2005/08/10 22:08:17 36.95N 104.86W 5. 4.9 New Mexico
USGS Felt map for this earthquake
USGS Felt reports page for Intermountain Western US
SLU Moment Tensor Solution
2005/08/10 22:08:17 36.95N 104.86W 5. 4.9 New Mexico
Best Fitting Double Couple
Mo = 2.34e+23 dyne-cm
Mw = 4.88
Z = 4 km
Plane Strike Dip Rake
NP1 5 53 -74
NP2 160 40 -110
Principal Axes:
Axis Value Plunge Azimuth
T 2.34e+23 7 84
N 0.00e+00 13 176
P -2.34e+23 76 327
Moment Tensor: (dyne-cm)
Component Value
Mxx -7.75e+21
Mxy 3.02e+22
Mxz -4.46e+22
Myy 2.25e+23
Myz 5.70e+22
Mzz -2.17e+23
----------####
##--------------######
####----------------########
####------------------########
#####--------------------#########
#####---------------------##########
######----------------------##########
#######----------------------###########
#######---------- ---------#########
########---------- P ---------######### T
########---------- ---------#########
########----------------------############
#########---------------------############
########---------------------###########
#########-------------------############
#########------------------###########
#########----------------###########
##########-------------###########
##########----------##########
###########-------##########
###########--#########
#######------#
Harvard Convention
Moment Tensor:
R T F
-2.17e+23 -4.46e+22 -5.70e+22
-4.46e+22 -7.75e+21 -3.02e+22
-5.70e+22 -3.02e+22 2.25e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/NEW/20050810220817/index.html
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August 10, 2005, NEW MEXICO, MW=5.0
Meredith Nettles
Goran Ekstrom
CENTROID, MOMENT TENSOR SOLUTION
HARVARD EVENT-FILE NAME C081005B
DATA USED: GSN
L.P. BODY WAVES: 37S, 48C, T= 40
SURFACE WAVES: 53S, 99C, T= 50
CENTROID LOCATION:
ORIGIN TIME 22:08:23.6 0.2
LAT 36.90N 0.02;LON 104.80W 0.01
DEP 12.0 FIX;HALF-DURATION 0.8
MOMENT TENSOR; SCALE 10**23 D-CM
MRR=-3.28 0.09; MTT=-0.37 0.09
MPP= 3.65 0.08; MRT=-0.53 0.27
MRP= 0.11 0.24; MTP=-0.65 0.08
PRINCIPAL AXES:
1.(T) VAL= 3.76;PLG= 2;AZM=261
2.(N) -0.38; 10; 171
3.(P) -3.37; 80; 360
BEST DOUBLE COUPLE:M0=3.6*10**23
NP1:STRIKE= 1;DIP=44;SLIP= -76
NP2:STRIKE=161;DIP=47;SLIP=-103
-------####
###----------######
####-------------######
#####---------------#######
######----------------#######
######------------------#######
######-------- -------#######
#######-------- P -------########
########------- --------#######
######------------------#######
T ######-----------------########
#######----------------#######
#########---------------#######
#########-------------#######
##########----------#######
#########--------######
##########---######
#######----
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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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STK = 160
DIP = 40
RAKE = -110
MW = 4.88
HS = 4
The surface-wave is preferred because of the greater quantity of data and sensitivity to source depth. The waveform inversion had enough data after selective editing of traces. In this case the surface-wave analysis provided a quality control on the waveform data. SDCO horizontals could not be used because of questions of instrument polarity. The waveform fit was based on the use of a lower than normal lowpass filter because of neither set of Greens functions are appropriate to this region.
