Tectonic interpretations of Holocene marine terraces, east coast of Coastal Range, Taiwan

Abstract

The east coast of the Coastal Range in Taiwan is well known for its multiple Holocene marine terraces and their very rapid uplift. The study area extends from Hualien to Taitung over ca 150 km of coastline. Here, we present some new data on the age and height of Holocene marine terraces, and we discuss their significance for Holocene coastal tectonics. The Holocene marine terrace sequence is subdivided into a maximum of 10 steps. The highest and oldest terrace, mostly underlain by transgressive deposits, represents the sea-level position of the culmination of Holocene sea-level rise and reaches up to ca 80 m above sea level. Transgressive deposits are radiocarbon dated at several sites, back to ca 13,000 yr BP. The lower terraces are mostly erosional ones, overlain by thin coral beds in situ, less than 1 m thick, and indicate successive lowering of relative sea level during the late Holocene. The uplift rate of the coast is very high, ranging from 5 to 15 m/ka. Three tectonic subregions, A–C, are identified, based on the pattern of marine terrace features and uplift rate. The presence of many steps during Holocene time implies that intermittent uplifts, associated with large earthquakes at intervals of one thousand to several hundred years, have repeatedly occurred in this coastal area, but with different time and amount at each subregion. The uplift of subregion A resulted from an onshore active fault (Milun fault). Causative faults for the uplift of the subregions B and C are not identified. Offshore active faults, striking obliquely to the coastline, appear to be causative faults.