USGS Felt map for this earthquake
USGS Felt reports page for Klamath Falls, Oregon
Inversion method: complete waveform
Stations used: HUMO ORV WDC YBH
Berkeley Moment Tensor Solution
Best Fitting Double-Couple:
Mo = 1.09E+23 Dyne-cm
Mw = 4.66
Z = 5. km
Plane Strike Rake Dip
NP1 165 -114 61
NP2 28 -54 37
Principal Axes:
Axis Value Plunge Azimuth
T 10.900 13 272
N 0.000 21 177
P -10.900 65 32
Event Date/Time: June 30, 2004 at 12:21:50 UTC
Event ID: at00000174
Moment Tensor: Scale = 10**22 Dyne-cm
Component Value
Mxx -1.373
Mxy -1.247
Mxz -3.442
Myy 9.818
Myz -4.541
Mzz -8.445
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####---------------
######-----------------##
#######-------------------###
#########--------------------####
##########--------------------#####
###########---------------------#####
############--------- ---------######
############--------- 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.
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NODAL PLANES
STK= 310.03
DIP= 69.75
RAKE= 142.31
OR
STK= 55.00
DIP= 55.00
RAKE= 25.00
DEPTH = 9.0 km
Mw = 4.63
Best Fit 0.8495 - 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, intreument 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. A nearly vertical strike-slip fault striking at 75 or 165 degrees is preferred. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0-180 degrees are sampled. |
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion WVOR 80 138 e+ YBH 256 209 i+ BEKR 182 261 e+ BMN 127 324 X WCN 172 326 X COR 318 359 e+ HOPS 214 429 X MNV 156 458 X CMB 181 465 X HLID 71 502 X
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) WVOR 80 138 YBH 256 209 BEKR 182 261 WDC 227 263 BMN 127 324 WCN 172 326 COR 318 359 HOPS 214 429 MNV 156 458 CMB 181 465 HLID 71 502 TPH 150 529 HVU 92 624 DUG 107 665 DAC 160 699 NEW 19 716 MSO 42 718 HWUT 92 726 JLU 101 759 MPU 106 766 PNT 4 790 BOZ 58 791 BW06 82 883 LLLB 353 941 WUAZ 131 1072 BBB 335 1255 EDM 20 1328 MOBC 329 1496 FNBB 355 1864 ULM 56 2071 WHY 339 2277 UALR 100 2560 SLM 89 2567 FVM 90 2575 FCC 36 2584 PVMO 94 2699 MPH 97 2740 UTMT 93 2771 USIN 89 2804 BLO 85 2854
Since the analysis of the surface-wave radiation patterns uses only spectral amplitudes and because the surfave-wave radiation patterns have a 180 degree symmetry, each surface-wave solution consists of four possible focal mechanisms corresponding to the interchange of the P- and T-axes and a roation of the mechanism by 180 degrees. To select one mechanism, P-wave first motion can be used. This was not possible in this case because all the P-wave first motions were emergent ( a feature of the P-wave 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 fits to the waveforms with the given mechanism are show below:
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This figure shows the fit to the three components of motion (Z - vertical, R-radial 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 0.02 3 lp c 0.05 3
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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 figures below show the observed spectral amplitudes (units of cm-sec) 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.
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Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
