Drivers, Modulators and Hazards of Collisional Orogens

传统的板块构造理论仅在板块边缘通过地壳变形和增厚来解释山带的形成，但理论和观测研究表明，变形也发生在板块内部。因此，板内变形和板边缘变形之间的联系以及相关的反馈机制仍然不清楚。为了解决这一问题，拟议的研究考虑了几个假设，如下所示。A)构造板块的解体导致板块边缘作用力的变化，从而导致板块构造的调整(造山楔的加宽或变窄)。B)位于会聚边缘的隆起的山带所产生的阻力，所施加的力量导致了有关构造板块的变形和最终的破坏。C)大地震在板块内部释放的应力可能在地震发生数年后缓慢传播到板块边缘，并影响当地的地震活动。这些假说将通过研究碰撞造山带前缘构造楔形体内数百年至数百万年的时间尺度内的变形，以及通过研究板块内变形引起的应力来检验。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体变形和形态的参数。根据板内地震活动记录，印度洋岩石圈在喜马拉雅造山带内既有缩短(褶皱)又有破裂收缩的现象。分裂过程影响传递到收敛板块边界的力的大小，这以喜马拉雅山脉表示。因此，我们将集中讨论现今喜马拉雅造山带的楔形构造。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。该研究计划预计的科学贡献将是发展一种理论，解释板块边缘和板块内部的变形之间的应力分配。这将以印度板块为例，确定应力从初期解体区域向收敛边界区域传播的机制和时间尺度。喜马拉雅楔形体中的应力分布和大小不仅仅是一个学术问题，因为了解喜马拉雅山脉的变形对于监测和预测地震危险很重要。此外，在更大的尺度上，这种方法将能够调查俯冲大地震与板块内和板块边缘的应力载荷之间的潜在动态联系。因此，预计这一计划将通过改进对地震活动根本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相结合的方式进行调查。特别是，这些问题将通过研究生领导的多学科项目加以解决，这些项目涉及以下内容：海底地球物理和地震学数据的汇编、综合和解释；板块边缘应力的计算；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测定断层活动的时间；这将是将近距离和远距离构造事件联系起来的关键一步，对于总体上的构造重建将是至关重要的。

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.