Location
2009/03/27 02:58:40 61.01 -138.41 1.0 5.0 Yukon, Canada (NRCAN)
2009/03/27 02:58:39 61.0820 -138.4780 10.0 5.10 Yukon, Canada (USGS/NEIC)
Arrival Times (from NRCAN)
NRCAN Arrival Times list
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 2009/03/27 02:58:38:9 61.01 -138.41 10.0 5.0 Yukon, Canada
Stations used:
AK.BMR AK.DIV AK.DOT AK.PAX AK.PNL AT.PMR CN.DAWY CN.DLBC
CN.WHY
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.24e+23 dyne-cm
Mw = 4.94
Z = 13 km
Plane Strike Dip Rake
NP1 285 70 75
NP2 143 25 125
Principal Axes:
Axis Value Plunge Azimuth
T 3.24e+23 62 172
N 0.00e+00 14 290
P -3.24e+23 24 27
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.48e+23
Mxy -1.18e+23
Mxz -2.39e+23
Myy -5.28e+22
Myz -3.43e+22
Mzz 2.01e+23
--------------
----------------------
#------------------- -----
#-------------------- P ------
##--------------------- --------
##----------------------------------
##------------------------------------
###-#########---------------------------
---###################------------------
----#########################-------------
----#############################---------
----################################------
-----#################################----
-----############## #################-
-----############## T ##################
------############ #################
------##############################
-------###########################
-------#######################
---------###################
----------###########-
--------------
Global CMT Convention Moment Tensor:
R T P
2.01e+23 -2.39e+23 3.43e+22
-2.39e+23 -1.48e+23 1.18e+23
3.43e+22 1.18e+23 -5.28e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090327025839/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 = 285
DIP = 70
RAKE = 75
MW = 4.94
HS = 13.0
Only the waveform inversion was applied. The initial USGS solution did not use the vertical and radial at the station DIV. Using the bandpass fitler band of 0.02 - 0.05 Hz,The solution was
H=17 km STK=285 DIP=80 RAKE=80 MW=4.85 FIT=0.7191.
When using slightly high frequency, e.g., 0.02 - 0.06 Hz, we get
H=13.0 km STK=285 DIP=70 RAKE=75 MW=4.94 FIT=0.8208. This is the final solution. We also use the NRCAN location.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
AEIC |
PGC |
USGS/SLU Moment Tensor Solution
ENS 2009/03/27 02:58:38:9 61.01 -138.41 10.0 5.0 Yukon, Canada
Stations used:
AK.BMR AK.DIV AK.DOT AK.PAX AK.PNL AT.PMR CN.DAWY CN.DLBC
CN.WHY
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.24e+23 dyne-cm
Mw = 4.94
Z = 13 km
Plane Strike Dip Rake
NP1 285 70 75
NP2 143 25 125
Principal Axes:
Axis Value Plunge Azimuth
T 3.24e+23 62 172
N 0.00e+00 14 290
P -3.24e+23 24 27
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.48e+23
Mxy -1.18e+23
Mxz -2.39e+23
Myy -5.28e+22
Myz -3.43e+22
Mzz 2.01e+23
--------------
----------------------
#------------------- -----
#-------------------- P ------
##--------------------- --------
##----------------------------------
##------------------------------------
###-#########---------------------------
---###################------------------
----#########################-------------
----#############################---------
----################################------
-----#################################----
-----############## #################-
-----############## T ##################
------############ #################
------##############################
-------###########################
-------#######################
---------###################
----------###########-
--------------
Global CMT Convention Moment Tensor:
R T P
2.01e+23 -2.39e+23 3.43e+22
-2.39e+23 -1.48e+23 1.18e+23
3.43e+22 1.18e+23 -5.28e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090327025839/index.html
