A~3000 years-old sequence of extreme revealed by marine and shore deposits east of Taiwan Serge Lallemand, Remi Lehu, Fabien Retif, Shu-Kun Hsu, Nathalie Babonneau, Gueorgui Ratzov, Maria-Angella Basseti, Laurent Dezileau, Meng-Long Hsieh, Stephane Dominguez Speaker : FX. Anjar Tri Laksono Adviser : Louis Loung-Yie Tsai Date : June 15, 2016 1
The Location of Study Area Fig.1. General map of the Ryukyu and Luzon subduction zones overlapping in Taiwan (Hsin et al., 2008). 2
Outline Geological, oceanic, and atmospheric setting Core sampling, data, and results Interpretation Conclusion Research progress 3
The collision between the North Luzon volcanic arc, represented by the Coastal Range and Lutao island, and the chinese continental margin, represented by the Central Range (Late Miocene- Early Pliocene). Geological setting of eastern Taiwan Source: Lallemand et al., 1997 Fig.2. Topographic map 4
Fig.3. Bathymetric map (Lallemand et al., 1997) The submarine slope east of the Coastal Range is relatively steep. Chimei Valley has about 10 km wide with a regular 6 o -7 o slope at 3 and 4 km depth. 5
Lutao Island uplifted at an average rate of 1.2 mm/yr during Late Holocene. The Holocene uplift rate of marine terraces in the north is 2-3 mm/yr and 9-10 mm/yr in the south. The present-day, in the north of Coastal Range subsides 20 mm/yr, however uplift 20 mm/yr in the south. 6
Table 1. Records of earthquakes and tsunami on Eastern Coast of Taiwan Year Magnitude Location 2003 6.8 Chengkong June 5, 1920 7.7 Hualien December 9, 1882 7.5 Taitung October 13, 1815 7.7 Hualien March 17, 1811 7.5 Hualien Tsunami in 1760 AD? Meiwa tsunami on April 24, 1771? Tsunami in 1850? No Evidence 7
The fastest current is located east of Taiwan. Oceanic setting, Kuroshio current The mean Kuroshio transports are ~30 ± 5 Sv (1 Sv = 10 6 m 3 /s). Annual mean surface rates, between 0 and 50 m, reaching up to 1.3 m/s (~2.5 knots) at a distance between 20 and 40 km from the east coast of Taiwan. The Kuroshio Current is thought to play a role in the transport of suspended material. 8
Taiwan is crossed by the tropic of Cancer (Northern tropic). Climate Typhoons hit Taiwan every year with a high frequency (3 or 4 per year in average). The deadliest typhoon is Typhoon Morakot occuring in August 2009. An early Holocene (10.7 to 8.4 ka) rainfall optimum among the late Quarternary climate record. 9
Core sampling, data, and results Sampling strategy Methods Data and results 10
Sampling strategy Location: 23 o 15.6 N and 121 o 39.0 E (KR03 on Figures 1 and 2) 9 cores offshore east Taiwan Depth: 1200 m below the sea level Basin far from channel and canyon Massive floodings hyperpycnal flows 11
Methods MSCL major chemical elements Beckman-Coulter LS 13-320 variation of the grain size Sand fraction composition 14C radiocarbon dating timing and age 210 Pb and 137 Cs the sedimentation rate and the age of the top of the core 12
Data and Results Fig.4. KR03 core logs and the detail description 13
Core description Fig.5. A: Undetermined Veneroida bivalves external sides, C: wood debris, D: silty fraction. 14
Table 2. Radiocarbon dates obtained in this study 15
Shore evidences for an extreme event in that age period Interpretation The stratigraphic and chronological data from the coastal terraces in the Chengkong-Papien area. 16
Age of shells vs age of sediment The shells present in the T-layer appear to be 1400 ± 150 years older than the sedimentary matrix. These hypotheses are proposed by: First hypothesis A lagoon origin with continental waters, thus dead carbon feeding the bivalves, removal of old shells into younger sediment, or marine shells fed by submarine groundwater discharges. Second hypothesis Buried within the sediment as attested by their endobionte hinge. Artesian coastal aquifers seep through the sediment along the shoreline and feed the buried bivalves with groundwater characterized by large reservoir ages. 17
Possible origin of the anomalous deposit It is 23 cm thick and unique within a monotonous clay sequence covering 3750 ± 150 years. It consists of five distinct deposits. The source of silts is likely turbidity surges. The presence of shallow water shells and wood fragments concentrated in the upper sequence is enigmatic. 18
The effect of submarine landslide Submarine landslide Turbidity current No silt and Fe anomaly in the T layer Silty layers concentrated in a short time range 19
The effect of a tsunami M w 8.7 earthquake might potentially occur in the southernmost subduction interface at a mean distance of 120 km (Hsu et al., 2012). M w 9 occur at a distance larger than 200 km based on the existence of a splay fault in the Ryukyu forearc (Lin et al., 2014). The westernmost of the Ryukyu subduction interface Tsunami deposits (ota et al., 2011) or alluvial fan (Hsieh and Rau, 2009)? Tsunami The west-dipping thrust fault at the eastern Taiwan margin Another segment of the Ryukyu subduction zone (Ando et al., 2013) 20
The effect of a typhoon Shells and wood deposits only once in the core KR03, this indicates that only a supertyphoon can possibly be a candidate. The Kuroshio Current can reach today 1.2 m/s and transport between 15 and 44.10 6 m 3 /s (Hsin et al., 2008). Small shells and wood debris Transported A tornado imbedded in a typhoon Deposited 21
Hydro-dynamical tests Generation TOPICS Modelling strategy Propagation SYMPHONIE Run-up computation Analytical theory of long wave run-up 22
Table 3. Input and output parameters of TOPICS simulations for 10 different submarine landslides sources. 23
A. Kuroshio Current parallels the coast from 23 o N. B. Kuroshio Current deviates southeast of Taiwan making a loop around the Lutao island C. The surface current was deeply modified by the anticlockwise wind rotation forcing in the study area. D. The strength decreases, however the surface current still highly perturbated. E. The Lutao island act as a shield for surface current. Fig.6. The pattern of surface currents 24
Fig.7. Results of hydro-dynamic modeling including seawater circulation and tsunami-triggered landslides. 25
Table 4. Nearest grid points used for the run-up computation η(x=0,t): run up oscillation on the shore. η(x,t): water oscillations in the last sea points. T: the travel time of the wave. L: the distance from this point to the shore. Table 5. Run-up computation s using the analytical solution of Choi et al. (2011) 26
Conclusions There are multiple-event characterized by four distinct turbidite silty layers and one top deposit made of shallow-living shells and wood debris without significant silty component. Events P1 to P4 resulted from nearby submarine landslide probably triggered by clustered earthquakes. Then a super typhoon or tsunami occured, resulting in the deposition of layer T. 27
Research Topic and study area Topic: Investigation of the tsunami event on the Eastern Coast of Taiwan. Goal: To better understand tsunami event on the eastern coast of Taiwan and to search for geological evidence of tsunamis. Benefit: to assess the risk for future tsunami hazards. Study area: marine terrace throughout Lu-Ye, Changping, and Tu-lan. 28
Research progress Methodology Facies analysis Sand composition counting XRF Explaination On process On process Future work 29
Temporary results Site 6 Beach gravel Site 1 Debris-flow gravel Beach gravel alluvial fan Volcanic fragments inside the alluvial fan deposit 30
Site 12 Site 17 Beach gravel Debris-flow gravel Beach gravel Debris-flow gravel Muddy sand Muddy sand contains Gastropod and Pelecypod shells Coral boulder 31
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