Assessment of earthquake-Induced ground liquefaction susceptibility for Hanoi city using geological and geomorphologic characteristics

Vietnam Journal of Earth Sciences 39(2), 139-154, DOI: 10.15625/0866-7187/39/2/9448 139 (VAST) Vietnam Academy of Science and Technology Vietnam Journal of Earth Sciences Assessment of earthquake-induced ground liquefaction susceptibility for Hanoi city using geological and geomor- phologic characteristics Bui Thi Nhung*1, Nguyen Hong Phuong1,2, Nguyen Ta Nam1 1Institute of Geophysics, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet street, Cau Giay District, Hanoi, Vietnam 2IRD, Sorbonne Universités, UPMC Univ Paris 06, Unité Mixte Internationale de Modélisation Mathé- matique et Informatiques des Systèmes Complexes (UMMISCO)32 venue Henri Varagnat, 93143 Bondy Cedex, France Received 02 November 2016. Accepted 31 March 2017 ABSTRACT In this paper, the earthquake-induced liquefaction susceptibility of Hanoi city is assessed using the recent pub- lished geological and geomorphologic data. A combination of classification methods based on the distribution of sedimentary deposits proposed by Youd and Perkins (1978) and geomorphologic units proposed by Iwasaki (1982) was applied. The subsurface lithology and geomorphologic maps were combined in a GIS platform for assessing the liquefaction susceptibility of Hanoi city. The resulting map shows that the liquefaction hazard of Hanoi city classified into four categories: high, moderate, low liquefaction potential and not likely areas. In the most of Hanoi area, the ground liquefaction potentials are mod- erate. The high liquefaction likely areas spread along the river beds and around the lake areas. The not likely and low liquefaction potential areas are observed mainly in the northwest and northeast of the study region such as Chan Chim, Soc Son, and Ba Vi mountains. The present map can help the scientists, engineers, and planners to have the general information on regional liquefaction potential of the Hanoi city. Keywords: Liquefaction susceptibility, sedimentary deposits, geomorphology, Hanoi city, GIS. ©2017 Vietnam Academy of Science and Technology 1. Introduction1 Liquefaction is a soil behavior phenome- non in which a saturated soil loses a substan- tial amount of strength due to high excess pore-water pressure generated by and accu- mulated during the strong earthquake (M≥5.0) *Corresponding author, Email: buinhung78@gmail.com ground shaking (Kuribayashi E., et al., 1975; Bird F.J and Bommer J.J., 2004a, 2004b). The direct evidence of this phenomenon is most often observed in saturated, loose (low density or uncompacted), sandy soils (such as Sand boils and lateral spreading), while its indirect evidence can be seen from the response of the constructions (Youd, 1993, Lew et al., 2000). Bui Thi Nhung, et al./Vietnam Journal of Earth Sciences 39 (2017) 140 Urban areas are most vulnerable to lique- faction hazards, and usually requiring a long time to be recovered after a disaster (Sinha and Goyal 2001). Liquefaction is the main cause of damage to soil structure and other materials which support a construction’s life and foundation (Susumu Yasuda, 2000). Dur- ing the last fifty years, the urban areas, partic- ularly those in the developing countries, while experiencing the explosive development, have been suffering heavy damage and losses from liquefaction and related phenomena. Hanoi, the capital of Vietnam, is one of the most populated cities of the country. Being situated upon the active Red river - Chay river fault zone, which, according to some geosci- entists, is capable of generating earthquakes with maximum magnitude of Mmax=7.0 (Phan Trong Trinh et al., 2012, 2013; Vu Thi Hoan et al., 2015; Ngo Thi Lu et al., 2016, Ngo Van Liem et al., 2016a, 2016b). According to the seismic zoning map of Vietnam published by the Institute of Geophysics, Hanoi belongs to the seismic zone with MSK intensity of VII-VIII (Nguyen Dinh Xuyen, 2008; Nguyen Hong Phuong et al., 2014a, 2014b; Bui Van Duan et al., 2013). Mean- while, the whole city is