Journal of Asian Earth Sciences 36 (2009) 67–73 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jaes Tsunami propagation scenarios in the South China Sea Dao My Ha a,*, Pavel Tkalich a, Chan Eng Soon a,b, Kusnowidjaja Megawati c a National University of Singapore, 14 Kent Ridge Road, Singapore 119223, Singapore b National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore c Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore article info abstract Article history: This paper studies extreme tsunami scenarios in the South China Sea potentially originated from a giant Received 20 May 2008 rupture along the Manila Trench. Tsunami height and arrival time to the major coasts along the SCS are Received in revised form 2 July 2008 computed using TUNAMI-N2-NUS model. Sensitivity of tsunami parameters to the rupture properties is Accepted 17 September 2008 explored numerically. For tsunami waves potentially originated from the Manila Trench, it is shown that the Sunda Shelf and the Natuna Islands may act as a natural barriers, sheltering southwest part of the South China Sea and Singapore Strait. Keywords: Ó 2008 Elsevier Ltd. All rights reserved. Tsunami propagation South China Sea Manila Trench 1. Introduction 2007; Dao et al., 2008; Romano et al., submitted for publication). The present paper describes scenario-based tsunami threat analy- After the tragic Indian Ocean tsunami in 2004, national scien- sis for the SCS. tific and forecasting establishments of the Indian Ocean Rim have started building capacity to provide efficient warnings of tsunami 2. Tsunami propagation model threat. Accurate process-based models have been applied and quick data-driven methodologies are being developed. While Paci- The tsunami propagation model TUNAMI-N2 used in this paper fic Tsunami Warning Centre (PTWC) and Japan Meteorological was originally developed in Disaster Control Research Center Agency (JMA) have mapped fault zones and other potential sources (Tohoku University, Japan) through the Tsunami Inundation Mod- of tsunami in the Pacific Ocean since the middle of last century, eling Exchange (TIME) Program (Goto et al., 1997). TUNAMI-N2 has study of tsunamigenic sources in the Indian Ocean have just been been utilized intensively in Japan to study propagation and coastal started. Very few studies have been conducted to assess tsunami amplification of tsunami in relation to different initial conditions threat in the South China Sea (SCS), which has been excluded from (Goto and Ogawa, 1992; Imamura and Shuto, 1989; Shuto and a consistent hazard mapping in the past. It is believed that there Goto, 1988; Shuto et al., 1990). The model has also been imple- are potential tsunami sources in the region due to the fault rupture mented widely to simulate tsunami propagation and run-up in along the Manila Trench. Even though the probability of strong the Pacific, Atlantic and Indian Oceans, with zoom-in at particular earthquakes from the Manila Trench is not very high, it may inev- areas of Japanese, Caribbean, Russian, and Mediterranean seas itably strike sometimes in the future (Megawati et al., 2009). (Yalciner et al., 2000, 2001, 2002; Yalciner, 2004; Zahibo et al., Singapore lies at the confluence of the Pacific Ocean and the In- 2003; Tinti et al., 2006). dian Ocean, southwest of the SCS, and thus national forecasting TUNAMI-N2 code has been improved by the authors (Dao and authorities have to be aware of tsunami threats from both sides. Tkalich, 2007) to capture the effects of the Earth’s curvature, Cori- Singapore is developing its national tsunami research and warning olis force, and wave dispersion on propagation of transoceanic tsu- capabilities, which will contribute eventually into the regional sci- nami. The initial condition of a tsunami is prescribed as a static entific and forecasting networks. Some tsunami propagation sce- instantaneous elevation of sea level identical to the vertical static narios from potential sources due to fault rupture along the coseismic displacement of the sea floor, as given by Mansinha Sunda Arc (Indian Ocean) were considered in the previous publica- and Smylie (1971) for inclined strike-slip and dip-slip faults. Initial tions by the authors (Tkalich et al., 2007a,b,c; Dao and Tkalich sea surface deformation due to multiple and non-simultaneous ruptures is calculated using the fault model of Mansinha and Smy- * Corresponding author. lie (1971) for each individual rupture, and the resulting surface E-mail address: [email protected] (M.H. Dao). deformation is linearly added to the current sea surface. Moving 1367-9120/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2008.09.009 68 M.H. Dao et al. / Journal of Asian Earth Sciences 36 (2009) 67–73 boundary conditions are applied at land boundaries to allow for AMI-N2 (named TUNAMI-N2-NUS) is thoroughly verified at test run-up calculation, and free transmitted wave condition is applied cases, laboratory experiments and real cases, and subsequently ap- at the open boundaries. The code is sped up three to four times by plied to scenario-based tsunami modeling in Indian Ocean (Dao optimizing loops and memory usage. The modified version of TUN- and Tkalich, 2007; Tkalich et al., 2007a,b; Dao et al., 2008). Fig. 1. (a) The active plate margins of South-East Asia, showing trenches, arcs, and main faults (Hutchison, 1989); (b) computational domain, a hypothetical earthquake source used in the study and observation points along South China Sea coasts. Fig. 2. Scenario A earthquake at the Manila Trench (left pane) and discrete model of 33 segments (right pane). M.H. Dao et al. / Journal of Asian Earth Sciences 36 (2009) 67–73 69 Table 1 shear faults as well as by submarine landslides at steep slopes of The fault parameters of the 33 discrete rectangular segments. the sea bed (see Fig. 1 adopted from Hutchison (1989)). Box Strike Dip Rake Depth Length Width Slip As shown in Fig. 1, largest earthquake related tsunami threat to no. (°) (°) (°) (km) (km) (km) (m) the communities along the SCS coast is coming from the Manila 1 324.46 21.78 90 7.50 40.41 19.30 5 Trench. The entire subduction zone extends from the south of 2 325.20 11.26 90 7.50 54.19 38.68 5 the main island of Philippines Archipelago to the south of Taiwan. 3 318.66 6.55 90 7.50 54.09 66.93 12 A plausible rupture scenario at the Manila Trench has been identi- 4 332.40 5.79 90 7.50 54.00 75.68 12 fied as scenario A as shown in Fig. 2 (see more details in Megawati 5 0.26 6.47 90 7.50 53.89 67.52 25 6 7.39 11.50 90 7.50 80.59 37.51 28 et al. (2009)). This scenario describes a rupture of the entire Trench 7 5.85 10.01 90 7.50 53.56 43.13 28 which has the maximum slip of 40 m at the middle part and grad- 8 355.99 8.46 90 7.50 53.43 51.06 28 ually reduces to 5 m at the two ends. The rupture extends over 9 358.34 7.18 90 7.50 53.28 60.09 30 1000 km and has a maximum width of 150 km. The sinuosity of 10 2.50 6.16 90 7.50 53.14 69.93 30 11 16.26 6.52 90 7.50 52.99 65.93 35 the rupture may lead to different focusing effects of potential tsu- 12 40.34 5.93 90 7.50 105.57 72.15 40 nami waves to vulnerable coasts facing the Manila Trench. This 13 35.93 5.36 90 7.50 52.60 79.67 40 scenario is identified as the worst-case and would generate an 14 21.46 5.70 90 7.50 78.62 74.61 35 earthquake with MW above 9. Moreover, taken into account the 15 352.23 3.28 90 7.50 78.24 129.36 30 rising time of the fault, we consider three possibilities of rupture 16 332.43 6.25 90 7.50 103.81 67.36 25 17 339.52 7.62 90 7.50 51.68 54.86 12 propagations which can be classified as simultaneous, south–north 18 341.26 9.89 90 7.50 46.82 41.97 5 (north-propagating) and north–south (south-propagating) rup- 19 326.63 28.87 90 35.00 37.50 37.27 5 tures. We also look into the possibility of significant tsunami at re- 20 351.15 25.45 90 35.00 54.14 43.11 5 mote coastal areas when moderate magnitude earthquakes occur. 21 333.50 30.86 90 35.00 134.88 34.22 12 22 357.94 20.98 90 35.00 53.76 53.11 28 Based on scenario A, sensitivity analysis is carried out for different 23 11.30 24.22 90 35.00 133.84 45.09 28 rupture directions and different scales of slip magnitude (for smal- 24 9.30 18.22 90 35.00 53.29 61.36 28 ler earthquakes). 25 10.90 15.85 90 35.00 53.15 70.96 30 In order to approximate the initial sea surface deformation 26 47.78 12.76 90 35.00 105.90 88.63 40 model in TUNAMI-N2-NUS, the continuous rupture at the Manila 27 30.91 14.73 90 35.00 131.68 75.92 40 28 37.06 16.31 90 35.00 52.41 67.88 35 Trench is discretized by a fitting algorithm using small rectangles 29 24.75 23.79 90 35.00 104.39 44.85 30 (Fig.