Abstract:
At 22:15 Beijing Time on December 8, a magnitude 7.5 earthquake occurred offshore of eastern Honshu, Japan. Following the event, the Strong Motion Observation Center of the Institute of Engineering Mechanics, China Earthquake Administration, promptly initiated a rapid emergency response. Personnel were mobilized to collect, process, and conduct a preliminary analysis of the earthquake’s strong-motion records. Emergency products, including maps of instrumental seismic intensity and peak ground acceleration (PGA) distribution, were rapidly generated. Preliminary analysis results indicate that within a 200 km radius around the epicenter of this earthquake, there have historically been 21 earthquakes with magnitudes of 7.0 or greater, including 3 with magnitudes of 8.0 or greater. A total of 872 recorded waveforms had a PGA exceeding 10 cm/s². The calculated instrumental seismic intensity, based on the Chinese Seismic Intensity Scale (GB/T 17742—2020), ranged from 1.0 to 8.6 degrees. Station AOM010 recorded the highest intensity value of 8.6 degrees at an epicentral distance of 102.7 km, while station AOMH06, with the closest epicentral distance of 78 km, recorded an intensity of 7.5 degrees. The rapid production of products from strong motion observations aids in the swift assessment of post-earthquake situations, provides crucial support for disaster evaluation, emergency decision-making in affected countries, and offers immediate scientific backing for Chinese government agencies in formulating international emergency rescue plans for major earthquakes and assessing the potential impact of overseas seismic events on China.