Table 1 Summary of the data analysis

Latitude

Longitude

35–40°N

345.386 E

40–45°N

345.308 E

40–45°N

297.037 E

45–50°N

297.003 E

10–15°N

57.793 E

15–20°N

57.784 E

20–25°N

20.797 E

25–30°N

20.853 E

Age (100 Ma)

35.2

34.4

35.0

34.9

S (Fe + Ti wt%)

16.86

16.31

14.26

12.41

10.61

12.50

15.36

13.95

ε₁

3.91–6.37^a

4.04–5.53

3.49–5.38^b

2.96–4.54

3.23–3.60^c

3.15–4.37

3.29–5.81

3.06–5.74

ε_grain

6.60

6.56

6.41

6.29

6.17

6.29

6.49

6.39

Apparent depth (m)

500

400

300

350

Actual depth (m)

198–253

213–249

172–214

188–233

158–167

143–169

145–193

146–200

p (%)

1.8–27.8

9.1–25.7

9.5–32.8

17.7–41.1

29.6–35.6

19.8–37.7

6.0–36.4

5.8–39.6

tan δ1(×10⁻²)

1.05–1.53

1.03–1.31

0.77–1.07

0.58–0.81

0.53–0.58

0.61–0.79

0.81–1.25

0.68–1.10

σ1(×10⁻⁵ S/m)

1.14–2.71

1.16–2.01

0.75–1.61

0.48–1.02

0.48–0.58

0.54–0.96

0.74–2.02

0.58–1.76

ε₂

6.81–21.28

7.81–14.61

6.17–15.44

4.84–12.26

4.25–12.52^d

6.55–9.63

6.13–13.35

5.78–13.59

# of subsurface echoes

221

162

586

427

1025

1274

634

345