Journal Code Article ID Dispatch: 20.02.13 CE: J G R B 50122No.ofPages: 18 ME:

– 1 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 118, 1 18, doi:10.1029/2012JB009541, 2013 61 2 62 3 63 4 64 5 65 6 Ages and relative sizes of pre-2004 tsunamis in the Bay of Bengal 66 7 67 8 inferred from geologic evidence in the Andaman and Nicobar Islands 68

9 1 1 1 2 69 10 C. P. Rajendran, Kusala Rajendran, Vanessa Andrade, and S. Srinivasalu 70 11 Received 19 June 2012; revised 28 January 2013; accepted 2 May 2013. 71 12 72 [1] Geologic evidence along the northern part of the 2004 Aceh-Andaman rupture suggests 13 that this region generated as many as five tsunamis in the prior 2000 years. We identify this 73 14 evidence by drawing analogy with geologic records of land-level change and the tsunami in 74 15 2004 from Andaman and Nicobar Islands (A&N). These analogs include subsided mangrove 75 16 swamps, uplifted coral terraces, liquefaction, and organic soils coated by sand and coral 76 17 rubble. The pre-2004 evidence varies in potency, and materials dated provide limiting ages on 77 18 inferred tsunamis. The earliest tsunamis occurred between the second and sixth centuries A. 78 19 D., evidenced by coral debris of the southern Car Nicobar Island. A subsequent tsunami, 79 20 probably in the range A.D. 770–1040, is inferred from deposits both in A&N and on the 80 21 Indian subcontinent. It is the strongest candidate for a 2004-caliber earthquake in the past 81 22 2000 years. A&N also contain tsunami deposits from A.D. 1250 to 1450 that probably match 82 23 those previously reported from Sumatra and Thailand, and which likely date to the 1390s or 83 24 1450s if correlated with well-dated coral uplift offshore Sumatra. Thus, age data from A&N 84 25 suggest that within the uncertainties in estimating relative sizes of paleo-earthquakes and 85 26 tsunamis, the 1000 year interval can be divided in half by the earthquake or earthquakes of A. 86 27 D. 1250–1450 of magnitude >8.0 and consequent tsunamis. Unlike the transoceanic tsunamis 87 28 generated by full or partial rupture of the subduction interface, the A&N geology further 88 29 provides evidence for the smaller-sized historical tsunamis of 1762 and 1881, which may 89 30 have been damaging locally. 90 31 91 Citation: 32 Rajendran C. P., K. Rajendran, V. Andrade and S. Srinivasalu (2013), Ages and relative sizes of pre-2004 92 J. Geophys. Res. 118 33 tsunamis in the Bay of Bengal inferred from geologic evidence in the Andaman and Nicobar Islands, , , 93 doi:10.1029/2012JB009541. 34 94 35 95 36 1. Introduction et al., 2008; Monecke et al., 2008]. An older tsunami 96 (A.D. 780–990) has also been reported from Meulaboh 37 97 [2] The Mw 9.2 2004 earthquake and its accompanying [Monecke et al., 2008]. Reports from Sri Lanka concur with 38 tsunami were unprecedented, as there was no recognized an approximately 1000 year old tsunami [Ranasinghage 98 39 evidence that the Aceh-Andaman subduction zone plate et al., 2010]. Studies on the sediment cores from a lagoon 99 40 boundary could generate a megathrust earthquake and a on the southeastern coast of Sri Lanka suggest three 100 41 transoceanic tsunami. How often is a 2004-type earthquake tsunamis in the Indian Ocean between ~4000 and 5500 years 101 42 likely to occur? Initial results from the east coast of India ago and one event around 1600 years ago [Jackson, 2008]. 102 suggest that a predecessor of the 2004 tsunami occurred 43 Improving recurrence estimates of 2004-type events requires 103 ~1000 years ago on the east coast of India [Rajendran identification of synchronous evidence from other parts of 44 et al., 2006, 2011]. Studies elsewhere along the Indian 104 the 2004 rupture zone. The Andaman and Nicobar Islands 45 Ocean coasts have led to evidence of older tsunamis at Phra 105 (referred to as A&N) are key to constraining tsunami recur- 46 Thong (Thailand), Meulaboh (northern Sumatra, Indonesia), 106 rence because they together span and adjoin two thirds of the 47 F1 and Sri Lanka (see Figure 1 for locations). The penultimate 107 length of the 2004 rupture area (Figure 1). In A&N, the 2004 48 tsunami at Phra Thong is dated at A.D. 1300–1450, with 108 – event is recorded by evidence for coseismic uplift and subsi- 49 matching ages from Meulaboh (A.D. 1290 1400) [Jankaew dence, by liquefaction features and by tsunami deposits. 109 50 Some of these have been described previously [Rajendran 110 51 et al., 2007, Malik et al., 2011]. 111 Q1 All Supporting Information may be found in the online version of 52 this article. [3] Historical documents for the last 500 years that seem 112 53 1Centre for Earth Sciences, Indian Institute of Science, Bangalore, India. reliable do not point to any coastal flooding leading to major 113 54 2Department of Geology, Anna University, Chennai, India. loss of life on the east coast of India [Rajendran, 2012]. The 114 55 Corresponding author: C. P. Rajendran, Centre for Earth Sciences, earliest historically documented earthquake from this region 115 56 Indian Institute of Science, Bangalore 560012, India. (cprajendran@ is the 2 April 1762 earthquake (M ≥7.6) off Myanmar, which 116 57 ceas.iisc.ernet.in) caused a tsunami that affected the coasts of West Bengal and 117 58 ©2013. American Geophysical Union. All Rights Reserved. Bangladesh (Figure 1, inset) [Chhibber, 1934; Cummins, 118 2007]. This earthquake left sedimentary records near Port 59 2169-9356/13/2012JB009541 119 60 120 1 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 attempted to obtain multiple lines of evidence collated from 63 4 coseismic features, establish their chronology and regional 64 distribution, and use these to estimate the timing and size 5 65 of previous tsunamigenic earthquakes. Even though a 6 combination of multiple coseismic effects (like subsidence, 66 7 uplift, and liquefaction) and occurrence of varied types of 67 8 tsunami deposits make the A&N potentially well suited to 68 9 search for geological clues of pre-2004 events, the logistical 69 10 and administrative problems in reaching remote areas and 70 11 restrictions to visit tribal reserves prevented us from 71 12 accessing some potential investigative sites. Nevertheless, 72 13 our effort provides a starting point in documenting the 73 14 effects of a great earthquake in an important part of the 74 15 Andaman-Sumatra plate boundary. Based on the intermittent 75 observations made during the last 6 years, along the A&N, 16 76 covering regions from 7 to 14N latitude, this study presents 17 the first comprehensive regional database on the sedimentary 77 18 records of potential tsunamis or earthquakes of the past. 78 19 79 20 2. Tsunami Geology: Background and Methods 80 21 81 22 2.1. Evidence of Tsunamis Along Subduction-Zone 82 23 Coasts 83 24 [5] Great subduction-zone earthquakes and tsunamis 84 25 invariably leave a trail of telltale geomorphic features and 85 26 deposits on the shores of island arcs. Coseismic and 86 interseismic bending and unbending of the upper crust lead 27 87 to characteristic geomorphic responses. A great thrust earth- 28 quake occurs when ridge-push and slab-pull forces exceed 88 29 the strength of the locked interface thrust zone (Figure 2, F2 89 30 top panel). Thus, prior to such an earthquake, ridge-push 90 31 forces dominate, leading to upwarping of the crust, while 91 32 slab-pull forces overtake all other components of plate driv- 92 33 ing forces during coseismic and postseismic periods 93 34 [Spence, 1987; Lay et al., 1989]. For instance, interseismic 94 35 uplift in the A&N segment has been inferred from pre- 95 36 2004 emergence of coral platforms as well as dominance 96 37 of thrust faulting earthquakes on the overriding plate 97 [Rajendran et al., 2007; Andrade and Rajendran, 2011]. 38 Figure 1. Regional map of the northern Indian Ocean 98 [6] Tsunami-deposited sands in conjunction with subsided 39 countries showing the 2004 and 2005 ruptures [Chlieh coastal lowlands have been inferred as evidence for local 99 40 et al., 2007] and the 1679, 1881, and 1941 ruptures [Ortiz tsunamigenic earthquakes in Alaska, Cascadia (United 100 41 and Bilham, 2003; Rajendran et al., 2007]. The broken States), Chile, and Hokkaido (Japan) [Ovenshine et al., 101 42 black hinge line separates areas of 2004 coseismic uplift 1976; Atwater, 1987; Minoura et al., 1987; Nelson et al., 102 43 from subsidence. Filled circles are sites discussed in this 103 fi 1996; Nanayama et al., 2003; Cisternas et al., 2005; 44 study; lled squares are sites from other published work. Shennan and Hamilton, 2006]. Coseismic emergence of 104 Selected earthquake mechanisms are from Global CMT 45 – land along subduction-zone coasts has also been recorded 105 (gray: 2000 2004; red: 2004-present). Inset: index map of [Ota and Yamaguchi, 2004]. 46 the region showing the sources of known great earthquakes. 106 [7] Geological evidence of tectonism can often be 47 Abbreviations: BD: Bangladesh, WB: West Bengal, Kp: 107 48 deduced from the remains of subsided vegetation buried in 108 Kaveripattinam, Mp: Mamallapuram, Me: Meulaboh, MY: the regional stratigraphy. Where tsunami deposits are syn- 49 109 Myanmar, PT: Phra Thong, Sim: Simeulue, SL: Sri Lanka, chronous with subsidence, there is more certainty in ascrib- 50 TH: Thailand, Va: Vakarai. ing the causative event to tectonism. Coseismic subsidence 110 51 followed by a tsunami usually leads to swampy conditions 111 52 Blair in South Andaman [Malik et al., 2011]. The east coast in some places and debris deposition over preexisting 112 53 of India has experienced two previous transoceanic tsunamis surfaces, leading to mud-peat associations as well as buried 113 54 in 1881 and 1883 [Dominey-Howes et al., 2007], and the organic-rich soils (Figure 2, bottom panel). Deposition of 114 55 former caused a surge of 0.75 m (or more) at Car Nicobar tsunami sand over vegetated surfaces leading to sharp 115 56 (Figure 1, inset) [Rogers, 1883; Ortiz and Bilham, 2003]. contact between peat-rich soil and the overlying sand is 116 57 [4] This paper brings together a large sample of modern another depositional feature that is commonly observed in 117 58 analogs and ancient evidence to clarify recurrence intervals such situations. While coasts adjoining subduction zones 118 59 of earthquakes in A&N in the last 2000 years. Here, we have may preserve synchronous evidence for coseismic 119 60 120 2 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 63 4 64 5 65 6 66 7 67 8 68 9 69 10 70 11 71 12 72 13 73 14 74 15 75 16 76 17 77 18 78 19 79 20 80 Figure 2. Top panel shows (left) schematic representation of the subduction zone, showing major plate- 21 driving forces and tectonic and geomorphic features (RP: ridge push, SP: slab pull, NB: negative 81 22 buoyancy, SB: resistance to slab bending; modified after Spence [1987]); (center) gradual uplift (dark 82 23 arrow) and subsidence (gray arrow) during the preseismic period along the accretionary prism (AP); 83 24 (right) coseismic subsidence (dark arrow) and uplift (gray arrow) that occur on parts of the accretionary 84 25 prism. Bottom panel shows coastal processes during various stages of the seismic cycle: (left) static 85 26 conditions during interseismic period, (center) coseismic subsidence leading to submergence of land 86 27 and secondary effects such as liquefaction, (right) paleo-features preserved within the shallow sedimentary 87 fi 28 sections hundreds of years after the tsunamigenic earthquake (modi ed after Atwater et al. [2005]). 88 29 89 30 subsidence or emergence as well as tsunami deposits, distant by recent tsunamis help us attribute a similar origin to com- 90 31 shores preserve only the latter. For example, during the 2004 parable deposits in coastal stratigraphic sections. In addition 91 32 earthquake, subsidence and tsunami deposition occurred to the primary suite of criteria, some secondary effects of 92 33 along the near-source coasts of Sumatra [Moore et al., earthquakes can also be used to characterize previous events. 93 34 2006] and A&N [Rajendran et al., 2007], while the distant For example, preserved evidence of soil liquefaction has 94 35 shores like Thailand, Sri Lanka, and India are represented been used to estimate the effects of ground shaking, as in 95 36 solely by pervasive sand deposits [Choowong et al., 2007; the case of the A.D. 1700 Cascadia earthquake [Obermeier 96 37 Richmond et al., 2006; Srinivasalu et al., 2007]. and Dickenson, 2000; Takada and Atwater, 2004]. Previous 97 [8] Most studies focus on depositional aspects, but the fact studies along other subduction zones that use such criteria 38 98 that tsunami can also be an efficient erosive agent is gener- to identify past tsunamis or earthquakes have helped us 39 ally overlooked. Among different factors, high coastal relief develop a methodology to be followed. An additional advan- 99 40 appears to be most decisive in tsunami-driven erosion as it tage in the A&N is the availability of 2004 analogs of earth- 100 41 promotes high-velocity backflow [MacInnes et al., 2009], quake/tsunami effects for comparison [e.g., Atwater and 101 42 whereas on the low-relief coasts the net effect is that of Hemphill-Haley, 1997; Paris et al., 2007; Bourgeois, 102 43 deposition [Gelfenbaum and Jaffe, 2003; Umitsu et al., 2009; Goff et al., 2012]. Q2 103 44 2007]. Both pretsunami and posttsunami measurements are 104 45 necessary to quantify the coastal morphological changes 2.2. The 2004 Deposits of Andaman-Nicobar as Analogs 105 46 brought about by either deposition or erosion [Gelfenbaum [10] The islands of A&N occupy the northern half of the 106 47 and Jaffe, 2003; Jaffe and Gelfenbaum, 2007]. Although 2004 rupture, showing subsidence in its southern and uplift 107 fl 48 we observed areas of erosion, such as stripped coral ats in the northern parts, represented by drowned mangrove 108 and exposed tree roots in many parts of A&N, no quantita- forests and raised coral-encrusted beaches, respectively 49 109 tive studies on post-2004 erosional changes or any estima- (see Figure 1 for location). The southern Nicobar Islands 50 tion of tsunami flow speeds and flow direction from tsunami and South Andaman showed coseismic submergence during 110 51 deposits have been carried out in this region. 2004 (Figure 3a). Uplifted coral terraces showed coseismic F3 111 52 [9] A suite of diagnostic characteristics are used for the emergence along parts of A&N, especially Middle and 112 53 identification of paleo-tsunami deposits, including spatially North Andaman. Interseismic emergence of coral platforms 113 54 extensive deposition, inland and upward fining sequences, was noted also along the beaches of Campbell Bay 114 55 unconformable or erosional contacts with lower strata, and (Figure 3b). On these islands, the 2004 on-land tsunami 115 56 marine fossil assemblages, among them. Several of these deposits constitute coarse to fine sand deposits, mixed with 116 57 criteria have been validated through field studies of the shells and coral fragments or coral and/or organic debris 117 fi 58 2004 tsunami deposits [e.g., Bahlburg and Weiss, 2006; deposited over ne sandy beaches (Figure 3c). Deposits that 118 59 Moore et al., 2006; Switzer et al., 2012]. The evidence left share similar characteristics were reported along the Sumatra 119 60 120 3 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 63 4 64 5 65 6 66 7 67 8 68 9 69 10 70 11 71 12 72 13 73 14 74 15 75 16 76 17 77 18 78 19 79 20 80 21 81 22 82 23 83 24 84 25 85 26 86 27 87 28 88 29 89 30 90 31 91 32 92 33 Figure 3. (a) Coseismically subsided vegetation at Port Blair. (b) Pre-2004 emerged coral reef at 93 34 Campbell Bay. (c) Tsunami sand deposited over pre-2004 vegetated surface at Car Nicobar. (d) 2004 94 35 coseismic liquefaction feature at Diglipur. (e) Pre-2004 beach at Mus, Car Nicobar. (f) The same beach 95 36 showing extensive debris deposits after the 2004 tsunami. 96 37 97 coast [Moore et al., 2006]. The 2004 earthquake was also conditions at locations away from regular beach processes, 38 98 associated with soil liquefaction, which resulted in serve as pointers for previous sea surges [Etienne et al., 39 sandblows and sand boils in some parts of North Andaman 2011]. Thus, layers of sand or coral rubble overlying 99 40 (Figure 3d). organic-rich soil or regular beach facies sand found within 100 41 [11] Although there are no previous reports of boulder shallow stratigraphy are construed as evidence for previous 101 42 deposition along the beaches of A&N, the field evidence sea surges. 102 43 of the 2004 earthquake suggests that movement of large- [12] The nature of 2004 tsunami deposits varies along 103 44 sized coral debris did occur during the surge. Systematic A&N, probably controlled by the near-shore bathymetry, 104 45 posttsunami mapping of debris has not been done along coastal morphology, and composition and thickness of 105 46 A&N, but based on our pre-2004 visits to these coasts, we beach sand. Thus, the deposits consisted of fine to graded 106 47 note that the large boulders on these beaches were deposited sediments (~70 cm) to piles of coral debris consisting of 107 48 by the tsunami (Figures 3e and 3f). It has been observed that individual fragments mixed with calcareous sand and 108 the 2004 tsunami mobilized large volumes of boulders both organic material. Some of the larger pieces measured 49 109 near the earthquake source as well as along distant shores as ~50 cm across, but in general, the deposits showed no 50 in western Aceh and Thailand [Goto et al., 2007; Kelletat systematic variation in the size and were independent of 110 51 et al., 2007]. Near Lhok Nga, close to the earthquake source, the distance of transport. On the island of Car Nicobar, the 111 52 the tsunami deposited a bed of boulders, typically with long tsunami deposited a thick pile of sand, 500 m inland, and 112 53 axis of the individual pieces ranging from 0.7 to 1.5 m in littered the coasts with large-sized coral debris (Figure 3f). 113 54 length, at distances of 1 km from the coastline and 7 m above Where stream inlets were available, the waves carried debris 114 55 the mean sea level [Paris et al., 2007]. Large tsunamis are as far as 1–2 km inland along most parts of the islands—Car 115 56 known to have sufficient flow velocities to transport Nicobar, Hut Bay, Port Blair, and Interview Island 116 57 boulders from 15 to 25 m water depths that are deposited [Ramanamurthy et al., 2005]. Deposits on East Island, 117 58 along the beaches and inland waterways as the wave energy located on the northernmost part of the rupture, comprised 118 59 reduces. Such deposits, when preserved in favorable mostly remobilized larger-sized imbricated coral debris. 119 60 120 4 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 [13] We use the aforementioned depositional and geomor- 2.4. Tsunami Chronology 63 4 phic cues to look for previous tsunamis and earthquakes. [16] In this work spanning locations over an 800 km stretch 64 Selection of accessible sites was based primarily on the 5 from north to south and covering a variety of environments 65 coseismic effects of the 2004 earthquake, excluding national where stratigraphically controlled datable materials are di- 6 parks, tribal reserves, and military bases. We used satellite- 66 7 verse, we have bracketed the ages based on multiple samples 67 based geomorphology, followed by random ground checking, wherever possible. We used radiocarbon (14C) ages of wood, 8 68 to select sites for detailed studies. Preliminary exploratory peat, and mollusk shells selected from above, below, and/or 9 trenching and hand coring were done to examine the nature within the depositional event layers. Chronological constraints 69 10 of the substrata and depth to water table. Final site selections on previous tsunamis/earthquakes were developed based on 70 11 were based on the following observations: one, areas that were conventional beta counting and accelerator mass spectroscopy 71 12 coseismically uplifted or subsided; two, areas where streams (AMS) methods. Our samples provide only limiting ages 72 13 transported vegetative and coral debris inland; three, areas within which the tsunami may have occurred. This is because 73 14 where the 2004 tsunami debris including coarse calcareous of the uncertainty associated with the time of death of the 74 15 sand sheets and coral fragments were found; and four, sites organism/tree, which marks the onset of the radiocarbon clock. 75 of the 2004 soil liquefaction. 16 Parts of trees that might undergo in situ burial during subsi- 76 dence and those that are transported are associated with 17 2.3. Alternative Depositional Processes 77 18 varying degrees of uncertainty. 78 [14] Eustatic sea level changes can impact coastal pro- [17] Aside from the depositional and contextual uncer- 19 fl 79 cesses, and therefore, it is important to understand the in u- tainties, errors are also associated with analytical resolution 20 ence of previous long-term trends of sea level variations in [Lettis and Kelson, 2000]. For example, isotope fraction- 80 Æ 14 21 sediment deposition. Globally, the sea level was 121 5m ation and the residence time of C in the global and local 81 22 below present-day sea level at the time of the last glacial marine reservoir affect shell samples and their ages [Douka 82 23 maximum, and over the last 18,000 years, the sea level has et al., 2010]. It takes 200–500 years for the present-day 83 24 been steadily rising with two pulses of rapid rise (around carbon dioxide in the atmosphere to be equilibrated within 84 25 12,000 and 9500 years ago) [Fairbanks, 1989]. Sea level rise the ocean water column, which can possibly affect the age 85 26 has not been uniform due to variations in ice and water calibration of shell samples that are younger than 500 years. 86 volume, gravity, Earth’s rotation, shoreline configuration, 27 Postmortem recrystallization and inclusion of younger 87 and isostatic responses to deformation of crust and mantle 28 carbon during burial can also lead to lower age estimates. 88 [Clark et al., 1978]. Mid-Holocene high stands (~1–5m) 14 fi “ ” 29 Incorporation of C-de cient (or dead ) older carbon from 89 have been reported for some locations, but a general lower- limestone and other carbonate rocks has the reverse effect as 30 90 ing trend has been characteristic since late Holocene [Horton commonly observed in dating mollusks, marine and other- 31 et al., 2005; Woodroffe and Horton, 2005]. The studies on wise [e.g., Douka et al., 2010; Pigati et al., 2010]. 91 32 92 corals off Sumatra (Indonesia) suggest that sea level at this [18] Considering the aforementioned uncertainties, we 33 location is marked by a high stand around 5000 years ago, have used a relative grading criterion and classified the 93 fl 34 but the overprinting of tectonic processes might in uence samples as belonging to categories “A” and “B” (Table 1). T1 94 35 the general trend [Zachariasen et al., 1999]. Further north, This grading is based not only on radiocarbon analytical errors 95 36 around Car Nicobar, the sea level has remained steady for and the varying nature of samples but also on the uncertainties 96 37 the last 2500 years, but for a slight lowering trend of involving their stratigraphic context. Thus, ages of in situ roots 97 À1.0 m [Rajendran et al., 2008]. 38 or tree trunks are considered as “A” quality since they repre- 98 [15] Alternative mechanisms such as cyclones and storms sent coseismic subsidence, whereas an age estimate based on 39 can also act as depositional agents. A&N are located 99 40  peat or transported wood is considered as of lower quality 100 between 6 and 14 N, and tropical cyclones typically origi- (“B+”). Ages derived from shells are treated as “BÀ” due to 41 101 nate in such latitudes [Gill, 1982]. However, as an area their chemical interaction with the surroundings (Table 1). 42 straddling a zone of minimum Coriolis force [Gray, 2000], Only well-preserved shells collected from probable tsunami- 102 43 storm impact on A&N is minimal, which is also authenti- deposited debris layers were chosen for dating. 103 44 cated by documentary evidence on near absence of cyclone [19] Raw ages obtained from radiocarbon laboratories were 104 45 impacts on the islands since 1891 [India Meteorological corrected using CALIB version 6.1.1, with calibration curves 105 46 Department, 2008]. Historical records for the A&N exist intcal09 and marine09 used for terrestrial and marine samples, 106 47 from the British colonial period, and they do not refer respectively (Table 2) [Stuiver and Reimer, 1993; Reimer et al., T2 107 48 to any storm occurrences on these islands [Government 2009]. The marine reservoir correction for radiocarbon from 108 Gazetteer, 1908]. The trajectories of storms show either 49 Stewart Island, North Andaman (12 Æ 34 from Dutta et al. 109 northward or eastward trends until they make landfall on [2001]), and from the Nicobar Islands (32 Æ 70 from Southon 50 the distant northern and eastern shores of the Bay of Bengal. 110 51 et al. [2002]) has been applied to shell ages, as these locations 111 Further, if a region is prone to storm activity, their frequency are closest to the respective sampling sites. 52 is expected to be much more, compared to that of tsunami 112 53 occurrences, and their effects should be observable in the 113 54 shallow stratigraphy. Thus, storms cannot be considered as 3. Results From Field Investigations 114 55 an effective mechanism of coastal debris deposition along 115 56 A&N. Being the only other known mechanism, it is likely 3.1. Southern Nicobar Sites 116 57 that earthquake-generated tsunamis are the single most 3.1.1. Campbell Bay, Great Nicobar 117 58 effective depositional (as well as erosional) processes along [20] This island closest to the source of the 2004 earth- 118 > 59 this coast. quake experienced a coseismic subsidence of 1.5 m, and 119 60 120 5 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 fi 3 Table 1. Quality Criterion Followed in This Study for Classi cation of Samples to Develop Paleo-earthquake/Tsunami Age Estimates 63 4 Category Guiding Considerations 64 5 A Radiocarbon ages based on definitive repeat of a process. For example, roots of trees preserved in their growth position in a region that 65 6 experienced destruction due to coseismic subsidence/uplift in 2004. Wide-spread occurrence and in situ preservation of these features 66 7 and their association with complementary evidence such as synchronous tsunami deposition and/or liquefaction features are other 67 considerations in assigning an “A” quality to a sample. The best example presented in this study is an age estimate based on subsided 8 mangrove trees at Rangachanga, Port Blair. 68 9 B Ages based on intense ground shaking such as liquefaction and venting of sand, coseismic land level changes (uplift and subsidence), and 69 10 tsunami deposition. The likelihood that these ages pre- or postdate a depositional event makes this set of data inferior to the in situ root- 70 based age. A peat/organic-rich layer may form due to a number of processes. Similarly, a transported wood piece may be considerably 11 older than the time of its deposition. Postdepositional alteration (such as recrystallization and inclusion of younger carbon) can also 71 12 affect these ages. We correlate them with stratigraphic evidence of ground shaking, high-energy depositional events, or coseismic land 72 13 level changes. Thus, ages based on peat-rich soil underlying a tsunami deposit and those based on buried logs of wood and/or roots 73 that do not appear to be in their growth position are treated as B+. Ages inferred from molluscan shells are treated as BÀ when they 14 are based on multiple samples, suggestive of synchronous death and deposition. 74 15 75 16 76 17 its near-shore regions have remained waterlogged since location. For example, on the Laxman Beach (see Figure 4a, 77 18 then. The largest of the islands (1045 km2) south of 10N inset, for location), we saw evidence of top soil erosion 78 19 latitude has rugged topography, its hilly terrain closely exposing roots and coral reef at a depth of 0.5 to 1 m. Calcar- 79 20 Q4 bordering the narrow coast. Tsunami inundation on its east eous rock immediately below the present surface yielded an 80 21 coast was ~500 m on an average [Ramanamurthy et al., age of 2690–3330 cal years B.P., suggesting that a shallow 81 22 2005], and the deposits typically consisted of beds of coarse sea that facilitated the growth of coral reef existed along 82 23 sand mixed with pebble-sized coral fragments and shells. the coast ~3000 years ago. 83 24 We examined regions along the sandy beaches on its east 3.1.2. Car Nicobar 84 coast to select sites where the water table is deep enough [24] The pear-shaped island of Car Nicobar, located to the 25 2 85 26 to examine sections. One of our sites is on the Peakody north of Great Nicobar, covers an area of 127 km and shows 86 Beach, the headland part of the embayment, while the other amoreorlessflat topography (see Figure 1 for location). This 27 87 F4 is on the Laxman Beach (Figure 4a). island experienced 1–1.25 m subsidence during 2004, and the 28 88 [21] Currently occupied by modern vegetation, Peakody tsunami traveled ~1 km inland, the waves attaining a maxi- 29 Beach was partly destroyed by the tsunami, which uprooted mum height of ~7 m [Ramanamurthy et al., 2005; Rajendran 89 30 trees and organic debris that remain strewn about the beach et al., 2007]. Coral debris constituting pebbles, cobbles, and 90 31 (Figure 4a). Here the sedimentary sections exposed buried boulders were deposited on its sandy beaches. The shallow 91 32 peat of varying thickness as an intervening layer of varied coastal sections exposed deposition dominated by calcareous 92 33 thickness within the beach facies. In one of the representa- sand mixed with shells, which is interrupted by the deposition 93 34 tive sections presented here, we show association of peat of intervening layers of coral debris in some sections. Because 94 35 with the beach facies. The section (site CB-1) in Figure 4b of the long-distance inland transportation of debris, we 95 36 (~150 m inland and 1.5 m above the surf zone) exposed focused on sections that exposed most recent debris layers 96 37 calcareous sand mixed with shells at its base and on the mixed with pottery sherds representing a more recent event, 97 top. The intervening peat bed ~30 cm thick is laterally presumably the 1881 tsunami. Since we found these sites as 38 98 continuous for ~100 m, to the north and south (Figure 4b). good repositories of previous tsunamis that can be conclu- 39 The overlying calcareous sand mixed with shells is ~60 cm sively linked to a historically known tsunami, we focused on 99 40 thick and makes a sharp contact with the peat layer. sites on elevated berms along the foreshore region and further 100 41 [22] Unlike the organic-rich peaty soils of coastal marshes inland. Here we discuss sections at Sawai, Mus, Arong, and 101 42 overlain by tidal mud reported from regions of coseismic Kakkana (see Figure 5 for locations). F5 102 43 subsidence and submergence [e.g., Combellick, 1986], the [25] We found that most of the coarser rubble-sized debris 103 44 peat found in this section appears to have formed from was deposited 20–25 m from the surf zone, generally within 104 45 decayed local vegetation within depressions. The peat layers <100 m. Sizes of clasts and thickness of debris showed 105 46 formed in these depressions are not associated with any decreasing landward trend, with some exceptions especially 106 47 overlying layer of mud, but are bounded by calcareous sand where larger boulders were transported beyond ~500 m 107 48 on its top and bottom. We infer that this peat layer could through stream channels. Spatial extent and size distribution 108 have formed only by the sudden deposition of vegetative of tsunami boulder deposits are known to depend on the 49 109 matter, as it happened in 2004. The peat was dated at A.D. characteristics of their source (e.g., coral reefs and beach 50 1290–1680, and presuming that it formed from the organic rocks) and local coastal morphology. Although the magni- 110 51 debris deposited by the tsunami, it could be interpreted as tude of a paleo-tsunami cannot be derived from the nature 111 52 the maximum age of the depositional event. The overlying of these deposits, their synchronous occurrence with fine 112 53 calcareous sand is devoid of any organic or coral debris, sand and marine organisms suggests bed load and suspended 113 54 and we take this as an indication that the region had gener- transport modes, generally associated with high-energy 114 55 ally remained free of any major sea surges during the inter- waves [Paris et al., 2007]. 115 56 vening period. 3.1.2.1. Sites at Sawai 116 57 [23] We explored parts of this beach located to the north of [26] Located on the west coast of Car Nicobar, Sawai 117 58 CB-1 which generally showed an eroded landform implying beach was strongly impacted by the 2004 tsunami, and the 118 59 that the 2004 tsunami had an erosional impact in this most visible evidence is the freshly deposited coral debris, 119 60 120 6 60 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Table 2. Calibrated 14C Age Data for Samples From the Andaman and Nicobar Islands 14 Sample Name and C Age Calibrated Ageb Sample Location Lab Codea (years B.P.) (A.D., 2s Range) Categoryc Comments Campbell Bay (Subsided in 2004 by 1–3m) Peakody Beach (CB-1) 7N, 93.936E PEA-1/B/1 BS 2766 420 Æ 120 1290–1680 B+ Sample from peat bed between two calcareous sand layers. –

Car Nicobar (Subsided in 2004 by 1 1.25 m) TSUNAMIS PRE-2004 OF SIZES AND AGES AL.: ET RAJENDRAN Sawai (SW-1) 9.198N, 92.722E S/B1 NZA 32335 631 Æ 25 1540–1900 BÀ Gastropod embedded in lower coral debris layer. Sawai (SW-2) 9.199N, 92.724E S/B2 NZA 32336 660 Æ 25 1510–1880 BÀ Mus (MS-1) 9.241N, 92.791E MUS/B2/1 NZA 32331 1827 Æ 30 430–750 BÀ Gastropod from upper coral debris layer. MUS/B3/1 NZA 32332 2144 Æ 35 70–440 BÀ Gastropod from lower coral debris bed, associated with larger MUS/B3/1A NZA 32333 2221 Æ 30 B.C. 20–A.D. 360 BÀ clasts than the upper coral debris bed at same site. Arong (AG-1) 9.172N, 92.722E A1/L2/D NZA 30290 192 Æ 30 1730–1810 B+ Peat associated with pottery sherds and coral debris. Arong (AG-2) 9.171N, 92.723E A2/L2/D NZA 30292 75 Æ 30 1810–1920 B+ Arong (AG-3) 9.171N, 92.726E AR/W/1 NZA 32334 1277 Æ 30 1020–1300 BÀ Gastropod embedded in coral debris bed. Little Andaman (Uplifted in 2004 by 0.3 m) Hut Bay (HB-1) 10.583N, 92.557E GS/HUT/OT NZA 23366 753 Æ 35 1480–1660 BÀ Gastropod from a semiconsolidated coral debris deposit, on an uplifted terrace [Rajendran et al., 2007]. Ongi Tikri (HB-2) 10.583N, 92.567E OGT/2/D NZA 29612 1325 Æ 20 650–710 B+ Peat from shallow core in swamp, formed as a result of subsidence. Q3 Hut Bay (HB-3) 10.587N, 92.557E HUT/B/2 IP 130 Æ 30 1800–1890 B+ Peat overlying fine calcareous sand. Probably associated 7 Hut Bay (HB-4) 10.596N, 92.538E HUT/B/1 NZA 28061 92 Æ 30 1810–1930 B+ with subsidence. South Andaman (Subsided in 2004 by 1.0 m) Rangachanga (PB-1) 11.581N, 92.736E RG/N/OP/2 BS 4064 1110 Æ 70 770–1040 A Wood from in situ dead trees visible along stream bank, 1 m below RG/N/OP/01 NZA 33616 1229 Æ 20 770–880 A surface. Samples are roots of an old swamp of mangroves. RG/Shell/D IP 318 1359 Æ 76 880–1250 BÀ Gastropod associated with submerged trees (previous two samples). Rangachanga (PB-2) 11.575N, 92.732E Bur-1/C/2 BS 2739 480 Æ 70 1380–1520 B+ Peat overlying fine calcareous sand, associated with subsidence. Middle Andaman (Some Parts Uplifted by 0.6–1.5 m and Some Subsided by 0.5 m in 2004) Panchavadi (PV-1) 12.578N, 92.961E PA/Peat/1 BS 2505 1490 Æ 140 240–780 B+ Wood preserved in the sediment. Interview Island (IN-1) 12.815N, 92.664E In-2 NZA 36582 382 Æ 25 1450–1520 B+ Wood from transported tree trunks along a stream bank. In-3 NZA 37162 395 Æ 20 1440–1510 B+ Interview Island (IN-2) 12.842N, 92.653E Int/3/A NZA 38919 233 Æ 20 1640–1670 B+ Wood deposited with coral debris on uplifted terrace. North Andaman (Uplifted in 2004 by 0.6 m) Diglipur (DG-1) 13.247N, 92.973E MN/Sill1/S3 & BS 2521 1050 Æ 100 770–1210 B+ Peat from within sand dike [Rajendran et al., 2007]. East Island (EA-1) 13.627N, 93.05E E/E/II/1 NZA 34162 1291 Æ 20 1040–1220 BÀ Lamellibranch from coral debris deposits, over and underlain by E/E/II/2 NZA 34163 1201 Æ 20 1120–1300 BÀ fine calcareous sand. aLab code abbreviations: NZA, Rafter Radiocarbon Laboratory (New Zealand); BS, Radiocarbon dating laboratory at the Birbal Sahni Institute of Palaeobotany (Lucknow, India); IP, Institute of Physics (Bhubaneshwar, India). bRadiocarbon ages were calibrated using CALIB (Version 6.1.1) [Stuiver and Reimer, 1993]. Terrestrial samples were calibrated using the intcal09 data set. 14C ages for marine samples were calibrated using the marine09 data set with ΔR value taken as 12 Æ 34 years for the Andaman Islands and 32 Æ 70 for the Nicobar Islands [Dutta et al., 2001; Southon et al., 2002; Reimer et al., 2009]. The two sigma ranges have maximum area under the probability distribution curve. Ages are rounded off to the nearest decade. cClassification of samples (as discussed in Table 1). 