Vertical Crustal Motions due the Earthquake Cycle along the San Andreas Fault: Constraints from Tide Guages

Garrett Thornton
David Sandwell
Bridget R. Konter, University of Texas at El Paso


Sea level change has been continuously recorded along the California coastline at several tide gauge stations for the past 50-100 years. These stations provide a temporal record of sea level change, generally attributed to post-glacial rebound and ocean climate phenomena. However, geological processes, including displacements from large earthquakes, have also been shown to produce sea level variations. Furthermore, the vertical tectonic response to interseismic strain accumulation in regions of major fault bends has been shown to produce uplift and subsidence rates consistent with sea level trends. To investigate the long-term extent and implication of tectonic deformation on sea level change, we compare time series data from California tide gauge stations to model estimates of vertical displacements produced by earthquake cycle deformation. Using a 3-D semi-analytic viscoelastic model, we combine geologic slip rates, geodetic velocities, and historical seismic data to simulate both horizontal and vertical deformation of the San Andreas Fault System. Using this model, we generate a time-series of vertical displacements spanning the 100-year sea level record and compare this to tide gauge data provided by the Permanent Service for Mean Sea Level (PSMSL). Comparison between sea level data and geologically and geodetically constrained models confirms that the two are highly compatible. Vertical displacements are largely controlled by interseismic strain accumulation, however displacements from major earthquakes are also required to explain varying trends in the sea level data. Models based on elastic plate thicknesses of 30-50km and viscosities of 7x1018-2x1019 Pa-s produce vertical displacements at tide-gauge locations that explain long-term trends in the sea level record to a high degree of accuracy at nearly all stations. However, unmodeled phenomena are also present in the sea level data and require further inspection