M6.7 earthquake hits north of Okinawa

Wow! Okinawa got real lucky this time! 6.7 is not whistling Dixie! If that quake had been closer or heaven forbid right on that main island and at 4 am?? When most people are fast asleep!! I hate earthquakes!!

I live in Nago and was getting ready to get into the shower when I felt my apartment move, sway, and shake twice. The first one I was like "okay stop". It stopped for about two seconds and started again-I was ready to jump back in some clothes and head out the door. Needless to say, I waited about 10 minutes before getting in the shower.

I was sitting in my van after just buying some bananas in the supermarket & my van started shaking from side to side. But after living in the Kanto area for several years this Okinawa earthquake didn't seem so big.The time was 5:11 am

Precursor to something else? Stock your kitchens.

So where's the fault line go?

Pardon my ignorance - are tremors common in the Ryukyus? Are buildings there built to resist earthquakes?

ReformedBasher MAR. 03, 2014 - 09:30AM JST Pardon my ignorance - are tremors common in the Ryukyus? Are buildings there built to resist earthquakes?

I know that many of the buildings are full on concrete to withstand the typhoons that blow through the island chain. I don't know how well those same buildings would hold up against Earthquakes however.

Elbuda - the M scale used in Japan is not the same as the usual Richter moment scale we are more familiar with. There is no simple direct relationship, except that M6.7 is a lot less scary than 6.7 Richter. I am in Naha and it certainly woke me up, but no damage, panic, or sirens. As far as structural design is concerned, it would seem that anything built to withstand a major typhoon can survive a large earthquake, and vice versa.

Steve, no offense but pretty much everything in your comment is scientifically incorrect.

Steve As far as I know M6.7 is Magnitude 6.7 on the Richter Scale. A Japanese 6 (out of a possible maximum of 7) is very, very strong. This one probably wasn't so bad because it was so deep but there is always a tsunami risk of course.

The building code is the same anywhere within Japan so it should have the same strength that was built under the same edition.

@steve The magnitude scale is a unified scale, I believe you are mixed up with the shindo scale. The magnitude scale is the power released at the epicenter where as shindo is the amount of movement at any certain location that was registering. I believe the Richter scale is based on the same logic as the shindo scale.

The building code might be the same, but the knowledge of the construction workers in Okinawa is not to be compared at all.

ANOTHER pretty big one here in Okinawa @ 11:28 am

There was just another one about 2 minutes ago, not as long as the one earlier but shook my apartment pretty good.

@samuraiblue, thanks for the correction. I think the Shindo number in Naha was 3.7

@Weirauch - quite an insulting remark, so you must have facts to back it up.

@edwardw

Thanks for your reply.

Let's hope nothing worse happens in any case. (This article is a little scary http://www.stripes.com/news/experts-okinawa-well-overdue-for-quake-1.211230)

The stresses caused by typhoons and earthquakes on a structure are quite different.

@Steve

Shindo is always expressed in whole numbers, except for upper/lower 5, upper/lower 6. There is no decimal shindo.

It looks like the earlier quake was a shindo 3 in Naha, which is enough to wake you up but won't cause any damage even in an area with poorly constructed buildings.

How can the Richter Magnitude (maximum 9+) and the Japanese M scale (maximum 7) be exactly the same scale????

@nahaman - OMG, you mean pandabelle might have been mistaken? And maybe she was thinking about how timber-frame structures sometimes still used in mainland Japan can resist earthquakes but are more vulnerable to typhoons than reinforced concrete?

In any case, when I see new construction in Okinawa, the concrete and rebar are not spared and new buildings (even 2-story residences) look like they will be here for a long time, come earthquake or typhoon. The tallest building in Okinawa is only 28 stories, IIRC, and most are much lower.

nahaman - the Richter scale and the Moment magnitude scale (MMS) tend to be similar when it comes to measuring medium-sized earthquakes, but they deviate at the upper and lower ends of the scale. Nowadays the size of an earthquake is usually given according to the M scale, though the older Richter scale is still used in some countries, notably Russia.

The Japanese seismic intensity scale (no M) is an indication of the local intensity of the tremor; one earthquake has a single magnitude, but the intensity varies according to the location. For example the first 3/11 quake had a magnitude of 9.0, but the intensity varied from a maximum of 7 (top of the scale) along the eastern coast of Japan to a barely-noticable 1 in far-off Okinawa. And in most of the rest of the world, of course, the earthquake was not felt at all except by machinery set up for the purpose.

@Pandabelle

The stresses caused by typhoons and earthquakes on a structure are quite different.

I was just reading about this a while ago. Agreed, the stresses are different. There seem to be various techniques to counter earthquakes, including dampers. Solid concrete I guess is a mixed blessing. Okay for smaller quakes, but requires strong reinforcement/foundations for larger ones otherwise building will collapse?

I saw the wall behind our kitchen sink the other day. Concrete blocks with large cracks, apparently from the Great Hanshin earthquake. A bit of a worry.

From what I read and was told before going to Okinawa all buildings are built to be typhoon and earthquake resistant.

@steve

OMG, you mean pandabelle might have been mistaken? And maybe she was thinking about how timber-frame structures sometimes still used in mainland Japan can resist earthquakes but are more vulnerable to typhoons than reinforced concrete?

I wasn't mistaken, and I am not a "she".

Reinforced concrete alone can be a very poor choice of building in an earthquake, it needs to be designed to mitigate the seismic forces via dampers, ductile joints, etc. For small houses, sure, no problem.

If I'm not mistaken the primary goal of typhoon resistant construction is to resist penetrative forces - objects moving at a high velocity due to the winds.

The Japanese Shindo scale (1-7) is an analogue of the Modified Mercali scale used internationally (I-XII) - both measure the shaking at a particular location, which corresponds somewhat to the energy released in a quake (measured by the Moment magnitude scale) but not as a direct relationship.

This M6.7 quake is M6.7 regardless of where the measurement took place as that is a measure of the physical properties of the quake. Shindo varies by location and is not a particularly scientific measurement, it's an approximation of the shaking of the quake. So a deep M6.7 quake may result in low shindo shaking, (1-2) but if it's shallower the same quake could produce much higher shaking (shindo > 5-).

Most important for hurricane/typhoon resistance, besides enough strength to resist direct wind force, is maintaining the integrity of the structure so wind does not increase the internal pressure. Flying objects are not a big issue. People here seem to prefer reinforced concrete for that integrity since even roofs can be joined integrally to walls. But it is also amazing that there are still so many flimsily-built postwar houses still standing here. For earthquake, I don't see sliding joints or dampers used but I have not observed any very big buildings going up. It was mentioned that building codes are uniform in Japan, so adding typhoon resistance in vulnerable places like Okinawa must involve cost if not compromise. In small houses the commonly-used grade beams probably offer more protection than footings when the walls have plenty of shear strength. I don't know what Shindo they are designed for, but I do wonder at all the apartment buildings with open ground floor parking.

There are also several aftershock but seems no Tsunami as well. which is very good.

Here is map that i looking at https://dl.dropboxusercontent.com/u/6272985/Photo%20Mar%2003%2C%2012%2002%2045%20PM.png

Oh man, I hope everyone there is doing okay. According to this post there aren't any reports of injuries, hopefully it stays that way and no one gets hurt. <3

A pity it did not hit Tokyo. The ultimate is coming for Shinzo Abe.

but everything in Japan are earthquake proof.I have been in Japan it s very safety wen there is a earthquake.