2007/06/12 07:23:43 37.54N 118.88W 14 4.6 California
USGS Felt map for this earthquake
USGS Felt reports page for California
SLU Moment Tensor Solution 2007/06/12 07:23:43 37.54N 118.88W 14 4.6 California Best Fitting Double Couple Mo = 8.41e+22 dyne-cm Mw = 4.55 Z = 14 km Plane Strike Dip Rake NP1 131 85 -165 NP2 40 75 -5 Principal Axes: Axis Value Plunge Azimuth T 8.41e+22 7 265 N 0.00e+00 74 149 P -8.41e+22 14 357 Moment Tensor: (dyne-cm) Component Value Mxx -7.82e+22 Mxy 1.23e+22 Mxz -2.07e+22 Myy 8.19e+22 Myz -9.08e+21 Mzz -3.67e+21 ---- ------- -------- P ----------- ----------- -------------# ----------------------------## ###--------------------------##### ######-----------------------####### ########---------------------######### ###########------------------########### #############---------------############ ################------------############## ###############---------############### T #################-----################# ###################--################## #####################--################# ###################-------############## ################-----------########### #############---------------######## ##########--------------------#### ######------------------------ #--------------------------- ---------------------- -------------- Harvard Convention Moment Tensor: R T F -3.67e+21 -2.07e+22 9.08e+21 -2.07e+22 -7.82e+22 -1.23e+22 9.08e+21 -1.23e+22 8.19e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20070612072343/index.html |
This is a preliminary UCB moment tensor solution for the event located 14 km SE of Mammoth Lakes, CA; 37.539N 118.876W; Z=14km; ML=5.1; (USGS/UCB Joint Notification System) on June 12, 2007 at 12:23:43 UTC. Other information about this event can be viewed at: http://earthquake.usgs.gov/recenteqsus/Quakes/nc51182810.php Reviewed by: Guilhem UCB Seismological Laboratory Inversion method: complete waveform Stations used: CMB, HELL, KCC, ORV, SAO and GSC Berkeley Moment Tensor Solution Best Fitting Double-Couple: Mo = 9.96E+22 Dyne-cm Mw = 4.60 Z = 14 Plane Strike Rake Dip NP1 41 8 82 NP2 310 172 82 Principal Axes: Axis Value Plunge Azimuth T 9.956 11 266 N 0.000 79 85 P -9.956 0 176 Event Date/Time: June 12, 2007 at 12:23:43 UTC Event ID: nc51182810 Moment Tensor: Scale = 10**22 Dyne-cm Component Value Mxx -9.839 Mxy 1.507 Mxz -0.138 Myy 9.457 Myz -1.907 Mzz 0.382 ------- ------------------- ------------------------- ----------------------------# #----------------------------#### ######----------------------####### #########-------------------######### #############---------------########### ################----------############# ###################-------############### #####################---################# # ##################################### # T #################----################ # ################-------############## #################-----------########### ###############---------------######### ############-------------------###### #########-----------------------### ######--------------------------# ##--------------------------- ------------------------- ---------- ------ ---- P Lower Hemisphere Equiangle Projection |
STK = 40 DIP = 75 RAKE = -5 MW = 4.55 HS = 14
The wavefrom inversion is preferred. The surface-wave amplitude solution is comparable.
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 0.5 305 75 35 4.07 0.2787 WVFGRD96 1.0 310 80 30 4.08 0.2911 WVFGRD96 2.0 305 70 30 4.19 0.3678 WVFGRD96 3.0 310 85 20 4.24 0.4065 WVFGRD96 4.0 310 95 -10 4.28 0.4345 WVFGRD96 5.0 305 85 -20 4.32 0.4512 WVFGRD96 6.0 40 65 -5 4.37 0.4791 WVFGRD96 7.0 40 65 -5 4.40 0.5028 WVFGRD96 8.0 40 70 0 4.44 0.5241 WVFGRD96 9.0 40 70 0 4.47 0.5388 WVFGRD96 10.0 40 70 0 4.49 0.5449 WVFGRD96 11.0 40 75 0 4.50 0.5437 WVFGRD96 12.0 40 75 -5 4.52 0.5514 WVFGRD96 13.0 40 75 -5 4.54 0.5581 WVFGRD96 14.0 40 75 -5 4.55 0.5594 WVFGRD96 15.0 40 75 -5 4.56 0.5560 WVFGRD96 16.0 40 75 -5 4.57 0.5493 WVFGRD96 17.0 40 75 -5 4.58 0.5394 WVFGRD96 18.0 40 75 -5 4.59 0.5267 WVFGRD96 19.0 40 75 -5 4.60 0.5126 WVFGRD96 20.0 40 75 -5 4.61 0.4964 WVFGRD96 21.0 40 70 -10 4.63 0.4799 WVFGRD96 22.0 40 70 -10 4.63 0.4617 WVFGRD96 23.0 40 70 -10 4.64 0.4420 WVFGRD96 24.0 40 70 -10 4.64 0.4220 WVFGRD96 25.0 40 75 -10 4.64 0.4009 WVFGRD96 26.0 35 60 -15 4.65 0.3815 WVFGRD96 27.0 210 70 -5 4.64 0.3689 WVFGRD96 28.0 125 95 -40 4.67 0.3668 WVFGRD96 29.0 305 85 35 4.68 0.3642
The best solution is
WVFGRD96 14.0 40 75 -5 4.55 0.5594
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. |
The following figure shows the stations used in the grid search for the best focal mechanism to fit the surface-wave spectral amplitudes of the Love and Rayleigh waves.
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The surface-wave determined focal mechanism is shown here.
NODAL PLANES STK= 307.90 DIP= 71.25 RAKE= 158.83 OR STK= 44.99 DIP= 70.00 RAKE= 20.00 DEPTH = 13.0 km Mw = 4.64 Best Fit 0.8593 - P-T axis plot gives solutions with FIT greater than FIT90
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion ISA 170 211 iP_D TPNV 105 242 eP_X GSC 143 310 eP_X SNCC 187 480 -12345 WVOR 2 544 eP_X
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. |
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) ISA 170 211 TPNV 105 242 GSC 142 310 WVOR 2 544 DUG 59 603 GLA 142 619 NOQ 57 679 MPU 64 687 HVU 46 704 WUAZ 106 708 CTU 58 709 SRU 74 751 HLID 28 768 HWUT 52 773 BMO 9 823 AHID 46 880 MVCO 89 920 REDW 44 938 TPAW 43 942 SNOW 44 951 LOHW 44 972 IMW 41 973 BW06 51 983 HAWA 357 985 BOZ 32 1083 RWWY 62 1102 MSO 20 1109 RLMT 41 1163 NLWA 341 1168 ISCO 74 1180 NEW 6 1200 EGMT 30 1381 MNTX 114 1395 LAO 42 1455 AMTX 96 1572 CBKS 79 1680 DGMT 40 1700 JCT 108 1924 KSU1 78 1950 ECSD 63 1999 AGMN 50 2214 SCIA 70 2244 MIAR 91 2297 NATX 99 2304 JFWS 67 2496 EYMN 54 2504 HDIL 73 2571 COWI 59 2629 VBMS 94 2648 GLMI 63 2962 BRAL 94 3003 AAM 69 3035 ACSO 73 3108 TZTN 81 3127 GOGA 87 3227 ERPA 69 3339 BLA 79 3382 MCWV 74 3382 NHSC 86 3528 CBN 76 3622 CNNC 81 3658 BINY 68 3667 LONY 64 3756 NCB 65 3790 LBNH 64 3971 PKME 62 4166
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:
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 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 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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files: