USGS/SLU Moment Tensor Solution ENS 2007/10/31 03:04:54:0 37.43 -121.77 9.7 5.5 California Stations used: BK.BDM BK.CMB BK.CVS BK.FARB BK.HOPS BK.JRSC BK.KCC BK.MCCM BK.MNRC BK.PKD BK.SAO CI.EDW2 CI.GSC CI.LRL CI.MLAC CI.MPM CI.MPP CI.PHL CI.RCT CI.SCZ2 CI.SHO G.SCZ IM.NV31 LB.BMN LB.TPH NN.PAH TA.M07A TA.M08A TA.N07B TA.N09A TA.O06A TA.O07A TA.O08A TA.P06A TA.P09A TA.Q07A TA.Q08A TA.Q09A TA.Q10A TA.R04C TA.R06C TA.R08A TA.R09A TA.R10A TA.S05C TA.S09A TA.S10A TA.S11A TA.U04C TA.V03C US.TPNV XQ.ME05 XQ.ME34 XQ.ME36 XQ.ME43 XQ.ME44 XQ.ME45 XQ.ME46 XQ.ME47 XQ.ME48 XQ.ME49 XQ.ME50 XQ.ME53 XQ.ME54 XQ.ME81 XQ.ME84 XQ.ME92 XQ.ME93 Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 2.09e+24 dyne-cm Mw = 5.48 Z = 18 km Plane Strike Dip Rake NP1 55 90 10 NP2 325 80 180 Principal Axes: Axis Value Plunge Azimuth T 2.09e+24 7 280 N 0.00e+00 80 55 P -2.09e+24 7 190 Moment Tensor: (dyne-cm) Component Value Mxx -1.93e+24 Mxy -7.04e+23 Mxz 2.97e+23 Myy 1.93e+24 Myz -2.08e+23 Mzz -3.17e+16 -------------- ---------------------- ####------------------------ #######----------------------- ###########----------------------- #############--------------------### ################---------------####### ##################-----------########### ##################-------############# T ###################---################# ###################-################### ####################-----################# #################---------################ #############-------------############## ###########----------------############# #######--------------------########### ###------------------------######### ---------------------------####### --------------------------#### --------------------------## ------ ------------- -- P --------- Global CMT Convention Moment Tensor: R T P -3.17e+16 2.97e+23 2.08e+23 2.97e+23 -1.93e+24 7.04e+23 2.08e+23 7.04e+23 1.93e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20071031030454/index.html |
STK = 55 DIP = 90 RAKE = 10 MW = 5.48 HS = 18.0
The NDK file is 20071031030454.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2007/10/31 03:04:54:0 37.43 -121.77 9.7 5.5 California Stations used: BK.BDM BK.CMB BK.CVS BK.FARB BK.HOPS BK.JRSC BK.KCC BK.MCCM BK.MNRC BK.PKD BK.SAO CI.EDW2 CI.GSC CI.LRL CI.MLAC CI.MPM CI.MPP CI.PHL CI.RCT CI.SCZ2 CI.SHO G.SCZ IM.NV31 LB.BMN LB.TPH NN.PAH TA.M07A TA.M08A TA.N07B TA.N09A TA.O06A TA.O07A TA.O08A TA.P06A TA.P09A TA.Q07A TA.Q08A TA.Q09A TA.Q10A TA.R04C TA.R06C TA.R08A TA.R09A TA.R10A TA.S05C TA.S09A TA.S10A TA.S11A TA.U04C TA.V03C US.TPNV XQ.ME05 XQ.ME34 XQ.ME36 XQ.ME43 XQ.ME44 XQ.ME45 XQ.ME46 XQ.ME47 XQ.ME48 XQ.ME49 XQ.ME50 XQ.ME53 XQ.ME54 XQ.ME81 XQ.ME84 XQ.ME92 XQ.ME93 Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 2.09e+24 dyne-cm Mw = 5.48 Z = 18 km Plane Strike Dip Rake NP1 55 90 10 NP2 325 80 180 Principal Axes: Axis Value Plunge Azimuth T 2.09e+24 7 280 N 0.00e+00 80 55 P -2.09e+24 7 190 Moment Tensor: (dyne-cm) Component Value Mxx -1.93e+24 Mxy -7.04e+23 Mxz 2.97e+23 Myy 1.93e+24 Myz -2.08e+23 Mzz -3.17e+16 -------------- ---------------------- ####------------------------ #######----------------------- ###########----------------------- #############--------------------### ################---------------####### ##################-----------########### ##################-------############# T ###################---################# ###################-################### ####################-----################# #################---------################ #############-------------############## ###########----------------############# #######--------------------########### ###------------------------######### ---------------------------####### --------------------------#### --------------------------## ------ ------------- -- P --------- Global CMT Convention Moment Tensor: R T P -3.17e+16 2.97e+23 2.08e+23 2.97e+23 -1.93e+24 7.04e+23 2.08e+23 7.04e+23 1.93e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20071031030454/index.html |
October 31, 2007, SAN FRANCISCO BAY AREA, CAL, MW=5.6 Goran Ekstrom Meredith Nettles CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: C200710310304A DATA: IU II CU IC GE L.P.BODY WAVES: 49S, 85C, T= 40 MANTLE WAVES: 15S, 15C, T=125 SURFACE WAVES: 50S, 104C, T= 50 TIMESTAMP: Q-20071031072823 CENTROID LOCATION: ORIGIN TIME: 03:04:59.7 0.2 LAT:37.44N 0.02;LON:121.78W 0.02 DEP: 15.2 1.0;TRIANG HDUR: 1.5 MOMENT TENSOR: SCALE 10**24 D-CM RR=-0.330 0.054; TT=-2.270 0.053 PP= 2.600 0.059; RT= 0.553 0.183 RP= 0.496 0.160; TP= 0.947 0.050 PRINCIPAL AXES: 1.(T) VAL= 2.887;PLG=11;AZM=282 2.(N) -0.344; 74; 52 3.(P) -2.543; 12; 189 BEST DBLE.COUPLE:M0= 2.71*10**24 NP1: STRIKE=326;DIP=74;SLIP=-179 NP2: STRIKE=235;DIP=89;SLIP= -16 ----------- ------------------- #####------------------ #########------------------ ############--------------### ###############----------###### ##############------######### T ################-############# ##############---############# ###############------############ ############----------########### #########-------------######### ######-----------------######## ##---------------------###### ----------------------##### -------- ----------## ------ P ---------- -- ------ |
