Ground tilt changes in Japan caused by the 2010 Maule, Chile, earthquake tsunami

Abstract

Oscillating ground tilt perturbations accompanied by the 2010 Maule, Chile, earthquake tsunami were observed over a broad inland area facing the Pacific Ocean coast in Japan by a high‐density tiltmeter network. Through an analysis of ground tilt data observed at more than 500 stations, we were able to obtain a detailed spatiotemporal distribution of the tsunami‐induced tilt changes and reveal a relationship between the tilt amplitude and the distance from the coast. At distances of 1 km or less, the peak tilt amplitudes were ~5 × 10–2 µrad and were almost constant with respect to the distance. At distances greater than 3 km, amplitudes were inversely proportional to the distance and reached ~5 × 10–3 µrad approximately 50 km away from the coast. The dominant ground tilting directions were almost the same as the direction orthogonal to the coastline. These observed ground tilt changes and their characteristics were successfully modeled with a loading deformation caused by sea level variations accompanied by the tsunami. Applying a two‐dimensional boxcar tsunami model to the observed data, we estimated the water volume per unit length of coast for the Maule earthquake tsunami to be 2–7 × 103 m3/m within the distance of 14–20 km seaward of the coastline.