2008/12/27 20:09:19 40.1400 24.0700 5.0 4.70
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
2008/12/27 20:09:19 40.1400 24.0700 5.0 4.70
Best Fitting Double Couple
Mo = 4.62e+22 dyne-cm
Mw = 4.41
Z = 5 km
Plane Strike Dip Rake
NP1 85 60 -109
NP2 300 35 -60
Principal Axes:
Axis Value Plunge Azimuth
T 4.62e+22 13 189
N 0.00e+00 17 95
P -4.62e+22 69 315
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.97e+22
Mxy 9.66e+21
Mxz -2.13e+22
Myy -2.08e+21
Myz 9.55e+21
Mzz -3.76e+22
##############
######################
############################
###--------------#############
#----------------------###########
---------------------------#########
------------------------------########
-------------- ----------------#######
-------------- P ------------------#####
--------------- -------------------#####
--------------------------------------###-
--------------------------------------#---
#------------------------------------##---
###-----------------------------######--
########-------------------###########--
#####################################-
####################################
##################################
##############################
########## ###############
####### T ############
### ########
Harvard Convention
Moment Tensor:
R T F
-3.76e+22 -2.13e+22 -9.55e+21
-2.13e+22 3.97e+22 -9.66e+21
-9.55e+21 -9.66e+21 -2.08e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20081227200919/index.html
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STK = 300
DIP = 35
RAKE = -60
MW = 4.41
HS = 5.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
2008/12/27 20:09:19 40.1400 24.0700 5.0 4.70
Best Fitting Double Couple
Mo = 4.62e+22 dyne-cm
Mw = 4.41
Z = 5 km
Plane Strike Dip Rake
NP1 85 60 -109
NP2 300 35 -60
Principal Axes:
Axis Value Plunge Azimuth
T 4.62e+22 13 189
N 0.00e+00 17 95
P -4.62e+22 69 315
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.97e+22
Mxy 9.66e+21
Mxz -2.13e+22
Myy -2.08e+21
Myz 9.55e+21
Mzz -3.76e+22
##############
######################
############################
###--------------#############
#----------------------###########
---------------------------#########
------------------------------########
-------------- ----------------#######
-------------- P ------------------#####
--------------- -------------------#####
--------------------------------------###-
--------------------------------------#---
#------------------------------------##---
###-----------------------------######--
########-------------------###########--
#####################################-
####################################
##################################
##############################
########## ###############
####### T ############
### ########
Harvard Convention
Moment Tensor:
R T F
-3.76e+22 -2.13e+22 -9.55e+21
-2.13e+22 3.97e+22 -9.66e+21
-9.55e+21 -9.66e+21 -2.08e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20081227200919/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 3 br c 0.12 0.25 n 4 p 2The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 320 50 -20 4.23 0.6694
WVFGRD96 1.0 320 55 -20 4.23 0.6841
WVFGRD96 2.0 315 40 -25 4.32 0.7293
WVFGRD96 3.0 315 40 -30 4.35 0.7561
WVFGRD96 4.0 310 40 -40 4.37 0.7767
WVFGRD96 5.0 300 35 -60 4.41 0.7885
WVFGRD96 6.0 290 35 -75 4.44 0.7883
WVFGRD96 7.0 110 60 -80 4.46 0.7707
WVFGRD96 8.0 105 60 -85 4.49 0.7842
WVFGRD96 9.0 120 70 -65 4.48 0.7522
WVFGRD96 10.0 320 60 0 4.37 0.7340
WVFGRD96 11.0 320 65 5 4.37 0.7270
WVFGRD96 12.0 325 65 20 4.38 0.7218
WVFGRD96 13.0 325 70 25 4.39 0.7180
WVFGRD96 14.0 325 70 25 4.40 0.7149
WVFGRD96 15.0 325 70 25 4.40 0.7128
WVFGRD96 16.0 325 70 25 4.41 0.7093
WVFGRD96 17.0 325 70 25 4.41 0.7056
WVFGRD96 18.0 330 70 35 4.43 0.7033
WVFGRD96 19.0 330 70 35 4.43 0.7001
WVFGRD96 20.0 330 70 35 4.44 0.6967
WVFGRD96 21.0 330 70 35 4.45 0.6907
WVFGRD96 22.0 330 70 35 4.46 0.6861
WVFGRD96 23.0 330 70 35 4.46 0.6813
WVFGRD96 24.0 330 70 35 4.47 0.6761
WVFGRD96 25.0 330 70 35 4.47 0.6705
WVFGRD96 26.0 330 70 35 4.48 0.6646
WVFGRD96 27.0 330 70 35 4.49 0.6585
WVFGRD96 28.0 335 70 40 4.49 0.6531
WVFGRD96 29.0 335 70 40 4.50 0.6475
The best solution is
WVFGRD96 5.0 300 35 -60 4.41 0.7885
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 br c 0.12 0.25 n 4 p 2
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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=Sat Dec 27 16:16:23 MST 2008