Location
2014/04/08 10:14:32 -20.486 -70.933 7.0 5.7 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 2014/04/08 10:14:32:0 -20.49 -70.93 7.0 5.7 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 = 2.24e+24 dyne-cm
Mw = 5.50
Z = 16 km
Plane Strike Dip Rake
NP1 209 57 103
NP2 5 35 70
Principal Axes:
Axis Value Plunge Azimuth
T 2.24e+24 74 155
N 0.00e+00 11 22
P -2.24e+24 11 289
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.13e+22
Mxy 6.04e+23
Mxz -6.88e+23
Myy -1.89e+24
Myz 6.62e+23
Mzz 1.98e+24
-----------###
------------------#---
------------------####------
----------------#########-----
----------------############------
---------------###############------
------------################-------
- P ----------###################-------
- ---------####################-------
-------------######################-------
------------#######################-------
------------######### ###########-------
-----------########## T ##########--------
---------########### ##########-------
---------#######################--------
--------#######################-------
-------######################-------
------#####################-------
----####################------
---##################-------
-###############------
#########-----
Global CMT Convention Moment Tensor:
R T P
1.98e+24 -6.88e+23 -6.62e+23
-6.88e+23 -9.13e+22 -6.04e+23
-6.62e+23 -6.04e+23 -1.89e+24
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140408101432/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 = 5
DIP = 35
RAKE = 70
MW = 5.50
HS = 16.0
The NDK file is 20140408101432.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
USGSMT |
GCMT |
USGS/SLU Moment Tensor Solution
ENS 2014/04/08 10:14:32:0 -20.49 -70.93 7.0 5.7 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 = 2.24e+24 dyne-cm
Mw = 5.50
Z = 16 km
Plane Strike Dip Rake
NP1 209 57 103
NP2 5 35 70
Principal Axes:
Axis Value Plunge Azimuth
T 2.24e+24 74 155
N 0.00e+00 11 22
P -2.24e+24 11 289
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.13e+22
Mxy 6.04e+23
Mxz -6.88e+23
Myy -1.89e+24
Myz 6.62e+23
Mzz 1.98e+24
-----------###
------------------#---
------------------####------
----------------#########-----
----------------############------
---------------###############------
------------################-------
- P ----------###################-------
- ---------####################-------
-------------######################-------
------------#######################-------
------------######### ###########-------
-----------########## T ##########--------
---------########### ##########-------
---------#######################--------
--------#######################-------
-------######################-------
------#####################-------
----####################------
---##################-------
-###############------
#########-----
Global CMT Convention Moment Tensor:
R T P
1.98e+24 -6.88e+23 -6.62e+23
-6.88e+23 -9.13e+22 -6.04e+23
-6.62e+23 -6.04e+23 -1.89e+24
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140408101432/index.html
|
Regional Moment Tensor (Mwr)
Moment magnitude derived from a moment tensor inversion of
complete waveforms at regional distances (less than ~8
degrees), generally used for the analysis of small to
moderate size earthquakes (typically Mw 3.5-6.0) crust
or upper mantle earthquakes.
Moment
2.13e+17 N-m
Magnitude
5.5
Percent DC
71%
Depth
13.0 km
Updated
2014-04-08 10:52:00 UTC
Author
us
Catalog
us
Contributor
us
Code
us_c000palw_mwr
Principal Axes
Axis Value Plunge Azimuth
T 1.981 75 98
N 0.278 3 199
P -2.260 15 290
Nodal Planes
