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Unformatted text preview: the Nax is . USGS moment
tens or s olution 2004
Indian Oc ean
ear thquake To give an ex ample, in the 2004 Indian Oc ean earthquak e, the
moment tens or s olution gives two nodal planes , one dipping
northeas t at 13 degrees and one dipping s outhwes t at 79 degrees .
In this c as e the earthquak e c an be c onfidently as s oc iated with the
plane dipping s hallowly to the northeas t, as this is the orientation of
the s ubduc ting s lab as defined by his toric al earthquak e loc ations
and plate tec tonic models . Fault plane s olutions are us eful for defining the s ty le of faulting in
s eis mogenic volumes at depth for whic h no s urfac e ex pres s ion of
the fault plane ex is ts , or where the fault trac e is c overed by an
oc ean. A mos t beautifully s imple ex ample of a s uc c es s ful tes t of
the hy pothes is of s ea floor s preading was the demons tration that the s ens e of motion along
oc eanic trans form faults is oppos ite to what would be ex pec ted in c las s ic al geologic
interpretation of the offs et oc eanic ridges . This was done by c ons truc ting fault plane s olutions
of earthquak es in oc eanic faults , whic h s howed beac h ball plots of s trik e s lip nature (s ee
figures ), with one nodal plane parallel to the fault and the s lip in the direc tion required by the
idea of s ea floor s preading from the ridges .
Fault plane s olutions als o play ed the k ey role in the dis c overy that the deep earthquak e
z ones in s ome s ubduc ting s labs are under c ompres s ion, others are under tens ion. Beach Ball Calculator  There are s everal programs available to prepare Foc al Mec hanis m Solutions (FMS)[whi c h?].
BBC, a MATLAB bas ed tool box , is available to prepare the beac h ball diagrams . This
s oftware plots the firs t motion polarity data arrived at different s tations . The c ompres s ion and
dilation are s eparated us ing mous e help. A final diagram is prepared automatic ally . en.wikipedia.or g /wiki/Focal_mechanism 3/3...
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This document was uploaded on 02/04/2014.
- Spring '14