Date: Mon, 26 Mar 2001 22:24:37 +0900
From: Koji Okumura 
Subject: [eq-geo-net 184] Akinada (Hiroshima) Earthquake of March 24
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Dear all:

Here is information on the March 24 2001
Akinada (Hiroshima) Earthquake.

Epicenters of aftershocks and historic earthquakes
together with quaternary faults are show in:
http://home.hiroshima-u.ac.jp/~kojiok/akinada.jpg
Several earthquakes have occurred in south of Hiroshima
in the past 300 years.  The activity here is
distinct compared with the surrounding quiet areas.

Tectonics:  The hypocenter is in the subducting
slab of the Philippine Sea Plate.  Trench-parallel
extension may not be very common in subducting plate.
However, tearing of the slab into portions with
different dip may associate normal faults.  Anyhow,
we do not know the shape of the slab very well.

The Headquarters for Earthquake Research Promotion
Home Page prepares some information.

http://www.jishin.go.jp/main/chousa/01mar2/p05.gif
   by National Research Institute for Earth Science and
      Disaster Prevention:  on slab shape

http://www.jishin.go.jp/main/chousa/01mar2/p04.gif
   by Geographical Survey Institute on GPS results.

Damage: 2 killed and a few hundred were injured.
Structural damage is not severe except for
very old wooden houses and unstable structures
on steep slopes.  We (Nakata, myself and
graduate students) surveyed cemeteries to
see toppled tombstones.  However, there are
only minor twist or offset of stones.  Toppling
occurred only on very unstable fill.

Liquefaction: The areas surrounding the epicenter
are not prone to liquefaction due to the lack of
alluvial lowland.  We observed only one small-scale
sand blow on a filled ground.  Fairly extensive
liquefaction is reported in souther part of
Hiroshima city.  Hiroshima is located on a alluvial
lowland of delta and most of coastal area is
reclaimed.  The liquefaction presumably took place
in the reclaimed area.  Details are not studied yet.

Source Process:

http://wwweic.eri.u-tokyo.ac.jp/yuji/Aki-nada/