Ups and downs of the U.S. West Coast: Implications of eight decades of vertical deformation measurements for seismic hazards and sea level impacts
Along active plate boundaries, vertical deformation of the crust results from strain accumulation between major earthquakes. Observations of this vertical deformation are important to constrain where faults are currently locked and may slip in future earthquakes, particularly when integrated with horizontal deformation imaged by GPS. Additionally, the vertical motion of the land along the coast can either enhance or counteract the effects of the global process of sea level rise on a local basis. In this presentation, I will show how observations of relative sea level change made at tide gauges and repeated leveling surveys can be used to measure the pattern and rate of vertical deformation over timescales of several decades to over a century. I will also review satellite-based estimates of vertical deformation and sea level rise made over the past two decades to assess the level of agreement between techniques and examine changes in deformation rates over time. Tectonic deformation is the dominant signal along the Cascadia portion of the coast, and is consistent with along-strike variation in locking behavior on the plate interface. Rates of vertical motion are lower along the transform portion of the plate boundary and include anthropogenic effects, but there are significant tectonic signals, particularly in the western Transverse Ranges where the crust is shortening across reverse faults. I will highlight emerging insights and outstanding questions derived from the vertical deformation rate field for understanding hazards from earthquakes and coastal inundation related to sea level rise.