2011/07/14 06:59:09 50.12 0.75 10.0 4.30 England/France
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2011/07/14 06:59:09:0 50.12 0.75 10.0 4.3 England/France
Stations used:
BN.EKB BN.SBD BN.WOL CH.BALST CH.BNALP CH.BOURR CH.EMV
CH.GIMEL CH.SENIN FR.OG35 GB.CWF GB.EDI GB.HTL GB.JSA
GB.SWN1 G.ECH GE.WLF GR.TNS
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 3.63e+21 dyne-cm
Mw = 3.64
Z = 9 km
Plane Strike Dip Rake
NP1 83 71 159
NP2 180 70 20
Principal Axes:
Axis Value Plunge Azimuth
T 3.63e+21 28 41
N 0.00e+00 62 223
P -3.63e+21 1 132
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.61e+14
Mxy 3.21e+21
Mxz 1.17e+21
Myy -7.98e+20
Myz 9.51e+20
Mzz 7.98e+20
------########
---------#############
-----------#################
------------########### ####
-------------############ T ######
--------------############ #######
---------------#######################
---------------#########################
---------------#########################
----------------##########################
----------------#######################---
----------------####################------
#---------------###############-----------
######---------#######------------------
###############-------------------------
###############-----------------------
##############----------------------
#############----------------- -
############---------------- P
###########----------------
#########-------------
######--------
Global CMT Convention Moment Tensor:
R T P
7.98e+20 1.17e+21 -9.51e+20
1.17e+21 -5.61e+14 -3.21e+21
-9.51e+20 -3.21e+21 -7.98e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20110714065909/index.html
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STK = 180
DIP = 70
RAKE = 20
MW = 3.64
HS = 9.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2011/07/14 06:59:09:0 50.12 0.75 10.0 4.3 England/France
Stations used:
BN.EKB BN.SBD BN.WOL CH.BALST CH.BNALP CH.BOURR CH.EMV
CH.GIMEL CH.SENIN FR.OG35 GB.CWF GB.EDI GB.HTL GB.JSA
GB.SWN1 G.ECH GE.WLF GR.TNS
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 3.63e+21 dyne-cm
Mw = 3.64
Z = 9 km
Plane Strike Dip Rake
NP1 83 71 159
NP2 180 70 20
Principal Axes:
Axis Value Plunge Azimuth
T 3.63e+21 28 41
N 0.00e+00 62 223
P -3.63e+21 1 132
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.61e+14
Mxy 3.21e+21
Mxz 1.17e+21
Myy -7.98e+20
Myz 9.51e+20
Mzz 7.98e+20
------########
---------#############
-----------#################
------------########### ####
-------------############ T ######
--------------############ #######
---------------#######################
---------------#########################
---------------#########################
----------------##########################
----------------#######################---
----------------####################------
#---------------###############-----------
######---------#######------------------
###############-------------------------
###############-----------------------
##############----------------------
#############----------------- -
############---------------- P
###########----------------
#########-------------
######--------
Global CMT Convention Moment Tensor:
R T P
7.98e+20 1.17e+21 -9.51e+20
1.17e+21 -5.61e+14 -3.21e+21
-9.51e+20 -3.21e+21 -7.98e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20110714065909/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 0.06 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 0.5 180 65 15 3.41 0.4704
WVFGRD96 1.0 175 90 0 3.40 0.5043
WVFGRD96 2.0 180 70 20 3.51 0.6039
WVFGRD96 3.0 180 70 20 3.54 0.6413
WVFGRD96 4.0 180 65 20 3.57 0.6631
WVFGRD96 5.0 180 65 20 3.58 0.6741
WVFGRD96 6.0 180 70 20 3.59 0.6798
WVFGRD96 7.0 175 80 15 3.58 0.6826
WVFGRD96 8.0 180 70 25 3.63 0.6865
WVFGRD96 9.0 180 70 20 3.64 0.6865
WVFGRD96 10.0 180 70 20 3.65 0.6847
WVFGRD96 11.0 175 85 20 3.64 0.6835
WVFGRD96 12.0 175 85 20 3.65 0.6814
WVFGRD96 13.0 175 85 20 3.66 0.6779
WVFGRD96 14.0 175 80 15 3.66 0.6735
WVFGRD96 15.0 175 80 15 3.67 0.6682
WVFGRD96 16.0 175 85 15 3.68 0.6615
WVFGRD96 17.0 175 85 15 3.69 0.6537
WVFGRD96 18.0 175 85 15 3.69 0.6460
WVFGRD96 19.0 175 85 15 3.70 0.6374
WVFGRD96 20.0 175 85 15 3.71 0.6278
WVFGRD96 21.0 175 85 15 3.72 0.6176
WVFGRD96 22.0 175 85 15 3.72 0.6062
WVFGRD96 23.0 175 85 15 3.73 0.5962
WVFGRD96 24.0 175 85 15 3.73 0.5854
WVFGRD96 25.0 175 85 15 3.74 0.5740
WVFGRD96 26.0 175 85 15 3.75 0.5626
WVFGRD96 27.0 175 85 15 3.75 0.5519
WVFGRD96 28.0 175 85 15 3.76 0.5409
WVFGRD96 29.0 175 85 15 3.77 0.5296
The best solution is
WVFGRD96 9.0 180 70 20 3.64 0.6865
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 component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
hp c 0.02 n 3 lp c 0.06 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. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of 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=Thu Jul 14 15:32:20 CDT 2011