The ANSS event ID is usp000g8hv and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000g8hv/executive.
2008/06/04 14:02:42 36.510 -106.355 5.0 3.7 New Mexico
USGS/SLU Moment Tensor Solution
ENS 2008/06/04 14:02:42:0 36.51 -106.36 5.0 3.7 New Mexico
Stations used:
IU.ANMO IW.SMCO TA.118A TA.126A TA.127A TA.227A TA.N21A
TA.N22A TA.O18A TA.O19A TA.O20A TA.O21A TA.P16A TA.P17A
TA.P18A TA.P19A TA.P20A TA.Q16A TA.Q20A TA.Q21A TA.Q22A
TA.R17A TA.R18A TA.R19A TA.R20A TA.R21A TA.S17A TA.S18A
TA.S19A TA.S21A TA.T22A TA.U17A TA.U20A TA.U24A TA.U26A
TA.V15A TA.V17A TA.V18A TA.V20A TA.V21A TA.V22A TA.V25A
TA.V26A TA.W16A TA.W17A TA.W18A TA.W19A TA.W21A TA.W24A
TA.W25A TA.W26A TA.X15A TA.X16A TA.X18A TA.X19A TA.X20A
TA.X21A TA.X23A TA.X24A TA.X25A TA.X26A TA.Y16A TA.Y17A
TA.Y18A TA.Y19A TA.Y20A TA.Y25A TA.Y26A TA.Y27A TA.Z16A
TA.Z17A TA.Z18A TA.Z19A TA.Z20A TA.Z25A TA.Z26A TA.Z27A
US.AMTX US.ISCO US.MVCO US.SDCO US.WUAZ UU.SRU
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 3.76e+21 dyne-cm
Mw = 3.65
Z = 15 km
Plane Strike Dip Rake
NP1 330 81 -150
NP2 235 60 -10
Principal Axes:
Axis Value Plunge Azimuth
T 3.76e+21 14 99
N 0.00e+00 59 344
P -3.76e+21 27 197
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.63e+21
Mxy -1.36e+21
Mxz 1.33e+21
Myy 3.20e+21
Myz 1.33e+21
Mzz -5.65e+20
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#---------------------
######----------------------
########----------------------
############--------------########
##############-------###############
################--####################
################---#####################
##############------####################
############----------####################
###########------------###################
#########---------------############# ##
########-----------------############ T ##
#####--------------------########### #
#####---------------------##############
###-----------------------############
#-------------------------##########
----------- -----------#########
--------- P ------------######
-------- -------------####
---------------------#
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Global CMT Convention Moment Tensor:
R T P
-5.65e+20 1.33e+21 -1.33e+21
1.33e+21 -2.63e+21 1.36e+21
-1.33e+21 1.36e+21 3.20e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080604140242/index.html
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STK = 235
DIP = 60
RAKE = -10
MW = 3.65
HS = 15.0
The NDK file is 20080604140242.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:
hp c 0.02 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 245 70 20 3.41 0.3312
WVFGRD96 1.0 245 65 20 3.44 0.3445
WVFGRD96 2.0 245 60 25 3.49 0.3580
WVFGRD96 3.0 240 55 10 3.49 0.3652
WVFGRD96 4.0 240 55 10 3.50 0.3769
WVFGRD96 5.0 240 55 10 3.51 0.3917
WVFGRD96 6.0 240 55 10 3.52 0.4078
WVFGRD96 7.0 240 55 10 3.54 0.4238
WVFGRD96 8.0 240 55 10 3.55 0.4380
WVFGRD96 9.0 235 60 0 3.56 0.4520
WVFGRD96 10.0 235 55 -5 3.58 0.4658
WVFGRD96 11.0 235 55 -5 3.60 0.4762
WVFGRD96 12.0 235 55 -5 3.61 0.4843
WVFGRD96 13.0 235 60 -10 3.62 0.4907
WVFGRD96 14.0 235 60 -10 3.64 0.4949
WVFGRD96 15.0 235 60 -10 3.65 0.4965
WVFGRD96 16.0 235 60 -10 3.66 0.4960
WVFGRD96 17.0 235 55 -10 3.67 0.4935
WVFGRD96 18.0 235 55 -10 3.67 0.4896
WVFGRD96 19.0 235 55 -10 3.68 0.4839
WVFGRD96 20.0 235 55 -10 3.70 0.4773
WVFGRD96 21.0 235 55 -10 3.71 0.4690
WVFGRD96 22.0 235 55 -15 3.72 0.4601
WVFGRD96 23.0 235 55 -15 3.73 0.4504
WVFGRD96 24.0 235 55 -15 3.73 0.4397
WVFGRD96 25.0 235 55 -15 3.74 0.4287
WVFGRD96 26.0 235 55 -15 3.74 0.4174
WVFGRD96 27.0 235 55 -15 3.75 0.4056
WVFGRD96 28.0 230 55 -20 3.75 0.3940
WVFGRD96 29.0 230 55 -20 3.75 0.3829
The best solution is
WVFGRD96 15.0 235 60 -10 3.65 0.4965
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
hp c 0.02 n 3 lp c 0.10 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= 334.98
DIP= 79.99
RAKE= -155.00
OR
STK= 240.35
DIP= 65.41
RAKE= -11.02
DEPTH = 18.0 km
Mw = 3.78
Best Fit 0.8859 - 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 CUS.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 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00