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 0.05 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 25 50 -60 4.62 0.4585
WVFGRD96 1.0 20 45 -65 4.65 0.4832
WVFGRD96 2.0 20 45 -65 4.71 0.5397
WVFGRD96 3.0 10 45 -80 4.74 0.5545
WVFGRD96 4.0 10 50 -75 4.77 0.5505
WVFGRD96 5.0 360 50 -85 4.80 0.5556
WVFGRD96 6.0 360 50 -85 4.81 0.5298
WVFGRD96 7.0 360 50 -85 4.81 0.4895
WVFGRD96 8.0 180 35 -90 4.83 0.4914
WVFGRD96 9.0 110 70 30 4.70 0.4650
WVFGRD96 10.0 110 70 30 4.70 0.4524
WVFGRD96 11.0 225 65 -35 4.74 0.4452
WVFGRD96 12.0 230 70 -30 4.74 0.4481
WVFGRD96 13.0 225 65 -30 4.74 0.4546
WVFGRD96 14.0 225 65 -30 4.74 0.4602
WVFGRD96 15.0 225 70 -30 4.74 0.4679
WVFGRD96 16.0 225 70 -30 4.74 0.4755
WVFGRD96 17.0 225 70 -25 4.75 0.4796
WVFGRD96 18.0 225 70 -25 4.76 0.4859
WVFGRD96 19.0 225 70 -25 4.76 0.4869
The best solution is
WVFGRD96 5.0 360 50 -85 4.80 0.5556
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 0.014 3 lp c 0.05 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. |
NODAL PLANES
STK= 5.40
DIP= 52.84
RAKE= -73.99
OR
STK= 160.00
DIP= 40.00
RAKE= -109.99
DEPTH = 4.0 km
Mw = 4.88
Best Fit 0.8921 - P-T axis plot gives solutions with FIT greater than FIT90
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The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion ANMO 213 265 eP_- ISCO 348 323 iP_D Y22C 211 370 eP_X CBKS 64 496 iP_C
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.
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 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. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0-180 degrees are sampled. |
Sta Az(deg) Dist(km) SDCO 327 105 ISCO 348 323 CBKS 64 496 MNTX 185 585 WMOK 112 601 TUC 228 748 BW06 330 761 KSU1 69 762 HWUT 314 776 LTX 172 852 JCT 145 857 GLA 248 1007 LAO 354 1088 GSC 264 1090 HLID 315 1094 NATX 119 1100 TPH 280 1100 DAC 270 1141 UALR 98 1155 BAR 250 1179 CCM 80 1209 ISA 267 1230 MWC 260 1232 FVM 80 1281 SLM 77 1300 WVOR 302 1328 MSO 328 1330 PVMO 88 1355 MPH 94 1359 SIUC 82 1387 OXF 96 1422 UTMT 88 1430 SAO 274 1478 LTL 114 1484 USIN 81 1523 WVT 88 1525 PLAL 93 1527 WDC 290 1586 HAWA 315 1606 WCI 79 1643 ULM 23 1644 HUMO 298 1669 LRAL 100 1684 LON 313 1774 TTW 316 1824 GNW 314 1887 EDM 343 1926 PGC 317 1992 LLLB 324 2036 SHB 319 2077 OZB 315 2137 ALLY 69 2187 MCWV 74 2201 KAPO 45 2273 NHSC 93 2285 EDB 316 2291 SADO 60 2324 PHC 318 2358 CBN 78 2423 SDMD 75 2460 KGNO 62 2519 VLDQ 52 2533 FCC 14 2550 GAC 59 2627 PAL 71 2705 FNBB 337 2773 HRV 67 2902 KNDN 356 2961 MGTN 355 2993 DLBC 331 3011 BOXN 355 3013 LMQ 56 3053 LDGN 355 3099 GLWN 356 3107 ILKN 350 3113 GALN 348 3138 ACKN 355 3147 COWN 354 3180 LUPN 355 3233 GGN 62 3292 ICQ 53 3314 WHY 331 3380 LMN 61 3453 QILN 14 3513
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 velocity model used for the waveform fit is a modified Utah model .
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 0.014 3 lp c 0.04 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:
