Quantification of rupture directivity effects on strong ground motion during the 8 January 2022 MS6.9 Menyuan earthquake in Qinghai, China

On 8 January 2022, an M S 6.9 earthquake occurred in the Menyuan county, Qinghai province at northeastern margin of Tibetan Plateau. A dense observatory network consisting accelerographs and intensity meters has obtained many acceleration recordings this region, which previously had only a few strong motion recordings. Using data recorded by 141 micro-electro mechanical system (MEMS)-based within 100 km causative fault, we investigated spatial distribution attenuation characteristics near-source ground during event. The observed response spectra were compared with prediction using NGA-West2 models. It was found that, long-period section >1.0 s, rupture forward direction (southeast epicenter) greater than prediction, while observations on northwest side lower prediction. Through quantitative analysis residuals, that directivity effects motions controlled azimuth relative to fault along-strike projected length rupture, mainly affected portion s. In direction, spectral accelerations (SAs) periods 1.0–10.0 s enhanced 1.18–1.56 times average. backward (northwest epicenter), SAs 0.63–0.86 (M W 6.6) exhibited obvious period-dependence narrowband characteristics, amplification strongest 5.0 factors straight directions underestimated empirical model. Two typical velocity pulse records their significantly amplified long 1.0 peak values 4.0–6.0 near characteristic period pulses. This related resonance excited specific periodic pulse. Our study provides reference quantifying for both moderate major shallow crustal earthquakes MEMS region.