Moment Tensor 20060503152640

Location

2006/05/03 15:26:40 -20.19 -174.12 55

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

SLU Moment Tensor Solution 2006/05/03 15:26:40 Best Fitting Double Couple Mo = 9.89e+27 dyne-cm Mw = 7.93 Z = 80 km Plane Strike Dip Rake NP1 30 70 60 NP2 269 36 144 Principal Axes: Axis Value Plunge Azimuth T 9.89e+27 55 262 N 0.00e+00 28 41 P -9.89e+27 19 142 Moment Tensor: (dyne-cm) Component Value Mxx -5.40e+27 Mxy 4.71e+27 Mxz 1.82e+27 Myy -1.05e+26 Myz -6.52e+27 Mzz 5.50e+27 -------------- ---------------------# ------------------------#### -------------------------##### ---------################--####### ------######################--###### ----########################------#### ---##########################--------### --##########################----------## --##########################-------------# -########## #############--------------# ########### T ############---------------- ########### ###########----------------- #######################----------------- ######################------------------ ####################------------------ #################------------------- ##############------------ ----- ###########------------- P --- #######---------------- -- #--------------------- -------------- Harvard Convention Moment Tensor: R T F 5.50e+27 1.82e+27 6.52e+27 1.82e+27 -5.40e+27 -4.71e+27 6.52e+27 -4.71e+27 -1.05e+26

Epicenter: -20.035 -174.227 MW 7.9 USGS MOMENT TENSOR SOLUTION Depth 79 No. of sta: 13 Moment Tensor; Scale 10**20 Nm Mrr= 3.97 Mtt=-0.01 Mff=-3.96 Mrt= 0.22 Mrf= 7.34 Mtf= 1.29 Principal axes: T Val= 8.44 Plg=58 Azm=281 N 0.02 8 177 P -8.46 30 82 Best Double Couple:Mo=8.5*10**20 NP1:Strike=147 Dip=17 Slip= 59 NP2: 359 76 99 ###---- #########-------- ############--------- -#############----------- --##############------------- --################------------- -#################------------- --####### #######------- ---- --####### T #######------- P ---- --####### #######------- ---- ---################-------------- ---################-------------- ---###############------------- ----##############------------- ----#############------------ ----##########----------- ----########--------- -------##-------# ----###

May 3, 2006, TONGA, MW=7.9 Natasha Maternovskaya Goran Ekstrom CENTROID, MOMENT TENSOR SOLUTION HARVARD EVENT-FILE NAME M050306A DATA USED: GSN MANTLE WAVES: 48S, 85C, T=150 CENTROID LOCATION: ORIGIN TIME 15:27: 8.7 0.5 LAT 20.33S 0.04;LON 174.03W 0.05 DEP 65.5 1.7;HALF-DURATION 24.6 MOMENT TENSOR; SCALE 10**28 D-CM MRR= 0.59 0.01; MTT=-0.17 0.01 MPP=-0.42 0.01; MRT= 0.11 0.02 MRP= 0.75 0.02; MTP=-0.28 0.01 PRINCIPAL AXES: 1.(T) VAL= 0.99;PLG=62;AZM=266 2.(N) -0.05; 12; 18 3.(P) -0.94; 26; 114 BEST DOUBLE COUPLE:M0=1.0*10**28 NP1:STRIKE=228;DIP=22;SLIP= 122 NP2:STRIKE= 14;DIP=72;SLIP= 78 ----------# ---------#####--### ------##########------# -----#############--------- ----###############---------- ----################----------- ---#################----------- ---##################------------ --####### #########------------ --####### T ########------------- --####### ########------ ---- -#################------- P --- -################-------- --- -###############------------- -#############------------- ###########------------ ########----------- ##---------

Data set

The following broadband stations passed the QC and were used for the source inversion. DUG EGMT HAWA HLID ISCO MIAR NEW WUAZ WVOR

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

Phase    Gsac Command              Comment
 P    cut A -30 A       CUTH = 95+0.3*DEPTH  
SH    cut T1 -60 T1     CUTH = 95+0.6*DEPTH
SV    cut T0 -60 T0     CUTH = 95+0.6*DEPTH

where the 95 is a maximum filter duration, DEPTH is in km, and the CUTH in sec

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 0.0050 2
lp c 0.0100 2
int
br c 0.12 0.2 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   FH(s)  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   29.   76.   59.   7.89     0.908 0.338E-04     0.907     0.953 0.152E-04  42.6

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