Abstract
In this paper, we focus on why intraplate seismic initiation and migration occurs, which has widely been considered to be caused by static stress triggering caused by earthquakes, as well as post-seismic slips. To illustrate the mechanism underlying large earthquakes, in particular the migration caused by two key episodes that occurred after 1500 in the Bohai-Zhangjiakou Fault Zone (BZFZ) of North China, we developed a high-resolution three-dimensional viscoelastic finite element model that includes the active faults with vertical segmentation, their periodical locking, and the lithosphere heterogeneity. We used the birth and death of element groups to simulate stress intensity changes during the two episodes (named Episode I and II), with our results showing that the Tangshan earthquake was primarily triggered by the Sanhe-Pinggu M8.0 earthquake in 1679, whereas the Zhangbei M6.2 earthquake in 1998 was not triggered by earthquakes in Episode I. According to our work, the calculated stress changes in the different segments of the fault zone correspond to the magnitude of the triggered earthquakes. Further, the largest stress decrease was near the Sanhe-Pinggu fault and occurred the largest earthquake in Episode I, whereas the largest stress increase was near the Tangshan fault and occurred during the largest earthquake in Episode II. Given the above, we propose a model for seismic migration to describe the dynamic mechanisms of earthquake migration within the BZFZ and North China, in which the factors affecting both the seismic migration path and intensity primarily include the distance between the triggered active fault and the original fault, the coupling of the active faults, the location and scale of the low-velocity anomaly, its distance from the active fault, and the location and scale of the crustal thinning.
Highlights
Increasing amount of historical evidence regarding the intraplate earthquakes shows episodic seismicity and clustering seismic migration within some mid-continents, including North China and New Madrid [1,2]
To study the influence of vertical segmentation, we divide each active fault into a locking section and a non-locking section based on the bottom boundary of the upper crust, where sections of different mechanical properties join via a brittle–ductile transition and most big earthquakes in North China happened
We established a three-dimensional Maxwell viscoelastic model including all active faults within the BohaiZhangjiakou Fault Zone (BZFZ) with different spatial patterns, vertical segmentations, and lithospheric heterogeneity to illustrate the mechanism behind large historical earthquake migrations
Summary
Increasing amount of historical evidence regarding the intraplate earthquakes shows episodic seismicity and clustering seismic migration within some mid-continents, including North China and New Madrid [1,2]. In our work, we used a high-resolution three-dimensional viscoelastic FEM model that considers active faults with vertical segmentation, their periodic locking, and the lithosphere heterogeneity to illustrate the mechanism of large earthquake migrations in the BZFZ between the two key episodes after 1500, i.e., the Sanhe-Pinggu M8.0 earthquake in 1679 and the Zhangbei M6.2 earthquake in 1998.
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