Earthquake Spectra

The 23 October 2004 Niigata Ken Chuetsu, Japan, earthquake ( _Mw =6.6) was the most significant earthquake to affect Japan since the 1995 Kobe earthquake, killing 48 people and injuring 4,160. Hundreds of major landslides destroyed entire upland villages and, together with permanent ground deformations, caused extensive damage to roads, rail lines and other lifelines, resulting in major economic disruption and an estimated cost of U.S. $40 billion. Two reconnaissance teams supported by EERI surveyed the earthquake damage soon after the event, employing new technologies such as handheld global positioning systems, satellite imagery, and light detection and ranging, which facilitated more rapid and detailed data collection than was possible in previous earthquake damage surveys.

The Niigata Ken Chuetsu earthquake was a shallow, moderate-sized event producing strong shaking and considerable land failure damage across a significant region of Niigata Prefecture in central Japan. Moment tensor solutions indicate the main shock as being pure reverse faulting on a fault striking 30° east of north, roughly parallel to the mapped active faults and to the structural trends of the region, with nodal planes that dip down to the west at about 50° and down to the east at about 40°. The main shock was followed by an unusual number of large aftershocks. An extensive field investigation identified only minor surface faulting. Hanging wall effects accompanied by unusually high accelerations were observed, with peak horizontal accelerations of 1.75 g recorded at Tohkamachi and 1.33 g recorded at Ojiya.

The Niigata Ken Chuetsu earthquake induced significant geotechnical and geologic failures throughout the affected region. The most prevalent geotechnical observations from this earthquake are related to ground failure, including landslides in natural ground, failures of highway embankments and residential earth fills, and limited liquefaction in alluvial deposits. The absence of considerable levee deformations and surface faulting was noted. This paper documents the geotechnical aspects of the Niigata Ken Chuetsu earthquake as related to earth structures, liquefaction, and surface faulting; landslides are discussed in an accompanying paper.

The Niigata Ken Chuetsu earthquake triggered a vast number of landslides in the epicentral region. Landslide concentrations were among the highest ever measured after an earthquake, and most of the triggered landslides were relatively shallow failures parallel to the steep slope faces. The dense concentration of landslides can be attributed to steep local topography in relatively weak geologic units, adverse hydrologic conditions caused by significant antecedent rainfall, and very strong shaking. Many of the landslides could be discerned from high-resolution satellite imagery acquired immediately after the earthquake.

The 23 October 2004 Niigata Ken Chuetsu, Japan, earthquake ( _Mw =6.6) significantly damaged many buildings. Major damage was generally confined to areas where very strong ground motions and/or permanent ground displacement occurred in the epicentral region. Outside this region, however, in Nagaoka about 1,000 buildings were completely destroyed, and almost 50,000 sustained some damage. Closer to or in the epicentral region, Ojiya, Kawaguchi, and Yamakoshi all sustained major building damage, with many traditional Japanese houses collapsing. A newer and larger type of housing specific to the region, which has full-perimeter reinforced concrete walls, generally performed very well. A promptly and widely employed safety inspection program appears to have functioned well.

After landslides, damage to lifelines was the next most notable feature of the 23 October 2004 Niigata Ken Chuetsu, Japan, earthquake ( _Mw =6.6). Roads and highways sustained damage at over 6,000 locations; rail lines, water systems, and wastewater systems sustained major damage; and over 300,000 customers lost electric power. Nagaoka's water supply was disrupted by the failure of electric power, which illustrates lifeline interaction, and Ojiya's water treatment plant almost lost its intake of raw water. Nagaoka's 1,079-km-long water system sustained damage at 287 locations, and Ojiya's 329-km-long water system sustained damage at 102 locations. In 2,672 km of wastewater piping, damage was sustained at over 9,000 locations, with manhole settlement or uplift at over 1,300 locations. The pattern of refugees was strongly influenced by the availability of lifeline services—primarily, electric power.

With the possible exception of the Shinkansen railway, transportation structures for the most part performed well in the Niigata Ken Chuetsu earthquake. There were no collapses. The damage appeared limited and repairable, indicating generally good performance despite the severe ground motions in the epicentral region. The reconnaissance team visited every bridge structure crossing the Uono and Shinano rivers in the epicentral region. All but two of the highway bridges inspected were open for at least limited traffic, and those two appeared to be open for emergency vehicles. Significant damage was observed on the Shinkansen high-speed railway, as well as on some local railway lines, but all appeared repairable. A historic first was the earthquake's derailment of a high-speed Shinkansen train.

The Niigata Ken Chuetsu earthquake reconnaissance provided an opportunity to test several advanced data collection technologies, including light detection and ranging, global positioning system data linked to photos and video, very high resolution satellite imagery, geographic information systems, and Internet map servers. The experience gained showed that these technologies offer the engineering community valuable data both in the field and afterward if properly deployed. Information technology solutions should either aid in the reconnaissance itself or be easy to use in the field. Standards and best practices are needed for deploying advanced technologies within the challenging framework of field reconnaissance.

Following the 23 October 2004 Niigata Ken Chuetsu, Japan, _Mw 6.6 earthquake, LIDAR (light detection and ranging) technology was used to create ultra high-resolution three-dimensional digital terrain models of the earthquake damage. Two reconnaissance teams traveled with tripod-mounted LIDAR that allowed for the rapid collection of post-earthquake failure geometries of ground, structures, and lifelines prior to modification by post-disaster recovery efforts and natural processes, with range accuracies of approximately 2.5 cm and targets illuminated up to 400–700 m from the sensor. LIDAR offers several benefits: (1) detailed failure morphologies of damaged ground and structures, measured remotely and in a way not feasible by conventional means; (2) exploration and visualization of damage on a computer screen is enabled, in orientations and scales that were previously impossible, providing better definition of the failure surfaces, deformation patterns, and morphologies required for understanding failure modes; and (3) archived ultra-high-resolution data for evaluation of analytical and numerical models of deformation. High-resolution images and movies of LIDAR data can be viewed at http://walrus.wr.usgs.gov/geotech/Niigata/ and the online pages of Earthquake Spectra.

The Niigata Ken Chuetsu earthquake struck a mostly rural and mountainous part of Niigata prefecture in Japan. Forty-eight people died, and 551 were severely injured. Over 100,000 people required emergency shelter, and nearly 3,500 households are living in temporary housing. The prefecture government has estimated earthquake damages at 3 trillion yen (about $30 billion), and at least 1,000 workers lost their jobs. The primary issues involve lack of access to rural settlements because of landslides, effects on elderly populations, and the long-term effects on the agricultural economy and lifestyle of the region. Because of extensive landsliding, many communities will also have to face difficult decisions regarding possible relocation or abandonment of their village sites. Based on the experiences of other earthquakes, it is clear that this process will take many years to resolve, and that much of the region will be permanently changed by this earthquake.