Harvard EPS Colloquium:<br>
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<p class="MsoNormal" style="line-height: normal;"><i><span style="font-size: 10pt;">Please
join us for our next Spring 2010 Colloquium</span></i><span style="font-size: 10pt;"> on <b>Monday, March 29<sup>th</sup> @
4pm:</b> </span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; text-align: center; line-height: normal;" align="center"><b><span style="font-size: 14pt; color: rgb(23, 54, 93);">Sarah Stewart-Mukhopadhyay</span></b><span style="font-size: 10pt; color: rgb(23, 54, 93); text-transform: uppercase;"></span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; text-align: center; line-height: normal;" align="center"><span style="font-size: 10pt; color: rgb(23, 54, 93); text-transform: uppercase;">Harvard University</span><span style="font-size: 10pt; color: rgb(23, 54, 93);"></span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; text-align: center; line-height: normal;" align="center"><span style="font-size: 10pt; color: rgb(23, 54, 93);">(<a href="http://www.fas.harvard.edu/%7Eplanets/stewart.html" target="_blank">http://www.fas.harvard.edu/~planets/stewart.html</a>)<b></b></span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; text-align: center; line-height: normal;" align="center"><span style="font-size: 14pt; color: rgb(23, 54, 93);">"Impact
crater formation via dynamic fault weakening"</span></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; text-align: center; line-height: normal;" align="center"><b><span style="font-size: 10pt; color: rgb(23, 54, 93);"><br></span></b></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; text-align: center; line-height: normal;" align="center"><b><span style="font-size: 10pt;">Colloquium will be held in Haller Hall</span></b></p>
<p class="MsoNormal" style="margin-bottom: 0.0001pt; text-align: center; line-height: normal;" align="center"><b><span style="font-size: 10pt;"> (Geo-Museum 102)<br>
<i>Please join us for a reception following the talk, in the 4th Fl. lounge of
Hoffman</i></span></b><span style="font-size: 10pt;"></span></p>
<p class="MsoNormal"> </p><p><font face="Times New Roman" size="3">Abstract:</font></p>
<p><font face="Times New Roman" size="3">Impact craters are the most
common landform on planetary surfaces; however, the mechanics of the
final stage of crater formation is still not fully understood. The end
stage of formation involves the collapse of a hemispherical transient
cavity. Around small craters, the limited amount of collapse preserves
a bowl-shaped cavity. In contrast, the observed shallow depths and
complex
inner morphologies of large craters require very low shear strength
in the collapsing material. Because the observed amount of collapse
cannot be reproduced using quasi-static (laboratory) values for the
frictional strength of fractured rock, a temporary weakening mechanism
is necessary. Currently, most researchers assume that acoustic waves
transiently fluidize the rock. I will present simulations investigating
an alternative hypothesis that craters collapse along a network of
impact-generated
faults that weaken during long displacements at high slip velocities.
The model reproduces the simple to complex crater transition and major
geologic features observed around terrestrial craters. Finally, I will
discuss implications for the formation of multi-ring impact basins and
applications to planetary evolution.</font></p>
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