2013/05/29 03:16:29 52.891 -4.680 8.0 3.80 Wales
The location used is that given by BGS Other locations are given:
BGS 2013/05/29 03:16:29.2 52.891 -4.680 8 3.8 EMSC 2013/05/29 03:16:26 52.90 -4.90 8.0 4.2 ML NEIC 2013/05/29 03:16:23 52.955 -5.220 9.95 3.9 mb
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2013/05/29 03:16:29:2 52.89 -4.68 8.0 3.8 Wales
Stations used:
BN.LLW EI.IDGL EI.IGLA GB.CCA1 GB.CLGH GB.CWF GB.DYA GB.EDI
GB.ESK GB.FOEL GB.HTL GB.JSA GB.MCH1 GB.SWN1 GE.VAL
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.02e+21 dyne-cm
Mw = 3.47
Z = 11 km
Plane Strike Dip Rake
NP1 68 86 -140
NP2 335 50 -5
Principal Axes:
Axis Value Plunge Azimuth
T 2.02e+21 24 195
N 0.00e+00 50 73
P -2.02e+21 30 300
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.21e+21
Mxy 1.06e+21
Mxz -1.16e+21
Myy -1.04e+21
Myz 5.74e+20
Mzz -1.73e+20
##############
-------###############
--------------##############
-----------------#############
---------------------#############
-----------------------#############
----- ------------------############
------ P -------------------#########---
------ --------------------####-------
------------------------------#-----------
--------------------------#####-----------
---------------------###########----------
-----------------###############----------
-----------#####################--------
-----###########################--------
###############################-------
##############################------
#############################-----
########## #############----
######### T ############----
###### ############-
##############
Global CMT Convention Moment Tensor:
R T P
-1.73e+20 -1.16e+21 -5.74e+20
-1.16e+21 1.21e+21 -1.06e+21
-5.74e+20 -1.06e+21 -1.04e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20130529031629/index.html
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STK = 335
DIP = 50
RAKE = -5
MW = 3.47
HS = 11.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2013/05/29 03:16:29:2 52.89 -4.68 8.0 3.8 Wales
Stations used:
BN.LLW EI.IDGL EI.IGLA GB.CCA1 GB.CLGH GB.CWF GB.DYA GB.EDI
GB.ESK GB.FOEL GB.HTL GB.JSA GB.MCH1 GB.SWN1 GE.VAL
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.02e+21 dyne-cm
Mw = 3.47
Z = 11 km
Plane Strike Dip Rake
NP1 68 86 -140
NP2 335 50 -5
Principal Axes:
Axis Value Plunge Azimuth
T 2.02e+21 24 195
N 0.00e+00 50 73
P -2.02e+21 30 300
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.21e+21
Mxy 1.06e+21
Mxz -1.16e+21
Myy -1.04e+21
Myz 5.74e+20
Mzz -1.73e+20
##############
-------###############
--------------##############
-----------------#############
---------------------#############
-----------------------#############
----- ------------------############
------ P -------------------#########---
------ --------------------####-------
------------------------------#-----------
--------------------------#####-----------
---------------------###########----------
-----------------###############----------
-----------#####################--------
-----###########################--------
###############################-------
##############################------
#############################-----
########## #############----
######### T ############----
###### ############-
##############
Global CMT Convention Moment Tensor:
R T P
-1.73e+20 -1.16e+21 -5.74e+20
-1.16e+21 1.21e+21 -1.06e+21
-5.74e+20 -1.06e+21 -1.04e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.EU/20130529031629/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 0.10 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 0.5 105 45 -85 3.22 0.1786
WVFGRD96 1.0 330 90 5 3.07 0.1989
WVFGRD96 2.0 150 75 -15 3.24 0.2939
WVFGRD96 3.0 150 75 -10 3.29 0.3205
WVFGRD96 4.0 150 60 -15 3.34 0.3401
WVFGRD96 5.0 150 45 -15 3.39 0.3657
WVFGRD96 6.0 330 40 -20 3.41 0.3874
WVFGRD96 7.0 335 45 -10 3.40 0.3986
WVFGRD96 8.0 330 40 -20 3.47 0.4095
WVFGRD96 9.0 335 45 -10 3.45 0.4128
WVFGRD96 10.0 335 45 -10 3.46 0.4138
WVFGRD96 11.0 335 50 -5 3.47 0.4145
WVFGRD96 12.0 340 50 5 3.47 0.4124
WVFGRD96 13.0 340 50 0 3.47 0.4126
WVFGRD96 14.0 340 50 0 3.48 0.4112
WVFGRD96 15.0 340 50 0 3.49 0.4059
WVFGRD96 16.0 340 55 0 3.49 0.4032
WVFGRD96 17.0 340 55 0 3.50 0.3972
WVFGRD96 18.0 340 55 0 3.51 0.3930
WVFGRD96 19.0 340 55 0 3.51 0.3885
WVFGRD96 20.0 335 55 -15 3.52 0.3827
WVFGRD96 21.0 335 55 -15 3.53 0.3778
WVFGRD96 22.0 335 55 -15 3.54 0.3717
WVFGRD96 23.0 335 55 -15 3.54 0.3650
WVFGRD96 24.0 160 60 10 3.56 0.3564
WVFGRD96 25.0 160 60 10 3.56 0.3504
WVFGRD96 26.0 165 60 15 3.55 0.3439
WVFGRD96 27.0 165 60 15 3.56 0.3380
WVFGRD96 28.0 165 60 15 3.57 0.3321
WVFGRD96 29.0 165 60 15 3.57 0.3258
The best solution is
WVFGRD96 11.0 335 50 -5 3.47 0.4145
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 0.10 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=Wed May 29 04:49:39 CDT 2013