917
WVFGRD96 64.0 230 55 -80 4.50 0.5861
WVFGRD96 65.0 235 55 -75 4.50 0.5802
WVFGRD96 66.0 235 55 -75 4.51 0.5727
WVFGRD96 67.0 240 60 -65 4.52 0.5656
WVFGRD96 68.0 240 60 -65 4.52 0.5597
WVFGRD96 69.0 240 60 -65 4.52 0.5531
The best solution is
WVFGRD96 49.0 55 40 -80 4.43 0.6470
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 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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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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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 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=Sun Feb 15 18:49:04 CST 2009
Last Changed 2009/02/15