Location
Location ANSS
The ANSS event ID is ci37507576 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ci37507576/executive.
2015/12/30 01:48:57 34.191 -117.413 7.0 4.4 Canada
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2015/12/30 01:48:57:0 34.19 -117.41 7.0 4.4 Canada
Stations used:
AZ.BZN AZ.CRY AZ.FRD AZ.KNW AZ.LVA2 AZ.MONP2 AZ.RDM AZ.RRSP
AZ.SND AZ.TMSP AZ.TRO AZ.WMC BC.CPX BC.SFX BC.TJX BC.UABX
BK.HELL BK.KCC BK.ORV BK.SAO BK.SUTB CI.ADO CI.ARV CI.BAK
CI.BAR CI.BBR CI.BC3 CI.BCW CI.BEL CI.BLY CI.CCC CI.CIA
CI.CWC CI.DAN CI.DEC CI.DGR CI.DPP CI.EDW2 CI.FOX2 CI.FUR
CI.GLA CI.GMR CI.GSC CI.HEC CI.IKP CI.IRM CI.ISA CI.MLAC
CI.MOP CI.MPP CI.MTP CI.MUR CI.MWC CI.NCH CI.NEE2 CI.NJQ
CI.OAT CI.OSI CI.PASC CI.PLM CI.PMD CI.RPV CI.RRX CI.SCI2
CI.SDD CI.SHO CI.SMR CI.SMW CI.SNCC CI.SPG2 CI.SVD CI.SWS
CI.SYN CI.SYP CI.TUQ CI.VCS CI.VES CI.WAS2 CI.WOR IU.TUC
LB.MVU LB.TPH NC.MCB NN.CTC NN.LHV NN.MPK NN.PAH NN.PRN
NN.QSM NN.RUB NN.SHP NN.SPR3 NN.V12A NN.VCN PB.B082A
PB.B086A PB.B088A PY.BPH09 PY.BPH13 TA.R11A US.TPNV UU.KNB
UU.PKCU UU.SZCU UU.TCRU UU.VRUT UU.ZNPU YN.BCCC YN.JFS1
YN.JORD YN.RHIL YN.TR01
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.94e+22 dyne-cm
Mw = 4.33
Z = 10 km
Plane Strike Dip Rake
NP1 35 85 20
NP2 303 70 175
Principal Axes:
Axis Value Plunge Azimuth
T 3.94e+22 18 261
N 0.00e+00 69 48
P -3.94e+22 10 167
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.54e+22
Mxy 1.37e+22
Mxz 4.96e+21
Myy 3.31e+22
Myz -1.27e+22
Mzz 2.34e+21
--------------
----------------------
-------------------------###
-------------------------#####
--------------------------########
#########-----------------##########
##############------------############
###################-------##############
######################---###############
########################--################
#######################-----##############
## #################---------###########
## T ################-----------##########
# ##############---------------#######
#################------------------#####
##############---------------------###
############-----------------------#
##########------------------------
######------------------------
###-------------- --------
-------------- P -----
---------- -
Global CMT Convention Moment Tensor:
R T P
2.34e+21 4.96e+21 1.27e+22
4.96e+21 -3.54e+22 -1.37e+22
1.27e+22 -1.37e+22 3.31e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20151230014857/index.html
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 35
DIP = 85
RAKE = 20
MW = 4.33
HS = 10.0
The NDK file is 20151230014857.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
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.
| SLU |
USGSMT |
SCAL |
USGS/SLU Moment Tensor Solution
ENS 2015/12/30 01:48:57:0 34.19 -117.41 7.0 4.4 Canada
Stations used:
AZ.BZN AZ.CRY AZ.FRD AZ.KNW AZ.LVA2 AZ.MONP2 AZ.RDM AZ.RRSP
AZ.SND AZ.TMSP AZ.TRO AZ.WMC BC.CPX BC.SFX BC.TJX BC.UABX
BK.HELL BK.KCC BK.ORV BK.SAO BK.SUTB CI.ADO CI.ARV CI.BAK
CI.BAR CI.BBR CI.BC3 CI.BCW CI.BEL CI.BLY CI.CCC CI.CIA
CI.CWC CI.DAN CI.DEC CI.DGR CI.DPP CI.EDW2 CI.FOX2 CI.FUR
CI.GLA CI.GMR CI.GSC CI.HEC CI.IKP CI.IRM CI.ISA CI.MLAC
CI.MOP CI.MPP CI.MTP CI.MUR CI.MWC CI.NCH CI.NEE2 CI.NJQ
CI.OAT CI.OSI CI.PASC CI.PLM CI.PMD CI.RPV CI.RRX CI.SCI2
CI.SDD CI.SHO CI.SMR CI.SMW CI.SNCC CI.SPG2 CI.SVD CI.SWS
CI.SYN CI.SYP CI.TUQ CI.VCS CI.VES CI.WAS2 CI.WOR IU.TUC
LB.MVU LB.TPH NC.MCB NN.CTC NN.LHV NN.MPK NN.PAH NN.PRN
NN.QSM NN.RUB NN.SHP NN.SPR3 NN.V12A NN.VCN PB.B082A
PB.B086A PB.B088A PY.BPH09 PY.BPH13 TA.R11A US.TPNV UU.KNB
UU.PKCU UU.SZCU UU.TCRU UU.VRUT UU.ZNPU YN.BCCC YN.JFS1
YN.JORD YN.RHIL YN.TR01
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.94e+22 dyne-cm
Mw = 4.33
Z = 10 km
Plane Strike Dip Rake
NP1 35 85 20
NP2 303 70 175
Principal Axes:
Axis Value Plunge Azimuth
T 3.94e+22 18 261
N 0.00e+00 69 48
P -3.94e+22 10 167
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.54e+22
Mxy 1.37e+22
Mxz 4.96e+21
Myy 3.31e+22
Myz -1.27e+22
Mzz 2.34e+21
--------------
----------------------
-------------------------###
-------------------------#####
--------------------------########
#########-----------------##########
##############------------############
###################-------##############
######################---###############
########################--################
#######################-----##############
