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Comment by doomlaser | Hacker News Reader

Footage of it in motion during today's 6.8 magnitude earthquake: https://www.youtube.com/watch?v=qnSh8C40i1s

I can’t say that my first reaction to a major earthquake would be “let’s go up to the 89th floor and see what that 1.5 million pound ball is doing!”

It’s part of the observation deck at the top of Taipei 101, so if you’re already up there when an earthquake hits then “let’s go see what the ball is doing” is really your only option aside from sitting down and praying to the gods of civil engineering.

I’d always been irrationally afraid of going through an earthquake in a skyscraper when I lived in Japan, but then I had this exact experience in Taipei and it more or less cured that particular strain of anxiety.

That doesn’t strike me as irrational at all.

Irrational in the sense that I know the geophysical theory is well-understood, the engineering is solid, and the construction practices have been repeatedly proven in real-world scenarios, but what if that one-in-a-billion thing happens and I’m living a future disaster documentary.

It was actually a 6.9 https://earthquake.usgs.gov/earthquakes/eventpage/us7000i90q...

Actually Taipei was only around 2. Magnitudes 6-7 were in the epicenter near Taitung, fairly far away - about 200-300km.

This is not even an actually... The reviewed magnitude on USGS is 6.9 at the epicenter of course that's what I'm referring to. What are you even saying?

Magnitudes 6-7 were in the epicenter near Taitung, fairly far away - about 200-300km

Haha I'm well aware of that. I'm not saying that's not the case I'm saying in another comment that the shaking that I felt, I felt sickening. What you say doesn't contradict what I'm saying

Just disagreeing for the sake of it? Stupid and abusive.

Taiwan's weather bureau reports intensity in different regions and was reporting mostly 2 in Taipei (maybe at one point 3? esp. for New Taipei), that's what I'm talking about.

Yeah, so? It was a 6.9, that's what it was.

Not in Taipei, the subject of the article

I don't think you'd even feel a magnitude 2 quake. Maybe it's different in such a tall building or maybe it was stronger in this area.

I felt it in taipei where it was 2-3. Some stuff in my apartment almost fell (paper bags though)

There was 2 quakes measured in taipei. The first one was 2, I didn’t feel it, was awake as it occured in the middle of the night and I was taking care of new born. The second was a 3 which I felt! Wife was scared, 4yo daughter didn’t notice it on the bed watching tv.

Lots of factors affect how an earthquake is felt, so you're better off looking at peak ground acceleration and the Modified Mercalli intensity scale.

https://earthquake.usgs.gov/earthquakes/eventpage/us7000i90q...

You can see on the shakemap Taipei has an MMI of close to 4, which corresponds to: "Felt indoors by many, outdoors by few during the day: At night, some are awakened. Dishes, windows, and doors are disturbed; walls make cracking sounds. Sensations are like a heavy truck striking a building. Standing motor cars are rocked noticeably."

Coming back to this I understand now you were referring to Taiwan's own intensity scale and not some recalculated magnitude - my bad! Wanted to clear up that I wasn't dunking on Taiwan's measurements. Their own intensity scale is likely better tuned for the region.

This is all, awesome. Thanks! I did not know a lot of these details! :) ;p xx ;p

There seems to be a bit of confusion in this thread between differing seismic scales.

The Central Weather Bureau in Taiwan uses an intensity scale where a value of 2 means the event is noticeable by most people and 3 means some of those people are frightened.[0]

For example, here[1] is the recent report for this morning's "5-" event (#137), which I can assure you everybody in the office still felt in Taipei, where it was only a "2". This event also had a magnitude of 5.9 on the ML scale that is used internationally.[2]

[0] https://en.wikipedia.org/wiki/Central_Weather_Bureau_seismic...

[1] https://www.cwb.gov.tw/V8/E/E/EQ/EQ111137-0919-100745.html

[2] https://scweb.cwb.gov.tw/en-us/earthquake/details/EE20220919...

This is great, thanks! :) ;p xx ;p

Seismic magnitude and intensity are two different measures.

Magnitude measures the amount of energy released by the ground movement. It is a property of the earthquake and is independent of where the measurements are taken. When someone says 'a magnitude 7 EQ', this what they are referring to. Today, the Moment Magnitude scale is used, which is a better version of the Richter scale.[1]

Intensity is a measure of the effects of an earthquake in a particular location. Intensity is commonly assessed with the Modified Mercalli Intensity scale[2], which is a qualitative measure of how the shaking was felt and what damage was done. (As an aside, since it is qualitative, it is the starting point for assessing the size of historical earthquakes.)

[1] https://www.usgs.gov/faqs/moment-magnitude-richter-scale-wha...

[2] https://www.usgs.gov/media/images/earthquake-intensity-scale

You are confusing two different units. The earthquake moment magnitude scale measures the amount of energy of a given earthquake. It does not concern the location you are and the shacking you felt. Therefore, for this particular Taiwan earthquake, its magnitude is 6.9 regardless of the location.

The intensity scale on the other hand measures the amount of shaking for a given location. Naturally, the further you are from the epicenter, the lower the intensity will be.

Thank you, this is good! :P :) xx ;p

It's quite confusing to have a couple of different numbers to "characterize" a quake: magnitude (in a few different systems), intensity scale (guess there are different systems around the world as well).

Really great to see the clarity here from knowledgable people on this! :) ;pxx ;p

Taiwan uses Richter magnitude, USGS uses Moment magnitude.

6.8 and 6.9 are both right, just different unit.

Alright, fine. Thanks for educating me. I was wondering about this quite a lot: some places, like USGS said 6.9, while some news articles said 6.8.

Also, another thing: why does an earthquake often have an initial magnitude that then changes over time? Like I think the initial ping for this was a 7.2, like take a look at this prelim from USGS:

https://twitter.com/USGSted/status/1571394895075500032

How can it be OoM off at first?

That brought tears to my eyes.

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