Earthquake -induced deep-seated landslide and landscape evolution process at Hungtsaiping, Nantou County, Taiwan Chia-Ming Lo 1* Wei-Kai Huang 2 Ming-Lang Lin 3 *1 Department of Civil and Disaster Prevention ngineering! "ational #nited #niversit$! Miaoli! % ai&an' 2 Disaster Prevention %e(hnolog$ )esear(h Center! inote(h ngineering Consultants! +n('! %a ipei 1,! %a i&an! )'.'C' 3 Department of Civil ngineering! "ational %ai&an #niversit$! % aipei! %ai&an! )'.'C' *Corresponding /uthor0 -mail0 pp24gmail'(om or pp24$ahoo'(om't& Abstract %he Chi-(hi earth5ua6e 7magnitude 8'9: on eptemer 21! 1;;; triggered numerous landslides in (en tra l %ai&an' / par ti( ula rl$ lar ge! dee p-s ea ted landslide o((urred at Hungtsaip ing ! 16ilometers north of the epi(enter' <ield investigation and lands(ape evolution anal$sis revealed an irregular pattern of displa(ement ve(tors! indi(ating that this failure me(hanism is highl$ (omple=' %his paper presents the results of site investigations in (on>un(tion &ith simulations of lands(ape evolution asso(iated &ith this landslide' /nal$sis of lands(ape evolution &as ased on topographi( maps produ(ed at seven different times as &ell as aerial photographs ta6en et&een 1;99 and 2,,9' Landslide site investigation in(luded field re(onnaissan(e! geomorphologi( anal$sis! geoph$si(al e=ploration! orehole logs! and laorator$ e=periments' Comprehensive geologi( investigation led us to (on(lude that the materials involved in the landslide are (olluvial deposits' Lands(ape evolution involved at least three large landslide events! t&o previous ro(6slides 7the first triggered during the 1;19 "antou earth5ua6e and another event o((urring in 1;3: as &ell as the 1;;; (olluvium slide 7triggered during the Chi-(hi earth5ua6e:' ?$ ta6ing into a((ount the sour(e of the (ollapsed mass! &e &ere ale to reprodu(e the three landslide events using a 3D dis(rete element model' Cali ration of the parameters used in the numeri(al model &as ased on the strength (hara(teristi(s of the ro(6 mass as &ell as the morpholog$ of the landslide deposits' Ke$ Wor ds0 the Chi-( hi earth 5ua6 e! dee p-sea ted land slide! land s(ap e evol ution ! 3D dis(rete element model' 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 1
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in (entral %ai&an' / parti(ularl$ large! deep-seated landslide o((urred at Hungtsaiping! 1
6ilometers north of the epi(enter' <ield investigation and lands(ape evolution anal$sis revealed an
irregular pattern of displa(ement ve(tors! indi(ating that this failure me(hanism is highl$ (omple='
%his paper presents the results of site investigations in (on>un(tion &ith simulations of lands(ape
evolution asso(iated &ith this landslide' /nal$sis of lands(ape evolution &as ased on topographi(
maps produ(ed at seven different times as &ell as aerial photographs ta6en et&een 1;99 and 2,,9'
Landslide site investigation in(luded field re(onnaissan(e! geomorphologi( anal$sis! geoph$si(al
e=ploration! orehole logs! and laorator$ e=periments' Comprehensive geologi( investigation led
us to (on(lude that the materials involved in the landslide are (olluvial deposits' Lands(ape
evolution involved at least three large landslide events! t&o previous ro(6slides 7the first triggered
during the 1;19 "antou earth5ua6e and another event o((urring in 1;3: as &ell as the 1;;;
(olluvium slide 7triggered during the Chi-(hi earth5ua6e:' ?$ ta6ing into a((ount the sour(e of the
(ollapsed mass! &e &ere ale to reprodu(e the three landslide events using a 3D dis(rete elementmodel' Caliration of the parameters used in the numeri(al model &as ased on the strength
(hara(teristi(s of the ro(6 mass as &ell as the morpholog$ of the landslide deposits'
Ke$ Words0 the Chi-(hi earth5ua6e! deep-seated landslide! lands(ape evolution! 3D dis(rete
near the sour(e of the sliding Bone and the a=is of the anti(line! &hi(h presented numerous talus
deposits! (ontinuous re(ession along the (liff lines! and dip slope landslides' Later monitoring and
surve$s revealed severe landslide disasters throughout the range of the three sliding masses
follo&ing torrential rain events! there$ indi(ating that the sour(e area and the (olluvium remain
prone to landslides' +n previous topographi( maps! Lo et al' dis(overed large-s(ale (hanges in the
topograph$ at Hungtsaiping et&een 1;, and 1;3! &hi(h led to the re(ent (overing! (ollapse! and
erosion of the old (olluvium 7Lo et al'! 2,,;:' )eferral to earth5ua6es in %ai&an during the last
(entur$ sho&ed that topographi( (hanges in that area &ere li6el$ asso(iated &ith a series of ma>or
earth5ua6es in "antou during 1;19 and 1;18 7Huang et al'! 2,12:' Ho&ever! little resear(h has een
(ondu(ted on these histori(al landslide events or the evolution of the terrain'
Man$ studies have e=amined the me(hanisms underl$ing the large-s(ale! deep-seated landslide
at Hungtsaiping' "evertheless! limitations in surve$ data and monitoring (onditions still leave a
numer of matters to e investigated! and man$ other large-s(ale landslide (ases have indi(ated that
the 6inemati(s and velo(it$ (hara(teristi(s are important anal$sis indi(es 7Chang et al'! 2,,A Dong
et al'! 2,,;A Lo et al'! 2,11:' During large-s(ale ro(6slide! entire sliding masses generall$ rea6 up
into numerous pie(es! there$ transforming into deris avalan(hes 7sturBstroms:! are remar6ale
geologi(al phenomenon 7teven and imon! 2,,9:' Kinemati(s during a landslide and (hanges in
velo(it$ are determinant of the landslides damage potential! &hi(h (an o((ur &ithin >ust se(onds
7Hungr! 2,,8:' Dong et al' 72,,;: also mentioned that the dire(tion of the earth5ua6e sho(6&aves!
the dire(tion in &hi(h the sliding mass is moving! and landslide me(hanisms are (ru(ial to resear(hon large-s(ale landslides' Ho&ever! the (omple= topographi(al evolution resulting from the large-
s(ale landslide at Hungtsaiping re5uired numeri(al simulations to aid in e=planation' Des(riing the
various (hanges that o((ur during landslide events (ould help to gain understanding into the
(omple= me(hanisms underl$ing landslides! assist in planning treatment pro>e(ts! and fa(ilitate
predi(tions related to the future evolution of the site'
)e(entl$! dis(rete element method has een &idel$ applied in the simulation of landslides' %he
advantage of this approa(h lies in its ailit$ to simulate the onds and separation of strata material
as &ell as the ehavior of landslides &ith large displa(ements after (ollision intera(tions' %his
approa(h is ased fundamentall$ on the results of me(hani(al testing and field investigations'
elo(ities and displa(ements re(orded during simulations are important parameters (apale of
graduall$ unveiling the pro(ess of large-s(ale landslides 7Chang et al'! 2,,A %ang et al'! 2,,;A Lo et
al'! 2,11A Lo et al'! 2,1:' Chang 72,11: used P<C2D to reprodu(e the Hungtsaiping landslide
(aused $ the Chi-(hi earth5ua6e and further integrated data from (ore drilling and field
investigations to enhan(e des(riptions of (hanges and deposition (hara(teristi(s asso(iated &ith
re(ent landslides in the area' Ho&ever! (omple= geologi(al stru(tures! su(h as the distriution of
anti(lines and s$n(lines! regulate the dire(tion of landslide movement! su(h that using a 3D
approa(h to reprodu(e this landslide is a more reasonale approa(h'
/((ordingl$! &e e=amined the histor$ and topographi(al evolution at Hungtsaiping using
topographi( maps from various time periods to deal &ith the uni5ue geologi(al stru(tures and
(omple= 6inemati( me(hanisms of this large-s(ale! deep-seated landslide' %he use of P<C3D made
it possile to re(reate the landslides that o((urred at Hungtsaiping in 1;19 and 1;;; in order to
e=amine the landslide pro(esses and me(hanisms in detail' %herefore! the stud$ is uni5ue in its use
