1997/05/16 01:23:20 40.58N 114.99W 5 4.4 Nevada
USGS Felt map for this earthquake
USGS Felt reports page for Intermountain Western US
SLU Moment Tensor Solution 1997/05/16 01:23:20 40.58N 114.99W 5 4.4 Nevada Best Fitting Double Couple Mo = 1.22e+22 dynecm Mw = 3.99 Z = 11 km Plane Strike Dip Rake NP1 30 50 100 NP2 225 41 78 Principal Axes: Axis Value Plunge Azimuth T 1.22e+22 5 127 N 0.00e+00 8 36 P 1.22e+22 81 247 Moment Tensor: (dynecm) Component Value Mxx 4.35e+21 Mxy 5.92e+21 Mxz 1.36e+20 Myy 7.45e+21 Myz 2.48e+21 Mzz 1.18e+22 ############## ###################### ##################### ################# ################## ################ ################ ################# ################ ################# ####### ########## ###### P ########## ###### ########### ############### ################ ################ ########### # ############ T ############# ################ ################## ############## Harvard Convention Moment Tensor: R T F 1.18e+22 1.36e+20 2.48e+21 1.36e+20 4.35e+21 5.92e+21 2.48e+21 5.92e+21 7.45e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/19970516012320/index.html 
Stations used: BW06(Z), HWUT(T,R), DUG, KNB, LDS, CMB, ORV, BMN(Z), MIN(Z), WDC, YBH, WVOR(Z), ELK(R,Z) OSU MOMENT TENSOR SOLUTION http://quakes.oce.orst.edu/momenttensor/1997/solutions/970516_0123.ap.20_30s9km Event: northern Nevada Date/Time: 97/ 5/16 1:23:20 Lat./Lon.: 40.580 114.990 mb/Ms: 4.4 0.0 Depth (km): 9.0 Stations Used: 13 Moment Tensor: Scale = 10**21 dyn cm Component Value Component Value Mxx 2.275 Myy 7.516 Mxy 5.819 Myz 0.043 Mxz 1.258 Mzz 9.791 Source Composition: (Type/%) DC/ 76 CLVD/ 24 Iso/ 0 Principal Axes: Axis Value Plunge Azimuth T 11.302 2 123 N 1.360 7 213 P 9.942 83 17 Best Fitting DoubleCouple: Mo = 1.06E+22 dyn cm Mw = 3.98 Plane Strike Rake Dip NP1 40 81 47 NP2 206 100 43 ####### ################## ############### ############## ################ ################ ################# ################# ################ ########## ######## ########## P ######## ######### ######### ################### ################### ################## #################### ################# ################### T ##################### ####################### ####################### ################### ####### Lower Hemisphere Equal Area Projection 
STK = 30 DIP = 50 RAKE = 100 MW = 3.99 HS = 11.0
The surfacewave is preferred because of its fit to waveforms.
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.

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 0.5 235 35 90 3.44 0.3010 WVFGRD96 1.0 275 65 10 3.48 0.3012 WVFGRD96 2.0 275 55 10 3.62 0.3894 WVFGRD96 3.0 275 50 5 3.67 0.4946 WVFGRD96 4.0 270 50 10 3.70 0.5647 WVFGRD96 5.0 270 50 15 3.71 0.6105 WVFGRD96 6.0 270 55 20 3.74 0.6378 WVFGRD96 7.0 260 45 50 3.77 0.6684 WVFGRD96 8.0 260 45 55 3.81 0.7032 WVFGRD96 9.0 250 45 70 3.85 0.7367 WVFGRD96 10.0 250 45 70 3.86 0.7564 WVFGRD96 11.0 260 45 60 3.86 0.7654 WVFGRD96 12.0 230 40 55 3.87 0.7699 WVFGRD96 13.0 230 40 55 3.88 0.7664 WVFGRD96 14.0 235 40 45 3.89 0.7543 WVFGRD96 15.0 235 40 50 3.90 0.7408 WVFGRD96 16.0 240 40 40 3.90 0.7217 WVFGRD96 17.0 45 60 55 3.91 0.7015 WVFGRD96 18.0 45 65 55 3.90 0.6841 WVFGRD96 19.0 45 65 50 3.92 0.6681 WVFGRD96 20.0 45 70 50 3.91 0.6552 WVFGRD96 21.0 40 70 60 3.95 0.6423 WVFGRD96 22.0 45 75 55 3.95 0.6324 WVFGRD96 23.0 45 75 55 3.96 0.6251 WVFGRD96 24.0 40 75 60 3.97 0.6167 WVFGRD96 25.0 40 75 65 3.98 0.6066 WVFGRD96 26.0 45 80 60 3.98 0.5981 WVFGRD96 27.0 45 80 60 3.99 0.5875 WVFGRD96 28.0 50 90 60 3.98 0.5775 WVFGRD96 29.0 230 85 60 3.98 0.5692
The best solution is
WVFGRD96 12.0 230 40 55 3.87 0.7699
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 0.02 n 3 lp c 0.10 n 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. 
The following figure shows the stations used in the grid search for the best focal mechanism to fit the surfacewave spectral amplitudes of the Love and Rayleigh waves.

The surfacewave determined focal mechanism is shown here.
NODAL PLANES STK= 30.00 DIP= 49.99 RAKE= 100.00 OR STK= 225.34 DIP= 41.03 RAKE= 78.31 DEPTH = 11.0 km Mw = 3.99 Best Fit 0.9180  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 ELK 311 28 iP_C BMN 266 190 eP_+ DUG 102 190 eP_+ HWUT 67 310 eP_X TPH 215 338 iP_D MNV 230 362 iP_D WVOR 305 368 eP_X LDS 158 397 eP_X TPNV 196 418 iP_D KNB 154 438 iP_+ BW06 60 513 eP_X WDC 272 639 12345 YBH 284 661 12345
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) BMN 266 190 DUG 102 190 HWUT 67 310 TPH 215 338 MNV 230 362 WVOR 305 368 LDS 158 397 TPNV 196 418 KNB 154 438 MLAC 227 467 BW06 60 513 DAC 206 529 CWC 211 533 CMB 240 544 SCZ 234 712 OSI 208 740 KNW 192 777 RDM 193 789 DGR 194 790 SND 191 793 CRY 192 794 FRD 191 799 ISCO 93 803 COR 306 814 LVA2 190 814 NEW 350 871 ANMO 127 977 TUC 156 992 CCM 90 2061 SLM 88 2130 WVT 93 2415
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 0.02 n 3 lp c 0.10 n 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 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
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: