Seasonal Modulation of Crustal Seismicity in Northeastern Japan Driven by Snow Load

Numerous studies have reported that surface hydrological loading can seasonally modulate seismicity rates at crustal depths. For example, substantial winter snow accumulation occurs across the Japanese Islands, and these snowy regions appear to have seasonally modulated the occurrence of previous large inland earthquakes. Therefore, it is important to investigate the impact of seasonal stress changes on crustal seismicity to deepen our understanding of earthquake generation. Here we constrain seasonal changes in the surface load across northeastern Japan using Global Navigation Satellite System surface displacements and evaluate the potential relationship between temporal trends in inland seismicity and estimated seasonal stress changes. The spatial distribution of the seasonal surface load is consistent with snow depth along the Sea of Japan. The inland seismicity beneath northeastern Japan is modestly modulated by the seasonal stress changes that are induced by the annual snow load. However, this seasonal response is weaker than that in other regions. This weak modulation may be due to the small surface-load-induced stress perturbation relative to the long-term-averaged stressing rate and/or the limited presence of crustal fluids to trigger seismicity in Japan. The number of earthquakes can be seasonally controlled by surface processes, such as snow accumulation and melt. Therefore, it is important to estimate the temporal stress changes where earthquakes occur to clarify the role of surface processes in the timing of earthquake occurrence. Here we estimate seasonal changes in surface mass from a dense array of surface displacement observations across northeastern Japan and compare the timing of shallow earthquake occurrence with the stress changes induced by the estimated surface mass. The estimated seasonal surface mass can be explained using snow depth observations along the Sea of Japan. The seasonal stress changes induced by the snow appear to weakly control the number of earthquakes in northeastern Japan. The reason why the number of earthquakes does not vary much seasonally may be because the seasonal stress changes are small compared to the long-term stressing rate. The spatial distribution of seasonal surface load across northeastern Japan is estimated using Global Navigation Satellite System displacement observations The stress amplitude induced by the estimated seasonal surface load modestly modulates the inland seismicity This weaker modulation may be due to smaller stress change perturbations and the lower likelihood of unclogging saturated fractures