Location
2014/04/19 20:54:42 -20.021 -70.913 9.0 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 2014/04/19 20:54:42:0 -20.02 -70.91 9.0 5.8 Chile
Stations used:
C.GO01 C.GO02 CX.MNMCX CX.PATCX CX.PB01 CX.PB04 CX.PB06
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 = 3.89e+24 dyne-cm
Mw = 5.66
Z = 18 km
Plane Strike Dip Rake
NP1 150 65 70
NP2 11 32 126
Principal Axes:
Axis Value Plunge Azimuth
T 3.89e+24 64 26
N 0.00e+00 18 159
P -3.89e+24 18 255
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.44e+23
Mxy -6.10e+23
Mxz 1.66e+24
Myy -3.14e+24
Myz 1.75e+24
Mzz 2.80e+24
#############-
-##################---
---#####################----
----######################----
------#######################-----
--------#######################-----
---------############ #########-----
----------############ T #########------
-----------########### #########------
-------------######################-------
-------------######################-------
--------------#####################-------
--- ---------####################-------
-- P ----------###################------
-- ------------################-------
-----------------##############-------
-----------------############-------
------------------#########-------
------------------######------
--------------------#-------
---------------#####--
-------#######
Global CMT Convention Moment Tensor:
R T P
2.80e+24 1.66e+24 -1.75e+24
1.66e+24 3.44e+23 6.10e+23
-1.75e+24 6.10e+23 -3.14e+24
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140419205442/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 = 150
DIP = 65
RAKE = 70
MW = 5.66
HS = 18.0
The NDK file is 20140419205442.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 2014/04/19 20:54:42:0 -20.02 -70.91 9.0 5.8 Chile
Stations used:
C.GO01 C.GO02 CX.MNMCX CX.PATCX CX.PB01 CX.PB04 CX.PB06
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 = 3.89e+24 dyne-cm
Mw = 5.66
Z = 18 km
Plane Strike Dip Rake
NP1 150 65 70
NP2 11 32 126
Principal Axes:
Axis Value Plunge Azimuth
T 3.89e+24 64 26
N 0.00e+00 18 159
P -3.89e+24 18 255
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.44e+23
Mxy -6.10e+23
Mxz 1.66e+24
Myy -3.14e+24
Myz 1.75e+24
Mzz 2.80e+24
#############-
-##################---
---#####################----
----######################----
------#######################-----
--------#######################-----
---------############ #########-----
----------############ T #########------
-----------########### #########------
-------------######################-------
-------------######################-------
--------------#####################-------
--- ---------####################-------
-- P ----------###################------
-- ------------################-------
-----------------##############-------
-----------------############-------
------------------#########-------
------------------######------
--------------------#-------
---------------#####--
-------#######
Global CMT Convention Moment Tensor:
R T P
2.80e+24 1.66e+24 -1.75e+24
1.66e+24 3.44e+23 6.10e+23
-1.75e+24 6.10e+23 -3.14e+24
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140419205442/index.html
|
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
5.36e+17 N-m
Magnitude
5.8
Percent DC
85%
Depth
8.0 km
Updated
2014-04-19 21:31:16 UTC
Author
us
Catalog
us
Contributor
us
Code
us_b000prk0_mwr
Principal Axes
Axis Value Plunge Azimuth
T 5.168 51 76
N 0.370 6 338
P -5.538 39 243
Nodal Planes
