I found a Chinese book with some more details; it's not comprehensive and doesn't list individual defensive lines, but it's somewhat useful nevertheless.
The book is 重探抗戰史（一）：從抗日大戰略的形成到武漢會戰（1931-1938） or roughly, "Revisiting the History of the Second Sino-Japanese War (part 1): From the Formation of Strategy to the Battle of Wuhan (1931-1938)". In it there's a short section covering defensive works constructed for the upcoming war:
- Most were designed by Hans von Seeckt
- Land-based defensive lines were centered around the capital, Nanking
- Defensive lines were spread all around China in six areas:
- Jiang-Zhe (江浙), area around Nanking/Shanghai; these were almost 70% complete by the start of the war
- Shantung (山東)
- Jicha (冀察), the Hebei and Chahar provinces around Peking
- Jinsui (晉綏), the Shanxi and Suiyuan provinces
- Henan (河南), almost 90% complete by the start of the war
- South-Eastern (東南)
- The most important Jiang-Zhe area was composed of three lines, permanent defensive works including 470 bunkers, all protecting the approach from Shanghai to Nanking:
- Songhu (淞滬), a.k.a. Shanghai
- Wufu (吳福), along Suzhou Creek and Fushan Creek
- Xicheng (錫澄), near Wuxi
- Those defensive works were not utilised to their fullest extent due to the chaotic retreat from Shanghai and the lack of artillery which was still being shipped to China.
From other books I've also read that the chief defensive works were the two lines between Shanghai and Nanking, Wufu and Xicheng. It seems the Chinese bet heavily on Japan invading from Shanghai upriver.