Tide gauge records of uplift along the northern Pacific‐North American plate boundary, 1937 to 2001

Abstract

Vertical crustal motions at 15 sites along the northern Pacific‐North America plate boundary are determined using relative sea level changes from tide gauge records. Our analysis is based on monthly mean sea levels, from which barometric pressure and seasonal effects are removed. The records are corrected for common‐mode oceanographic variations. These records are statistically examined for non‐linear behavior related to glacial isostatic, tectonic and postseismic effects. To estimate land uplift rates, the local effect of global sea level rise is removed from the relative sea level rates. Slow rates of vertical motion are observed along the southern strike‐slip plate boundary. The extremely rapid uplift of the northern strike‐slip boundary can be attributed entirely to viscoelastic postglacial rebound associated with tidewater‐glacier retreat in Glacier Bay and regional post‐Little Ice Age deglaciation. Isostatic modeling indicates a mantle viscosity of ∼2 × 1019–5 × 1019 Pa s, similar to that found elsewhere along the Pacific‐North America plate margin. At Yakutat, near the transition of plate motion from strike‐slip to subduction, complex non‐linear behavior is evident, with a significant change in uplift rate following the 1979 St. Elias earthquake. Non‐linear uplift rates are predominant within the 1964 Great Alaskan earthquake near‐field. Rapid uplift at Kodiak during a 3.5 year period starting mid‐1964 totaled 47 ± 8 cm. Anchorage, Seward and Seldovia exhibited oscillatory uplift in the period immediately following the earthquake until mid‐1972. Since mid‐1972, uplift rates have increased steadily at Anchorage, Seward, Cordova, and Valdez. During this period Nikiski and Kodiak show decreasing uplift rates.