How Strong Was The Earthquake In Chiang Mai?

[licentiapoetica]

I have searched the Internet and Thai Visa but have been unable to find out how strong the recent earthquake was here in CM. I know it was 6.8 at the epicenter in Burma - but what if the epicenter had been right here in Chiang Mai and the earthquake had been felt in the same way it did for us last week here in CM. What number would it have been given on the Richer Scale? 4? 4.5? I have no idea. Does anyone know? Or can this even be calculated?

[TacoBoy]

If it was a 6.8 epicenter in Chiang Mai it would be very Strong and Violent. The type of quake would determine how much damage and type of shaking from the different type of shock waves.

When the quake hit in Burma last wee, I was in Chiang Rai in a single story detached brick and morter 10 year old house. Decent construction by Thai standards.

Felt and looked like the house was going to fall down. It rocked and swayed very violently. Could not stand up and maintain balance properly. Quake felt here nearly a minute.

And this was maybe 90 kilometers from the epicenter

[Jingthing]

I used to live in earthquake country and experienced dozens of quakes. I have never heard of Richter being expressed for any location other than at the epicenter. However, an experienced quake rider could probably have fun guessing, IF the quake felt had been at the epicenter, what would the richter be. But even then there are so many factors, such as depth of the quake and type of soil. The closest I got to a big quake was 3 miles from a 6.9 epicenter. You don't forget that.

Edited March 31, 2011 by Jingthing

[folium]

Licentiapoetica

As ever not a simple answer.

Earthquakes are measured in 2 ways;

Magnitude momentum, which covers the amount of energy released and the degree of vertical displacement, on a scale of 1 to, in theory, infinity.

This is measured on the MMS, or Magnitude Momentum Scale, which has largely superseded the Richter Scale since 1979. The Richter Scale, devised in 1935, for comparing Californian quakes, is now only used for smaller (sub 3.0) quakes. So if you hear a journalist referring to it they are probably 30 years out of date!

Intensity, which covers what is actually felt and experienced by people in the impact area, or beyond. Measured on a scale (Modified Mercalli) of I to XII.

The relationship between the two is fairly close but never absolute. Usually a 6.8 magnitude will produce an intensity between VII-IX (minor to considerable damage) in the immediate area of the epicentre (and obviously decreases as you move away in most cases), but this is very much determined by the depth of the focus (where the quake actually begins under the surface) and the underlying geology, plus factors like level of building standards etc. The epicentre often causes confusion as it is not where an earthquake originated from but is merely the point on the surface immediately above the actual focus of the quake.The depth of the focus is of crucial importance.

In terms of the quake here I attach the USGS maps plotting intensity which you can reverse engineer to give an idea of magnitude. CM experienced an intensity of approx III which would correspond to a magnitude of 3.8 to 3.9.

Hope this helps.

[Lizard2010]

Hope it did not too much damage as it could put people of visiting.

[lannarebirth]

Licentiapoetica

As ever not a simple answer.

Earthquakes are measured in 2 ways;

Magnitude momentum, which covers the amount of energy released and the degree of vertical displacement, on a scale of 1 to, in theory, infinity.

This is measured on the MMS, or Magnitude Momentum Scale, which has largely superseded the Richter Scale since 1979. The Richter Scale, devised in 1935, for comparing Californian quakes, is now only used for smaller (sub 3.0) quakes. So if you hear a journalist referring to it they are probably 30 years out of date!

Intensity, which covers what is actually felt and experienced by people in the impact area, or beyond. Measured on a scale (Modified Mercalli) of I to XII.

The relationship between the two is fairly close but never absolute. Usually a 6.8 magnitude will produce an intensity between VII-IX (minor to considerable damage) in the immediate area of the epicentre (and obviously decreases as you move away in most cases), but this is very much determined by the depth of the focus (where the quake actually begins under the surface) and the underlying geology, plus factors like level of building standards etc. The epicentre often causes confusion as it is not where an earthquake originated from but is merely the point on the surface immediately above the actual focus of the quake.The depth of the focus is of crucial importance.

In terms of the quake here I attach the USGS maps plotting intensity which you can reverse engineer to give an idea of magnitude. CM experienced an intensity of approx III which would correspond to a magnitude of 3.8 to 3.9.

Hope this helps.

