Quakes 'A Concern', Say Thai Scientists

[webfact]

GEOLOGY

Quakes 'a concern', say Thai scientists

By Janjira Pongrai

The Nation

Several fault lines in Thailand have destructive potential, say geologists

A major fault line in Burma that caused Thursday's earthquakes is connected to a fault line in Thailand and both possess "similar seismic behaviours", a Chulalongkorn University geologist said yesterday.

"The quakes in Burma have caused us concern," said Assoc Professor Panya Jarusiri, noting the greater length of the Mae Chan fault line in Thailand, at 250 km, compared to the 150km length of the Mengxing fault line in Burma.

"What is a relief is that the quakes are inland and would cause less devastating effects than those occurring on sea beds," he added.

Asked of the chances of the Mae Chan fault line causing earthquakes in the future, Panya said: "The chances are there, but we can never tell when. A fault like Mae Chan yields the possibility of one quake in a 600year period, at a possible size of 6.07.0 on the Richter scale."

There are two other "locations of concern" in Thailand, Panya said: the Three Pagoda fault line in Kanchanaburi and Ratchaburi provinces and the Khlong Marui fault in the southern provinces of Surat Thani, Krabi and Phang Nga. Both fault lines regularly cause small earthquakes of 2.03.0 magnitude, with the greatest possible quake being 6.0.

Professor Thanawat Jarupongsakul, another CU geologist, said Thursday's quakes stemmed from fault lines connected to others in China and Laos that have caused a total of 27 quakes of magnitude 6.07.0 since 1973.

The greatest quake in 1988, at 7.1 magnitude in Sichuan, caused 700 deaths, while another three years ago was 6.3.

Of 13 fault lines in Thailand covering 22 provinces, there are four groups of active frontlines: those at Sri Sawat and Three Pagodas Pass in Kanchanaburi province; at Sakaing in the west; and the Khlong Marui fault covering Surat Thani, Krabi and Ranong.

Of the 22 provinces, 11 are in the North, six are in the South, three are in the West and two are in the Northeast.

Despite the tremors felt in Bangkok, the jolts have not impacted or damaged highrise buildings because their foundations are deep below the capital's top layer of soft clay, Thanawat said.

History of quakes in Thailand

The first recorded earthquake was a major quake in 1015 in presentday Lampang province, which caused much of the ancient kingdom of Yonok Nakhon to collapse into a huge crater, the remains of which are now just a large pond.

A moderate quake in 1545, in the heart of the Chiang Mai kingdom, caused heavy damage to property.

In 1935, a 6.5magnitude quake was reported in Nan and a 5.9 quake was reported in 1975 in Tak's Tha Song Yang district.

In 1994, a 5.1Richter quake in Phayao caused damage to buildings and schools.

-- The Nation 2011-03-26

[JetsetBkk]

Quakes 'A Concern', Say Thai Scientists

"What is a relief is that the quakes are inland and would cause less devastating effects than those occurring on sea beds," he added.

You gotta love Thai 'scientists'.

[PhilHarries]

The first recorded earthquake was a major quake in 1015 in presentday Lampang province, which caused much of the ancient kingdom of Yonok Nakhon to collapse into a huge crater, the remains of which are now just a large pond.

Couldn't have been much of a Kingdom if it ended up in the bottom of a pond.

I'd hazard a guess that's just the edited highlights of the story.

The thing with seismic events is that they occur along well known fault lines some known to be active and some not. But all we can any with any certainty is that those fault lines that are not active is that they have not experienced a tremor within the period of written history. It must have experienced earthquakes or it wouldn't be there. The fault line still lies there, dormant whilst others around the region slip and slide away relieving the stress in the Earth's crust. If one of these active faults locks up then the stress is redistributed and looks for another weak point in the crust.

As for earthquakes under the land causing less damage than those under the seabed tell that to the residents of San Francisco back in 1906.

[Crushdepth]

The first recorded earthquake was a major quake in 1015 in presentday Lampang province, which caused much of the ancient kingdom of Yonok Nakhon to collapse into a huge crater, the remains of which are now just a large pond.

Wow...apocalyptic.