based on a sandy- clayed sediment of Holocene-Pleistocene age, upon a largely distributed Holocene aquifer (qh) with thickness changing from 0 m (where the aquifer crops out in the surface) up to 37.5 m, making the average thickness of about 12 m (Vu Thanh Tam et al., 2014). The down- town districts of Hanoi, with the densest population, highest speed of construction and urban development, are believed to be ex- posed to high liquefaction risk if an earth- quake occurs. Liquefaction susceptibility of the Old Hanoi city has been assessed by Nguyen Hong Phuong et al., (2002, 2007, 2013, 2014a), using the methodology proposed by Youd and Perkins (1978). In this paper, we present the results of the assessment of earth- quake-induced liquefaction hazard for the ex- panded Hanoi city using methods which allow combining geological and geomorphologic characteristics. 2. Data and methods 2.1. Geological and Engineering-geological data In order to get information on geological characteristics to be used in the assessment of the liquefaction of the Hanoi region, the pre- viously published researches on geology of Hanoi has been collected and analyzed (Geo- logical map of Hanoi, General Department of Geology and Minerals of Vietnam, 2005; Vu Thanh Tam et al., 2014) and the Engineering- Geological map of Hanoi in scale of 1: 25,000 by Ngo Quang Toan et al., 2015 (Figure 1). According to the published data, Hanoi is founded in the crystalline basement of Neo- proterozoic-Lower Cambric age (NP-є), cov- ered by the formations of Mesozoic, Neogenic and Quaternary ages. Within the boundary of Hanoi city, there are 11 different stratigraphic units having ages from Neoproterozoic to Kainozoic distributed with the total thickness of over 3600 m. The petrographic setting comprises formations of marine, terrigenous, volcanic terrigenous, vol- canic, artificial, ruins, river, lake, and marshy origins. There are 6 Pre-Quaternary strati- graphic units not cropping out in the study area, including the Chay river (NP-є sc), the Khon Lang (T2a kl), the Na Khuat (T2 nk), the Ha Coi (J1-2 hc), the Tam Lung (J3-K1 tl) and the Vinh Bao (N2 vb). The outcrop 5 Quater- nary stratigraphic units are described below: The Lower Pleistocene sediment of the Le Chi formation (aQ1 lc) is distributed at the depth from -45 m to about -70 ÷ -80 m, which lies upon the Pliocene sediment. The thick- ness of the formation is changing from 2.5 m to 24.5 m. The Middle and Upper Pleistocene sedi- ment of the Hanoi formation (aQ2-3hn) is Vietnam Journal of Earth Sciences 39(2), 139-154 141 widely distributed in the Hanoi region at the depth from -33.0 ÷ -78.0 m, with the thickness changing from 33.0 m to 40.0 m. The Upper Pleistocene sediment of the Vinh Phuc formation (aQ3vp) crops out in the surface in the northern part of Hanoi region, including majority of Dong Anh district, a part of Soc Son district and another small part of Co Nhue commune, Xuan Dinh, with the thickness changing from 9.0 m to 23.5 m. Based on the petrographic content, the formation can be di- vided into two members: the lower member (aQ3 vp1) comprises pebble, powder containing granule, yellowish-grey clay with the thickness changing from 4.0 to 13.5 m, and the upper member (aQ3 vp2) comprises clayey sand, silty sand, brown to reddish variegated clay sedi- ments containing plant detritus and peat of dif- ferent origins, such as lake, swamps, marine with total thickness changing from 5.0 to 10.0m. Figure 1. Distribution of sediment deposits in the Hanoi region (Ngo Quang Toan, 2015; Vu Thanh Tam, 2014) Bui Thi Nhung, et al./Vietnam Journal of Earth Sciences 39 (2017) 142 The Upper Pleistocene sediment of the Hai Hung formation (aQ3hh) is widely distributed in the Hanoi region, but mostly covered by the Holocene series, with the thickness ranking between 9 to 24 m, and the average thickness is 18.5 m. In fact, this is a transitional layer between the Pleistocene and the Holocene sediments, which also plays the role of a wa- ter resistant boundary between the Pleistocene and the Holocene aquifers. The