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Lithospheric Density Structure of Andaman Subduction Zone from Joint Modelling of Gravity and Geoid Data

Lithospheric Density Structure of Andaman Subduction Zone from Joint Modelling of Gravity and Geoid Data

Indian Journal of Geo Marine Sciences Vol. 47 (05), May 2018, pp. 931-936

Lithospheric Density Structure of Andaman Zone from Joint Modelling of Gravity and Geoid data

R. Yadav1, 2 & V. M. Tiwari1* 1CSIR – National Geophysical Research Institute, Hyderabad, 2Academy of Scientific &Innovative Research (AcSIR), CSIR-National Geophysical Research Institute, Hyderabad, India [E.Mail: [email protected]]

Received 07 September 2016 ; revised 30 October 2016

The Andaman subduction zone is the result of the oblique convergence of that dives beneath Eurasian (Sunda) plate and one of the most seismically active . Structure and dynamics of the subduction zone are still a matter of investigations, inspite of a several studies were carried out earlier. In the present study, we have delineated the 2D density structure of the Andaman subduction zone through the joint modelling of gravity and geoid data set derived from the satellite altimetry and interpreted it in term of dynamics of the . The major features of the density structures are : subduction of Indian plate up to ~ 180 km depth; anomalously thicker oceanic crust below the Ninetyeast Ridge, Sewell rise and in the shelf region; comparatively thin lithosphere under the overriding plate. Further, the lowest gravity anomaly marks the interaction of subducting oceanic crust with overriding upper mantle.

[Keywords: Andaman, Gravity, Geoid, Density Structure, Seismogenesis] Introduction studies 16 & 17. All these investigations have facilitated Subduction zones are the results of complex to delineate the structural configuration of the geodynamic processes that evolve due to the Andaman subduction zone. While the gravity convergence of two tectonic plates, wherein one of anomaly pattern was used to understand structural them slides beneath the other and takes over its variations along the Andaman arc, sparse distribution journey towards the deep mantle. Such process causes of seismological and GPS stations over the Andaman the tumbling of the plates in the subduction zone Islands makes such studies confined to the analysis of causing significant forces to drive the plates and data obtained at a few stations. This resulted in the leading to several natural hazards like volcanoes and diminished structural image of the subsurface, causing earthquakes. Some of the noted examples of most the structures to be poorly resolved. active subduction zones of the world are Andaman- The present study is based on the analysis of a , Andean, and Hellenic etc., which have been profile along 100 N, running perpendicular to the loci of the devastating earthquakes1- 3. Most of the structural trend of the Andaman subduction zone. earthquakes occurred within the Andaman region This zone is a typical example of the oblique (ANR) are related to the subduction of the Indian subduction and formed due to the subduction of plate. AR has not yet experienced any large Indo-Australian oceanic plate beneath the Eurasian 18, 19 & 20 earthquake events of Mw > 8.0 reported till now. The (Sunda) plate . The western part of this zone is only documented seismic event in the ANR is the outlined by Ninetyeast Ridge (NER) that runs 1881 of Mw 7.9 event according to the historical approximately parallel to the trench. The complex records4. However, the Sumatra mega-earthquake of dynamic processes occurring in this region are 26th December, 2004 caused a chain of aftershock in evidenced by the presence tectono-morphological the rupture area of about 1300 km including the ANR5 features which form parallel to the Islands like the & 6 and prompted geoscientists to re-look into the fore-arc, back-arc, volcanic-arc (Sewell rise) according detailed structural architecture below the region. to Weeks et al21. The work of Radhakrishna et al,8 in Most of the earlier studies in the Andaman this region is based on 2D density structural region are based on gravity 1, 7 & 8, seismology 9, 10, 11 & 12, modelling computed from gravity anomaly observed Global Positioning System (GPS) 13, 14 & 15 and seismic over five different profiles running perpendicular to 932 INDIAN J. MAR. SCI., VOL. 47, NO. 05, MAY 2018

