Drivers, Modulators and Hazards of Collisional Orogens

传统的板块构造理论解释了山带的形成是由于地壳变形和仅在板块边缘加厚，但理论和观测研究表明，变形也发生在板块内部。因此，板内和板缘变形之间的联系以及相关的反馈机制仍不清楚。为了解决这个问题，提出的研究考虑了以下几个假设。a)构造板块的分裂导致作用于板块边缘的力的变化，从而导致板块构造的调整（造山带的变宽或变窄）。b)汇聚边缘上升的山带所带来的阻力施加的力导致有关构造板块的变形和最终破坏。c)大地震在板块内部释放的应力可能缓慢地传播到板块边缘，并在地震发生数年后影响当地的地震活动性。这些假设将通过在数百年到数百万年的时间尺度上检查碰撞造山带正面构造楔的变形，并通过研究板块内板内变形引起的应力来验证。在活动造山带中可以直接观测到上地壳的变形，并建立了控制构造楔变形和形态的参数。根据板块内地震活动的记录，印度洋岩石圈在喜马拉雅造山带内收缩的同时也在发生缩短（褶皱）和破裂。分裂过程影响了转移到收敛板块边界的力的大小，这表示为喜马拉雅。因此，我们将集中讨论喜马拉雅造山带现今的楔块。这个复杂的动态系统允许对项目假设进行定性和定量测试。预计该研究项目的科学贡献将是发展一种理论，解释板块边缘和板块内部变形之间的应力分配。这将允许确定机制和时间尺度的传播应力从一个早期的分裂区域到一个收敛的边界地带，利用印度板块为例。喜马拉雅楔体的应力分布和大小不仅仅是一个学术问题，因为了解喜马拉雅的变形对监测和预测地震危险很重要。此外，在更大的范围内，这种方法将允许调查俯冲大地震与板块内及其边缘的应力载荷之间的潜在动态联系。因此，预计该计划将通过改进对此类地震活动的潜在原因的理解来提高地质灾害预测的可靠性。该计划提出的假设和在实施过程中出现的问题将通过现场，实验室和数值实验研究的结合进行调查。特别是，这些问题将通过研究生领导的多学科项目来解决，涉及以下方面：海底地球物理和地震数据的汇编、综合和解释；沿板缘应力的计算；造山楔演化的数值模拟板块-板块边缘相互作用的地球动力学模拟以及详细的实地研究和微观结构分析。在整个过程中，我们将寻求开发新的方法来直接确定断层活动的日期；这将是连接近地和远地构造事件的关键步骤，对一般的构造重建具有根本的重要性。

Conventional plate tectonic theory explains the formation of mountain belts by crustal deformation and thickening only at the plate margins, yet theoretical and observational studies have indicated that deformation also occurs in plate interiors. Accordingly, the connections between intraplate and plate margin deformations and the associated feedback mechanisms remain unclear. To address this, the proposed study considers several hypotheses, as follows. a) Break-up of a tectonic plate leads to changes of the forces acting at the plate margins and thus to adjustments in plate tectonics (widening or narrowing of the orogenic wedge). b) The resistance imparted by a rising mountain belt at a convergent margin exerts forces that lead to the deformation and eventual failure of the tectonic plate in question. c) Stresses released by mega-earthquakes in the plate interior may propagate slowly to the plate margins and influence local seismicity years after earthquake occurrence. These hypotheses will be tested by examining deformation within the frontal tectonic wedge of a collisional orogen at timescales of centuries to millions of years and by studying the stresses induced by intraplate deformation within the undergoing plate. Upper crustal deformation can be observed directly in active orogens, and the parameters controlling the deformation and morphology of tectonic wedges have been well established. According to records of intraplate seismicity, the Indian Ocean lithosphere is both shortening (folding) and breaking up coeval with contraction within the Himalayan orogen. The break-up process influences the amount of force transferred to the convergent plate boundary, which is expressed as the Himalaya. Therefore, we will concentrate on the present-day wedge of the Himalayan orogen. This complex dynamic system allows both qualitative and quantitative testing of the project hypotheses. The projected scientific contribution of the research program will be the development of a theory explaining the partitioning of stresses between deformation at plate margins and plate interiors. This will allow determination of the mechanisms and timescales of propagation of stress from an incipient breakup area to a convergent boundary zone, utilising the Indian plate as an example. The distribution and magnitude of stresses in the Himalayan wedge is not merely an academic question, because understanding of the deformation across the Himalaya is important for monitoring and prediction of seismic hazard. Furthermore, at a larger scale, this approach will allow investigation of the potential dynamic links between subduction mega-earthquakes and stress loading within the plate and along its margins. Therefore, it is expected that this program will increase the reliability of geohazard predictions through improvements in the understanding of the underlying causes of such seismicity. The hypotheses presented by this program and the questions arising during its implementation will be investigated through a combination of field, laboratory and numerical experimental studies. In particular, the questions will be tackled through multidisciplinary projects led by graduate students and involving the following: compilation, synthesis and interpretation of ocean floor geophysical and seismological data; calculation of the stresses along plate margins; numerical modelling of the evolution of orogenic wedges; geodynamic modelling of plate–plate margin interaction; and detailed field studies and microstructural analyses. Throughout this process, we shall seek to develop novel ways to date fault activity directly; this will be a crucial step in linking near and remote tectonic events and will be of fundamental importance for tectonic reconstructions in general.