Dynamic rupture propagation on geometrically complex fault with along-strike variation of fault maturity: insights from the 2014 Northern Nagano earthquake

Ryosuke Ando,Yannis Panayotopoulos,Tomokazu Kobayashi,Kazutoshi Imanishi

doi:10.1186/s40623-017-0715-2

Abstract

Understanding the effect of the complex fault geometry on the dynamic rupture process and discriminating it from the complexity originating from the rheological properties of faults, is an essential subject in earthquake science. The 2014 Northern Nagano earthquake, which occurred near the end zone of a major active fault system, provided unique observations that enabled us to investigate both the detailed geometrical fault structure and surface deformation patterns as well as the temporal sequence led up from a prominent foreshock activity. We first develop a geometrical fault model with a substantial variation along strike, and a model for the regional stress field, which is well constrained by the observations. This significant along-strike variation in fault geometry probably reflects the difference of fault maturity at the end zone of the complex fault system. We used this model in order to conduct a set of dynamic rupture simulations using the highly efficient spatiotemporal boundary integral equation method. Based on our simulations, we show that the observed surface deformation can be reasonably explained as the effect of the non-planar fault geometry with a number of branch faults and bends.Graphical abstract.

Highlights

The geometry of natural fault surfaces tends to become smoother and simpler as the cumulative slip becomes larger (e.g., Wesnousky 1988)
We focus on the effect of the spatially varying complexity of the fault geometry on the Numerical method The dynamic rupture problems are numerically solved by assuming the fault geometry, the on-fault stress state and the friction law as the initial and boundary conditions
We investigated the origin of the complex patterns observed in the wave radiation and surface displacement of the 2014 Northern Nagano earthquake sequence

Summary

Introduction

The geometry of natural fault surfaces tends to become smoother and simpler as the cumulative slip becomes larger (e.g., Wesnousky 1988). The InSAR image confirms that the prominent surface breaks occurred along a part of the surface trace of the Kamishiro fault (Fig. 3) as reported based on the field surveys (Okada et al 2015). This appears to be in contrast to the kinematic slip inversion results based on InSAR (Yarai et al 2015) and by strong motion records (Asano et al 2015), which showed that a significant amount of the fault slip occurred at the relatively deeper parts of the northern half of the fault rather than that of the southern part

Objectives

Results

Conclusion