That's interesting and I was not aware of that type of measurement. Like Jingthing I too have been in dozens of fairly large earthquakes including the largest ever recorded. I usually can't feel anything less than a 5 and since the one here in Chiang Mai was barely preceptible here and lasted only a few seconds and since we didn't know the epicenter yet I considered it 5ish. Good to know about this other way to measure intensity.

[Ricardo]

It was noticeable for a good 30 seconds, at our house in Mae-Jo, but didn't rattle all the tiles or 'twang' the metal roof-structure, which the 5.2 Richter-Scale a couple of years ago did, so I would guestimate 3-4 on the scale, had it been on our local Mae-Rim to San-Sai fault-line.

[upupandaway]

It was quite noticeable here in Chiang Mia on the 17th floor.

[folium]

Unless you are a human seismograph you cannot estimate the magnitude (energy released) of a quake. What you can do is estimate the intensity of a quake as you see the evidence all around you. For instance the Loma Prieta quake in California in 1989 was experienced very differently by the crowd in Candlestick Park stadium compared to the folks in the Marina District. The same magnitude quake (6.9MMS) was a III at the stadium but a level VI/VII intensity in the Marina District.

This is why the USGS has a "DID YOU FEEL IT-TELL US" application as first hand evidence is the only way that Intensity can be measured and is in many ways more important than just magnitude. While individually open to exaggeration, as an area wide average it is very indicative of the impact of a quake. I attach the hyperlink to the intensity data as registered by people all over Thailand, and further afield, for last week's quake in Burma. You too can contribute next time! (Look for the MMI, Modified Mercalli Intensity readings).

My link (and click on the Responses tab)

We all know that Chang is a relatively high alcohol strength beer, the interesting issue is the impact it has, and why! Studying earthquakes is no different.

The most powerful earthquake ever recorded (in magnitude terms) was the Valdivia quake, 1960, in Chile weighing in at 9.5, but it "only" killed 2500-5000 people. The Tangshan quake in China 1976 was "only" a magnitude 7.8 but killed up to 700,000.

Edited March 31, 2011 by folium

[lannarebirth]

Unless you are a human seismograph you cannot estimate the magnitude (energy released) of a quake. What you can do is estimate the intensity of a quake as you see the evidence all around you. For instance the Loma Prieta quake in California in 1989 was experienced very differently by the crowd in Candlestick Park stadium compared to the folks in the Marina District. The same magnitude quake (6.9MMS) was a III at the stadium but a level VI/VII intensity in the Marina District.

This is why the USGS has a "DID YOU FEEL IT-TELL US" application as first hand evidence is the only way that Intensity can be measured and is in many ways more important than just magnitude. While individually open to exaggeration, as an area wide average it is very indicative of the impact of a quake. I attach the hyperlink to the intensity data as registered by people all over Thailand, and further afield, for last week's quake in Burma. You too can contribute next time! (Look for the MMI, Modified Mercalli Intensity readings).

My link (and click on the Responses tab)

We all know that Chang is a relatively high alcohol strength beer, the interesting issue is the impact it has, and why! Studying earthquakes is no different.

The most powerful earthquake ever recorded (in magnitude terms) was the Valdivia quake, 1960, in Chile weighing in at 9.5, but it "only" killed 2500-5000 people. The Tangshan quake in China 1976 was "only" a magnitude 7.8 but killed up to 700,000.

Well I stand corrected. I was never in the Chilean Earthquake but experienced the 1964 Alaskan quake from northern British Columbia, At a distance of some 400 miles it still sent half our house tumbling down the hill.

Anyhow, the first thing I thought of when I felt this quake in CM was that Korea Air had rescheduled their flights. Felt about the same as when their 747 takes off.

Lasting nearly four minutes, it was the most powerful recorded earthquake in U.S. and North American history, and the second most powerful ever measured by seismograph.^[3] It had a magnitude of 9.2, at the time making it the second largest earthquake in recorded history.^[2][4]

[JRA]

I felt two quakes in Seattle in the past 15 years the last being 2001 and it felt like I was on a dock on a lake when the waves hit and I don't recall the scale but I will never foregt that...the one in 96 I hardly noticed except my gf in Seattle was pissed I didnt call her within an hour.

I guess the one here in CM depends where you were but I was on the 4th floor of my building and it seemed to last at least 30-40 seconds and I had no doubt it was a quake because I couldn't imagine something rocking my size building...I will never forget this quake either because I was so surprised by it.

I remember Mt. St Helens as well 30 years ago looking at the sky and wondering why the clouds seemed so different.

[mic6ard]

I'll give it around a 4 on the richter.