Preliminary Reconnaissance : The 2004 Mid Niigata Prefecture Earthquake

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0.1 th edition : 2004-10-28
0.0 th edition : 2004-10-27

Notice : This is a preliminary report. Please note that this might include erroneous information or misunderstanding. Following report is made based on the opinion of the author, Riki Honda, and it does not necessarily reflect those of the Disaster Prevention Research Institute, Kyoto University.
Let us emphasize that our report is preliminary and does not cover all serious damages. There have been many strong aftershocks and they are worsening the situation. For further information, refer to the information provided by newspapers etc, too.

Introduction

On October 23, 2004, at 5:56pm (8:56 p.m. GMT), a huge earthquake with a magnitude of 6.8 in JMA Magnitude (Japan Meteorological Agency Magnitude) hit the Mid Niigata area in Japan. In Ojiya City, Niigata prefecture, Shindo (JMA seismic intensity scale) hit 6+ (ouf of 7). The JMA named the earthquake "The Mid Niigata Prefecture Earthquake in 2004." As of the morning of October 27th, thirty-one were killed, more than 2,200 were injured and more than 100,000 people were in evacuation, according to the report.

We departed for Niigata 6 hours after the earthquake and started our preliminary site investigation 12 hours after the earthquake had occurred. Following is a brief report of our reconnaissance.

Date : October 23rd to 25th. (Reconnaissance was held on 24th.)
Members :
- SAWADA, Sumio (Associate Professor, DPRI, Kyoto University) : Leader of the team.
- TAKAHASHI, Yoshikazu (Assistant Professor, Dept. of Urban Management, Kyoto University.) (His report is also available here, but only in Japanese.)
- HONDA, Riki (Assistant Professor, DPRI, Kyoto University.)

Note : figures in [ ] denote pictures listed below each paragraph.

Damage Reports

Kashiwaza City and Oguni Town :

We arrived at Kashiwazaki City in the early morning of October 24th, 2004. The area was still suffering from blackout and most traffic lights were not working. The store facing the Route 8 was in business but without electricity supply.
On the Route 291, between Kashiwazaki City and Ojiya City, some manholes rose out of the ground. In the Nanokamachi Town, the slope collapsed [2112], and road surface subsided inequally, causing gaps as high as one meter [2105, 2106, 2110]. There were many similar road subsides in many places in Ojiya City. Landslide occurred on the slope on the south of the route [2104]. Liquefaction induced the sand boiling at the foot of the slope [2103].
Ojiya City (near the Ojiya Exit of Kan-etsu Expressway)

The Sakuramachi Bridge, the bridge of Kan-etsu Expressway, striding over the Route 291, had its girder collide lightly with the top of the abutment [2115]. The liquefaction-induced sand boil left its trace [2119] at the foot of the pier. Apparently, no damage was observed with the support [2116].

At the toll gate of Ojiya Exit, which was closed due to the damage of the Kan-etsu expressway, the road surface had minor damage [2124]. The house in front of the gate suffered severe damage. The first (ground) floor was totally crushed [2121, 2122] and its rock-made fence was destroyed [2123]. Some other houses and buildings in the neighborhood were also damaged. For example, a house had its ceramics-made roofing tiles ("Kawara" in Japanese) severely damaged [2128].

Almost all tomb stones fell down [2117, 2118] in the garden of the stone store located about 100m in the west of the Sakuramachi Bridge. Different stones fell in different directions and no clear trend was seen in the falling direction, which suggests that the ground motion did not exhibit strong directivity (in this site). The store itself was not severely damaged. It indicates that the ground motion might have been large in the high frequency component.
Ojiya City (incl. Motomachi Town, Honmachi Town and Wakaba District)

Several manholes were raised due to the liquefaction of the surrounding ground [2147, 2149]. (We were hit by quite a strong aftershock when we were studying these manholes. Horrifying experience.) The liquefaction caused the tilt of the electric poles [2151] and traffic lights [2150] in several places. The cut electric cable put the car in the trouble [2152]. Another car was left at an awkward position because the ground subsided leaving the manhole unsunk [2993].

In Hon-machi Town, the Futaara-Jinja Shrine had its gates and other ornaments severely damaged. [2194, 2195]

The route 291 was blocked because of the gap of as high as 1m [2137] and it prevented us from visiting Kawaguchi City.
K-Net Ojiya Observation Station

K-net is the strong observation network covering the whole nation of Japan with high density. For further information, visit their website. The peak acceleration recorded at the Ojiya observation station [2197] (map) exceeded 1,500 gal and its strong motion has the JMA seismic intensity of 7, the severest level.
The observation site is in the middle of the flat area. There are a school ground in the north-west [2200], a small paddy field in the south-west [2202], and a school gym in the north-east direction. Judging from the fact that it is next to the paddy field, the ground might be quite soft, which could have affected the strong motion records.

Near this site, some manholes were raised [2201, 2205]. There was a car left upside-down [2204], near one of the raised manholes. (There was a scarce track on the road connecting the car and the manhole. I guess that the car hit the raised manhole and turned over.)
In the vicinity of this site, some houses seemed to be undamaged [2206, 2209] and some were damaged [2210, 2203]. The Jigenji temple, which is also located near the observation site, was damaged [0089, 0090] and most of the tomb stones in the temple garden fell down.
~~Nagaoka~~ Ojiya City (neighborhood of the ~~Nagaoka~~ Ojiya Station)
(Corrected. Thanks to Prof. Shimomura, Nagaoka University of Technology.)

In the mall near the ~~Nagaoka~~ Ojiya Station, the surface of the road was not severely damaged [2133]. However, many stores suffered various types of damage, including pier collapse [2134] and fall-off of the wall [2131]. Most of the shops that had no external damage also suffered various damage inside, such as scattering of the goods, or fall of the shelves. (We did not take pictures of the inside of the damaged houses or stores, to pay respect to the feeling of the owners.)
Shinkansen, or Super Express Train, Derailed near Tokamachi Town.

The Super Express Train (Shinkansen) derailed due to the strong shake of the earthquake[2179]. There were some damages on the piers located 10 to 100m away in the north direction from the derailed point [2183, 2185, 2186, 2188, 2189, 2191]. The tag on the pier says their construction started in 1977 and finished in 1979.

Liquefaction occurred at the foot of the piers which were 10 to 20m away in the north direction from the above-mentioned piers, and the boiled sand reached 70 to 90cm [2162, 2159, 2160]. The gap between the pier and the ground indicates the large displacement the pier experienced [2157, 2158, 2161].

On the top of the wall-type pier, which was just under the derailed cars, there was a fall-off of concrete pieces.

Although the piers were damaged as described above, I believe that these were not the reason of the derailing of the train. Their performance was well acceptable because they survived such a strong earthquake with relatively small damage.
Ojidaya Ohashi Bridge

The Ojidaya Ohashi Bridge on the Route 17, striding over the Shinano (River), had one of its piers damaged, the second from the south-east end [2139]. The concrete fell off on the side facing the north-east to south-east direction [2140]. The X-shaped crack was found on the south-west side [2143]. The gap between lateral bars was about 20cm [2142].
Embankment near the Yoita Bridge

The embankment near the Yoita bridge had several cracks which were 10 to 40cm wide, 1.5 to 2.0m deep [2215, 2217], and several tens of meters long [2214]. Some part of the embankment settled and lost its original height.

Closing Remarks

Thank you for reading up to here. If you have some comments, corrections or questions, please make contact to :

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Acknowledgments

The reconnaissance was conducted under the great leadership of Prof. Sawada, (DPRI, Kyoto Univ.) and with great support of Prof. Takahashi (Dept. Urban Management Engng., Kyoto Univ.). They also contributed some pictures shown above.

-- Riki Honda. All rights reserved. 2004.