Geological Setting
Hokkaido is Japan’s northernmost and least developed island. The USGS website says that, “the preliminary location and focal-mechanism of this earthquake imply that it occurred as the result of thrust-faulting on the plate interface between the overriding North American plate (which extends into the north- east corner of the Eurasian landmass) and the subducting Pacific plate.”
It was a Magnitude 8.0 quake happening around 5:00 a.m. on Septem ber 26, 2003. About an hour later there was another at about Magnitude 7.1. It affected a 400 km-wide area along the southern coast of the island.
Both the USGS and the EERI sites describe the importance of the area’s history for magnitude 8.0+ earthquakes. There have been three in the same southern area in the last 50 years. Historical evidence from a quake in 1952 shows that some slip distribution happened along the same fault segment.
Landscape and Infrastructure
The first quake caused some tsunamis along the southern coast. The EERI website says that, “despite the large magnitude and high PGA levels, the observed ground failure, liquefaction, and structural, port, and lifeline damage were remarkably minimal.” They report that the hypocenter was located at latitude 41.9° north and longitude144.1° east, at a depth of 42 km.
Damages such as liquefaction and landslides were localized and minor for the most part. The earthquakes did cause embankment and fill failures which “produced cracks, slumps, and in some cases lateral spreads accompanied by sand boils, indicat ing an association with soil liquefaction.
These failures were most common in deep fills that had been constructed to provide a smooth grade for roads passing from valley bot toms to adjacent upland areas. Locally, such fill and embankment failures caused significant damage, especially to roads.” (EERI) I found someone’s personal website with photos after the earthquakes which show the road damages. Unfortunately the website was in Japanese so I don’t have information to the exact location of the photos (see below).
Human Impact
There is conflicting information about the number of deaths attributed to this quake. Some sites say none, others say anywhere from 2-10. There were some fishermen who disappeared in the tsunami, and some cars that were thrown into the water near a port. Otherwise there are just reports for injuries which also ranged from 300-500.
Phone lines and electricity managed to escape the earthquake relatively unharmed. The main problem was damage to sewer systems. Manholes were displaced and lifted up by a few meters. The EERI site says that, “In all cases, the uplift appeared to be related to liquefaction of the pipeline backfill material, and damage was aligned with the layout of the pipe network.”
http://news.bbc.co.uk/2/hi/in_depth/photo_gallery/3142916.stm
http://www.daisuki-tokachi.net/harunirephot/2003-9-26-jisin.htm
Hokkaido is Japan’s northernmost and least developed island. The USGS website says that, “the preliminary location and focal-mechanism of this earthquake imply that it occurred as the result of thrust-faulting on the plate interface between the overriding North American plate (which extends into the north- east corner of the Eurasian landmass) and the subducting Pacific plate.”
It was a Magnitude 8.0 quake happening around 5:00 a.m. on Septem ber 26, 2003. About an hour later there was another at about Magnitude 7.1. It affected a 400 km-wide area along the southern coast of the island.
Both the USGS and the EERI sites describe the importance of the area’s history for magnitude 8.0+ earthquakes. There have been three in the same southern area in the last 50 years. Historical evidence from a quake in 1952 shows that some slip distribution happened along the same fault segment.
Landscape and Infrastructure
The first quake caused some tsunamis along the southern coast. The EERI website says that, “despite the large magnitude and high PGA levels, the observed ground failure, liquefaction, and structural, port, and lifeline damage were remarkably minimal.” They report that the hypocenter was located at latitude 41.9° north and longitude144.1° east, at a depth of 42 km.
Damages such as liquefaction and landslides were localized and minor for the most part. The earthquakes did cause embankment and fill failures which “produced cracks, slumps, and in some cases lateral spreads accompanied by sand boils, indicat ing an association with soil liquefaction.
These failures were most common in deep fills that had been constructed to provide a smooth grade for roads passing from valley bot toms to adjacent upland areas. Locally, such fill and embankment failures caused significant damage, especially to roads.” (EERI) I found someone’s personal website with photos after the earthquakes which show the road damages. Unfortunately the website was in Japanese so I don’t have information to the exact location of the photos (see below).
Human Impact
There is conflicting information about the number of deaths attributed to this quake. Some sites say none, others say anywhere from 2-10. There were some fishermen who disappeared in the tsunami, and some cars that were thrown into the water near a port. Otherwise there are just reports for injuries which also ranged from 300-500.
Phone lines and electricity managed to escape the earthquake relatively unharmed. The main problem was damage to sewer systems. Manholes were displaced and lifted up by a few meters. The EERI site says that, “In all cases, the uplift appeared to be related to liquefaction of the pipeline backfill material, and damage was aligned with the layout of the pipe network.”
http://news.bbc.co.uk/2/hi/in_depth/photo_gallery/3142916.stm
http://www.daisuki-tokachi.net/harunirephot/2003-9-26-jisin.htm
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