The ANSS event ID is usb000i86c and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usb000i86c/executive.
2013/07/07 08:38:59 36.457 -112.555 5.2 3.5 Arizona
USGS/SLU Moment Tensor Solution
ENS 2013/07/07 08:38:59:0 36.46 -112.56 5.2 3.5 Arizona
Stations used:
AE.W13A AE.X18A AE.Y14A AZ.KNW AZ.SND AZ.TRO AZ.WMC CI.ADO
CI.BC3 CI.BEL CI.BFS CI.DAN CI.FUR CI.GLA CI.GMR CI.GSC
CI.HEC CI.IRM CI.MPM CI.MUR CI.PDM CI.PLM CI.RRX CI.SVD
CI.SWS CI.TIN CI.TUQ CI.VTV IU.TUC PB.B082A PB.B086A
PB.B088A TA.214A TA.R11A TA.S22A TA.W18A TA.Y12C US.DUG
US.HWUT US.MVCO US.TPNV US.WUAZ UU.BGU UU.BRPU UU.CCUT
UU.HVU UU.KNB UU.LCMT UU.MPU UU.MTPU UU.PKCU UU.PSUT UU.SRU
UU.SZCU UU.TCRU UU.TMU
Filtering commands used:
cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.08 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.24e+21 dyne-cm
Mw = 3.50
Z = 17 km
Plane Strike Dip Rake
NP1 111 66 -129
NP2 355 45 -35
Principal Axes:
Axis Value Plunge Azimuth
T 2.24e+21 12 229
N 0.00e+00 35 130
P -2.24e+21 52 335
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.35e+20
Mxy 1.39e+21
Mxz -1.29e+21
Myy 1.05e+21
Myz 1.13e+20
Mzz -1.28e+21
--------######
--------------########
-------------------#########
----------------------########
-------------------------#########
------------ ------------#########
------------- P -------------#########
#------------- -------------##########
###----------------------------#########
#####---------------------------##########
#######-------------------------##########
##########----------------------##########
#############-------------------##########
###############----------------#########
####################-----------#########
###########################--######---
### ######################--------
## T #####################--------
####################-------
#####################-------
#################-----
###########---
Global CMT Convention Moment Tensor:
R T P
-1.28e+21 -1.29e+21 -1.13e+20
-1.29e+21 2.35e+20 -1.39e+21
-1.13e+20 -1.39e+21 1.05e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130707083859/index.html
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STK = 355
DIP = 45
RAKE = -35
MW = 3.50
HS = 17.0
The NDK file is 20130707083859.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 a -30 a 180 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.08 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 305 50 -90 3.19 0.3116
WVFGRD96 1.0 345 90 -5 3.22 0.3039
WVFGRD96 2.0 170 80 -10 3.29 0.3469
WVFGRD96 3.0 170 75 -5 3.34 0.3453
WVFGRD96 4.0 10 30 -10 3.41 0.3576
WVFGRD96 5.0 10 30 -10 3.41 0.4042
WVFGRD96 6.0 5 35 -15 3.40 0.4310
WVFGRD96 7.0 5 35 -20 3.40 0.4469
WVFGRD96 8.0 5 30 -15 3.45 0.4558
WVFGRD96 9.0 5 35 -15 3.45 0.4654
WVFGRD96 10.0 0 35 -25 3.45 0.4726
WVFGRD96 11.0 0 40 -25 3.45 0.4793
WVFGRD96 12.0 -5 40 -35 3.47 0.4854
WVFGRD96 13.0 355 40 -40 3.48 0.4910
WVFGRD96 14.0 355 45 -35 3.48 0.4959
WVFGRD96 15.0 355 45 -35 3.49 0.4997
WVFGRD96 16.0 355 45 -35 3.49 0.5019
WVFGRD96 17.0 355 45 -35 3.50 0.5026
WVFGRD96 18.0 355 45 -35 3.51 0.5025
WVFGRD96 19.0 355 50 -35 3.53 0.5015
WVFGRD96 20.0 355 50 -35 3.53 0.4994
WVFGRD96 21.0 350 50 -35 3.55 0.4970
WVFGRD96 22.0 350 50 -35 3.56 0.4930
WVFGRD96 23.0 350 50 -35 3.56 0.4876
WVFGRD96 24.0 350 50 -35 3.57 0.4812
WVFGRD96 25.0 350 50 -35 3.58 0.4737
WVFGRD96 26.0 350 50 -35 3.59 0.4652
WVFGRD96 27.0 350 50 -35 3.59 0.4565
WVFGRD96 28.0 350 50 -35 3.60 0.4470
WVFGRD96 29.0 350 50 -35 3.61 0.4377
The best solution is
WVFGRD96 17.0 355 45 -35 3.50 0.5026
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 a -30 a 180 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.08 n 3 br c 0.12 0.25 n 4 p 2
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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 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