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写教师节的作文-致维吾尔族同胞觉醒书
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begin{document}
title{Research plan under the Post-doctorate program at xx University}
%subtitle{aa}
author{Robert He}
date{2008/04/23}
maketitle
section{Research Title}
~~~~Crustal seismic anisotropy in the xx using Moho P-to-S converted phases.
section{Research Background & Purposes}
~~~~Shear- wave splitting analyses provide us a new way to study the seismic
structure and mantle dynamics in the crust and mantle. The crustal anisotropy is
developed
due
to
various
reasons
including
lattice- preferred
orientation
(LPO)
of
mineral crystals and oriented cracks.
newline
Traditionally, the earthquakes occurring in the curst and the subducting plates
are selected to determine the seismic anisotropy of the crust. However, none of
these methods can help us to assess the anisotropy in the whole crust. Because
crustal earthquakes mostly are located in the upper crust, they do not provide
information
of
lower
crust.
On
the
other
hand,
earthquakes
in
the
subducting
plates
provide information of the whole crust but combined with upper mantle. However,
it
’
s
difficult
to extract the sole contribution
of the
crust from
the measurement.
Fortunately P-to-S converted waves (Ps) at the Moho are ideal for investigation
of crustal seismic anisotropy since they are influenced only by the medium above
the Moho. Moho. Figure ref{crustalspliting}~schematically shows the effects of
shear wave splitting on Moho Ps phases. Initially, a near-vertically incident P
wave generates a radially polarized converted shear wave at the crust-mantle
boundary.
The
phases,
polarized
into
fast
and
slow
directions,
progressively
split
in time as they propagate through the anisotropic media. Here, the Ps waves can
be obtained from teleseismic receiver function analysis.
%
%
begin{figure}[htbp]
begin{center}
includegraphics[width=0.47textwidth]{}
caption{The effects of shear wave splitting in the Moho P to S converted phase.
Top shows a schematic seismogram in the fast/slow coordinate system with split
horizontal Ps components.(cited from: McNamara and Owens, 1993)}
label{crustalspliting}
end{center}
end{figure}
%
%
The Korean Peninsula is composed of three major Precambrian massifs, the Nangrim,
Gyeongii,
and
Yeongnam
massifs({geomap}).
The
Pyeongbuk-Gaema
Massif
forms
the
southern
part
of
Liao-Gaema
Massif
of
southern
Manchuria,
and
the
Gyeonggi
and
Mt.
Sobaeksan
massifs
of
the
peninsula
are
correlated
with
the
Shandong
and
Fujian
Massifs of China.
%
begin{figure}[htbp]
begin{center}
includegraphics[width=0.755textwidth]{}
caption{Simplified geologic map. NCB: North China block; SCB: South China
block.(cited from: Choi et al., 2006)}
label{geomap}
end{center}
end{figure}
%
Our purpose of the study is to measure the shear wave splitting parameters in the
crust of the Korean Peninsula. The shear wave splitting parameters include the
splitting time of shear energy
between the fast and slow directions, as well as fast-axis azimuthal direction in
the
Korean
Peninsula.
These
two
parameters
provide
us
constraints
on
the
mechanism
causing the crustal anisotropy. From the splitting time, the layer thickness of
anisotropy will be estimated. Whether crustal anisotropy mainly contributed by
upper
or
lower
crustal
or
both
will
be
determined.
Based
on
the
fast-axis
azimuthal
direction, the tectonic relation between northeastern China and the Korean
peninsula will be discussed.
section{Research Methods}
~~~~Several methods have been introduced for calculation of receiver functions.
An
iterative
deconvolution
technique
may
be
useful
for
this
study
since
it
produces
more
stable
receiver
function
results
than
others.
The
foundation
of
the
iterative
deconvolution approach is a least-squares minimization of the difference between
the observed horizontal seismogram and a predicted signal generated by the
convolution of an iteratively updated spike train with the vertical-component
seismogram. First, the vertical component is cross-correlated with the radial
component
to
estimate
the
lag
of
the
first
and
largest
spike
in
the
receiver
function
(the optimal time is that of the largest peak in the absolute sense in the
cross-correlation signal). Then the convolution of the current estimate of the
receiver function with the vertical-component seismogram is subtracted from the
radial- component
seismogram,
and
the
procedure
is
repeated
to
estimate
other
spike
lags
and
amplitudes.
With
each
additional
spike
in
the
receiver
function,
the
misfit
between the vertical and receiver-function convolution and the radial component
seismogram is reduced, and the iteration halts when the reduction in misfit with
additional spikes becomes insignificant.
newline
For all measurement methods of shear-wave splitting, time window of waveform
should be selected. Conventionally the shear-wave analysis window is picked
manually.
However,
manual window selection is laborious and
also very
subjective;
in many cases different windows give very different results.
newline
In our study, the automated S-wave splitting technique will be used, which
improves the quality of shear-wave splitting measurement and removes the
subjectivity in window selection. First, the splitting analysis is performed for
a
range
of
window lengths. Then a cluster analysis is applied
in order
to
find the
window
range
in
which
the
measurements
are
stable.
Once
clusters
of
stable
results
are found, the measurement with the lowest error in the cluster with the lowest
variance is presented for the analysis result.