Earth Science: Strata, Volcanoes, Earthquakes, Weather and Celestial Motion
Earth science in the Tottori paper links maps, cross-sections and data tables to processes: strata record deposition, volcanoes and earthquakes record plate motion, and celestial diagrams record Earth's rotation and revolution. The strands are 大地の変化, 気象, 天体, 地層, 火山 and 地震.
Rocks, strata and fossils
Sedimentary rocks form in layers. The law of superposition says lower layers are older if not overturned. Fossils give relative age. Igneous rocks are plutonic (granite, coarse, slow cooling) or volcanic (basalt, fine, rapid cooling). The sequence is weathering, erosion, transport, deposition, compaction and cementation.
Volcanoes and earthquakes
Magma rises at plate boundaries and hotspots. Volcano shape depends on lava viscosity. The earthquake focus is underground; the epicenter is on the surface. P waves arrive first and pass through solids and liquids; S waves arrive later and cannot pass liquid. The P–S time difference increases with distance.
Weather and sky
Pressure falls with altitude; wind flows from high to low pressure. Warm fronts bring steady rain; cold fronts bring short heavy rain. Earth rotates west to east, so the Sun and stars appear to move east to west. Seasons come from the tilt of Earth's axis, not distance from the Sun.
Worked example
A station records a P wave at 10:00:00 and an S wave at 10:00:10. If Vp = 6 km/s and Vs = 3 km/s, find the epicentral distance. Reasoning: d/3 − d/6 = 10, so d/6 = 10 and d = 60 km.
Traps
- Saying S waves pass through the outer core.
- Assuming the top layer is always youngest.
- Confusing focus and epicenter.
- Explaining seasons by distance from the Sun.
- Reading isobars as wind direction rather than pressure.