Earthquake activity - Formosahut forum

Call me crazy, but for years now, which is nothing in geologic terms of course, I've been waiting for 'a bit one' to hit southern Taiwan. The earthquake activity since January 20 is interesting. Earthquakes such as this one off the coast of Kaohsiung are not very common, and it took place during a string of quakes off the east coast, the most recent being today. (For the latest, see http://www.cwb.gov.tw/V7e/earthquake/quake_index.htm).

It's impossible to predict quakes, other than to say that they will happen. But I believe there is a fault running north of Kaohsiung and another of the Hengchun peninsula that are both ripe for a major shift. Given all the major quakes in this region in the last decade, it would be silly to presume that we are not in a very active period.

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Since i have been here most of the major quakes have occured in the north, central and central-east coast regions and a quick check of records shows that historically, that's where they usually happen. Major earthquakes in the south are pretty rare - the biggest in the Taidong area in recorded history seems to be a 6.1 in Dec 2, 1943, causing 139 deaths.
The biggest known tsunami causing earthquake occured in 1867 off the coast of Keelung - it resulted in hundreds of deaths.

Here's a list of the biggest ones to have affected TW in the last couple of hundred years.

http://en.wikipedia.org/wiki/List_of_earthquakes_in_Taiwan

I can't find any record of a major earthquake happening in the Kaohsiung area. Are you saying that you think the recent earthquake there could be a sign of future activity there, or rather that it may be a trigger for earthquakes in other places?

The biggest quake to affect Kaohsiung since I've been here was the Hengchun quake of 2006. There were actually two 7.0 quakes occurring within an hour or two of each other. This is the event that knocked out some communications lines to parts of E. Asia, including Hong Kong. See http://en.wikipedia.org/wiki/2006_Hengchun_Earthquake.

After that quake, there was a lot of activity in that area. Here's a map of activity for January 07, the month following the Hengchen quake.

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It looks like what I thought was a quake in Tainan that happened in the early 1900's was actually the 1906 Meishan quake. http://en.wikipedia.org/wiki/1906_Meishan_earthquake. That was just north of Tainan, I believe.

I guess the reason I'm expecting more activity is because the first decade or so that I lived in Taiwan, mostly in Kaohsiung, there was virtually no major activity in southern Taiwan. But since 2006, it has been more active. And it seems that the E. Asian and SE Asian regions in general have been more active in recent years.

But ultimately, I'm just on my toes for quakes, having experienced some big ones. You can see a storm coming, but you can't see an earthquake coming. It just happens. In that respect, it's a little bit like running into a snake. You know you're going to see another one, but you can't know when, although predicting an encounter with a snake is arguably much easier than predicting an earthquake.

That 'map of activity' is bizarre! It's ridiculous how much seismic activity there is here. I'm pretty sure i recall those twin earthquakes - some good friends of mine were giving birth to twins on that same night. Later, when we heard that they were actually separate earthquakes, I remember we did re-remark on the coincidence, and wondered what kind of portent that might have been.

There are actually a few earthquake predicting theories around, though there aren't too many examples of people using them to accurately predict an earthquake - they seem much better at predicting them in hindsight. The most celebrated cases seem to be these onen from China:

'In 1969, a warning was issued at the Tientsin People's Park Zoo, just two hours before the earthquake struck. This warning was based upon odd behaviors in various animals in the zoo, including, but not limited to; giant pandas, deer, sharks, tigers, and yaks.'
http://en.wikipedia.org/wiki/Earthquake_prediction
Another report states:
'In February 1975 hibernating snakes abandoned their hideouts in the north-eastern city of Haicheng. The city was evacuated and February 4, the region was hit by a 7.3 magnitude earthquake. More than 1.000 people were killed, but considering the densely populated area the prediction an evacuation was considered a great success.'
http://blogs.scientificamerican.com/history-of-geology/2011/12/12/can-animals-sense-ear...

The article does qualify this by saying there were also other indicators, including a series of pre-shocks, which have been the cause of the animals being spooked.

But anyway, i am keeping an eye on the chooks.

That's an interesting article. I had no idea people had actually taken action based at least in part on animal behavior. Smart.

I was getting frustrated trying to find information of offshore faults around Taiwan, so I've been collecting articles. My knowledge of tectonic terminology is not quite up to speed, but a quick look at what I've gathered seems to suggest that, although much is known about what's going on down there, there still is a lot that we don't know.

It appears the activity off southern Taiwan is the result of a strike-skip fault or faults, a new term for me. It's fascinating stuff. I'm putting what I can find in a directory located at http://formosahut.com/seismology/. It's a raw directory listing. I won't pretend that I've read all of this stuff yet.

Also, most of those files are pdf files, so if you're like me, you'll prefer to right click on them and save them to your desktop rather than waiting for them to load in your browser.

Hmmmm... I have noticed an abundance of tiny little frogs hopping around recently, but I'm assuming that's just a birds and bees thing.

It appears the activity off southern Taiwan is the result of a strike-skip fault or faults, a new term for me.

Here are a few more new ones for you (taken from your earthquake resources page):

"Typical subduction trench-accretionary wedge-forearc basin-volcanic arc type
configuration is observed in the southern part of the study area"

Even if you condensed it to an acronym and called it - STAWFBVATC - it's still quite a mouthful.

The 'strike-skip fault' that you refer to is, i think, also commonly known as the 'strike-slip' fault - the kind where the plate boundaries slide past each other in a roughly horizontal way.

The other main kinds seem to be 'dip-slip faults' - where the plates move up or down against each other. The 'thrust fault' is one of these and that was the kind that caused the Boxing Day tsunami.

I assume it's only these up-down kinds that can cause tsunamis.

You're right about the frogs, though they look more like toads to me - i was drving down my drive the other night and it looked like a biblical plague of them.

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Weird. Small earthquake right under our feet 'even as we speak'. Actually that's the third or fourth time i have noticed a quake with its epicentre right here - all about the same size.

Strike-slip it is; I stand corrected. There have been a number of small quakes in this area over the last three days. I was struck by one of those articles that separated Taiwan into five (I think, could have been four) specific seismic zones. That demonstrates what a complex little island Taiwan is, geologically speaking. Things seem to be shifting in all directions at once here, sort of like the winds over the last few days.

I thought this graphic seemed ominous. Where is Taiwan?

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It's probably just a coincidence, but the animals in the neighborhood were going crazy last night. In addition to the dogs barking and whining, the cat was climbing the screen door at midnight. I got up this morning and noticed that Hualian had six quakes last night. Also, there was a 5.0 off the coast of Taitung about an hour ago.

Didn't notice anything unusual here last night, though dogs were barking a lot before the 6.0 last week. However, i have to say the dogs bark a lot around here anyway.

This is an unusual location for a quake:

Find quake info at http://www.cwb.gov.tw/V7e/earthquake/Data/quake/EE0214130838030.htm.

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