2006/01/11 10:02:36 43.55N 127.19W 30. 4.9 Offshore Oregon
USGS Felt map for this earthquake
USGS Felt reports page for Pacific Northwest US
SLU Moment Tensor Solution 2006/01/11 10:02:36 43.55N 127.19W 30. 4.9 Offshore Oregon Best Fitting Double Couple Mo = 1.00e+24 dynecm Mw = 5.30 Z = 29 km Plane Strike Dip Rake NP1 117 77 149 NP2 215 60 15 Principal Axes: Axis Value Plunge Azimuth T 1.00e+24 31 72 N 0.00e+00 57 277 P 1.00e+24 11 169 Moment Tensor: (dynecm) Component Value Mxx 8.60e+23 Mxy 3.91e+23 Mxz 3.21e+23 Myy 6.36e+23 Myz 3.83e+23 Mzz 2.24e+23   ####### ############ ################ ################### ######################## ##################### ##### ######################### T ##### ############################# ###### ########################################## ###################################### ################################## ########################### ####################### ############## ###### ##### ### ##   P    Harvard Convention Moment Tensor: R T F 2.24e+23 3.21e+23 3.83e+23 3.21e+23 8.60e+23 3.91e+23 3.83e+23 3.91e+23 6.36e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/NEW/20060111100236/index.html 
USGS Fast Moment Tensor Solution 06/01/11 10:02:36.42 OFF COAST OF OREGON Epicenter: 43.548 127.191 MW 5.6 USGS MOMENT TENSOR SOLUTION Depth 14 No. of sta: 10 Moment Tensor; Scale 10**17 Nm Mrr=0.01 Mtt=2.31 Mff= 2.32 Mrt=0.13 Mrf=0.46 Mtf=1.62 Principal axes: T Val= 2.89 Plg= 8 Azm= 73 N 0.04 80 218 P 2.85 5 342 Best Double Couple:Mo=2.9*10**17 NP1:Strike=117 Dip=81 Slip= 178 NP2: 208 88 9   P #  #### ####### ########## ############# ############## ################### T ####################### ############################## ################################ ########################### #################### ############# ######### ####### #### #  
CENTROID, MOMENT TENSOR SOLUTION HARVARD EVENTFILE NAME C011106B DATA USED: GSN L.P. BODY WAVES: 57S,112C, T= 40 SURFACE WAVES: 69S,152C, T= 50 CENTROID LOCATION: ORIGIN TIME 10:02:35.4 0.2 LAT 43.32N 0.01;LON 127.41W 0.01 DEP 18.2 1.0;HALFDURATION 1.4 MOMENT TENSOR; SCALE 10**24 DCM MRR=0.17 0.04; MTT=1.46 0.04 MPP= 1.62 0.04; MRT=0.14 0.08 MRP=0.24 0.08; MTP=1.39 0.03 PRINCIPAL AXES: 1.(T) VAL= 2.17;PLG= 4;AZM= 69 2.(N) 0.15; 82; 191 3.(P) 2.02; 7; 339 BEST DOUBLE COUPLE:M0=2.1*10**24 NP1:STRIKE=114;DIP=82;SLIP=178 NP2:STRIKE= 24;DIP=88;SLIP= 8   P ###  ###### ######### ########## ########### T ############## ###################### ########################### ################################ ############################## ###################### ############### ########### ######### ###### ####  
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the station distribution are given in Figure 1.

STK = 215 DIP = 60 RAKE = 15 MW = 5.30 HS = 29
This solution may be acceptable. The major problem is that it an offshore event and that the wave propagation model should include the effects of a source in an oceanic crust and then wave propagation into continental crust. The waveform solution should be OK since the event was large enough so that low frequencies could be used in the waveform inversion. The use of these low frequencies should mean that the solution is relatively insensitive to source structure and to the oceancontinent transition. Note that the waveform comparisons could not be made at greater depths because such Greens functions were not computed. Finally, the depth control is not that good, although the preferred deeper depth gives better waveform fits.
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 0.014 3 lp c 0.033 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 210 90 10 4.95 0.3471 WVFGRD96 1.0 210 90 5 4.96 0.3582 WVFGRD96 2.0 210 85 10 5.00 0.3884 WVFGRD96 3.0 30 75 5 5.03 0.4065 WVFGRD96 4.0 25 65 20 5.07 0.4217 WVFGRD96 5.0 25 60 20 5.09 0.4343 WVFGRD96 6.0 25 60 20 5.11 0.4430 WVFGRD96 7.0 30 70 10 5.10 0.4499 WVFGRD96 8.0 25 55 20 5.15 0.4567 WVFGRD96 9.0 30 65 5 5.14 0.4581 WVFGRD96 10.0 30 65 5 5.14 0.4586 WVFGRD96 11.0 30 75 5 5.14 0.4590 WVFGRD96 12.0 215 60 25 5.18 0.4660 WVFGRD96 13.0 215 60 25 5.18 0.4727 WVFGRD96 14.0 215 60 25 5.19 0.4789 WVFGRD96 15.0 215 60 25 5.19 0.4845 WVFGRD96 16.0 215 60 20 5.20 0.4900 WVFGRD96 17.0 215 60 20 5.21 0.4954 WVFGRD96 18.0 215 60 20 5.21 0.5000 WVFGRD96 19.0 215 60 20 5.22 0.5040 WVFGRD96 20.0 215 60 15 5.23 0.5077 WVFGRD96 21.0 215 60 20 5.25 0.5133 WVFGRD96 22.0 215 60 20 5.25 0.5167 WVFGRD96 23.0 215 60 20 5.26 0.5195 WVFGRD96 24.0 215 60 20 5.27 0.5217 WVFGRD96 25.0 215 60 15 5.27 0.5237 WVFGRD96 26.0 215 60 15 5.28 0.5260 WVFGRD96 27.0 215 60 15 5.29 0.5281 WVFGRD96 28.0 215 60 15 5.29 0.5296 WVFGRD96 29.0 215 60 15 5.30 0.5309
The best solution is
WVFGRD96 29.0 215 60 15 5.30 0.5309
The mechanism correspond to the best fit is

