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| :::Earthquake Geologic Investigation And Data Bank Compilation On Active Aaults |
The goals of active fault investigation are: (1) Pinpointing the location of a fault; (2) unravelling the
nature of the fault; (3) analyze the rate of activity, and (4) decipher the recurrence period of the fault
so as to mitigate seismic hazards. The main work items for fiscal year 2002 are mainly the Chelungpu Fault,
the Changhua Fault, the Hsincheng Fault, the Hsinhua Fault and the Meishan Fault. Bore hole investigation
conducted on these included: 350 m for the Hsincheng Fault; 864 m for the Chelungpu Fault, 50 m for the
Meishan Fault; and 450 m for the Hsinhua Fault, the sum total is 1714 m. Areas where surficial geologic
investigation was conducted included the Hsincheng Fault and the section between Tachienshan Fault, Chushan
to Changhushan. In addition, trenching and geophysical exploration works were contracted works conducted by
a commercial company.
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| A. |
Hsincheng Fault |
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Surficial geology: Following more detailed surficial geologic investigation the location of the Hsincheng
Fault has been more precisely defined. The result from the current fiscal year combined with past result
rendered better control of the fault trace. In one section of the fault, from Touchienhsi in the north to
the vicinity of the Chungcheng Bridge, the fault extends in a SE direction to Hsiaping, near the north of
Toufeng. Within this length of 16 km, there averaged at least one control point per km extent. Between the
area north of Touchienhsi and Fengshanhsi, however, there is not sufficient evidence to verify an extension
of the HsinchengFault.
Subsurface geology: In fiscal year 2002 5 bore holes were finished: Hsincheng No. 1, to 200m; Hsincheng No.
2, to 50m; Hsincheng No. 3, to 30 - 40m; Hsincheng No. 4, to 30 - 40m; No. 5, to 30 - 40m. Four lines of
seismic survey were also finished.
Observatioin on paleoseismicity aand the rate of sliding: The Hsincheng Fault was originally classified as
Type 2 active fault. New outcrops revealed that the hanging wall was overthrust onto gravels of Terrace
Deposits, and correlating the hanging wall with the footwall idicated that the Hsincheng Fault had been
active at least twice. The fault trace and location have become clearer. The has been under periodical
surveying, as data accumulate, the sliding rate will be clearly revealed.
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| B. |
Chelungpu Fault |
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Surficial geology: The September 21 2000 Chi-Chi earthquake was the result of activity of the Chelungpu
Fault. There was surface rupture extending for over 100 km from Shuangchi, Neiwan in the north to turn west
to Fengyuan, and then due south to Tungtouo, Nantou.
Subsurface geology: In the 2002 fiscal year, four investigation bore holes were drilled, these were: the
Takeng hole on the hanging wall; the Chushan holes, one each on the hanging wall 600 m east of the surface
rupture, and the footwall; and at Tungtou at about 135 m east of the rupture.
Paleoseismicity investigation and sliding rate: Related to this research trenching was conducted at
Chushan, at the Chinese crabapple orchard at Chungliao, at a temple at Wufeng, at the Wenshan Farm, and at
the Central Park in Taichung. Syn-seismic deformation of the Chi-Chi earthquake indicated the south boundary
of the earthquake may extend as far as the Meishan Fault in the southwest, and the Luliao Fault at the
northwwest is also an important boundary.
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| C. |
Meishan Fault |
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Surface geology: The Meishan Fault is an earthquake fault that had been active in 1906. Topographic and
geologic features afforded the judgement that the fault had been under influence of the Chukou Fault and the
Chiuchunkeng Fault. The Chiuchunkeng Fault was designated type 1 active fault, since it cuts across low-level
terrace deposits.
Subsurface geology: Both bore hole and trenching exploration were slated, however, due to objection from
land owner, trenching was abandoned. Mudstone from bore hole core showed shearing, but rather slight, it
was judged that the main fault zone had not been encountered.
Paleoseismicity investigation and rate of sliding: Trenching investigation was performed at the Tapumei
Farm, town of Talin, Chiayi. No sign of faulting was detected.
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| D. |
Hsinhua Fault |
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Surface geology: The Hsinhua Fault was an earthquake fault that was active in 1946. During the Holocene, it
might have been active a number of times.
Subsurface geology: Four bore holes were drilled, signs of faulting were very conspicuous. From seismic
results indicate that after passing through Peishih, the fault might have continued in a northward extent.
Structures formed from sliding were wide, manifesting a wide fault disturbed zone.
Paleoseismicity investigation and sliding rate: In the four trenches excavated for the exploration of the
Hsinhua Fault there were signs of fault displacement of the 1946 Hsinhua Fault. Features indicative of
several past earthquake activities were observed, manifesting occurrences of two big earthquakes in Holocene
time. Investigation during the current year showed evidence that the Hsinhus Fault had three active episodes
in Holocene time. Past investigation indicated that recent activities are mainly creeping.
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| E. |
GIS system on active faults |
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A five-year program "Plan for establishing a data bank on earthquake geology and information on active
faults" was initiated in 2002. The scheduled progress was 5 faults per year, and to conclude detailed
investigation on 25 active faults in the five-year period. To accommodate the vast quantity of data, the
data bank was planned in Arc GIS system.
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