Holocene sediment of the Thai Binh formation (Qtb) is cropping out in the south- ern part of the Red river within the boundary of Hanoi city. The thickness of this layer changes from 0 to 26.0 m, the average thick- ness is 6.15 m. According to the petrographic content, this formation can be divided into two members: the lower member comprises pebble, sand, silty sand mixed with clay with the thickness changing from 1.0 to 9.0 m, and the upper member comprises brown silty sand, clayey silt, sandy clay mixed with plant detritus, with the thickness changing from 3 to 19.0 m (General Department of Geology and Minerals of Vietnam, 2005; Vu Thanh Tam et al., 2014, Ngo Quang Toan, 2015). 2.2. Geomorphologic data Geomorphological information the Hanoi region is taken from the geo-morphologic map of Hanoi region by Dao Dinh Bac et al., 2010 (Figure 2). The geo-morphologic characteris- tics of the Hanoi region can be described as follows: The first feature is that Hanoi is located at the center of a low plain, the southern part of which is having deltaic plain features, and the northern part is having the lower course river plain features. In the entire large and plain region, the rel- atively high elevation terraces of Pleistocene age can always be found in the northern, northeastern and western margins. The second high elevation type, which is lower than the latter and more complicatedly distributed are the riverbeds bounded high edges, sometimes creating the natural dams, quite common at the rivers crossings like the Red river and Nhue river junction, or the high edges bound- ing the present Red river and outside the Hoan Kiem lake, or the larger highland along the ancient Red river near the West lake. Vietnam Journal of Earth Sciences 39(2), 139-154 143 The second topographic element here is the low depression area in the center of the region, which before the appearance of the dam system have usually been accreted by a smooth alluvial layer during flooding sea- sons, and also served as a drainage to let the flood water out from the West lake to the southeastern direction. That is the reason why in the western and southern areas of the Old Thang Long - Hanoi nowadays exit so many lakes, and coupled with branches of the Nhue and To Lich rivers exit the long flood drainage channels, known as the Lu and Set rivers. Figure 2. Geomorphologic distribution of the Hanoi region (Dao Dinh Bac, 2010) Bui Thi Nhung, et al./Vietnam Journal of Earth Sciences 39 (2017) 144 The distribution of the Pleistocene terrace 1(Q13vp) suggests the opening tendency to the east and southeast directions of the Red river bed. During the creation period of this ter- race, the Day river’s mouth was the mouth of Red river (the terrace 1 was located on two sides of the Day river bed). Then, during the Upper Holocene (Q23), the Red river stream abruptly crossed its terrace 1, rushing east- ward through the Hanoi area to go southward subjected to the dynamics of the neotectonic regime (after a long period of moving to the northeastern and eastern directions, the Red river bed was finally fit into the central gra- ben, while a branch of the Duong river flows steadily to the present lower settlement (named Luc Dau Giang). In addition, the ap- pearance of the remained abrasive or dam mudflats around the Imperial Citadel of Thang Long allow to determine the places with stable engineering-geological contents. The second feature is that Hanoi is clamped between the two highlands distribut- ed symmetrically with each other crossing the Red river, with transformation from the abso- lute subsidence of the central plain to the slight uplift of the denudated hill-shape sur- face and the pediment in the midland, fol- lowed by tectonic blocks with an uplift am- plitude such as Ba Vi and Tam Dao. The third feature is that the high elevated alluvial terraces and the ancient pediment in the northern part of Hanoi are degraded due to long erosion and washout period, now having a solid foundation and no longer affected by the Red river’s flooding waters. In addition, in Hanoi region there are many places where the remained ancient river beds, lakes and swamps now are affected by human activities and replaced by urban areas. 2.3. Methods Youd and Hoose (1977) when analyzing Vietnam Journal of Earth Sciences 39(2), 139-154 145 the information on 21 earthquakes recorded worldwide within the period from 1811 to 1976 have concluded that the liquefaction susceptibility is related to geological charac- teristics. Using this result and some additional data, Youd and Perkins (1978) have addressed the liquefaction susceptibility of various types of soil deposits by assigning a qualitative sus- ceptibility rating based upon general deposi- tional environment and geologic age of the deposit. The relative susceptibility ratings of Youd and Perkins (1978) shown in Table 1 indicate that recently deposited relatively un- consolidated soils such as Holocene-age river channel, floodplain, and delta deposits and uncompacted artificial fills located below the groundwater table have high to very high liq- uefaction susceptibility. Sands and silty sands are particularly susceptible to liquefaction. Silts and gravels also are susceptible to lique- faction, and some sensitive clays have exhib- ited liquefaction-type strength losses (Updike, et. al., 1988). Such deposits as an alluvial fan and plain, beach, high wave energy, glacial till, talus, residual soils, tuff and compacted fill in general not susceptible to liquefaction. For each deposit type, the liquefaction sus- ceptibility is decreasing by the ages, from young (< 500 years) to old (Pre-Pleistocene), except for the loess, which is always suscepti- ble to liquefaction during strong earthquakes no matter the age is of Holocene or Pleisto- cene. The Holocene sediments are more sus- ceptible to liquefaction than the Pleistocene ones, and the Pre-Pleistocene sediments are rarely liquefied. Iwasaki et al. (1982) proposed another ap- proach based on the relationship between liq- uefaction events and the geomorphologic characteristic of the place where the liquefac- tion occurred. The data published by Ku- ribayashi and Tatsuoka (1975) was used in- cluding 44 liquefaction caused earthquakes recorded in Japan during a 96 year period since 1872 (with magnitudes M = 5.2 ÷ 8.2) referencing to the certain geomorphologic conditions. The results show that the earth- quake-triggered liquefactions mostly occurred in alluvial sandy sediments, especially in the reclamation areas, river beds or present lakes. The authors proposed a set of criteria for mi- cro-zoning of liquefaction susceptibility based on the geomorphologic information as shown in Table 2. As can be seen from Table 2, the high possibility of liquefaction is concentrated in the places as the present river- or lake beds, ancient riverbeds, swamps, reformed lands or lowlands in sand dunes. The medium lique- faction susceptibility is assigned for such structures as the fan, floodplain, other plains or natural dams. The rocky mountains are not susceptible to liquefaction, and in general, the rocky areas or areas with bedrocks are consid- ered not subject to liquefaction. 3. Results and disscusion 3.1. Asessment of liquefaction susceptibility of the Hanoi region based on the geological characteristics Using the information on geologic age, soil/geologic conditions of the Hanoi region, petrographic types taken from the engineer- ing-geologic map of Hanoi (Figure 1), the relative susceptibility ratings according to Youd and Perkins (1978) shown in Table 1 was applied to each geological unit by assign- ing the weighting values as shown in Table 3, where the weighting values rank from 1 to 4, indicating the increasing level of liquefaction susceptibility. The results obtained from table 3 then were used in a GIS platform to compile a thematic map showing the distribution of liquefaction susceptibility of the Hanoi region based on the geological characteristics (Figure 3). Bui Thi Nhung, et al./Vietnam Journal of Earth Sciences 39 (2017) 146 Table 1. Liquefaction Susceptibility of Sedimentary Deposits (from Youd and Perkins, 1978) Type of Deposit General Distribution of Cohesionless Sediments in Deposits Likelihood that Cohesionless Sediments when Saturated would be Susceptible to Liquefaction (by Age of Deposit) < 500 yr Modern Holocene < 11 ka Pleistocene 11 ka - 2Ma Pre-Pleistocene > 2 Ma (a) Continental Deposits River channel Locally variable Very High High Low Very Low Flood plain Locally variable High Moderate Low Very Low Alluvial fan and plain Widespread Moderate Low Low Very Low Marine terraces and plains Widespread --- Low Very Low Very Low Delta and fan-delta Widespread High Moderate Low Very Low Lacustrine and playa Variable High Moderate Low Very Low Colluvium Variable High Moderate Low Very Low Talus Widespread Low Low Very Low Very Low Dunes Widespread High Moderate Low Very Low Loess Variable High High High Unknown Glacial till Variable Low Low Very Low Very Low Tuff Rare Low Low Very Low Very Low Tephra Widespread High High ? ? Residual soils Rare Low Low Very Low Very Low Sebka Locally variable High Moderate Low Very Low (b) Coastal Zone Delta Widespread Very High High Low Very Low Esturine Locally variable High Moderate Low Very Low Beach High Wave Energy Widespread Moderate Low Very Low Very Low Low Wave Energy Widespread High Moderate Low Very Low Lagoonal Locally variable High Moderate Low Very Low Fore shore Locally variable High Moderate Low Very Low (c) Artificial Uncompacted Fill Variable Very High --- --- --- Compacted Fill Variable Low --- --- --- Table 2. Liquefaction Susceptibility of geomorphologic units (Iwasaki, 1982) Rank Geomorphologic units Liquefaction susceptibility A Present river bed, old river bed, swamp, reclaimed land and inter-dune lowland Liquefaction likely B Fan, natural levee, sand dune, flood plain, beach and other plains Liquefaction possibly C Terrace, hill and mountain Liquefaction not likely Vietnam Journal of Earth Sciences 39(2), 139-154 147 Table 3. Liquefaction susceptibility of sedimentary deposits defined in the Hanoi city Lithological genesis Geologic age Sediment description Classification** Terrigeno-us T2đg2 Limestone 1 T2ađg22 T2ađg1 T2nk2 Conglomerate T2nk1 Claystone T2dg Sandy gritstone J12hc1 Shales, granule, gritstone PR3єtk3 Shales 1 Clayey silt 1 PR1tn Shales, Sandy gritstone 1 P2νd Eruptive facies, Shales, Sandy gritstone 1 T1cn3 Volcanic rocks, limestone 1 Sandy gritstone, conglomerate σνT1bν Clay shales, siltstone, marl, Dunite, Peridotite, gabrodibas 1 Effusive Terrigenous T2kl Tuffaceous sandstone 1 Limestone Shales T23sb1 Shales, limestone 1 Siltstone, sandstone Clayey silt 1 Base eruption T1vn2 Clay, Clayey silt 1 Shales, volcanic rocks, limestone 1 Sandstone, Sandy gritstone, conglomerate T1vn1 Tuffaceous Acid eruption J3-K1tl Siltstone 1 Porphyrictic trachyte, rhyolite, Shales Artificial Compacted Fill 1 Uncompacted Fill 4 Marine Q212hh2 Silty Sand, Clayey silt 3 Shales, granule, sandy gritstone 2 mQ212hh Clayey silt 3 amQ23tb Fluvial abQ212hh Sandy mixed grit 3 aQ13vp Clay 3 aQ23tb1 Silty Sand, Clayey silt 3 aQ23tb2 Clay, Silty Sand, Clayey silt 3 Yellow-grey, black-grey fine-grained Sand with re- mains of plant and mollusc shell 4 aQ13vp1 Clay, Silty Sand, Clayey silt 3 Fluvio-Proluvial apQ1 2-3hn Granule, claystone 2 aQ23tb1 Clayey silt, Silty Sand 3 Fluvio-lacustrine, swamp albQ23tb Brownish grey mud, Blackish grey mud brearing plant debris and mollusc shell 4 lbQ212hh Mud with blackish grey sand, Fine-grained Sand with dark grey clayey silt bearing plant debris lbQ13vp Clayey, sandy soil, kaolin clay, clay with blackish grey flora humus 3 **Note: 1- Non-Liquefiable, 2- Low susceptibility to liquefaction, 3- Moderate susceptibility to liquefaction, 4- High susceptibility to liquefaction Vietnam Journal of Earth Sciences 39(2), 139-154 148 As can be seen from Figure 3, based on the geological characteristics, the majority of Hanoi’s territory has moderate liquefaction susceptibility. The highest susceptibility to liquefaction can be found in the lowland plain, where the whole area is subsided 5-6 m and divided by a complicated system of rivers, channels, lakes and ponds. The area is characterized by sediments of river-lake and swamp origin (albQ23tb), with narrow distri- bution found in Dong Anh and some down- town places, the young sediments (aQ23tb) distributed along the Red river and Duong river beds. The main contents of these sedi- ments are gray to dark gray biopelite sandy and clayish silts, mixed with plant detritus. The other sediments are of the lake-swamp origin (lbQ21-2hh) distributed at the 1.5 to 20 m depth from the surface, with the aver- age thickness of 13.5 m comprise greenish grey to dark grey biopelite sandy and clayish silts, mixed with plant detritus are also large- ly distributed in the downtown area and in the Thanh Tri district. Figure 3. Map of liquefaction susceptibility of Hanoi city obtained from the Youd and Perkins (1978) method Vietnam Journal of Earth Sciences 39(2), 139-154 149 The moderate liquefaction susceptibility zone occupies the flat plain area distributed in two sides of the Red river bank, with compli- cated geological structure comprises the Hol- ocene sediments of marine and river origins, for example the (Q21-2hh) sediments, widely distributed in downtown Hanoi, the Tu Liem and Thanh Tri Districts, with thickness chang- ing between 0.4 to 4 m, average thickness of 1.5 m, and comprise silty clay mixed with sand. The other are the (Q23tb, Q13vp) sedi- ments, comprise mainly yellowish gray silty clay, sand, and sandy silt, mixed with the pebble, underlay by plastic pebble mixed with clay, clayey sand bearing plant remains, dis- tributed widely in the Hanoi region. The mountain area located in the northern and southwestern parts of the city and the Soc Son mountain in the north, which comprise hard schists, are not liquefiable. 3.2. Assessment of liquefaction susceptibility of the Hanoi region based on the geomor- phological characteristics Using the geomorphologic map of the Ha- noi region (Figure 2), the susceptibility stand- ards according to Iwasaki (1982) shown in Table 2 was applied to each geomorphologic unit by assigning the weighting values as de- scribed in the previous section, where the weighting values rank from 1 to 4, indicating the increasing level of liquefaction suscepti- bility. The results obtained are shown in table 4 and then were used to compile a thematic map showing the distribution of liquefaction susceptibility of the Hanoi region in a GIS environment (Figure 4). As can be seen from Figure 4, according to the geomorphologic characteristics, the major- ity of Hanoi’s territory has moderate liquefac- tion susceptibility. It should be noted that, for the geomorphologic case (Figure 4), the zone with high susceptibility to liquefaction are larger in compare with the corresponding zone in the geological case (Figure 3). Beside the rivers, lakes and swamps areas, which are the same in both cases, in Figure 4 the outside dam mudflats, low mudflats and the accumu- lative surface of the present streams have been added to the high liquefaction susceptibility zone that stretching from northern to southern parts of Hanoi, including the whole Thanh Tri and Gia Lam districts. In addition, in Figure 4, the zone with low susceptibility to liquefac- tion, which distributed mainly in the north- eastern and northwestern parts of the city are expanded in a narrow belt along the western boundary of the city, while the northeastern area is also enlarged to the south, occupying most of the Soc Son district. The zone com- prises the limestone mountains, hard shales, the highlands of the alluvial terraces, degrad- ed ancient pediment due to a long process of erosion and washout, which have the solid foundation. 