The best fit as a function of depth is given in the following figure:

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 observedpredicted 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 0.014 3 lp c 0.033 3

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. 
NODAL PLANES STK= 204.99 DIP= 75.00 RAKE= 34.99 OR STK= 104.72 DIP= 56.36 RAKE= 161.88 DEPTH = 28.0 km Mw = 5.37 Best Fit 0.8253  PT axis plot gives solutions with FIT greater than FIT90
The Pwave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion HUMO 105 360 eP_X WDC 129 507 ePn HAWA 60 682 eP_+ WVOR 97 708 eP SAO 145 898 ePn MNV 124 949 eP HLID 86 1032 eP MSO 66 1102 eP_+ HWUT 94 1299 eP MWC 140 1302 eP AHID 88 1310 eP REDW 85 1321 eP_+ MOOW 83 1325 eP SNOW 85 1328 eP LOHW 84 1338 eP LKWY 79 1348 eP BW06 87 1435 eP_+
Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surfacewave radiation pattern search program srfgrd96.
The velocity model used for the search is a modified Utah model .
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 Lovewave spectral amplitudes, respectively.
These were input to the search program which examined all depths between 1 and 25 km
and all possible mechanisms.

Pressuretension axis trends. Since the surfacewave 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 Taxes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here. 
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 0180 degrees are sampled. 
Sta Az(deg) Dist(km) HUMO 105 360 WDC 129 507 LON 48 553 GNW 36 562 HAWA 60 682 WVOR 97 708 SAO 145 898 MNV 124 949 HLID 86 1032 MSO 66 1102 ISA 137 1151 GSC 132 1278 HWUT 94 1299 MWC 140 1302 AHID 88 1310 REDW 85 1321 MOOW 83 1325 SNOW 85 1328 LOHW 84 1338 BW06 87 1435 BAR 139 1516 GLA 133 1586 SIT 342 1609 WUAZ 118 1622 RWWY 90 1649 LAO 71 1682 PHWY 90 1801 ISCO 96 1839 TUC 126 1901 SDCO 102 1938 MNTX 117 2320 CBKS 94 2352 PMR 332 2475 KSU1 90 2593 LTX 119 2618 WMOK 102 2628 EYMN 67 2796 JCT 112 2817 MIAR 98 3053 MPH 94 3316 OXF 94 3390 WVT 90 3435 WCI 86 3462 LTL 102 3512 AAM 77 3518 ACSO 80 3646 LRAL 95 3665 ERPA 76 3812 MCWV 80 3919 GOGA 92 3929 CBN 81 4179 MVL 78 4181 NCB 70 4193 NHSC 90 4212 SMY 305 4362 DWPF 97 4409
Since the analysis of the surfacewave radiation patterns uses only spectral amplitudes and because the surfavewave radiation patterns have a 180 degree symmetry, each surfacewave solution consists of four possible focal mechanisms corresponding to the interchange of the P and Taxes and a roation of the mechanism by 180 degrees. To select one mechanism, Pwave first motion can be used. This was not possible in this case because all the Pwave first motions were emergent ( a feature of the Pwave wave takeoff angle, the station location and the mechanism). The other way to select among the mechanisms is to compute forward synthetics and compare the observed and predicted waveforms.
The velocity model used for the waveform fit is a modified Utah model .
The fits to the waveforms with the given mechanism are show below:
This figure shows the fit to the three components of motion (Z  vertical, Rradial and T  transverse). For each station and component, the observed traces is shown in red and the model predicted trace in blue. The traces represent filtered ground velocity in units of meters/sec (the peak value is printed adjacent to each trace; each pair of traces to plotted to the same scale to emphasize the difference in levels). Both synthetic and observed traces have been filtered using the SAC commands:
hp c 0.014 3 lp c 0.033 3
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 100200 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 figures below show the observed spectral amplitudes (units of cmsec) at each station and the
theoretical predictions as a function of period for the mechanism given above. The modified Utah model earth model
was used to define the Green's functions. For each station, the Love and Rayleigh wave spectrail amplitudes are plotted with the same scaling so that one can get a sense fo the effects of the effects of the focal mechanism and depth on the excitation of each.
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files: