2008/08/17 05:56:59 41.1830 -124.1970 17.0 4.60 California
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2008/08/17 05:56:59 41.1830 -124.1970 17.0 4.60 California
Best Fitting Double Couple
Mo = 7.59e+22 dyne-cm
Mw = 4.52
Z = 20 km
Plane Strike Dip Rake
NP1 350 90 -75
NP2 80 15 -180
Principal Axes:
Axis Value Plunge Azimuth
T 7.59e+22 43 65
N 0.00e+00 15 170
P -7.59e+22 43 274
Moment Tensor: (dyne-cm)
Component Value
Mxx 6.72e+21
Mxy 1.84e+22
Mxz 1.27e+22
Myy -6.72e+21
Myz 7.22e+22
Mzz -1.78e+15
----##########
--------##############
-----------#################
-------------#################
---------------###################
----------------####################
------------------####################
-------------------########## ########
-------------------########## T ########
-------- ----------######### ########-
-------- P ----------####################-
-------- ----------####################-
---------------------####################-
---------------------##################-
#--------------------#################--
#-------------------################--
#-------------------##############--
##-----------------############---
##---------------##########---
####-------------######-----
#######---------------
##########----
Harvard Convention
Moment Tensor:
R T F
-1.78e+15 1.27e+22 -7.22e+22
1.27e+22 6.72e+21 -1.84e+22
-7.22e+22 -1.84e+22 -6.72e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080817055659/index.html
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STK = 350
DIP = 90
RAKE = -75
MW = 4.52
HS = 20.0
The waveform inversion is preferred.
The following compares this source inversion to others
SLU Moment Tensor Solution
2008/08/17 05:56:59 41.1830 -124.1970 17.0 4.60 California
Best Fitting Double Couple
Mo = 7.59e+22 dyne-cm
Mw = 4.52
Z = 20 km
Plane Strike Dip Rake
NP1 350 90 -75
NP2 80 15 -180
Principal Axes:
Axis Value Plunge Azimuth
T 7.59e+22 43 65
N 0.00e+00 15 170
P -7.59e+22 43 274
Moment Tensor: (dyne-cm)
Component Value
Mxx 6.72e+21
Mxy 1.84e+22
Mxz 1.27e+22
Myy -6.72e+21
Myz 7.22e+22
Mzz -1.78e+15
----##########
--------##############
-----------#################
-------------#################
---------------###################
----------------####################
------------------####################
-------------------########## ########
-------------------########## T ########
-------- ----------######### ########-
-------- P ----------####################-
-------- ----------####################-
---------------------####################-
---------------------##################-
#--------------------#################--
#-------------------################--
#-------------------##############--
##-----------------############---
##---------------##########---
####-------------######-----
#######---------------
##########----
Harvard Convention
Moment Tensor:
R T F
-1.78e+15 1.27e+22 -7.22e+22
1.27e+22 6.72e+21 -1.84e+22
-7.22e+22 -1.84e+22 -6.72e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080817055659/index.html
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This is a preliminary NCSS moment tensor solution for the event located
14 km NNW of Trinidad, CA; 41.1830N 124.1968W; Z=17.0km; ML=4.50;
(USGS/UCB Joint Notification System) on 08/17/2008 05:56:59:580 UTC.
Other information about this event can be viewed at:
http://earthquake.usgs.gov/recenteqsus/Quakes/nc51207076.php
Reviewed by:
Dreger
UCB Seismological Laboratory
Inversion method: complete waveform
Stations used: BK.WDC BK.YBH BK.GASB BK.HUMO BK.JCC NC.KRMB
Berkeley Moment Tensor Solution
Best Fitting Double-Couple:
Mo = 1.10E+23 Dyne-cm
Mw = 4.63
Z = 11 km
Plane Strike Rake Dip
NP1 159 79 84
NP2 41 151 13
Event Date/Time: 08/17/2008 05:56:59:580
Event ID: 51207076
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-------------------################################--
---------------------################################--
---------------------################################--
-----------------------############### ##############--
-------------------------############## T ##############---
-------------------------############## ##############---
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----------- P ---------------###########################---
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#--------------------------##--------
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Lower Hemisphere Equiangle Projection
Deviatoric Solution:
Principal Axes:
Axis Value Plunge Azimuth
T 10.656 50 56
N 0.536 11 160
P -11.192 38 259
Source Composition:
Type Percent
DC 90.4
CLVD 9.6
Iso 0.0
Moment Tensor: Scale = 10**22 Dyne-cm
Component Value
Mxx 1.544
Mxy 0.542
Mxz 3.890
Myy -3.479
Myz 9.747
Mzz 1.935
###########
#######################
---############################
-------##############################
----------##############################-
-------------###############################-
---------------###############################-
----------------################################-
-------------------################################--
---------------------################################--
---------------------################################--
-----------------------############### ##############--
-------------------------############## T ##############---
--------------------------############# ##############---
--------------------------##############################---
---------------------------#############################---
-----------------------------############################----
----------- --------------############################---
----------- P ---------------###########################---
----------- ----------------#########################----
------------------------------#########################----
------------------------------#######################----
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------------------------------####################-----
------------------------------##################-----
-----------------------------################----
----------------------------###############----
---------------------------#############-----
-------------------------############----
#---------------------###########----
###-------------##############-
#######################
###########
Lower Hemisphere Equiangle Projection
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The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for 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 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 from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 170 45 90 3.97 0.2682
WVFGRD96 1.0 170 45 90 4.02 0.2526
WVFGRD96 2.0 350 45 90 4.15 0.3113
WVFGRD96 3.0 145 50 -85 4.20 0.2106
WVFGRD96 4.0 170 80 80 4.15 0.1940
WVFGRD96 5.0 310 5 45 4.16 0.2513
WVFGRD96 6.0 175 85 80 4.18 0.3105
WVFGRD96 7.0 170 90 80 4.19 0.3610
WVFGRD96 8.0 350 90 -80 4.29 0.3988
WVFGRD96 9.0 175 90 80 4.31 0.4525
WVFGRD96 10.0 350 90 -75 4.33 0.5008
WVFGRD96 11.0 175 90 75 4.36 0.5436
WVFGRD96 12.0 175 90 75 4.38 0.5811
WVFGRD96 13.0 175 90 75 4.40 0.6136
WVFGRD96 14.0 355 90 -70 4.42 0.6412
WVFGRD96 15.0 175 90 70 4.44 0.6639
WVFGRD96 16.0 175 90 70 4.46 0.6816
WVFGRD96 17.0 170 90 75 4.47 0.6950
WVFGRD96 18.0 350 90 -75 4.49 0.7043
WVFGRD96 19.0 350 90 -75 4.50 0.7095
WVFGRD96 20.0 350 90 -75 4.52 0.7110
WVFGRD96 21.0 350 90 -75 4.54 0.7092
WVFGRD96 22.0 170 90 75 4.56 0.7038
WVFGRD96 23.0 170 90 80 4.56 0.6955
WVFGRD96 24.0 170 90 80 4.58 0.6848
WVFGRD96 25.0 350 90 -85 4.59 0.6717
WVFGRD96 26.0 170 90 85 4.60 0.6562
WVFGRD96 27.0 170 90 85 4.61 0.6382
WVFGRD96 28.0 170 0 -90 4.62 0.6164
WVFGRD96 29.0 180 0 -80 4.62 0.5940
The best solution is
WVFGRD96 20.0 350 90 -75 4.52 0.7110
The mechanism correspond 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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 and because the velocity model used in the predictions may not be perfect. 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 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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| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms. 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. |
Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
The WUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Mon Aug 18 10:32:30 CDT 2008