|
|
Moment tensor inversion summary for event 2009/03/27 02:58
Date: 2009/03/27
Time: 02:58 (UTC)
Region: Yukon Territory
Mw=5.0
Location:
Lat. 60.9670; Lon. -138.3647; Depth 15 km
(Best-fitting depth from moment tensor inversion)
Solution quality: good;
Number of stations = 6
Best Double Couple:
strike dip rake
Plane 1: 297.0 49.6 91.3
Plane 2: 115.0 40.4 88.4
Moment Tensor Parameters:
Mo = 3.09237e+23 dyn-cm
Mxx = -2.50; Mxy = -1.29; Mxz = -0.42
Myy = -0.48; Myz = -0.26; Mzz = 2.98
Principal Axes:
value azimuth plunge
T: 3.02 218.67 85.31
N: 0.15 116.15 1.02
P: -3.17 26.07 4.58
|
********************************************************************
This is a preliminary centroid-moment-tensor (CMT) solution for an
earthquake occurred in West Canada or adjacent regions. To best
view this message, please set the font to Courier New, 10 points,
and single spacing. If you have any questions, please contact
pgc_info@pgc.nrcan.gc.ca
********************************************************************
CNSN Earthquake Report:
origin time: 2009 3 27 2: 58: 39.00
hypocenter: 61.08 -138.48 17.00 km
ML: 4.8
CNSN CMT Solution:
-1.6526368 -1.2456304 -0.0766009
-1.2456304 -0.2123804 -0.3621007 x 1.0E+16 Nt-m
-0.0766009 -0.3621007 2.1155586
centroid depth: 14 km
seismic moment: 0.23E+17 Nt-m
Mw: 4.85
CLVD component: 30.6%
Iso. component: 3.5%
average misfit: 0.405
( A class-B3 solution. The fit is good. )
Best Double Couple Solutions :
nodal plane(1) strike / dip / slip: 111 / 43 / 76
nodal plane(2) strike / dip / slip: 309 / 49 / 102
------------
----------------- P
-------------------- ---
###############---------------
####################------------
########################----------
--############ ##########---------
---########### T ############-------
----########## #############------
------#########################-----
-------#######################----
---------#####################-#
--------------###########----#
--------------------------
--------------------
------------
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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 0.06 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 0.5 260 65 -90 4.82 0.5037
WVFGRD96 1.0 125 45 90 4.76 0.4917
WVFGRD96 2.0 90 85 -85 5.05 0.5391
WVFGRD96 3.0 290 90 80 4.98 0.6036
WVFGRD96 4.0 290 90 80 4.94 0.6502
WVFGRD96 5.0 290 85 80 4.92 0.6853
WVFGRD96 6.0 290 85 80 4.91 0.7165
WVFGRD96 7.0 295 80 80 4.90 0.7458
WVFGRD96 8.0 290 75 80 4.91 0.7717
WVFGRD96 9.0 290 70 80 4.92 0.7955
WVFGRD96 10.0 290 70 80 4.94 0.8062
WVFGRD96 11.0 290 70 80 4.94 0.8166
WVFGRD96 12.0 280 70 75 4.94 0.8208
WVFGRD96 13.0 285 70 75 4.94 0.8211
WVFGRD96 14.0 285 70 75 4.93 0.8164
WVFGRD96 15.0 285 70 75 4.93 0.8090
WVFGRD96 16.0 285 70 75 4.93 0.7986
WVFGRD96 17.0 285 70 75 4.93 0.7862
WVFGRD96 18.0 285 70 75 4.93 0.7721
WVFGRD96 19.0 285 75 75 4.93 0.7581
WVFGRD96 20.0 290 75 80 4.96 0.7452
WVFGRD96 21.0 290 75 80 4.96 0.7301
WVFGRD96 22.0 290 80 80 4.96 0.7144
WVFGRD96 23.0 290 80 80 4.96 0.6997
WVFGRD96 24.0 295 80 80 4.97 0.6844
WVFGRD96 25.0 295 85 80 4.97 0.6689
WVFGRD96 26.0 295 85 80 4.98 0.6543
WVFGRD96 27.0 295 85 80 4.98 0.6391
WVFGRD96 28.0 115 90 -75 4.99 0.6241
WVFGRD96 29.0 295 90 75 4.99 0.6097
The best solution is
WVFGRD96 13.0 285 70 75 4.94 0.8211
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
|
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 0.06 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.
|
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 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
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=Sat Mar 28 12:29:34 CDT 2009
Last Changed 2009/03/27