Location

2007/06/12 07:23:43 37.54N 118.88W 14 4.6 California

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports page for California

Focal Mechanism

 SLU Moment Tensor Solution
 2007/06/12 07:23:43 37.54N 118.88W 14 4.6 California
 
 Best Fitting Double Couple
    Mo = 8.41e+22 dyne-cm
    Mw = 4.55 
    Z  = 14 km
     Plane   Strike  Dip  Rake
      NP1      131    85   -165
      NP2       40    75    -5
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   8.41e+22      7     265
     N   0.00e+00     74     149
     P  -8.41e+22     14     357



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx    -7.82e+22
       Mxy     1.23e+22
       Mxz    -2.07e+22
       Myy     8.19e+22
       Myz    -9.08e+21
       Mzz    -3.67e+21
                                                     
                                                     
                                                     
                                                     
                     ----   -------                  
                 -------- P -----------              
              -----------   -------------#           
             ----------------------------##          
           ###--------------------------#####        
          ######-----------------------#######       
         ########---------------------#########      
        ###########------------------###########     
        #############---------------############     
       ################------------##############    
          ###############---------###############    
        T #################-----#################    
          ###################--##################    
        #####################--#################     
        ###################-------##############     
         ################-----------###########      
          #############---------------########       
           ##########--------------------####        
             ######------------------------          
              #---------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
 -3.67e+21  -2.07e+22   9.08e+21 
 -2.07e+22  -7.82e+22  -1.23e+22 
  9.08e+21  -1.23e+22   8.19e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20070612072343/index.html
        
This is a preliminary UCB moment tensor solution for the event located
14 km SE of Mammoth Lakes, CA; 37.539N 118.876W; Z=14km;  ML=5.1;
(USGS/UCB Joint Notification System) on June 12, 2007 at 12:23:43 UTC.
Other information about this event can be viewed at:
http://earthquake.usgs.gov/recenteqsus/Quakes/nc51182810.php

Reviewed by:
Guilhem
UCB Seismological Laboratory

Inversion method:   complete waveform
Stations used:      CMB, HELL, KCC, ORV, SAO and GSC
 
 Berkeley Moment Tensor Solution
 
 Best Fitting Double-Couple:
    Mo = 9.96E+22 Dyne-cm
    Mw = 4.60
    Z  = 14
    Plane   Strike   Rake   Dip
     NP1       41       8    82
     NP2      310     172    82
 
 Principal Axes:
    Axis    Value   Plunge   Azimuth
      T     9.956      11      266
      N     0.000      79       85
      P    -9.956       0      176
 
 Event Date/Time: June 12, 2007 at 12:23:43 UTC
 Event ID:        nc51182810
 Moment Tensor: Scale = 10**22 Dyne-cm
    Component   Value
       Mxx     -9.839
       Mxy      1.507
       Mxz     -0.138
       Myy      9.457
       Myz     -1.907
       Mzz      0.382
 
                                               
                                               
                    -------                    
              -------------------              
           -------------------------           
         ----------------------------#         
       #----------------------------####       
      ######----------------------#######      
     #########-------------------#########     
    #############---------------###########    
    ################----------#############    
   ###################-------###############   
   #####################---#################   
   #   #####################################   
   # T #################----################   
   #   ################-------##############   
    #################-----------###########    
    ###############---------------#########    
     ############-------------------######     
      #########-----------------------###      
       ######--------------------------#       
         ##---------------------------         
           -------------------------           
              ----------   ------              
                    ---- P                     
                                               
     Lower Hemisphere Equiangle Projection
 

	

      STK = 40
      DIP = 75
     RAKE = -5
       MW = 4.55
       HS = 14

The wavefrom inversion is preferred. The surface-wave amplitude solution is comparable.

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
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   305    75    35   4.07 0.2787
WVFGRD96    1.0   310    80    30   4.08 0.2911
WVFGRD96    2.0   305    70    30   4.19 0.3678
WVFGRD96    3.0   310    85    20   4.24 0.4065
WVFGRD96    4.0   310    95   -10   4.28 0.4345
WVFGRD96    5.0   305    85   -20   4.32 0.4512
WVFGRD96    6.0    40    65    -5   4.37 0.4791
WVFGRD96    7.0    40    65    -5   4.40 0.5028
WVFGRD96    8.0    40    70     0   4.44 0.5241
WVFGRD96    9.0    40    70     0   4.47 0.5388
WVFGRD96   10.0    40    70     0   4.49 0.5449
WVFGRD96   11.0    40    75     0   4.50 0.5437
WVFGRD96   12.0    40    75    -5   4.52 0.5514
WVFGRD96   13.0    40    75    -5   4.54 0.5581
WVFGRD96   14.0    40    75    -5   4.55 0.5594
WVFGRD96   15.0    40    75    -5   4.56 0.5560
WVFGRD96   16.0    40    75    -5   4.57 0.5493
WVFGRD96   17.0    40    75    -5   4.58 0.5394
WVFGRD96   18.0    40    75    -5   4.59 0.5267
WVFGRD96   19.0    40    75    -5   4.60 0.5126
WVFGRD96   20.0    40    75    -5   4.61 0.4964
WVFGRD96   21.0    40    70   -10   4.63 0.4799
WVFGRD96   22.0    40    70   -10   4.63 0.4617
WVFGRD96   23.0    40    70   -10   4.64 0.4420
WVFGRD96   24.0    40    70   -10   4.64 0.4220
WVFGRD96   25.0    40    75   -10   4.64 0.4009
WVFGRD96   26.0    35    60   -15   4.65 0.3815
WVFGRD96   27.0   210    70    -5   4.64 0.3689
WVFGRD96   28.0   125    95   -40   4.67 0.3668
WVFGRD96   29.0   305    85    35   4.68 0.3642

The best solution is

WVFGRD96   14.0    40    75    -5   4.55 0.5594

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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was

hp c 0.02 n 3
lp c 0.10 n 3
Figure 3. Waveform comparison for depth of 8 km
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.

