The strike of the C by the
c f
exposures cutting the young sediments (Chen et al., 2005) are located on short lineaments, G2 and G3. Thus, some portions of the Chishan Fault are certainly active
ult. However, we must consider that even in these locations, the fault trace appeared as simple lineament without positive evidence for morphological
ormation.
The fact that the upper part of the Holocene deposits at Loc. 3 is unfaulted m be one reason why we cannot see the morphological expression such as fault scarplet.
This also suggests that the recurrence interval is rather long, more than several thousand years. In any case, the preservation of deformed morphology is surprisingly poor in the mudstone areas. Thus we may miss to trace some of active faults in other very erodible mudstone areas. It is difficult to identify tectonic deformation on othe lineaments, and probably most of the lineaments, parallel to the main part of the Chishan Fault (G1) can be structural relief reflecting different lithology of bedrock, which is related to geologic structure defined by the Chishan Fault, but lineam
y be active trace, because it makes some morphological boundary. One of unsolved problems is if the above-mentioned fault exposures are located on the single trace G1 with curving, or other short lineament G2 or G3. A trace of G1, except the southern margin and northern margin, is very straight, and suggests the Chishan Fault is a high angle reverse fault.
Shyu et al (2005) mapped en echelon arrangement of several segments of the
-2. Activity of the Kaoping River Fault
is an active reverse fault with upthrown side is west and with est-dipping fault plane. Shyu et al. (2005) inferred that the left-lateral component for
ping River. GPS measurement also supports this deformation (Hu et al., 2007
cluding the southern part, where the original tectonic scarp is removed by er
Chesham Fault, each of which is associated with right-lateral offset. Field evidence was not available to confirm the strike-slip mentioned by Shyu et al (2005) and GPS measurement by Hu et al. (2007) from our observation, however.
In the Lingkou Mountains, lineaments are few except for major lineament I and J group, because most of the mountains is underlain by Lingkou Conglomerate and lacks the distinctive alternation of sandstone and mudstone. Instead, landslide densely developed especially on the eastern margin of the mountains or terraces.
IV
We provided the positive evidence to prove that the north-south striking Kaoping River Fault
w
the Kaoping River Fault, judging from apparent offset of mountains on both sides of the Kao
) . We agree with this arrangement of the mountains. However, the Chishan Fault does not necessarily continue straightly. Apparent left lateral slip can be created by shortening of the crust due to reverse fault. No morphologic expression showing left-lateral offset is available from our observation so far. We would like to emphasize that the Kouping River Fault is a reverse fault, which has been activated repeatedly at least during the late Quaternary under E-W compression.
It is difficult to establish the slip rate of the Kaoping River Fault, however, because of several reasons described before. Possible vertical slip rate is an order of several tens cm/ka. The length of the confirmed active trace is only about 5 km, but total length in
osion, will be more than 30 km. This is long enough to be a seismogenetic fault, which is capable to cause large earthquakes of magnitude 7 (Shyu et al., 2005).
IV-3. Relation between the Chishan Fault and the Kaoping River Fault
We have shown that the Chishan Fault and Kaoping River Fault are active faults.
Fig. 13 illustrates the three dimensional picture showing both faults. Two confronting major faults striking north-south have contributed to the formation of tectonic basin of the Pingtung Plain. The oldest terrace, deformed by the Kaoping River Fault, is T2, with possible age of ca.125, 000 years old, and this fault truncates the Chishan Fault which has geologically longer history than the Kaoping River Fault. We can assume that the Kaoping River Fault with west-dipping plane can be branched from preexisted Chishan Fault with east-dipping fault plane. When the Chishan Fault has started the activity after Miocene, stress field might be different from the present-day
E-W compressive stress field, in which present activity of both faults accommodated (Hu et
nd gravel beds, in addit
e ridge and neament in between is characteristic morphology of the study area. We consider that eologic structure and followed by the diffe
al., (2007). Further work is required to interpret the relation between these two active faults.
Better preservation of tectonic morphology on the Kaoping River Fault is originated from that this fault deforms T2 underlain by sand a
ion to its supposed younger origin. In contrast, most of actual fault trace of the Chishan Fault is expressed as a lineament, connecting depression or streams on the shattered zone of the Chishan Fault, even it dislocates younger deposits. Instead, high standing sandstone ridge on the hanging wall and alternation of sandston
li
structural relief, originally derived from g
rential erosion is unique morphology in the Chungliao Mountains area. We must recognize that it is difficult to trace the geomorphic evidence for active fault in the mudstone area where intensive erosion is taken place.
Figure 13. Three dimensional diagrams showing major active faults in the Pingtung Plain and Chungliao Mountains area.
V. Conclusions
1) We have mapped two active faults, the Chishan Fault, striking NNE-SSW and the Kaoping River Fault with N-S trend in the southern Taiwan. Both faults are reverse faults, probably with high angle fault plane. Newly found geomorphic evidence for the i
orphologic expression of the Chishan Fault, oblique to the present shortening direction, is often rather poor, just
xpressed as lineament following the shattered zone. High-standing sandstone ridge f the Chungliao Mountains and several lineaments along the Chishan Fault are dentification as an active fault is the back-tilting of the terrace (lineament a-a’) for the Chishan Fault and east facing flexural scarps limiting the eastern boundary of T2 and T3 for Kaoping River Fault. No evidence for the strike-slip component for both faults is observed.
2) The Chishan fault, created in Miocene time, has longer history than the Kaoping River Fault. Since the present study area is under the E-W compression, N-S trending Kaoping River Fault, which has activated during the last ca. 100,000 years has a better geomorphic expression as prominent east facing flexural scarp.
3) Both faults are probably seismogenetic faults, but the exact amount of offset and slip rate during the late Quaternary are not determined.
4) The Chishan Fault may have multiple traces. M
e o
structural relief following the geologic structure related to the Chishan Fault.
Understanding structural relief and its distinction from the actual tectonic relief is one of the important problems in the area where presence of soft mudstone or alternation of sandstone and shale is predominated
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國科會補助出席國際會議報告
會議中文名稱：美國地球物理聯合會2007秋季 會
議英文名稱：American Geophysical Union (AGU) 2007 Fall Meeting 年
AGU 2007 Fall Meeting Programs AGU 2007 Fall Meeting Abstracts光碟 部份與會人士發表之相關資料
、其他
會議舉辦時間：2007/1
會議舉行地點：Moscone Center, San Francisco, California, U. S. A.
加會議經過
此次會議時間由於鄰近美國耶誕假期，舊金山至台北直飛班機機票均已售 罊，因此取道洛杉磯轉機，增加了不少飛行時間。
metry Chi-Chi Earthquake
an
ces, National Taiwan Univ., Taiwan, R.O.C.
附錄：發表論文摘要(共計四篇)
Ground Displacements and Fault-plane Geo beneath: a case of 1999
(Mw 7.6) at Tsaotun in Central Taiw
Yu-Ting Kuo1, Mong-Han Huang1, Yue-Gau Chen1, Jean-Philippe Avouac2
1 Dept. of Geoscien
2 Division of Geological and Planetary Sciences, Caltech, California, U.S.A.
Abstract
Long-term ground deformation recorded in deformed geomorphic surfaces is
supposed to be the cumulative strain produced by associated active structure and certainly related to the subsurface structure geometry. Moreover, by time domain
the deformation also can be divided into components: co-, post-, and inter-seismic.
A case that may demonstrate the entire process is at Tsaotun in central Taiwan,
where widely developed geomorphic surfaces have long been noticed and surface ruptures of 1999 Taiwan Chi-Chi earthquake (Mw 7.6) ran though. Landform
investigation, geodetic work, sub-pixel comparison of aerial photos, and D-InSAR analysis are conducted to reconstruction the entire deformation process mentioned
abov
tion
rial photographs to obtain detailed horizontal displacement across the surface ult bends beneath greater and more rapid in
coseismic ground displacement cannot tirely match the long-term surface deformation recorded in the geomorphic surfaces.
owever, by the post-seismic ground displacements obtained from InSAR a few other e.
In our previous study, we have used sub-pixel correlation on high-resolu
ae
ruptures, which has revealed that the fa
the southern segment. Nevertheless, the en
H
active structures, such as secondary strike-slip faults, may play a role to e earthquake.
By available co- and post-seismic ground displacements, we successfully rebuild a
sur of
when, wh r. Our
result zation
plan for the
Give a scientific purpose in the title] Interseismic modeling in
Ray Y. Chuang1, M. Meghan Miller2, J. Bruce H. Shyu3, Yue-Gau Chen1
Road, Taipei, 10617, Taiwan
3Department für Geo- und Umweltwissenschaften, Ludwig-Maximilians-Universität
The island of Taiwan lies at the junction of the Eurasian and Philippine Sea
long regarded as one of the major collisional suture zones, to the east and a fault-and-thrust belt to the west across the island. Based on recent published geolo
depth but locked at deeper part in the southern section. In western Taiwan, active accommodate the tentative stress accumulation in a larg
fault-plane model at Tsaotun. Using this model we can satisfactorily explain the
face deformation in different time domain. The model also describe the details ere, and how much the rate of the ground displacements would occu
is undoubtedly valuable to improve the building code and to assist urbani purpose of seismic hazard mitigation.
the Taiwan region
1Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt
2Department of Geological Sciences, Central Washington University, 400 E.
University Way, WA 98926, USA
Munich, Luisenstr. 37, 80333 München, Germany
plates. The convergence between two plates forms the Longitudinal Valley, which has been
gical map and relevant studies, several major active faults are currently acting in Taiwan.
