Linkage of deep lithospheric structures to intraplate earthquakes: A perspective from multi-source and multi-scale geophysical data in the South China Block

Abstract

The relationship between intraplate earthquakes and intraplate deformation is one of the great conundrums faced by plate tectonics theory. In particular, large earthquakes are more common in Eurasia than in other continents around the world. Formed by the Neoproterozoic collision of the Cathaysia Block and the Yangtze Craton along the Jiangnan Orogenic Belt, the South China Block is well known for its relative stability in the Cenozoic era. However, numerous intraplate earthquakes have occurred in the Yangtze Craton and their mechanism is not well known. Incomplete understanding of the deep geological structure and deep-shallow coupling mechanism has led to two hypotheses about the nature and origin of intraplate earthquakes in the area: the far-field effects of plate subduction and the internal deformation of intraplate lithosphere. In this paper we attempt to provide a new perspective to the intraplate earthquake mechanism in the South China Block. In doing so, we have collected and reviewed multi-source and multi-scale high-precision geophysical data to improve the interpretation of the South China Block at depths from 1000 km to 1 km. The data interpretations help clarify the coupling relationship between the lithospheric structures and intraplate earthquakes in the South China Block. This paper emphasizes the strong structural heterogeneity in the South China Block. In plan view, the block is a mosaic structure formed by the assembly of various continental micro-blocks along several weak zones since the Neoproterozoic. In cross section, the structures of different units are segmented by detachment faults. For our analysis, we have used a three-layer model to describe the coupling of the asthenosphere-lithosphere, lithospheric mantle-crust and within the crust in the South China Block. The three cascade effects are coupled to form an intraplate earthquake triggering mechanism in the Yangtze Craton. The subduction effects of the Pacific Plate and the blocking by the Yangtze Craton are considered to cause a large-scale stress concentration in the Huaying Mountain fold-and-thrust belt; combined with three sets of detachment layers as internal factors, this stress results in numerous small-magnitude intraplate earthquakes occurring in the stable craton. This paper suggests that the deep structures can control the shallow tectonic processes and the plate tectonic responses and that the lithospheric strength can affect the triggering of intraplate earthquakes.