Surface-Wave Focal Mechanism

The following figure shows the stations used in the grid search for the best focal mechanism to fit the surface-wave spectral amplitudes of the Love and Rayleigh waves.
Location of broadband stations used to obtain focal mechanism from surface-wave spectral amplitudes

The surface-wave determined focal mechanism is shown here.


  NODAL PLANES 

  
  STK=     307.90
  DIP=      71.25
 RAKE=     158.83
  
             OR
  
  STK=      44.99
  DIP=      70.00
 RAKE=      20.00
 
 
DEPTH = 13.0 km
 
Mw = 4.64
Best Fit 0.8593 - P-T axis plot gives solutions with FIT greater than FIT90

First motion data

The P-wave first motion data for focal mechanism studies are as follow:

Sta Az(deg)    Dist(km)   First motion
ISA       170  211 iP_D
TPNV      105  242 eP_X
GSC       143  310 eP_X
SNCC      187  480 -12345
WVOR        2  544 eP_X

Surface-wave analysis

Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surface-wave radiation pattern search program srfgrd96.

The velocity model used for the search is a modified Utah model .

Data preparation

Digital data were collected, instrument response removed and traces converted to Z, R an T components. Multiple filter analysis was applied to the Z and T traces to obtain the Rayleigh- and Love-wave spectral amplitudes, respectively. These were input to the search program which examined all depths between 1 and 25 km and all possible mechanisms.
Best mechanism fit as a function of depth. The preferred depth is given above. Lower hemisphere projection

Pressure-tension axis trends. Since the surface-wave spectra search does not distinguish between P and T axes and since there is a 180 ambiguity in strike, all possible P and T axes are plotted. First motion data and waveforms will be used to select the preferred mechanism. The purpose of this plot is to provide an idea of the possible range of solutions. The P and T-axes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here.


Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the Love and Rayleigh wave radiation patterns. 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. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0-180 degrees are sampled.

Love-wave radiation patterns

Rayleigh-wave radiation patterns

Broadband station distributiuon

Sta Az(deg)    Dist(km)   
ISA	  170	  211
TPNV	  105	  242
GSC	  142	  310
WVOR	    2	  544
DUG	   59	  603
GLA	  142	  619
NOQ	   57	  679
MPU	   64	  687
HVU	   46	  704
WUAZ	  106	  708
CTU	   58	  709
SRU	   74	  751
HLID	   28	  768
HWUT	   52	  773
BMO	    9	  823
AHID	   46	  880
MVCO	   89	  920
REDW	   44	  938
TPAW	   43	  942
SNOW	   44	  951
LOHW	   44	  972
IMW	   41	  973
BW06	   51	  983
HAWA	  357	  985
BOZ	   32	 1083
RWWY	   62	 1102
MSO	   20	 1109
RLMT	   41	 1163
NLWA	  341	 1168
ISCO	   74	 1180
NEW	    6	 1200
EGMT	   30	 1381
MNTX	  114	 1395
LAO	   42	 1455
AMTX	   96	 1572
CBKS	   79	 1680
DGMT	   40	 1700
JCT	  108	 1924
KSU1	   78	 1950
ECSD	   63	 1999
AGMN	   50	 2214
SCIA	   70	 2244
MIAR	   91	 2297
NATX	   99	 2304
JFWS	   67	 2496
EYMN	   54	 2504
HDIL	   73	 2571
COWI	   59	 2629
VBMS	   94	 2648
GLMI	   63	 2962
BRAL	   94	 3003
AAM	   69	 3035
ACSO	   73	 3108
TZTN	   81	 3127
GOGA	   87	 3227
ERPA	   69	 3339
BLA	   79	 3382
MCWV	   74	 3382
NHSC	   86	 3528
CBN	   76	 3622
CNNC	   81	 3658
BINY	   68	 3667
LONY	   64	 3756
NCB	   65	 3790
LBNH	   64	 3971
PKME	   62	 4166

Waveform comparison for this mechanism

Since the analysis of the surface-wave radiation patterns uses only spectral amplitudes and because the surfave-wave radiation patterns have a 180 degree symmetry, each surface-wave solution consists of four possible focal mechanisms corresponding to the interchange of the P- and T-axes and a roation of the mechanism by 180 degrees. To select one mechanism, P-wave first motion can be used. This was not possible in this case because all the P-wave first motions were emergent ( a feature of the P-wave wave takeoff angle, the station location and the mechanism). The other way to select among the mechanisms is to compute forward synthetics and compare the observed and predicted waveforms.

The velocity model used for the waveform fit is a modified Utah model .

The fits to the waveforms with the given mechanism are show below:

This figure shows the fit to the three components of motion (Z - vertical, R-radial and T - transverse). For each station and component, the observed traces is shown in red and the model predicted trace in blue. The traces represent filtered ground velocity in units of meters/sec (the peak value is printed adjacent to each trace; each pair of traces to plotted to the same scale to emphasize the difference in levels). Both synthetic and observed traces have been filtered using the SAC commands:

hp c 0.02 n 3
lp c 0.10 n 3

Discussion

The Future

Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.

Acknowledgements

Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface

Appendix A


Spectra fit plots to each station

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 Jun 13 08:34:31 CDT 2007