2008/12/16 05:20:00 55.583 13.534 10.0 4.7 Sweden
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
2008/12/16 05:20:00 55.583 13.534 10.0 4.7 Sweden
Best Fitting Double Couple
Mo = 2.32e+22 dyne-cm
Mw = 4.21
Z = 14 km
Plane Strike Dip Rake
NP1 30 80 25
NP2 295 65 169
Principal Axes:
Axis Value Plunge Azimuth
T 2.32e+22 25 255
N 0.00e+00 63 50
P -2.32e+22 10 161
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.87e+22
Mxy 1.18e+22
Mxz 1.44e+21
Myy 1.54e+22
Myz -9.79e+21
Mzz 3.35e+21
--------------
---------------------#
------------------------####
------------------------######
--------------------------########
--------------------------##########
###############-----------############
#####################-----##############
########################################
#########################----#############
########################--------##########
#######################-----------########
#### ###############--------------######
### T ##############----------------####
### #############-------------------##
#################---------------------
##############----------------------
############----------------------
#########---------------------
######------------- ------
#--------------- P ---
------------
Harvard Convention
Moment Tensor:
R T F
3.35e+21 1.44e+21 9.79e+21
1.44e+21 -1.87e+22 -1.18e+22
9.79e+21 -1.18e+22 1.54e+22
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20081216052000/index.html
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STK = 30
DIP = 80
RAKE = 25
MW = 4.21
HS = 14.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
2008/12/16 05:20:00 55.583 13.534 10.0 4.7 Sweden
Best Fitting Double Couple
Mo = 2.32e+22 dyne-cm
Mw = 4.21
Z = 14 km
Plane Strike Dip Rake
NP1 30 80 25
NP2 295 65 169
Principal Axes:
Axis Value Plunge Azimuth
T 2.32e+22 25 255
N 0.00e+00 63 50
P -2.32e+22 10 161
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.87e+22
Mxy 1.18e+22
Mxz 1.44e+21
Myy 1.54e+22
Myz -9.79e+21
Mzz 3.35e+21
--------------
---------------------#
------------------------####
------------------------######
--------------------------########
--------------------------##########
###############-----------############
#####################-----##############
########################################
#########################----#############
########################--------##########
#######################-----------########
#### ###############--------------######
### T ##############----------------####
### #############-------------------##
#################---------------------
##############----------------------
############----------------------
#########---------------------
######------------- ------
#--------------- P ---
------------
Harvard Convention
Moment Tensor:
R T F
3.35e+21 1.44e+21 9.79e+21
1.44e+21 -1.87e+22 -1.18e+22
9.79e+21 -1.18e+22 1.54e+22
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20081216052000/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 0.5 200 75 -30 3.86 0.3190
WVFGRD96 1.0 200 70 -20 3.87 0.3438
WVFGRD96 2.0 200 60 -20 3.99 0.4334
WVFGRD96 3.0 15 55 -25 4.04 0.4707
WVFGRD96 4.0 10 60 -15 4.01 0.4984
WVFGRD96 5.0 10 65 -10 4.02 0.5173
WVFGRD96 6.0 10 70 -10 4.03 0.5296
WVFGRD96 7.0 20 75 -10 4.07 0.5388
WVFGRD96 8.0 20 70 -15 4.11 0.5487
WVFGRD96 9.0 25 75 -5 4.13 0.5517
WVFGRD96 10.0 30 75 20 4.16 0.5583
WVFGRD96 11.0 30 75 30 4.18 0.5647
WVFGRD96 12.0 30 75 30 4.19 0.5690
WVFGRD96 13.0 30 80 25 4.20 0.5712
WVFGRD96 14.0 30 80 25 4.21 0.5720
WVFGRD96 15.0 30 80 25 4.22 0.5706
WVFGRD96 16.0 30 80 25 4.22 0.5699
WVFGRD96 17.0 30 80 25 4.23 0.5664
WVFGRD96 18.0 30 85 20 4.24 0.5625
WVFGRD96 19.0 30 85 20 4.25 0.5584
WVFGRD96 20.0 30 85 20 4.25 0.5532
WVFGRD96 21.0 30 85 20 4.26 0.5474
WVFGRD96 22.0 30 85 20 4.27 0.5406
WVFGRD96 23.0 30 85 20 4.27 0.5338
WVFGRD96 24.0 210 90 -20 4.28 0.5240
WVFGRD96 25.0 30 85 20 4.28 0.5200
WVFGRD96 26.0 30 85 20 4.29 0.5125
WVFGRD96 27.0 30 85 20 4.29 0.5047
WVFGRD96 28.0 30 85 20 4.30 0.4966
WVFGRD96 29.0 30 85 20 4.30 0.4884
WVFGRD96 30.0 210 90 -20 4.31 0.4781
WVFGRD96 31.0 30 85 20 4.32 0.4744
WVFGRD96 32.0 30 85 20 4.32 0.4675
WVFGRD96 33.0 30 85 20 4.33 0.4609
WVFGRD96 34.0 30 85 20 4.34 0.4547
WVFGRD96 35.0 30 85 20 4.35 0.4500
WVFGRD96 36.0 30 85 20 4.36 0.4458
WVFGRD96 37.0 30 85 20 4.37 0.4417
WVFGRD96 38.0 30 80 25 4.38 0.4387
WVFGRD96 39.0 30 80 25 4.39 0.4359
WVFGRD96 40.0 115 60 -5 4.42 0.4403
WVFGRD96 41.0 115 60 -5 4.43 0.4399
WVFGRD96 42.0 115 60 -5 4.44 0.4401
WVFGRD96 43.0 115 60 -5 4.44 0.4401
WVFGRD96 44.0 115 60 -5 4.45 0.4401
WVFGRD96 45.0 115 60 -5 4.46 0.4401
WVFGRD96 46.0 115 60 -5 4.46 0.4399
WVFGRD96 47.0 120 70 0 4.48 0.4404
WVFGRD96 48.0 120 70 0 4.49 0.4412
WVFGRD96 49.0 120 70 0 4.49 0.4418
WVFGRD96 50.0 120 70 0 4.50 0.4423
The best solution is
WVFGRD96 14.0 30 80 25 4.21 0.5720
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=Tue Dec 16 05:17:59 MST 2008