Abstracts 231 SOLAR SIGNALS FROM 14C IN TREE RINGS ELISABETTA PIERAZZO Lunar and Planetary Laboratory, The University of Arizona, Tucson, Arizona 85721 USA and SILVIA SARTORI Department of Physics, University of Padova, Padova, Italy 14C The record in wines has shown many interesting features. The strongest signal which is imprinted in it comes from the 11-year solar cycle. Another possible feature could be a frequency modulation of solar origin, also detectable, despite the limited length of the record (carrier period 11 years, modulating period 22 years). The solar signature is also present in annual tree rings, though weaker; the length of the record is short, in any case. Long tree-ring records are now available in decadal and bi-decadal sequences. However, as it is well known, conventional spectral analysis of such temporal sequences, is affected by aliasing, which is always present in equispaced sequences where a signal lies beyond the Nyquist frequency. Thus, it is difficult to clearly define the real presence of solar cycles on the scale of centuries. Alaasing can be avoided in the analysis of unequispaced time sequences. On the other hand, unequispaced sequences ask for other more sophisticated treatments, such as Bayesian analysis. A comparison is carried out between the detectability of signals of solar origin in unequispaced and equispaced sequences, when the latter contain aliased frequencies. A frequency modulation model for wines is compared with an annual sequence in tree rings, for the last 400 years. DETERMINING RECURRENCE INTERVALS OF GREAT SUBDUCTION ZONE EARTHQUAKES IN SOUTHERN ALASKA BY RADIOCARBON DATING GEORGE PLAFKER, K R LAJOIE U S Geological Survey, Menlo Park, California 94025 USA and MEYER RUBIN U S Geological Survey, Reston, Virginia 22092 USA Rupture on the eastern segment of the Aleutian arc subduction zone produced the great 1964 Alaska earthquake and caused vertical and horizontal tectonic displacements over more than 14C 140,000 km2. dates from subaerial peat and forest layers submerged below the pre-1964 high- tide level indicate the 1964 earthquake was preceded by gradual regional interseismic subsidence 14C of 2.5-9.5 mm/yr for at least 800 years. Older dates from buried layers of peat and rooted tree stumps yield recurrence intervals for 1964-type tectonic events of about 600-950 years and interseismic subsidence rates of 3-5 mm/yr over the past 3000 years in the area of Copper River 14C delta on the mainland. dates from peat and driftwood on emergent marine terraces on Middleton Island at the outer edge of the continental shelf in the Gulf of Alaska yield recurrence .