2007/05/23 19:09:15 22.02N 96.27W 10 5.6 Gulf of Mexico
USGS Felt map for this earthquake
USGS Felt reports page for Gulf of Mexico
SLU Moment Tensor Solution 2007/05/23 19:09:15 22.02N 96.27W 10 5.6 Gulf of Mexico Best Fitting Double Couple Mo = 3.16e+24 dyne-cm Mw = 5.60 Z = 11 km Plane Strike Dip Rake NP1 190 75 -160 NP2 95 71 -16 Principal Axes: Axis Value Plunge Azimuth T 3.16e+24 3 322 N 0.00e+00 65 225 P -3.16e+24 25 53 Moment Tensor: (dyne-cm) Component Value Mxx 9.98e+23 Mxy -2.79e+24 Mxz -5.95e+23 Myy -4.57e+23 Myz -1.06e+24 Mzz -5.41e+23 ##########---- #############--------- T ############------------- # ###########--------------- ################------------ --- #################------------ P ---- #################------------- ----- #################----------------------- #################----------------------- ##################------------------------ -################------------------------- ----#############------------------------- ---------########----------------------### ---------------##--------------######### ---------------######################### --------------######################## -------------####################### ------------###################### ----------#################### ---------################### -------############### ---########### Harvard Convention Moment Tensor: R T F -5.41e+23 -5.95e+23 1.06e+24 -5.95e+23 9.98e+23 2.79e+24 1.06e+24 2.79e+24 -4.57e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20070523190916/index.html |
May 23, 2007, GULF OF MEXICO, MW=5.6 Meredith Nettles CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: C200705231909A DATA: IU II CU IC L.P.BODY WAVES: 63S, 132C, T= 40 MANTLE WAVES: 35S, 36C, T=125 SURFACE WAVES: 73S, 159C, T= 50 TIMESTAMP: Q-20070523231809 CENTROID LOCATION: ORIGIN TIME: 19:09:20.3 0.1 LAT:22.03N 0.01;LON: 96.31W 0.01 DEP: 17.6 0.7;TRIANG HDUR: 1.5 MOMENT TENSOR: SCALE 10**24 D-CM RR= 0.313 0.036; TT= 1.150 0.034 PP=-1.460 0.041; RT= 0.111 0.084 RP= 0.646 0.098; TP= 2.660 0.034 PRINCIPAL AXES: 1.(T) VAL= 2.883;PLG=10;AZM=327 2.(N) 0.307; 77; 187 3.(P) -3.187; 8; 59 BEST DBLE.COUPLE:M0= 3.03*10**24 NP1: STRIKE=103;DIP=77;SLIP= 1 NP2: STRIKE= 13;DIP=89;SLIP= 167 #########-- ##########------ ## T #########--------- #### #########--------- #################--------- P #################---------- - #################-------------- --###############---------------- -----############---------------- ----------#######---------------- ----------------#---------------- ---------------################ --------------################# -------------################ -----------################ ---------############## ------############# --######### |
STK = 190 DIP = 75 RAKE = -160 MW = 5.60 HS = 11
Only the surface-wave technique was used. The surface-wave grid search used periods greater than 30 seconds only. The synthetics displayed are approximate because the CUS model does not have a realistic upper mantle for describing the waveforms at long periods. Surprisingly the solution is very comparable to that of the Global CMT