Plane Strike Dip Rake
NP1 159 84 96
NP2 293 9 45
|
|
April 19, 2014, NEAR COAST OF NORTHERN CHILE, MW=5.8
Goran Ekstrom
CENTROID-MOMENT-TENSOR SOLUTION
GCMT EVENT: C201404192054A
DATA: II IU MN IC G LD DK CU GE
KP
L.P.BODY WAVES: 59S, 77C, T= 40
SURFACE WAVES: 124S, 202C, T= 50
TIMESTAMP: Q-20140420094752
CENTROID LOCATION:
ORIGIN TIME: 20:54:48.7 0.2
LAT:19.96S 0.02;LON: 71.33W 0.02
DEP: 19.5 0.9;TRIANG HDUR: 2.0
MOMENT TENSOR: SCALE 10**24 D-CM
RR= 5.290 0.212; TT=-0.692 0.114
PP=-4.600 0.150; RT= 0.787 0.251
RP=-4.970 0.348; TP= 1.540 0.078
PRINCIPAL AXES:
1.(T) VAL= 7.358;PLG=68;AZM= 87
2.(N) -0.232; 5; 346
3.(P) -7.128; 22; 254
BEST DBLE.COUPLE:M0= 7.24*10**24
NP1: STRIKE=335;DIP=23;SLIP= 78
NP2: STRIKE=168;DIP=67;SLIP= 95
##---------
-----########------
-------###########-----
--------##############-----
---------###############-----
----------#################----
----------#################----
-----------######### ######----
------------######## T #######---
-- -------######## #######---
-- P -------##################---
- --------#################--
-------------###############---
------------###############--
------------#############--
-----------###########-
-----------#######-
--------###
|
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:
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 2.0 335 40 -95 5.43 0.3985
WVFGRD96 4.0 305 70 45 5.43 0.2658
WVFGRD96 6.0 155 85 75 5.49 0.3884
WVFGRD96 8.0 155 85 75 5.57 0.4687
WVFGRD96 10.0 155 80 75 5.59 0.5522
WVFGRD96 12.0 155 75 75 5.61 0.6178
WVFGRD96 14.0 155 70 75 5.63 0.6652
WVFGRD96 16.0 155 65 75 5.65 0.6917
WVFGRD96 18.0 150 65 70 5.66 0.7016
WVFGRD96 20.0 150 65 70 5.67 0.6988
WVFGRD96 22.0 150 65 70 5.69 0.6887
WVFGRD96 24.0 150 65 70 5.69 0.6682
WVFGRD96 26.0 145 70 65 5.70 0.6427
WVFGRD96 28.0 145 70 65 5.71 0.6122
WVFGRD96 30.0 145 70 65 5.72 0.5778
WVFGRD96 32.0 145 70 65 5.72 0.5404
WVFGRD96 34.0 145 70 65 5.73 0.5008
WVFGRD96 36.0 150 75 70 5.72 0.4630
WVFGRD96 38.0 155 80 75 5.71 0.4301
WVFGRD96 40.0 155 80 80 5.86 0.4068
WVFGRD96 42.0 155 80 80 5.85 0.3679
WVFGRD96 44.0 155 80 75 5.85 0.3337
WVFGRD96 46.0 155 80 75 5.85 0.3032
WVFGRD96 48.0 145 75 65 5.85 0.2775
WVFGRD96 50.0 145 75 65 5.85 0.2550
WVFGRD96 52.0 145 70 60 5.86 0.2356
WVFGRD96 54.0 145 70 60 5.86 0.2205
WVFGRD96 56.0 145 70 60 5.86 0.2079
WVFGRD96 58.0 140 70 55 5.87 0.1970
WVFGRD96 60.0 140 70 55 5.87 0.1875
WVFGRD96 62.0 140 70 55 5.88 0.1790
WVFGRD96 64.0 140 70 60 5.88 0.1718
WVFGRD96 66.0 140 70 60 5.89 0.1656
WVFGRD96 68.0 140 75 55 5.88 0.1609
WVFGRD96 70.0 140 75 55 5.88 0.1577
WVFGRD96 72.0 140 75 55 5.89 0.1549
WVFGRD96 74.0 140 75 60 5.90 0.1528
WVFGRD96 76.0 140 75 60 5.90 0.1509
WVFGRD96 78.0 145 70 65 5.91 0.1490
WVFGRD96 80.0 145 70 65 5.92 0.1492
WVFGRD96 82.0 145 70 65 5.92 0.1497
WVFGRD96 84.0 150 65 70 5.93 0.1499
WVFGRD96 86.0 155 65 80 5.94 0.1501
WVFGRD96 88.0 150 70 75 5.94 0.1516
WVFGRD96 90.0 150 70 75 5.95 0.1546
WVFGRD96 92.0 150 70 75 5.95 0.1558
WVFGRD96 94.0 355 20 110 5.97 0.1556
WVFGRD96 96.0 155 70 80 5.97 0.1590
WVFGRD96 98.0 355 20 110 5.98 0.1601
WVFGRD96 100.0 160 70 90 5.99 0.1627
WVFGRD96 102.0 165 75 95 6.00 0.1645
WVFGRD96 104.0 325 15 70 6.01 0.1671
WVFGRD96 106.0 325 15 70 6.02 0.1694
WVFGRD96 108.0 320 15 65 6.02 0.1739
The best solution is
WVFGRD96 18.0 150 65 70 5.66 0.7016
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
|
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 Sun Apr 20 10:21:50 CDT 2014