In eastern Taiwan, the Longitudinal Valley fault, the most dominant fault within the suture zone, is locked at the northern section and is creeping at shallow
faults imbricate and propagate to the west above a major Taiwan detachment at
depth. Based on ?, most of the active thrust faults and tear faults in western Taiwan
the locking of the subduction zones along the Ryukyu and Manila Trenches constrain the interseismic deformation across the Taiwan region and accumulate
are locked. The locking and creeping of the active faults around Taiwan as well as
strain which may be released during future earthquakes.
analyze GPS data from 1990-1997 by what?. This time span excludes the effects of
block model across the Taiwan region to quantify kinematically consistent estimates
ibe the GPS velocities and locking The GPS constrained block model provides estimates of present-day fault slip
ial within the entire Taiwan region.
Implications of river morpholo hu fault in NW Vietnam
to active Dien Bien Phu fault, we use 1/50,000 topographic data AS
In order to characterize interseismic deformation around Taiwan region, we
large earthquakes in the century, especially the Chi-Chi earthquake. For better understanding interseismic coupling and fault slip, we construct a three-dimensional
of block motions and fault slip rates. The model combined elastic half-space and block motions based on the backslip model to descr
faults.
rates and seismic potent
gy response to Dien Bien P
Kuang-Yin Lai1, Yue-Gau Chen1, Doan Dinh Lam2
1 Institute of Geosciences, National Taiwan University, P.O. Box 13-318, Taipei 106, Taiwan
2 Institute of Geological Sciences, Vietnamese Academy of Science and Technology, Hanoi, Vietnam
Abstract
In northern Vietnam, most rivers are flowing southeastward sub- or parallel to the valley of Red River and characterized by long but narrow catchments. The Dien Bien Phu fault is associated with the most seismically active zone in Vietnam and situated in the potential eastern boundary of the rotating southeastern Tibetan block.
It cuts the Da River, the largest tributary of Red River in northwest Vietnam and has distorted the drainage basin resulting in complex river patterns. To assess the river
ogy response morphol
and TER images to map the precise river courses and digital elevation model data of SRTM to retrieve and analyze the river profiles. From the mapping results, the N-S striking fault results in three conspicuous north-trending river valleys coincided
with the different fault segments to facilitate the measurement and reconstruction of the offsets along the fault. Further combining the longitudinal profile analysis we obtain ca. 10 km offsets by deflected river as the largest left-lateral displacement recorded along the active fault. The restored results show the downstream paleochannel of the Da River had been abandoned and becomes two small tributaries in opposite flow directions at present due to differential crustal uplift. Also the
resent crisscross valley at the junction of the Da River and the fault is resulted from the ca
The implication of elevated lacustrine sediments in the middle reach of the Yarlung-Tsangpo and Nyang River,
e-Gau Chen1, Ling-Ho Chung1, in Lai1, Ray Y. Chuang1, Shujun Zhao2, Gongming Yin2 and Zhongquan Cao3 . tate Key Laboratory of Earthquake Dynamics, Institute of Geology, China
nteraction mechanisms among climate, crustal uplift and related erosion proc
p
pture by another river which has been also deflected by the neotectonics.
Based on our observations on river response, the Dien Bien Phu fault is a sinistral dominant fault with an uplift occurring in its eastern block. Furthermore the active Dien Bien Phu fault does not cut through the Red River northward indicating the western block of the fault can not be regarded as a single rigid block. There should be possible to find NW-SE trending faults paralleling to Red River to accommodate the deformation of the western block of the fault.
Tibet
Shao-Yi Huang1, Yu-Nung Lin1, Jingwei Liu2 ,Yu Kuang-Y
1. Department of Geosciences, National Taiwan University 2 S
Earthquake Administration
3. Seismological Bureau of Tibet Autonomous Region
The i
esses in the orogenic belt became one of the popular topics in the past decade, especially in the collisional margin of Eurasian Plate and Indian Plate where stands the most spectacular plateau in the world in terms of elevation and geomorphology.
We investigated the outcrops of lacustrine deposits in the lower terraces of the Nyang River and established the stratigraphic column for entire depositional sequence.
Woods and charcoals were collected for radiocarbon dating and sands for optical stimulated luminescence (OSL). Based on our observation, the alluvial and lacustrine environments occurred alternatively. Among them two well developed varve layers were identified in the sequence.
The occurrence of varve strata and moraine-related delta facies have raised subsequent questions such as did the breakout of the dammed lake strike this drainage repeatedly? What is the mechanism of the dammed lakes, were the paleolakes dammed by monsoon driven valley glacier or tectonic structures? And, the timing of the paleolakes will be crucial as well.
Based on the preliminary radiocarbon and OSL dates from the bottom and the top of the depositional succession, the paleolakes took place no younger than 20ka. The interbeded sand and silt recorded abundant ripple cross beds, parallel lamination, and syndepositional deformation, representing the transition of environments from
Based on the preliminary radiocarbon and OSL dates from the bottom and the top of the depositional succession, the paleolakes took place no younger than 20ka. The interbeded sand and silt recorded abundant ripple cross beds, parallel lamination, and syndepositional deformation, representing the transition of environments from