Location

2006/08/15 23:53:47 -21.17 -176.28 156

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	HARVARD CMT
Mw=6.2 2006/08/16 23:53:47 EVID: LAT: 21.17S, LON: 176.28W, DEPTH: 160 Mw: 6.2, mb: 0.0, Ms: 0.0 Mo= 0.240E+26 (dyne-cm) No. of Stations: 31, GAP: 62 Error (clvd/dc)*100= 44.73 Bandpass: 12 - 60 sec Nodal plane parameters strike dip rake NP1: 358 81 -117 NP2: 251 28 -20 #######-------- ###########---------- ##################--------- #########--------##########---- #######-----------#############-- #####--------------###############- #####---------------################# ####-----------------################## ###-------------------################# ##--------------------################# ##--------------------################# #---------------------################# #-------- ----------######### ##### #-------- P ----------######### T ##### -------- ----------######### #### --------------------############### -------------------############## -----------------############## ---------------############ ------------######### --------####### Stat Dist Az Misfit Stat Dist Az Misfit A05A 84 32 0.24 ATKA 73 1 1.04 CASY 64 205 0.90 CHTO 91 289 0.11 COLA 88 11 0.67 COLD 90 9 1.15 DAV 63 289 0.37 EGMT 90 38 0.19 FITZ 54 262 0.21 FORT 50 247 ***** ISCO 89 46 0.18 K06A 81 38 0.21 K08A 82 38 0.15 KKM 71 284 0.13 KMBL 55 245 4.67 KSM 75 277 0.17 LCO 92 122 0.20 LDM 69 284 0.41 MBWA 59 257 0.40 N06A 80 39 0.21 N12A 83 41 0.11 NEW 86 35 0.19 O04C 79 39 0.23 PPLA 85 10 1.11 QSPA 68 180 1.38 RPN 60 109 0.36 SBA 57 184 1.55 SWS 78 48 0.26 TATO 75 304 0.73 VNDA 57 185 2.39 WRAB 46 262 0.69 Misfit > 1 heavily downweighted	06/08/15 23:53:47.22 FIJI REGION Epicenter: -21.172 -176.277 MW 6.1 USGS MOMENT TENSOR SOLUTION Depth 156 No. of sta: 61 Moment Tensor; Scale 10**18 Nm Mrr=-0.12 Mtt= 0.34 Mpp=-0.23 Mrt=-0.17 Mrp=-1.69 Mtp= 1.14 Principal axes: T Val= 2.05 Plg=34 Azm=127 N 0.04 35 9 P -2.09 37 248 Best Double Couple:Mo=2.1*10**18 NP1:Strike=275 Dip=35 Slip= -3 NP2: 8 88 -125 ######- ###########------ ############--------- ##############----------- #######---------#####-------- ####-------------########------ ##---------------###########--- #----------------#############--- -----------------###############- -----------------################ ------ --------################ ------ P -------####### ####### ----- -------####### T ###### ---------------####### ###### -------------################ -----------############## ---------############ -------########## -######	August 15, 2006, FIJI REGION, MW=6.1 Goran Ekstrom CENTROID, MOMENT TENSOR SOLUTION HARVARD EVENT-FILE NAME C081506D DATA USED: GSN L.P. BODY WAVES: 74S,180C, T= 40 MANTLE WAVES: 57S, 92C, T=125 CENTROID LOCATION: ORIGIN TIME 23:53:50.6 0.1 LAT 21.15S 0.01;LON 175.78W 0.01 DEP 163.4 0.5;HALF-DURATION 2.8 MOMENT TENSOR; SCALE 10**25 D-CM MRR= 0.02 0.02; MTT= 0.32 0.02 MPP=-0.34 0.02; MRT=-0.30 0.01 MRP=-1.76 0.01; MTP= 0.61 0.02 PRINCIPAL AXES: 1.(T) VAL= 1.87;PLG=42;AZM=121 2.(N) 0.09; 21; 10 3.(P) -1.96; 41; 261 BEST DOUBLE COUPLE:M0=1.9*10**25 NP1:STRIKE=283;DIP=21;SLIP= 2 NP2:STRIKE=191;DIP=89;SLIP= 111 ########--- ############------- ####----------###------ ###------------########---- #---------------##########--- #----------------###########--- ----------------##############- -----------------##############-- ----- ---------###############- ----- P --------################- ----- --------####### ####### --------------######## T ###### --------------######## ###### -------------################ -----------################ ---------############## -------############ ---########

Deviatoric Moment Tensor Solution

The following broadband stations were used for the source inversion: A05A ATKA CASY CHTO COLA COLD DAV EGMT FITZ FORT ISCO K06A K08A KKM KMBL KSM LCO LDM MBWA N06A N12A NEW O04C PPLA QSPA RPN SBA SWS TATO VNDA WRAB

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.)]

All observed and Greens function waveforms are corrected to instrument response to ground velocity in meters/sec for the passband of 0.01 - 5 Hz. Next tre traces were bandpass filtered by the application of the following high- and low-pass stages:

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

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

For this data set the favored solution is

WVFMTD96  160.0  358.   81. -117.   6.22     0.470 0.273E-06     0.673     0.720 0.155E-06  44.7

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.

Fit with Distance

Fit with Azimuth

Comparison of the observed traces (red) and solution predicted traces (blue) 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.

Detailed Waveform Comparison

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.

Inversion Details