The ANSS event ID is usp000g2eu and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000g2eu/executive.
2008/03/27 01:07:14 36.465 -113.581 5.0 3.7 Arizona
USGS/SLU Moment Tensor Solution
ENS 2008/03/27 01:07:14:0 36.47 -113.58 5.0 3.7 Arizona
Stations used:
CI.GLA CI.GSC CI.LDF TA.112A TA.113A TA.114A TA.115A
TA.116A TA.N13A TA.O10A TA.O11A TA.O12A TA.P12A TA.P13A
TA.P18A TA.Q10A TA.Q11A TA.Q12A TA.Q13A TA.Q14A TA.Q16A
TA.Q18A TA.R10A TA.R11A TA.R12A TA.R13A TA.R14A TA.R15A
TA.R19A TA.S10A TA.S11A TA.S12A TA.S13A TA.S17A TA.T11A
TA.T12A TA.T13A TA.T14A TA.T15A TA.T16A TA.T17A TA.T18A
TA.U10A TA.U11A TA.U12A TA.U13A TA.U14A TA.U15A TA.U16A
TA.U17A TA.V11A TA.V12A TA.V13A TA.V14A TA.V15A TA.V17A
TA.V18A TA.V19A TA.W12A TA.W13A TA.W14A TA.W15A TA.W16A
TA.W17A TA.W18A TA.W19A TA.X13A TA.X14A TA.X15A TA.X16A
TA.X18A TA.X19A TA.Y12C TA.Y13A TA.Y14A TA.Y15A TA.Y16A
TA.Y17A TA.Y19A TA.Z14A TA.Z15A TA.Z16A US.DUG US.ELK
US.WUAZ UU.BGU UU.CCUT UU.SRU
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 0.07 n 3
Best Fitting Double Couple
Mo = 4.47e+21 dyne-cm
Mw = 3.70
Z = 10 km
Plane Strike Dip Rake
NP1 220 70 -50
NP2 332 44 -150
Principal Axes:
Axis Value Plunge Azimuth
T 4.47e+21 15 282
N 0.00e+00 37 24
P -4.47e+21 49 173
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.75e+21
Mxy -6.15e+20
Mxz 2.44e+21
Myy 3.95e+21
Myz -1.38e+21
Mzz -2.20e+21
--------------
#######---------------
##############-------------#
##################-----#######
##################################
#####################----###########
####################-------###########
###################-----------##########
# #############--------------#########
## T ############---------------##########
## ##########------------------#########
##############--------------------########
#############---------------------########
###########----------------------#######
##########-----------------------#######
########----------- ----------######
######------------ P ----------#####
####------------- ----------####
##-------------------------###
#------------------------###
---------------------#
--------------
Global CMT Convention Moment Tensor:
R T P
-2.20e+21 2.44e+21 1.38e+21
2.44e+21 -1.75e+21 6.15e+20
1.38e+21 6.15e+20 3.95e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080327010714/index.html
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STK = 220
DIP = 70
RAKE = -50
MW = 3.70
HS = 10.0
The NDK file is 20080327010714.ndk The waveform inversion is preferred.
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.
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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.
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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 0.07 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 40 45 -85 3.34 0.2444
WVFGRD96 1.0 230 75 10 3.32 0.2441
WVFGRD96 2.0 230 75 15 3.42 0.2875
WVFGRD96 3.0 230 90 -45 3.52 0.2997
WVFGRD96 4.0 225 80 -55 3.58 0.3373
WVFGRD96 5.0 220 75 -55 3.60 0.3767
WVFGRD96 6.0 220 70 -55 3.61 0.4088
WVFGRD96 7.0 220 70 -50 3.62 0.4313
WVFGRD96 8.0 215 65 -55 3.69 0.4504
WVFGRD96 9.0 215 65 -55 3.70 0.4620
WVFGRD96 10.0 220 70 -50 3.70 0.4651
WVFGRD96 11.0 220 70 -45 3.70 0.4639
WVFGRD96 12.0 225 75 -40 3.71 0.4600
WVFGRD96 13.0 225 75 -40 3.71 0.4550
WVFGRD96 14.0 225 75 -40 3.72 0.4475
WVFGRD96 15.0 230 80 -35 3.73 0.4388
WVFGRD96 16.0 230 80 -35 3.73 0.4305
WVFGRD96 17.0 230 85 -30 3.75 0.4219
WVFGRD96 18.0 50 90 30 3.76 0.4127
WVFGRD96 19.0 50 90 30 3.76 0.4046
WVFGRD96 20.0 50 90 30 3.77 0.3958
WVFGRD96 21.0 55 80 35 3.77 0.3886
WVFGRD96 22.0 230 90 -30 3.78 0.3778
WVFGRD96 23.0 55 80 35 3.79 0.3732
WVFGRD96 24.0 55 80 35 3.79 0.3652
WVFGRD96 25.0 55 80 35 3.80 0.3569
WVFGRD96 26.0 55 80 35 3.81 0.3489
WVFGRD96 27.0 55 80 35 3.81 0.3407
WVFGRD96 28.0 55 80 30 3.82 0.3325
WVFGRD96 29.0 55 75 30 3.83 0.3243
The best solution is
WVFGRD96 10.0 220 70 -50 3.70 0.4651
The mechanism corresponding to the best fit is
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The best fit as a function of depth is given in the following figure:
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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 0.07 n 3
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| 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. |
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| 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.
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The surface-wave determined focal mechanism is shown here.
NODAL PLANES
STK= 60.00
DIP= 74.99
RAKE= 54.99
OR
STK= 309.72
DIP= 37.71
RAKE= 154.96
DEPTH = 8.0 km
Mw = 3.85
Best Fit 0.8937 - P-T axis plot gives solutions with FIT greater than FIT90
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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.
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| 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. |
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| 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. |
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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