Location
2008/10/08 09:53:01 60.6990 -143.6240 8.0 5.20 Alaska
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports page for
Focal Mechanism
SLU Moment Tensor Solution
2008/10/08 09:53:01 60.6990 -143.6240 8.0 5.20 Alaska
Best Fitting Double Couple
Mo = 7.67e+23 dyne-cm
Mw = 5.19
Z = 17 km
Plane Strike Dip Rake
NP1 299 66 -97
NP2 135 25 -75
Principal Axes:
Axis Value Plunge Azimuth
T 7.67e+23 21 34
N 0.00e+00 6 301
P -7.67e+23 68 195
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.68e+23
Mxy 2.84e+23
Mxz 4.64e+23
Myy 2.00e+23
Myz 2.10e+23
Mzz -5.68e+23
##############
######################
###################### ###
####################### T ####
-######################## ######
-------#############################
##-------------#######################
##-------------------###################
##----------------------################
###-------------------------##############
####---------------------------###########
####-----------------------------#########
#####------------- --------------#######
####------------- P ---------------#####
#####------------ -----------------###
#####--------------------------------#
######------------------------------
#######---------------------------
#######-----------------------
#########------------------#
##############---#####
##############
Harvard Convention
Moment Tensor:
R T F
-5.68e+23 4.64e+23 -2.10e+23
4.64e+23 3.68e+23 -2.84e+23
-2.10e+23 -2.84e+23 2.00e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081008095301/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 = 135
DIP = 25
RAKE = -75
MW = 5.19
HS = 17.0
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
AEIC |
SLU Moment Tensor Solution
2008/10/08 09:53:01 60.6990 -143.6240 8.0 5.20 Alaska
Best Fitting Double Couple
Mo = 7.67e+23 dyne-cm
Mw = 5.19
Z = 17 km
Plane Strike Dip Rake
NP1 299 66 -97
NP2 135 25 -75
Principal Axes:
Axis Value Plunge Azimuth
T 7.67e+23 21 34
N 0.00e+00 6 301
P -7.67e+23 68 195
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.68e+23
Mxy 2.84e+23
Mxz 4.64e+23
Myy 2.00e+23
Myz 2.10e+23
Mzz -5.68e+23
##############
######################
###################### ###
####################### T ####
-######################## ######
-------#############################
##-------------#######################
##-------------------###################
##----------------------################
###-------------------------##############
####---------------------------###########
####-----------------------------#########
#####------------- --------------#######
####------------- P ---------------#####
#####------------ -----------------###
#####--------------------------------#
######------------------------------
#######---------------------------
#######-----------------------
#########------------------#
##############---#####
##############
Harvard Convention
Moment Tensor:
R T F
-5.68e+23 4.64e+23 -2.10e+23
4.64e+23 3.68e+23 -2.84e+23
-2.10e+23 -2.84e+23 2.00e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081008095301/index.html
|
Moment tensor inversion summary for event 2008/10/08 09:53
Date: 2008/10/08
Time: 09:53 (UTC)
Region: Cape Yakataga Region of Alaska
Mw=5.0
Location:
Lat. 60.6989; Lon. -143.7639; Depth 5 km
(Best-fitting depth from moment tensor inversion)
Solution quality: good;
Number of stations = 8
Best Double Couple:
strike dip rake
Plane 1: 343.8 59.9 -37.3
Plane 2: 94.7 58.4 -144.0
Moment Tensor Parameters:
Mo = 3.50196e+23 dyn-cm
Mxx = 1.38; Mxy = 2.41; Mxz = -1.19
Myy = 0.39; Myz = 1.57; Mzz = -1.78
Principal Axes:
value azimuth plunge
T: 3.35 39.59 0.93
N: 0.30 130.47 43.54
P: -3.65 308.61 46.45
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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 0.5 170 25 -10 5.16 0.3079
WVFGRD96 1.0 170 25 -10 5.18 0.3162
WVFGRD96 2.0 170 35 -15 5.12 0.3302
WVFGRD96 3.0 170 20 -20 5.20 0.3473
WVFGRD96 4.0 170 20 -20 5.19 0.3820
WVFGRD96 5.0 165 20 -30 5.19 0.4185
WVFGRD96 6.0 155 20 -45 5.19 0.4528
WVFGRD96 7.0 145 20 -60 5.19 0.4852
WVFGRD96 8.0 145 25 -60 5.18 0.5117
WVFGRD96 9.0 140 25 -70 5.19 0.5388
WVFGRD96 10.0 135 25 -75 5.21 0.5633
WVFGRD96 11.0 135 25 -75 5.21 0.5772
WVFGRD96 12.0 135 25 -75 5.20 0.5887
WVFGRD96 13.0 135 25 -75 5.20 0.5990
WVFGRD96 14.0 135 25 -75 5.20 0.6014
WVFGRD96 15.0 135 25 -75 5.19 0.6020
WVFGRD96 16.0 130 25 -80 5.19 0.6031
WVFGRD96 17.0 135 25 -75 5.19 0.6034
WVFGRD96 18.0 130 25 -80 5.19 0.6024
WVFGRD96 19.0 130 25 -80 5.19 0.6007
WVFGRD96 20.0 130 25 -80 5.22 0.6011
WVFGRD96 21.0 130 25 -80 5.22 0.5974
WVFGRD96 22.0 130 20 -75 5.22 0.5946
WVFGRD96 23.0 125 20 -85 5.22 0.5915
WVFGRD96 24.0 125 20 -85 5.22 0.5885
WVFGRD96 25.0 125 20 -85 5.22 0.5856
WVFGRD96 26.0 300 70 -90 5.23 0.5817
WVFGRD96 27.0 300 70 -90 5.23 0.5775
WVFGRD96 28.0 300 70 -90 5.23 0.5728
WVFGRD96 29.0 300 70 -90 5.23 0.5683
WVFGRD96 30.0 115 20 -95 5.24 0.5633
WVFGRD96 31.0 300 70 -85 5.25 0.5574
WVFGRD96 32.0 300 70 -85 5.25 0.5525
WVFGRD96 33.0 300 70 -85 5.25 0.5465
WVFGRD96 34.0 300 70 -85 5.26 0.5404
WVFGRD96 35.0 295 75 -85 5.26 0.5347
WVFGRD96 36.0 295 75 -85 5.26 0.5288
WVFGRD96 37.0 295 75 -85 5.26 0.5228
WVFGRD96 38.0 295 75 -85 5.26 0.5165
WVFGRD96 39.0 295 75 -80 5.27 0.5112
WVFGRD96 40.0 300 75 -80 5.40 0.5159
WVFGRD96 41.0 300 75 -80 5.41 0.5138
WVFGRD96 42.0 300 75 -80 5.41 0.5115
WVFGRD96 43.0 300 75 -80 5.42 0.5084
WVFGRD96 44.0 300 75 -80 5.42 0.5049
WVFGRD96 45.0 300 75 -80 5.43 0.5011
WVFGRD96 46.0 300 75 -80 5.43 0.4966
WVFGRD96 47.0 300 75 -80 5.44 0.4922
WVFGRD96 48.0 295 80 -80 5.44 0.4874
WVFGRD96 49.0 295 80 -80 5.44 0.4831
WVFGRD96 50.0 295 80 -80 5.45 0.4785
The best solution is
WVFGRD96 17.0 135 25 -75 5.19 0.6034
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 CUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01
CUS Model with Q from simple gamma values
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
1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00
9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00
10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00
20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00
0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 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 Oct 8 18:17:08 CDT 2008
Last Changed 2008/10/08