Tuesday, April 12, 2011

Faults and Plates

I’m not an expert of earthquakes, but ZACL has mentioned fault, so I decided to write this blog. First, I live in Yokohama, but about six months a year, I live in San Dimas, California which is close to famous San Andreas Fault. I don’t know how close it is though. According to my digital Britannica, the total movement along the fault during the last few million years appears to have been several miles. There are many faults all over Southern California, so we cannot avoid all.

About Plates, please see the attached photo and find two red arrows toward the bottom.
The left arrow is the Philippine Plate. The right arrow is the Pacific Plate. On March 11th, the Pacific Plate pushed the Land (Japan) Plate and caused the 9.0 earthquake. “X” was the epicenter.

On the photo, above left shows a cross section of the plates, and downward movement of the Pacific Plate (see red arrows), pushing the Land Plate upward. The red dot shows the point the earthquake occurred.

Yearly, according to Asahi, in the western Japan, the Philippine Plate moves 4 to 5 cm, and in the eastern Japan, the Pacific Plate moves 8 to 9 cm toward the bottom of the Land Plate. So, all these movements have been piling up over the years, and sometimes, this stress causes earthquakes.

After 9.0 erupted on March 11th, so far, five aftershocks of above 7.0 already occurred. Experts have said this trend will continue in a diminishing way for six months to a year, but it is still possible to have 8.0. Last few days, I felt three pretty big jolts. In Yokohama, they were 3 and 4, but in the northeast, they were 7.1 and probably 6 and high 5. It’s so many, it’s hard to keep track.

This morning, I was walking toward a commercial building and saw a worker filling a crack with cement next to a wet concrete corner of the foundation. I chatted with him for a while. The building had three or four cracked glass panels after the earthquake, but they were already fixed.

It must have cost the owner a lot of money to fix all that. Concrete buildings withstood the tsunami, but for smaller earthquakes like magnitude five or so, concrete buildings probably cost a lot of money to fix cracks. So far, I see wooden houses and apartments have survived with almost no problem for magnitude 5 or 4.


kristieinbc said...

You must be very used to earthquakes since you spend your time living in two different earthquake zones! Has this earthquake made you feel more uneasy about living in such hot spots?

keiko amano said...


LOL. Yes, I live in two hot spots, but not at the same time!

It was right after the Northridge earthquake, I was in Triangle Park, North Carolina. I was taking an IBM class. Our class went to dinner and talking about the earthquake. I guess nobody experienced eathquake in their lives. So, I told them it was quite common in Japan, and I lived close to San Andreas Fault which is the major fault. Boy, all their faces looked terrified. I guess I scared them.

ashok said...


Do you go under a table or bed when there is an earthquake or run outdoors?

keiko amano said...


On 3/11, I was in a sushi bar. It shook more than I ever felt and for more than two minutes, so after a minute or so, I ducked my head and sat under the counter. I wrote about the experience in "Earthquake." Peple here always stay calm and don't seem to do anything. Throughout my life, my mother never hid herself when earthquake came. It came quite often. Almost every vacation I came home to Japan, I had one earthquake, but we never went under our table or went outside. That 9.0 was probably about 6 in Yokohama. That was the largest I've ever experienced in my life.
When an earthquake happens, it's best to stay indoor and go under a strong desk or table because you might get hit by some kind of debris. Do you get earthquakes in India? Did Sumatra earthquake affect your country?