Location
Location ANSS
The ANSS event ID is uw10763723 and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/uw10763723/executive.
2009/01/30 13:25:04 47.786 -122.585 62.2 4.67 Washington
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2009/01/30 13:25:04:0 47.79 -122.58 62.2 4.7 Washington
Stations used:
BK.HUMO CN.HNB CN.HOPB CN.LLLB CN.PGC CN.PNT CN.SNB CN.VGZ
IU.COR LI.LTH US.BMO US.HAWA US.NLWA UW.BRAN UW.IZEE
UW.KENT UW.LEBA UW.LON UW.LTY UW.OFR UW.OMAK UW.OPC UW.PASS
UW.WISH UW.YACT
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 7.59e+22 dyne-cm
Mw = 4.52
Z = 55 km
Plane Strike Dip Rake
NP1 218 80 -165
NP2 125 75 -10
Principal Axes:
Axis Value Plunge Azimuth
T 7.59e+22 4 351
N 0.00e+00 72 249
P -7.59e+22 18 82
Moment Tensor: (dyne-cm)
Component Value
Mxx 7.22e+22
Mxy -2.16e+22
Mxz 1.75e+21
Myy -6.56e+22
Myz -2.24e+22
Mzz -6.59e+21
## T #########
###### #############
##########################--
########################------
########################----------
--#####################-------------
----###################---------------
-------###############------------------
---------############--------------- -
-----------#########----------------- P --
--------------#####------------------ --
----------------#-------------------------
----------------##------------------------
--------------######--------------------
------------###########-----------------
----------###############-------------
--------#####################-------
------############################
---###########################
--##########################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-6.59e+21 1.75e+21 2.24e+22
1.75e+21 7.22e+22 2.16e+22
2.24e+22 2.16e+22 -6.56e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090130132504/index.html
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Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 125
DIP = 75
RAKE = -10
MW = 4.52
HS = 55.0
The NDK file is 20090130132504.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 |
PNSN |
USGS/SLU Moment Tensor Solution
ENS 2009/01/30 13:25:04:0 47.79 -122.58 62.2 4.7 Washington
Stations used:
BK.HUMO CN.HNB CN.HOPB CN.LLLB CN.PGC CN.PNT CN.SNB CN.VGZ
IU.COR LI.LTH US.BMO US.HAWA US.NLWA UW.BRAN UW.IZEE
UW.KENT UW.LEBA UW.LON UW.LTY UW.OFR UW.OMAK UW.OPC UW.PASS
UW.WISH UW.YACT
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 7.59e+22 dyne-cm
Mw = 4.52
Z = 55 km
Plane Strike Dip Rake
NP1 218 80 -165
NP2 125 75 -10
Principal Axes:
Axis Value Plunge Azimuth
T 7.59e+22 4 351
N 0.00e+00 72 249
P -7.59e+22 18 82
Moment Tensor: (dyne-cm)
Component Value
Mxx 7.22e+22
Mxy -2.16e+22
Mxz 1.75e+21
Myy -6.56e+22
Myz -2.24e+22
Mzz -6.59e+21
## T #########
###### #############
##########################--
########################------
########################----------
--#####################-------------
----###################---------------
-------###############------------------
---------############--------------- -
-----------#########----------------- P --
--------------#####------------------ --
----------------#-------------------------
----------------##------------------------
--------------######--------------------
------------###########-----------------
----------###############-------------
--------#####################-------
------############################
---###########################
--##########################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-6.59e+21 1.75e+21 2.24e+22
1.75e+21 7.22e+22 2.16e+22
2.24e+22 2.16e+22 -6.56e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090130132504/index.html
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P-wave first motion solution from the University of Washington
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20090130 13:24 8.0 km NE of Poulsbo, WA
Lat=47.78550, Lon=-122.56833, Depth=62.7, Md=4.5
Moment magnitude 4.5
Scalar moment 6.90939 * 1022 dyn-cm
Percent double couple 97.0%
Percent CLVD 3.0%
Moment tensor elements (* 1022 dyn-cm) Mxx: 6.71259
Mxy: -1.3965 Mxz: -0.25936
Mxy: -1.3965 Myy: -6.4187 Myz: -1.5988
Mxz: -0.25936 Myz: -1.5988 Mzz: -0.29381
Fault Option 1 Fault Option 2
Strike(deg) 128.0 220.0
Dip(deg) 81.0 80.0
Rake(deg) -10.0 -171.0
Velocity Model:
P Velocity (km/s) Top of Layer (km)
5.40 0.0
6.38 4.0
6.59 9.0
6.73 16.0
6.86 20.0
6.95 25.0
7.80 41.0
Shear wave velocities are calculated from the Pwave
velocities using a Vp/Vs ratio of 1.78.