Plane Strike Dip Rake
NP1 197 60 86
NP2 24 30 96
|
|
April 8, 2014, NEAR COAST OF NORTHERN CHILE, MW=5.6
Howard Koss
CENTROID-MOMENT-TENSOR SOLUTION
GCMT EVENT: C201404081014A
DATA: II IU CU MN LD G GE DK IC
L.P.BODY WAVES: 97S, 152C, T= 40
MANTLE WAVES: 35S, 39C, T=125
SURFACE WAVES: 133S, 235C, T= 50
TIMESTAMP: Q-20140408085258
CENTROID LOCATION:
ORIGIN TIME: 10:14:38.8 0.1
LAT:20.64S 0.01;LON: 71.16W 0.01
DEP: 12.7 0.4;TRIANG HDUR: 1.5
MOMENT TENSOR: SCALE 10**24 D-CM
RR= 1.610 0.030; TT= 0.041 0.019
PP=-1.650 0.028; RT=-0.838 0.065
RP=-2.360 0.121; TP=-0.359 0.017
PRINCIPAL AXES:
1.(T) VAL= 2.965;PLG=61;AZM=115
2.(N) 0.089; 4; 17
3.(P) -3.053; 28; 285
BEST DBLE.COUPLE:M0= 3.01*10**24
NP1: STRIKE= 4;DIP=17;SLIP= 76
NP2: STRIKE=198;DIP=73;SLIP= 94
---------##
-------------####--
-------------########--
--------------##########---
--------------############---
--------------##############---
-- ---------###############--
--- P --------################---
--- -------#################---
-------------####### #######---
------------######## T #######---
-----------######## #######--
----------##################---
---------#################---
--------################---
------##############---
----############---
########---
|
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:
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 25 45 -85 5.25 0.3927
WVFGRD96 4.0 255 10 -40 5.37 0.3503
WVFGRD96 6.0 295 10 0 5.36 0.4701
WVFGRD96 8.0 330 10 35 5.43 0.5430
WVFGRD96 10.0 0 20 65 5.45 0.6101
WVFGRD96 12.0 5 25 70 5.47 0.6705
WVFGRD96 14.0 5 30 70 5.49 0.7070
WVFGRD96 16.0 5 35 70 5.50 0.7179
WVFGRD96 18.0 0 35 65 5.50 0.7080
WVFGRD96 20.0 360 35 65 5.51 0.6845
WVFGRD96 22.0 355 35 60 5.52 0.6572
WVFGRD96 24.0 350 40 50 5.52 0.6237
WVFGRD96 26.0 350 40 50 5.53 0.5882
WVFGRD96 28.0 345 45 40 5.54 0.5517
WVFGRD96 30.0 345 45 40 5.55 0.5151
WVFGRD96 32.0 345 45 40 5.55 0.4770
WVFGRD96 34.0 345 45 40 5.55 0.4381
WVFGRD96 36.0 340 45 35 5.56 0.3995
WVFGRD96 38.0 340 40 35 5.56 0.3630
WVFGRD96 40.0 0 20 70 5.66 0.3428
WVFGRD96 42.0 345 35 40 5.67 0.3124
WVFGRD96 44.0 345 35 40 5.67 0.2870
WVFGRD96 46.0 340 40 35 5.68 0.2637
WVFGRD96 48.0 165 45 25 5.72 0.2465
WVFGRD96 50.0 165 50 25 5.72 0.2328
WVFGRD96 52.0 165 50 25 5.73 0.2186
WVFGRD96 54.0 165 55 20 5.74 0.2072
WVFGRD96 56.0 160 60 15 5.73 0.1967
WVFGRD96 58.0 165 60 20 5.74 0.1876
WVFGRD96 60.0 160 65 15 5.74 0.1806
WVFGRD96 62.0 160 70 15 5.74 0.1742
WVFGRD96 64.0 160 70 15 5.74 0.1706
WVFGRD96 66.0 160 70 15 5.74 0.1675
WVFGRD96 68.0 160 75 15 5.75 0.1658
WVFGRD96 70.0 330 70 20 5.73 0.1644
WVFGRD96 72.0 330 70 20 5.73 0.1650
WVFGRD96 74.0 330 65 20 5.73 0.1660
WVFGRD96 76.0 330 65 20 5.74 0.1669
WVFGRD96 78.0 330 60 20 5.74 0.1680
WVFGRD96 80.0 330 60 20 5.75 0.1694
WVFGRD96 82.0 330 55 20 5.75 0.1712
WVFGRD96 84.0 15 50 95 5.73 0.1743
WVFGRD96 86.0 15 50 95 5.74 0.1768
WVFGRD96 88.0 15 50 95 5.75 0.1881
WVFGRD96 90.0 10 45 90 5.76 0.1931
WVFGRD96 92.0 10 45 90 5.76 0.1963
WVFGRD96 94.0 360 45 75 5.77 0.2072
WVFGRD96 96.0 360 45 75 5.77 0.2116
WVFGRD96 98.0 355 45 70 5.78 0.2141
WVFGRD96 100.0 355 45 70 5.79 0.2230
WVFGRD96 102.0 365 40 80 5.79 0.2261
WVFGRD96 104.0 -15 50 50 5.80 0.2298
WVFGRD96 106.0 -15 50 50 5.80 0.2348
WVFGRD96 108.0 -15 50 50 5.81 0.2379
The best solution is
WVFGRD96 16.0 5 35 70 5.50 0.7179
The mechanism correspond 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:
|
|
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
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.
|
|
|
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 Tue Apr 8 08:56:13 CDT 2014