Moment Tensor 20070523044146

Location

2007/05/23 04:41:46 52.32 -31.81 10

Moment Tensor Comparison

The following compares this source inversion to the USGS Rapid Moment Tensor Solution and to the Harvard CMT solutions, if they are available.

SLU USGS GLOBAL CMT POLET

SLU Moment Tensor Solution 2007/05/23 04:41:46 Best Fitting Double Couple Mo = 5.31e+24 dyne-cm Mw = 5.75 Z = 5 km Plane Strike Dip Rake NP1 204 85 -104 NP2 95 15 -20 Principal Axes: Axis Value Plunge Azimuth T 5.31e+24 38 307 N 0.00e+00 14 206 P -5.31e+24 48 99 Moment Tensor: (dyne-cm) Component Value Mxx 1.13e+24 Mxy -1.19e+24 Mxz 1.99e+24 Myy -2.17e+23 Myz -4.66e+24 Mzz -9.08e+23 ############## ###################--- #####################------- ####################---------- #####################------------- ###### ############--------------- ####### T ############---------------- ######## ###########------------------ #####################------------------- #####################--------------------- ####################---------- --------- -##################----------- P --------- -#################------------ --------# -################----------------------- --##############-----------------------# --############-----------------------# --##########-----------------------# ---########---------------------## ---#####--------------------## -----#------------------#### ---#####-------####### ############## Harvard Convention Moment Tensor: R T F -9.08e+23 1.99e+24 4.66e+24 1.99e+24 1.13e+24 1.19e+24 4.66e+24 1.19e+24 -2.17e+23

07/05/23 04:41:46.72 NORTHERN MID-ATLANTIC RIDGE Epicenter: 52.325 -31.803 MW 5.6 USGS MOMENT TENSOR SOLUTION Depth 6 No. of sta: 74 Moment Tensor; Scale 10**17 Nm Mrr=-2.66 Mtt= 0.04 Mpp= 2.61 Mrt=-0.35 Mrp=-0.25 Mtp= 0.11 Principal axes: T Val= 2.63 Plg= 3 Azm= 93 N 0.08 7 183 P -2.71 82 340 Best Double Couple:Mo=2.7*10**17 NP1:Strike=176 Dip=43 Slip=-100 NP2: 9 48 -81 ##----# #####--------#### #####-----------##### ######-------------###### #######---------------####### #######----------------######## #######----------------######## ########------- -------######## ########------- P -------###### ########------- ------####### T ########----------------####### ########----------------######### ########--------------######### ########-------------########## ########-----------########## #######---------######### #######------######## #######--######## #---###

May 23, 2007, NORTHERN MID-ATLANTIC RIDGE, MW=5.7 Goran Ekstrom CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: C200705230441A DATA: II IU CU IC L.P.BODY WAVES: 65S, 114C, T= 40 MANTLE WAVES: 56S, 71C, T=125 SURFACE WAVES: 85S, 195C, T= 50 TIMESTAMP: Q-20070523091402 CENTROID LOCATION: ORIGIN TIME: 04:41:47.9 0.1 LAT:52.44N 0.01;LON: 31.63W 0.01 DEP: 12.0 FIX;TRIANG HDUR: 1.7 MOMENT TENSOR: SCALE 10**24 D-CM RR=-3.750 0.035; TT=-0.156 0.036 PP= 3.910 0.032; RT= 0.109 0.110 RP=-0.810 0.101; TP= 0.589 0.030 PRINCIPAL AXES: 1.(T) VAL= 4.073;PLG= 6;AZM= 98 2.(N) -0.226; 3; 7 3.(P) -3.843; 83; 247 BEST DBLE.COUPLE:M0= 3.96*10**24 NP1: STRIKE=192;DIP=39;SLIP= -85 NP2: STRIKE= 5;DIP=51;SLIP= -94 #######-### #######-------##### #######----------###### #######-------------####### #######--------------######## #######----------------######## ######-----------------######## #######-----------------######### #######------- -------######### ######-------- P -------####### ######-------- -------####### T #####------------------####### ######----------------######### #####---------------######### #####--------------######## ####-----------######## ###---------####### #-----#####

USGS research CMT: maintained and developed by Jascha Polet at UC Santa Barbara. This is a research system and solutions are *not* official USGS earthquake magnitudes. AUTOMATIC solution, not reviewed by a seismologist -------------------------------------------------- General region : 2007csak NORTHERN MID-ATLANTIC RID surface waves (3.0,3.5,7,7.5 mHz) Stations used : BFO CCM FFC KEV KIV KONO SJG Origin time: 2007 143 4 41 46 Original location (lat,lon,depth) : 52.3000 -31.8000 10 Moment tensor (x1.e26 dyncm) : Mrr : -0.041193 Mtt : -0.002937 Mff : 0.044130 Mrt : 0.028318 Mrf : 0.054103 Mtf : 0.006140 T-axis: moment= 0.075 plunge= 27.241 azimuth= 285.313 N-axis: moment= 0.000 plunge= 10.196 azimuth= 20.626 P-axis: moment= -0.075 plunge= 60.609 azimuth= 129.248 best double couple: Mo= 0.075(x1.e26 dyncm) Mw=5.8 tau= 2.3 nodal planes (strike/dip/slip): 350.99/ 19.99/-121.19 203.78/ 73.00/-79.33 Centroid location : 51.964 -31.953 19.205 Centroid time : -5.369 Variance reduction (%) : 45 *********** ****-------oooo**** ***-------------ooooo *** **---------------oo ooo ** **--------------oo ooo ** *---------------oo oo * *---------------oo oo * **--------------oo o ** *----T---------oo oo * **-------------oo o ** **------------oo + o ** **------------o o ** *-----------oo P o * **----------o oo ** *---------oo o * *--------o o * **----- o oo ** **----oo oo ** ***-o oo*** **** o**** *********** 0- 30- 60- 90- 120- 150- 180- 210- 240- 270- 300- 330- z-comp: 0 0 0 2 1 0 0 1 1 0 1 0 r-comp: 0 0 0 2 1 0 0 1 1 0 0 0 t-comp: 0 0 0 2 2 0 0 1 0 0 0 0 Total number of traces used = 16 number of runs = 6 starttime = Tue May 22 23:01:37 MDT 2007 endtime = Tue May 22 23:13:15 MDT 2007 inversion time = Tue May 22 23:13:12 MDT 2007 - Tue May 22 23:13:14 MDT 2007 Solution produced by inversion of channels with var red > 2%

Data set

The following broadband stations passed the QC and were used for the source inversion. AAM ACSO ANMO ANTO ARU ASCN BBSR BINY BLA BRAL BW06 CBN CCM CMB CNNC COLA COR COWI CRAG DBIC DGMT DUG DWPF ECSD EGAK EGMT EYMN FFC FURI GLA GLMI GNI GOGA GRGR HAWA HDIL HKT HLID HUMO HWUT ISCO ISP JCT JFWS KBL KBS KEV KIEV KIV KMBO KSU1 KVTX LPAZ MCWV MNTX MVCO NATX NEW NLWA NNA OBN PAL PMR RCBR RSSD SCIA SDDR SDV SIT SJG SKAG SSPA TEIG TGUH TLY TPAW TUC TZTN VBMS WMOK WRAK WUAZ WVOR YBH

Deviatoric Moment Tensor Inversion

All observed and Greens function waveforms are corrected to instrument response to ground velocity in meters/sec for the passband of 0.004 - 5 Hz. The traces were then lowpass filtered at 0.25 Hz and interpolated to a sample rate of 1 second.

For the deviatoric moment tensor inversion, the observed traces and Green's functions are read in an cut using the following commands

Processing parameters

#####
#	Driver script for the teleseismic waveform inversion
#
#	The depth HS must be of the form 0010 for a depth of 1.0 km
#       of 6700 for a depth of 670.0 km
#
#	The Filter_Band is an integer with the following meansing
#
#	FILTER_BAND	1/FH	1/FL
#	1		60	12	for Mw < 6.4
#	2		100	20	6.4 =< Mw < 6.8 
#	3		120	40	6.8 =< Mw < 7.2 
#	4		143	80	7.2 =< Mw < 9.3 
#####
#	Source duration - halfwidth of triangular function
#	this filters only the Green functions
#
#	halfwidth = 1.05 * 10-8 * M0^1/3 (M0 is dyne-cm)
#
#	MW	   half-width (sec)
#	5.0         0.75
#	6.0         2.45
#	7.0         7.7
#	8.0        24.5
#	9.0        74.3
#                       0.5*(MW - 9)
#  or half-width=74.3*10
#  or echo 5.58 |  awk '{print 74.3*exp(0.5*log(10.0)*(0800 - 9.0)) }'
#####
#  Processing window for P (use SAC variable A for P arrival
#  	Start   A  - 30
#  	End     A  + 2*HALFWIDTH + 0.03*HS + 30 + 1/FH
#  Processing window for SH (use SAC variable T0 for SH arrival
#  	Start   T0 - 60
#  	End     T0 + 2*HALFWIDTH + 0.06*HS + 30 + 1/FH
#  Processing window for SV (use SAC variable T1 for SV arrival
#  	Start   T1 - 60
#  	End     T1 + 2*HALFWIDTH + 0.06*HS + 30 + 1/FH
#	
#	The term involving HS serves to include the depth phases and
#	to exclude the PP or SS at most distanace
#####

The cut windows attempt to include the P, pP, sP, pS, S and sS arrivals. However, oen must be very careful about the fact that PP may be included in some distance ranges.

The waveforms are then bandpass filtered by the application of the following high- and low-pass stages (an optional microseism filter):

hp c 0.0167 2
lp c 0.0833 2
int
br c 0.12 0.25 n 4 p 2

The traces were next integrated to ground displacment in meters. Finally the observed data are interpolated to ahve the same sampling at the Green's functions.
NOTE: this was done for speed. The proper sequence is to read traces, filter and then cut - gsac will be modified to introduce a command CUTWR to define the cut upon a write.

The source inversion is a multipass operation since a lower frequency filter band is used for larger earthquakes and since a search is made over depth. Up to three passed of the outer loop are made, after which the moment magnitude is determined and filter settings readjusted. The inner loop over depth samples all depths from 0 to 800 km with 5 km increments in depth to 50 km, followed by 10 km depth sampling for the remaining range.

The following filter ranges are used according to the moment magnitude Mw:

   FILTER_BAND   1/FH(s)  1/FL(s)
       1           60     12      Mw < 6.4
       2          100     20      6.4 < Mw <= 6.9
       3          120     40      Mw > 6.9

The map displays the distribution of stations used for this source inversion.

Location of the earthquake (yellow star) and great circle path from the epicenter to each station (red) [created using GMT (Wessel, P., and W. H. F. Smith, New version of Generic Mapping Tools released, EOS Trans. AGU, 76 329, 1995.)]

For this data set the favored solution is

WVFMTD96   80.0  205.   61.  116.   5.55     0.218 0.422E-06     0.209     0.490 0.196E-06   6.3

The following figures show the sensitivity of the goodness of fit parameter so source depth, the waveform comparison as a function of epicentral distance in degrees and the source to station azimuth

Depth Sensitivity

Goodness of fit as a function of source depth. The measure is 1 - SUM (o -p)² / SUM o². A value of 1.0 is the best fit. The best double couple mechanism for the solution depth is plotted above goodness of fit value to indicate how the mefhanism may change with depth.

Detailed Waveform Comparison

P-wave Z component

Comparison of the observed traces (red) and solution predicted traces (blue) ordered in terms of increasing epicentral distance. Each pair of traces is annotated with the station name, epicentral distance in degrees, source to station azimuth in degrees. Each pair of traces is plotted with the same scale and the peak amplitudes are indicated at the lect of each trace. Finally the time shift between the P-wave first arrival picked and the the theoretical P-wave first arrival in the predicted trace is indicated, with a positive sign indicating that the predicted trace has been shifted to the right by the given number of seconds. as a function of source to station azimuth in degrees (D). The purpose of this display is to highlight the azimuthal dependence on the first motion. The traces are annotated with the station name at the top.

SH-wave T component

SV-wave R component

Inversion Details

Output of wvfmtd96 for the best depth..

Grid Search

For the grid search, the observed traces and Green's functions are read in an cut using the following commands