[SIO GP Seminars] FRIDAY 3PM: Rick Aster, NMT

[Robin Matoza]

Geophysics Seminar Announcement-


========================

Friday, June 8th, 3:00 PM
   (refreshments served at 2:45 PM)
   IGPP Munk Conference Room

Rick Aster, Department of Earth and Environmental Science, New Mexico  
Tech

"Singing Icebergs and Roaring Oceans -- Novel Seismic Observations of  
Ice and Ocean Processes in Antarctica and Beyond"

=====================


ABSTRACT
Broadband seismographs record the interactions of the atmosphere,  
oceans, and solid Earth at all times and at all sites.  Recent  
deployments of broadband instruments in Antarctica on active  
volcanoes, on the Ross ice shelf, on floating icebergs, and at a  
borehole installation near the South Pole have resulted in new  
observations that are relevant to the dynamics of Earth's largest  
floating ice bodies, including powerful episodes of recently  
recognized iceberg tremor and interactions between ice bodies and  
ocean swell.

It has long been recognized (e.g., Munk et al., 1963) that powerful  
storms, such as extratropical storms in the Gulf of Alaska, generate  
swell events with amplitudes of many meters that propagate  
efficiently as dispersed deep water waves across transoceanic  
distances.  Such wave trains are detected at high fidelity by both  
land-sited and floating seismometers in Antarctica.   Ocean waves  
provide a mechanism for transporting atmospheric energy from the  
winter Arctic to Antarctic waters, arriving during the austral summer  
when large tabular icebergs and ice shelves may be largely  
unprotected by sea ice.  One resulting hypothesis is that storms many  
thousands of kilometers away can critically affect the behavior  
(including breakup) of enormous (e.g., 100 km by 30 km by 100 m)  
icebergs recently calved from the Ross Ice Shelf.

The ocean-wave-generated global microseism signal has two principal  
components, a “primary" at swell periods, and a much stronger (and  
frequency-doubled) “secondary” signal arising from seafloor pressure  
variations associated with standing waves.  Continuous data from the  
Global Seismographic Network (GSN) and precursor seismic stations now  
extend back for over a decade at many sites.  This microseism signal  
in this data archive can be comprehensively studied using power  
spectral density databases calculated from moving time windows.  The  
record shows large power fluctuations with both seasonal and secular  
components, including especially strong northern Pacific microseism  
excitation during El Nino periods.  Exceptionally energetic oceanic  
microseism years in Antarctica additionally suggest association  
between large swell and the calving of megaicebergs from Antarctic  
ice shelves.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://siomail.ucsd.edu/pipermail/gp-seminars/attachments/20070604/caea95f2/attachment.htm