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= 189.99 DIP= 75.00 RAKE= -160.00 OR STK= 94.60 DIP= 70.71 RAKE= -15.92 DEPTH = 11.0 km Mw = 5.60 Best Fit 0.9580 - 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 KVTX 345 618 -12345 TEIG 103 858 -12345 HKT 3 864 -12345 JCT 340 986 -12345 NATX 8 1076 -12345 VBMS 26 1252 -12345 TGUH 132 1308 -12345 BRAL 41 1343 -12345 MNTX 321 1389 -12345 MIAR 10 1398 -12345 WMOK 351 1415 -12345 AMTX 341 1505 -12345 OXF 25 1525 -12345 DWPF 63 1634 -12345 ANMO 327 1730 -12345 GOGA 43 1772 -12345 TUC 311 1821 -12345 CCM 14 1827 -12345 CBKS 351 1876 -12345 KSU1 359 1878 -12345 NHSC 49 1995 -12345
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
Sta Az(deg) Dist(km) KVTX 345 618 TEIG 103 858 HKT 3 864 JCT 340 986 NATX 8 1076 VBMS 26 1252 TGUH 132 1308 BRAL 41 1343 MNTX 321 1389 MIAR 10 1398 WMOK 351 1415 AMTX 341 1505 OXF 25 1525 DWPF 63 1634 319A 311 1645 Y22C 324 1682 219A 313 1684 318A 310 1705 ANMO 327 1730 119A 315 1740 218A 312 1743 GOGA 42 1772 Z19A 317 1775 118A 314 1781 217A 310 1791 Z18A 315 1816 TUC 311 1821 Y19A 319 1823 CCM 14 1827 117A 312 1834 216A 309 1855 X19A 320 1861 Z17A 314 1862 Y18A 317 1864 CBKS 351 1876 KSU1 359 1878 116A 310 1909 X18A 319 1913 Y17A 315 1917 W19A 321 1921 Z16A 313 1936 W18A 321 1944 115A 310 1958 Y16A 314 1976 Z15A 312 1989 NHSC 49 1995 W17A 319 2006 X16A 316 2010 TZTN 35 2013 MVCO 328 2041 Y15A 313 2044 Z14A 311 2054 W16A 317 2064 X15A 315 2072 WUAZ 319 2083 113A 308 2085 Y14A 312 2094 X14A 314 2119 W15A 316 2121 112A 306 2140 HDIL 16 2143 SMCO 334 2143 ISCO 338 2146 Y13A 311 2150 W14A 315 2182 GLA 307 2187 X13A 313 2198 Y12C 310 2201 T16A 322 2202 V14A 316 2212 W13A 314 2234 BLA 39 2260 T15A 320 2262 BCIP 127 2271 U14A 318 2272 V13A 315 2290 CNNC 47 2302 T14A 319 2312 SRU 327 2316 W12A 313 2321 V12A 314 2346 PFO 307 2350 ACSO 29 2365 MVU 324 2365 T13A 318 2365 109C 305 2369 JFWS 12 2369 S14A 321 2369 ECSD 359 2392 RWWY 337 2395 V11A 314 2396 R14A 322 2400 S13A 319 2401 T12A 316 2401 U11A 315 2429 GSC 311 2470 S12A 318 2471 T11A 317 2471 MCWV 35 2487 U10A 314 2499 R12A 320 2505 Q13A 322 2513 AAM 25 2524 TPNV 315 2526 CBN 41 2535 S11A 317 2536 DUG 326 2537 RSSD 346 2538 P13A 323 2551 Q12A 321 2571 R11A 319 2573 N15A 327 2577 HWUT 330 2587 SNCC 303 2592 BW06 335 2596 O13A 324 2601 P12A 322 2608 N14A 326 2612 Q11A 320 2612 S10A 316 2614 R10A 318 2618 ISA 310 2621 M15A 328 2622 SDDR 93 2626 S09A 315 2646 O12A 323 2658 Q10A 318 2661 AHID 332 2667 P11A 321 2669 R09A 317 2669 TPH 316 2669 N13A 325 2671 M14A 327 2674 SSPA 36 2682 ERPA 31 2684 S08C 314 2702 O11A 322 2705 M13A 326 2709 REDW 334 2710 SNOW 334 2714 Q09A 318 2715 HELL 311 2719 N12A 324 2721 P10A 320 2721 LOHW 334 2722 TPAW 334 2726 GLMI 20 2731 V05C 309 2746 R08A 316 2750 K14A 329 2752 L13A 327 2756 M12A 325 2757 N11A 323 2761 P09A 319 2761 IMW 334 2763 FLWY 335 2769 Q08A 317 2770 O10A 321 2771 U05C 310 2787 T06C 311 2790 N10A 322 2802 R07C 314 2802 O09A 320 2807 RLMT 338 2809 K13A 328 2810 M11A 324 2811 V04C 308 2813 L12A 326 2821 BMN 320 2828 P08A 318 2835 U04C 309 2841 S06C 313 2850 K12A 327 2854 S05C 312 2857 R06C 315 2858 V03C 308 2861 M10A 323 2864 LAO 344 2865 L11A 325 2866 J13A 329 2877 N09A 321 2877 O08A 319 2880 P07A 317 2881 EYMN 7 2893 CMB 313 2899 AGMN 1 2900 L10A 324 2901 HAST 308 2904 HLID 329 2904 N08A 320 2912 M09A 322 2913 SAO 309 2914 J12A 328 2915 R05C 314 2915 BINY 36 2917 I13A 330 2918 O07A 318 2920 K11A 326 2929 G15A 334 2949 R04C 313 2953 BOZ 336 2955 P06A 316 2961 PAL 40 2962 LAVA 314 2967 N07B 319 2968 J11A 327 2969 L09A 323 2970 M08A 321 2975 K10A 325 2979 H13A 331 2981 O06A 317 2986 P05C 315 2989 BNLO 310 2990 DGMT 348 3003 F15A 335 3010 H12A 330 3010 I11A 328 3016 Q04C 313 3019 M07A 320 3022 J10A 326 3023 K09A 324 3024 N06A 318 3024 G13A 332 3025 L08A 322 3025 F14A 334 3047 O05C 316 3051 Q03C 312 3056 WVOR 322 3061 E15A 335 3070 SUTB 314 3072 K08A 323 3073 J09A 325 3075 I10A 327 3077 L07A 321 3077 ELFS 317 3078 H11A 329 3084 O04C 316 3085 MCCM 311 3097 M06C 319 3098 EGMT 340 3111 H10A 328 3114 J08A 324 3118 K07A 322 3118 D15A 336 3122 I09A 326 3122 MOD 320 3132 F12A 331 3133 O03C 315 3134 E13A 333 3141 HATC 317 3142 G11A 330 3154 M05C 318 3154 HOPS 312 3156 NCB 35 3156 I08A 325 3165 MSO 334 3165 D14A 335 3168 H09A 327 3171 J07A 323 3171 L05A 320 3177 SJG 93 3177 LONY 33 3185 F11A 330 3189 K06A 322 3189 G10A 328 3191 P01C 313 3201 D13A 334 3212 M03C 317 3216 H08A 326 3217 G09A 328 3226 K05A 321 3226 M04C 318 3228 E11A 331 3231 I07A 324 3234 C14A 335 3241 D12A 333 3249 F10A 329 3252 L04A 319 3256 F09A 328 3267 I06A 323 3267 C13A 334 3269 O01C 314 3273 K04A 320 3274 N02C 315 3274 M02C 317 3275 YBH 318 3285 J05A 321 3286 E10A 330 3288 G08A 327 3293 D11A 332 3296 BBSR 63 3311 LBNH 37 3314 F08A 328 3322 B13A 335 3327 G07A 326 3331 H06A 324 3331 J04A 320 3340 D10A 331 3344 E09A 329 3344 I05A 323 3348 HUMO 319 3356 L02A 318 3373 A13A 336 3376 H05A 324 3379 B12A 334 3385 G06A 325 3386 E08A 328 3391 M01C 317 3391 F07A 326 3394 I04A 321 3396 D09A 330 3397 K02A 319 3402 J03A 320 3404 C10A 332 3409 HAWA 328 3410 B11A 333 3417 G05A 324 3427 A12A 335 3429 D08A 329 3429 F06A 326 3433 NEW 332 3438 E07A 328 3440 H04A 323 3441 J02A 320 3445 B10A 332 3446 C09A 331 3456 A11A 334 3463 I03A 321 3464 K01A 318 3472 F05A 325 3482 C08A 330 3494 G04A 323 3495 D07A 328 3496 B09A 332 3501 E06A 326 3502 I02A 320 3502 COR 322 3505 H03A 322 3511 A10A 333 3520 C07A 329 3539 F04A 324 3542 D06A 328 3544 E05A 326 3548 PKME 37 3548 G03A 323 3552 B08A 330 3555 H02A 321 3556 A09A 332 3568 C06A 328 3602 D05A 326 3607 E04A 325 3607 F03A 323 3611 C05A 328 3628 FFC 354 3646 D04A 326 3649 E03A 324 3654 A07A 330 3664 B06A 329 3680 B05A 328 3693 C04A 326 3702 D03A 325 3706 A06A 330 3724 NLWA 325 3731 A05A 329 3748 B04A 326 3757 A04A 328 3761 C03A 326 3810 GRGR 101 3837 BBGH 98 4011 CRAG 330 4786 WRAK 332 4809 SIT 331 4999 SKAG 334 5153
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:
hp c 0.005 n 3 lp c 0.02 n 3 br c 0.12 0.25 n 4 p 2
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
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 CUS 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: