The ANSS event ID is nc51182810 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nc51182810/executive.
2007/06/12 07:23:43 37.540 -118.868 7.9 4.6 California
USGS/SLU Moment Tensor Solution
ENS 2007/06/12 07:23:43:0 37.54 -118.87 7.9 4.6 California
Stations used:
BK.CMB BK.ORV CI.CLC CI.CWC CI.FUR CI.GLA CI.GRA CI.GSC
CI.ISA CI.JRC2 CI.MPM CI.RCT CI.SHO CI.SPG2 CI.TIN CI.TUQ
CI.VES IW.REDW US.DUG US.MVCO US.TPNV US.WUAZ US.WVOR
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 8.41e+22 dyne-cm
Mw = 4.55
Z = 12 km
Plane Strike Dip Rake
NP1 305 76 159
NP2 40 70 15
Principal Axes:
Axis Value Plunge Azimuth
T 8.41e+22 24 261
N 0.00e+00 65 92
P -8.41e+22 4 353
Moment Tensor: (dyne-cm)
Component Value
Mxx -8.10e+22
Mxy 2.02e+22
Mxz -1.06e+22
Myy 6.70e+22
Myz -3.06e+22
Mzz 1.40e+22
--- P --------
------- ------------
---------------------------#
----------------------------##
------------------------------####
#######-----------------------######
############------------------########
#################-------------##########
####################---------###########
#######################------#############
##########################--##############
#### ####################-##############
#### T ##################-----############
### #################--------#########
#####################------------#######
##################----------------####
###############-------------------##
############----------------------
#######-----------------------
#---------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
1.40e+22 -1.06e+22 3.06e+22
-1.06e+22 -8.10e+22 -2.02e+22
3.06e+22 -2.02e+22 6.70e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20070612072343/index.html
|
STK = 40
DIP = 70
RAKE = 15
MW = 4.55
HS = 12.0
The NDK file is 20070612072343.ndk The waveform inversion is preferred.
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
USGS/SLU Moment Tensor Solution
ENS 2007/06/12 07:23:43:0 37.54 -118.87 7.9 4.6 California
Stations used:
BK.CMB BK.ORV CI.CLC CI.CWC CI.FUR CI.GLA CI.GRA CI.GSC
CI.ISA CI.JRC2 CI.MPM CI.RCT CI.SHO CI.SPG2 CI.TIN CI.TUQ
CI.VES IW.REDW US.DUG US.MVCO US.TPNV US.WUAZ US.WVOR
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 8.41e+22 dyne-cm
Mw = 4.55
Z = 12 km
Plane Strike Dip Rake
NP1 305 76 159
NP2 40 70 15
Principal Axes:
Axis Value Plunge Azimuth
T 8.41e+22 24 261
N 0.00e+00 65 92
P -8.41e+22 4 353
Moment Tensor: (dyne-cm)
Component Value
Mxx -8.10e+22
Mxy 2.02e+22
Mxz -1.06e+22
Myy 6.70e+22
Myz -3.06e+22
Mzz 1.40e+22
--- P --------
------- ------------
---------------------------#
----------------------------##
------------------------------####
#######-----------------------######
############------------------########
#################-------------##########
####################---------###########
#######################------#############
##########################--##############
#### ####################-##############
#### T ##################-----############
### #################--------#########
#####################------------#######
##################----------------####
###############-------------------##
############----------------------
#######-----------------------
#---------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
1.40e+22 -1.06e+22 3.06e+22
-1.06e+22 -8.10e+22 -2.02e+22
3.06e+22 -2.02e+22 6.70e+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
|
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
 |
The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) the waveform inversion are shown in the next figure.
|
|
|
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's 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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 35 70 -30 4.25 0.4588
WVFGRD96 2.0 30 65 -35 4.37 0.5828
WVFGRD96 3.0 215 75 -25 4.37 0.6229
WVFGRD96 4.0 40 90 20 4.38 0.6523
WVFGRD96 5.0 40 90 20 4.41 0.6768
WVFGRD96 6.0 40 85 15 4.43 0.6960
WVFGRD96 7.0 40 70 10 4.46 0.7121
WVFGRD96 8.0 45 65 15 4.50 0.7269
WVFGRD96 9.0 45 70 15 4.51 0.7385
WVFGRD96 10.0 40 75 15 4.52 0.7458
WVFGRD96 11.0 40 70 15 4.54 0.7525
WVFGRD96 12.0 40 70 15 4.55 0.7558
WVFGRD96 13.0 40 75 15 4.56 0.7556
WVFGRD96 14.0 40 75 15 4.57 0.7517
WVFGRD96 15.0 40 75 10 4.58 0.7455
WVFGRD96 16.0 40 75 10 4.59 0.7369
WVFGRD96 17.0 40 80 10 4.59 0.7268
WVFGRD96 18.0 40 80 10 4.60 0.7162
WVFGRD96 19.0 40 80 10 4.61 0.7044
WVFGRD96 20.0 40 80 10 4.61 0.6914
WVFGRD96 21.0 40 85 10 4.62 0.6784
WVFGRD96 22.0 40 85 10 4.63 0.6650
WVFGRD96 23.0 40 85 10 4.63 0.6516
WVFGRD96 24.0 40 90 10 4.64 0.6379
WVFGRD96 25.0 220 90 -10 4.64 0.6249
WVFGRD96 26.0 40 90 10 4.65 0.6120
WVFGRD96 27.0 220 90 -10 4.65 0.5992
WVFGRD96 28.0 220 90 -10 4.66 0.5866
WVFGRD96 29.0 40 90 10 4.67 0.5744
The best solution is
WVFGRD96 12.0 40 70 15 4.55 0.7558
The mechanism corresponding to the best fit is
|
|
|
The best fit as a function of depth is given in the following figure:
|
|
|
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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 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. The time scale is relative to the first trace sample. |
|
| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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:
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.
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.
|
|
|
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 = 12.0 km
Mw = 4.63
Best Fit 0.8185 - P-T axis plot gives solutions with FIT greater than FIT90
 |
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.
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.
|
|
|
|
| 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. |
|
|
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
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