This study presents the results of continuously measured ground acceleration and pore water pressure at a liquefaction-prone site in reclaimed land in the Tokyo Bay area. The site was monitored over the past two years since November 2020, recording earthquakes, including one with a maximum horizontal acceleration of 162.7 Gal, leading to an excess pore water pressure increase of 19.4 kPa. This study also proposes an influence index of acceleration on pore water pressure for liquefaction assessment. We calculated the new index I_pw, which successfully explained the impact of seismic motion on the rise of excess pore water pressure. Additionally, it was validated by applying I_pw to a series of shaking table tests under a 1G condition. As a result, the validity of the index I_pw with the seismic duration threshold determined by the acceleration level was confirmed as a case study.