What Makes People Respond to "Did You Feel It?"?

The data compilation of "Did You Feel It?" (DYFI) and other similar Internet-based macroseismic intensity databases relies on the voluntary responses from Internet users. A region of no responses could mean no perceivable ground shakings or no volunteers submitting responses. We examined the earthquake and socioeconomic conditions that affected the number of DYFI responses received for a region. A resulting statistical model described the expected number of DYFI responses received for an earthquake. We also showed that residents in California and the central and eastern United States followed similar behavior in responding to DYFI, despite the vast difference in seismicity for the two regions. This study allows for a quantitative definition of completeness for DYFI data. The presented modeling technique is applicable to other Internet-based macroseismic intensity databases.