Location
IGN Location
The following location was used for the source inversion.
2010/04/22 01:24:00 35.2635 -6.2918 120.0 4.70 Moroc
SLU Location
The program
elocate
was used with the same WUS model used for the source inversion to determine the source parameters. In addition the location provided data to compare the observed first motions to the nodal planes derived from the waveform inversion. The output of this location is given in the file elocate.txt.
Focal Mechanism
SLU Moment Tensor Solution
ENS 2010/04/22 01:24:00:0 35.26 -6.29 120.0 4.7 Moroc
Stations used:
IB.NKM IG.CEUT XB.PM01 XB.PM03 XB.PM04 XB.PM05 XB.PM06
XB.PM07 XB.PM08 XB.PM12 XB.PM13 XB.PS01 XB.PS02 XB.PS03
XB.PS42
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.67e+22 dyne-cm
Mw = 4.31
Z = 70 km
Plane Strike Dip Rake
NP1 285 57 123
NP2 55 45 50
Principal Axes:
Axis Value Plunge Azimuth
T 3.67e+22 62 249
N 0.00e+00 27 86
P -3.67e+22 7 352
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.46e+22
Mxy 7.51e+21
Mxz -9.58e+21
Myy 6.43e+21
Myz -1.37e+22
Mzz 2.81e+22
--- P --------
------- ------------
----------------------------
------------------------------
----------------------------------
-----------------------------------#
-----###############----------------##
--#########################----------###
##############################-------###
##################################---#####
####################################-#####
############# ###################---####
############# T ##################------##
############ #################--------
##############################----------
###########################-----------
#######################-------------
##################----------------
----######--------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.81e+22 -9.58e+21 1.37e+22
-9.58e+21 -3.46e+22 -7.51e+21
1.37e+22 -7.51e+21 6.43e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100422012400/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 = 55
DIP = 45
RAKE = 50
MW = 4.31
HS = 70.0
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
SLUFM |
SLU Moment Tensor Solution
ENS 2010/04/22 01:24:00:0 35.26 -6.29 120.0 4.7 Moroc
Stations used:
IB.NKM IG.CEUT XB.PM01 XB.PM03 XB.PM04 XB.PM05 XB.PM06
XB.PM07 XB.PM08 XB.PM12 XB.PM13 XB.PS01 XB.PS02 XB.PS03
XB.PS42
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.67e+22 dyne-cm
Mw = 4.31
Z = 70 km
Plane Strike Dip Rake
NP1 285 57 123
NP2 55 45 50
Principal Axes:
Axis Value Plunge Azimuth
T 3.67e+22 62 249
N 0.00e+00 27 86
P -3.67e+22 7 352
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.46e+22
Mxy 7.51e+21
Mxz -9.58e+21
Myy 6.43e+21
Myz -1.37e+22
Mzz 2.81e+22
--- P --------
------- ------------
----------------------------
------------------------------
----------------------------------
-----------------------------------#
-----###############----------------##
--#########################----------###
##############################-------###
##################################---#####
####################################-#####
############# ###################---####
############# T ##################------##
############ #################--------
##############################----------
###########################-----------
#######################-------------
##################----------------
----######--------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.81e+22 -9.58e+21 1.37e+22
-9.58e+21 -3.46e+22 -7.51e+21
1.37e+22 -7.51e+21 6.43e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100422012400/index.html
|
First motions and takeoff angles from an elocate run.
|
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.
