High Frequency Near‐Field Ground Motion Excited by Strike‐Slip Step Overs

Abstract

We performed dynamic rupture simulations on step overs with 1–2 km step widths and present their corresponding horizontal peak ground velocity distributions in the near field within different frequency ranges. The rupture speeds on fault segments are determinant in controlling the near‐field ground motion. A Mach wave impact area at the free surface, which can be inferred from the distribution of the ratio of the maximum fault‐strike particle velocity to the maximum fault‐normal particle velocity, is generated in the near field with sustained supershear ruptures on fault segments, and the Mach wave impact area cannot be detected with unsustained supershear ruptures alone. Sub‐Rayleigh ruptures produce stronger ground motions beyond the end of fault segments. The existence of a low‐velocity layer close to the free surface generates large amounts of high‐frequency seismic radiation at step over discontinuities. For near‐vertical step overs, normal stress perturbations on the primary fault caused by dipping structures affect the rupture speed transition, which further determines the distribution of the near‐field ground motion. The presence of an extensional linking fault enhances the near‐field ground motion in the extensional regime. This work helps us understand the characteristics of high‐frequency seismic radiation in the vicinities of step overs and provides useful insights for interpreting the rupture speed distributions derived from the characteristics of near‐field ground motion.

The Near‐Fault Ground Motion Characteristics of Sustained and Unsustained Free Surface‐Induced Supershear Rupture on Strike‐Slip Faults

“…We present synthetic ground motion records lowpass filtered to this frequency and also filtered using a 1 Hz low‐frequency filter and a 1‐ to 3‐Hz bandpass filter, respectively. The filter we adopt is a finite impulse response filter (Hu et al, ). The time histories in Figure correspond well to the overall patterns of ground motion and timing seen in Figures and .…”

Dynamic Rupture Simulation of the 1833 Songming, Yunnan, China,M8.0 Earthquake: Effects From Stepover Location and Overlap Distance

“…However, to the north of the hypocenter, we find that the area with intensities of Ⅹ and Ⅸ in Figure 16b decreases compared to that in Figure 16a, while the area with an intensity of Ⅷ increases in the fault‐normal direction. This can be explained by the stopping phase effect on the main fault (Hu et al., 2018). When we adopt the optimal Yangzonghai stepover rupture model for the wave propagation modeling (Figure 16c), the intensity distribution north of the hypocenter is almost identical to the corresponding area in Figure 16b.…”

“…However, to the south of the hypocenter, the area with an intensity of Ⅺ decreases while with the area with intensities of Ⅸ and Ⅷ increases in the fault‐normal direction compared to Figure 16b. Likewise, this phenomenon is also caused by the stopping phase effect of the main fault rupture (Hu et al., 2018).…”