Extreme events from hundreds years to glacial cycle: insights from Quaternary terraces across the Taiwan mountain belt

Abstract:

Based on different age determinations on Quaternary fluvial terraces distributed across the Taiwan mountain belt, we provide insights on possible and intriguing extreme events, tectonic and/or climate, at different time scales from hundreds years to glacial cycles (i.e., hundreds of thousands years). First in the foreland foothills of western Taiwan, based on Be10 cosmogenic and C14 dating the Puakua tableland reveals a recurrent time of about 100-120 Ka of terrace deposits, which are characterized by 4-5 levels of lateritic terraces, with a long-term uplift rate of 1.5-2 mm/yr in the last 450 Ka. Secondly in the eastern Central Range of the Hsinwulyu River, based on linear tilting model and GPS short-term geodetic rate, it exhibits 8-10 levels of recurrent river terrace deposits occurred about every 5 thousands years in the past 50 Ka or so, under a regional uplift rate of 2-8 mm/yr. Finally in the Longitudinal Valley, a plate suture between the rapid moving Philippine Sea plate and the stable Eurasian plate, based on the C14 dating and abundant geodetic data, including leveling, GPS and creep meter, we infer a recurrent time of about 400-600 years for 8-10 levels of uplifted fluvial terraces on the hanging wall of the Longitudinal Valley fault with an uplift rate of 2-3 cm/yr during the past 5-6 Ka. It is still too early to draw any conclusion on scientific explanations for these three types of possible extreme events at a recurrent time of 0.5 ka, 5 ka and 11 ka, respectively. However, possible scenario and causative mechanisms might be anticipated, for instance the global climate influence such as glacial cycle, or regional tectonic effect such as cluster of mega earthquakes in different areas of the Taiwan mountain belt. On the other hand, comparing the terraces in the three different geological/tectonic setting, we found that the recurrent time of terrace deposits shows an inverse proportional relationship to the uplift rate in the local areas, which requires further investigations in terms of data and physical theory.