Deformation in the Guerrero seismic gap, Mexico, from leveling observations

The Pacific coast of Guerrero state in Mexico is recognized as the 'Guerrer o seismic gap', with a high probability of producing a large subduction ear thquake (M > 8). A study of the vertical surface deformation was undertaken to understand the interseismic process of elastic strain accumulation. Fou r leveling lines were installed in the states of Guerrero and Michoacan. St arting in 1995, several high-accuracy leveling surveys have been carried ou t on those profiles once every year. The vertical uplift rate across the Gu errero coastal region, as determined through the changes in repeated leveli ng surveys, suggests the accumulation of elastic strain at both ends of the gap. In contrast, the sense of tilting in the middle of the gap is opposit e to that observed at the ends and suggests significant changes in the geom etry of the locked zone and perhaps even slow strain release.