Location

Location ANSS

2017/11/30 21:47:31 39.205 -75.421 8.1 5.3 Delaware

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2017/11/30 21:47:31:0  39.21  -75.42   8.1 5.3 Delaware
 
 Stations used:
   IU.SSPA LD.BRNJ LD.KSCT LD.LUPA LD.MMNY LD.MVL LD.ODNJ 
   LD.PAL LD.TRNY LD.UCCT LD.WUPA N4.K57A N4.L56A N4.L59A 
   N4.M55A N4.M57A N4.M63A N4.N58A N4.O54A N4.P57A N4.P61A 
   N4.Q56A N4.R55A N4.R58B N4.R61A N4.S57A N4.S61A N4.T57A 
   N4.T59A N4.T60A N4.U59A N4.V61A NE.QUA2 NE.TRY NE.WSPT 
   NE.YLE PE.PAHR PE.PALB TA.L61B US.MCWV 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 2.34e+22 dyne-cm
  Mw = 4.18 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1      357    69   148
   NP2      100    60    25
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.34e+22     38     316
    N   0.00e+00     52     147
    P  -2.34e+22      5      50

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.03e+21
       Mxy    -1.88e+22
       Mxz     6.72e+21
       Myy    -6.55e+21
       Myz    -9.60e+21
       Mzz     8.58e+21
                                                     
                                                     
                                                     
                                                     
                     #######-------                  
                 ############----------              
              ################------------           
             ##################-----------           
           ######   ###########----------- P         
          ####### T ############----------   -       
         ########   ############---------------      
        #########################---------------     
        #########################---------------     
       -#########################----------------    
       ---#######################----------------    
       -----######################---------------    
       -------####################---------------    
        ---------#################-------------#     
        --------------###########----------#####     
         ------------------------##############      
          -----------------------#############       
           ----------------------############        
             -------------------###########          
              ------------------##########           
                 --------------########              
                     ---------#####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  8.58e+21   6.72e+21   9.60e+21 
  6.72e+21  -2.03e+21   1.88e+22 
  9.60e+21   1.88e+22  -6.55e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20171130214731/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 = 100
      DIP = 60
     RAKE = 25
       MW = 4.18
       HS = 3.0

The NDK file is 20171130214731.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMWR
 USGS/SLU Moment Tensor Solution
 ENS  2017/11/30 21:47:31:0  39.21  -75.42   8.1 5.3 Delaware
 
 Stations used:
   IU.SSPA LD.BRNJ LD.KSCT LD.LUPA LD.MMNY LD.MVL LD.ODNJ 
   LD.PAL LD.TRNY LD.UCCT LD.WUPA N4.K57A N4.L56A N4.L59A 
   N4.M55A N4.M57A N4.M63A N4.N58A N4.O54A N4.P57A N4.P61A 
   N4.Q56A N4.R55A N4.R58B N4.R61A N4.S57A N4.S61A N4.T57A 
   N4.T59A N4.T60A N4.U59A N4.V61A NE.QUA2 NE.TRY NE.WSPT 
   NE.YLE PE.PAHR PE.PALB TA.L61B US.MCWV 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 2.34e+22 dyne-cm
  Mw = 4.18 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1      357    69   148
   NP2      100    60    25
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.34e+22     38     316
    N   0.00e+00     52     147
    P  -2.34e+22      5      50

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.03e+21
       Mxy    -1.88e+22
       Mxz     6.72e+21
       Myy    -6.55e+21
       Myz    -9.60e+21
       Mzz     8.58e+21
                                                     
                                                     
                                                     
                                                     
                     #######-------                  
                 ############----------              
              ################------------           
             ##################-----------           
           ######   ###########----------- P         
          ####### T ############----------   -       
         ########   ############---------------      
        #########################---------------     
        #########################---------------     
       -#########################----------------    
       ---#######################----------------    
       -----######################---------------    
       -------####################---------------    
        ---------#################-------------#     
        --------------###########----------#####     
         ------------------------##############      
          -----------------------#############       
           ----------------------############        
             -------------------###########          
              ------------------##########           
                 --------------########              
                     ---------#####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  8.58e+21   6.72e+21   9.60e+21 
  6.72e+21  -2.03e+21   1.88e+22 
  9.60e+21   1.88e+22  -6.55e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20171130214731/index.html
	
egional Moment Tensor (Mwr)
Moment	2.029e+15 N-m
Magnitude	4.1 Mwr
Depth	3.0 km
Percent DC	76 %
Half Duration	–
Catalog	US
Data Source	US3
Contributor	US3
Nodal Planes
Plane	Strike	Dip	Rake
NP1	355	55	146
NP2	106	62	40
Principal Axes
Axis	Value	Plunge	Azimuth
T	1.891e+15 N-m	47	323
N	0.252e+15 N-m	43	135
P	-2.143e+15 N-m	4	229

        

Magnitudes

mLg Magnitude


(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.

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 using wvfgrd96

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 o DIST/3.3 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.06 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    1.0   100    60    20   4.12 0.6153
WVFGRD96    2.0   100    65    25   4.15 0.6340
WVFGRD96    3.0   100    60    25   4.18 0.6378
WVFGRD96    4.0   100    60    25   4.19 0.6257
WVFGRD96    5.0    90    55    10   4.20 0.6059
WVFGRD96    6.0    85    55   -10   4.20 0.5980
WVFGRD96    7.0    85    55   -10   4.21 0.5985
WVFGRD96    8.0    90    60   -15   4.20 0.5991
WVFGRD96    9.0    90    60   -15   4.21 0.5998
WVFGRD96   10.0    85    55   -10   4.23 0.5974
WVFGRD96   11.0    90    60   -15   4.22 0.5960
WVFGRD96   12.0    90    60   -15   4.23 0.5935
WVFGRD96   13.0    85    60   -10   4.23 0.5906
WVFGRD96   14.0    85    60   -10   4.23 0.5873
WVFGRD96   15.0    85    60   -10   4.24 0.5836
WVFGRD96   16.0    85    60   -10   4.24 0.5798
WVFGRD96   17.0    85    65   -10   4.25 0.5765
WVFGRD96   18.0    85    65   -10   4.25 0.5738
WVFGRD96   19.0    85    65   -10   4.26 0.5707
WVFGRD96   20.0    85    60   -10   4.27 0.5659
WVFGRD96   21.0    85    65   -10   4.27 0.5613
WVFGRD96   22.0    85    65   -10   4.28 0.5571
WVFGRD96   23.0    85    65   -10   4.28 0.5527
WVFGRD96   24.0    90    65    10   4.29 0.5494
WVFGRD96   25.0    90    65    10   4.30 0.5466
WVFGRD96   26.0    90    65    10   4.30 0.5439
WVFGRD96   27.0    90    65    10   4.31 0.5409
WVFGRD96   28.0    90    65    10   4.32 0.5375
WVFGRD96   29.0    90    70    10   4.32 0.5345

The best solution is

WVFGRD96    3.0   100    60    25   4.18 0.6378

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 o DIST/3.3 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.06 n 3 
br c 0.12 0.25 n 4 p 2
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:

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.model 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 Thu Nov 30 19:14:35 CST 2017