[meteorite-list] Web-Based Program Calculates Effects of an Earth Impact

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:12 2004
Message-ID: <200404072116.OAA15786_at_zagami.jpl.nasa.gov>

http://uanews.org/cgi-bin/WebObjects/UANews.woa/2/wa/SRStoryDetails?ArticleID=8820


WEB-BASED PROGRAM CALCULATES EFFECTS OF AN EARTH IMPACT
>From Lori Stiles, UA News Services, 520-621-1877
April 7,2004

------------------------------
Contact Information

H. Jay Melosh
520-621-2806
jmelosh_at_lpl.arizona.edu

Robert Marcus
marcus34_at_email.arizona.edu

Gareth Collins
520-626-5065
gareth_at_lpl.arizona.edu

Related Web site
Earth Impact Effects Program
http://www.lpl.arizona.edu/impacteffects

------------------------------------------
 

Next time an asteroid or comet is on a collision course with Earth you can
go to a web site to find out if you have time to finish lunch or need to
jump in the car and DRIVE.

University of Arizona scientists are launching an easy-to-use, web-based
program that tells you how the collision will affect your spot on the globe
by calculating several environmental consequences of its impact.

Starting today, the program is online at
http://www.lpl.arizona.edu/impacteffects

You type in your distance from the predicted impact site, the size and type
of projectile (e.g. ice, rock, or iron) and other information. Then the
Earth Impact Effects Program calculates impact energies and crater size. It
next summarizes thermal radiation, seismic shaking, ejecta deposition (where
all that flying stuff will land), and air-blast effects in language that
non-scientists understand.

For those who want to know how all these calculations are made, the web page
will include "a description of our algorithm, with citations to the
scientific sources used," said Robert Marcus, a UA undergraduate in the
UA/NASA Space Grant Program. He discussed the project recently at the 35th
Lunar and Planetary Science Conference meeting in Houston, Texas.

Marcus developed the web site in collaboration with planetary sciences
Regentsı Professor H. Jay Melosh and research associate Gareth Collins of
UAıs Lunar and Planetary Laboratory.

Melosh is a leading expert on impact cratering and one of the first
scientists reporters call when rumors of big, Earth-smashing objects begin
to circulate.

Reporters and scientists both want to know the same thing: how much damage a
particular collision would wrack on communities near the impact site.

The web site is valuable for scientists because they don't have to spend
time digging up the equations and data needed to calculate the effects,
Melosh said. Similarly, it makes the information available to reporters and
other non-scientists who don't know how to make the calculations.

"It seemed to us that this is something we could automate, if we could find
some very capable person to help us construct the website," Melosh said.

That person turned out to be Marcus, who is majoring in computer engineering
and physics. He applied to work on the project as a paid intern through the
UA/NASA Space Grant Program.

Marcus built the web-based program around four environmental effects. In
order of their occurrence, they are:

1) Thermal radiation. An expanding fireball of searing vapor occurs at
impact. The program calculates how this fireball will expand, when maximum
radiation will occur, and how much of the fireball will be seen above the
horizon.

The researchers based their radiation calculations on information found in
"The Effect of Nuclear Weapons." This 1977 book, by the U.S. Defense
Department and U.S. Department of Energy, details "considerable research
into what different degrees of thermal radiation from blasts will do,"
Melosh noted.

"We determine at a given distance what type of damage the radiation causes,"
Marcus said. "We have descriptions like when grass will ignite, when plywood
or newspaper will ignite, when humans will suffer 2nd or 3rd degree burns."

2) Seismic shaking. The impact generates seismic waves that travel far from
the impact site. The program uses California earthquake data and computes a
Richter scale magnitude for the impact. Accompanying text describes shaking
intensity at the specified distance from the impact site using a modified
Mercalli scale This is a set of 12 descriptions ranging from "general
destruction" to "only mildly felt."

Now suppose the dinosaurs had this program 65 million years ago. They could
have used it to determine the environmental consequences of the
15-kilometer-diameter asteroid that smashed into Earth, forming the
Chicxulub Crater.

The program would have told them to expect seismic shaking of magnitude 10.2
on the Richter scale. They also would have found (supposing that the
continents were lined up as they are now) that the ground would be shaking
so violently 1,000 kilometers (600 miles) away in Houston that dinosaurs
living there would have trouble walking, or even standing up.

If the Chicxulub Crater-impact occurred today, glass in Houston would break.
Masonry and plaster would crack. Trees and bushes would shake, ponds would
form waves and become turbid with mud, sand and gravel banks would cave in,
and bells in Houston schools and churches would ring from ground shaking.

3) Ejecta deposition. The team used a complicated ballistics travel-time
equation to calculate when and where debris blown out of the impact crater
would rain back down on Earth. Then they used data gathered from
experimental explosions and measurements of craters on the moon to calculate
how deep the ejecta blanket would be at and beyond the impact-crater rim.

They also determined how big the ejecta particles would be at different
distances from impact, based on observations that Melosh and UAıs Christian
J. Schaller published earlier when they analyzed ejecta on Venus.

OK, back to the dinosaurs. Houston would have been covered by an
80.8-centimeter- (32-inch-) thick blanket of debris, with particles
averaging 2.8 mm (about 1/8th inch) in size. They would have arrived 8
minutes and 15 seconds after impact (meaning they got there at more than
4,000 mph).

4) Air blast. Impacts also produce a shock wave in the atmosphere that, by
definition, moves faster than the speed of sound. The shock wave creates
intense air pressure and severe winds, but decays to the speed of sound
while itıs still close to the fireball, Melosh noted. "We translate that
decreasing pressure in terms of decibels ‹ from ear-and-lung-rupturing
sound, to being as loud as heavy traffic, to being only as loud as a
whisper."

The program calculates maximum pressures and wind velocities based on test
results from pre-1960s nuclear blasts. Researchers at those blasts erected
brick structures at the Nevada Test Site to study blast wave effects on
buildings. The UA team used that information to describe damage in terms of
buildings and bridges collapsing, cars bowled over by wind, or forests being
blown down.

Dinosaurs living in Houston would have heard the Chicxulub impact as loud as
heavy traffic and basked in 30 mph winds.
Received on Wed 07 Apr 2004 05:16:36 PM PDT