120 119 118 117 116 115 114 113 112 111 110 109 108 107 106 105 104 103 102 101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 63 4 64 5 65 6 66 7 67 8 68 9 69 10 70 11 71 12 72 13 73 14 74 15 75 16 76 17 77 18 78 19 79 20 Figure 4. (a) Photograph and profile of Peakody Beach at Campbell Bay, after the 2004 tsunami. 80 fi fi 21 Location of section CB-1, which is outside the frame of Figure 4a, is identi ed on the beach pro le. (b) 81 22 Sedimentary section CB-1 ~150 m inland showing a layer of peat sandwiched between the layers of 82 calcareous sand (CS). 23 83 24 84 25 85 26 86 27 87 28 88 29 89 30 90 31 91 32 92 33 93 34 94 35 95 36 96 37 97 38 98 39 99 40 100 41 101 42 102 43 103 44 104 45 105 46 106 47 107 48 108 49 109 50 Figure 5. (a) Index map of Car Nicobar Island showing sites discussed in the text. (b–e) Sections at 110 51 Sawai for Figure 5b, Mus for Figure 5c, Arong for Figure 5d, and Kakkana for Figure 5e are shown on 111 fi 52 the top, with corresponding beach pro les at the bottom. Photographs of selected sections showing debris Q5112 53 deposits and materials used for dating are in Figures 6 and S1. 113 54 114 55 ~500 m inland. Here we present observations from two sites, sedimentary sequence consists of a lower bed of calcareous 115 56 SW-1 and SW-2, located on the lee side of a 3 m high berm, sand mixed with fine shell fragments overlain by a 50 cm 116 57 ~170 m and 400 m inland (Figure 5b). The section at SW-1 thick coral debris layer consisting of pebble-sized pieces 117 fi 58 on the southern bank of a stream exposed alternating layers mixed with coarse- to ne-grained sand. A layer of calcare- 118 59 of coral debris and calcareous sand (Figure 5b). The ous sand (devoid of coral clasts) overlies the bed of debris. A 119 60 120 8 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 second band of coral debris, mixed with sand and shells, half [28] Presence of well-preserved shells found within the 63 fi 4 the thickness of its lower counterpart occurs above this ungraded mix of ne- and coarse-grained sand is a unique 64 calcareous sand, which is overlain by a thin layer of grayish, feature of the lower bed of debris in both these sections. 5 65 organic-rich calcareous sand. The top grayish layer of The intervening beds of calcareous sand in these sections 6 calcareous sand forms the basal surface for the 2004 debris contain shell fragments, but are devoid of any intact shells. 66 7 F6 deposition (Figure 6a). The top layer of calcareous sand that represents the more 67 8 [27] Section at SW-2, located ~400 m inland on a stream recent and part of regular deposition is also devoid of any 68 9 bank, exposed two layers of coral debris and an intervening well-preserved shells. Thus, the synchronous occurrence of 69 10 layer of calcareous sand, as observed at SW-1. However, the shells, coral fragments, and ungraded sand seems to be 70 11 debris consists of pebble-sized coral fragments mixed with unique to the suspended load from the neritic zone, mobi- 71 12 coarse- to fine-grained sand, and both the layers are thinner lized by high-energy waves. We collected more than half a 72 13 compared to their correlatives at SW-1. The top debris layer dozen intact and well-preserved molluscan shells from the 73 14 (~20 cm) is overlain by a ~60 cm thick organic-rich sand coral debris; their surfaces are fresh and shining, suggesting 74 15 layer and a thin layer of white calcareous sand. The upward sudden burial and minimal weathering (Figure 6a, inset). 75 reduction in the size of individual fragments and the progres- Calibrated AMS dates based on multiple samples from the 16 76 sive landward thinning were observed at both these sites lower layers in both these trenches suggest a sea inundation 17 which is generally explained as due to the landward decrease that occurred sometime from A.D. 1510 to 1900 (Table 2). 77 18 in flow velocity. At SW-2, we also recorded some pottery The upper bed of coral debris at SW-1 could not be dated 78 19 sherds mixed with the debris layer. as it did not yield any intact shells; however, its association 79 20 80 21 81 22 82 23 83 24 84 25 85 26 86 27 87 28 88 29 89 30 90 31 91 32 92 33 93 34 94 35 95 36 96 37 97 38 98 39 99 40 100 41 101 42 102 43 103 44 104 45 105 46 106 47 107 48 108 49 109 50 110 51 111 52 112 53 113 54 114 55 115 56 116 57 Figure 6. Photographs of sections at sites (a) SW-1 at Sawai, (b) MS-1 at Mus, (c) AG-3 at Arong, and 117 58 (d) KK-1 at Kakkana. Insets: gastropods (Cypraea sp.) for Figures 6a and 6b, Conus planorbis for 118 Q6 59 Figure 6c, and closer views of debris and pottery sherds for Figure 6d. 119 60 120 9 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 with pottery shreds suggests a younger age for its deposition, The peat samples mark the maximum age of the depositional 63 4 possibly due to the A.D. 1881 tsunami. This evidence helps event, and the calcareous debris and pottery sherds represent 64 us to link the lower bed of debris to an earlier tsunami of the tsunami run up and return flow. 5 65 limiting maximum age between A.D. 1500 and 1900. [32] A third section at AG-3 located ~300 m inland and at 6 3.1.2.2. Site at Mus an elevation of ~6 m above the present surf zone is from a 66 7 67 [29] Mus is located at the northern corner of Car Nicobar shallow dug well. A remarkable feature in this section is 8 where the 2004 deposits are represented mostly by coral the occurrence of the cobble-sized coral fragments at an 68 9 debris, located on low cliffs >6 m above the surf zone elevation and distance far beyond the reach of any other 69 10 (Figure 5a for location). Sedimentary sections along this modes of coastal surges [e.g., Morton et al., 2007]. At a 70 11 coast expose beds of coral debris that alternate with calcare- depth of ~1 m, this section revealed a nearly 50 cm thick 71 12 ous sand, as observed at the sites of Sawai discussed previ- layer of coral debris mixed with calcareous sand and intact 72 13 ously. Here we present a 2 m thick section, which exposed shells (Figures 5d and 6c). The coral fragments showed a 73 fi 14 two layers of coral deposits mixed with well-preserved ning upward sequence, and the lower level consisted of 74 fl 15 shells (site MS-1; Figures 5c and 6b). The lowermost bed graded deposits suggesting a decrease in ow velocity. A 75 at this site located on the seaward edge of a 5 m high plat- thick bed of calcareous sand, partly under water, underlies 16 76 form is ~50 cm thick and consists of upward grading cobble the coral debris. The shell from the debris deposits provided 17 to boulder-sized pieces comparable to the 2004 coral debris an AMS radiocarbon date of A.D. 1020–1300 (Table 2), 77 18 at this site. indicating an event that is temporally distinct from those 78 19 [30] A distinctive feature of calcareous sand that cements reported from Mus and Sawai. An upper layer of calcareous 79 20 the coral debris is the abundance of foraminifers, belonging sand with streaks of organic-rich material was found at 80 21 Q7 to Amphistegina sp., Operculina ammonoides, Elphidium ~25 cm below the present surface. This could possibly corre- 81 22 crispum, E. craticulatum, Quinqueloculina sp., Ammonia spond to the submergence observed at AG-1 and AG-2, but 82 23 beccarrii, Triloculina rotunda, and Ammonia dentata. The there was no peat associated with this layer. 83 24 intervening beds of calcareous sand are devoid of any coral 3.1.2.4. Kakkana 84 25 fragments or well-preserved foraminiferal shells. Whatever [33] The 2004 tsunami had deposited coral debris along 85 26 has been preserved appears to have been reworked and the beaches of Kakkana, located on the southern part of 86 recrystallized. The upper bed of coral debris, ~30 cm thick, the Car Nicobar Island. The study site KK-1 is located at 27 87 consisted of pebble-sized coral fragments, and as observed ~25 m from the surf zone, on a 1 m high terrace, within a 28 at SW-1 and SW-2, the debris consisted of a well-preserved local depression between two beach ridges (Figures 5a and 88 29 assemblage of gastropod species like Conus planorbis, 5e). The 0.75 m deep section exposed a 50 cm thick layer 89 30 which represent the intertidal zone and a depth up to 70 m of calcareous sand mixed with pebble-sized coral fragments 90 31 (Figure 6b). Just as in the case of foraminifers, the assem- and pottery sherds that occurs over the hard coralline bed 91 32 blage of gastropod species is exclusive to the layer of coral (Figure 6d). The pottery sherds could not be dated as they 92 33 debris and they are mostly found embedded within the large contained no quartz, but based on their shallow depth, we 93 34 boulders. Calibrated AMS radiocarbon dates of selected consider this as historically recent deposition, most likely 94 35 gastropods from the lower bed suggest age ranging from by the 1881 tsunami that is known to have affected the Car 95 – 36 B.C. 20 to A.D. 360 and A.D. 70 440; those from the upper Nicobar Coast. Further, their reddish color and grainy 96 – 37 sequence were dated at A.D. 430 750 (Table 2). Although texture are comparable to the pottery sherds obtained from 97 the conjecture is that these specimens were synchronously AG-1 at Arong, associated with peaty material dated at A. 38 98 deposited, they are considered as the maximum age of the D. 1730–1810. 39 depositional event. 99 40 3.1.2.3. Arong 3.2. Sites at Hut Bay, Little Andaman and Port Blair, 100 41 [31] On the coast of Arong located on the west coast of South Andaman 101 42 Car Nicobar, the 2004 tsunami deposition was more aggres- 3.2.1. Hut Bay, Little Andaman 102 43 sive compared to the previous sites. Here the coral debris [34] Hut Bay, the administrative center of Little Andaman 103 44 occurs as far as 250 m inland even covering platforms >5m and the fourth largest (734 km2) among the northern 104 45 above the sea level. We examined two sites (AG-1 and Andaman group of islands, is located on the west of the 105 46 AG-2), at distances of 50 and 250 m, respectively, from the hinge line that separates areas of subsidence and uplift 106 F7 47 surf zone (Figure 5 and S1 in the auxiliary material). Site at (Figures 1 and 7a). Here the coseismic uplift was about 107 48 AG-1 exposed a layer of coral debris, mostly pebble-sized, 30 cm, and it is noted for the extensive debris deposition along 108 but mixed with calcareous sand at 0.5 m depth and making a the inland channels [Rajendran et al., 2007]. During the 2004 49 109 sharp contact with the beach sand. Immediately above this is tsunami, the waves traveled ~1 km through inland creeks and 50 a10–20 cm thick layer of blackish organic sand mixed deposited sand, coral, and organic debris, and we have used 110 51 with pottery, similar to that at SW-2. The laterally extensive this as analog in our search for previously transported debris. 