3.3. Asessment of liquefaction susceptibility of the Hanoi region based on the geological and geomorphological characteristics As discussed by some authors, the sedimen- tary deposits play the main role in liquefaction susceptibility of a certain region (Ganapathy Pattukandan Ganapathy, Ajay S. Rajawat, 2012). In this study, the petrographic units in the map on Figure 3 and the geomorphologic units in the map in Figure 4 were assigned the weight values of 60 % and 40%, respectively and were integrated into a map of liquefaction susceptibility of Hanoi city, shown in Figure 5. Bui Thi Nhung, et al./Vietnam Journal of Earth Sciences 39 (2017) 150 Table 4. Liquefaction susceptibility of the geomorphologic units defined in the Hanoi city Type of relief Geomorphologic units Classification*** I. Collective denudation relief Late Miocene plain surface 1 Miocene-Pliocene plain surface Late Pliocene Pediment surface divided by surface washed slopes, slope angle 8-12°; height <20 m (the Chan Chim mountain), 33-40 m height (the Ba Vi mountain). II. Erosional denudation relief Gravitational denudation slopes, 350-450 m height (the ChanChim moun- tain) and up to 1200 m (the Ba Vi mountain), slope angle > 30 degrees. 1 Erosional denudative slopes, 75-200 m height (the ChanChim mountain) and height >40 m (the Ba Vi mountain), slope angle>20° Surface washed slopes - deluvian accumulative slopes, 20-100 m height, slope angle 8-15°. Surface washed slopes, 200-300 m height, slope angle 15-20°. Surface washed slopes, 40-80 m height, slope angle 10-15°. Post-pediment denudation surface, erosional - accumulative surface, with small ripple mounds. III. Flow-generated relief Mixed river flood accumulation surface, Q12-1 age. 1 Late-middle Pleistocene grade II river terrace, Q12-1 age. Late-middle Pleistocene grade I river terrace, Q11 age. 12-14 m height, well preserved. Height <10m, strongly fragmented. Denudation remain of 5-6 m height. Young eluvial, diluvium drift of Q23 age. 2 Inside-dike alluvial flat, high river bed alluvial flat, height 6-7 m, late-middle Holocene age. (Ba vi area >10 m 3 Inside-dike alluvial flat, valley alluvial flat, 4-5 m height, with streams and drainage canals. 4 Ouside-dike alluvial flat, ~10 m height, Late Holocene age (normal river segment). Ouside-dike alluvial flat, low alluvial flat, 7-8 m height (normal river segment) Ouside-dike alluvial flat, river bed alluvial flat originated from old float- ing ground (floating islands), non-divided Holocene age, 7-8 m height, (river branch) 4 Ouside-dike alluvial flat, Late Holocene floating ground. Old river bed and horseshoe-shape lake 4 Old river bed, Holocene age foot mud flat lake, canal and old floating ground. Present river bed. Accumulation-denudation gutter. 2 Late Pleistocene-Holocene Lacustrine marsh accumulate surface, Q12-Q2 3 River-marsh accumulation surface along old valley gutter, Late-middle Holocene age Q22-1. 4 Late Holocene River-lake-swamp acculation surface Q23. Multi-sourced current stream bottom accumulation surface. IV. Marine-river- generated relief Marine-river-generated relief. Remnant low-lying plain of early Holocene delta Q22-1 3 V. Karst- generated relief Karst- generated relief. Tropical karst limestone mountains with pyramid and cone remnant tops. 1 Mountain and group of remnant limestone mountains on the plain. Flooding marginal Karst field 2 ***Note: 1- Non-Liquefiable, 2- Low susceptibility to liquefaction, 3- Moderate susceptibility to liquefaction, 4- High susceptibility to liquefaction Vietnam Journal of Earth Sciences 39(2), 139-154 151 Figure 4. Map of liquefaction susceptibility of Hanoi city obtained from the Iwasaki (1982) method As can be seen in Figure 5, after integra- tion of liquefaction susceptibility based on both geological and geomorphologic charac- teristics, moderate liquefaction susceptibility is still dominated by the entire Hanoi region. The equivalence in zoning shapes of the two maps in Figure 5 and Figure 3 can be ex- plained by the weighting rule applied in compiling these maps. A slight difference between these maps is observed in the west- ern suburb and in the northwestern part of the city, where the none-liquefiable zone in Figure 3 is less than the same zone in Figure 5. The difference between two maps in Figure 5 and Figure 4 is considerable, where the zone with high liquefaction susceptibility in Figure 5 is much less in the area in com- pare with that zone in Figure 4. It should also be noted that, the use of the 1:320,000 