Strong ground motion simulation for the 2014 M_W6.1 Ludian，Yunnan earthquake

Based on the intensity and aftershock distribution, researchers unanimously agree that the rupture of the 2014 M_W6.1 Ludian, Yunnan earthquake exhibits a certain degree of complexity. Zhang et al （2015） used broadband strong motion records within a 250 km range from the epicenter, along with full waveform data of near-field and far-field broadband body wave data, to invert the rupture process of the Ludian M_W6.1 earthquake base on both a single fault model and two intersecting conjugate fault models. Their results indicate that the Ludian M_W6.1 earthquake was a complex seismic event, characterized by the successive rupture of two conjugate faults in the northwest and northeast directions. Significant progress has been made in studying the characteristics of strong ground motion related to the Ludian earthquake and associated issues. The existing conclusions about the distribution of seismic parameters in affected region are directly inferred or indirectly synthesized from existing data, yet the seismic characteristics caused by complex seismic source ruptures have not been considered.

To investigate the influence of different rupture process models on ground motion simulation of the M_W6.1 Ludian earthquake, a hybrid broadband ground motion simulation method known as the GP method （Graves, Pitraka, 2010） was applied to synthesize acceleration, velocity waveforms, and acceleration response spectra in the near-field area based on kinematic source models. The source models used for comparison in this study are derived from Zhang et al （2015）, which includes two single fault rupture models and one intersecting conjugate fault model. The study adopted the crustal velocity structure model of the Yunnan region to calculate the Green’s function.

The GP method combines a deterministic approach in the low-frequency range （ f＜1 Hz） with a semi-stochastic approach in the high-frequency range （ f ＞1 Hz）. For f＜1 Hz, this methodology allows for a theoretically rigorous representation of fault rupture and wave propagation effects, to generate ground motion waveforms and amplitudes. In contrast, high-frequency （ f ＞1 Hz） ground motions are modeled through random source radiation, simplified theoretical wave propagation, and scattering effects.Simulation results for representative sites were compared with observed strong motion recordings, and the impacts of three different source rupture models on strong ground motions were analyzed. The results demonstrate that for moderate earthquakes with limited fault dimensions, differences in strong ground motion characoncernedcteristics among different source rupture models with similar seismic moments are not pronounced in far fields but are distinct in near-fields. Additionally, the distributions of intensity measurements of ground motions are provided, and it is found that the simulation results based on the conjugate fault model are more consistent with the field-surveyed macroseismic intensity of M_W6.1 Ludian earthquake, Yunnan in 2014. This indicates that the source rupture model plays a crucial role in the spatial distribution pattern of strong ground motions and their characteristics. Therefore, elaborate source rupture models are of great value for reasonably estimating the peak ground acceleration, peak ground velocity, frequency spectrum, duration, and time history of seismic motion in the near-source area, as well as assessing seismic hazard in area.

This article reveals the influence of complex focal rupture processes on the characteristics and spatial distribution of strong ground motion.