of three-dimensional simulations to represent the sliding ehavior of old (olluvium under (omple=
geologi(al (onditions' We also too6 into a((ount the (hara(teristi(s of previous earth5ua6es to
present a more (omprehensive histor$ of landslides over the last (entur$' %he sustantial
availailit$ of data and surve$ results provided an invaluale referen(e for use in (larif$ing ho&earth5ua6es indu(e the development of landslides' %he primar$ o>e(tives of this stud$ are as
follo&s0
7a: +nvestigating topographi(al (hanges and landslide me(hanisms at Hungtsaiping over the
last (entur$A
7: %he appli(ation of 3-D dis(rete element method for the re-(reation of earth5ua6e-indu(ed
1;! 1;;1! 1;;! 1;;;! and 2,,3 as &ell as data related to earth5ua6es and heav$ rain disasters
over the last (entur$'
?ased on our anal$sis of the maps et&een 1;, and 2,,3 7<ig' 2: and the times of various
landslides in the past! &e divided the entire landslide area into si= Bones! numered from + to +'
.ur anal$sis results are as follo&s0
7a: / (omparison of the terrain in 1;, and 1;3 revealed that large-s(ale landslides ma$
have o((urred in @ones + and ++ et&een 1;, and 1;3' %he landslide in @one +
7appro=imatel$ 192 ha in area! sliding dire(tion to&ards "22FW: (ut off the Longfeng
Cree6! for(ing it to veer north! resulting in a ninet$-degree turn near iasui6u ?ridge "o'
2' %he (olluvial la$er that formed after the re(ent landslide e(ame liding Masses /! ?!
and C at Hungtsaiping' %he landslide in @one ++ &as larger 7appro=imatel$ 2, ha in area!
sliding dire(tion to&ards "3FW:' %he 1;, map sho&ed that upper slopes in @one ++
&ere gentler! and lo&er slopes steeper! &hereas the 1;3 map indi(ated the opposite' %he
resulting deposits formed the sliding mass on the north&est side of Hungtsaiping toda$'
7: %o understand the (ause of this landslide! &e referred to the resear(h (ondu(ted $ Cheng
and Eeh 72,,: on earth5ua6es of the last (entur$ and found that a series of earth5ua6es
o((urred in "antou in 1;19 and 1;18' in(e the estalishment of instrumental oservation
in "antou in 1;! fe& ma>or earth5ua6es have o((urred' Ho&ever! four severe
earth5ua6es too6 pla(e starting in /ugust of 1;19! resulting in sustantial alterations in the
terrain' .ur preliminar$ spe(ulation is that the earlier landslides at Hungtsaiping &eretriggered $ these earth5ua6es! and the signifi(ant topographi(al (hanges that ensued
et&een 1;, and 1;3 help to e=plain the e=isten(e of thi(6 (olluvium over the edro(6
&ithin the ranges of liding Masses /! ?! and C! and also e=plains &h$ the masses did not
result in a s&ift landslide follo&ing the Chi-(hi earth5ua6e'
7(: /nal$sis of topograph$ for the period et&een 1;88 and 2,,3 revealed that the sliding
mass in @one ++ &as alread$ dividing into t&o masses' +n terms of the geologi(al
sliding distan(e for the earlier landslide! su(h that most of the landslide material (ame to a rest on
the slope fa(e' /lthough the thi(6ness of the resulting (olluvium rea(hed 3, m to m! the material
&as &ea6 in terms of strength and stiffness' .n a((ount of this! the Chi-(hi earth5ua6e merel$
(aused the sliding masses to move along the ro(6 and soil interfa(e rather than produ(ing a ma>or
landslide disaster' %he aove! is a des(ription of landslides and geologi(al evolution in the
Hungtsaiping areas over the last (entur$' We (omined e=isting data to (onstru(t numeri(al models
of t&o ma>or landslides at Hungtsaiping 71;19 1;;;: in order to provide an a((urate e=planation
of the landslide histor$ and geologi(al evolution in the area'
<ig'3 +nvestigation of geolog$ and orehole logs otained in the surve$ing and mapping of strataunderl$ing the Hungtsaiping landslide' We also list the lo(ations of oreholes and resistivit$
e=ploration 7Dong et al'! 2,,;:'
a' Geologi(al map of the landslide area'
' Profile //-// and ??-?? a(ross the slide dire(tions &ith resistivit$ surve$ lines 7Chang et
al'! 2,11:'
(' Cross-se(tions /-/! ?-?! C-C! and D-D sho& the topograph$! geologi(al stru(tures! and
and )oth! 2,,A Poisel et al'! 2,,:' %hus! &e emplo$ed P<C3D for the simulation and
interpretation of the 6inemati( pro(esses in three events asso(iated &ith the Hungtsaiping landslide'
%he elements of the P<C model in(lude parti(les and &alls' %he sliding surfa(e of the (ollapse area
in the Hungtsaiping landslide model &as (onstru(ted using 8!,,, &all elements ased on a
11m DM from the mapping of underl$ing strata and geologi(al stru(tures' <igure a presents a
re(onstru(tion of the geologi(al stru(ture asso(iated &ith the sliding surfa(e prior to the series of
earth5ua6e events in "antou in 1;,' %he total length from ast to West &as 3!89m and the total
&idth from "orth to outh &as 2!92m' %he sliding mass &as (onstru(ted using 2,!1 spheri(al
elements &ith a radius of 8' meters as &ell as 1!38; spheri(al elements divided into three lo(6s
7<ig'! 9:! resulting in a total volume of appro=imatel$ 33 million (ui( meters'
%he ehavior of granular media at the ma(ros(opi( s(ale depends on the (onta(t me(hani(al
propertiesA ho&ever! there is no straightfor&ard solution to the sele(tion of these parameters'
nsuring reliailit$ in the use of P<C models as simulation tools re5uires the estalishment of
reasonale relationships et&een numeri(al parameters and the me(hani(al (hara(teristi(s found in
a(tual situations 7Pot$ond$ and Cundall! 2,,:' We adopted e=perimental methods for the
optimiBation of P<C models &ith regard to unia=ial (ompression tests in order to (al(ulate
appropriate ma(ro-parameters for model generation &ith the aim of otaining an a((urate
reprodu(tion of the ma(ro-parameters of the ro(6 material' %hese parameters in(luded unia=ial
(ompression strength 7#C:! Eoungs modulus! and Poissons ratio 7Eoon! 2,,8:' <or ond
modelling! ma(ro-parameters for the intera(tion of t&o (ir(ular parti(les in(lude normal and shear stiffness! normal and shear onds! and the Coulom fri(tion (oeffi(ient! &hi(h must e otained
during the (aliration step' <a6himi 72,,: proposed a slightl$ overlapping intera(tion of (ir(ular
parti(les to resolve the failure envelope and the ratio of un(onfined (ompressive strength to tensile
strength! &hi(h tends to e lo&er than that of ro(6' We applied dimensional anal$sis in the
(aliration of DM for andstone &ith the aim of mimi(6ing the deformation and failure
(hara(teristi(s in stress paths 7<a6himi and illegas! 2,,8:' /lthough there is no straightfor&ard
the distriutions of the s$n(line a=is and strata! Masses / and ? moved to&ard the
s$n(line a=is! (oming to a rest &hen the$ hit Mass C' / gradual loss of onding strength in
Masses / and ? during the sliding and impa(t resulted in their rea6ing up into pie(es and
led to the a((umulation of a sustantial amount of sandstone deris over Mass C 7 <ig'
;7a:-tep 2:' %he impa(t of Masses / and ? a((elerated the movement of Mass C to&ard
the north&est! &hi(h (ompressed and then (ut off the Eonglu Cree6! for(ing it to veer
to&ard the north&est 7<ig' ;7a:-tep 3:' / signifi(ant 5uantit$ of landslide material also
a((umulated in the ne& rivered! at &hi(h point appro=imatel$ et&een 38 and 2 of
the onds in the three sliding masses had alread$ ro6en' %his (aused the entire ro(6 mass
to graduall$ fragment into pie(es'
7: 1;19-1;18 "antou earth5ua6e events0 %he seismi( for(es during the earth5ua6es initiated
the displa(ement of Masses /! ?! and C 7<ig' ;7:-tep : and in(reased the proportion of
ro6en onds in the three masses to et&een 81 and 8' %hese three masses graduall$
formed a massive (olluvial deposit! mainl$ (omprising soil (entered over the s$n(line
a=is' With the sliding of Masses / and ?! (ollisions and fragmentation shifted their
movement in the same dire(tion to the &est 7<ig' ;7:-tep :' Mass C (ontinued
(ompressing the rivered of the Eonglu Cree6! &hi(h eventuall$ deviated north&est!
ultimatel$ arriving at its (urrent lo(ation 7<ig' ;7:-tep 9:' <urthermore! as Mass C
moved north&est! it undermined the support of Masses / and ?! there$ (ausing them to
slide slightl$ to the north&est' /ppro=imatel$ 18 of the material in the front portiona(tuall$ passed the erosion gullies to the &est! su(h that the$ a((umulated in the rivered
7<ig' ;7:-tep 9:' <ollo&ing the 1;19-1;18 "antou earth5ua6e events! the sliding masses
temporaril$ stailiBedA ho&ever! a signifi(ant 5uantit$ of unstale (olluvial material still
resided on the strata and s$n(line a=is' %his material eventuall$ pla$ed a (riti(al role in the
Chi-(hi earth5ua6e'
7(: 1;;; Chi-(hi earth5ua6e0 <ollo&ing the series of earth5ua6es in "antou! the primar$
sliding masses at Hungtsaiping remained fairl$ stale for 2 $ears until the Chi-(hi
earth5ua6e (aused the old sliding masses to move on(e again' %he main landslide involved
the large (olluvial deposit that had a((umulated over the s$n(line a=is' mall-s(ale
movements in the large (olluvial deposit o((urred along the ro(6 and soil interfa(e!
(ausing the ground surfa(e to shift and deform 7Dong et al'! 2,,;:' eismi( a((eleration
data 7<ig'1,: &as (olle(ted from %C#,82! the seismi( station nearest Hungtsaiping! for
(onversion into the seismi( parameters 7velo(it$ or displa(ement: re5uired for P<C3D
programming' %his made it possile to monitor the displa(ement of elements in various
lo(ations 7<ig' 11: and there$ strengthen our e=planation of ho& the Chi-(hi earth5ua6e
moved the old landslide material' .ur simulation results sho& that the Chi-(hi earth5ua6e
propelled the old sliding masses to move in roughl$ three dire(tions 7<ig' ;7(:-tep 8:A
Masses / and ? mainl$ moved &est 7e(oming the (urrent liding Mass /:! and the 23
of the material in the front spread over Mass C' %he s$n(line a=is divided Mass C into t&o
portions! sliding north&est and north! respe(tivel$ to e(ome the (urrent liding Masses ?
and C 7<ig' ;7(:-tep :' Despite persistent seismi( for(es! the sliding masses did not
displa$ large-s(ale deformation or slide for ver$ long distan(es' Ho&ever! oservation of
the elements in various lo(ations revealed that in addition to differen(es in sliding
dire(tion! the surfa(e and ottom elements of the sliding masses also differed in the degree
of displa(ement! &hi(h resulted in var$ing degrees of geomorphologi(al (hange andJor
destru(tion' During the Chi-(hi earth5ua6e! liding Mass / moved primaril$ to&ard the&est! resulting in displa(ement of 1,'2 m at the top and 11'31 m at the ottom eing!
&hi(h is slightl$ less than the displa(ements asso(iated &ith liding Masses ? and C' <or
this reason! the upper stru(ture of liding Mass / presented damage' +n (ontrast! liding
Mass ? moved north&est and under&ent the largest displa(ements at the0 '91 m at the top
and 1;';9 m at the ottom' %his led to the formation of tension near the top! &hi(h (reated
minor s(arps and small ponds' lightl$ ulging from (ompression! the slope of liding
Mass ? displa$ed relativel$ little displa(ements of 18' m at the top and 1;';3 m at the
ottom! &hi(h resulted in a small! shallo& landslide near the left an6 of the Eonglu
Cree6' <inall$! liding Mass C moved mainl$ to&ard the north &ith displa(ements of
1;'11 m at the top and 1;'3 m at the ottom'
Dis(rete element numeri(al modeling of the three earth5ua6e-(aused landslides provided
important ph$si(al (onstraints! &hi(h &ere (ompared &ith field oservations' %his led to
ad>ustments in the reported (hara(teristi(s of the events' )esear(h into the series of earth5ua6es in
"antou! as &ell as studies on the Chi-(hi earth5ua6e 7Lo et al'! 2,,A Chang et al'! 2,11A Lee et al'!
1;;;: and earlier studies asso(iated &ith those earth5ua6es provided aundant a(6ground
information &ith &hi(h to investigate possile fa(tors governing the 6inemati(s of these large
earth5ua6e-indu(ed landslides' ?ased on previous studies using numeri(al simulation! &e (an
dis(uss in greater detail the possile reasons for the movement of slide masses follo&ing these
events' / (omparison of the simulation results related to the Chi-(hi earth5ua6e otained using
P<C3D &ith parti(le image velo(imetr$ te(hnolog$ 7P+: 7Lo et al'! 2,,: revealed that the
oundaries and movement dire(tion of (olluvium &ere nearl$ a perfe(t mat(h 7<ig'12:' We found
eviden(e of a $n(line! i'e'! M-s$mmetr$ minor folds of thin-edded siltstone and sandstone la$ers
&ithin a massive shale 7%anliaoti hale: out(rop on the river an6 of Eonglu stream! &hi(h appears
to have pla$ed a (ru(ial role in these events' ?et&een 1;, and 1;3! it pla$ed an important role in
determining the dire(tion of sliding 7<ig' ;7a: mass ? and mass C: and defle(ted the dire(tion of the
Eonglu stream to&ard the north&est' %his e=posed the toe of liding Mass /! &hi(h resulted ininstailit$ and eventual failure' %he Chi-(hi earth5ua6e (aused slip displa(ement in liding Masses
/! ?! and C of appro=imatel$ 2'91 meters et&een 1;; and 2,,3' %he (onditions asso(iated &ith
phenomenon are &orth dis(ussing' +n the simulation! the areas surrounding all +Ds 2,2, and 2,38
presented large displa(ement of appro=imatel$ 1;'1 m' +n (omparison! the area surrounding all +Ds
82; and 889 on the lo&er slope had displa(ement of onl$ 1' m' %he (onditions that led to su(h
large differen(es in displa(ement ma$ have (aused deformations in the mass of the (olluvium!
resulting in the formation of tension (ra(6s on the sliding surfa(e'
%ale 1 Comparison results of unia=ial (ompression test in a((ordan(e &ith Hoe6O?ro&n failure
(riterion and P<C model
%ale 2 "umeri(al parameters used in P<C modeling
<ig' 3D illustration of geologi(al la$ers ased on the mapping of underl$ing strata
a' Mid-thi(6 sandstone sho&ing geologi(al s$n(line and anti(line stru(tures
' hale0 )e(onstru(tion of sliding surfa(es in <ig 3 &ith modifi(ations ased on topographi(
maps from 1;,' /lso sho&n is the s(ope of possile landslide sour(es0 masses /! ?! and C
<ig'9 "umeri(al modeling of the Hungtsaiping landslide
<ig' 8 Geologi(al strength inde= and distriution of samples otained during field investigation
<ig' %he results of simulation unia=ial (ompression test<ig' ;7a: imulation results of landslide event asso(iated &ith the series of earth5ua6es in "antou
in 1;19
<ig' ;7: imulation results of landslide event asso(iated &ith the series of earth5ua6es in "antou
in 1;19-1;18
<ig' ;7(: imulation results of old landslide (aused $ Chi-(hi earth5ua6e
<ig'1, eismi( re(ords at %C#,82 in 7a: the verti(al! 7: "orth-outh! and 7(: ast-West dire(tions
<ig'11 7a: the monitoring lo(ation of numeri(al modelA 7: the displa(ement of all elements<ig'12 Comparison results of simulation of Chi-(hi earth5ua6e events