2014/04/06 09:06:51 -20.791 -70.779 15.7 4.8 Chile
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2014/04/06 09:06:51:0 -20.79 -70.78 15.7 4.8 Chile
Stations used:
CX.MNMCX CX.PATCX CX.PB01 CX.PB04 CX.PB07 CX.PB08 CX.PB09
CX.PB10 CX.PB11 CX.PB12 CX.PB14 CX.PB15 CX.PB16 CX.PSGCX
GT.LPAZ IU.LVC
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.20e+22 dyne-cm
Mw = 4.27
Z = 26 km
Plane Strike Dip Rake
NP1 120 75 85
NP2 319 16 108
Principal Axes:
Axis Value Plunge Azimuth
T 3.20e+22 60 23
N 0.00e+00 5 121
P -3.20e+22 30 214
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.62e+21
Mxy -8.25e+21
Mxz 2.43e+22
Myy -6.32e+21
Myz 1.32e+22
Mzz 1.59e+22
--------------
-###############------
#######################-----
##########################----
##############################----
#################################---
--################## ############---
-----################ T #############---
-------############## #############---
----------#############################---
-------------##########################---
---------------#########################--
------------------######################--
--------------------##################--
------------------------##############--
----------------------------#########-
-------- -----------------------#-
------- P -----------------------#
----- ----------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
1.59e+22 2.43e+22 -1.32e+22
2.43e+22 -9.62e+21 8.25e+21
-1.32e+22 8.25e+21 -6.32e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140406090651/index.html
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STK = 120
DIP = 75
RAKE = 85
MW = 4.27
HS = 26.0
The NDK file is 20140406090651.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2014/04/06 09:06:51:0 -20.79 -70.78 15.7 4.8 Chile
Stations used:
CX.MNMCX CX.PATCX CX.PB01 CX.PB04 CX.PB07 CX.PB08 CX.PB09
CX.PB10 CX.PB11 CX.PB12 CX.PB14 CX.PB15 CX.PB16 CX.PSGCX
GT.LPAZ IU.LVC
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.20e+22 dyne-cm
Mw = 4.27
Z = 26 km
Plane Strike Dip Rake
NP1 120 75 85
NP2 319 16 108
Principal Axes:
Axis Value Plunge Azimuth
T 3.20e+22 60 23
N 0.00e+00 5 121
P -3.20e+22 30 214
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.62e+21
Mxy -8.25e+21
Mxz 2.43e+22
Myy -6.32e+21
Myz 1.32e+22
Mzz 1.59e+22
--------------
-###############------
#######################-----
##########################----
##############################----
#################################---
--################## ############---
-----################ T #############---
-------############## #############---
----------#############################---
-------------##########################---
---------------#########################--
------------------######################--
--------------------##################--
------------------------##############--
----------------------------#########-
-------- -----------------------#-
------- P -----------------------#
----- ----------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
1.59e+22 2.43e+22 -1.32e+22
2.43e+22 -9.62e+21 8.25e+21
-1.32e+22 8.25e+21 -6.32e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140406090651/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:
cut a -30 a 180 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 295 50 90 3.99 0.4402
WVFGRD96 4.0 110 30 80 4.05 0.3369
WVFGRD96 6.0 205 10 -5 4.04 0.3767
WVFGRD96 8.0 195 5 -15 4.13 0.4593
WVFGRD96 10.0 180 10 -30 4.14 0.5463
WVFGRD96 12.0 175 15 -40 4.15 0.6092
WVFGRD96 14.0 170 15 -45 4.17 0.6553
WVFGRD96 16.0 165 15 -45 4.19 0.6864
WVFGRD96 18.0 120 75 85 4.20 0.7158
WVFGRD96 20.0 120 75 80 4.22 0.7387
WVFGRD96 22.0 120 75 85 4.24 0.7533
WVFGRD96 24.0 120 75 85 4.26 0.7611
WVFGRD96 26.0 120 75 85 4.27 0.7626
WVFGRD96 28.0 315 15 105 4.29 0.7571
WVFGRD96 30.0 120 75 85 4.30 0.7459
WVFGRD96 32.0 120 75 85 4.31 0.7289
WVFGRD96 34.0 120 75 85 4.32 0.7063
WVFGRD96 36.0 310 15 100 4.32 0.6808
WVFGRD96 38.0 295 15 85 4.33 0.6527
WVFGRD96 40.0 310 10 100 4.47 0.6236
WVFGRD96 42.0 120 80 90 4.48 0.5871
WVFGRD96 44.0 120 80 90 4.48 0.5493
WVFGRD96 46.0 290 10 80 4.49 0.5114
WVFGRD96 48.0 285 10 75 4.49 0.4738
WVFGRD96 50.0 275 10 65 4.49 0.4371
WVFGRD96 52.0 275 15 60 4.49 0.4025
WVFGRD96 54.0 285 15 65 4.48 0.3706
WVFGRD96 56.0 300 90 -75 4.46 0.3414
WVFGRD96 58.0 120 90 75 4.46 0.3194
WVFGRD96 60.0 120 90 70 4.45 0.3011
WVFGRD96 62.0 150 60 90 4.47 0.2871
WVFGRD96 64.0 125 50 -70 4.51 0.2806
WVFGRD96 66.0 125 50 -70 4.51 0.2757
WVFGRD96 68.0 130 50 -65 4.52 0.2709
WVFGRD96 70.0 95 30 -85 4.49 0.2701
WVFGRD96 72.0 95 30 -85 4.50 0.2737
WVFGRD96 74.0 100 30 -80 4.51 0.2777
WVFGRD96 76.0 100 30 -80 4.51 0.2798
WVFGRD96 78.0 105 30 -75 4.53 0.2834
WVFGRD96 80.0 105 30 -75 4.53 0.2863
WVFGRD96 82.0 110 30 -70 4.54 0.2890
WVFGRD96 84.0 110 30 -70 4.54 0.2912
WVFGRD96 86.0 110 30 -70 4.55 0.2933
WVFGRD96 88.0 115 30 -65 4.55 0.2953
WVFGRD96 90.0 115 30 -65 4.56 0.2965
WVFGRD96 92.0 110 25 -75 4.55 0.2999
WVFGRD96 94.0 110 25 -75 4.55 0.3034
WVFGRD96 96.0 110 25 -75 4.55 0.3066
WVFGRD96 98.0 115 25 -70 4.56 0.3091
WVFGRD96 100.0 115 25 -70 4.56 0.3115
WVFGRD96 102.0 120 25 -70 4.57 0.3141
WVFGRD96 104.0 120 25 -70 4.57 0.3166
WVFGRD96 106.0 120 25 -70 4.57 0.3188
WVFGRD96 108.0 120 25 -70 4.57 0.3207
The best solution is
WVFGRD96 26.0 120 75 85 4.27 0.7626
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
cut a -30 a 180 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 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. |
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.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, 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: