Location

2014/02/26 00:00:07 -30.679 121.187 0.0 4.6 Australia

Arrival Times (from USGS)

Felt Map

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2014/02/26 00:00:07:0 -30.68 121.19 0.0 4.6 Australia Stations used: AU.BLDU AU.FORT AU.KMBL AU.MEEK AU.MORW AU.MUN IU.NWAO 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 = 4.07e+22 dyne-cm Mw = 4.34 Z = 1 km Plane Strike Dip Rake NP1 221 64 114 NP2 355 35 50 Principal Axes: Axis Value Plunge Azimuth T 4.07e+22 63 170 N 0.00e+00 22 30 P -4.07e+22 16 293 Moment Tensor: (dyne-cm) Component Value Mxx 2.39e+21 Mxy 1.22e+22 Mxz -2.04e+22 Myy -3.17e+22 Myz 1.25e+22 Mzz 2.93e+22 ---------##### ----------------###### ---------------------######- ----------------------##------ ---------------------######------- -------------------##########------- - --------------#############------- -- P ------------###############-------- -- ----------##################------- ---------------###################-------- -------------######################------- ------------#######################------- -----------########################------- ---------########### ##########------- --------############ T ##########------- -------############ #########------- -----#########################------ ----########################------ -########################----- ######################------ ##################---- ###########--- Global CMT Convention Moment Tensor: R T P 2.93e+22 -2.04e+22 -1.25e+22 -2.04e+22 2.39e+21 -1.22e+22 -1.25e+22 -1.22e+22 -3.17e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140226000007/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 = 50
       MW = 4.34
       HS = 1.0

The NDK file is 20140226000007.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

USGS/SLU Moment Tensor Solution ENS 2014/02/26 00:00:07:0 -30.68 121.19 0.0 4.6 Australia Stations used: AU.BLDU AU.FORT AU.KMBL AU.MEEK AU.MORW AU.MUN IU.NWAO 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 = 4.07e+22 dyne-cm Mw = 4.34 Z = 1 km Plane Strike Dip Rake NP1 221 64 114 NP2 355 35 50 Principal Axes: Axis Value Plunge Azimuth T 4.07e+22 63 170 N 0.00e+00 22 30 P -4.07e+22 16 293 Moment Tensor: (dyne-cm) Component Value Mxx 2.39e+21 Mxy 1.22e+22 Mxz -2.04e+22 Myy -3.17e+22 Myz 1.25e+22 Mzz 2.93e+22 ---------##### ----------------###### ---------------------######- ----------------------##------ ---------------------######------- -------------------##########------- - --------------#############------- -- P ------------###############-------- -- ----------##################------- ---------------###################-------- -------------######################------- ------------#######################------- -----------########################------- ---------########### ##########------- --------############ T ##########------- -------############ #########------- -----#########################------ ----########################------ -########################----- ######################------ ##################---- ###########--- Global CMT Convention Moment Tensor: R T P 2.93e+22 -2.04e+22 -1.25e+22 -2.04e+22 2.39e+21 -1.22e+22 -1.25e+22 -1.22e+22 -3.17e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140226000007/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    1.0    -5    35    50   4.34 0.8440
WVFGRD96    2.0   180    70    70   4.43 0.8258
WVFGRD96    3.0   190    65    80   4.44 0.7786
WVFGRD96    4.0   180    25    60   4.40 0.7587
WVFGRD96    5.0    -5    80    65   4.46 0.7493
WVFGRD96    6.0   170    90   -55   4.45 0.7377
WVFGRD96    7.0   165    80   -45   4.45 0.7314
WVFGRD96    8.0   165    80   -45   4.45 0.7344
WVFGRD96    9.0   160    70   -40   4.43 0.7363
WVFGRD96   10.0   160    70   -45   4.47 0.7251
WVFGRD96   11.0   160    70   -45   4.47 0.7276
WVFGRD96   12.0   160    65   -40   4.47 0.7276
WVFGRD96   13.0   160    65   -40   4.47 0.7257
WVFGRD96   14.0   155    60   -40   4.46 0.7225
WVFGRD96   15.0   155    60   -40   4.46 0.7194
WVFGRD96   16.0   155    60   -40   4.47 0.7149
WVFGRD96   17.0   155    60   -40   4.47 0.7093
WVFGRD96   18.0   155    60   -40   4.48 0.7034
WVFGRD96   19.0   155    60   -40   4.48 0.6980
WVFGRD96   20.0   155    60   -45   4.52 0.6856
WVFGRD96   21.0   155    60   -45   4.52 0.6779
WVFGRD96   22.0   155    60   -45   4.53 0.6692
WVFGRD96   23.0   145    55   -55   4.53 0.6602
WVFGRD96   24.0   145    55   -55   4.54 0.6515
WVFGRD96   25.0   145    55   -55   4.54 0.6419
WVFGRD96   26.0   145    55   -55   4.55 0.6316
WVFGRD96   27.0   130    50   -70   4.54 0.6212
WVFGRD96   28.0   130    50   -70   4.55 0.6116
WVFGRD96   29.0   130    50   -70   4.55 0.6018

The best solution is

WVFGRD96    1.0    -5    35    50   4.34 0.8440

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 CUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
CUS Model with Q from simple gamma values
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
  1.0000  5.0000  2.8900  2.5000 0.172E-02 0.387E-02 0.00  0.00  1.00  1.00 
  9.0000  6.1000  3.5200  2.7300 0.160E-02 0.363E-02 0.00  0.00  1.00  1.00 
 10.0000  6.4000  3.7000  2.8200 0.149E-02 0.336E-02 0.00  0.00  1.00  1.00 
 20.0000  6.7000  3.8700  2.9020 0.000E-04 0.000E-04 0.00  0.00  1.00  1.00 
  0.0000  8.1500  4.7000  3.3640 0.194E-02 0.431E-02 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 Wed Feb 26 09:24:06 CST 2014