Location

2015/05/19 18:36:02 36.661 -120.901 1.7 4.0 California

ML Magnitude


(a) ML computed using the IASPEI formula; (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.

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  2015/05/19 18:36:02:0  36.66 -120.90   1.7 4.0 California
 
 Stations used:
   BK.BDM BK.BKS BK.BL67 BK.BRK BK.CMB BK.HAST BK.JRSC BK.MCCM 
   BK.MHC BK.ORV BK.PACP BK.PKD BK.RAMR BK.SAO BK.SCZ BK.TCHL 
   BK.THIS BK.TRAM BK.TSCN BK.VAK BK.WENL CI.ARV CI.CWC 
   CI.EDW2 CI.MLAC CI.MPP CI.PHL CI.SBC CI.SMM IM.NV31 NC.AFD 
   NC.BBGB NC.LDH NC.MCB NC.PAGB NC.PMPB NN.CTC NN.KVN NN.MPK 
   NN.PNT NN.RUB NN.WAK NP.MOD TA.O03E 
 
 Filtering commands used:
   cut o DIST/3.3 -20 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.66e+22 dyne-cm
  Mw = 4.08 
  Z  = 12 km
  Plane   Strike  Dip  Rake
   NP1       61    81   155
   NP2      155    65    10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.66e+22     24      15
    N   0.00e+00     63     222
    P  -1.66e+22     11     110

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.10e+22
       Mxy     8.68e+21
       Mxz     7.04e+21
       Myy    -1.32e+22
       Myz    -1.24e+21
       Mzz     2.21e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 --############   #####              
              -----############ T ########           
             -----#############   #########          
           -------###########################        
          ---------###########################       
         ----------#########################---      
        -----------#######################------     
        ------------####################--------     
       -------------#################------------    
       --------------#############---------------    
       --------------##########------------------    
       ---------------######---------------------    
        ---------------#--------------------   -     
        ------------####-------------------- P -     
         -------#########-------------------         
          #################-------------------       
           #################-----------------        
             #################-------------          
              ##################----------           
                 #################-----              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.21e+21   7.04e+21   1.24e+21 
  7.04e+21   1.10e+22  -8.68e+21 
  1.24e+21  -8.68e+21  -1.32e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150519183602/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 = 155
      DIP = 65
     RAKE = 10
       MW = 4.08
       HS = 12.0

The NDK file is 20150519183602.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
UCB
 USGS/SLU Moment Tensor Solution
 ENS  2015/05/19 18:36:02:0  36.66 -120.90   1.7 4.0 California
 
 Stations used:
   BK.BDM BK.BKS BK.BL67 BK.BRK BK.CMB BK.HAST BK.JRSC BK.MCCM 
   BK.MHC BK.ORV BK.PACP BK.PKD BK.RAMR BK.SAO BK.SCZ BK.TCHL 
   BK.THIS BK.TRAM BK.TSCN BK.VAK BK.WENL CI.ARV CI.CWC 
   CI.EDW2 CI.MLAC CI.MPP CI.PHL CI.SBC CI.SMM IM.NV31 NC.AFD 
   NC.BBGB NC.LDH NC.MCB NC.PAGB NC.PMPB NN.CTC NN.KVN NN.MPK 
   NN.PNT NN.RUB NN.WAK NP.MOD TA.O03E 
 
 Filtering commands used:
   cut o DIST/3.3 -20 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.66e+22 dyne-cm
  Mw = 4.08 
  Z  = 12 km
  Plane   Strike  Dip  Rake
   NP1       61    81   155
   NP2      155    65    10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.66e+22     24      15
    N   0.00e+00     63     222
    P  -1.66e+22     11     110

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.10e+22
       Mxy     8.68e+21
       Mxz     7.04e+21
       Myy    -1.32e+22
       Myz    -1.24e+21
       Mzz     2.21e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 --############   #####              
              -----############ T ########           
             -----#############   #########          
           -------###########################        
          ---------###########################       
         ----------#########################---      
        -----------#######################------     
        ------------####################--------     
       -------------#################------------    
       --------------#############---------------    
       --------------##########------------------    
       ---------------######---------------------    
        ---------------#--------------------   -     
        ------------####-------------------- P -     
         -------#########-------------------         
          #################-------------------       
           #################-----------------        
             #################-------------          
              ##################----------           
                 #################-----              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.21e+21   7.04e+21   1.24e+21 
  7.04e+21   1.10e+22  -8.68e+21 
  1.24e+21  -8.68e+21  -1.32e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150519183602/index.html
	
** CISN Moment Tensor Solution Message **

Event Information:
------------------
Event ID     : nc72451856
Magnitude    : 4.02 Ml
Origin Time  : 2015/05/19 18:36:01.73
Latitude     :   36.6705
Longitude    : -120.8800
Depth (km)   : 0.0
Nearest town : 38.4 km (23.9 mi) SSW of South Dos Palos, CA
MT Web page  : http://www.ncedc.org/mt/nc72451856_MT.html
Further Information at:
http://earthquake.usgs.gov/earthquakes/eventpage/nc72451856

Moment Tensor Information:
--------------------------
Solution Status    : Reviewed by: Peggy
Inversion method   : complete waveform
Mw                 : 3.82 (authoritative)
M0                 : 6.64e+21 Dyne-cm
Depth (km)         : 1.5 (not authoritative)
Variance Reduction : 74%
Solution version   : 3
Solution time      : 2015/05/20 16:16:37 UTC

Stations used:
Name       Dist (km)  Azimuth     VR(%)   ZCorr
-------------------------------------------------
BK.PKD       86         159       78       44
NC.PMPB      51         172       73       38
BK.SCZ       47         260       70       39
BK.SAO       51         281       67       40
BK.HAST      67         242       59       39
BK.PACP      52         316       80       39

Best Fitting Deviatoric Mechanism:
----------------------------------
 Moment Tensor (Aki & Richards Convention):
    Scale = 1.0e+21 Dyne-cm
    Component   Value
       Mxx     -6.073
       Mxy     -2.619
       Mxz     -0.634
       Myy      2.410
       Myz     -3.036
       Mzz      3.663

 Principal Axes: Scale = 1.0e+21 Dyne-cm
    Axis Value(dev) Plunge   Azimuth
     T    6.256     48.251    278.763
     N    0.769     40.565    115.192
     P   -7.025      8.226     18.084

 Source Composition:
    Type   Percent
     DC      78
     CLVD    22
     Iso     (null)




                            -----------
                      ------------------   --
                  ---------------------- P ------
               -------------------------   ---------
             ###--------------------------------------
           #########------------------------------------
          #############----------------------------------
         #################--------------------------------
       ######################-------------------------------
      ##########################-----------------------------
      ############################---------------------------
     ###############################--------------------------
    ##################################-----------------------##
    ####################################--------------------###
    ##############   ######################---------------#####
    ############## T ########################-----------#######
   ###############   ############################---############
    ###########################################################
    ###########################################################
    ###########################################################
    ###########################################################
     #########################################################
      ---####################################################
      --------###############################################
       -----------------------------------------############
         -----------------------------------------########
          -----------------------------------------######
           -----------------------------------------####
             ----------------------------------------#
               -------------------------------------
                  -------------------------------
                      -----------------------
                            -----------

     Lower Hemisphere Equiangle Projection



Best Fitting Double Couple Mechanism:
-------------------------------------
    Plane   Strike   Rake   Dip
     NP1      319     136    65
     NP2       71      33    51


                            -----------
                      ------------------   --
                  ---------------------- P ------
               -------------------------   ---------
             ###--------------------------------------
           ##########-----------------------------------
          ##############---------------------------------
         ##################-------------------------------
       #######################------------------------------
      ##########################-----------------------------
      ############################---------------------------
     ###############################--------------------------
    ##################################-----------------------##
    ####################################--------------------###
    ##############   ####################------------------####
    ############## T ######################---------------#####
   ###############   #######################------------########
    #########################################----------########
    ##########################################-------##########
    ############################################--#############
    ############################################-##############
     ########################################----#############
      --#################################---------###########
      ------########################---------------##########
       ---------------------------------------------########
         -------------------------------------------######
          -------------------------------------------####
           ------------------------------------------###
             ----------------------------------------#
               -------------------------------------
                  -------------------------------
                      -----------------------
                            -----------

     Lower Hemisphere Equiangle Projection
        

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 o DIST/3.3 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.10 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   310    50   -40   3.66 0.2126
WVFGRD96    2.0   300    50   -70   3.85 0.2821
WVFGRD96    3.0   315    60   -45   3.84 0.2845
WVFGRD96    4.0   160    55    15   3.84 0.2999
WVFGRD96    5.0   160    60    20   3.88 0.3242
WVFGRD96    6.0   160    60    15   3.91 0.3428
WVFGRD96    7.0   155    65    10   3.94 0.3572
WVFGRD96    8.0   160    60    15   3.99 0.3716
WVFGRD96    9.0   160    60    15   4.02 0.3799
WVFGRD96   10.0   155    65    10   4.04 0.3863
WVFGRD96   11.0   155    65    15   4.06 0.3905
WVFGRD96   12.0   155    65    10   4.08 0.3911
WVFGRD96   13.0   155    65    10   4.09 0.3901
WVFGRD96   14.0   155    65    10   4.11 0.3866
WVFGRD96   15.0   155    65    10   4.12 0.3814
WVFGRD96   16.0   155    65     5   4.13 0.3754
WVFGRD96   17.0   155    65     5   4.14 0.3675
WVFGRD96   18.0   155    65     0   4.15 0.3593
WVFGRD96   19.0   155    65     0   4.16 0.3504
WVFGRD96   20.0   155    65     0   4.16 0.3402
WVFGRD96   21.0   155    65     0   4.17 0.3289
WVFGRD96   22.0   155    65     0   4.17 0.3190
WVFGRD96   23.0   155    65     0   4.18 0.3080
WVFGRD96   24.0   155    65    10   4.18 0.2968
WVFGRD96   25.0   155    65    10   4.18 0.2854
WVFGRD96   26.0   155    65    10   4.18 0.2742
WVFGRD96   27.0   155    65    10   4.18 0.2630
WVFGRD96   28.0   155    65    10   4.18 0.2521
WVFGRD96   29.0   155    65    10   4.18 0.2417

The best solution is

WVFGRD96   12.0   155    65    10   4.08 0.3911

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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.10 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:

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 Sun Jul 5 12:02:26 CDT 2015