Seasonal modulation of interseismic strain buildup in northeastern Japan driven by snow loads.

Distinct periodic variations with annual frequencies are often found in the time series of continuous Global Positioning System (GPS) site coordinates in northeastern Japan. They show maximum arc-normal contraction of a few millimeters as well as maximum subsidence of 1 to 2 centimeters, both in March. In northeastern Japan, it snows heavily on the western flank of the backbone range, attaining a maximum depth of several meters in March. When observed snow depths were compared with the load distribution estimated from the GPS data, the surface loads caused by the snow were found to be largely responsible for the annual displacement of GPS sites. The snow load modulates secular strain buildup in northeastern Japan due to the Pacific Plate subduction, but its relevance to the seasonal change of earthquake occurrences remains uncertain.