Location
SLU - Elocate
The SLU elocate solution using the WUS model is given in elocate.txt.
This solution is about 22 km WSW (az of 236) of the NEIC solution.
NEIC
2010/04/23 10:03:06 -37.5300 -72.9700 32.0 6.00 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 2010/04/23 10:03:06:1 -37.53 -72.97 32.0 6.0 Chile
Stations used:
XY.U01B XY.U03B XY.U04B XY.U05B XY.U07B XY.U08B XY.U09B
XY.U10B XY.U11B XY.U12B XY.U15B XY.U26B XY.U27B XY.U28B
XY.U29B XY.U30B XY.U32B XY.U34B XY.U35B XY.U36B XY.U40B
XY.U41B XY.U42B XY.U43B XY.U44B XY.U45B XY.U46B XY.U51B
XY.U52B XY.U53B XY.U56B XY.U57B XY.U59B XY.U61B XY.U62B
XY.U63B XY.U64B XY.U65B XY.U66B
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 7.00e+24 dyne-cm
Mw = 5.83
Z = 35 km
Plane Strike Dip Rake
NP1 140 85 65
NP2 39 25 168
Principal Axes:
Axis Value Plunge Azimuth
T 7.00e+24 44 25
N 0.00e+00 25 142
P -7.00e+24 35 251
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.45e+24
Mxy -3.07e+22
Mxz 4.21e+24
Myy -3.55e+24
Myz 4.62e+24
Mzz 1.10e+24
##############
######################
-##########################-
---###########################
------############## ##########-
--------############# T ##########--
-----------########### ###########--
-------------########################---
---------------######################---
-----------------#####################----
-------------------###################----
--------------------##################----
------- ------------###############-----
------ P -------------#############-----
------ ---------------##########------
-------------------------#######------
-------------------------#####------
--------------------------#-------
-----------------------###----
-------------------########-
##---------###########
##############
Global CMT Convention Moment Tensor:
R T P
1.10e+24 4.21e+24 -4.62e+24
4.21e+24 2.45e+24 3.07e+22
-4.62e+24 3.07e+22 -3.55e+24
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20100423100306/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 = 140
DIP = 85
RAKE = 65
MW = 5.83
HS = 35.0
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
GCMT |
SLUFM |
USGS/SLU Moment Tensor Solution
ENS 2010/04/23 10:03:06:1 -37.53 -72.97 32.0 6.0 Chile
Stations used:
XY.U01B XY.U03B XY.U04B XY.U05B XY.U07B XY.U08B XY.U09B
XY.U10B XY.U11B XY.U12B XY.U15B XY.U26B XY.U27B XY.U28B
XY.U29B XY.U30B XY.U32B XY.U34B XY.U35B XY.U36B XY.U40B
XY.U41B XY.U42B XY.U43B XY.U44B XY.U45B XY.U46B XY.U51B
XY.U52B XY.U53B XY.U56B XY.U57B XY.U59B XY.U61B XY.U62B
XY.U63B XY.U64B XY.U65B XY.U66B
Filtering commands used:
hp c 0.02 n 3
lp c 0.05 n 3
Best Fitting Double Couple
Mo = 7.00e+24 dyne-cm
Mw = 5.83
Z = 35 km
Plane Strike Dip Rake
NP1 140 85 65
NP2 39 25 168
Principal Axes:
Axis Value Plunge Azimuth
T 7.00e+24 44 25
N 0.00e+00 25 142
P -7.00e+24 35 251
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.45e+24
Mxy -3.07e+22
Mxz 4.21e+24
Myy -3.55e+24
Myz 4.62e+24
Mzz 1.10e+24
##############
######################
-##########################-
---###########################
------############## ##########-
--------############# T ##########--
-----------########### ###########--
-------------########################---
---------------######################---
-----------------#####################----
-------------------###################----
--------------------##################----
------- ------------###############-----
------ P -------------#############-----
------ ---------------##########------
-------------------------#######------
-------------------------#####------
--------------------------#-------
-----------------------###----
-------------------########-
##---------###########
##############
Global CMT Convention Moment Tensor:
R T P
1.10e+24 4.21e+24 -4.62e+24
4.21e+24 2.45e+24 3.07e+22
