**1. Introduction**

Located on the convergent margin of the Eurasian plate, the Japanese archipelago features many tectonic, volcanic, and coastal lakes that are well suited for studies of Quaternary intraplate tectonics. A famous and often studied tectonic lake in Japan is Lake Biwa (Figure 1). Along the west coast, an extremely active fault system in Japan designated as the Biwakoseigan Fault zone runs north to south (Figure 1).

The ca. 1.5-Ma-old present Lake Biwa (82 m a s l.) on south-central Honshu Island is the largest freshwater lake in Japan, measuring 22.6 km wide by 68 km long (Figure 1). Lake Biwa is divided into two basins. The *Northern Lake* is a deep basin with a maximal depth of 104 m and average depth of 40 m. The much smaller *Southern Lake* is extremely shallow with average depth of about 3 m. Herein we summarize and discuss that the tectonic basin formation in the paleo and present Lake Biwa basin as an example of intraplate basin formation.
