Tectonic Earth Processes: Plates, Quakes, and Mountains
What this domain tests
This domain covers plate tectonics, earthquakes, volcanoes, deformation, and mountain building. Questions ask you to relate boundary types to earthquake depth, volcano style, faulting, and topographic features.
Plate boundaries
Lithospheric plates move over the asthenosphere. Divergent boundaries create mid-ocean ridges and rift valleys, with shallow earthquakes and basaltic volcanism. Convergent boundaries produce trenches, volcanic arcs, and fold-thrust belts; ocean-continent and ocean-ocean convergence involve subduction, while continent-continent collision builds high mountains. Transform boundaries produce strike-slip faults and shallow earthquakes.
Earthquakes and seismic waves
Earthquakes occur at a focus; the epicenter is the surface point above it. Elastic rebound releases stored strain. P waves are compressional and fastest, traveling through solids and liquids. S waves are shear waves, slower, and cannot pass through liquids. Surface waves are slowest and often most damaging. The S-wave shadow zone beyond 103 degrees reveals the liquid outer core. Magnitude measures energy; intensity measures shaking effects.
Volcanoes and deformation
Low-viscosity basaltic magma produces shield volcanoes and lava flows. High-viscosity andesitic or rhyolitic magma traps gas and produces explosive stratovolcanoes or calderas. Normal faults form under tension, reverse and thrust faults under compression, and strike-slip faults under shear. Folds include anticlines, synclines, and monoclines.
Worked example
A region has an oceanic trench, earthquakes from shallow to deep, andesitic stratovolcanoes, and a fold-thrust belt. Identify the boundary. Deep earthquakes require a subducting slab, the trench marks subduction, andesitic magma forms when water released from the slab melts the mantle wedge, and compression builds the fold-thrust belt. The setting is a convergent boundary with subduction.
Traps
- Divergent boundaries have shallow earthquakes, not deep ones.
- Transform boundaries lack the arc volcanism of subduction zones.
- Normal faults indicate tension; reverse faults indicate compression.
- S waves do not travel through liquid, so they disappear beyond the shadow zone.
- Magnitude is not the same as intensity.