UCB Seismological Laboratory Inversion method: complete waveform Stations used: CMB MCCM ORV PKD RO4C SO5C Berkeley Moment Tensor Solution Best Fitting Double-Couple: Mo = 2.05E+24 Dyne-cm Mw = 5.48 Z = 14 Plane Strike Rake Dip NP1 146 -178 89 NP2 56 -1 88 Principal Axes: Axis Value Plunge Azimuth T 2.049 1 281 N 0.000 88 173 P -2.049 2 11 Event Date/Time: October 31, 2007, 03:04:54.82 UTC Event ID: nc40204628 Moment Tensor: Scale = 10**24 Dyne-cm Component Value Mxx -1.898 Mxy -0.766 Mxz -0.070 Myy 1.900 Myz -0.039 Mzz -0.002 ------ P ------------ ---- #------------------------ ####------------------------- ########------------------------- ##########------------------------# ############--------------------##### ##############-----------------######## ###############------------########### T ################---------############## #################-----################# ####################-#################### ###################--#################### ################-------################## ############-----------################ #########---------------############### #####--------------------############ #------------------------########## -------------------------######## ------------------------##### ------------------------# ------------------- ------- Lower Hemisphere Equiangle Projection |
(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.
(a) ML computed using the IASPEI formula for Horizontal components; (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
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:
cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 55 90 0 5.03 0.2169 WVFGRD96 2.0 235 80 10 5.14 0.2937 WVFGRD96 3.0 235 80 0 5.19 0.3294 WVFGRD96 4.0 235 80 -5 5.22 0.3579 WVFGRD96 5.0 235 80 -10 5.26 0.3833 WVFGRD96 6.0 235 80 -10 5.29 0.4076 WVFGRD96 7.0 235 80 -10 5.31 0.4332 WVFGRD96 8.0 235 80 -15 5.35 0.4596 WVFGRD96 9.0 235 80 -15 5.37 0.4766 WVFGRD96 10.0 235 80 -15 5.39 0.4908 WVFGRD96 11.0 235 80 -15 5.40 0.5029 WVFGRD96 12.0 235 85 -15 5.42 0.5126 WVFGRD96 13.0 55 90 15 5.43 0.5186 WVFGRD96 14.0 55 90 15 5.44 0.5245 WVFGRD96 15.0 55 90 15 5.45 0.5283 WVFGRD96 16.0 55 90 10 5.46 0.5311 WVFGRD96 17.0 55 90 10 5.47 0.5329 WVFGRD96 18.0 55 90 10 5.48 0.5340 WVFGRD96 19.0 55 90 10 5.49 0.5335 WVFGRD96 20.0 55 90 10 5.50 0.5315 WVFGRD96 21.0 55 90 10 5.51 0.5286 WVFGRD96 22.0 235 85 -15 5.52 0.5256 WVFGRD96 23.0 55 90 10 5.53 0.5192 WVFGRD96 24.0 55 90 10 5.53 0.5130 WVFGRD96 25.0 55 90 10 5.54 0.5058 WVFGRD96 26.0 235 85 -10 5.54 0.4988 WVFGRD96 27.0 235 85 -10 5.55 0.4903 WVFGRD96 28.0 235 85 -10 5.56 0.4812 WVFGRD96 29.0 235 80 -10 5.56 0.4717
The best solution is
WVFGRD96 18.0 55 90 10 5.48 0.5340
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 component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 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. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of 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= 59.99 DIP= 80.00 RAKE= 29.99 OR STK= 324.26 DIP= 60.51 RAKE= 168.49 DEPTH = 11.0 km Mw = 5.54 Best Fit 0.8679 - 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 Dist First motion
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, 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. |
The distribution of broadband stations with azimuth and distance is
Listing of broadband stations used
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:
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:
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 Model after 8 iterations ISOTROPIC KGS FLAT EARTH 1-D CONSTANT VELOCITY LINE08 LINE09 LINE10 LINE11 H(KM) VP(KM/S) VS(KM/S) RHO(GM/CC) QP QS ETAP ETAS FREFP FREFS 1.9000 3.4065 2.0089 2.2150 0.302E-02 0.679E-02 0.00 0.00 1.00 1.00 6.1000 5.5445 3.2953 2.6089 0.349E-02 0.784E-02 0.00 0.00 1.00 1.00 13.0000 6.2708 3.7396 2.7812 0.212E-02 0.476E-02 0.00 0.00 1.00 1.00 19.0000 6.4075 3.7680 2.8223 0.111E-02 0.249E-02 0.00 0.00 1.00 1.00 0.0000 7.9000 4.6200 3.2760 0.164E-10 0.370E-10 0.00 0.00 1.00 1.00
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files: