Anatomy of a Subduction Zone from Ocean Mantle to Crust: Seismicity and Seismic Structure in Northern Chile

点击翻译按钮获取中文摘要

The principal aim of this project is the investigation of subduction-related seismic structures, including the fine-scale structure of the megathrust shear zone and underlying oceanic plate, and of earthquake sources in the northern Chile forearc employing a suite of innovative methods of seismicity processing, imaging and interpretation. We will exploit the specific situation, where an extraordinarily high rate of seismicity has been recorded for almost ten years on a large number of seismic stations, including the permanent IPOC network and several temporary networks. Northern Chile, in particular the recently installed MEJIPE network on the Mejillones peninsula, also offers a rare chance to monitor at least a part of the seismogenic zone onshore. We therefore expect to image the structural and seismic architecture of this subduction zone at highest possible resolution.In order to image seismic structures in detail, we will apply a recently developed micro seismic migration-based approach, complemented by the modelling of near-source reflections and conversions and the estimation of local variations of the Poisson ratio from precise differential arrival times. We will also characterize the earthquake sources themselves using moment tensor inversion in the time domain and the analysis of seismogram spectra to derive other source parameters like stress drop and radiation efficiency.The synthesis of the results will allow to test, if the major seismic signatures in the subduction system are fluid controlled. Processes such as dewatering of hydrated minerals, trapping and pressurization of fluids and fluid migration should leave a strong imprint on the elastic parameters and the spatio-temporal characteristics of seismicity. This imprint will be detectable by our study, e.g. as zones of ultra low velocity and/or anomalous high local Vp/Vs ratios.An important component of the project will be the detailed study of seismicity and related physical processes in the deepest, upper ocean mantle layer of the newly confirmed shallow triple seismic zone in northern Chile. Eventually this will contribute to advance the understanding of intermediate depth earthquakes in general.