Analysis of ground motion characteristics and near-fault effects for the September 5, 2022, MS6.8 Luding earthquake

Using the three component acceleration records of the National Strong Motion Observation Network System (NSMONS) and the National Seismic Intensity Rapid Reporting and Earthquake Early Warning Network, the ground motion attenuation characteristics, spatial distribution, source rupture direction, and near-fault pulse characteristics of the Luding M_S6.8 earthquake were analyzed. Comparing the observed values of peak ground acceleration (PGA), peak ground velocity (PGV), pseudo-spectral acceleration (PSA), and 90% significant duration (SD) with several typical ground motion prediction equations (GMPE), it was found that the ground motion attenuation characteristics of this earthquake are consistent with GMPE for the southwest region, but overall lower than the global model average level. In the comparison of between-event residuals, this earthquake exhibits different characteristics from the same magnitude thrust type earthquake. The within-event residuals reflect that the anelastic attenuation in the Luding region is slightly weaker than that in the Menyuan region. In terms of spatial distribution of ground motion parameters, the PGV and PSA with a period of 1.0 to 8.0 s have significantly higher intensity in the southeast direction of the epicenter than in other directions. Based on PGV, it is speculated that the source rupture direction of the earthquake was 151°, which is close to the fault strike of 163°. Pulse-like ground motions were identified in up to 12 sets of near-fault records with pulse periods significantly lower than historical earthquakes of similar magnitudes. Stations with pulse peak values greater than 40 cm·s⁻¹ in the pulse dominant direction of the velocity time history all appeared in the narrow band area ahead of the rupture direction. The distribution area of near-fault pulses is highly correlated with the distribution of high macroseismic intensity areas and landslide areas, and it is necessary to pay attention to the impact of near-fault pulses in seismic fortification.