Relocating the historical 1951 Hualien earthquake in eastern Taiwan based on tide gauge record.

A sequence of large earthquakes happened along the Longitudinal Valley in eastern Taiwan in 1951. The first three (and largest) earthquakes took place near the harbour city of Hualien at the northern tip of the valley during the first day, the second of which (‘Event II’) severely damaged the city. The epicentre of Event II had previously been allocated at some 15 km offshore, which would result in a vertical subsidence of the Hualien city according to model calculations for the supposed seismic source mechanism. However, the Hualien tide gauge record speaks the opposite—the site experienced a co-seismic uplift by 255 mm due to Event II. We conduct a series of numerical grid-search simulations and determine a most likely scenario for the earthquake sequence. We assert that Event II's hypocentre was actually on land (rather than offshore), right along the recognized active Milun Fault below the city of Hualien at a very shallow depth. This result advances our understanding of the spatio-temporal seismotectonic behaviour associated with these historical events, and is important towards the assessment of the potential seismic and tsunami hazards of the region. [ABSTRACT FROM AUTHOR]