Instantaneous deformation and kinematics of the India-Australia Plate

Abstract

S U M M A R YActive intraplate deformation of the India-Australia Plate is now being captured by far-field global positioning system (GPS) measurements as well as measurements on a few islands located within the deforming zone itself. In this paper, we combine global and regional geodetic solutions with focal mechanisms of earthquakes to derive the present-day strain field of the India-Australia Plate. We first compile an updated catalogue of 131 Indian intraplate earthquakes (M > 5) spanning the period between the two Asian mega earthquakes of Assam 1897 and Sumatra 2004. Using Haines and Holt's numerical approach applied to a fully deformable India-Australia Plate, we show that the use of GPS data only or earthquakes data only has severe drawbacks, related, respectively, to the small number of stations and the incompleteness of the earthquakes catalogue. The combined solution avoids underestimation of the strain inherent to the Kostrov summation of seismic moments and provides details that cannot be reached by pure GPS modelling. We further explore the role of heterogeneity of the India-Australia Plate and find that the best model, in terms of geodetic vectors fit, relative distribution of strain, style and direction of principal strain from earthquakes, is obtained using the surface heat-flow as a proxy for rheological weakness of the oceanic lithosphere. The present-day deformation is distributed around the Afanasy Nikitin Chain in the Central Indian Basin (CIB)-where it is almost pure shortening-and within the Wharton Basin (WB) off Sumatra-where it is almost pure lateral strike-slip. The northern portion of NinetyEast ridge (NyR) appears as a major discontinuity for both strain and velocity. The new velocity field gives an India/Australia rotation pole located at 11.3 • S, 72.8 • E (−0.301 • Myr −1 ) overlapping with previous solutions, with continental India moving eastward at rates ranging from 13 mm yr −1 (southern India) to 26 mm yr −1 (northern India) with respect to Australia. Taking into account the intraplate velocity field in the vicinity of the Sumatra trench, we obtain a convergence rate of 46 mm yr −1 towards N18 • E at the epicentre of the 2004 Aceh megaearthquake. The predicted instantaneous shortening in the CIB and WB and extension near Chagos-Laccadive are in good agreement with the finite deformation measured from plate reconstructions and seismic profiles, suggesting a continuum of deformation since the onset of intraplate deformation around 7.5-8 Ma. Since no significant change in India convergence is detected at that time, we suggest that the intraplate deformation started with the trenchward acceleration of Australia detaching from India along a wide left-lateral oceanic shear band activating the NyR line of weakness as well as north-south fracture zones east of it. The predicted total amount of left lateral finite strain along these faults is in the range 110-140 km.

Do ridge–ridge–fault triple junctions exist on Earth? Evidence from the Aden–Owen–Carlsberg junction in the NW Indian Ocean

“…Since this kind of triple junction is often unstable, it was probably abandoned when a change of the Arabia-India kinematics caused the activation of the newly imaged fault together with the formation of the Beautemps-Beaupré Basin. The latest kinematic reorganization in the Indian Ocean occurred ~8 Ma ago and corresponds to the onset of intraplate deformation in the India-Australia plate dated at 7.5-8 Ma by ODP drillings (Cochran, 1990;Chamot-Rooke et al, 1993;Delescluse and Chamot-Rooke, 2007), which nearly coincides with kinematic change along the Carlsberg Ridge between 11 and 9 Ma (Merkouriev and DeMets, 2006).…”

Seismic evidence of a two-layer lithospheric deformation in the Indian Ocean

“…The deformation seems to have initiated B15 Ma ago 6 and was enhanced around 8 Ma ago when the Tibetan plateau attained its maximum elevation 7 . The weak rheology of the Ninety East Ridge (NER) acts as a boundary for strain orientation and deformation style 5,8,9 , causing different types of deformation in the Central Indian Basin (CIB) and the Wharton Basin (WB). To the west of the NER in the CIB, deformation is taking place along E-W trending high-angle thrust faults and associated folds [1][2][3] due to the N-S compression resulting from the continental collision of India with Eurasia.…”

The 2 March 2016 Wharton Basin Mw 7.8 earthquake: High stress drop north‐south strike‐slip rupture in the diffuse oceanic deformation zone between the Indian and Australian Plates

“…Global plate motion models indicate that internal deformation within the diffuse boundary between the Indian and Australian plates accommodates~11 mm/yr of relative movement [e.g., Wiens et al, 1985;Gordon et al, 1990;Royer et al, 1997;Delescluse and Chamot-Rooke, 2007;Demets et al, 2010]. The broad region has hosted numerous major and great earthquakes.…”