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Subduction systems globally terminate, allowing plate-motion to be transferred from the oceanic megathrust onto continental and/or oceanic transform faults. The mechanism of this kinematic transition over earthquake timescales is, however, poorly understood due to a lack of relevant data. Here, we study the 2016 Mw 7.8 Kaikōura Earthquake in New Zealand, the first large instrumentally-recorded earthquake across a subduction-termination, to investigate this transfer mechanism in detail. We find that the Kaikōura Earthquake, unlike standard subduction earthquakes globally, involved a predominance (∼80%) of coseismic-slip on upper-plate faults and minor triggered-slip on the underlying oceanic subduction-thrust. In the months following the earthquake, the subduction-thrust accommodated most of the earthquake's afterslip down-dip of its co-seismic rupture zone. This top-down strain-release mechanism is in accord with local geological, geodetic and historical seismicity data which suggest that the bulk of plate-convergence (>75%) is accommodated in the upper-plate. We suggest, therefore, that this alternative strain-release mechanism, which is distinct from standard plate-boundary earthquakes, is characteristic of subduction-terminations and results in the majority of seismic/tsunami hazard being on steep near-surface faults.

The Dead Sea transform system (DST) is the boundary between the Arabian and African plates, where left-lateral transform motion has largely accommodated the opening of the Red Sea basin during the last 15-20 My. One of the key questions related to this plate boundary is whether the DST crosses the crust and mantle lithosphere, and how the rheologically different units composing the lithosphere interact during strong deformation? Another major question is how important is the rifting (transform-perpendicular extension) deformation component at the DST? We address these questions using the internally consistent finite element thermo-mechanical modelling of the lithospheric deformation constrained by high-resolution geophysical observations and especially by the recent geophysical data of the DESERT Project. From our modelling, we conclude that the DST lithospheric structure is controlled by the plate-scale transform displacement within a relatively cold and strong lithosphere. In such a lithosphere, shear strain is localized in a narrow (20-40 km wide) vertical decoupling zone (VDZ), which crosses the entire lithosphere and even continues into the asthenosphere. In the upper crust the deformation localizes at one or two major faults located at the top of this zone. The location of the VDZ is controlled by the temperature of the uppermost mantle prior to the transform motion. Most of the lithospheric structures imaged along the DESERT seismic line is explained by the 105 km transform motion combined with less than 4 km transform-perpendicular extension. Uplift of the Arabian Shield adjacent to the DST can be explained by young ($

We employ 2-D thermo-mechanical modelling to study possible mechanisms for generating large-scale crustal magmas in the Altiplano^Puna region of the Central Andes. The peak of ignimbrite activity in the late Miocene and Pliocene is associated in space and time with tectonic shortening and plateau uplift. A seismic low-velocity zone and other geophysical observations indicate that partial melting in the mid-crust is still present under the ignimbrite province today. We show that neither radiogenic heat production in a thickening crust, nor shear heating due to tectonic shortening, nor heat brought by intrusions of arc magmas into the mid-crust can heat the mid-crust to the degree and within the time frame suggested by the geologic, petrologic and geophysical observations. A viable mechanism to achieve high temperatures within the time constraints is convective heat and mass transfer by partially molten lower crust which itself was heated by enhanced mantle heat flow, possibly associated with delamination of the mantle lithosphere during tectonic shortening and intensified magmatic arc activity. The thermo-mechanical models explain the mid-crustal low-velocity zone and the high and strongly variable surface heat flow observed in the Altiplano. Convection by bulk flow of the crust appears when the middle and lower crust are mechanically weak (quartz-dominated rheology), the basal heat flow from the mantle is high (s 60 mW/m 2 ) and tectonic shortening is active. We argue that these conditions are satisfied in the Central Andes orogen. 6 2002 Elsevier Science B.V. All rights reserved.

In this study, we use the technique of petrophysical modeling [Sobolev, S.V., Babeyko, A.Yu., 1994. Modelling of mineralogical composition, density and elastic wave velocities in the anhydrous rocks. Surv. Geophys. 15, 515–544.] to construct mineralogical, density, and velocity models of the deep Martian crust. Calculations are performed in two steps. First, given bulk chemical composition and PT conditions, the equilibrium mineralogical composition is calculated by numerical thermodynamic simulation. Effect of kinetics on mineral transformations was modeled by accepting a “freezing” temperature. Second, density and velocities are calculated from the mineralogy. In computations, bulk chemical composition of the crust was accepted to be the average of four basaltic SNC meteorites (Shergotty, Zagami, BETA79001, lithologies A and B). Four various temperature models of the crust were considered: with the temperature gradient of 21, 13, 6, and 2 K/km. The mineral composition of the consolidated crust varies with depth due to a gabbro–eclogite type transition; density and velocities increase correspondingly. The generally accepted data on the structure of the outer layer of the Moon are taken into account in modeling the outer (∼11 km), porous layer of the planet. The maximum thickness of the crust was determined from the condition that the density at the crust–mantle boundary equals 3.45–3.5 g/cm 3 . The computations showed that, in the case of a cold marsotherm, the crustal density at a depth of 60 km ranges from 3.3 to 3.5 g/cm 3 , and at a depth of 120 km, it is ∼3.5 g/cm 3 . In the case of a hot marsotherm, the density 3.45 g/cm 3 is reached at a depth of 150 km; 3.5 g/cm 3 , at a depth of ∼170 km. The consolidated crust may be divided into several zones according to the distribution of density and its seismic-wave velocities. Regions with a high heat flow have a low velocity (and density) zone in the 10–120-km depth range, underlain by a zone of steep gradients of these parameters. For small temperature gradients, computations yield a qualitatively different picture. In the ∼10 to (30–65)-km depth range, the density and velocities are approximately constant. From 30–65 to 80–120 km follows a zone of steep gradients. Below velocities and density are nearly constant or slightly decrease down to the crust–mantle boundary. Since density in the lowermost crust exceeds values of ∼3.5 g/cm 3 , the lower crust is likely to be gravitationally unstable over geologic time intervals.