Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake

Approximately one year after the Great Hanshin (Kobe) Earthquake, two New Zealand geologists were invited to help with the Geological Survey of Japan's paleoearthquake/active fault studies in the Kobe/Awaji area. Trenches excavated across the Nojima fault, which ruptured during the Great Hanshin Earthquake, showed evidence of past surface rupture earthquakes, with the age of the penultimate earthquake estimated at approximately 2000 years. A trench across the Higashiura fault, located 3-4 km southeast of the Nojima fault, revealed at least two past surface rupture earthquakes. The timing of the older earthquakes is not yet known, but pottery fragments found in the trench constrain the timing of the most recent earthquake at less than 500-600 years. Historical records for this part of Japan suggest that within the last 700 years there has been only one regionally felt earthquake prior to the 1995 Great Hanshin Earthquake, and this was the AD 1596 Keicho Earthquake. It thus seems reasonable to suggest that the Higashiura fault was, at least in part, the source of the AD 1596 Keicho Earthquake.

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Distribution of fault rocks in the fracture zone of the Nojima Fault at a depth of 1140 m: Observations from the Hirabayashi NIED drill core

Island Arc ◽

10.1046/j.1440-1738.2001.00339.x ◽

2001 ◽

Vol 10 (3-4) ◽

pp. 411-421 ◽

Cited By ~ 23

Author(s):

Kenta Kobayashi ◽

Satoshi Hirano ◽

Takashi Arai ◽

Ryuji Ikeda ◽

Kentaro Omura ◽

...

Keyword(s):

Fracture Zone ◽

Drill Core ◽

Fault Rocks ◽

Nojima Fault

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Fault rocks and past to recent fluid characteristics from the borehole survey of the Nojima fault ruptured in the 1995 Kobe earthquake, southwest Japan

Journal of Geophysical Research Atmospheres ◽

10.1029/2000jb900086 ◽

2000 ◽

Vol 105 (B7) ◽

pp. 16161-16171 ◽

Cited By ~ 62

Author(s):

Tomoyuki Ohtani ◽

Koichiro Fujimoto ◽

Hisao Ito ◽

Hidemi Tanaka ◽

Naoto Tomida ◽

...

Keyword(s):

Southwest Japan ◽

Fault Rocks ◽

Kobe Earthquake ◽

Nojima Fault ◽

Fluid Characteristics

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Tree-ring response to the 1995 M<sub>w</sub> 7.2 Kobe earthquake, southwest Japan

10.5194/nhess-2017-381 ◽

2017 ◽

Author(s):

Sujian Lin ◽

Aiming Lin

Keyword(s):

Tree Rings ◽

Lateral Displacement ◽

Fault Scarp ◽

Fagus Crenata ◽

Southwest Japan ◽

Fagus Crenata Blume ◽

Kobe Earthquake ◽

Seismic Fault ◽

Beech Tree ◽

Nojima Fault

Abstract. The 1995 Mw 7.2 Kobe earthquake produced an ~ 18 km-long surface rupture zone with a maximum right-lateral displacement of ~ 1.8 m along the pre-existing active Nojima Fault in southwest Japan. Field investigations showed that the co-seismic surface ruptures caused severe damage to trees, some of which survived the disaster during the past twenty years along the co-seismic fault scarp. Analysis of tree-rings from the trunk of a 46-year-old Beech tree (Fagus crenata Blume) revealed that the tree was cracked by earthquake-induced damage and that the tree-rings grown during the five-year period after the 1995 earthquake become sharply narrower in width compared to those grown before the earthquake. Our findings indicate that the earthquake damaged trees along the co-seismic fault scarp and hindered the growth of tree-rings by severing the roots. Thus, the results support the idea that older trees growing along or around fault zones can be used for identifying seismic fault events and for dendrochronological studies related to geomorphological processes.

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