## #################---------###########
## T ################-----------##########
# ##############---------------#######
#################------------------#####
##############---------------------###
############-----------------------#
##########------------------------
######------------------------
###-------------- --------
-------------- P -----
---------- -
Global CMT Convention Moment Tensor:
R T P
2.34e+21 4.96e+21 1.27e+22
4.96e+21 -3.54e+22 -1.37e+22
1.27e+22 -1.37e+22 3.31e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20151230014857/index.html
|
Regional Moment Tensor (Mwr)
Moment 3.761e+15 N-m
Magnitude 4.32
Depth 9.0 km
Percent DC 89%
Half Duration –
Catalog US (us10004ac5)
Data Source US3
Contributor US3
Nodal Planes
Plane Strike Dip Rake
NP1 215 76 -1
NP2 305 89 -166
Principal Axes
Axis Value Plunge Azimuth
T 3.862 9 79
N -0.210 76 309
P -3.652 10 171
|
TMTS
Moment 4.942e+15 N-m
Magnitude 4.40
Depth 5.0 km
Percent DC 91%
Half Duration –
Catalog CI (ci37507576)
Data Source CI2
Contributor CI2
Nodal Planes
Plane Strike Dip Rake
NP1 306 68 175
NP2 37 86 22
Principal Axes
Axis Value Plunge Azimuth
T 5.051 19 264
N -0.225 67 48
P -4.825 12 169
|
Magnitudes
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.
ML Magnitude
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.
Context
The left panel of the next figure presents the focal mechanism for this earthquake (red) in the context of other nearby events (blue) in the SLU Moment Tensor Catalog. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors). Thus context plot is useful for assessing the appropriateness of the moment tensor of this event.
Waveform Inversion using wvfgrd96
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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Location of broadband stations used for waveform inversion
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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 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 30 90 0 3.99 0.4222
WVFGRD96 2.0 210 85 -5 4.10 0.5548
WVFGRD96 3.0 210 80 -30 4.18 0.6130
WVFGRD96 4.0 210 80 -30 4.21 0.6645
WVFGRD96 5.0 210 80 -25 4.23 0.7046
WVFGRD96 6.0 210 80 -25 4.25 0.7346
WVFGRD96 7.0 215 90 -20 4.27 0.7602
WVFGRD96 8.0 210 80 -25 4.31 0.7801
WVFGRD96 9.0 210 85 -20 4.32 0.7896
WVFGRD96 10.0 35 85 20 4.33 0.7958
WVFGRD96 11.0 35 80 20 4.35 0.7956
WVFGRD96 12.0 35 80 20 4.36 0.7912
WVFGRD96 13.0 210 90 -15 4.37 0.7825
WVFGRD96 14.0 35 80 15 4.38 0.7769
WVFGRD96 15.0 210 90 -15 4.39 0.7660
WVFGRD96 16.0 210 90 -15 4.39 0.7559
WVFGRD96 17.0 35 85 15 4.40 0.7480
WVFGRD96 18.0 215 90 -15 4.40 0.7344
WVFGRD96 19.0 35 85 15 4.41 0.7251
WVFGRD96 20.0 35 85 15 4.42 0.7133
WVFGRD96 21.0 215 90 -15 4.42 0.6996
WVFGRD96 22.0 215 90 -15 4.43 0.6873
WVFGRD96 23.0 215 90 -15 4.43 0.6748
WVFGRD96 24.0 215 90 -15 4.44 0.6622
WVFGRD96 25.0 215 90 -10 4.44 0.6493
WVFGRD96 26.0 215 90 -10 4.45 0.6371
WVFGRD96 27.0 215 90 -10 4.45 0.6246
WVFGRD96 28.0 215 90 -10 4.46 0.6122
WVFGRD96 29.0 215 90 -10 4.46 0.5996
The best solution is
WVFGRD96 10.0 35 85 20 4.33 0.7958
The mechanism corresponding to the best fit is
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Figure 1. Waveform inversion focal mechanism
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The best fit as a function of depth is given in the following figure:
|
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Figure 2. Depth sensitivity for waveform mechanism
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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 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 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.
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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.
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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:
- The origin time and epicentral distance are incorrect
- The velocity model used for the inversion is incorrect
- The velocity model used to define the P-arrival time is not the
same as the velocity model used for the waveform inversion
(assuming that the initial trace alignment is based on the
P arrival time)
Assuming only a mislocation, the time shifts are fit to a functional form:
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.
Velocity Model
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
Last Changed Sat Apr 27 02:12:06 AM CDT 2024