|
|
Location of broadband stations used for waveform inversion
|
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 0.5 170 50 -70 3.44 0.1403
WVFGRD96 1.0 165 50 -75 3.49 0.1451
WVFGRD96 2.0 170 50 -70 3.59 0.1781
WVFGRD96 3.0 175 55 -65 3.66 0.1785
WVFGRD96 4.0 20 40 -20 3.69 0.1749
WVFGRD96 5.0 25 45 -5 3.70 0.1906
WVFGRD96 6.0 30 45 5 3.73 0.2094
WVFGRD96 7.0 30 50 10 3.74 0.2291
WVFGRD96 8.0 30 45 5 3.80 0.2457
WVFGRD96 9.0 30 45 10 3.81 0.2631
WVFGRD96 10.0 30 45 10 3.83 0.2802
WVFGRD96 11.0 30 50 15 3.84 0.2958
WVFGRD96 12.0 30 50 10 3.85 0.3100
WVFGRD96 13.0 30 55 15 3.86 0.3224
WVFGRD96 14.0 30 55 15 3.87 0.3335
WVFGRD96 15.0 30 55 10 3.88 0.3434
WVFGRD96 16.0 30 55 10 3.89 0.3520
WVFGRD96 17.0 30 60 15 3.90 0.3594
WVFGRD96 18.0 30 60 15 3.91 0.3661
WVFGRD96 19.0 30 60 15 3.92 0.3718
WVFGRD96 20.0 30 60 15 3.92 0.3768
WVFGRD96 21.0 30 60 15 3.94 0.3806
WVFGRD96 22.0 30 60 15 3.94 0.3841
WVFGRD96 23.0 30 60 15 3.95 0.3869
WVFGRD96 24.0 30 60 15 3.96 0.3894
WVFGRD96 25.0 30 60 15 3.96 0.3912
WVFGRD96 26.0 35 60 20 3.97 0.3927
WVFGRD96 27.0 35 60 20 3.98 0.3944
WVFGRD96 28.0 35 60 20 3.99 0.3958
WVFGRD96 29.0 35 60 20 3.99 0.3968
WVFGRD96 30.0 35 60 20 4.00 0.3975
WVFGRD96 31.0 35 60 20 4.01 0.3981
WVFGRD96 32.0 35 60 20 4.01 0.3984
WVFGRD96 33.0 35 60 20 4.02 0.3984
WVFGRD96 34.0 35 60 20 4.03 0.3984
WVFGRD96 35.0 35 60 20 4.03 0.3984
WVFGRD96 36.0 35 60 20 4.04 0.3981
WVFGRD96 37.0 35 60 20 4.05 0.3979
WVFGRD96 38.0 30 65 20 4.06 0.3984
WVFGRD96 39.0 30 65 20 4.07 0.3989
WVFGRD96 40.0 40 50 25 4.16 0.3940
WVFGRD96 41.0 35 55 25 4.16 0.3962
WVFGRD96 42.0 35 55 25 4.16 0.3986
WVFGRD96 43.0 35 55 25 4.17 0.4009
WVFGRD96 44.0 35 60 30 4.18 0.4033
WVFGRD96 45.0 35 60 30 4.18 0.4054
WVFGRD96 46.0 35 60 30 4.19 0.4071
WVFGRD96 47.0 35 60 30 4.20 0.4091
WVFGRD96 48.0 35 60 30 4.20 0.4109
WVFGRD96 49.0 35 60 30 4.21 0.4122
WVFGRD96 50.0 35 60 30 4.21 0.4135
WVFGRD96 51.0 40 55 30 4.22 0.4151
WVFGRD96 52.0 40 55 35 4.23 0.4166
WVFGRD96 53.0 40 55 35 4.23 0.4182
WVFGRD96 54.0 40 55 35 4.23 0.4195
WVFGRD96 55.0 40 55 35 4.24 0.4208
WVFGRD96 56.0 40 55 35 4.24 0.4218
WVFGRD96 57.0 45 50 40 4.25 0.4234
WVFGRD96 58.0 45 50 40 4.26 0.4253
WVFGRD96 59.0 45 50 40 4.26 0.4266
WVFGRD96 60.0 45 50 40 4.27 0.4278
WVFGRD96 61.0 45 50 40 4.27 0.4288
WVFGRD96 62.0 50 45 40 4.28 0.4294
WVFGRD96 63.0 50 45 40 4.28 0.4306
WVFGRD96 64.0 50 45 40 4.28 0.4312
WVFGRD96 65.0 50 45 45 4.29 0.4317
WVFGRD96 66.0 55 45 50 4.30 0.4323
WVFGRD96 67.0 55 45 50 4.30 0.4331
WVFGRD96 68.0 55 45 50 4.31 0.4335
WVFGRD96 69.0 55 45 50 4.31 0.4337
WVFGRD96 70.0 55 45 50 4.31 0.4338
WVFGRD96 71.0 55 45 50 4.31 0.4336
WVFGRD96 72.0 55 45 50 4.32 0.4331
WVFGRD96 73.0 55 45 55 4.32 0.4325
WVFGRD96 74.0 55 45 55 4.33 0.4322
WVFGRD96 75.0 55 45 55 4.33 0.4314
WVFGRD96 76.0 55 45 55 4.33 0.4307
WVFGRD96 77.0 60 45 60 4.34 0.4299
WVFGRD96 78.0 60 45 60 4.34 0.4291
WVFGRD96 79.0 60 45 60 4.34 0.4281
WVFGRD96 80.0 60 45 60 4.34 0.4272
WVFGRD96 81.0 60 45 60 4.34 0.4257
WVFGRD96 82.0 60 45 60 4.35 0.4247
WVFGRD96 83.0 60 45 65 4.35 0.4233
