Seismicity and lithospheric structure in active subduction, relic subduction and intracontinental settings

Abstract

Earthquakes occur in a wide range of depths and different tectonic settings. A comprehensive understanding of them can be difficult, this needs acknowledgement from various perspectives, e.g. source properties of earthquakes, such as locations, focal mechanisms, rupture processes; thermal structure, and morphology of seismogenic lithosphere(s); laboratory rock deformation experiments. In this dissertation, three seismogenic regions within distinct tectonic settings are selected, this includes the relic subduction zone in the westernmost Mediterranean, the active northwestern South America subduction zone, and the Reelfoot Rift within the continental interior. In the westernmost Mediterranean, we provide a high-resolution seismic pattern at depths of ~100km using grid-searching and double-difference techniques. A systematic analysis of the clustering seismic pattern indicates this seismicity is associated with active necking and breakoff of the Alboran slab, which is progressing from north to south. For the northwestern South America subduction zone, we provide a well resolved teleseismic P-wave tomography model and investigate the configuration of this subduction zone utilizing teleseismic tomography. Results reveal NE-SW trending Caribbean plate and Nazca plate, with the subduction of Nazca plate overlapping with CAR between 5°~8°N. This leads to a reinterpretation of the nature of some notable features in the region, namely the Caldas tear and the Bucaramanga nest. In the Reelfoot Rift region, we analyse P-wave attenuation from records of teleseismic events, and provide insights into possible rheology properties of the upper mantle beneath the Reelfoot Rift. Results show relatively low attenuation within the Reelfoot Rift region, indicating the Reelfoot Rift might not be a weak zone. Meanwhile, an association between the attenuation and occurrence of seismicity is revealed, this conveys that the lateral variation of attenuation along the strike of the Reelfoot Rift region might be responsible for the NMSZ. Exploration of seismic patterns and lithosphere structures across these three different regions contributes to our understanding of the occurrence of earthquakes under different tectonic settings. P-wave attenuation from records of teleseismic events, and provide insights into possible rheology properties of the upper mantle beneath the Reelfoot Rift. Results show relatively low attenuation within the Reelfoot Rift region, indicating the Reelfoot Rift might not be a weak zone. Meanwhile, an association between the attenuation and occurrence of seismicity is revealed, this conveys that the lateral variation of attenuation along the strike of the Reelfoot Rift region might be responsible for the NMSZ. Exploration of seismic patterns and lithosphere structures across these three different regions contributes to our understanding of the occurrence of earthquakes under different tectonic settings.