-4.62e+24 3.07e+22 -3.55e+24
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20100423100306/index.html
|
CENTROID-MOMENT-TENSOR SOLUTION
GCMT EVENT: C201004231003A
DATA: II IU CU IC G GE
L.P.BODY WAVES:102S, 212C, T= 40
MANTLE WAVES: 55S, 68C, T=125
SURFACE WAVES: 104S, 221C, T= 50
TIMESTAMP: Q-20100423182021
CENTROID LOCATION:
ORIGIN TIME: 10:03:10.1 0.1
LAT:37.67S 0.01;LON: 73.27W 0.01
DEP: 28.0 0.4;TRIANG HDUR: 2.5
MOMENT TENSOR: SCALE 10**25 D-CM
RR= 0.345 0.007; TT= 0.066 0.005
PP=-0.410 0.007; RT= 0.913 0.022
RP=-0.877 0.020; TP= 0.200 0.005
PRINCIPAL AXES:
1.(T) VAL= 1.323;PLG=52;AZM= 33
2.(N) 0.029; 10; 136
3.(P) -1.351; 36; 234
BEST DBLE.COUPLE:M0= 1.34*10**25
NP1: STRIKE= 8;DIP=13;SLIP= 142
NP2: STRIKE=135;DIP=82;SLIP= 80
##########-
#################--
#####################--
---######################--
-----############ #######--
--------########## T ########--
---------######### #########-
------------###################--
-------------##################--
---------------################--
-----------------##############--
----- ----------###########--
----- P ------------#########--
---- --------------######--
-----------------------#---
---------------------##
----------------###
---------##
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First motions and takeoff angles from an elocate run.
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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
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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 0.05 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 0.5 290 40 -90 5.34 0.1842
WVFGRD96 1.0 110 45 -90 5.39 0.1962
WVFGRD96 2.0 110 50 -90 5.48 0.2344
WVFGRD96 3.0 110 45 85 5.55 0.2496
WVFGRD96 4.0 100 45 70 5.59 0.2323
WVFGRD96 5.0 70 60 20 5.60 0.2064
WVFGRD96 6.0 65 75 0 5.62 0.2001
WVFGRD96 7.0 65 75 -5 5.64 0.1998
WVFGRD96 8.0 135 85 75 5.62 0.1998
WVFGRD96 9.0 140 80 75 5.63 0.2250
WVFGRD96 10.0 140 80 75 5.64 0.2486
WVFGRD96 11.0 140 80 75 5.64 0.2703
WVFGRD96 12.0 140 80 75 5.65 0.2897
WVFGRD96 13.0 140 80 75 5.66 0.3077
WVFGRD96 14.0 140 80 75 5.66 0.3241
WVFGRD96 15.0 140 80 75 5.67 0.3391
WVFGRD96 16.0 140 80 75 5.68 0.3529
WVFGRD96 17.0 140 80 70 5.69 0.3657
WVFGRD96 18.0 140 80 70 5.70 0.3776
WVFGRD96 19.0 140 80 70 5.71 0.3884
WVFGRD96 20.0 140 80 70 5.71 0.3983
WVFGRD96 21.0 140 80 70 5.73 0.4073
WVFGRD96 22.0 140 80 70 5.74 0.4159
WVFGRD96 23.0 135 85 70 5.74 0.4238
WVFGRD96 24.0 135 85 70 5.75 0.4314
WVFGRD96 25.0 140 85 70 5.76 0.4383
WVFGRD96 26.0 140 85 70 5.77 0.4446
WVFGRD96 27.0 140 85 70 5.78 0.4502
WVFGRD96 28.0 140 85 70 5.79 0.4552
WVFGRD96 29.0 140 85 70 5.79 0.4593
WVFGRD96 30.0 315 90 -70 5.79 0.4616
WVFGRD96 31.0 140 85 70 5.81 0.4652
WVFGRD96 32.0 140 85 70 5.81 0.4671
WVFGRD96 33.0 140 85 65 5.82 0.4684
WVFGRD96 34.0 140 85 65 5.83 0.4692
WVFGRD96 35.0 140 85 65 5.83 0.4695
WVFGRD96 36.0 140 85 65 5.83 0.4694
WVFGRD96 37.0 135 90 65 5.83 0.4689
WVFGRD96 38.0 315 90 -65 5.83 0.4681
WVFGRD96 39.0 315 90 -65 5.83 0.4668
The best solution is
WVFGRD96 35.0 140 85 65 5.83 0.4695
The mechanism correspond to the best fit is
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Figure 1. Waveform inversion focal mechanism
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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
hp c 0.02 n 3
lp c 0.05 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.
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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
The Future
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.
Acknowledgements
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.
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:
DATE=Tue Nov 9 07:00:13 MST 2010
Last Changed 2010/04/23