Location
2014/04/07 13:43:21 -20.218 -70.822 10.0 5.8 Chile
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports main page
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2014/04/07 13:43:21:0 -20.22 -70.82 10.0 5.8 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 = 4.03e+24 dyne-cm
Mw = 5.67
Z = 14 km
Plane Strike Dip Rake
NP1 288 63 121
NP2 55 40 45
Principal Axes:
Axis Value Plunge Azimuth
T 4.03e+24 60 243
N 0.00e+00 27 92
P -4.03e+24 13 356
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.60e+24
Mxy 6.92e+23
Mxz -1.66e+24
Myy 7.97e+23
Myz -1.50e+24
Mzz 2.80e+24
---- -------
-------- P -----------
----------- --------------
------------------------------
----------------------------------
-----------------------------------#
-------#####------------------------##
-#####################---------------###
###########################----------###
################################------####
##################################---#####
############## ###################-#####
############## T ##################---####
############# #################------#
###############################---------
############################----------
#########################-----------
#####################-------------
--############----------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.80e+24 -1.66e+24 1.50e+24
-1.66e+24 -3.60e+24 -6.92e+23
1.50e+24 -6.92e+23 7.97e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140407134321/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 = 40
RAKE = 45
MW = 5.67
HS = 14.0
The NDK file is 20140407134321.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
USGSMT |
USGS/SLU Moment Tensor Solution
ENS 2014/04/07 13:43:21:0 -20.22 -70.82 10.0 5.8 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 = 4.03e+24 dyne-cm
Mw = 5.67
Z = 14 km
Plane Strike Dip Rake
NP1 288 63 121
NP2 55 40 45
Principal Axes:
Axis Value Plunge Azimuth
T 4.03e+24 60 243
N 0.00e+00 27 92
P -4.03e+24 13 356
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.60e+24
Mxy 6.92e+23
Mxz -1.66e+24
Myy 7.97e+23
Myz -1.50e+24
Mzz 2.80e+24
---- -------
-------- P -----------
----------- --------------
------------------------------
----------------------------------
-----------------------------------#
-------#####------------------------##
-#####################---------------###
###########################----------###
################################------####
##################################---#####
############## ###################-#####
############## T ##################---####
############# #################------#
###############################---------
############################----------
#########################-----------
#####################-------------
--############----------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.80e+24 -1.66e+24 1.50e+24
-1.66e+24 -3.60e+24 -6.92e+23
1.50e+24 -6.92e+23 7.97e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140407134321/index.html
|
Body-wave Moment Tensor (Mwb)
Moment magnitude derived from a moment tensor inversion of long-period
(~10 - 100 s) body-waves (P-, SH- ) at teleseismic distances (~30 to ~90 degrees).
Moment
5.56e+17 N-m
Magnitude
5.8
Percent DC
27%
Depth
6.0 km
Updated
2014-04-07 14:07:25 UTC
Author
us
Catalog
us
Contributor
us
Code
us_c000p8us_mwb
Principal Axes
Axis Value Plunge Azimuth
T 4.546 56 208
N 1.651 18 90
P -6.196 28 350
Nodal Planes
Plane Strike Dip Rake
NP1 275 76 109
NP2 41 23 39
|
|
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.
|
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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:
cut a -30 a 180
rtr
taper w 0.1
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 2.0 85 45 75 5.43 0.4617
WVFGRD96 4.0 40 45 15 5.47 0.4650
WVFGRD96 6.0 30 40 -5 5.52 0.5503
WVFGRD96 8.0 45 30 30 5.62 0.6255
WVFGRD96 10.0 55 35 45 5.64 0.7022
WVFGRD96 12.0 60 35 55 5.66 0.7492
WVFGRD96 14.0 55 40 45 5.67 0.7661
WVFGRD96 16.0 50 45 40 5.67 0.7630
WVFGRD96 18.0 50 45 40 5.68 0.7472
WVFGRD96 20.0 45 50 30 5.69 0.7234
WVFGRD96 22.0 45 50 30 5.70 0.6979
WVFGRD96 24.0 45 50 30 5.71 0.6651
WVFGRD96 26.0 45 50 30 5.72 0.6289
WVFGRD96 28.0 45 50 25 5.72 0.5913
WVFGRD96 30.0 45 50 25 5.73 0.5517
WVFGRD96 32.0 45 50 25 5.73 0.5110
WVFGRD96 34.0 30 65 -20 5.74 0.4730
WVFGRD96 36.0 220 60 25 5.76 0.4429
WVFGRD96 38.0 220 65 25 5.77 0.4186
WVFGRD96 40.0 225 50 30 5.85 0.4038
WVFGRD96 42.0 225 55 30 5.86 0.3877
WVFGRD96 44.0 225 55 30 5.87 0.3710
WVFGRD96 46.0 225 55 25 5.87 0.3550
WVFGRD96 48.0 225 55 25 5.88 0.3405
WVFGRD96 50.0 225 60 25 5.89 0.3275
WVFGRD96 52.0 225 60 25 5.89 0.3154
WVFGRD96 54.0 205 55 -30 5.90 0.3035
WVFGRD96 56.0 205 65 -10 5.91 0.2959
WVFGRD96 58.0 205 65 -10 5.92 0.2906
WVFGRD96 60.0 205 65 -10 5.92 0.2825
WVFGRD96 62.0 120 65 -30 5.94 0.2776
WVFGRD96 64.0 125 65 -30 5.94 0.2816
WVFGRD96 66.0 205 65 -30 5.92 0.2729
WVFGRD96 68.0 120 75 -30 5.96 0.2763
WVFGRD96 70.0 120 75 -30 5.96 0.2755
WVFGRD96 72.0 120 75 -30 5.97 0.2812
WVFGRD96 74.0 120 80 -25 5.97 0.2758
WVFGRD96 76.0 120 80 -25 5.98 0.2813
WVFGRD96 78.0 120 80 -25 5.98 0.2823
WVFGRD96 80.0 120 80 -20 5.98 0.2829
WVFGRD96 82.0 120 80 -20 5.99 0.2855
WVFGRD96 84.0 120 80 -20 6.00 0.2906
WVFGRD96 86.0 120 80 -20 6.00 0.2879
WVFGRD96 88.0 120 85 -20 6.00 0.2915
WVFGRD96 90.0 120 85 -20 6.01 0.2934
WVFGRD96 92.0 120 85 -20 6.01 0.2928
WVFGRD96 94.0 120 85 -20 6.02 0.2967
WVFGRD96 96.0 300 90 15 6.01 0.2982
WVFGRD96 98.0 300 90 15 6.01 0.2971
WVFGRD96 100.0 120 85 -15 6.03 0.3032
WVFGRD96 102.0 175 70 -85 6.04 0.3014
WVFGRD96 104.0 350 20 -95 6.04 0.3055
WVFGRD96 106.0 350 20 -95 6.04 0.3079
WVFGRD96 108.0 60 55 35 5.95 0.3106
The best solution is
WVFGRD96 14.0 55 40 45 5.67 0.7661
The mechanism correspond to the best fit is
|
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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
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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
|
|
Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated.
|
|
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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
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.
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 Mon Apr 7 10:23:15 CDT 2014