Location

2013/06/14 11:53:01 60.892 -149.973 37.8 3.8 Alaska

Arrival Times (from USGS)

Felt Map

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2013/06/14 11:53:01:0 60.89 -149.97 37.8 3.8 Alaska Stations used: AK.BAL AK.BRLK AK.CAST AK.CNP AK.GLI AK.KTH AK.RC01 AK.SCM AK.SSN AK.TRF AT.MENT AT.PMR AT.SVW2 AT.TTA IU.COLA Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 6.53e+21 dyne-cm Mw = 3.81 Z = 42 km Plane Strike Dip Rake NP1 220 55 -80 NP2 23 36 -104 Principal Axes: Axis Value Plunge Azimuth T 6.53e+21 9 303 N 0.00e+00 8 34 P -6.53e+21 77 164 Moment Tensor: (dyne-cm) Component Value Mxx 1.58e+21 Mxy -2.81e+21 Mxz 1.91e+21 Myy 4.46e+21 Myz -1.27e+21 Mzz -6.04e+21 ############## #####################- #######################--### ###################--------### ##############-------------#### # T ############---------------##### ## ##########------------------##### ##############--------------------###### ############----------------------###### ############-----------------------####### ###########------------------------####### ##########---------- ------------####### #########----------- P -----------######## #######------------ ----------######## #######-------------------------######## #####-------------------------######## ####-----------------------######### ###----------------------######### #--------------------######### #-----------------########## -----------########### ############## Global CMT Convention Moment Tensor: R T P -6.04e+21 1.91e+21 1.27e+21 1.91e+21 1.58e+21 2.81e+21 1.27e+21 2.81e+21 4.46e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130614115301/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 = 220
      DIP = 55
     RAKE = -80
       MW = 3.81
       HS = 42.0

The NDK file is 20130614115301.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

USGS/SLU Moment Tensor Solution ENS 2013/06/14 11:53:01:0 60.89 -149.97 37.8 3.8 Alaska Stations used: AK.BAL AK.BRLK AK.CAST AK.CNP AK.GLI AK.KTH AK.RC01 AK.SCM AK.SSN AK.TRF AT.MENT AT.PMR AT.SVW2 AT.TTA IU.COLA Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 6.53e+21 dyne-cm Mw = 3.81 Z = 42 km Plane Strike Dip Rake NP1 220 55 -80 NP2 23 36 -104 Principal Axes: Axis Value Plunge Azimuth T 6.53e+21 9 303 N 0.00e+00 8 34 P -6.53e+21 77 164 Moment Tensor: (dyne-cm) Component Value Mxx 1.58e+21 Mxy -2.81e+21 Mxz 1.91e+21 Myy 4.46e+21 Myz -1.27e+21 Mzz -6.04e+21 ############## #####################- #######################--### ###################--------### ##############-------------#### # T ############---------------##### ## ##########------------------##### ##############--------------------###### ############----------------------###### ############-----------------------####### ###########------------------------####### ##########---------- ------------####### #########----------- P -----------######## #######------------ ----------######## #######-------------------------######## #####-------------------------######## ####-----------------------######### ###----------------------######### #--------------------######### #-----------------########## -----------########### ############## Global CMT Convention Moment Tensor: R T P -6.04e+21 1.91e+21 1.27e+21 1.91e+21 1.58e+21 2.81e+21 1.27e+21 2.81e+21 4.46e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130614115301/index.html

Magnitudes

ML Magnitude

(a) ML computed using the IASPEI formula for Horizontal components; (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.

(a) ML computed using the IASPEI formula for Vertical components (research); (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.

Context

The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).

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:

hp c 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2

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   250    45   -90   3.06 0.2517
WVFGRD96    1.0   285    85     0   3.08 0.2093
WVFGRD96    2.0   255    45   -90   3.20 0.2874
WVFGRD96    3.0   290    75    10   3.25 0.2488
WVFGRD96    4.0   300    55    25   3.30 0.2467
WVFGRD96    5.0   145    30   -15   3.26 0.2770
WVFGRD96    6.0   140    30   -25   3.27 0.3127
WVFGRD96    7.0   135    30   -30   3.28 0.3337
WVFGRD96    8.0   125    25   -35   3.35 0.3430
WVFGRD96    9.0   125    25   -35   3.34 0.3474
WVFGRD96   10.0   135    30   -30   3.33 0.3489
WVFGRD96   11.0   135    30   -30   3.33 0.3498
WVFGRD96   12.0   135    30   -30   3.33 0.3511
WVFGRD96   13.0   135    30   -30   3.34 0.3519
WVFGRD96   14.0   240    80   -60   3.36 0.3533
WVFGRD96   15.0   240    80   -60   3.37 0.3572
WVFGRD96   16.0   245    85   -55   3.38 0.3614
WVFGRD96   17.0   245    85   -55   3.39 0.3650
WVFGRD96   18.0   245    85   -55   3.40 0.3678
WVFGRD96   19.0   240    65   -50   3.43 0.3717
WVFGRD96   20.0   240    65   -50   3.44 0.3781
WVFGRD96   21.0   240    65   -50   3.46 0.3839
WVFGRD96   22.0   240    65   -50   3.47 0.3901
WVFGRD96   23.0   235    60   -55   3.48 0.3973
WVFGRD96   24.0   230    55   -55   3.49 0.4043
WVFGRD96   25.0   230    55   -55   3.50 0.4127
WVFGRD96   26.0   230    55   -55   3.51 0.4224
WVFGRD96   27.0   225    55   -60   3.53 0.4335
WVFGRD96   28.0   225    55   -65   3.54 0.4460
WVFGRD96   29.0   225    55   -65   3.55 0.4608
WVFGRD96   30.0   225    55   -65   3.56 0.4770
WVFGRD96   31.0   225    55   -65   3.58 0.4942
WVFGRD96   32.0   230    55   -65   3.59 0.5130
WVFGRD96   33.0   225    55   -70   3.61 0.5298
WVFGRD96   34.0   225    55   -70   3.62 0.5439
WVFGRD96   35.0   225    55   -70   3.63 0.5538
WVFGRD96   36.0   225    55   -70   3.64 0.5602
WVFGRD96   37.0   220    50   -75   3.65 0.5652
WVFGRD96   38.0   220    50   -75   3.67 0.5698
WVFGRD96   39.0   215    50   -80   3.69 0.5732
WVFGRD96   40.0   220    55   -80   3.79 0.5746
WVFGRD96   41.0   220    55   -80   3.80 0.5796
WVFGRD96   42.0   220    55   -80   3.81 0.5805
WVFGRD96   43.0   215    50   -85   3.82 0.5780
WVFGRD96   44.0   215    50   -85   3.83 0.5773
WVFGRD96   45.0   215    50   -85   3.84 0.5730
WVFGRD96   46.0    25    40   -95   3.84 0.5686
WVFGRD96   47.0    25    40   -95   3.85 0.5625
WVFGRD96   48.0   215    50   -85   3.85 0.5542
WVFGRD96   49.0    30    40   -90   3.86 0.5461

The best solution is

WVFGRD96   42.0   220    55   -80   3.81 0.5805

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

hp c 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2

Figure 3. Waveform comparison for selected depth

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 model 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 Dec 7 00:21:29 CST 2015