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updated coseismic slip model and its stress drop model of 2010 Maule,Chile earthquake
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Reference:
Estimates of stress drop and crustal tectonic stress from the February 27 2010 Maule, Chile earthquake: Implications for fault strength

Journal of Geophysical Research - Solid Earth, 2011

Karen Luttrell, Xiaopeng Tong, David Sandwell, Benjamin Brooks, Michael Bevis

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origin of the cartesian coordinate 
This origin is used when converting from local coordinate to the
lat/lon coordinate from the source_center.dat and source.dat. 

Lon:-73 deg
Lat:-36 deg

fault location and geometry:
xo: -69.877808 km 
yo: 20.084353 km
zo: 0.000000 km 
length: 670.614969 km
width: 260.000000 km
dip: 15.000000 deg
strike: 16.800980 deg

xo, yo, zo is location of the center 
of the top edge of the fault plane in 
cartesian coordinates. 
 
More descriptions:
The xo and yo are the relative location in cartesian coordinates
with respect to the origin of the cartesian coordinate assuming the
positive x means the center top of the fault is to the east of the  
origin  (Lon:-73 deg Lat:-36 deg.)
postive y means the center top of the fault is to the north of the  
origin  (Lon:-73 deg Lat:-36 deg.)

In this case the xo -69.877808 km means the center top of the fault is  
to the west of the origin -69.877808 km.
  the yo 20.084353 km means the center top of the fault is to the  
north of the origin -69.877808 km.


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Format of source.dat:

x1(km) x2(km) x3(km) x4(km) y1(km) y2(km) y3(km) y4(km) strike-slip(cm) dip-slip(cm)

x1,x2,x3,x4 are the along-strike location of the four corners of the rectangular fault patches.
y1,y2,y3,y4 are the along-dip location of the four corners of the rectangular fault patches.

      strike
    1---------4---->        
   d \         \       
    i \    c    \      
     p \         \
        2---------3

Each rectangular fault patches is 19.7km by 20km.
strike-slip is negative, corresponding to right-lateral.
dip-slip is positive, corresponding to thrust.

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Format of source_center.dat:
xc(km)  yc(km)  strike-slip(cm) dip-slip(cm) 

xc, yc are the location of the center of the rectangular fault patches. 
Each rectangular fault patches is 19.7km by 20km. 
strike-slip is negative, corresponding to right-lateral.
dip-slip is positive, corresponding to thrust.

More descriptions:
In the source.dat or source_center.dat there is no x and y coordinates  
only along-strike distance and along-dip distance.
The along strike distance have the positive direction toward the  
strike direction of the fault (the fault strike direction is defined  
in seismology)
and starts at the zero (always positive in this definition).
The along dip distance have the positive direction toward the updip  
direction of the fault and starts at the top edge of the fault (always  
negative
in this definition).

Note the notation of xo, yo has nothing to do with the notation of x1, x2, x3, x4, y1, y2, y3, y4, xc, yc. 

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Format of stressdrop.dat:
x(km)  y(km)  stress-drop along strike-slip direction (Mpa) stress-drop along dip-slip(Mpa)

The x and y of stressdrop.dat is similar to the xc and yc in the source_center.dat.
interp.com is a script to interpolate source_center.dat to prepare the stress drop calculation.
x, y are interpolated xc and yc at 1 km sampling interval. 
stress drop are calculated using stressdrop_fft.m. 
Positive sign means stress drop and negative sign is stress increase. 

The result are shown in stress_drop1.eps stress_drop2.eps stress_drop3.eps

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The trans_corrd.m is a script to transform the x, y locations on the fault plane into geographic coordinates.