ALBERT

Description: The evolution of hyper-slow oceanic rifts, like the Terceira Rift (TR) in the Azores, is still poorly understood. Here we examine the distribution of strain and magmatism in the portion of the TR making up the Nubia-Eurasia plate boundary. We use S. Miguel Island because it stretches most of the TR width, which allows to investigate the TR's architecture and shedding light on TR's age and mode of deformation. From topography and structural analysis, and new measurements of 380 faults and dikes, we show that: (1) S. Miguel has two main structural directions, N150 and N110, mostly concentrated in the eastern part of the island as an onshore continuation of the faults observed offshore in the NE (N110 faults) and SW (N140) TR walls; (2) A new N50-N80 fault system is identified in S. Miguel; (3) Fault and dike geometries indicate that eastern S. Miguel comprises the TR's northern boundary, and the lack of major faults in central and western S. Miguel indicates that rifting is mostly concentrated at master faults bounding the TR. Based on TR's geometry, structural observations and plate kinematics, we estimate that the TR initiated between 1.4 and 2.7 Ma ago, and that there is no appreciable sea-floor spreading associated with rifting. Based on plate kinematics, on the new structural data, and on S. Miguel's structural and volcanic trends, we propose that the eastern two thirds of S. Miguel lie along a main TR-related transform fault striking N70-80, which connects two widely separated N130-150 TR-trending segments.

Description: Tsunami modeling commonly accepts the shallow-water system as governing equations where the major difficulty is the correct treatment of the non-conservative term due to bathymetry variations. The finite volume method for solving the shallow-water equations with such source terms has received great attention in the two last decades. The built-in conservation property, the capacity to correctly treat discontinuities, and the ability to handle complex bathymetry configurations preserving some steady-state configurations (well-balanced scheme) make the method very efficient. Nevertheless, it is still a challenge to build an efficient numerical scheme, with very few numerical artifacts (e.g. small numerical diffusion, correct propagation of the discontinuities, accuracy and robustness), to be used in an operational environment, and that is able to better capture the dynamics of the wet-dry interface and the physical phenomena that occur in the inundation area. In the first part of this paper, we present a new second-order finite volume code. The code is developed for the shallow-water equations with a non-conservative term based on the hydrostatic reconstruction technology to achieve a well-balanced scheme and an adequate dry/wet interface treatment. A detailed presentation of the numerical method is given. In the second part of the paper, we highlight the advantages of the new numerical technique. We benchmark the numerical code against analytical, experimental and field results to assess the robustness and the accuracy of the numerical code. Finally, we use the 28 February 1969 North East Atlantic tsunami to check the performance of the code with real data. This article is protected by copyright. All rights reserved.