Preliminary Observations on the Tokachi-Oki, Japan, Earthquake of September 26, 2003

EERI Special Earthquake Report — December 2003

Learning from Earthquakes

EERI dispatched a reconnaissance The earthquake was the third mag- an apparently anomalous recording team to Hokkaido, Japan, within nitude 8.0+ to strike the southeast- at the Hiroo City Hall, behind the days of the earthquake. The EERI ern portion of Hokkaido in the last bluff overlooking the nearby Port of team was composed of Scott Ash- 50 years. The earthquake hypocen- Tokachi (~0.45 g). Acceleration re- ford and Yohsuke Kawamata from ter was located at latitude 41.9° sponse spectra for Hiroo and Toma- the Department of Structural Engi- north and longitude144.1° east, at a komai are presented in Figure 2. neering at the University of Califor- depth of 42 km. The slip distribution nia, San Diego, and Robert Kayen inverted from seismograms shows The low damage levels are not fully of the Coastal and Marine Geology this was a rupture of the same fault understood, but may be associated Unit of the United States Geologi- segment as that of the 1952 Toka- with the unusually high frequency of cal Survey (USGS). The EERI team chi-Oki M8.2 quake. Both events the major loading cycles. Ground was joined by David Keefer of the were megathrust earthquakes that motion durations were typical of an USGS, Albert (Keh-Jian) Shou of resulted from segmented rupture of M8 event. In the southeastern coast- the National Chung-Hsing University the Pacific plate beneath the Hok- al areas close to the rupture, signifi- in Taiwan, and Takanori Arimura of kaido-Tohoku accretionary prism. cant loading (>0.05g) had durations Kobe University in Japan, who in- ranging from approximately 1.5 to 3 vestigated landslides. Takahiro Seismological Aspects minutes. On the Japanese Shindo Sugano of the Port and Airport Re- intensity scale, the region from Ura- search Institute (PARI) guided the Accelerations recorded by seismic kawa west of Erimo peninsula to Ku- team in assessing the performance networks of Hokkaido indicate a re- shiro felt intensity 5-6; other portions of port facilities. The cooperation of gion of high-intensity motion from the of Hokkaido and northern Tohoku, PARI is gratefully acknowledged. Hiroo area to Kushiro City, with PGA Honshu felt motions of intensity 2-4. The reconnaissance effort was par- values in the range of 0.35 to 0.6g tially supported with funding from the (Figure 1). The highest PGA (1.0g) is National Science Foundation under grant # CMS-0131895, as well as by the Pacific Earthquake Engineering Research Center and the USGS.

Introduction The primary M8.0 tremor occurred at 4:50 a.m. local time on Septem- ber 26, 2003, and was followed by a M7.1 tremor at 6:08 a.m. The quakes affected a 400 km-wide area along the coastal areas of southern and southeastern Hokkaido Island. Both events triggered ground failures. The primary event produced tsunami run-ups along the shoreline of southern Hokkaido that reached maximum heights of 4 meters in the areas of Taiki and Erimo. However, despite the large magnitude and high PGA levels, the observed ground failure, liquefaction, and structural, port, and lifeline damage Figure 1. Observed effects of the earthquake. Peak ground accelerations were remarkably minimal. and tsunami wave run-up heights as reported by JMA, PARI, and other orga- nizations.