111 52 organic-rich layer is suggestive of submergence and conse- The sections discussed here are close to the beach on the 112 53 quent destruction/deposition of vegetation. Presence of southeastern part of the island (Figures 7 and S2). 113 54 embedded pottery sherds suggests proximity to human settle- [35] Site HB-1 is located ~500 m inland, on the banks of a 114 55 ments and a safe distance from the active surf zone. Although creek where we identified a ~50 cm thick deposit consisting 115 56 the pottery could not be dated due to poor quartz content, peat of loose coral fragments mixed with assorted shells embed- 116 57 from this layer was dated at A.D. 1730–1810. The section at ded in calcareous sand (Figure 7a). This debris layer makes 117 fi 58 AG-2 also exposed a peat layer at a depth of 0.75 m, which an abrupt contact with the underlying ne-grained calcare- 118 – 59 was dated at A.D. 1810 1920 (Figures 5d and S1 and Table 2). ous sand devoid of any shells and coral fragments, which 119 60 120 10 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 63 4 64 5 65 6 66 7 67 8 68 9 69 10 70 11 71 12 72 13 73 14 Figure 7. (a) A view of a creek at Hut Bay located on the first terrace above MSL, with its location 74 15 marked on the map (inset). (b) A close view of the section at site HB-1 along the creek showing a debris 75 16 layer underlain by calcareous sand (CS). More details are in Figure S2. 76 17 77 18 is also hardened with aging. The top of this layer is bounded arguably the most reliable evidence for previous submer- 78 19 by a layer of reworked soil, consisting of fragments of gence that also mimics the 2004 coseismic subsidence. With 79 20 wood and organic matter, possibly formed from occasional the hinge line passing barely west of Port Blair, South 80 21 breaching of the channel. The debris layer consisted of a Andaman displayed dramatic signatures of interseismic 81 22 few well-preserved shells. As observed in the sections at emergence of land (Figure 2), as reported earlier by 82 23 Car Nicobar, with their shining surface and intact conditions, Rajendran et al. [2007]. Although the tsunami inundation 83 24 Q8 these gastropod shells (some representing Cypraea sp.) are was minimal (200–250 m) on the eastern coast of South 84 25 likely to have been mobilized from the neritic zone along Andaman, coseismic land level changes (subsidence) were 85 26 with the coral debris and near-shelf sediments. Their absence profound. GPS-based estimate of coseismic subsidence 86 in the lower calcareous sand suggests that these marine was ~1.0 m at Port Blair [Rajendran et al., 2007]. The 27 87 shells are not carried inland by regular wave transport. A coseismic subsidence led to submergence and eventual 28 sample collected from the debris yielded an AMS date of destruction of large areas of mangrove vegetation due to 88 29 A.D. 1480–1660, which we treat as the maximum age for water logging. The tsunami traveled ~250 m inland along 89 30 deposition of the bed. the creeks, leaving deposits constituting mostly of coarse- 90 31 [36] We also inspected a site, HB-2, at Ongi Tikri, ~1 km grained sand. Submergence followed by tsunami inundation 91 32 west of the jetty at Hut Bay where the 2004 tsunami had deposited sand on the vegetated surfaces. Using the 2004 92 33 deposited several tree trunks and organic debris (Figures 7 coseismic subsidence and consequent destruction of man- 93 34 and S2a). Had such deposition occurred in the past, we groves as a template, we explored sites along creeks and 94 35 would expect to see peat layers in the shallow stratigraphy. marshes to identify potential evidence of previous subsi- 95 36 Trenching here was not possible due to water logging, and dence events and characteristic depositional markers. 96 37 therefore, we obtained shallow cores, using a handheld [39] At Rangachanga, located ~8 km south of Port Blair, 97 corer. The 75 cm to 1 m deep cores bottomed on hard calcar- several mangrove swamps submerged coseismically, and 38 98 eous stratum, probably a buried coral reef. A layer of peat we searched for evidence of previous subsidence along the 39 with an average thickness of ~30 cm was found in the cores banks of its creeks and streams. Here we report details of 99 40 at a depth of ~50 cm below the present surface (Figure S2b), what appeared to be a previous subsidence and consequent 100 41 overlain by organic-rich soil. A sample of this peat provided destruction of trees along the 10 m wide creek called 101 42 calibrated radiocarbon age of A.D. 650–710, probably repre- Burmanallah, where remains of a fossil root zone become 102 43 sentative of the maximum age of a paleo-sea surge. The peat visible during low tide. Remains of tree trunks and in situ 103 44 may have been formed from the transported material or from roots of Rhizophora (the most common species of man- 104 45 the in situ vegetation. groves in the Andaman Islands) were found in growth 105 46 [37] As we explored other sites, we found further evidence position at ~1 m depth (PB-1; Figures 8a, 8b, 8c, 8d, 8e, F8 106 47 for laterally extensive peat- rich deposits, though much and S3). These were not spatially isolated and they could 107 fi 48 younger in age, as exempli ed by the sections at HB-3 and be traced all along the creek, on both the banks. Shallow pits 108 HB-4, which showed a 10–20 cm thick layer of peaty layer excavated on the banks of the creek ~50 m inland and cur- 49 109 overlying the buried coral reef formation. Peat from the rently supporting sparse vegetation exposed buried remains 50 section at HB-3 (not shown in Figure S2), located on the of trees at ~50 cm depth, suggesting that the area was previ- 110 51 southern end of Hut Bay beach provided an age of A.D. ously occupied by richer vegetation. Samples of in situ tree 111 52 1800–1890. A similar stratigraphy was observed also at HB- trunks from sites across the creek yielded ages ranging from 112 53 4, north of HB-3, and the peat at a depth of 60 cm and was A.D. 770–880 to 770–1040 (Figures 8e and S3 and Table 2), 113 54 dated at A.D. 1810–1930 (Figure S2c and Table 2). These ages which may be treated as the approximate age of the subsi- 114 55 falling in the age bracket of the 1881 earthquake correlate well dence event. Peat-rich soil from the top layers contained 115 56 with the younger tsunami deposits of Car Nicobar. many molluscan shells indicative of a sea surge. The shell 116 57 3.2.2. Port Blair, South Andaman was dated at A.D. 880–1250, which we consider as the max- 117 58 [38] Among the various sites that we examined in South imum limiting age for the subsidence event. This laterally 118 59 Andaman, Port Blair, the capital town of A&N, provided extensive paleo-root zone that spatially coincides with a 119 60 120 11 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 63 4 64 5 65 6 66 7 67 8 68 9 69 10 70 11 71 12 72 13 73 14 74 15 75 16 76 17 77 18 78 19 79 20 80 21 81 22 82 23 83 24 84 25 85 26 86 Figure 8. (a, b) Location maps showing sites (PB-1 and PB-2) in South Andaman. (c) Map of the 27 87 Burmanallah creek where mangrove swamp was submerged by ~1 m. (d) An east-west profile across 28 the creek. (e) View of the west bank of the creek that exposed the paleo-root zone at ~1 m depth. (f) 88 29 Section (PB-2) about 2 km south of the Burmanallah creek showing a layer of peat and a very thin layer 89 30 of calcareous sand (CS). 90 31 91 32 wide area of 2004 subsidence compels us to favor an analo- relatively closer to the surf zone, but this is not an isolated 92 33 gous tectonic cause for its occurrence. exposure and the paleosol-sand association at similar depth 93 34 [40] Severe droughts that drive up salinities in the coastal is widely observed even at locations 500 m inland of the surf 94 35 waters above the normal concentrations can be an alternate zone. As discussed earlier in section 2.3, a storm-driven depo- 95 36 mechanism for the passive death of mangroves. However, sition cannot be a realistic mechanism for these localities. The 96 “ ” 37 this type of destruction can cause dying back, which age of this feature is remarkable as it falls in the same bracket 97 means gradual and progressive destruction rather than with what is reported from Phra Thong and Meulaboh. 38 98 sudden death as due to tectonic subsidence. Further, 39 speleothem-based studies from this region rule out drastic 3.3. Sites at Middle Andaman 99 40 changes in monsoon pattern that could lead to extreme 3.3.1. Panchavadi 100 41 drought conditions in this region during the past 1500 years [42] Most parts of Middle Andaman, including the islands 101 42 [Laskar et al., 2011]. Mechanisms like accumulation of silt on the west, registered coseismic uplift of about 1 m, and this 102 43 during floods or from landslides can also cause destruction region straddles the 2004 hinge line [Kayanne et al., 2007; 103 44 of mangroves. Both these scenarios can be discounted Rajendran et al., 2007]. The uplift on the eastern side of 104 45 because the site is away from river mouth and hilly regions. Middle Andaman raised the mangrove swamps by ~1 m 105 46 [41] We excavated a few trenches ~2 km south of the above the high-tide line resulting in mortality, mainly due 106 47 above mentioned location and within 50 m from the present to depletion of soil salinity [Ray and Acharyya, 2011]. 107 48 shoreline, where the 2004 tsunami had deposited thin beds Assuming that such areas are likely to preserve the evidence 108 of fine sand. Some sections exposed a veneer of fine sand of similar previous episodes of uplift in the past, we exam- 49 109 deposited over organic-rich paleosol ~50 cm below the pres- ined a sedimentary section near the confluence of a river 50 ent surface (section not shown here). Nearby sections also with sea at a location called Panchavadi (PV-1; Figure S4). 110 51 showed buried organic soils, but the sand layers were too The natural exposure on the side of the sea showed a line 111 52 thin and almost indistinguishable. Here we show one section of peat and roots representing an old vegetated horizon 112 53 (PB-2) located 40 m from the present surf zone, where a below a calcareous debris layer embedded with mollusks, 113 54 20 cm thick peat layer occurs between two calcareous sand 75 cm below the surface (Figure S4). A root from this layer 114 55 beds and the peat provided a date of A.D. 1380–1520 was dated at A.D. 240–780 (Table 2), possibly representing 115 56 (Figure 8f and Table 2). Sand peat couplets showing abrupt the time of destruction of the then prevailing vegetation. The 116 57 depositional contacts within the coastal swamps are consid- obvious question is whether this feature represents an earlier 117 58 ered typical of tsunami deposition, and in such sequences tectonic event. Although suggestive of an uplift event, the 118 59 peat represents the maximum age. Our site is located single and isolated date with wider variation from the mean 119 60 120 12 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 precludes conclusive interpretation. However, this date is we explored sites along the banks of streams and inlets, 63 4 comparable to what was obtained for tsunamigenic boulder and here we discuss observations at two sections. 64 beds at Mus in Car Nicobar (A.D. 430–750), and we have [44] One section (IN-1) on the southern part of this island, 5 65 included this date in the database. Aside from local elevation ~200 m from the surf zone, exposed a layer of decaying 6 changes due to tectonism, alternate mechanisms like silt organic-rich debris, beneath a 50 cm thick deposit of calcar- 66 7 deposition during frequent river-borne floods or from land- eous sand mixed with mud (Figures 9a, 9b, and S5). The op- 67 8 slides from the hills may also be considered as causes for posite bank of the 4 m wide stream also showed similar 68 9 destruction of the vegetation. depositional features. Such extensive deposits of coralline 69 10 3.3.2. Interview Island debris mixed with shells and transported tree trunks far 70 11 [43] Interview Island, located on the western side of nland are considered unusual. Against the low-energy back- 71 12 Middle Andaman, is noted for the 2004 coseismic uplift of ground deposition dominated by coarse- to fine-grained sand 72 13 coral beds and deposition of tsunami debris on the elevated and mud, rolled up trunks of decayed trees represent a tran- 73 14 beaches and along the banks of inland streams (Figures 1 sient high-energy regime. We consider that only a tsunami 74 F9 15 and 9a). The western part of Interview Island experienced comparable to the 2004 event could have deposited such 75 uplift of ~1 m which exposed a ~50 m wide coral platform extensive debris. Wood samples from either banks of this 16 76 [Rajendran et al., 2008]. An assemblage of tree trunks, coral stream yielded calibrated dates of A.D. 1440–1510 and A. 17 debris, and cultural artifacts including the remains of boats D. 1450–1520 (Figures 9a, 9b, and S5 and Table 2). 77 18 78 were carried onto this raised beach. Debris was also [45] Evidence for an earlier tsunami comes also from 19 transported far inland (>250 m) through channels on the another section (IN-2) in Interview Island, which is about 79 20 west coast of this island. In our search for earlier deposits, 1 km north of IN-1 (Figures 1 and S6). Indications of 2004 80 21 tsunami deposits consisting of coral debris and other organic 81 22 debris are still visible at distance 250 m from the surf zone. 82 23 Trenches excavated in a runnel beyond a 4 m high terrace, 83 24 located 150 m away from the present shoreline, exposed a 84 25 layer of coralline debris mixed with pieces of wood and peat 85 26 at a depth of 70 cm (Figures 9a, 9c, and S6). Wood from this 86 layer was dated at A.D. 1640–1670 (Table 2). Closest to this 27 87 time window are two historically known earthquakes in the 28 region, the A.D. 1679 [Iyengar et al., 1999] and A.D. 88 29 1762 events [Chhibber, 1934; Cummins, 2007]. Age from 89 30 IN-1 provides a reliable maximum limiting date for a possi- 90 31 ble tsunami that is correlative with the dates of coral uplifts 91 32 obtained from northern Sumatra [Meltzner et al., 2010, 92 33 2012], and that from IN-2 provides either a maximum age 93 34 for the A.D. 1679 tsunami or a minimum age for the A.D. 94 35 1762 tsunami. It should be mentioned here that compared 95 36 to the 1679 earthquake and a more recent earthquake in 96 ≥ 37 1941 (M 7.5), the historical records on the 1762 earthquake 97 are categorical on an associated tsunami [Rajendran et al., 38 98 2007; Rajendran, 2012]. 39 99 40 3.4. Sites at North Andaman 100 41 3.4.1. Diglipur 101 42 [46] Located on the east coast of North Andaman, 102 43 Diglipur experienced coseismic uplift of ~1m and is one 103 44 region noted for soil liquefactions (see Figure 1 for location). 104 45 This is the only site where coseismic liquefactions are 105 46 known to have occurred during the 2004 earthquake 106 47 (Figure 3d). A cluster of sand blows occurs along the eastern 107 48 bank of Magarnalla, a major river channel, which we 108 explored for likely paleo-liquefaction features. A 2 m deep 49 109 trench on its eastern bank exposed a 4 cm thick sand dike 50 (Figure S7). The physical setting of the riverbank character- 110 51 ized by a shallow water table and sandy source bed with a 111 52 superjacent cap of thick clay is conducive for the generation 112 53 Figure 9. (a) Sites (IN-1 and IN-2) at Interview Island. (b) of liquefaction on ground shaking. Within the dikes, the 113 54 West-facing view of an inlet along which organic debris was sediment appears to be light colored and fine grained, which 114 55 transported 1 km inland; inset is a close view of the section makes them stand out from the host sediment. Presence of 115 56 at IN-1 on the south bank of the stream. (c) Section at angular clasts within the dike is consistent with short- 116 57 IN-2 showing the coral debris mixed with wood; inset shows lived upwelling from the vent observed in such features 117 58 wood pieces used for dating. More details are in Figures S5 [Obermeier and Jibson, 1995]. The peat sample within the 118 – 59 and S6. older sand dike was dated at A.D. 770 1210 (DG-1; 119 60 120 13 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 Table 2). This age shows a remarkable correlation with 63 4 that of the subsided paleo-root horizon close to Port Blair, 64 South Andaman. 5 65 3.4.2. East Island, North Andaman 6 66 [47] East Island marks the northern terminus of the 2004 7 rupture where coseismic uplift of ~1.5 m exposes ~100 m 67 8 of the coast (EA-1; Figures 1a, and S8). As the farthest 68 9 island along the archipelago, we consider that paleo- 69 10 seismological or tsunami evidence from here is crucial to 70 11 constrain the size of past ruptures. Although the 2004 71 12 tsunami did not inundate the northern Andaman coast much, 72 13 East Island is an exception. Here the tsunami apparently 73 14 moved coralline boulders from the near-shore regions onto 74 15 the uplifted coast. The ~120 m wide impact zone littered 75 with coral debris shows progressive landward reduction in 16 76 individual sizes, with general imbrication suggestive of the 17 F10direction transport (Figures 10b, 10c, and S8). The telltale 77 18 indications of coastal uplift during the 2004 earthquake 78 19 and the presence of tsunami-mobilized boulders motivated 79 20 us to explore the shallow stratigraphy of the older coastal 80 21 terrace, and here we present a representative section. 81 22 [48] The site (EA-1) discussed here is ~4 m above mean 82 23 Q9 sea level (MSL) and 80 m inland of the pre-2004 coastline 83 24 (Figure 10b). The trenches exposed a thin layer of cobble- 84 25 sized coral debris, at a depth of ~50 cm, below a layer of 85 26 thick gray calcareous sand (Figure 10d). They generally 86 bottomed on grayish calcareous sand, suggesting regular 27 87 deposition representing paleo-beach facies. The section stra- 28 tigraphy here is comparable to what was observed at the sites 88 29 in the southern island of Car Nicobar. Along the coasts of 89 30 both these islands, the 2004 tsunami deposits mostly 90 31 consisted of coral debris. As in the case of sections at Car 91 32 Nicobar, the intervening beds of calcareous sand were 92 33 devoid of any intact mollusks, but they were fully preserved 93 34 within the coral debris (Figure 10d). The multiple lamelli- 94 35 branch shells obtained from the debris layer were dated at 95 – – 36 A.D. 1040 1220 and A.D. 1120 1300 (Table 2). These 96 37 dates may represent the maximum limiting ages for an earth- 97 quake that occurred between A.D. 770 and 1040, an interval 38 98 constrained from the date of dead root zone near Port Blair. 39 99 40 100 41 4. Discussion 101 42 [49] The ~800 km stretch of A&N represents about two 102 43 thirds of the 2004 rupture, which has not experienced a sim- 103 44 ilar episode in the documented history. The availability of 104 45 land with evidence of deformation as well as the 2004 105 46 tsunami deposition makes this segment ideal for exploring 106 47 the proxies of past tectonic events. We evaluate a variety 107 of evidence gathered from different locations marked by dif- 48 108 ferent depositional/deformational environments to identify 49 potential geologic indicators of past earthquakes/tsunamis. 109 50 In this study we have generated additional database on tsu- 110 51 F11nami chronology of the Indian Ocean tsunamis (Figure 11). 111 52 112 53 4.1. Age Constraints on the Earliest Two Tsunamis 113 54 [50] The earliest events of high-energy deposition were Figure 10. (a) Photograph of the uplifted coast of East 114 55 identified in Car Nicobar. Almost all the deposits we have Island, marked on the location map in the inset. (b) Beach 115 56 discussed here are located >3 m above the present sea level, profile showing the trench location. (c) Imbricated boulders 116 57 some as high as 6 m, and at distances of 200–300 m inland, showing the westward direction of the 2004 tsunami trans- 117 58 regions considered to be beyond the reach of storm surges. port. (d) Section showing coral debris layer ~0.5 m with 118 – 59 Further, the stratigraphy representing the last 1000 2000 years shells. More details are in Figure S8. 119 60 120 14 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 [51] Evidence of an early tsunami was obtained from 63 – 4 Mamallapuram (A.D. 410 557) located on the southeastern 64 coast of India in a previous study [Rajendran et al., 2006]. 5 65 This age matches with the maximum limiting date obtained 6 from the upper coral debris bed at Car Nicobar. In this con- 66 7 text, the age of 1640 cal years B.P. attributed to a sand bed 67 8 from a core obtained from a lagoon in southeastern Sri 68 9 Lanka is also noteworthy [Jackson, 2008]. Anecdotal refer- 69 10 ence comes from the Mahavamsa chronicles of Sri Lanka, 70 11 which mentions about a sea surge dated to ~B.C. 200 [see 71 12 Geiger, 1912, p. 147]. The Mahavamsa “tsunami,” if true, 72 13 could be an earlier event, as compared to the earliest tsunami 73 – 14 evidence (B.C. 20 A.D. 440) from Car Nicobar. 74 15 4.2. The ~1000 Year Old Tsunami (A.D. 770–1040) 75 16 76 [52] The shallow stratigraphy of A&N shores and the 17 chronology of the inferred sedimentary markers suggest a 77 18 major tectonic event accompanied by regional sea flooding 78 19 during A.D. 770 and 1040, the most reliable evidence being 79 20 the paleo-mangrove root horizon near Port Blair (Figure 11). 80 21 Ages obtained from the paleo-liquefaction at Diglipur and 81 22 shell from the debris deposits at Arong (Car Nicobar) and 82 Figure 11. A graphical representation of the spatial and tem- 23 East Island (northern Andaman) also show convergence. 83 poral relation of samples from inferred paleo-earthquake/ 24 Within the margins of error estimates, this earthquake/ 84 tsunami depositional layers. Ages plotted are from the present tsunami probably correlates with the A.D. 780–990 tsunami 25 study and previous studies. Radiocarbon ages are calibrated 85 26 marker bed on the Aceh coast [Monecke et al., 2008]. With 86 using CALIB; error bars represent two sigma standard devia- its imprints not only on the Sumatran coast but also on 27 87 tions from the mean with maximum area under the probability the shores of Nicobar, Andaman, Tamil Nadu (India) and 28 distribution curve. Gray arrowheads denote maximum limiting Sri Lanka, the tsunami that occurred between 800 and 88 29 ages. Legend shows symbols for different qualities of data: 89 “ ” 1040 years ago seems comparable to the 2004 event. A max- 30 A (red squares), ages based on subsided in situ vegetation; imum limiting shell date obtained from East Island, located 90 31 “B+” (purple polygons), ages based on wood, peat, and 91 “ À“ at the northern terminus of the 2004 rupture, is an indication 32 uplifted vegetated horizons; B (blue triangles), ages based that the ~1000 year old predecessor was its true mimic. The 92 33 on shells. The dates from the east coast of India are indicated OSL date of 1017 Æ 165 years obtained from the sand 93 as Kaveripattinam (Kp) and Mamallapuram (Mp). Probable 34 deposits at Kaveripattinam and the radiocarbon age of A. 94 ranges for tsunami events are shown by gray-shaded bands, 35 D. 1019–1160 obtained from Mamallapuram, located on 95 considering only the A- and B+-quality samples; for the the southeastern shore of the Indian mainland, may also 36 1881 and 1762/1679 tsunamis, they are historically confirmed; 96 37 correspond to the evidence for a major transoceanic tsunami 97 and for the approximately fourteenth and approximately tenth during this interval, called the “Chola” (after the Chola kings 38 98 century A.D. events, ages are from Jankaew et al. [2008], of South India) tsunami [Rajendran et al., 2006, 2011]. 39 Q10 Monecke et al. [2008], and Meltzner et al. [2012]. The age range 99 fi These dates are also correlative with the uranium series 40 for events prior to the approximately fth century A.D. is uncer- age obtained on the earliest coral uplift (A.D. 956) reported 100 41 tain due to fewer samples. Abbreviations: Me: Meulaboh, PT: from northern Sumatra [Meltzner et al., 2012] and the 101 42 Phra Thong, Sim: Simeulue, Va: Vakarai, GN: Great Nicobar, uplifted coral terraces of A&N [Rajendran et al., 2008]. 102 43 CN: Car Nicobar, LA: Little Andaman, SA: South Andaman, 103 – 44 MA: Middle Andaman, NA: North Andaman. 4.3. The Late Medieval Tsunamis (A.D. 1250 1450) 104 45 [53] The evidence from some of the sites from A&N 105 46 (Campbell Bay, Hut Bay, Port Blair, and Interview Island) 106 47 shows only one or two layers of debris separated by thick suggests one or more tsunamis that may have impacted this 107 48 calcareous sand, and their temporal spacing is inconsistent region in the late medieval times (A.D. 1290 and 1680). 108 with the expected frequency of tropical storms. The sea level However, it is necessary to develop a better constrained 49 109 at Car Nicobar has remained more or less steady over the last chronological database for the putative late medieval tsu- 50 2000 years, ruling out the possibility of major shoreline migra- nami from A&N, by identifying more reliable stratigraphic 110 51 tion. These inferences from a storm-free coast favor tsunami markers and their regional representation. Further, we are 111 52 transportation as the preferred mechanism for the inland depo- yet to discover any unambiguous exposures of the late medi- 112 53 sition of coral debris. Thus, the calibrated AMS radiocarbon eval event on the Tamil Nadu coast of India [Rajendran 113 54 dates of the shells (B.C. 20–A.D. 440 and A.D. 430–750) from et al., 2011]. Though this event apparently occurred during a 114 55 the lower layer and upper level debris sequence represent period when the coastal towns of Tamil Nadu (South India) 115 56 maximum limiting ages for the two tsunamis in the early part remained culturally active, archival information on such a 116 57 of the first millennium. Additional ages of early tsunamis or major tsunami is surprisingly nonexistent. Although the evi- 117 – 58 earthquakes are obtained from the sites in Hut Bay (A.D. dence for a late medieval sea incursion (A.D. 1350 1450) is 118 – – 59 650 710) and Middle Andaman (A.D. 240 780). obtained from Sumatra and Thailand [Jankaew et al., 2008; 119 60 120 15 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 3 Monecke et al., 2008], the lack of evidence (as yet) along the 2004 tsunami. The answer to this question will have implica- 63 4 Indian and Sri Lankan coasts may have implications on its tions on rupture lengths and recurrence cycle of earthquakes 64 size. The question that needs to be asked here is whether the and tsunamis along this subduction zone. 5 65 causative earthquake/s of the late medieval tsunami/s were 6 caused by a full rupture analogous to the 2004 event or they 66 7 [57] Acknowledgments. The Indian National Centre for Ocean Infor- 67 were produced by partial rupture earthquakes. More than one mation Services, Ministry of Earth Sciences, and the Department of Science 8 tsunami during this time interval is an implied possibility, and Technology (DST), Government of India, funded this work. We would 68 9 suggesting episodes of earthquake clustering around A.D. like to record our special thanks to Jody Bourgeois, an anonymous reviewer, 69 and Brian Atwater for their detailed suggestions, corrections, and criticisms 10 1390 and 1450, based on the U-Th ages of coral uplifts on the earlier versions of the manuscript. P.M. Mohan (Unit of Pondicherry 70 11 identified at Simeulue, Northern Sumatra, by Meltzner et al. University in Port Blair), Anil Earnest (Centre for Mathematical Modelling 71 12 [2010, 2012]. and Computer Simulation, Bangalore), Terry Machado, and D. Raju 72 (both from the Centre for Earth Science Studies, Trivandrum) are thanked 13 for their assistance during some phases of the fieldwork. V.A. and C.P.R. 73 14 4.4. Historical Tsunamis acknowledge funding from the Council of Scientific and Industrial 74 [54] The evidence for the 1881 tsunami is mainly repre- Research, India, through the Shyama Prasad Mukherjee Fellowship and 15 the DST for the Ramanujan Fellowship, respectively. Radiocarbon dating 75 16 sented by the coral breccias from Car Nicobar aside from a was conducted at the Rafter Radiocarbon Laboratory, New Zealand, and 76 17 peaty sand sequence in Hut Bay, Little Andaman. The peat the Birbal Sahni Institute of Palaeobotany, India. 77 beds at Arong on the Car Nicobar Coast dated at A.D. 18 78 1730–1810 and A.D. 1810–1920 provide maximum limiting References 19 ages of the 1881 tsunami. The evidence for this event in the 79 20 Andrade V. and K. Rajendran (2011), Intraplate response to the Great 2004 80 shallow stratigraphy is highly localized, mostly from sites at Sumatra–Andaman earthquake: A study from the Andaman segment, 21 Car Nicobar, which complies with the tsunami propagation Bull. Seismol. Soc. Am., 101, 506–514, doi: 10.1785/0120100155. 81 22 models that suggest predominant effects along the Car Atwater B. F. and E. Hemphill-Haley (1997), Recurrence Intervals for Great 82 Earthquakes of the Past 3,500 Years at Northeastern Willapa Bay, 23 Nicobar Coast [Ortiz and Bilham, 2003]. The 1883 Krakatoa Washington, U.S. Geological Survey Professional Paper 1576, United 83 24 eruption was a contemporary tsunami event in the Indian States Government Printing Office, Washington, D.C., 108 p. 84 25 Ocean [Pelinovsky et al., 2005], but its effect on the Nicobar Atwater B. F., S. Musumi-Rokkaku, K. Satake, T. Yoshinobu, U. Kazue 85 and D. K. Yamaguchi (2005), The Orphan Tsunami of 1700—Japanese 26 Islands was most likely minimal. Clues to a Parent Earthquake in North America, U.S. Geological Survey 86 27 Professional Paper 1707, United States Government Printing Office, 87 Washington, D.C., 144 p. 28 5. Conclusions Atwater B. F. (1987), Evidence of great Holocene earthquakes along the 88 29 outer coast of Washington State. Science 236, 942–944, doi:10.1126/ 89 [55] We have developed a chronology of paleo-tsunamis science.236.4804.942. 30 that affected A&N. The relative sizes of the events have Bahlburg H. and R. Weiss (2006), Sedimentology of the December 26, 90 31 been assessed on the basis of regional distribution of geolog- 2004 Sumatra tsunami deposits in eastern India (Tamil Nadu) and Kenya. 91 – 32 ical proxies and compared to the available data from South Int. J. Earth Sci., 96, 1195 1209. 92 Bourgeois J. (2009), Geologic effects and records of tsunamis, in The 33 India, Sri Lanka, Sumatra, Indonesia, and Thailand. Among Sea, vol. 15, Tsunamis, edited by Bernard E.N. and A. R. Robinson, 93 34 the previous tsunamis, the event that occurred between the pp. 53–91, Cambridge, Harvard University Press. 94 eighth and eleventh centuries A.D. seems not only relatively Chhibber H. L. (1934), The Geology of Burma, pp. 47–70, McMillan, 35 London. 95 36 better represented in the stratigraphy at various sites along Chlieh M., J. Avouac, V. Hjorleifsdottir, T. A. Song, C. Ji, K. Sieh, A. 96 37 A&N but also elsewhere in the Indian Ocean countries. Sladen, H. Hebert, L. Prawirodirdjo, Y. Bock and J. Galetzka (2007), 97 Another tsunami or more than one tsunami may have Coseismic slip and afterslip of the great Mw 9.15 Sumatra-Andaman 38 – 98 occurred in the late medieval period (thirteenth to fifteenth earthquake of 2004, Bull. Seismol. Soc. Am. 97(1A) S152 S173, doi: 39 10.1785/0120050631. 99 century A.D.). Our age estimates of this tsunami regionally Choowong M., N. Murakoshi, K. Hisada, P. Charusiri, V. Daorerk, T. 40 have a wider variation from the mean. The dates of late Haroentitirat, V. Chutakositkanon, K. Jankaew, and P. Kanjanapayont 100 41 (2007), Erosion and deposition by the 2004 Indian Ocean tsunami in 101 medieval tsunami deposits reported from Thailand and – 42 Phuket and Phang-nga provinces, Thailand. J Coast Res 23, 1270 1276. 102 Sumatra cluster around thirteenth century A.D. It is possible Cisternas M., B. F. Atwater, F. Torrerjon, Y. Sawai, G. Machuca, M. Lagos, 43 that there may have been more than one tsunami that A. Eipert, C. Youlton, I. Salgado, T. Kamataki, M. Shishikura, C. P. 103 44 affected the Bay of Bengal region during the interval from Rajendran, J. K. Malik, Y. Rizal, and M. Husni (2005), Predecessors of 104 fi the giant 1960 Chile earthquake, Nature, 437, 404–407, doi:10.1038/ 45 thirteenth to fteenth century A.D. However, the available nature03943. 105 46 data are not able to constrain the actual sizes of these Clark J. A., W. E. Farrell, and W. R. Peltier (1978), Global changes in 106 tsunamis. The historical 1881 tsunami is well represented postglacial sea level: A numerical calculation, Quaternary. Res., 9, 47 – 107 by its deposits on the Car Nicobar Island and minimally in 265 287. 48 Combellick R. A. (1986), Chronology of late-Holocene earthquakes in 108 Hut Bay (Little Andaman) located to the north, which agrees 49 southcentral Alaska: Evidence from buried organic soils in upper 109 with the estimated rupture dimensions of the 1881 earth- Turnagain Arm, Geol. Soc. Am. Abstracts with Programs, 18, 569. 50 quake [Ortiz and Bilham, 2003]. Cummins P. R. (2007), The potential for giant tsunamigenic earthquakes 110 51 in the northern Bay of Bengal, Nature 449,75–78, doi:10.1038/ 111 [56] A question that has important geodynamical and nature06088. 52 hazard implications is whether the 2004 earthquake had Dominey-Howes D., P. Cummins, and D. Burbidge (2007), Historic records 112 53 any full-size predecessors. The combined regional database of teletsunami in the Indian Ocean and insights from numerical modeling, 113 – 54 – Nat Hazards, 42,1 17, doi: 10.1007/s11069-006-9042-9. 114 from the A&N suggests that the 800 1100 year old event Douka K., T. F.G. Higham and R. E. M. Hedges (2010), Radiocarbon 55 is comparable to the transoceanic nature of the 2004 tsunami dating of shell carbonates: Old problems and new solutions, Munibe 115 56 and another transoceanic tsunami or tsunamis that occurred Suplemento 31,18–27. 116 around A.D. 1450. The current database on the A.D. 1450 Dutta K., R. Bhushan and B. L. K. Somayajulu (2001), ΔR correction 57 values for the Northern Indian Ocean, Radiocarbon 43, 483–485. 117 58 tsunami or a cluster needs to be augmented to constrain Etienne S., M Buckley, R. Paris, A.K. Nandasena, K. Clark, L Strotz, C. 118 59 whether or not its size was truly comparable to that of the Chagué-Goff, J Goff, B. Richmond (2011), The use of boulders for 119 60 120 16 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 characterizing past tsunamis: Lessons from the 2004 Indian Ocean and Meltzner A. J., K. Sieh, H.-W. Chiang, C.-C. Shen, B. W. Suwargadi, D. H. 3 2009 South Pacific tsunamis, Earth Sci Rev. 107,76–90. Natawidjaja, B. E. Philibosian and R. W. Briggs (2012), Persistent 63 4 Fairbanks R. G. (1989), A 17,000-year glacio-eustatic sea level record: termini of 2004- and 2005-like ruptures of the Sunda megathrust, 64 fl 5 In uence of glacial melting rates on the Younger Dryas event and J. Geophys. Res. 117, B04405, doi: 10.1029/2011JB008888. 65 deep-ocean circulation, Nature, 342, 637–642. Minoura K., S. Nakaya, and Y. Sato (1987), Traces of tsunami recorded in 6 Geiger W. (1912). The Mahavamsa or The Great Chronicle of Ceylon, lake deposits, examples from Jusan, Shiura-mura, Aomori [in Japanese 66 7 translated from Pali, Oxford University Press, London, 300 p. with English abstract], Zishin 2 (40), 183–196. 67 Gelfenbaum G. and B. Jaffe (2003), Erosion and sedimentation from the Monecke K., W. Finger, D. Klarer, W. Kongko, B. G. McAdoo, 8 17 July, 1998 Papua New Guinea tsunami, Pure Appl. Geophys.160, A. L. Moore and S. U. Sudrajat (2008), A 1,000-year sediment record 68 9 1969–1999, doi: 10.1007/s000024-003-2416-y. of tsunami recurrence in northeast Sumatra, Nature, 455, 1232–1234, 69 Gill A. E., (1982), Atmosphere-ocean dynamics, 662 p, New York, doi:10.1038/nature07374. 10 Academic. Moore A., Y. Nishimura, G. Gelfenbaum, T. Kamataki, and R. Triyono 70 11 Q11 Goff J., P. Liu, B. Higman, R. Morton, B. Jaffe, H. Fernando, P. Lynett, H. (2006), Sedimentary deposits of the 26 December 2004 tsunami on the 71 12 Fritz, C. Synolakis, and S. Fernando (2006), Sri Lanka field survey after northwest coast of Aceh, Indonesia. Earth, Planets, and Space, 58, 72 the December 2004 Indian Ocean tsunami. Earthquake Spectra, 22, S155. 253–258. 13 Goff J., C. Chagué-Goff, S. Nichol, B. Jaffe, D. Dominey-Howes, (2012), Morton R. A., G. Gelfenbaum, and B. E. Jaffe (2007), Physical criteria for 73 14 Progress in palaeo-tsunami research, Sediment. Geol., 243-244,70–88, distinguishing sandy tsunami and storm deposits using modern examples. 74 doi:10.1016/j.sedgeo.2011. 11.002. Sediment. Geol., 200, 184–207. 15 Goto K., S. A. Chavanich, F. Imamura, P. Kunthasap, T. Matsui, K. Nanayama F., K. Satake, R. Furukawa, K. Shimokawa, B. F. Atwater, 75 16 Minoura, D. Sugawara, and H. Yanagisawa (2007), Distribution, origin K. Shigeno, and S. Yamaki (2003), Unusually large earthquakes inferred 76 – 17 and transport process of boulders deposited by the 2004 Indian Ocean from tsunami deposits along the Kuril trench, Nature, 424, 660 663, 77 tsunami at Pakarang Cape, Thailand, Sediment. Geol. 202, 821–837, doi:10.1038/nature01864. 18 doi:10.1016/j.sedgeo.2007.09.004. Nelson A. R., I. Shennan and A. J. Long (1996), Identifying coseismic 78 19 Government Gazetteer (1908), The Andaman and Nicobar Local Islands subsidence in tidal-wetland stratigraphic sequences at the Cascadia 79 Local Gazetteer, Office of the Superintendent of Government Printing, subduction zone of western North America, J. Geophys. Res. 101, 20 Calcutta, 167 p. 6115–6135, doi: 10.1029/95JB01051. 80 21 Gray W. M. (2000), in Storms, edited by Pilke R. J and R. S. Pilke, Obermeier S. F. and S. E. Dickenson (2000). Liquefaction evidence for the 81 Q12 – 22 Routledge, vol. 1, pp. 145 163. strength of ground motions resulting from late Holocene Cascadia sub- 82 Horton B. P., P. L. Gibbard, G. M. Milne, R. J. Morley, C. Purintavaragul, duction earthquakes, with emphasis on the event of 1700 A.D, Bull. 23 and J. M. Stargardt, (2005), Holocene sea levels and palaeoenvironments Seismol. Soc. Am., 90, 876–896, doi:10.1785/0119980179. 83 24 Malay-Thai Peninsula, southeast Asia, Holocene, 15, 1199–1213. Obermeier S. F. and R. W. Jibson (1995), Using liquefaction-induced 84 Q13 India Meteorological Department (2008), Tracks of Cyclones and Depres- features for paleoseismic analysis, U.S. Geol. Surv. Open-File Rep., 25 sions in the Bay of Bengal 1891-2007 [electronic], Chennai. 94-663, 100 p. 85 26 Jaffe B. and G. Gelfenbaum, (2007), A simple model for calculating Ortiz M. and R. Bilham (2003), Source area and rupture parameters of the 86 tsunami flow speed from tsunami deposits, Sed. Geol., 200, 347–361, 31 December 1881 Mw = 7.9 Car Nicobar earthquake estimated from tsu- 27 doi: 10.1016/j.sedgeo.2007.01.013. namis recorded in the Bay of Bengal. J. Geophys. Res. 108 (B4) 2215, 87 28 Iyengar R. N., D. Sharma, and J. M. Siddiqui (1999). Earthquake history of doi:10.1029/2002JB001941. 88 29 Indian medieval times, Indian J Hist. Sci., 34, 181–237. Ota Y. and M. Yamaguchi (2004), Holocene coastal uplift in the western 89 Jackson K. L. (2008), Paleo-tsunami history recorded in Holocene coastal Pacific Rim in the context of late Quaternary uplift, Quaternary Int., 30 lagoon sediments, southeastern Sri Lanka. Open access thesis paper, 120, 105–117, doi: 10.1016/j.quaint.2004.01.010. 90 31 233 p., Univ. of Miami, Coral Gables, Fla. Ovenshine A. T., D. E. Lawson, and S. R. Bartsch-Winkler (1976), The 91 Jankaew K., B. F. Atwater, Y. Sawai, M. Choowong, T. Charoentitirat, Portage River silt-an intertidal deposit caused by the 1964 Alaska 32 M. E. Martin and A. Prendergast (2008), Medieval forewarning of the earthquake, U. S. Geol. Survey J. Res., 4, 151–162. 92 33 2004 Indian Ocean tsunami in Thailand, Nature 455, 1228–1231, Paris R., F. Lavigne, P. Wassmer, and J. Sartohadi (2007), Coastal sedimen- 93 34 doi:10.1038/nature07373. tation associated with the December 26, 2004 tsunami in Lhok Nga, west 94 Kayanne H., Y. Ikeda, T. Echigo, M. Shishikura, T. Kamataki, K. Satake, Banda Aceh (Sumatra, Indonesia), Mar. Geol., 238,93–106. 35 J. N. Malik, S. R. Basir, G. K. Chakrabortty, and A. K. G. Roy (2007), Pelinovsky E., B. H. Choi, A. Stromkov, I. Didenkulova, and H. S. Kim 95 36 Coseismic and postseismic creep in the Andaman Islands associated with (2005), Analysis of tide-gauge records of the 1883 Krakatau tsunami, in 96 the 2004 Sumatra-Andaman earthquake, Geophys. Res. Lett., 34, L01310, Tsunamis: Case Studies and Recent Developments, edited by K. Satake, 37 doi: 10.1029/2006GL028200. Dordrecht: Springer, pp. 57–77. doi:10.1007/1-4020-3331-1-4. 97 38 Kelletat D., S. Scheffers and A. Scheffers (2007), Field signatures of the Pigati J. S., J. A. Rech and J. C. Nekola (2010), Radiocarbon dating of 98 39 SE-Asian mega-tsunami along the west coast of Thailand compared to small terrestrial gastropod shells in North America, Quat. Geochronol., 99 Holocene paleo-tsunami from the Atlantic region, Pure Appl. Geophys. 5, 519–532, doi:10.1016/j.quageo.2010.01.001. 40 164, 413–431. Rajendran C. P., K. Rajendran, T. Machado, T. Satyamurthy, P. Aravazhi, 100 41 Laskar A. H., S. Raghav, M. G. Yadava, R. A. Jani, A. C. Narayana, and R. and M. Jaiswal (2006), Evidence of ancient sea surges at the 101 Ramesh (2011). Potential of stable carbon and oxygen isotope variations Mamallapuram coast of India and implications for previous Indian Ocean 42 of speleothems from Andaman Islands, India, for paleo-monsoon recon- tsunami events, Curr. Sci. India, 91, 1242–1247. 102 43 struction, J. Geol. Res., Article ID 272971, 7, doi:10.1155/2011/272971 Rajendran C. P., K. Rajendran, A. Earnest, R. Anu, T. Machado, and 103 Lay T., L. Astiz, H. Kanamori, and D. H. Christensen (1989), Temporal J. Freymueller (2007), The style of crustal deformation and seismic 44 variation of large intraplate earthquakes in coupled subduction zones, history associated with the 2004 Indian Ocean earthquake: A perspective 104 45 Phys. Earth Planet. Int., 54, 258–312, doi: 10.1016/0031-9201(89) from the Andaman-Nicobar Islands, Bull. Seismol. Soc. Am., 97,S174–S191 105 46 90247-1. doi: 10.1785/0120050630. 106 Lettis W. R. and K. I. Kelson (2000), Applying geochronology in Rajendran C. P., K. Rajendran, S. Srinivasalu, V. Andrade, P. Aravali, and 47 paleoseismology, in Quaternary Geology Methods and Applications, J. Sanwal (2011), Geoarcheological evidence of a Chola period tsunami 107 48 AGU Reference Shelf 4, edited by Noller J. S., J. M. Sowers, and W. from an ancient port at Kaveripattinam on the south-eastern of India, 108 R. Lettis, American Geophysical Union, Washington, pp. 479–496, Geoarchaeology, 26, 867–887, doi: 10.1002/gea.20376. 49 doi:10.1029/RF004 Rajendran C.P. (2012), Was the 1941 Andaman earthquake tsunamigenic? 109 50 MacInnes B. T., J. Bourgeois, T. K. Pinegina and E. A. Kravchunovskaya Comments on “Inundation studies for Nagapattinam region on the 110 51 (2009), Tsunami geomorphology: Erosion and deposition from the 15 east coast of India due to tsunamigenic earthquakes from the 111 November 2006 Kuril Island tsunami, Geology, 37, 995–998, Andaman region” by Srivastava et al. 2012. Nat. Hazards, DOI 52 doi:10.1130/G30172A.1. 10.1007/s11069-012-0403-2. 112 53 Malik J. N., M. Shishikura, T. Echigo, Y. Ikeda, K. Satake, H. Kayanne, Y. Rajendran K., C. P. Rajendran, A. Earnest, G. V. Ravi Prasad, K. Dutta, 113 Sawai, C.V.R. Murty and O. Dikshit (2011), Geologic evidence for two D. K. Ray, and R. Anu (2008), Age estimates of coastal terraces in the 54 pre-2004 earthquakes during recent centuries near Port Blair, South Andaman and Nicobar Islands and their tectonic implications, 114 55 Andaman Island, India, Geology, 39, 559–562, doi:10.1130/G31707.1 Tectonophysics 455,53–60, doi:10.1016/j.tecto.2008.05.004. 115 56 Meltzner A. J., K. Sieh, H.-W. Chiang, C.-C. Shen, B. W. Suwargadi, D. H. Ramanamurthy M. V., S. Sundaramoorthy, Y. Pari, V. Ranga Rao, 116 Natawidjaja, B. E. Philibosian, R. W. Briggs and J. Galetzka (2010), P. Mishra, M. Bhat, T. Usha, R. Venkatesan, and B. R. Subramanian 57 Coral evidence for earthquake recurrence and an A.D. 1390–1455 cluster (2005), Inundation of seawater in Andaman and Nicobar Islands and parts 117 58 at the south end of the 2004 Aceh–Andaman rupture, J. Geophys. Res. of Tamil Nadu coast during 2004 Sumatra tsunami, Curr. Sci. India, 88, 118 115, B10402, doi: 10.1029/2010JB007499. 1736–1740. 59 119 60 120 17 1 RAJENDRAN ET AL.: AGES AND SIZES OF PRE-2004 TSUNAMIS 61 2 62 Ranasinghage P. N., J. D. Ortiz, A. L. Moore, C. Siriwardana, and Srinivasalu S., N. Thangadurai, A. D. Switzer, V. Ram Mohan, and 3 B. G. McAdoo (2010), Signatures of paleo-coastal hazards in back-barrier T. Ayyamperumal (2007), Erosion and sedimentation in Kalpakkam 63 4 environments of eastern and southeastern Sri Lanka, Abstract NH21A-1397 (N. Tamil Nadu, India) from the 26th December 2004 tsunami, Mar. Geol., 64 Q14 – 5 presented at 2010 Fall Meeting, AGU, San Francisco. 240,65 75. 65 Ray S.K. and A. Acharyya (2011), Coseismic uplift, slow plant mortality Stuiver M. and P. J. Reimer (1993), Extended 14C data base and revised 6 and ecological impact in North Andaman following December 2004 CALIB 3.0 14C age calibration program, Radiocarbon 35, 215–230. 66 > – Q15 7 (Mw 9.2) earthquake, Curr. Sci. India, 101, 218 222. Subarya C., M. Chlieh, L. Prawirodirdjo, J-P. Avouac, Y. Bock, K. Sieh, A. 67 Reimer P. J., et al., (2009), IntCal09 and Marine09 Radiocarbon Age J. Meltzner, D. H. Natawidjaja, and R. McCaffrey (2006), Plate boundary 8 Calibration Curves, 0–50,000 years cal BP, Radiocarbon, 51, 1111–1150. deformation associated with the great Sumatra-Andaman earthquake, 68 9 Richmond B. M., B. E. Jaffe, G. Gelfenbaum, and R. A. Morton Nature, 440,46–51, doi:10.1038/nature04522. 69 (2006), Geologic Impacts of the 2004 Indian Ocean Tsunami on Switzer A. D., S. Srinivasalu, N. Thangadurai, and V. Ram Mohan (2012), 10 Indonesia, Sri Lanka, and the Maldives, Z. Geomorph. N. F, Suppl. Bedding structures in Indian tsunami deposits that provides clues to the 70 11 Vol.146, 235–251. dynamics of tsunami inundation, Geol. Soc. London, Spec. Publ., 71 12 Rogers R. E. (1883), Memorandum on the earthquake of the 31st December 361,61–77, doi 10.1144/SP361.6. 72 1881 and the great sea-waves resulting there from, as shown on the Takada K. and B. F. Atwater (2004), Evidence for liquefaction identified in 13 diagrams of the tidal observatories in the Bay of Bengal, in General peeled slices of Holocene deposits along the lower Columbia River, 73 14 Report on the Operations of the Survey of India 1881–1882, Government Washington, Bull. Seismol. Soc. Am., 94,550–575, doi:10.1785/0120020152. 74 Printing Office, Calcutta, pp. 70–73. Umitsu M., C. Tanavud and B. Patanakanog (2007), Effects of landforms on 15 Shennan I. and S. Hamilton (2006), Coseismic and pre-seismic subsidence tsunami flow in the plains of Banda Aceh, Indonesia, and Nam Khem, 75 16 associated with great earthquakes in Alaska, Quaternary Sci. Rev., 25, Thailand, Mar. Geol., 242, 141–153, doi: 10.1016/j.margeo.2006.10.030. 76 – 17 1 8, doi:10.1016/j. quascirev.2005.09.002. Woodroffe S. A. and B. P. Horton (2005) Holocene sea-level changes in the 77 Southon J. R., M. Kashgarian, M. Fontugne, B. Metivier, and W. W-S. Yim Indo-Pacific, J. Asian Earth Sci., 25,29–43. 18 (2002), Marine reservoir corrections for the Indian Ocean and Southeast Zachariasen J., K. Sieh, F. W. Taylor, R. L. Edwards, and W. S. Hantoro 78 19 Asia, Radiocarbon, 44, 167–180. (1999), Submergence and uplift associated with the giant 1833 Sumatran 79 Spence W. (1987), Slab pull and the seismotectonics of subducting subduction earthquake: Evidence from coral microatolls, J. Geophys. 20 lithosphere, Rev. Geophys., 25,55–69, doi:10.1029/RG025i001p00055. Res., 104, 895–919, doi: 10.1029/1998JB900050. 80 21 81 22 82 23 83 24 84 25 85 26 86 27 87 28 88 29 89 30 90 31 91 32 92 33 93 34 94 35 95 36 96 37 97 38 98 39 99 40 100 41 101 42 102 43 103 44 104 45 105 46 106 47 107 48 108 49 109 50 110 51 111 52 112 53 113 54 114 55 115 56 116 57 117 58 118 59 119 60 120 18