Groundwork on Did You Feel It (DYFI) in the Korean Peninsula toward a new generation system of earthquake intensity estimations

Seismic intensity is important in terms of seismic hazard because it categorizes felt ground shaking and damage. In general, the intensity is obtained through field investigation or by instrumental intensity converted from seismograph observations, empirically. Unlike the conventional approach, USGS Did You Feel It (DYFI) system has collected intensity information based on real-time online surveys for the community since the early 1990's. After the 2016 Gyeongju and 2017 Pohang earthquakes, quicker compiling has been requested for intensity information of strong ground motion in the Korean Peninsula. This suggests that DYFI can play an important role in a next-generation intensity collection system. In this work, we test applicability of the DYFI system to earthquakes in the Korean Peninsula with additional modifications. We derived a relationship between community responses in the USGS DYFI (i.e., Community Weighted Sum; CWS) and the Korean-peninsula-optimized Community Decimal Intensity (KCDI ≃0.47+0.27×CWS), by comparing the CWS with intensity values reported by the Korea Meteorological Administration for Gyeongju and Pohang earthquakes. The intensity-distance relationship from this study shows a higher linearity than raw data of the USGS DYFI. In addition, the maximum intensity (KCDI=7.2) is more comparable to that from the field measurement (VIII) than the USGS's original value (6.6). Intensity distribution maps from the KCDI values are more reliable presenting radiation patterns and site effects compared to results using the conventional felt intensity reporting. From this, we confirm that the community response-based intensity distributions can be even more useful near the epicenter than instrumental observations in the case of regions with enough community reponses though the lack of seismic stations.