Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Arjun, S.

Hameed, T. S. S.

Kalarani

Kurian, N. P.

Prakash, T. N.

Praveen, S. S.

Shanavaz, C. P.

English

Hydraulic Engineering Repository

Conference Paper, Published VersionPraveen, S. S.; Kalarani; Shanavaz, C. P.; Arjun, S.; Kurian, N. P.;Hameed, T. S. S.; Prakash, T. N.Numerical Modelling Studies on Tsunami Inundation alongthe Lakshadweep IslandsZur Verfügung gestellt in Kooperation mit/Provided in Cooperation with:Kuratorium für Forschung im Küsteningenieurwesen (KFKI)Verfügbar unter/Available at: https://hdl.handle.net/20.500.11970/109940Vorgeschlagene Zitierweise/Suggested citation:Praveen, S. S.; Kalarani; Shanavaz, C. P.; Arjun, S.; Kurian, N. P.; Hameed, T. S. S.;Prakash, T. N. (2010): Numerical Modelling Studies on Tsunami Inundation along theLakshadweep Islands. In: Sundar, V.; Srinivasan, K.; Murali, K.; Sudheer, K.P. (Hg.): ICHE2010. Proceedings of the 9th International Conference on Hydro-Science & Engineering,August 2-5, 2010, Chennai, India. Chennai: Indian Institute of Technology Madras.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010 Numerical Modelling Studies On Tsunami Inundation Along The Lakshadweep Islands                      407    NUMERICAL MODELLING STUDIES ON TSUNAMI INUNDATION ALONG THE LAKSHADWEEP ISLANDS S.S Praveen1, Kalarani2, C. P. Shanavaz3, S.Arjun4, N.P Kurian5, T.S.S Hameed6 and T.N.Prakash7  Abstract: The disastrous tsunami of December 26, 2004 exposed the urgent need for identifying vulnerable coasts and planning mitigation measures. Historical statistics show occurrence of tsunamigenic earthquakes from locations like Carnicobar, Sumatra and North Andaman in Bay of Bengal and Makran in the Arabian Sea. The west coast of India is vulnerable to tsunami from Makran as well as from the east. Though the tsunami inundation has been studied reasonably well for the mainland coastline of India, no study has been carried out for the Lakshadweep islands, located in the Arabian Sea. This paper studies the tsunami run up and inundation along the four inhabited islands of Lakshadweep. The simulation results show that Lakshadweep islands are not as vulnerable to tsunami as the mainland coast.  Keywords: Tsunami; Simulation; Inundation; Run-up; Modelling; TWS        INTRODUCTION  The coastline of South India experienced the most devastating tsunami due to an earthquake of magnitude 9.3 off the coast of Sumatra in Indonesia on December 26, 2004. As most of the tsunamis are generated by submarine earthquakes the possibility of a similar event in the near future cannot be ruled out completely. The west coast of India is vulnerable to tsunami from Makran as well as from the Andaman-Sumatra subduction zone. Though the tsunami inundation has been studied reasonably well for the mainland coastline of India, studies are scarce for the Lakshadweep islands, located in the Arabian Sea, except for the works of Praveen et al.(2009) and Arjun et al.(2009). One of the essential requirements of a Tsunami Warning System is the setup of tsunami inundation models which can predict inundation and run-up along a coastline for a given set of seismic parameters. These models have to be set-up for each coast and calibrated/validated using past tsunami field data.        1-3 JuniorResearch Fellow, Marine Sciences Division, Centre for Earth Science Studies, Thiruvananthapuram 695 031,        India, Email:praveensakalya@gmail.com 4    Senior Research Fellow, Marine Sciences Division, Centre for Earth Science Studies, Thiruvananthapuram 695 031,         India, Email:arjunsmenon@gmail.com 5-7 Scientist, Marine Sciences Division, Centre for Earth Science Studies, Thiruvananthapuram 695 031, India, Email:        npkurian@gmail.com   Proceedings of ninth International Conference on Hydro-Science and Engineering (ICHE 2010), IIT Madras, Chennai, India. 2 - 5  August 2010 Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010 Numerical Modelling Studies On Tsunami Inundation Along The Lakshadweep Islands                      408  Fig. 1. Geographical map of the inhahibted islands of Lakshadweep  In the event of a tsunamigenic earthquake, appropriate decision on issue of warnings and/or evacuation of coastal population, can be taken by referring to such maps. This paper attempts to analyze the numerically simulated tsunami run-up and inundation along the four inhabited islands of Lakshadweep for the tsunami generated by the earthquakes of Makran 1945 and Sumatra 2004. Four Islands selected for this study are Chetlat, Kadmat, Androth and Kavarati (Fig. 1). Chetlat is the northernmost inhabited island of the group with an approximate area of 1sq. km. Kadmat is the longest island next to Agatti in the Lakshadweep group of Islands with a large lagoon and abundant coral growth. Androth is the nearest  island in the group to the main land and is oriented in the east-west direction with no lagoon. Kavaratti is the third largest island in the north south direction with a shallow lagoon enclosed by coral reef on the west.  METHODOLOGY The simulations were performed with the help of a numerical model (TUNAMI N2) which adequately models the physics of tsunami propagation from source to the coast using fixed computational grid using nested grids. The model was set-up and calibrated at Centre for Earth Science Studies (CESS), Thiruvananthapuram (Kurian et al., 2006 and Praveen et. al 2009). Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010 Numerical Modelling Studies On Tsunami Inundation Along The Lakshadweep Islands                      409Numerical simulations for estimating tsunami inundation require two types of data inputs: 1) Source data, encapsulating the geology and seismology of the event and 2) Ocean Bathymetry and coastal topography. The model uses finite grids for the propagation of tsunami. The entire domain is divided into four grids A,B,C and D (Fig.2). Almost the entire Indian Ocean is taken as the outer grid namely Grid A, and three sub-grids B, C and D each lie within the outer one. Grid D is the coastal area for which the run-up and inundation is computed. Starting from Grid D each outer grid will be expanding thrice the corresponding inner grid. The topographic data for the D grid was taken from the survey conducted by CESS. The accuracy of the bathymetric data has been considerably improved in the present study when compared with the previous studies (Praveen et al., 2009 and Arjun et al., 2009) by using C-Map in the B,C and D grids instead of GEBCO. The fault parameters for the simulations were taken from Mohamed Chlieh et al. (2007) and are given in Table 1.  Fig. 2. The pattern of four depth grids used for the model  Table 1. Source parameters of 1945 EQ and 2004 Sumatra EQ Source Parameters Sumatra Makran Slip 15m 15m Fault Length 680km 200km Fault Width 150km 100km Strike 342° 270° Dip 15° 15° Rake 90° 90° Depth 20km 30km  RESULTS AND DISCUSSION Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010 Numerical Modelling Studies On Tsunami Inundation Along The Lakshadweep Islands                      410 Fig 3. (a to d) shows the run-up obtained at the four islands due to 26 December, 2004 Sumatra tsunami. Out of the four Islands a maximum run-up of around 2m is obtained around the north of Androth and north-east of Kavaratti. An inundation of around 144m is obtained at the northern portion of the island. The least run-up  of 0.5m is noticed in the northern portion of Chetlat.   In the island of Androth where the maximum run-up and inundation is noticed in the northern part, no significant inundation is seen in the other parts of the Island. A maximum run-up of around 0.5m and 0.86m is obtained in the northern sectors of Kadmat and Chetlat respectively. When the southern and eastern coasts of both the islands show insignificant run-up and practically no inundation, a meagre inundation of 25m is observed on the north -north west coast of Chetlat. The Kavaratti Island shows a varying run-up of around 2m and 1m in the north-east and south-east sectors respectively, and makes a noticeable inundation of 500m in the northeastern region coinciding with the highest run-up point of that island.                              Fig. 4 shows the run-up obtained at the four Islands due to Makran 1945 tsunami. As in the case of Sumatra, the highest run-up is found on the northern part of Androth; however the value is only 1.85m. The least run-up is found on the southern sector of Chetlat. For Kadmat the simulation shows higher run-up for the entire coast when compared with Sumatra. The Fig. 3. Simulated tsunami run-ups for selected Islands in the Lakshadweep for 2004 Sumatra: (a)Chetlat, (b) Kadmat, (c) Androth and (d)  Kavaratti (a) (b) (c) (d) Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010 Numerical Modelling Studies On Tsunami Inundation Along The Lakshadweep Islands                      411simulation results of Kavaratti shows some similarities with the output of Sumatra. The maximum run-up is obtained at the north east with an inundation of 600m.                             Fig. 4. Simulated tsunami run-ups for selected Islands in the Lakshadweep for 1945 Makran earthquake: (a) Chetlat, (b) Kadmat, (c) Androth and (d)  Kavaratti   Thus the simulation for both Makran and Sumatra shows higher run-up values only on the northern portion of the Islands. In contrast, the Sumatra tsunami was catastrophic for the mainland coast of Kerala (Kurian et al., 2006a,b) with a maximum run-up of upto 5m. In addition to the direct waves, the reflected waves from eastern side of the Laccadive-Maldive Ridge (LMR) and the east coast of Africa also contributed to the calamity along the Kerala coast ( Murty et al. 2008). It can be deduced  that the tsunami cannot make an impact on the Lakshadweep islands since the adjoining sea are very deep resulting in practically very less shoaling and causing direct reflection of the waves after hitting the island. But the shallow lagoons, wherever present, can cause some shoaling and resultant amplification of tsunami causing higher run up. When compared to the mainland, the tsunamis from Sumatra and Makran have produced only negligible inundation in the islands. No noticeable inundation is seen since the backshore is higher than the run-up level. It can finally be concluded that the Lakshadweep islands are least vulnerable when compared to the mainland coast.  CONCLUSIONS (a) (c) (b) (d) Proceedings of ICHE2010, IIT Madras, Aug 2-5,2010 Numerical Modelling Studies On Tsunami Inundation Along The Lakshadweep Islands                      412 A study of the run-up and inundation along the four inhabited islands of Lakshadweep for the tsunami generated by the Makran 1945 and Sumatra 2004 earthquakes showed that the run-up and inundation are much less when compared to the mainland coast. This is attributed to the deep seas around the Lakshadweep islands which does not generate much of shoaling. Moreover, the islands by virtue of their steep slope cause reflection of waves. The amplification is also trivial in the northern and western side of these islands with lagoons even for a tsunami propagating from the western side like the Makran.   ACKNOWLEDGEMENTS  This work forms part of a project funded by the Ministry of Earth Sciences. The authors are thankful to Dr.B.R.Subramanian, Project Director, ICMAM Project Directorate, Ministry of Earth Sciences, Dr. M.V Ramana Murthy, Project Director, National Institute of Ocean Technology, Dr. R.S Kankara, Scientist, ICMAM Project Directorate and  Dr.M.Baba, former Director, CESS for the support and encouragement extended towards the work.  M/s L. Sheela Nair, P.Dhanya and V.R. Shamji have provided valuable support for the study.   REFERENCES  Arjun S, Kalarani, Dhanya P, Praveen S.S, Reshmi A.K, Kurian N.P, Ramana Murthy M.V, Shahul Hameed T.S and Prakash T.N (2009), Numerical simulation of the Makran 1945 tsunami on the southwest coast and Lakshadweep islands of India., Marine Geodesy Special Issue on Tsunamis (in print).  Kurian N.P, Prakash T.N and Baba. M (2006b). Field observations on the Tsunami impact along the Kerala coast, southwest India, In: Tad S.Murty, U.Aswathnarayana and N.Nirupama (Eds.), The Indian Ocean Tsunami, Taylor & Francis, 323-337  Kurian, N. P., Abilash P.Pillai, , Rajith, B. T. Murali Krishnan, and P. Kalaiarasan. 2006a. Inundation characteristics and geomorphological impacts of December 2004 tsunami on Kerala coast.Current Science 90:240–249 Mohamed Chlieh, Jean-Philippe Avouac, Vala Hjorleifsdottir, Teh-Ru Alex Song, Chen Ji, Kerry Sieh, Anthony Sladen, Helene Hebert, Linette Prawirodirdjo, Yehuda Bock, John Galetzka (2007). Coseismic slip and afterslip of the Great Mw 9.15 Sumatra-Andaman Earthquake of 2004, Bulletin of the Seismological Society of America, 97, 152-173 Murty T.S., Kurian N.P. and Baba.M 2008. Roles of reflection, energy trapping and secondary undulations in the tsunami on Kerala coast, Int. Journ. Ecol. & Dev., 10(S08): 100-114 Praveen S.S, Reshmi A.K,.Dhanya P, Arjun S, Kalarani,. Kurian N.P,. Ramana Murthy M.V, Shahul Hameed T.S and Prakash T.N, (2009) Numerical Simulation of 26 December 2004 Tsunami on the Southwest coast and Lakshadweep islands of India. Marine Geodesy Special Issue on Tsunamis (in print).  

Numerical Modelling Studies on Tsunami Inundation along the Lakshadweep Islands

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Numerical Modelling Studies on Tsunami Inundation along the Lakshadweep Islands

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