WVFGRD96 84.0 60 45 65 4.36 0.4219
WVFGRD96 85.0 60 45 65 4.36 0.4205
WVFGRD96 86.0 60 45 65 4.36 0.4188
WVFGRD96 87.0 60 45 65 4.36 0.4172
WVFGRD96 88.0 65 45 70 4.37 0.4160
WVFGRD96 89.0 65 45 70 4.37 0.4146
WVFGRD96 90.0 65 45 70 4.37 0.4133
WVFGRD96 91.0 65 45 70 4.37 0.4117
WVFGRD96 92.0 65 45 70 4.37 0.4103
WVFGRD96 93.0 65 45 70 4.37 0.4084
WVFGRD96 94.0 65 45 70 4.37 0.4069
WVFGRD96 95.0 65 45 70 4.37 0.4051
WVFGRD96 96.0 65 45 70 4.38 0.4030
WVFGRD96 97.0 65 45 75 4.38 0.4014
WVFGRD96 98.0 65 45 75 4.38 0.3993
WVFGRD96 99.0 65 45 75 4.38 0.3976
WVFGRD96 100.0 70 45 80 4.39 0.3956
WVFGRD96 101.0 70 45 80 4.39 0.3939
WVFGRD96 102.0 70 45 80 4.39 0.3917
WVFGRD96 103.0 70 45 80 4.39 0.3900
WVFGRD96 104.0 70 45 80 4.39 0.3881
WVFGRD96 105.0 70 45 80 4.39 0.3859
WVFGRD96 106.0 260 45 95 4.40 0.3830
WVFGRD96 107.0 260 45 95 4.40 0.3810
WVFGRD96 108.0 70 45 80 4.40 0.3794
WVFGRD96 109.0 70 45 80 4.40 0.3776
WVFGRD96 110.0 70 45 80 4.40 0.3751
WVFGRD96 111.0 70 45 80 4.40 0.3728
WVFGRD96 112.0 260 40 90 4.41 0.3704
WVFGRD96 113.0 260 40 90 4.41 0.3689
WVFGRD96 114.0 260 40 90 4.41 0.3666
WVFGRD96 115.0 80 50 90 4.41 0.3650
WVFGRD96 116.0 260 40 90 4.41 0.3629
WVFGRD96 117.0 80 50 90 4.41 0.3606
WVFGRD96 118.0 80 50 90 4.41 0.3591
WVFGRD96 119.0 255 40 85 4.42 0.3571
WVFGRD96 120.0 255 40 85 4.42 0.3550
WVFGRD96 121.0 255 40 85 4.42 0.3532
WVFGRD96 122.0 255 40 85 4.42 0.3510
WVFGRD96 123.0 250 40 80 4.42 0.3491
WVFGRD96 124.0 250 40 80 4.42 0.3471
WVFGRD96 125.0 245 40 75 4.43 0.3449
WVFGRD96 126.0 245 40 75 4.43 0.3432
WVFGRD96 127.0 245 40 75 4.43 0.3410
WVFGRD96 128.0 240 40 70 4.44 0.3390
WVFGRD96 129.0 240 40 70 4.44 0.3374
WVFGRD96 130.0 240 40 70 4.44 0.3353
WVFGRD96 131.0 240 40 70 4.44 0.3334
WVFGRD96 132.0 235 40 65 4.45 0.3312
WVFGRD96 133.0 235 40 65 4.45 0.3299
WVFGRD96 134.0 235 40 65 4.45 0.3281
WVFGRD96 135.0 235 40 65 4.45 0.3260
WVFGRD96 136.0 235 40 60 4.46 0.3250
WVFGRD96 137.0 235 40 60 4.46 0.3230
WVFGRD96 138.0 235 40 60 4.46 0.3216
WVFGRD96 139.0 235 40 60 4.46 0.3204
The best solution is
WVFGRD96 70.0 55 45 50 4.31 0.4338
The mechanism corresponding to the best fit is
|
|
Figure 1. Waveform inversion focal mechanism
|
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 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
|
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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.
|
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:
- The origin time and epicentral distance are incorrect
- The velocity model used for the inversion is incorrect
- The velocity model used to define the P-arrival time is not the
same as the velocity model used for the waveform inversion
(assuming that the initial trace alignment is based on the
P arrival time)
Assuming only a mislocation, the time shifts are fit to a functional form:
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.
Discussion
Acknowledgements
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:
Last Changed Wed May 23 10:01:11 CEST 2012