4 ms·

I’m a bit out of my depth here, so someone more knowledgeable correct me if my understanding is wrong. In the article, they’re stating they believe it’s seismi

I’m a bit out of my depth here, so someone more knowledgeable correct me if my understanding is wrong. In the article, they’re stating they believe it’s seismic activity because it’s occurring within some distance of these fault scarps, which also appear to be where the surface displays lines in the images shown in the article? How are they dismissing it’s not a result of material from space striking the surface? Is it that their sensors are able to disambiguate if the source is from the surface vs deeper in the moon?

flukus 7y ago
> How are they dismissing it’s not a result of material from space striking the surface? The earthquakes are magnitude 5.5, plugging that into an energy calculator (http://earthalabama.com/energy.html#/ http://earthalabama.com/energy.html#/) gives a result of 0.2 Hiroshima bombs, which I think would be noticeable.
- IanSanders 7y ago
  I wonder if the calculation requires correction due to moon/earth mass difference.
  - saagarjha 7y ago
    Moment magnitude is generally supposed to be correlated to the amount of energy released, so I would tend to think that it wouldn’t need correction.
- sandworm101 7y ago
  >> 0.2 Hiroshima bombs, which I think would be noticeable. Maybe not. Hiroshima wasn't all that big on geological scales. A medium-sized meteor stroking the moon would have equivalent energy. Tidal forces can also break meteors up, spreading them into streams of smaller bits that land over a period of time. So I am not so dismissive of potential impacts.
deleted 7y ago
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acollins1331 7y ago
Yes, you can estimate the depth below the surface by reading the seismic arrival times. There are compressional waves that travel along the surface, which travel at different speeds than the pressure and compressional waves going straight through the moon.
mannykannot 7y ago
I think quakes last noticeably longer than impacts, at least if they are large enough. On Earth, there's a fairly well-established empirical correlation[1]. Putting a magnitude of 5.5 into the formula given here suggests a duration of about 70s, if that relationship holds on the Moon. [1]https://en.wikipedia.org/wiki/Earthquake_duration_magnitude https://en.wikipedia.org/wiki/Earthquake_duration_magnitude

flukus 7y ago

> How are they dismissing it’s not a result of material from space striking the surface? The earthquakes are magnitude 5.5, plugging that into an energy calculator (http://earthalabama.com/energy.html#/ http://earthalabama.com/energy.html#/) gives a result of 0.2 Hiroshima bombs, which I think would be noticeable.

IanSanders 7y ago
I wonder if the calculation requires correction due to moon/earth mass difference.
- saagarjha 7y ago
  Moment magnitude is generally supposed to be correlated to the amount of energy released, so I would tend to think that it wouldn’t need correction.
sandworm101 7y ago
>> 0.2 Hiroshima bombs, which I think would be noticeable. Maybe not. Hiroshima wasn't all that big on geological scales. A medium-sized meteor stroking the moon would have equivalent energy. Tidal forces can also break meteors up, spreading them into streams of smaller bits that land over a period of time. So I am not so dismissive of potential impacts.

deleted 7y ago

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acollins1331 7y ago

Yes, you can estimate the depth below the surface by reading the seismic arrival times. There are compressional waves that travel along the surface, which travel at different speeds than the pressure and compressional waves going straight through the moon.

mannykannot 7y ago

I think quakes last noticeably longer than impacts, at least if they are large enough. On Earth, there's a fairly well-established empirical correlation[1]. Putting a magnitude of 5.5 into the formula given here suggests a duration of about 70s, if that relationship holds on the Moon. [1]https://en.wikipedia.org/wiki/Earthquake_duration_magnitude https://en.wikipedia.org/wiki/Earthquake_duration_magnitude