[folium]

The first recorded earthquake was a major quake in 1015 in presentday Lampang province, which caused much of the ancient kingdom of Yonok Nakhon to collapse into a huge crater, the remains of which are now just a large pond.

Couldn't have been much of a Kingdom if it ended up in the bottom of a pond.

I'd hazard a guess that's just the edited highlights of the story.

The thing with seismic events is that they occur along well known fault lines some known to be active and some not. But all we can any with any certainty is that those fault lines that are not active is that they have not experienced a tremor within the period of written history. It must have experienced earthquakes or it wouldn't be there. The fault line still lies there, dormant whilst others around the region slip and slide away relieving the stress in the Earth's crust. If one of these active faults locks up then the stress is redistributed and looks for another weak point in the crust.

As for earthquakes under the land causing less damage than those under the seabed tell that to the residents of San Francisco back in 1906.

Sorry, it's not quite that simple.....

There are probably millions of faults and fault systems that are completely unknown to us, some of huge significance. For instance it was only in1999 that the Puente Hills Fault was mapped which is located directly beneath Los Angeles, and it took another 4 years of research for geologists to work out that it was capable of generating major earthquakes.

Similarly the Sept 2010 quake that hit Christchurch, NZ occurred on a previously unknown fault line, despite the fact that some 200 faults had been located in that area of NZ. It just underlines the fact that our knowledge (and understanding) of fault systems is still massively incomplete

Also excuse me for being a little pedantic, but it is now widely accepted that the 1906 quake had an offshore epicentre which then caused a rupture along the San Andreas fault, north and south. This is backed up by the occurrence of a small tsunami as witnessed by survivors and by data from the tidal gauge at the Praesidio.

The amount of damage caused by an earthquake is far more complicated than just it starting off/on shore. It is usually the secondary effects that are the main issue, ie tsunami, fires, landslides. San Francisco was destroyed by the fires not by the earthquake. It is also important to bear in mind the location of the epicentre in relation to areas of population (the key difference between the 2 Christchurch quakes), the depth of the quake (again important in the NZ cases), the time of day, underlying geology, levels of preparation and standard of buildings are all important considerations when assessing levels of damage.

For instance the similar-magnitude Northridge quake in LA in 1993 killed 72 while Kobe exactly a year later lost 6500 people due largely to the different geology and the construction of its buildings. Many homes in Kobe predated the 1981 building codes that laid down earthquake proofing standards and the problem was made worse by the fact that many also had heavy tile roofs, designed to be typhoon resistant, on a light wooden frame- disastrous in a quake scenario. Furthermore the population of the two areas (Kobe area and San Fernando Valley ) were roughly the same (about 2 million), so they make interesting if somewhat superficial comparisons, as no 2 quakes are ever the same in their characteristics or effects.

Sorry to bang on but it is my pet subject...as you may have gathered!

[JetsetBkk]

<snip>

Sorry to bang on but it is my pet subject...as you may have gathered!

All interesting stuff - thanks! But I had to chuckle when I read that the 'scientist' supposedly said "What is a relief is that the quakes are inland and would cause less devastating effects than those occurring on sea beds,"

Less devastating when inland? I think he has tsunamis on his mind and is not thinking too clearly.

I'd rather have a 7.0 earthquake right under the boat I'm on, than right under my house.

[Phatcharanan]

I had to chuckle when I read that the 'scientist' supposedly said "What is a relief is that the quakes are inland and would cause less devastating effects than those occurring on sea beds,"

Less devastating when inland? I think he has tsunamis on his mind and is not thinking too clearly.

Now come on...........he did get that info from Wikipedia.

[sunholidaysun1]

You dont need to be a scientist to know the earthquakes are a major concern !! Im crapping myself waiting for the next one.

[folium]

Cut the poor guy some slack!

It probably got somewhat lost in translation but it is absolutely true that almost every major (>8.5 MMS) quake since proper records began in 1900 has been offshore in subduction zones (where oceanic plate is driven under continental), in the form of megathrust earthquakes.

So while you may be pretty safe on your boat as long as you are some distance from the coast (check out the footage of a Japanese fishing boat off the coast of Sendai during the tsunami 2 weeks ago), the worst earthquakes almost all have offshore epicentres.