scale geomorphologic map and the much bigger 1:25,000 scale engineering-geologic map leads to the different reliability of the two results. However, this fact does not affect the final results thanks to the weighting rule de- scribed above. In general, the geomorpholog- ic characteristics clearly affect the liquefac- tion susceptibility in the areas with higher elevation, of denudation origin. Bui Thi Nhung, et al./Vietnam Journal of Earth Sciences 39 (2017) 152 4. Conclusion In this paper, using published geologic and geomorphologic information of Hanoi (Dao Dinh Bac, 2010; Phan Trong Trinh, 2012, Vu Thanh Tam, 2014; Ngo Quang Toan, 2015), the ground liquefaction potential have been assessed using the methods proposed by Youd and Perkins (1978) and Iwasaki (1982). The obtained thematic maps of liquefaction suscep- tibility based on the subsurface lithology char- acteristics (Figure 3) and geomorphologic characteristics (Figure 4) are assigned with the weighting values of 60% and 40%, respective- ly and integrated into a final GIS map of lique- faction susceptibility of Hanoi city (Figure 5). Figure 5. Map of liquefaction susceptibility of Hanoi city based on the geologic and geomorphologic characteristics The resulting map shows that the liquefac- tion susceptibility of Hanoi city is classified into four categories: high, moderate, low sus- ceptibility to liquefaction and not liquefiable. The highest potential of liquefaction is ob- served in a zone spreading along the ancient Red river’s bed and some places in the down- town area, which are the Late-Holocene sedi- mentary deposits comprise sand, fine sand mixed with dark gray clayish silt-bearing plant humus, brownish gray mud with the high level of ground water. The zone contains Vietnam Journal of Earth Sciences 39(2), 139-154 153 such geomorphologic units as rivers, lakes, swamps and low alluvial plains. The zone with the moderate potential of liquefaction occupies the majority of the city’s area, stretching along both sides of the Red river’s bank, comprise such petrographic units as clay, clayish silt, sand, sandy silts of Holocene age and such geomorphologic units as plains of the river and marine origin and alluvial plains. The northwestern and northeastern mountainous areas of Hanoi known as the Soc Son, Chan Chim and Ba Vi are not liquefiable or having low liquefaction susceptibility, which comprise claystone, sandstone, hard rock of denudation origin. It is worth empha- sizing that the buildings and pipelines in the zone with high and moderate potential of liq- uefaction are vulnerable to damage due to horizontal displacement during earthquakes. Soil liquefaction is a major cause of dam- age during earthquakes. The liquefaction sus- ceptibility map displays the zones with lique- faction potential, or the risk of initiation of liquefaction during future earthquakes and can be used as the input for calculation and map- ping of liquefaction hazard map of the study area. Being a qualitative function of geologic and geomorphologic characteristics, the lique- faction susceptibility is independent with the seismicity of a certain region. Therefore, the use of other region-dependent elements as seismicity, geotechnical information is con- sidered as the next step for the research of liquefaction assessment. The obtained liquefaction susceptibility map provides useful information for the urban seismic hazard assessment and seismic risk management, mitigation and reduction for Hanoi city. The map can be used as the refer- ence for civil and geotechnical engineers for antiseismic design of the new constructed buildings or restoration of old and damaged buildings. In general, the obtained liquefac- tion susceptibility map displays a portrayal of the liquefaction susceptibility of the Hanoi city as the preliminary information for the regional research. References Bird JF, Bommer JJ, 2004b. Earthquake Losses due to Ground Failure. Submitted to Engineering Geology, 75(2), 147-179. Bird Juliet F, Bommer Julian J., 2004a. 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