Pictorial 4 : Timing and Displacement of the Most Recent Surface Faulting on the Hatano Fault of the Median Tectonic Line Active Fault System, Southwest Japan
Pictorial 4 : Timing and Displacement of the Most Recent Surface Faulting on the Hatano Fault of the Median Tectonic Line Active Fault System, Southwest Japan
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图 4：日本西南部正中构造线活动断层系波多野断层最近一次地表断层的时间和位移
DOI：
10.5026/jgeography.112.4_plate7
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发表时间：
2003
影响因子：
3.1
通讯作者：
S. Toda
中科院分区：
文献类型：
--
作者：
H. Goto;H. Tsutsumi;S. Toda
日本中部构造线活动断层系统（MTL）是日本最活跃的内陆断层之一，其平均滑动速率高达5-10 mm/a。然而，由于缺乏古地震学数据，特别是与最近的地表断层活动有关的时间和位移，人们对MTL的长期地震危险性知之甚少。我们在爱媛县土井町的波多野断层上进行了一次海沟挖掘调查，能够精确地确定最近的断层活动的时间。调查地点位于冲积扇上0.8米高的面向山脉的断层崖之间。我们首先在断层上挖掘了两条沟，以精确定位断层痕迹。断层切割全新世沉积物暴露在每个沟槽的两侧。断裂带的视位移方向是向南的，这与沟址周围的断层陡坎相一致。然后，我们挖掘了两个平行于断层带的沟，以揭示与过去地震有关的水平位移的地层证据。沟壁上暴露的沉积物包含了过去3500年B. P.发生的两次断层活动的证据。最近一次沿波多野断层沿着的地表断层活动发生在公元1520 cal A.D和1660 cal A. D之间。这是第一次古地震学数据，限制MTL最近断层事件的时间。根据古河道存款的偏移量，我们估计在最近的断裂事件中，向北的右旋位移为2.5 ± 0.5 m，垂直位移为0.3-0.5 m。
The Median Tectonic Line active fault system (MTL), with an average slip rate as high as 5-10 mm/yr, is one of the most active inland faults in Japan. However, the long-term seismic risk of the MTL has been poorly known, because of insufficient paleoseismological data, especially timing and displacement associated with the most recent surface faulting.We carried out a trench excavation survey across the Hatano fault in Doi town, Ehime Prefecture, and were able to precisely determine the timing of the latest faulting event. The survey site is located between range-facing fault scarps level 0.8 m high on an alluvial fan. We first excavated two trenches across the fault to precisely locate fault traces. Faults cutting Holocene sediment were exposed on both walls of each trench. The sense of apparent displacement across the fault zone is down to the south, which is consistent with fault scarps around the trench site. Then we excavated two trenches parallel to the fault zone to expose stratigraphic evidence of horizontal displacement associated with past earthquakes.The sediment exposed on the trench walls contains evidence of two faulting events in the past 3500 years B.P. The most recent surface faulting along the Hatano fault occurred between 1520 cal A.D and 1660 cal A.D. This is the first paleoseismological data that precisely constrain the timing of the most recent faulting event of the MTL. We have estimated 2.5 ± 0.5 m right-lateral displacement and 0.3-0.5 m vertical displacement up to the north during the most recent faulting event based on an offset of paleo-channel deposit.