Location

2014/03/24 11:26:38 -19.843 -70.852 17.6 5.5 Chile

Arrival Times (from USGS)

Felt Map

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2014/03/24 11:26:38:0 -19.84 -70.85 17.6 5.5 Chile Stations used: C.GO01 CX.PATCX CX.PB01 CX.PB04 CX.PB07 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 = 3.76e+24 dyne-cm Mw = 5.65 Z = 22 km Plane Strike Dip Rake NP1 160 70 80 NP2 7 22 116 Principal Axes: Axis Value Plunge Azimuth T 3.76e+24 64 54 N 0.00e+00 9 163 P -3.76e+24 24 258 Moment Tensor: (dyne-cm) Component Value Mxx 1.16e+23 Mxy -2.95e+23 Mxz 1.18e+24 Myy -2.50e+24 Myz 2.59e+24 Mzz 2.38e+24 ############-- ---################--- ------##################---- -------####################--- ---------#####################---- ----------######################---- ------------######################---- -------------############ ########---- -------------############ T ########---- ---------------########### ########----- ---------------######################----- ---- ---------#####################----- ---- P ----------####################----- --- ----------####################---- -----------------##################----- -----------------################----- -----------------###############---- -----------------############----- -----------------#########---- -----------------######----- ----------------#----- ----------#### Global CMT Convention Moment Tensor: R T P 2.38e+24 1.18e+24 -2.59e+24 1.18e+24 1.16e+23 2.95e+23 -2.59e+24 2.95e+23 -2.50e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140324112638/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 = 160
      DIP = 70
     RAKE = 80
       MW = 5.65
       HS = 22.0

The NDK file is 20140324112638.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

USGS/SLU Moment Tensor Solution ENS 2014/03/24 11:26:38:0 -19.84 -70.85 17.6 5.5 Chile Stations used: C.GO01 CX.PATCX CX.PB01 CX.PB04 CX.PB07 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 = 3.76e+24 dyne-cm Mw = 5.65 Z = 22 km Plane Strike Dip Rake NP1 160 70 80 NP2 7 22 116 Principal Axes: Axis Value Plunge Azimuth T 3.76e+24 64 54 N 0.00e+00 9 163 P -3.76e+24 24 258 Moment Tensor: (dyne-cm) Component Value Mxx 1.16e+23 Mxy -2.95e+23 Mxz 1.18e+24 Myy -2.50e+24 Myz 2.59e+24 Mzz 2.38e+24 ############-- ---################--- ------##################---- -------####################--- ---------#####################---- ----------######################---- ------------######################---- -------------############ ########---- -------------############ T ########---- ---------------########### ########----- ---------------######################----- ---- ---------#####################----- ---- P ----------####################----- --- ----------####################---- -----------------##################----- -----------------################----- -----------------###############---- -----------------############----- -----------------#########---- -----------------######----- ----------------#----- ----------#### Global CMT Convention Moment Tensor: R T P 2.38e+24 1.18e+24 -2.59e+24 1.18e+24 1.16e+23 2.95e+23 -2.59e+24 2.95e+23 -2.50e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140324112638/index.html

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   350    45   -90   5.36 0.4202
WVFGRD96    4.0   165    30    85   5.42 0.2900
WVFGRD96    6.0   250     5   -10   5.44 0.4305
WVFGRD96    8.0   255     5    -5   5.52 0.5278
WVFGRD96   10.0   290     5    35   5.53 0.6308
WVFGRD96   12.0   310    10    55   5.55 0.7106
WVFGRD96   14.0   165    75    85   5.58 0.7768
WVFGRD96   16.0   165    75    85   5.59 0.8266
WVFGRD96   18.0   165    70    85   5.61 0.8617
WVFGRD96   20.0   160    70    80   5.63 0.8821
WVFGRD96   22.0   160    70    80   5.65 0.8915
WVFGRD96   24.0   160    70    80   5.66 0.8909
WVFGRD96   26.0   160    70    80   5.67 0.8828
WVFGRD96   28.0   160    70    80   5.68 0.8682
WVFGRD96   30.0   160    70    80   5.69 0.8472
WVFGRD96   32.0   160    70    85   5.70 0.8200
WVFGRD96   34.0   160    70    85   5.71 0.7880
WVFGRD96   36.0   160    70    85   5.72 0.7538
WVFGRD96   38.0   160    70    85   5.72 0.7202
WVFGRD96   40.0   350    15    95   5.86 0.6903
WVFGRD96   42.0   160    75    85   5.86 0.6531
WVFGRD96   44.0   160    75    85   5.87 0.6170
WVFGRD96   46.0   160    75    85   5.87 0.5830
WVFGRD96   48.0   160    70    85   5.88 0.5517
WVFGRD96   50.0   160    70    80   5.89 0.5221
WVFGRD96   52.0   160    75    80   5.89 0.4954
WVFGRD96   54.0   160    75    80   5.89 0.4709
WVFGRD96   56.0   160    75    80   5.90 0.4487
WVFGRD96   58.0   160    75    80   5.91 0.4282
WVFGRD96   60.0   160    75    80   5.91 0.4093
WVFGRD96   62.0   160    75    80   5.92 0.3923
WVFGRD96   64.0   155    80    75   5.92 0.3786
WVFGRD96   66.0   155    80    75   5.92 0.3663
WVFGRD96   68.0   160    80    80   5.93 0.3547
WVFGRD96   70.0   160    85    80   5.92 0.3457
WVFGRD96   72.0   160    85    85   5.93 0.3372
WVFGRD96   74.0   340    90   -80   5.93 0.3310
WVFGRD96   76.0   160    90    85   5.93 0.3253
WVFGRD96   78.0   160    90    85   5.94 0.3198
WVFGRD96   80.0   340    85   -85   5.94 0.3195
WVFGRD96   82.0   335    80   -80   5.93 0.3184
WVFGRD96   84.0   335    80   -80   5.94 0.3199
WVFGRD96   86.0   325    70   -80   5.93 0.3243
WVFGRD96   88.0   325    65   -85   5.93 0.3302
WVFGRD96   90.0   135    25   -95   5.94 0.3401
WVFGRD96   92.0   135    25   -95   5.95 0.3485
WVFGRD96   94.0   140    25   -95   5.95 0.3539
WVFGRD96   96.0   320    65   -90   5.96 0.3598
WVFGRD96   98.0   320    65   -95   5.97 0.3651
WVFGRD96  100.0   150    25   -80   5.97 0.3694
WVFGRD96  102.0   320    65   -95   5.98 0.3737
WVFGRD96  104.0   140    30   -90   5.97 0.3769
WVFGRD96  106.0   140    30   -90   5.97 0.3805
WVFGRD96  108.0   155    30   -75   5.99 0.3853

The best solution is

WVFGRD96   22.0   160    70    80   5.65 0.8915

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 Mon Mar 24 12:07:06 CDT 2014