http://spike.ess.washington.edu/SEIS/EQ_Special/WEBDIR_09013013245p/MT.html
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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:
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 0.5 40 80 -10 3.68 0.1774
WVFGRD96 1.0 40 90 0 3.70 0.1934
WVFGRD96 2.0 40 90 0 3.81 0.2479
WVFGRD96 3.0 40 90 0 3.85 0.2697
WVFGRD96 4.0 310 85 20 3.91 0.2870
WVFGRD96 5.0 130 90 -20 3.93 0.3021
WVFGRD96 6.0 130 85 -20 3.96 0.3176
WVFGRD96 7.0 130 85 -15 3.99 0.3327
WVFGRD96 8.0 130 85 -20 4.02 0.3472
WVFGRD96 9.0 130 85 -20 4.04 0.3573
WVFGRD96 10.0 310 90 15 4.05 0.3644
WVFGRD96 11.0 310 90 15 4.07 0.3717
WVFGRD96 12.0 310 90 15 4.09 0.3794
WVFGRD96 13.0 310 90 15 4.10 0.3871
WVFGRD96 14.0 130 85 -15 4.11 0.3957
WVFGRD96 15.0 130 85 -15 4.13 0.4037
WVFGRD96 16.0 130 85 -10 4.14 0.4120
WVFGRD96 17.0 130 85 -10 4.15 0.4202
WVFGRD96 18.0 130 85 -10 4.16 0.4290
WVFGRD96 19.0 130 85 -10 4.17 0.4375
WVFGRD96 20.0 130 85 -10 4.18 0.4456
WVFGRD96 21.0 130 85 -10 4.20 0.4537
WVFGRD96 22.0 130 85 -10 4.21 0.4614
WVFGRD96 23.0 130 85 -10 4.22 0.4685
WVFGRD96 24.0 130 85 -5 4.23 0.4758
WVFGRD96 25.0 130 85 -5 4.24 0.4829
WVFGRD96 26.0 130 85 -5 4.25 0.4897
WVFGRD96 27.0 130 85 -5 4.26 0.4960
WVFGRD96 28.0 130 85 -5 4.26 0.5018
WVFGRD96 29.0 130 85 -5 4.27 0.5070
WVFGRD96 30.0 130 85 -5 4.28 0.5119
WVFGRD96 31.0 130 85 -5 4.29 0.5169
WVFGRD96 32.0 130 85 -5 4.30 0.5214
WVFGRD96 33.0 130 85 -5 4.31 0.5257
WVFGRD96 34.0 130 80 -5 4.32 0.5298
WVFGRD96 35.0 130 80 -5 4.34 0.5340
WVFGRD96 36.0 130 80 -5 4.35 0.5382
WVFGRD96 37.0 130 80 -5 4.36 0.5426
WVFGRD96 38.0 130 85 -5 4.38 0.5473
WVFGRD96 39.0 130 85 -5 4.39 0.5536
WVFGRD96 40.0 125 75 -10 4.42 0.5606
WVFGRD96 41.0 125 75 -10 4.43 0.5644
WVFGRD96 42.0 125 75 -10 4.44 0.5670
WVFGRD96 43.0 125 75 -10 4.45 0.5691
WVFGRD96 44.0 125 75 -10 4.46 0.5712
WVFGRD96 45.0 125 75 -10 4.47 0.5728
WVFGRD96 46.0 125 75 -10 4.47 0.5739
WVFGRD96 47.0 125 75 -10 4.48 0.5747
WVFGRD96 48.0 125 75 -10 4.49 0.5761
WVFGRD96 49.0 125 75 -10 4.49 0.5772
WVFGRD96 50.0 125 75 -10 4.50 0.5779
WVFGRD96 51.0 125 75 -10 4.50 0.5780
WVFGRD96 52.0 125 75 -10 4.51 0.5788
WVFGRD96 53.0 125 75 -10 4.51 0.5792
WVFGRD96 54.0 125 75 -10 4.52 0.5790
WVFGRD96 55.0 125 75 -10 4.52 0.5797
WVFGRD96 56.0 125 75 -10 4.53 0.5795
WVFGRD96 57.0 125 75 -10 4.53 0.5787
WVFGRD96 58.0 125 75 -10 4.53 0.5789
WVFGRD96 59.0 125 75 -10 4.54 0.5782
WVFGRD96 60.0 125 75 -10 4.54 0.5776
WVFGRD96 61.0 125 75 -10 4.54 0.5771
WVFGRD96 62.0 125 75 -10 4.55 0.5762
WVFGRD96 63.0 125 75 -10 4.55 0.5756
WVFGRD96 64.0 125 75 -10 4.55 0.5740
WVFGRD96 65.0 125 75 -10 4.55 0.5734
WVFGRD96 66.0 125 75 -15 4.55 0.5720
WVFGRD96 67.0 125 75 -15 4.56 0.5718
WVFGRD96 68.0 125 75 -15 4.56 0.5703
WVFGRD96 69.0 125 75 -15 4.56 0.5689
The best solution is
WVFGRD96 55.0 125 75 -10 4.52 0.5797
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
hp c 0.02 n 3
lp c 0.06 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.
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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 Sun Apr 28 01:07:40 PM CDT 2024
