Risk Analysis DOI: 10.1111/risa.13306 Residents’ Reactions to Earthquake Early Warnings in Japan Kazuya Nakayachi , 1 Julia S. Becker, 2,* Sally H. Potter , 3 and Maximilian Dixon 4 This article empirically examines the effectiveness of earthquake early warning (EEW) in Japan based on experiences of residents who received warnings before earthquake shaking occurred. In Study 1, a survey (N = 299) was conducted to investigate residents’ experiences of, and reactions to, an EEW issued in Gunma and neighboring regions on June 17, 2018. The main results were as follows. (1) People’s primary reactions to the EEW were mental, not physical, and thus motionless. Most residents stayed still, not for safety reasons, but because they were focusing on mentally bracing themselves. (2) Residents perceived the EEW to be effective because it enabled them to mentally prepare, rather than take physical protective actions, before strong shaking arrived. (3) In future, residents anticipate that on receipt of an EEW they would undertake mental preparation as opposed to physical protective actions. In Study 2, a survey (N = 450) was conducted on another EEW issued for an earthquake offshore of Chiba Prefecture on July 7, 2018. Results were in line with those of Study 1, suggesting that the findings described above are robust. Finally, given people’s lack of impetus to undertake protective action on receipt of an EEW, this article discusses ways to enhance such actions. KEY WORDS: Earthquake; earthquake early warning; effectiveness of warning 1. INTRODUCTION 1.1. Potential Effectiveness of Earthquake Early Warning Earthquakes can cause rapid and substantial damage to property, the economy, and human life. Existing technology, in the form of an earthquake early warning (EEW) system, can provide a poten- tially life-saving amount of warning time of immi- nent strong earthquake shaking. Japan has invested 1 Faculty of Psychology, Doshisha University, Tatara, Kyotanabe- shi, Japan. 2 Joint Centre for Disaster Research, Massey University, Welling- ton, New Zealand (previously GNS Science, New Zealand). 3 Joint Centre for Disaster Research, GNS Science, Lower Hutt, New Zealand. 4 Washington Military Department, Washington State Emergency Management Division, Camp Murray, WA, USA. ∗ Address correspondence to Julia S. Becker, Joint Centre for Dis- aster Research, Massey University, PO Box 756, Wellington 6140, New Zealand; j.becker@massey.ac.nz. in such a system, which has officially been in opera- tion since 2007 (Fujinawa & Noda, 2013). In an earthquake, there are two main types of seismic waves: primary waves (P-waves) and sec- ondary waves (S-waves). P-waves propagate out- wards from the hypocenter of the earthquake and move faster than S-waves. Because of the way they move, no obvious shaking is created by the P-waves. They are followed by the slower S-waves, which cause ground shaking and subsequent damage. EEWs can be generated in two ways: (1) by de- tecting physical shaking at an earthquake’s source; and/or (2) by monitoring the progress of seismic waves (e.g., detecting P-waves before the shaking S-waves arrive). Both of these allow the sending of advanced notification of impending ground shaking to locations that have not yet been impacted. When an earthquake occurs, Japan’s EEW sys- tem automatically calculates the hypocenter and magnitude of the earthquake, and, using the Japan Meteorological Agency (JMA) intensity scale (JMA, 1 0272-4332/19/0100-0001$22.00/1 C  2019 Society for Risk Analysis