[unav_all] REMINDER - Webinar: Infrasonics and the USArray

Andy Frassetto andyf at iris.edu
Mon Sep 24 09:42:40 MDT 2012

The IRIS Transportable Array Working Group invites you to attend a 
webinar on "Infrasonics and the USArray" on September 26, 2012 from 2-3 
pm EDT (6-7 pm UTC). NOTE: Apologies to those who will be unable to 
attend because of Yom Kippur. You will be able to watch the entire 
webinar within a couple days; all webinars are recorded and posted to 
the IRIS webinar homepage.

Space for 100 attendees during the webinar is available on a first come, 
first serve basis. If you are interested, please reserve a spot now: 

After registering you will receive a confirmation email containing 
information about joining the webinar. Following the presentation there 
will be the opportunity for questions with the speaker. More information 
on IRIS research webinars, including links to previously recorded 
presentations, may be found here: http://www.iris.edu/hq/webinar/. 
Please contact Andy Frassetto (andyf at iris.edu) with any additional 
questions, concerns, or suggestions.

Presenter: Dr. Kristoffer T. Walker, University of California, San Diego

Summary: Atmospheric infrasound travels thousands of kilometers with 
little attenuation in atmospheric waveguides controlled by the 
temperature and wind structure. While Infrasonics shared a spot with 
Seismology during the proliferation of nuclear weapons in the early to 
mid 20th century, the ratification of the 1963 Limited Test Ban treaty 
pushed nuclear testing underground and interest for infrasound 
subsequently diminished. Recently, the adoption of the 1996 
Comprehensive Test Ban Treaty has led to a renewed interest in 
Infrasonics and the development of a 45-station global infrasonic array 
network. Hundreds of infrasonic studies have been published since then, 
and the average number of infrasound-related presentations at the Fall 
AGU Meeting is at an all-time high of about 40. These studies show that 
infrasound is a tool for a number of academic and practical studies. 
Infrasound can be used to study hypotheses surrounding natural events 
such as earthquakes, meteors, volcanoes, ocean wave interaction, aurora 
processes, meteorological vortices, and mass-wasting processes. 
Infrasound can also be used to measure the degree of anthropogenic 
activity in cities, as well as locate explosions, rocket launches, and 
jet trajectories. Atmospheric processes such as turbulence and the 
interaction of gravity waves can also be constrained with infrasound. 
Our ability to predict temperature and wind as a function of altitude 
have progressed to the point that one can now use these models as 
starting models to invert for second-order structure, which is useful 
above the middle stratosphere where direct measurements of winds are 
difficult to obtain.

The global infrasonic array network has an intra-station spacing of 2200 
km. Although each array comprises several microbarometers that permit 
one to pinpoint the direction from which infrasonic waves originate, the 
large intra-station spacing makes it impossible to study the finer 
details of how infrasonic ray paths move through atmospheric structure. 
The 70-km intra-station spacing of the USArray, either using 
seismometers or microphones, allows one to investigate these details in 
unprecedented spatial resolution.

In this presentation, I aim to briefly discuss infrasonic sources, 
propagation physics, and reception. I will then focus on recent UCSD 
studies of infrasound and gravity waves using USArray seismometers and 
microphones. I will briefly discuss the potential of using USArray 
seismometers and microphones in joint studies of sources of opposing 
oceanic waves. Lastly, I will conclude with a list of needed things to 
facilitate future infrasonics research and improve the ability of the 
infrasonics community to grow.

System Requirements
PC-based attendees
Required: Windows® 7, Vista, XP or 2003 Server
Macintosh®-based attendees
Required: Mac OS® X 10.5 or newer

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