Fig. 2

The spatial distribution of the mean USZ v_N data collected in this study. The red region represents the region where the mean USZ v_N exists (the mean USZ v_N maybe one or more). (a) The UK’s multiple mean USZ v_N values cover almost the whole of the UK; (b) The Tarim Basin, Loess Plateau and North China Plain in China have the same average USZ v_N; (c) The mean USZ v_N of the metamorphic rocks in the Kumamoto region of Japan; (d) The average USZ v_N of the Loess in Israel; (e) The mean USZ v_N values of the Chalk and Triassic sandstone in Western Europe; and (f) The average USZ v_N of the US Loess.