Marine Geology 357 (2014) 384–391

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Marine Geology

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Ambiguous correlation of precisely dated coral detritus with the tsunamis of 1861 and 1907 at Simeulue Island, Aceh Province, Indonesia

Shigehiro Fujino a,⁎, Kerry Sieh b,1, Aron J. Meltzner b,1,EkoYuliantoc, Hong-Wei Chiang d,1 a Active Fault and Earthquake Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Site C7 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan b Tectonics Observatory, California Institute of Technology, Pasadena, CA 91125, USA c Research Center for Geotechnology, Indonesian Institute of Sciences, Bandung, Indonesia d High-precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan, ROC article info abstract

Article history: Precise U–Th dates from coral detritus in two pre-2004 tsunami deposits on Simeulue Island in Aceh Province Received 7 March 2014 allow us to correlate the deposits with historically documented tsunamis in the recent few centuries, but because Received in revised form 19 September 2014 of potential discordance between the death dates of the corals and deposition of the sand layers, ambiguity in this Accepted 28 September 2014 correlation remains. Pits at coastal lowland sites exposed sand layers beneath the 2004 tsunami deposit at Available online 22 October 2014 Busung and Naibos on southern Simeulue Island. The layers share sedimentological characteristics with the de- Communicated by J.T. Wells posit of the 2004 tsunami, and are interpreted as pre-2004 tsunami deposits. Historical accounts document earth- quakes and tsunamis in 1907 and 1861 and suggest that the 1907 tsunami was larger locally than any others Keywords: historically. Nonetheless, U–Th analyses of coral boulders in the younger of two pre-2004 deposits at Busung tsunami deposit and in the lone deposit at Naibos yielded dates of death that overlap with 1861, but there were no tsunami layers coral boulder that could be directly dated to 1907. The younger pre-2004 sand deposit can be attributed to both the 1861 and Simeulue Island 1907 events, if the dated corals were killed by uplift in 1861 and subsequently entrained and deposited by the Aceh Province 1907 tsunami. A piece of coral in the older of the two pre-2004 sand layers at Busung dated to around AD 1783, and was deposited by an unknown tsunami that occurred after AD 1783, or possibly by the 1861 tsunami. The nearly equatorial latitude of the study sites minimizes potential for geological confusion between tsunami and storm. Our results show the difficulty in matching known events and geological records when using limiting maximum ages from allochthonous fossils, even with high precision radiometric dates. © 2014 Elsevier B.V. All rights reserved.

1. Introduction killed by coseismic subsidence, Nelson et al. (1995) significantly reduced the uncertainty in matching the age of dated material to an How wide can gaps be between the true age of a layer and ages from earthquake. its accompanying allochthonous fossils? Researchers commonly use In this study, we compare ages of coral detritus entrained in tsunami ages of plant or animal fossils in sediment layers to estimate the timing deposits with ages of historical earthquakes, by using uranium–thorium of events such as earthquakes and tsunamis, and to correlate those techniques with much greater precision than would have been afforded events with events at other sites, or with events from the historical re- by radiocarbon techniques. Our pit excavations exposed pre-2004 cord. However, in many cases allochthonous fossils may have died de- tsunami deposits from the past few centuries at two study sites on cades or centuries before their deposition. For example, leaf fragments Simeulue Island, Aceh Province, Indonesia. Although both sites lie atop from pre-2004 tsunami deposits at Phra Thong Island in southern the 2005 rupture patch, they are exposed to tsunamis from both the Thailand gave radiocarbon ages that differed from one another by hun- 2004 and 2005 patches (Fig. 1). dreds of years, despite their occurrence in the same layer (Jankaew Large tsunamigenic fault ruptures occur frequently along the Sunda et al., 2008). Similarly, Nelson (1992) reported that various materials megathrust. Off the coast of northern Sumatra, in the region of the 2004 from the same stratigraphic horizon can differ in radiocarbon age by MW 9.2 and 2005 (MW 8.6) ruptures, earthquakes potentially of M ~7.5 many hundreds of years. On the other hand, using in-situ plant fossils or greater occurred in 1861 and 1907 and resulted in tsunamis known to have affected the Acehnese coast (Newcomb and McCann, 1987). The 1861 earthquake caused heavy shaking at Nias Island and was ⁎ Corresponding author at: Graduate School of Life and Environmental Sciences, accompanied by a tsunami that affected more than 500 km of the University of Tsukuba, 1-1-1 Ten-noudai, Tsukuba, Ibaraki 305-8572, Japan. Sumatran coastline; it is regarded as an analog of 2005 in size and E-mail address: [email protected] (S. Fujino). 1 fl Now at: Earth Observatory of Singapore, Nanyang Technological University, 639798 spatial extent (Meltzner et al., 2012b)(Fig. 1). Sea oor displacement Singapore. of the 1907 earthquake caused a tsunami that devastated Simeulue

http://dx.doi.org/10.1016/j.margeo.2014.09.047 0025-3227/© 2014 Elsevier B.V. All rights reserved. S. Fujino et al. / Marine Geology 357 (2014) 384–391 385

experiences lower wave energy than open coasts. The Busung reef flat 15 N 150 B subsided gradually before the 2005 Nias–Simeulue earthquake but 100 2004 95 E patch rose more than 100 cm during the 2005 earthquake to be emerged 50 Simeulue Is. above high tide (Briggs et al., 2006)(Fig. 2). Interseismic subsidence 3°N in the decades prior to the earthquake gradually eroded the beach 50 1941 Andaman berm on the strand plain, but the coseismic uplift left the eroded Sea 96°E 2005 97° 50 patch E beach berm sequestered from further wave action on the emerged 150 100 2°N 100 reef flat (Fig. 2). Palm trees that had grown on the reef flat following 0 20 an earlier uplift were killed by the pre-2005 subsidence, but are now 10 N km 1881 Ph emerged as snags above high tide (Fig. 2). Both the 2004 and 2005 tsu- Banyak Is. namis surged through Gosong Bay, though the 2005 tsunami was not Busung fl S high enough to fully inundate the at across the berm, according to u Naibos local eyewitnesses. The 30–40 m wide plain behind the beach berm n 1847 d was a swampy flat before the 2004 tsunami but changed to grassland a because of the 2005 uplift and deposition of the 2004 tsunami sand. m An aerial photo taken just after the 2005 earthquake shows white e 2004 5 N Me sand deposited on the swampy flat by the tsunamis (Fig. 2A). g 100 E a Many coral boulders lie on the plain behind the beach berm. They t h Indian r were buried by the 2004 tsunami sand but still project above the ground Ocean u s t surface (Fig. 3). Some of them were transported from the reef by the B 2004 tsunami, though others could have been transported by one or more prior tsunami. In addition, some limestone boulders derived 1907 Ni 2005, 1861 from an alluvium apron behind the plain now lie atop the plain itself. These limestone boulders are re-crystallized and therefore can be A 0 Sumatra distinguished from corals transported by a tsunami. Shallow pit excavations and a trench made for a port construction at Fig. 1. Selected ruptures since the 19th century along the Sunda megathrust (A), and loca- Busung exposed two bioclastic sand layers (Units B1, B2) in muddy sed- tions of the study sites (B). Rupture zones are from Bilham et al. (2005), Briggs et al. (2006) iments beneath the 2004 tsunami deposit (Pits A and F, Figs. 2, 4, 5). and Meltzner et al. (2010). The 1907 location is speculative. Ph, Phra Thong Island; Me, Meulaboh; Ni, Nias Island. Dotted lines show 2004 and 2005 uplift contours in centime- Fieldwork included stratigraphic logging of the pit walls, geochronolog- ters, from Meltzner et al. (2012a). ic sample collection and GPS mapping. Approximately 1 m of sediment lies atop the mid-Holocene coral reef basement and consists of layers of coral rubble, blue sandy silt, Island and extended over 950 km along the Sumatran coast (Newcomb the lower bioclastic sand layer, black organic-rich peaty silt with abun- and McCann, 1987; McAdoo et al., 2006; Yogaswara and Yulianto, 2006; dant rootlets, the upper bioclastic sand layer, more of the black organic- Yulianto et al., 2010). Recent analysis of old seismograms suggests that rich peaty silt, and finally the 2004 tsunami sand, in ascending order the 1907 earthquake was a tsunami earthquake, with a magnitude of MS (Figs. 4, 5). The older bioclastic sand layer (Unit B1) separates organic- 7.8 ± 0.25 (Kanamori et al., 2010). rich silt and underlying blue sandy silt, and the younger one (Unit B2) is bounded both above and below by organic-rich silt. 2. Pre-2004 sand layers at Busung The coral rubble is composed of pieces of corals, articulated and disarticulated bivalves and calcareous algae. The blue sandy silt contains The Busung site is located in southwestern Simeulue Island. It is a fragments of shell and calcareous algae, and has abundant burrows. small strand plain developed on a coral reef basement, and located at Rootlets are observed in the sandy silt but are much less common the head of an embayment, Teluk Gosong (Gosong Bay). Because of its than in the peaty silt. Some or all of the rootlets in the sandy silt grew location inside the bay, protected behind a sandbar that has emerged downward from horizons in the peaty silt to penetrate Unit B1. The to become a small islet following tectonic uplift, the Busung site sandy silt is massive and does not show any laminations. The presence

