Despite its considerable magnitude the earthquake caused only localised light to moderate structural damage in Chiba, owing in part to Japan's advanced
earthquake engineering. The most significant effects occurred in Chōshi and
Katori cities, where a few walls collapsed and several buildings sustained damage. In
Funabashi city an elderly resident suffered a fatal heart attack during the quake, and a falling object caused one minor injury in
Kisarazu city.[5][6]
Background
A seismically volatile country, Japan frequently experiences natural disasters such as earthquakes, volcanic eruptions and tsunamis.[7] The entire archipelago forms a part of the
Pacific Ring of Fire, a massive belt of volcanoes and
trenches.[8] The largest of the islands,
Honshu is characterised by numerous
inland fault systems and large
subduction zones which are a result of the interaction between several
tectonic plates.[9] At the junction of the continental
Okhotsk Plate and the oceanic
Philippine Sea and
Pacific plates lies the populous
Kantō Region, which has had a long history of devastating earthquakes.[10]
Situated on the
Bōsō Peninsula in eastern Kantō, Chiba Prefecture is surrounded by a region of complex tectonic settings.[11] To the south the Philippine Sea Plate is subducted beneath Okhotsk Plate creating the offshore
Sagami Trench; the Pacific Plate subducts the region from the east, forming the
Japan Trench.[12] Despite this Chiba Prefecture has experienced relatively little effects from earthquakes.[13] Since 1923 most events have occurred well offshore, within the magnitude 5.0–6.0 Mj range, at somewhat shallow
focal depths.[14] The most significant earthquake, known as the
1987 Chiba-ken Toho-oki earthquake, occurred on 17 December 1987.
^千葉県東方沖を震源とする地震(確定報)(PDF) (Report) (in Japanese). Fire and Disaster Management Agency. 15 March 2012. Archived from
the original(PDF) on 19 April 2012. Retrieved 29 March 2012.
^"2: The Geology and Tectonics of the Tohoku Region". Development of Methodologies for the Identification of Volcanic and Tectonic Hazards to Potential HLW Repository Sites in Japan: The Tohoku Case Study (Report). Nuclear Waste Management Organization of Japan. March 2009. NUMO-TR-08-03.