the structural trend and have unveiled significant characterized by the sediments of Bengal Fan (Fig. 1), variations in crustal thickness of ~ 7 km along the which are subducted and deformed below the west of NER; ~ 40 km below the Andaman-Nicobar Andaman trench. The east dipping Benioff Zone ridge; ~ 13km below the Sewell rise. Further, within the Andaman arc exhibits depth extents 24 of Subrahmanyam et al, 7 reported on the crustal approximately 200 km. The Andaman trench thickness of NER and suggessted the crustal roots to witnesses thrust motion with a convergence rate 25 of follow the airy isostasy compensation model. These about 1.4 cm/year. The Andaman back-arc spreading results are based on the computation of 2D gravity centre accommodates the remaining plate motion and models prepared along the available seismic profile 22. makes its journey towards the Sumatra fault in the Recent results of Rao et al, 12 have added new south. Such oblique motions between the Indo- structural information utilizing variation of gravity Australian and Eurasian plates result in a sliver plate, gradient along N-S direction, computed from often referred as the Burma micro plate25. Several sediment corrected Bouguer gravity anomaly. north-south trending faults and thrusts are known to All these studies are focused on crustal thickness prevail within the Andaman-Nicobar ridge and in the variations within the Andaman subduction zone using adjacent offshore areas. Among these structural the gravity technique as an exploring tool for features, the most significant are the Jarwa thrust 26 revealing the crustal and lithospheric mantle structure. developed on the main island, However, using a single geophysical technique and (WAF) to the east of Andaman-Nicobar ridge 27 etc. relying on one single data set for exploring the Some of these faults are still active sources of subsurface structure is always an issue of debate. seismicity 24. Moreover, the reliability on the structural image of the subsurface obtained from such analysis is a major questionable issue. Thus, our workflow and analysis provide answers to such debates and allows us to move forward in addressing these issues by performing 2D joint modelling of the gravity and geoid data set for obtaining better constraint structural image of the subsurface. In this joint modelling approach, density model is computed by forward modelling approach, in which gravity and geoid responses of the geometries are compared with observed gravity and geoid data. The results of such modelling approach provide an improved model of the subsurface structure as compared to the earlier work of different researchers in this area. It is a general fact that the gravity anomaly decays at a faster rate with increase in depth as compared to that of the geoid anomaly. In this paper, we have presented a clear picture of the tectonic setting of the study area and the data sets used for modelling the subsurface. Finally, we summarize the 2D modelling technique used for addressing proposed objective, demonstrate the superiority of these techniques and workflow for imaging structural complexities in such a complex Fig.1 — Topography/ map is superimposed by the tectonic regime. Tectonics. NER is showing the Ninetyeast Ridge, Andaman Trench, Andaman Is (Island), Nicobar Is(Island), IB(Invisible Tectonic setting of the Andaman Subduction Zone Bank) , SR (Sewell Rise), AR (Alcock Rise), CB(Central Basin), Owing to its evolution during Oligocene-Miocene EAB (East Andaman Basin), CAB (Central Andaman Basin), times, the sedimentary islands of Andaman and WSR (West Sewell Ridge), NSR (North Sumatra Ridge), Gulf of Martaban, And MR (Mergui Ridge) Red colour east-west line is Nicobar form a part of the fore-arc sedimentary the 2D profile, and white line is the seismic line which is used for 23 complex . The western part of this island system, is upper crustal constraint. YADAV & TIWARI: STRUCTURE OF ANDAMAN SUBDUCTION ZONE 933

The Andaman basin lies between the Burma and Martaban, lying to the NE part of the study area Sumatra exhibiting an average width of 650 km from (Fig.1), indicated by yellow color represents shallow the to the Andaman and Nicobar bathymetry. Islands (Fig. 1). Predominance of oblique subduction below the Andaman arc resulted in strike-slip faulting Methodology parallel to the trench; back-arc extension and basin The workflow adopted for this study is shown in formation in the Andaman Sea26. However, the (Fig. 2). Gravity and geoid data are taken as input for of Andaman back-arc spreading is related to performing this operation. Using these data sets, an the leaky transform tectonics 28 inferred from the initial model is prepared with an aim to match the collision of Ninety East Ridge with that of the model from the observed anomalies. The model is Andaman trench during the middle or late Miocene29. constructed using a priori information obtained from Such ridge trench collision caused the opening of the controlled source seismic, seismic tomography and Andaman . The geological age of this event is other geophysical and geological published studies documented to be of about 13 m.y or Mid-Miocene 30. along the 1000 km long east-west profile up to a Kamesh Raju et al 31 have reported the sea floor depth of 200 km. For modelling, the first layer (sea) is spreading event that got started in the Andaman back- taken from the bathymetry data. Thereafter, two arc basin around 4 m.y ago. Such tectonic events are sediment layers are constructed out of which the the consequence of extrusion tectonics that triggered upper layer (upper sediment) is prepared from extension and rifting along the plane joining the the global sediment data and the lower layer (lower Sagaing and Sumatran fault systems. Several other sediment) is prepared from the available seismic tectonic features like seamounts are part of this profile 22, 31, 33, 17 & 34. Further, the lower sediment is tectonic evolution. Some of them like the Alcock and divided into five geological units of different densities Sewell seamounts were formed at 23 m.y., followed based upon available velocity model of the study area. by the formation of the East basin around 15 m.y, Once, the sediment layer constructions are achieved, further followed by the separation of the Alcock and the oceanic crust is then prepared on the basis of Sewell rises and the formation of the central initial studies made by Krishna et al 35. This oceanic Andaman basin during the last 4m.y. The central crust is divided into two parts, known as the basin is approximately 118 km wide 31 . subducting crustal plate and the overriding crustal plate. The subducting plate is further segregated into Data two different units (upper and lower subducting crust) Topography/bathymetry on the basis of global oceanic crustal thickness The bathymetry map (Fig. 1) of the Andaman studies 36, seismic measurements. Based on the region is presented using bathymetry data set, previous studies 7 and taking into account the increase of the General Bathymetric Chart of the (GEBCO) with values at 1-min grid spacing(http://www.gebco.net/data_and_products/grid ded_bathymetry_data/). The map reveals gentle sloping from NW which is covered by thick Bengal Fan sediments towards SW. The NER is clearly reflected up to 100 N. Further northward, Bengal fan sediments are underlain by the NER up to 170N, which is evident from single and multichannel seismic data 22 & 32.The average bathymetry over the NER is 2.5 km deep within the study area. High bathymetry is observed over the Alcock Rise (AR) and Sewell Rise (SR) seamounts which are are separated by low Fig.2 — Structural cartoon representation of Andaman subduction bathymetry of central Andaman basin (CAB). zone. The presence of Benioff zone is shown in this cartoon. The Shallow bathymetry (Fig. 1) is observed over the earthquake events indicated by red and green dots are taken from Mergui ridge (MR) and Mergui Trace (MT). two different sources (Engdahl et al., 2007 and USGS). Dashed red line is thickness of the lithosphere estimated on the basis of However, bathymetry is deeper in the Mergui Basin age. Bathymetry is also shown with dashed black line. Fault plane (MB) and East Andaman Basin (EAB). The Gulf of mechanisms of the earthquakes are from USGS. 934 INDIAN J. MAR. SCI., VOL. 47, NO. 05, MAY 2018

of density with the rise in pressure in a subducting Results and Discussion regime, the upper subducting crust is divided into Initial modelling of gravity and geoid anomaly three different zones. However, the lower subducting depicts a mismatch between the observed and crust is separated into five different zones. Similarly, computed anomaly. It was observed that the short the overriding plate is divided into four different wavelength of the observed anomalies exhibits zones and considering the presence of intrusive bodies mismatch with that of the computed anomalies. within the crust. After the construction of the crust, However, the computed long wavelength anomalies the lithosphere asthenosphere boundary (LAB) is exhibit a perfect match with the observed anomalies defined based on previous studies 7 & 8. To increase the due to the fact that the short wavelength is controlled robustness of the model and have control over the by the sediment and bathymetry layer and the long initial assumptions, different constraints like sediment wavelength anomaly is controlled by the Moho thickness, depth of LAB (obtained from age of undulations and LAB. The matching was performed lithosphere), and earthquake locations37 are used for with several iterations to obtain an optimal fit the preparation of the initial model. between the observed and computed data. Finally, a After constructing the model (Fig. 3), the gravity good match was obtained after fitting the geoid and geoid anomaly are calculated to match the anomaly with the LAB and gravity anomaly with observed data. To minimize the mismatch, model Moho. The modelling of the subsurface brought out parameters like density and depth are varied and the significant variations in the thickness of the crust process is carried out with several iterations. This from west to east of the subducting and overriding model is then finally taken and validated with the plate (Fig. 4). The depth to the Moho was observed to existing geology of the study region and be about 15 km to the west of NER and 16 km at NER interpretation. reducing to a minimum towards east (Fig. 4).

Fig.4 — Density Structure along the proposed profile (Fig.1): The computed (black line) and observed (red line) geoid /gravity anomalies show a good correlation between each other. The crustal and short wavelength structures are reflected from the gravity anomalies. The lithospheric and long wavelength

structures are reflected from these anomalies. With the help of Fig.3 — Workflow: The workflow adopted for such type of joint analysis of these two anomalies subsurface structures are modelling depicts the joint modelling of gravity and geoid delineated. The LAB is observed at ~ 80km depth at the anomaly. In this modelling technique, an initial model is taken for subducting plate, however, at the overriding plate this thickness computation and is modified iteratively according to the available varies from ~ 80km to 100 km. The Moho depth at the NER is geological and geophysical constraint, to establish a good match about 15 km and at the swell rise it is approximately 18km. between the observed and computed anomalies. Once a good fit is The depth of the slab is about 180 km. (NER = Ninetyeast obtained, the resultant model outputs the final density structure of Ridge, ALAB = above the lithosphere asthenosphere boundary, the subsurface. BLAB = below the lithosphere asthenosphere boundary). YADAV & TIWARI: STRUCTURE OF ANDAMAN SUBDUCTION ZONE 935

Towards the eastern part of the trench, the crust is deformation in the overriding plate is made by subducted beneath the overriding plate and makes its dehydration process in which the down going journey inside the slab up to 180 km. At the subducting plate in asthenosphere experiences overriding plate, the Moho uplifts up to 13 km extremely higher pressures and temperatures thereby towards east and dips down at the Sewell rise up to 17 making the water to get trapped in crust and mantle km and then follows a dipping trend towards the east modifying the density structure and causing (ocean- transition zone). seismicity. Mukhopadhyay and Krishna 38 and Subrahmanyam et al 7 opined that the crust is thicker at the NER on Conclusion the basis of gravity modelling with seismic as a Architecture of a complex Andaman subduction constraint. In this modelling approach, it was assumed zone is obtained in terms of 2D density model by joint that the gravity anomaly does not affect the LAB modelling of gravity and geoid anomalies. The variations. But for obtaining an exact crustal and average crustal thickness of the subducting plate is lithospehric structure, it is very much essential to less compared to the thickness under NER, seamount consider these variations. Subrahmanyam et al. 7 have and shelf in the east in overriding plate. The average modelled the thickness of NER using the Airy depth of LAB is found to be about 82 km where as the isostasy model along with the seismic section of 22. In depth varies from 75 km to 100 km for the overriding this approach, only one data set has been used to plate. The depth of subducting slab is about 180 km. obtain the thickness of NER. In addition, the gravity contributions from lithospheric depths are not Acknowledgments accounted. The modelling approach in the present This work has been carried out within the study, addresses these issues, where derived density framework of CSIR-NGRI project Geodynamics of structure is based on the modelling of multiple data North East and Andaman Subduction zone set i.e gravity and geoid. This approach would (GENIAS). Earthquake locations are downloaded minimum error for obtaining an optimal output from USGS portal. All Figures were created with considering that two data sets have different sensitise GMT software and modelling part was with IGMAS of depths. The present way of computation of LAB software. This work is a part of PhD thesis of one of thickness is mainly based on the use of constraint the authors (R. Yadav). derived from chronological data set of the Indian subducting plate. This constraint helps us to claim for References a more realistic output from the joint modelling 1 Grevemeyer, I. and Tiwari, V. M., Overriding plate controls approach. Similarly, for modelling the overriding spatial distribution of megathrust earthquakes in the Sunda– plate, sediment thickness obtained from the earlier Andaman subduction zone; Planet. Sci. Lett., 17, 31, 33 & 34 251(2006):199–208. studies have been considered for such 2 Casten, U. and Snopek, K., Gravity modelling of the Hellenic analysis. In this approach, the gravity anomaly is subduction zone—a regional study, Tectonophysics, matched by modifying the Moho configuration while 417(2006):183–200. the geoid anomaly is matched by varying the LAB 3 Zeumann, S., 3D Finite Element Modelling of the Central thickness. This process makes our modelling Andean subduction zone with realistic geometry, PhD thesis (2013). technique to be more efficient to deliver a stout 4 Ortiz, M. and Bilham, R., Source area and rupture parameters subsurface structure. The delineated structure (Fig 4) of the 31 December 1881 Mw=7.9 earthquake refines the deep and extent of subducting plate and estimated from recorded in the . characterizes the seismicity in the subducting and Journal of Geophysical Research, 108(2003):2215–2230. overriding plate. Most of the thrust faulting can be 5 Ammon, C.J., Ji, C., Thio, H.K., Robinson, D., Ni, S., Hjorleifsdottir, V., Kanamori, H., Lay, H., Das, located on the top of the subducting slab and up to the S., Helmberger, D., Ichinose, G., Polet J., and Wald, depth, where subducting plate meets the overriding D., Rupture process of the 2004 Sumatra–Andaman plate in the mantle. This observation is in accordance Earthquake. Science, 308(2005): 1133–1139. that intraplate earthquakes are caused by the internal 6 Ishii, M., Shearer, P.M., Houston, H., and Vidale, J.E., deformation of subducting and overriding plate. Extent, duration and speed of the 2004 Sumatra–Andaman earthquake imaged by Hi-Net array. Nature 435(2005): Model also shows that the NER internally deformed 933–936. the subducting plate. Density structure and seismicity 7 Subrahmanyam, C., Gireesh, R., Shyamchand, K. A., Raju, of the overriding plate indicate that internal K., and Gopala Rao, D., Geophysical characteristics of the 936 INDIAN J. MAR. SCI., VOL. 47, NO. 05, MAY 2018

ninety east ridge–Andaman /trench convergent . Geological Society of America Bulletin, 80(1969): zone. Earth Planet. Sci. Lett, 266(1/2),(2008):29–45. 1203–1230. 8 Radhakrishna, M., Lasitha, S., and Mukhopadhyay, M., 24 Mukhopadadhyay, M., Seismotectonics of subduction and Seismicity, gravity anomalies and lithospheric structure of Back-arc rifting under the Andaman sea. Tectonophysics, the Andaman arc, NE , Tectonophysics, 108(3-4)(1984):229-239,doi10.1016/0040-1951(84)90237-3 460(2008): 248–262. 25 Lay, T., Kanamori, H., Ammon, C.J., Nettles, M., Ward, 9 Kennett B.L.N., and Cummins P.R., The relationship of the S.N., Aster, R.C., Beck, S.L., Bilek, S.L., Brudzinski, M.R., seismic source and subduction zone structure for the 2004 Bulter, R., DeShon, H.R., Ekström, G., Satake, K., Sipkin, December 26 Sumatra–Andaman earthquake, Earth and S., The great Sumatra–Andaman earthquake of 2004. Planetary Science Letters 239(2005):1–8. Science, 308(2005): 1127–1333. 10 Pesicek, J. D., Thurber, C. H., Widiyantoro, S., Engdahl, E. 26 Roy, T.K., Geology and hydrocarbon prospects of Andaman– R., and DeShon, H. R., Complex slab subduction beneath Nicobar basin. In: Bhandari, L.L. (Ed.), Petroliferous Basins of northern Sumatra, Geophys. Res. Lett., 35(2008) L20303. India. Petroleum Asia Journal, 1(1983): 37–50. 11 Pesicek, J.D., Thurber, C, H., Zhang, H., DeShon, H. R., 27 Curray, J.R., Moore, D.G., Lawver, L.A., Emmel, F.J., Raitt, Engdahl, E. R., and Widiyantoro, S., Teleseismic R.W., Henry, M. and Kieckhefer R., Tectonics of the double‐difference relocation of earthquakes along the Andaman Sea and Burma. Geological and Geophysical Sumatra Andaman subduction zone using a 3 D model, Investigations of Continental Margins, 29(1979): 189–198, Journal of Geophysical Research, 115(2010), B10303, eds Watkins, J.S., Montadert, L. and Dickenson P., doi:10.1029/2010JB007443. Am. Assoc. Petrol. Geol. Mem. 12 Rao, N. P., Rao, C. N., Hazarika, P., Tiwari, V. M., Kumar, 28 Uyeda, S., and Kanamori, H., Back-arc opening and the M. R., and Singh, A., Structure and tectonics of the Andaman mode of subduction. Journal of Geophysical Research, subduction zone from modelling of seismological and gravity 84(1979):1049–61. data, New Frontiers in Tectonic Research, (2011):249–268. 29 Eguchi, T., Uyeda, and S., Maki, T., Seismotectonics and 13 Gahalaut, V. K., Nagarajan, B., Catherine, J. K., and Kumar, tectonic history of the Andaman Sea. Tectonophysics, S., Constraints on 2004 Sumatra–Andaman earthquake 57(1979):35–51. rupture from GPS measurements in Andaman–Nicobar 30 Curray, J.R., Emmel, F.J., Moore, D.G.,and Raitt, R.W., Islands, Earth Planet. Sci. Lett., 242(3) (2006):365–374. Structure, tectonics and geological history of the north eastern 14 Chlieh, M., Avouac, J. P., Sieh, K., Natawidjaja, D. H., and Indian Ocean. Nairn, A.E.M., Stehli, F.G. (Eds.), The Ocean John Galetzka, Heterogeneous coupling of the Sumatran Basins and Margins. The Indian Ocean, 6(1982): 399–450. megathrust constrained by geodetic and paleogeodetic 31 Kamesh Raju, K. A., Ramprasad, T., Romps., Rao, measurements. J. Geophys. Res., 113(2008) B05305, doi: Ramalingeswara, B., and Varghese, J., New insight into the 10.1029/2007JB004981. tectonic evoluation of the Andaman basin northeast Indian 15 Wiseman, K., Bürgmann, R., Freed, M. A., and Banerjee, P., Ocean. Earth and planetary Science Letters,221(2004): Viscoelastic relaxation in a heterogeous Earth fallowing the 145-162,doi:10.1016/S0012-821X(04)00075-5. 2004 Sumatra-Andaman earthquake, Earth and Planetary 32 Maurin, T., and Rangin. C., Structure and kinematics of the Science Letters, 431(2015):308-3017, doi:10.1016/j.epsl. Indo-Burmese Wedge: Recent and fast growth of the outer 2015.09.024. wedge. Tectonics, 28(2) (2009) 10.1029/2008TC002276. 16 Moeremans. R., Singh, C., Satish, Mukti M., McArdle, and 33 Racey, A., and Ridd, M. F., Petroleum Geology of . Johansen, K.,Seismic image of structural variations along the Geological Society, London, Memoirs, 45(2015): deformation front of the Andaman-Sumatra subduction zone: 109–115,doi.org/10.1144/M45.10 Implication for rupture propagation and tsunamigenisis. Earth and Planetary Science Letters, 386(2014): 34 Jourdain A., Singh C. S., Escartin J., Klinger Y., Kamesh 75-85, doi.org/10.1016/j.epsl.2013.11.003. Raju K.A., and McArdle J., Crustal accretion at a sedimented 17 Moeremans, R., and Singh, C., Satish, Seismic evidence of spreading centre in the Andaman Sea. The Geological society continental margin influence on the Ninety East ridge of America,44(5) (2016): 351-354.doi 10.1130/G37537.1 in the Bay of Bengal. Geophys Res.Lett,41(2014): 35 Krishna, K. S., Neprochnov, Y. P., Gopala Rao, D., and 7143-7150,doi:10.1002/2014G061598. Grinko, B. N., Crustal structure and tectonics of the 18 Fitch, T. J., Plate convergence, transcurrent faults, and initial Ninetyeast Ridge from seismic and gravity studies. deformation adjacent to southeast Asia and the western Tectonics, 20(2001): 416–433, doi:10.1029/2001TC900004. Pacific. J. Geophys. Res., 77(1972):4432–4460. 36 White, R.S., McKenzie., and O'Nions, Keith., Oceanic 19 Curray, J.R., Tectonics and history of the Andaman Sea Crustal Thickness From Seismic Measurements and Rare region. Journal of Asian Earth Sciences 25(2005): 187–232. Earth Element Inversions. Journal of Geophysical 20 Sieh, K., -Andaman earthquake: What happened and Research,97(13) (1992) :19,683-19715. what’s next? Nature, 434(2005): 573-574. 37 Engdahl, E. R., Villasenor, A., Deshon, R., and Thurber, 21 Weeks, L.A., Harbison, R.A., Peter, G., Island arc system C. F., Tele-seismic relocation and assessment of seismicity in Andaman Sea. American Association of Petroleum (1918–2005) in the region of 2004 Mw9.0 Sumatra- Geologists Bulletin 51(1967);1803–1815. Andaman and 2005 Mw8.6 Nias Island great earthquakes. 22 Gopala Rao, D., Krishna, K. S., and Sar, D., Crustal evolution Bull. Seismol. Soc. Am. 97(1A) (2007):43–61. and sedimentation history of the Bay of Bengal since the 38 Mukhopadhyay, M., Krishna, M.R.,Gravity anomalies and Cretaceous. J. Geophys. Res. 102(1997): 17,747–17,768. deep structure of the Ninety East Ridge north of the equator, 23 Rodolfo, K.S., Bathymetry and marine geology of the eastern Indian Ocean-a hot spot trace model. Marine Andaman basin, and tectonic implications for Southeast Geophysical Researches. 17,(1995): 201–216.

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