1 EERI Special Earthquake Report — December 2003 EERI Special Earthquake Report — December 2003

sourced from existing scars where such activity had clearly originated in the past as well. The earthquake caused several embankment and fill failures in the region around Toyoroko. These failures produced cracks, slumps, and in some cases lateral spreads accompanied by sand boils, indicat- ing an association with soil liquefac- Figures 2a and b. Acceleration response spectra for ground motions recorded at (a) Hiroo at 5% damping, and (b) Tomakomai at 5% damping. tion. These failures were most com- mon in deep fills that had been con- structed to provide a smooth grade Liquefaction Rivers, but no evidence of liquefaction was observed. for roads passing from valley bot- Liquefaction was observed over a toms to adjacent upland areas. broad geographic region, from Sap- Locally, such fill and embankment poro to Kitami, though it was quite Landslides failures caused significant damage, dispersed and localized. In addition, Reconnaissance carried out from a especially to roads. it was almost exclusively limited to fixed-wing aircraft, as well as by man-made fills. Locations where liq- automobile and foot, failed to yield Tsunami uefaction was observed are shown evidence of much significant land- on Figure 1. In farming country in slide activity on natural slopes. The The main shock produced coseismic northeastern Hokkaido, approxi- only known incident was a rock fall uplift of the seafloor southeast of the mately 10 km northeast of Kitami of a few hundred meters total vol- Hiroo Peninsula, generating a tsuna- City, four large ground failures oc- ume that was reported from a steep mi with shoreline wave heights of 2 curred over a 1 km2 area, the largest slope adjacent to the coastal high- to 3 m in numerous locations, and 4 being 50 m wide and 200 m long. way at Hiroo. However, material m in a few places. Two fishermen in Between 5,000 and 10,000 m3 of from this landslide had been re- Otsu were missing immediately fol- material is estimated to have been moved before members of the re- lowing the tsunami, presumably expelled. Though lateral movement connaissance team arrived at the drowned, and three cars were of the 1.5 m soil cap was limited to locale. Other landslides from natural washed into the harbor at the Port perhaps 1 m, the cap settled nearly slopes observed by the reconnais- of Tokachi. Other than that, the tsu- 3 m as a result of the evacuation of sance team consisted of scattered nami was responsible for very little the underlying sand, which clogged small rock falls, rock slides, and damage. In many cases, the waves drainage culverts for hundreds of debris slides on particularly steep did not exceed the height of the tsu- meters downstream. slopes. These had volumes ranging nami barriers, and in locations were from less than 100 to 10,000 cubic the backland was inundated, it was Sapporo, located approximately meters each, and most were just barely so and damage was light. 200 km from the epicenter, had a recorded PGA of 0.07g. The team observed one isolated incident of liquefaction in the Utsukushigaoka suburb of southern Sapporo. Sev- eral sand boils were observed in the area, a low spot in the surrounding Figure 3. Settle- neighborhood. Seven houses were ment in the damaged from settlement, with the Utsukushigaoka most severely damaged tilted up to suburb of south- 2.5 degrees (Figure 3). Liquefaction ern Sapporo. and structural damage were also observed in Sapporo after the 1968 Tokachi-Oki earthquake. The team visited sites where liquefaction had occurred in the 1968 earthquake, specifically in the Nishi-Naganuma area between the Ebetsu and Yubari

2 3 EERI Special Earthquake Report — December 2003 EERI Special Earthquake Report — December 2003

Of great concern to the Japanese mately 30 m from the wall behind a age overprints unrepaired damage government and tsunami research- paved area. The paved area was from the 1993 and 1994 earth- ers was that many people did not underlain by mixed soil-cement, and quakes. One warehouse at the heed the tsunami warning. Initial it may be that settlement of rubble- south end of the pier suffered severe surveys indicated that perhaps 50% fill beneath the soil-cement mixture, settlements and tilting in all three of the coastal residents ignored the rather than liquefaction, was the earthquakes, yet still remains in op- issued warnings. cause of the observed damage. Di- eration, though it is leaning badly. rectly adjacent to Pier 4 was a well- Performance of Port and instrumented quay wall test section The town of Hiroo hosts the Port of Harbor Facilities to study the behavior of improved Tokachi, and damage in the port and unimproved ground. The 130 and town was relatively minor, even Three major ports were affected by channels of data acquisition, includ- though accelerations as high as the earthquake, but most performed ing pore pressure transducers and 0.6g were recorded. Damage in the very well. The Port of Kushiro was downhole accelerometers, should town was primarily to stucco and the most severely damaged of the provide a wealth of new information plaster in older buildings. Sand boils ports on Hokkaido. It consists of for researchers. were widespread in new areas filled four western piers on the west side hydraulically within the last three of the Kushiro River and several The sections of Piers 1-3 that had years. However, sand boils were eastern piers including the Fisher- undergone improvement performed not observed elsewhere at the port, men’s Terminal. Piers 1 through 3 well. The unimproved areas of Piers where there had been liquefaction and the Fishermen’s Terminal were 1 and 2 suffered 10-15 cm of settle- in the 1993 and 1994 earthquakes. built prior to 1993, and had suf- ment behind the quay wall, and The height of tsunami run-up in the fered liquefaction and structural some signs of liquefaction were port was observed to be 2.5-3 m, damage from the 1993 Kushiro-Oki observed in the interior of both washing three cars and other debris and 1994 Hokkaido Toho-Oki earth- of these piers. Liquefaction and into the harbor, but not causing quakes. Piers 1 through 3, and to smaller settlements of less than 10 structural damage to port facilities. some extent the Fishermen’s Termi- cm were observed on Pier 3. Piers nal, have been improved by stone 1 through 3 were only briefly shut In the west, liquefaction was ob- columns and/or deep cement mixing down for inspection directly follow- served in the Port of Tomakomai, since 1994. All have caisson-type ing the earthquake. One section of but there was no resulting damage. quay walls. Pier 4 with a hybrid caisson-type One oil storage tank was consumed quay wall was closed for one day, by a fire, which is suspected to have Pier 4 was the most heavily dam- then reopened; the rest is closed resulted from strong shaking. aged, with lateral movements of the and will remain so for months. 14 m-deep quay wall of approxi- Lifelines mately 10 cm, and settlements be- Liquefaction and settlements were hind the wall from 60 to 100 cm observed at the Kushiro Fishermen’s By far, the most widespread dam- (Figure 4). Sand boils were ob- Terminal, as well as lateral move- age to lifelines was to the storm and served in an open area approxi- ment of the quay wall; this new dam- sanitary sewer systems. Significant uplift of manholes was reported from Urakawa in the west to Hamanaka in the east. The team observed up- lifts as high as 2 m in Otsu (Figure 5) and dozens as high as 1.5 m in a single subdivision of Shintoyo-Cho, Figure 4. immediately east of Kushiro City. In Pier 4, Port of all cases, the uplift appeared to be Kushiro. related to liquefaction of the pipeline backfill material, and damage was aligned with the layout of the pipe network. Many sanitary sewers had been repaired by the time the team came through.

