Abstract

Deterministic ground motions up to 0.5 Hz from a set of spontaneous dynamic ruptures of Mw 7.5 scenario earthquakes on a 160‐km right‐lateral seismic gap in the north China basin (NCB) have been simulated. Self‐similar heterogeneous initial stresses on the fault and a high‐resolution 3D velocity structure in the NCB have been used. We examine effects of self‐similar fault stresses and 3D basin structure on spontaneous ruptures and ground motions. Self‐similar stresses result in complex rupture behaviors such as jumped/triggered ruptures due to large stress variations. Sedimentary basin‐induced waves contribute to these complex rupture behaviors when the fault passes through a basin.

The directivity effect on peak ground velocity (PGV) is significantly reduced by self‐similar heterogeneous stresses because of frequent acceleration and deceleration of rupture fronts. Basin‐induced surface waves from the four bowl‐shaped basins in the study area amplify and prolongate ground motions, particularly within the basin between Tianjin and Beijing. Two basins at the two ends of the seismic gap cause large‐amplitude velocity pulses. Within the major basin between Tianjin and Beijing, the maximum peak amplitude of Fourier spectra of velocity synthetics occurs at the center of the basin, where the basin is deepest (3.49 km deep based on VS=1.5  km/s), with a low frequency of about 0.065 Hz in the heterogeneous models. Away from the basin center, the peak amplitude decreases and occurs at higher frequencies.

Buried ruptures due to a frictionally stable weak layer near the Earth’s surface significantly reduce slip, slip rate, and PGVs. However, the affected area for PGVs is limited to the vicinity of the fault trace. A larger slip‐weakening distance in the friction law reduces peak slip rates and PGVs but has little effect on slip amplitude, suggesting that slip rates have larger effects on the PGVs.

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