[meteorite-list] Seismic Event w/ Bolide?

From: Chris Peterson <clp_at_meteoritecentral.com>
Date: Wed, 17 Jan 2018 12:21:50 -0700
Message-ID: <ee1e316a-74f1-2a33-5bb5-5facd74c8604_at_alumni.caltech.edu>

I'd also like to point out that the description of "magnitude 2.0" is
rather sloppy. Seismographic magnitude scales (e.g. Richter,
moment-magnitude) attempt to provide a measure of the energy released by
an earth movement, at the epicenter, focus, or along the moving section.
It is completely separate from a measurement of intensity (e.g. modified
Mercalli scale). For a geological seismic event, the magnitude is fixed
but the intensity varies with distance and various geological factors.

What the seismometer was directly measuring here was intensity. Perhaps
by "magnitude 2.0" they meant the intensity was the same at the
measurement station as what would have been recorded if it were at the
epicenter of a magnitude 2.0 earthquake.

Anyway, the useful information is apparent in the actual data which show
the signature in terms of ground velocity versus time. From that it is
possible to derive actual information about the energy dissipated in the
atmosphere and delivered to the ground.

Typical kinetic energies for fireball events like this may be on the
order of 10^11 joules or more- say, 100 tons TNT equivalent.

Chris

*******************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On 1/17/2018 9:34 AM, Greg Redfern wrote:
> Thanks, Chris, that is what I thought.
>
> 2.0 - that is still some serious kinetic energy release.
>
> With fresh snow on the ground those space rocks will stick out like a sore
> thumb in open areas.....
>
> Good luck to all hunters.
>
> Sky Guy Greg
>
> Greg Redfern
> NASA JPL Solar System Ambassador <http://solarsystem.nasa.gov/ssa/home.cfm>
> Daily Blog <http://www.whatsupthespaceplace.com>
> Twitter <https://twitter.com/SkyGuyinVA>
> WTOP <http://wtop.com/section/tech/the-space-place-tech/>
>
> On Wed, Jan 17, 2018 at 11:03 AM, Chris Peterson via Meteorite-list <
> meteorite-list at meteoritecentral.com> wrote:
>
>> It's not uncommon for large fireballs to produce seismic signatures.
>> They're created by atmospheric shock waves hitting the ground. The bodies
>> themselves are nowhere near large enough to reach the ground intact, so all
>> that kinetic energy never results in cratering. ("Never" as in "only every
>> few hundred or thousand years".)
>>
>> Chris
>>
>> *******************************
>> Chris L Peterson
>> Cloudbait Observatory
>> http://www.cloudbait.com
>>
>> On 1/17/2018 7:22 AM, Greg Redfern via Meteorite-list wrote:
>>
>>> List,
>>>
>>> Has there been other bolide events that have had a seismic correlation? It
>>> is being reported that USGS recorded a 2.0 magnitude seismic event with
>>> this morning's Michigan et al bolide event.
>>>
>>> I would think that would have to equate to enough kinetic energy upon
>>> impact of the main body to create a crater of some size.
>>>
>>> Thoughts from experts like Mr. Matson ;-)
>>>
>>> Thanks.
>>>
>>> Sky Guy Greg
>>>
>>
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Received on Wed 17 Jan 2018 02:21:50 PM PST