ABQuarry 2004 and 2005 tsunami sand 2004 breach old coral Alluvial apron Pit F Pre-2005 seacliff boulder Road Post-2005 Pit A (Fig.3B) shoreline Stream Alluvial Water buffalos Pre-2005 apron Post-2005 shoreline berm N Fig. 3 Pre-2005 Quarry seacliff Pit F Former sandbar Swampy (now an island due to uplift in 2005) Emerged flat reef flat Limestone boulders 020 N Trees killed by pre-2005 subsidence Stream m

Fig. 2. (A) Aerial photo of the Busung study site, taken in May 2005. The coral reef flat emerged due to uplift in the 2005 Nias–Simeulue earthquake. Palm tree that had been killed by pre- 2005 subsidence stand on the emerged reef. White patches on the grassy coastal plain are sand from the 2004 (and, if any, 2005) tsunami. (B) Locations of excavated pits and selected boulders at Busung. Note that the orientation is different from (A). The former sandbar (post-2005 island) in the foreground in (A) is just off the map in (B). 386 S. Fujino et al. / Marine Geology 357 (2014) 384–391

A

Emerged reef flat Road Pit A Detail in B 2004 breach Goats Pre-2005 seacliff Modern coral Boulders

B

Tree

Old Coral Boulder

Fig. 3. (A) View of the study site at Busung (looking north). The pre-2005 beach berm behind the emerged reef flat was breached by the 2004 tsunami. The 2004 tsunami left coral boulders on the field. (B) A coral boulder projecting above the 2004 and 2005 tsunami deposit. This was not dated and its stratigraphic relationship to the paleotsunami deposits was not checked, but it must be older than the 2004 tsunami, given that a tree has grown on the boulder. of marine materials and the direct contact with the underlying coral clast in the entire sedimentary succession of Pit F at Busung. The reason layer suggest that the sandy silt was deposited in a sub-tidal or inter-tidal forthisisunknown,butdiatomsmayhavedissolvedbecauseof calm environment that arose probably due to the formation of the sea- some diagenetic effects such as high ground water temperature. ward beach berm. The peaty silt just under the 2004 tsunami sand is Unit B1 and the 2004 tsunami deposit are laterally continuous in Pit rich in rootlets and plant fragments. No marine materials such as fora- F(Fig. 4), whereas Unit B2 is patchy. All three units are also observed at minifers, coral fragments, and calcareous algae fragments were observed the same stratigraphic positions in Pit A, ~50 m away from Pit F (Fig. 5), in the peaty silt. This peaty silt, therefore, was probably deposited under a implying their lateral consistency at the study site. subaerial environment that was similar to the swampy flat just before The 2004 tsunami sand and the bioclastic sand layers (Units B1, B2) the 2004 and 2005 earthquakes and tsunamis. Diatoms are absent share some sedimentary features. They are all composed of multiple

Sand (Unit B2) Sampled for dating Sampled for dating 2004 and 2005 tsunami deposits (BSG-F1) (BSG-F2) Dirt berm Ground surface

A Seaward Detail in B Detail in C 1 m Landward

Sand (Unit B1) Coral platform basement Coral rubble Organic-rich silt 2004 and 2005

Fig.6C Unit B2

Unit B1 B C Silt Coral rubble

Fig. 4. (A) Photo of the northern face of Pit F at Busung. Two tsunami deposits (Units B1 and B2) and associated coral boulders are traced by red and yellow dashed lines. The 2004 and 2005 tsunami deposits are outlined by blue lines. (B) and (C) Close-up views of the northern face of pit F. S. Fujino et al. / Marine Geology 357 (2014) 384–391 387

Ground surface A B 2004 and 2005 tsunami deposits

Fig.6A Organic-rich Fig.6B 10 cm silt Burrows

Detail in C Unit B2

Detail in B Unit B1 Sandy Silt Pit bottom C 2004 and 2005 tsunami deposits

Coral boulder sampled for dating (GSG06-3)

Organic-rich 10 cm silt Unit B2

Unit B1

Burrows Sandy Silt

Pit bottom

Fig. 5. (A) View of Pit A at Busung. The coral boulder (GSG06-3) is outlined in yellow. (B) Southern face of Pit A. The thick sand layer at the top is the deposit from the 2004 and 2005 tsunami. A bioclastic sand layer (Unit B2, yellow dashed line) is within the organic-rich silt of a back-berm swamp. Another bioclastic sand layer (Unit B1, red dashed line) is above a sandy silt that was probably deposited in an inter-tidal or sub-tidal environment and below the organic-rich silt. (C) Eastern face of Pit A. The coral boulder that gave an age of AD 1865.9 ± 18.5 (GSG06-3) is lying on Unit B2. sub-layers, rich in marine materials and accompanied by coral boulders dated but they were already in their present positions prior to the (Fig. 6). The 2004 tsunami deposit is composed of alternating sub-layers 2004 and 2005 tsunamis, according to locals. Another old coral boulder of sand and silt (Fig. 6A), and accompanied by coral boulders as men- is on a beach ridge ~40 m landward of the pre-2005 sea cliff; a pit was tioned above. Units B1 and B2 each have a sharp erosional basal contact excavated beside it, exposing the boulder in profile (Fig. 7A). and contain sub-layers (Fig. 6B, C). Both units are rich in calcareous The sediment above the beach ridge sand is composed of sandy silt, a algae, coral fragments and other calcareous debris, indicating a seafloor pre-2004 bioclastic sand layer (Unit N), peaty organic-rich silt and the or beach source. Coral boulders up to a few decimeters in diameter are 2004 (or 2005, or both) tsunami sand, in ascending order. The peaty abundant in Units B1 and B2 (Figs. 4, 5). organic-rich silt has abundant rootlets and plant debris. As seen under preliminary microscopic observation, freshwater diatoms are abundant 3. Pre-2004 sand layers at Naibos in the peaty organic-rich silt, though they were not counted. The sandy silt between the beach ridge sand and the sand layer (Unit N) has less The Naibos site lies on a strand plain ~25 km north of the Busung site plant debris and rootlets than the upper peaty organic-rich silt. Diatoms (Fig. 1). The 2005 earthquake uplifted the Naibos site more than 0.5 m and other bioclasts are absent in the sandy silt. Given that both the (Briggs et al., 2006), expanding the coastal flat by a few tens of meters sandy silt and the peaty organic-rich silt were lying atop the beach seaward (Fig. 7A). As is the case at the Busung site, coral boulders ridge, these were likely deposited under subaerial environments. If the were left at the site. A 2 m coral boulder sits on a beach face in front of beach ridge had ever been below high-tide level and exposed to wave the study site (Fig. 7A). Another 2 m coral boulder and multiple smaller and tidal action, either during or after sedimentation of the silt layers, ones lie partly buried in a paddy field ~250 m inland. These were not it is likely to have been eroded and not preserved. 388 S. Fujino et al. / Marine Geology 357 (2014) 384–391

A Ground surface

Fine sand

Sandy silt Fine- to medium- sand with 2004 and 2005 calcareous algae tsunami deposits Sandy silt Fine- to medium- sand Sandy silt Fine- to medium- Organic-rich sand silt 10cm

B Medium- to coarse- sand with Organic-rich calcareous algae silt Unit B2 Silty fine sand

Organic-rich Medium- to coarse- silt sand with calcareous algae

Unit B1 10cm

Unit B1 C Organic-rich silt

Silty fine sand

Fine- to medium- sand with calcareous algae

Silty fine sand

Fine- to medium- Silt sand with 10cm calcareous algae Coral rubble

Fig. 6. (A) Close-up view of the 2004 (and, if any, 2005) tsunami deposit in Pit A at Busung. The deposit is composed of alternating sub-layers of sand and silt. See Fig. 5 for its position. (B) Close-up view of Unit B2 in Pit A at Busung. The deposit is composed of alternating sub-layers of silty fine sand and calcareous medium to coarse sand. See Fig. 5 for its position. (C) Close-up view of Unit B1 in Pit F at Busung. The deposit is composed of alternating sub-layers of silty fine sand and calcareous fine to medium sand. Unit B1 separates overlying organic-rich silt and underlying bluish-gray silt. See Fig. 4 for its position.

The pre-2004 bioclastic sand layer (Unit N) separates peaty organic- ages of past tsunami events. We sampled coral boulders from Pits A rich silt and underlying sandy silt (Fig. 7B, C). The unit is rich in marine and F at Busung and from the pit at Naibos (BSG-F1, BSG-F2, GSG06-3, materials and shows internal structure (Fig. 7C). Coarser sub-layers con- NBS-B; Figs.4,5,7,Table 1). sist of shells of calcareous algae mixed with fine to medium sand; the In each case, there are two possible age relationships between a coral finer sub-layer is composed of fine sand and is sandwiched between boulder and the deposit within which it was entrained: either the coral shell-rich coarser sub-layers (Fig. 7C). The lateral extent of Unit N is was killed by the event (such as a tsunami) that resulted in the boulder's not well determined, since the deposit could not be recognized in transport and ultimate deposition, or the coral died previously (possibly other pits at the site. from uplift in an earlier earthquake) and its outer surface predates the de- The old coral boulder rests directly atop Unit N (Fig. 7D, E), suggest- position. Given that the coral boulders' surfaces were all eroded to some ing simultaneous deposition of the layer and boulder. An alternative hy- degree and that their outer growth bands sustained substantial bioerosion pothesis, that the coral boulder and the underlying paleotsunami layer by boring organisms, the sampled boulders could have been older, by un- were from different tsunamis, is unlikely: it is improbable that a second known amounts of time, than the deposit with which they are associated. tsunami scoured down and left the boulder on exactly the same horizon Samples for dating were removed from each boulder, and the boul- with the initial tsunami sand layer, without leaving a second sand layer. ders were sliced and X-rayed to enable the counting of annual bands A portion of the coral boulder was chiseled off for dating. outward from each geochronologic sample to the outer edge of the boulder. The dating results are summarized in Table 1. 4. Dating U–Th sample ages suggest that the outermost of the preserved annu- al bands of the coral boulders from Unit B2 date to AD 1865.9 ± Coral boulders from within the pre-2004 bioclastic sand layers 18.5 years (GSG06-3; Pit A; Fig. 5) and AD 1521.8 ± 63.4 (BSG-F2; Pit (Units B1, B2, N) were dated with U–Th techniques to constrain the F; Fig. 4). Likewise, the outer preserved band of the boulder from Unit S. Fujino et al. / Marine Geology 357 (2014) 384–391 389

A D Dirt berm 2 m Pre-2005 seacliff coral boulder

in beach face k Coral boulder

1 m n a

coral boulder b Beach-ridge crest

m

a

e r Pit t Ground surface Inter-ridge swale 020 S

Breach m N 2 m coral Road boulder Detail in E c.a. 250 m inland Chiseled off Dirt berm for dating B Sand of Sand Ground surface (NBS-B) beach ridge (Unit N) 2004 tsunami sand Coral boulder Sand (Unit N) Scale (1 m) E Detail in C Coral boulder Interspace filled by organic-rich silt Sand of beach ridge

Pit bottom

Sand (Unit N) C Sandy silt 10 cm Organic-rich silt

Fine- to medium-sand with calcareous algae Fine sand

Fine- to medium-sand with calcareous algae

Sandy silt 10 cm

Fig. 7. (A) Location of the excavated pit at Naibos. (B) Photo of the northern face of the pit. (C) Close-up view of the pre-2004 tsunami sand layer (Unit N) in the northern face of the pit. The layer is separated into lower and upper coarser parts and a middle finer part, showing sub-layer structure. The coarser parts are rich in bioclasts. (D) Photo of the western face of the pit. The top of the tsunami sand layer corresponds to the bottom of the coral boulder. (E) Close-up view of the contact between the sand layer (Unit N) and bottom of the coral boulder (NBS-B). The top of the sand layer corresponds to the bottom of the coral boulder. The gap between the layer and part of the boulder was filled by organic-rich silt probably deposited after the boulder was emplaced.

B1 (BSG-F1; Pit F; Fig. 4) dates to AD 1783.4 ± 5.6. The outer preserved Busung, and past tsunami deposits (e.g. Benson et al., 1997). Such struc- band of the Naibos boulder (NBS-B; Fig. 7) dates to AD 1871.0 ± 12.7. ture is attributed to sedimentation from distinct phases of flow, such as from a sequence of tsunami inundations (e.g. Kon'no et al., 1961; 5. Discussion and conclusions Nanayama and Shigeno, 2006; Naruse et al., 2010). Abundant marine material in the sand layers reflects sediment transport from the sea, 5.1. Identification of the pre-2004 sand layers as tsunami deposits and excludes the possibility that a river flood or other processes that supply terrestrial sediments deposited the sand layers. The sand layers The existence of sub-layer structure, abundance of marine materials, were observed in limited number of pits but seem to be distributed con- lateral consistency and coral boulder accompaniment of the sand layers sistently in the strata at Busung: they are laterally continuous in the 15- at Busung and Naibos (Units B1, B2, N) indicate that the layers were m-wide pit face (Pit F) and are also observed in a pit 50 m away (Pit A). deposited by past tsunamis. Sub-layer structure is often observed in This lateral continuity is a common feature of modern tsunami deposits modern tsunami deposits including the 2004 tsunami deposit at (Morton et al., 2007).

Table 1 Summary of dating on coral boulders.

Sample Position Locality name Pit Age of sample (B.P.) Chemistry date Date of sample (AD) Annual bands after Date of the outermost preserved sample annual band (AD)

GSG06-3 Unit B2 Busong Pit A 153.0 ± 18.5 5/22/2007 1854.4 ± 18.5 11.5 ± 1.0 1865.9 ± 18.5 BSG-F2 Unit B2 Busong Pit F 503.0 ± 63.2 10/24/2007 1504.8 ± 63.2 17.0 ± 5.0 1521.8 ± 63.4 BSG-F1 Unit B1 Busong Pit F 228.5 ± 5.5 11/26/2007 1779.4 ± 5.5 4.0 ± 1.0 1783.4 ± 5.6 NBS-B Unit N Naibos – 141.8 ± 12.7 10/24/2007 1866.0 ± 12.7 5.0 ± 1.0 1871.0 ± 12.7 390 S. Fujino et al. / Marine Geology 357 (2014) 384–391

Conceivably, sand layers and coral boulders can also record excep- can be attributed to the 1861 tsunami or an unknown tsunami after tionally large storms, but the study sites are located well within the AD 1783. It is worth noting that the change in sedimentary facies low-latitude Coriolis minimum, where cyclone development is limited. through Unit B1, from a sub-tidal or inter-tidal sandy silt up to a Tropical storms can strike Simeulue Island, but they are rare and may supra-tidal peaty silt, would be consistent with uplift in 1861 at the never be strong. The only documented tropical storm in the vicinity of study site (Meltzner et al., 2012b). Simeulue was Tropical Storm Vamei, which formed off Borneo in Though we cannot definitively attribute sand layers at Busung and December 2001 and passed just north of Simeulue. Although Vamei Naibos to specific tsunamis, U– Th dating on entrained coral boulders had reached minimal typhoon status when it initially made landfall on gives improved age constraints for the timing of tsunamis in recent cen- the Malay Peninsula, just north of Singapore, it weakened quickly as it turies. But because of potential discordance between the death dates of crossed the Malay Peninsula (Juneng et al., 2007). Its sustained surface the corals and deposition of the sand layers, ambiguity in this correla- winds never exceeded 30 knots (55 km/h) as it crossed Sumatra or tion remains. Our results show the difficulty in matching known events passed north of Simeulue (Joint Typhoon Warning Center, 2002), and and geological records when using limiting maximum ages from it was small and compact. Indeed, although storms with intense rain, allochthonous fossils, even with high precision radiometric dates. wind, and waves form frequently in this region, they do not result in large sea-level fluctuations: at such low latitudes, it is not possible to Acknowledgments develop a large pressure gradient that could sustain a significant sea surface height differential (Koh Tieh-Yong, personal communication, We dedicate this paper to the memory of our friend Adi Rahman 2014). Putra, who assisted in fieldwork. We thank Katherine Whitlow for the fieldwork and Yuki Sawai for the diatom analysis. This study was sup- 5.2. Correlation with historical documents ported by JSPS and LIPI under the JSPS-LIPI Joint Research Program. This manuscript benefitted from the constructive comments by Brian The U–Th dates of coral boulders from Unit B2 in Pit A at Busung Atwater and an anonymous reviewer. This is Earth Observatory of (GSG06-3) and from Unit N at Naibos (NBS-B) substantially overlap Singapore contribution 67. the 1861 uplift and tsunami. Although sample BSG-F2 embedded in Unit B2 in Pit F is much older than sample GSG06-3 embedded in Unit B2 in Pit A 50 m away (Fig. 2, Table 1), we have high confidence in the Appendix A. Supplementary data stratigraphic correlations (Figs. 4, 5). The age discrepancy could easily be explained if BSG-F2 was a coral clast that had been long dead before Supplementary data associated with this article can be found in the being entrained and deposited in Pit F. We therefore take the age of the online version, at http://dx.doi.org/10.1016/j.margeo.2014.09.047. younger GSG06-3 as the best approximation (but still a maximum These data include Google map of the most important areas described bound) for the age of Unit B2. in this article. Meanwhile, we do not have age data that overlap the 1907 tsunami at either study site, though it is inferred from historical records that the References 1907 tsunami inundated both sites (Newcomb and McCann, 1987). Pos- sible causes of the absence of direct geological evidence for the 1907 Benson, B.E., Grimm, K.A., Clague, J.J., 1997. Tsunami deposits beneath tidal marshes on northwestern Vancouver Island, British Columbia. Quaternary Research 48, 192–204. tsunami include (1) post-depositional processes may have completely Bilham, R., Engdahl, E.R., Feldl, N., Satyabala, S.P., 2005. Partial and complete rupture of the erased the 1907 tsunami trace, or (2) Unit B2 may have been deposited Indo-Andaman plate boundary 1847–2004. Seismological Research Letters 76, by the 1907 tsunami instead of in 1861. In the first hypothesis, the 1907 299–311. http://dx.doi.org/10.1785/gssrl.76.3.299. Briggs, R.W., Sieh, K., Meltzner, A.J., Natawidjaja, D., Galetzka, J., Suwargadi, B., Hsu, Y.-J., tsunami deposit may have been thin and subtle and was later destroyed Simons, M., Hananto, N., Suprihanto, I., Prayudi, D., Avouac, J.-P., Prawirodirdjo, L., by bioturbation or erosion. In the second hypothesis, the 1861 earth- Bock, Y., 2006. Deformation and slip along the Sunda megathrust in the great 2005 quake uplifted and killed corals on the reef seaward of the study site, Nias–Simeulue earthquake. Science 311, 1897–1901. http://dx.doi.org/10.1126/ but the associated tsunami was not big enough to leave a robust deposit. science.1122602. Jankaew, K., Atwater, B.F., Sawai, Y., Choowong, M., Charoentitirat, T., Martin, M.E., In turn, the larger 1907 tsunami entrained corals killed by emergence in Prendergast, A., 2008. Medieval forewarning of the 2004 Indian Ocean tsunami in 1861 and transported them to the coastal plain. The second hypothesis Thailand. Nature 455, 1228–1231. http://dx.doi.org/10.1038/nature07373. is supported by the observation that the outer surface of coral boulder Joint Typhoon Warning Center, 2002. Annual Tropical Cyclone Report 2001 (http://www. usno.navy.mil/NOOC/nmfc-ph/RSS/jtwc/atcr/2001atcr.pdf). GSG06-3 was somewhat eroded, suggesting that the coral was dead Juneng, L., Tangang, F.T., Reason, C.J.C., Moten, S., Hassan, W.A.W., 2007. Simulation of and exposed for some time (several years or longer) before being de- tropical cyclone Vamei (2001) using the PSU/NCAR MM5 model. Meteorology and posited. Furthermore, uplifted coral microatolls in southern Simeulue Atmospheric Physics 97, 273–290. http://dx.doi.org/10.1007/s00703-007-0259-2. Kanamori, H., Rivera, L., Lee, W.H.K., 2010. Historical seismograms for unravelling a mys- and northern Nias gave ages corresponding to the 1861 earthquake terious earthquake: The 1907 Sumatra Earthquake. Geophysical Journal International and suggest that the 1861 earthquake was comparable to that in 2005 183, 358–374. http://dx.doi.org/10.1111/j.1365-246X.2010.04731.x. (Meltzner et al., 2012b). The Busung site was uplifted more than Kon'no, E., Iwai, J., Kitamura, N., Kotaka, T., Mii, H., Nakagawa, H., Onuki, Y., Shibata, T., Takayanagi, Y., 1961. Geological observations of the Sanriku coastal region damaged 100 cm by the 2005 earthquake (Briggs et al., 2006), but, based on eye- by the tsunami due to the Chile earthquake in 1960. Contributions from the Institute witness accounts, the associated tsunami was small and scarcely of Geology and Paleontology 52. Tohoku University (40 pp.). overtopped the beach berm there. Given that the 2005 earthquake McAdoo, B.G., Dengler, L., Prasetya, G., Titov, V., 2006. Smong: How an oral history saved thousands on Indonesia's Simeulue Island during the December 2004 and March appears to be an analog of 1861, it is plausible that the 1861 tsunami 2005 tsunamis. Earthquake Spectra 22, S661–S669. left little deposit, if any, on the coastal plains at Busung and Naibos. Meltzner, A.J., Sieh, K., Chiang, H.-W., Shen, C.-C., Suwargadi, B.W., Natawidjaja, D.H., The coral boulder from Unit B1 at Busung provided an age of AD Philibosian, B.E., Briggs, R.W., Galetzka, J., 2010. Coral evidence for earthquake recur- – – 1783.4 ± 5.6 years. The change in sedimentary facies across Unit B1 rence and an A.D. 1390 1455 cluster at the south end of the 2004 Aceh Andaman rupture. Journal of Geophysical Research 115, B10402. http://dx.doi.org/10.1029/ from bioturbated sandy silt upward to organic-rich peaty silt implies 2010JB007499. an environmental change due to uplift concurrent with the tsunami. Meltzner, A.J., Sieh, K., Chiang, H.-W., Shen, C.-C., Suwargadi, B.W., Natawidjaja, D.H., However, at present, coral microatoll studies have not found consistent Philibosian, B., Briggs, R.W., 2012a. Persistent termini of 2004- and 2005-like ruptures of the Sunda megathrust. Journal of Geophysical Research 117, B04405. http://dx.doi. evidence for coseismic uplift of southern Simeulue around the date of org/10.1029/2011JB008888. the boulder from Unit B1. If there really was no crustal deformation Meltzner, A.J., Sieh, K.E., Chiang, H., Wu, C., Shen, C., Gong, S., Suwargadi, B., Natawidjaja, around AD 1783, the dated coral boulder from Unit B1 may have already D.H., Switzer, A.D., Horton, B.P., Philibosian, B., 2012b. Coral microatoll paleogeodesy in Sumatra: details of the 1861 predecessor to the 2005 Nias–Simeulue earthquake. been dead when entrained by the tsunami to give an age older than the Abstract G11C-08 presented at the 2012 Fall Meeting, American Geophysical Union, actual deposition of Unit B1. In this scenario, sedimentation of Unit B1 San Francisco, California, 3-7 December. S. Fujino et al. / Marine Geology 357 (2014) 384–391 391

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