While damage to roads was not widely reported, the team observed

2 3 EERI Special Earthquake Report — December 2003

though some were subjected to way collapsed after the two columns reduced speeds and lane closures. supporting it failed. The windowed roof observatory of the Taiki Town Northeast of Hiroo, there was dam- Hall collapsed as a result of strong age to two bridges. In the Tomako- shaking. In both cases, no other mai area, the ground motion was just damage was reported in the main over 0.1g, but it was of long duration structures. Other buildings were and dominantly long period motion. damaged by excessive settlement, On the Shizukawa Bridge, the rela- for example, the Urakawa Elemen- tive movement between the abut- tary School, where concrete spalled ments and first piers resulted in sig- on columns after the entrance settled nificant damage to the shear keys (Figure 7). The airport at Kushiro (Figure 6), possibly as a result of was closed for one day due to the pounding. Even so, the bridge did collapse of the nonstructural hanging not collapse and was still in service. ceilings in the control tower and ter- In no case was damage observed minal building. Figure 5. Uplifted manhole near in the columns or at the foundation sewage treatment facility in Otsu. level, but it was concentrated at the Conclusions pier-superstructure connection. This The localized nature of the damage minor damage to Highway 336 be- appeared to be the result of excessive relative displacement, either is striking, considering the relatively tween the Rekifuna and Tokachi high levels of ground shaking caused Rivers. The approach fills to numer- transverse or longitudinal, depend- ing on the bridge. by this earthquake. The performance ous small bridges experienced set- of the Port of Kushiro piers, com- tlement, and many had been patched pared to the failures in the 1993 and with asphalt. Many slumps were also Buildings 1994 earthquakes, is worthy of fur- observed along the shoulder of the Building damage was also observed ther study. This earthquake adds sig- highway, but none large enough to over a large area, but it was localized nificantly to our knowledge base affect traffic. In Chobushi, the team and relatively limited. There was lo- on the initiation of liquefaction, as observed that ground failure on calized damage to the town halls of many of the sites that liquefied in Route 912 had completely closed both Kushiro and Taiki, where re- prior earthquakes did not do so here. the road. This failure appeared to corded PGAs were 0.46g. At Kush- Also of significance is the lack of result from collapse of a prism of iro, the reinforced concrete entrance- response to the tsunami evacuation embankment fill built over a lowland warning. This will certainly lead to and culvert. Most damage to road- additional public education and may ways appeared to be relatively minor affect worldwide disaster planning. and more of a maintenance issue.

There were no reports of power or telephone loss due to the earthquakes, though the team observed severely tilted telephone poles near Kushiro and a severed fiber optic cable on the Tokachi-Kako Bridge, where fill had settled 60 cm relative to the abutment.

Bridges For the most part, bridges performed quite well, with the exception of excessive relative movements between spans that led to shear key damage at the top of several piers, and some settlement of approach fills as noted Figure 6. Damaged shear key from earlier. All bridges were open to traf- the Shizukawa Bridge near Tomako- Figure 7. Damage to Urakawa Ele- fic when the team came through, mai City. mentary School.