Strong ground motion over a large area in northern Taiwan caused by the northward rupture directivity of the 2019 Hualien earthquake

•Strong ground motion occurred over a large area in northern Taiwan.•Rapid northward rupture with a large asperity caused the strong rupture directivity.•Directivity effect could be further coupled with the specific source radiation pattern.•A seismic gap in the source area increases awareness of big earthquakes in eastern Taiwan.